Steelmaking process

The steelmaking process involves producing steel from iron ore. Essential impurities such as nitrogen, silicon, phosphorus, sulfur, and excess carbon are removed from the base iron. Other elements such as manganese, nickel, chromium, and vanadium are added to create different grades of steel.

The basic infrastructure for steel manufacturing includes coke ovens and coal chemical plants, sintering plants, blast furnaces, steelmaking plants and rolling mills. This can be done through basic oxygen furnaces or electric arc furnaces.

In the first method, hot metal from the blast furnace is fed into a basic oxygen furnace after pretreatment and impurities removal. Molten steel is produced in liquid form and impurities are removed in gaseous form and as slag.

In the electric arc furnace process, scrap steel is melted using an electric arc generated by graphite electrodes. This can be used as ingots or fed into continuous casting processes. Gases and synthetic gases are also used in modern steelmaking. These are alternatives to blast furnace steelmaking methods that use oxygen.

Applications include blast furnace or coke gas, Corex gas, oxygen, steam, nitrogen and hydrogen. Acids are used in pickling plants to clean the surface of steel plates to remove rust.
Cooling water, steam and hot water are used at various locations throughout the steel plant.

Steel mills primarily use large butterfly valves for gas applications, or large gate and double-plate check valves. Where high-temperature applications are involved, metal-seated triple-offset valves are used. Gate, globe, check, and ball valves are smaller and suitable for a variety of utility applications.

The difference and characteristics of aluminum alloy continuous casting and rolling

 1.What is the continuous casting and rolling method

Continuous casting and rolling is a combination of continuous casting and rolling deformation to complete in one process, that is, the casting and rolling process is completed in the rotation of a pair of rolls. When molten aluminum is cooled and solidified, it receives a certain amount of pressure and produces a certain amount of plastic deformation.

Selection of Continuous Casting Nozzle and Study on Spray Characteristics

Abstract: This article discusses the selection and spray characteristics of large-size square and round billet continuous casting nozzles, and proposes suggestions for improving the nozzle arrangement. Keywords: square and round billet; continuous casting nozzle; spray characteristics

Basic knowledge of continuous casting and 11 issues for improving the quality of continuous casting slab

 1. What are the causes of longitudinal cracks on the surface of continuous casting slabs and their prevention methods?

Longitudinal cracks on the surface of continuous casting slabs will affect the quality of rolled products. For example, a longitudinal crack with a length of 300mm and a depth of 2.5mm leaves a 1125mm layered defect on the rolled plate. Severe longitudinal cracks will cause leaks and rejects.

Safe operation process of continuous casting and pouring steel

01 Tundish preparation

1. Check the wall, bottom and baking conditions of the tundish;

2. The middle contractor shall determine the middle contract number used on duty according to the middle contract situation, write it on the blackboard and explain and sign on the "Tundish Packaging Safety Use Record Sheet" in the duty room (such as: normal, spare, new package and baking status, Out of service);

Matching principle of continuous casting machine and steelmaking and rolling

Classification method of continuous casting machine

At present, continuous casting machines have been widely used in steel mills, with various forms and different uses. The name of the continuous casting machine is also very inconsistent. Now introduce the classification method of continuous casting machine according to general habits:

Continuous casting mold flux knowledge

 1. What is the role of continuous casting mold powder?

During the pouring process, powdery or granular slag is continuously added to the molten steel surface of the mold, which is called mold flux. The role of mold powder has the following aspects:

(1) Thermal insulation to prevent heat dissipation;

(2) Separate the air to prevent oxygen in the air from entering the molten steel to cause secondary oxidation, which will affect the quality of the steel; (3) Absorb and dissolve the inclusions that float up from the molten steel to the slag interface to purify the molten steel;

(4) There is a layer of slag film between the mold wall and the solidified shell for lubrication, reducing the drawing resistance and preventing the adhesion of the solidified shell and the copper plate; (5) Filling the air gap between the blank shell and the mold to improve Heat transfer in the mold.

A good mold flux should be able to fully play the role of the above five aspects to achieve the purpose of improving the surface quality of the cast slab and ensuring the smooth flow of continuous casting.

When and how to add mold flux for continuous casting is the most beneficial?

In the actual production process, the performance of mold powder is closely related to the operation of adding slag. The continuous casting production practice of domestic and foreign steel mills has proved that even if the mold powder is selected correctly, failing to use it correctly will cause no quality problems in the cast slab. When adding protective slag to the mold, the mold slag must be evenly distributed on the molten steel surface in the mold. When the molten steel level fluctuates, drifts, stops casting and other failures occur during the pouring process, corresponding measures must be taken. In the actual operation process, the following items should be paid attention to when adding mold powder.

The composition and use skills of the slide gate late nozzle

The sliding nozzle is composed of upper and lower sliding plates and 4 refractory bricks for the upper and lower nozzles. The pouring of each ladle of molten steel must pass through the upper and lower sliding plates and the upper and lower nozzles, so they are very strict. Firstly, they must have sufficient strength at high temperatures to withstand the static pressure of molten steel, and secondly, the upper and lower sliding plates are required. The sliding surface should be very smooth, flatness should be high, to ensure tight contact, to ensure that no molten steel leaks during the pouring process, but also to be resistant to erosion, erosion, and good thermal stability, so as to withstand sudden changes in temperature. Erosion and slag erosion.

The sliding nozzle device is composed of upper and lower slide plates made of refractory materials and a mechanical drive structure, and is installed outside the bottom of the ladle. The upper slide is fixed, and the lower slide is movable. According to the skateboarding method, it can be divided into three categories:

1) Linear reciprocating;

2) Linear propulsion;

3) Rotary type.

By driving the pull rod, the sliding plate slides back and forth in a straight line. When the casting holes on the upper and lower sliding plate blocks are staggered, the upper nozzle hole is filled with drainage sand, and the steel ladle can be loaded; when the casting holes overlap, the drainage sand automatically flows out. Pouring, and the pouring speed can be controlled by the degree of overlap of the casting holes.

The sliding plate is a key component that determines the function of the sliding nozzle, and plays a role of controlling and regulating the flow of molten steel. Due to the repeated contact of the sliding plate with high-temperature molten steel (especially the casting hole), the corrosion damage is serious and the use conditions are harsh. The skateboard is required to have good performances such as high strength, corrosion resistance, and peeling resistance. During the casting process, ensure that no molten steel leaks between the skateboards. The skateboard must have the following properties:

(1) Flatness of sliding surface ≤0.05mm;

(2) High mechanical strength;

(3) Strong corrosion resistance to molten steel and molten slag;

(4) Excellent anti-oxidation performance;

(5) Good thermal shock stability.

The sealing protection of the ladle sliding nozzle is mainly at the connection between the upper nozzle and the upper slide, and the lower slide and the lower nozzle. In the pouring process, generally after pouring one or two furnaces of molten steel, the lower slide plate and the nozzle must be replaced and reassembled. The sealing protection adopts fibrous or mortar gaskets to ensure the high cleanliness of the molten steel and the uniformity of the internal quality of the casting slab.

Sliding nozzle hydraulic transmission:

Large and medium-sized ladle generally use hydraulic transmission devices to solve the problem of opening and closing sliding nozzles. Hydraulic transmission is driven by liquid (common oil) as the working medium. Because the liquid has almost incompressible characteristics, when the liquid is filled with a closed container (consisting of oil pumps, pipes, valves, cylinders, etc.), the liquid is pressurized by the oil pump, and it can lose this pressure through pipes, valves, etc. It is transmitted to the oil cylinder very small, causing the oil cylinder to move and realizing hydraulic operation. Reasons for steel leakage between sliding nozzles and preventive measures

(1) The reason for the leakage of the gap between the drain and the lower sliding plate: the sliding plate is not baked after pre-installation; the cement is not evenly coated during installation, resulting in gaps; there are bricks in the cement, making it loose.

Preventive measures: The fire mud must be clean during installation, the joints must be evenly seamed, and can only be used after baking and drying.

(2) The reason for the leakage of the upper and lower slide plates: the sliding surface is not flat; the upper and lower slide plates are cracked at the edge of the injection hole; the adjustment operation is not tight or the front and back are uneven.

Preventive measures: pay attention to choosing flat skateboards. Do not use skateboards without steel hoops to prevent cracking at the edge of the injection hole; the adjustment operation should be tight and even before and after.

(3) The reason for the leakage of the gap between the upper nozzle and the upper sliding plate: the upper sliding plate and the upper sliding plate are not evenly coated with mud; the mass in the fire mud causes the male and female mouths to be insufficiently deep and disconnected; the gap is too large.

Preventive measures: the fire mud should be clean, and the joints should be evenly cracked.

LMM GROUP One stop sevice for steel industry slide gate plate nozzle 

Common problems of rolling rolls

 Roller is a tool for plastic deformation of (rolled material) metal, and it is an important consumable part for the efficiency of the rolling mill and the quality of the rolled material. Rolls are important parts of rolling mills in rolling mills. They use the pressure generated by a pair or a set of rolls to roll steel. It mainly bears the influence of dynamic and static load, abrasion and temperature change during rolling.

There are two types of rolling we usually use, cold rolling rolls and hot rolling rolls.

There are many types of materials made of cold rolling rolls, such as 9Cr, 9Cr2, 9Cv8 Crmov and so on. There are two requirements for this type of rolling:

1: The rolled surface must be quenched

2: The hardness of the surface must be HS45105

The materials manufactured by hot rolling generally include 60 Crmnmo, 55Mn2 and so on. The field of use of this type is very wide. It can be used in some processing such as section steel, bar, rebar, high, non-steel, and open, etc. It bears strong rolling force, severe wear and thermal influence, Moreover, it works at high temperatures and allows diameter wear per unit of work, so it does not require surface hardness, but only requires high strength, initial properties and heat resistance. Hot rolling only uses overall normalizing or fire, and the surface hardness requires HB190-270 hardness.

The common failure forms and reasons of rolls are as follows:

1. Cracks.

Roll cracks are mainly caused by excessive local pressure of the roll and rapid heat and cold of the roll. On the rolling mill, if the emulsion nozzle is blocked, causing poor local cooling conditions of the roll, cracks will occur. Due to the low temperature in winter, cracks are prone to occur compared to the season

2. Peeling.

If the cracks continue to develop, it will form lump or flake peeling. Those with light peeling can be re-ground and continue to be used. Rolls with severe peeling will be scrapped.

3. Make pits.

The pitting is mainly due to the welding seam or other debris entering the rolling mill, so that the roll surface is marked with pits of different shapes. Generally, rolls with pits must be changed. When the quality of the welding seam of the steel is not good, the rolling operation should be lifted and pressed down to prevent the pits from being scratched.

4. Sticking roller.

The reason for the sticking of the roll is that during the cold rolling process, broken chips, wave breaks and broken edges appear, and due to the high pressure and high temperature, it is very easy to form a bond between the steel band and the roll, resulting in a small area of ​​damage to the roll. Through grinding, the roll can be used continuously after the cracks on the surface of the roll are eliminated, but its service life is significantly reduced, and it is prone to spalling accidents in future use.

5. Le roller.

Rolling is mainly caused by the excessive reduction of the steel which causes heavy leather or slight folds and the deviation of the steel to produce heavy leather. When the roll is severely struck, sticky rolls will occur and the steel will be cracked. When the roll is slightly stretched, both the steel and the roll will be stamped.

6. Broken roller.

The main causes of roll breakage are overpressure (that is, excessive rolling pressure), defects in the roll (non-metallic inclusions, bubbles, etc.), and stress field caused by uneven roll temperature.

The effect of raw materials on the structure and hardness of high chromium cast iron rolls

 Preface

Rolls are one of the most consumed parts in steel production and occupy an important position in metallurgical equipment manufacturing and steel production. Because of its low cost and good adaptability, high chromium cast iron is still one of the most widely used roll materials for hot strip mills. With the improvement of modern energy saving and environmental protection requirements, how to reduce the cost of raw materials has become the most concerned issue of roll enterprises. The advantage of iron and steel materials lies in their reusability. The use of scrap iron and steel can not only realize the utilization of solid waste, but also greatly reduce the cost of raw materials. The production of high chromium cast iron rolls generally adopts electric furnace smelting and centrifugal casting methods. Electric furnace smelting is a smelting method that can maximize the use of scrap iron and steel. The widespread use of scrap rolls and scrap iron and steel has become a common practice in roll manufacturers. However, due to different waste raw materials, the same smelting and pouring may result in different as-cast structures, which will affect the process performance and final structure and performance of the roll. In order to reduce the production cost of high-chromium cast iron rolls, we use a high-chromium cast iron wear-resistant plate (25% Cr) as the main raw material to replace Cr-Fe alloy to produce high-chromium cast iron rolls. However, in the subsequent heat treatment, it was found that although the final composition of the batch of rolls and ferroalloy production rolls is not much different, there are certain differences in the heat treatment process between the two, and the tendency of differential temperature quenching to crack increases, but the reason is not clear. Therefore, how to reasonably use waste high chromium cast iron should also deeply analyze the solidification structure of the two types of rolls and their influence on the transformation of the roll heat treatment process and the final structure and performance.

This paper compares and analyzes the solidification structure of two rolls of the same size produced by the same process: one is made of high-carbon sponge iron, a small amount of scrap steel and ferroalloy raw materials; the other is made of high-chromium cast iron wear-resistant plates as the main raw material. At the same time, the difference in the structure and properties of the two rolls treated by the same heat treatment process is studied. The purpose is to provide test data for the rational use of waste materials and the adjustment of the heat treatment of the cast rolls to ensure the performance of the rolls through the study of the differences in structure and process performance.

Test materials and methods

The test materials were cut and cut on two high chromium cast iron rolls of the same specification. Both rolls are produced using the same smelting and pouring process. The difference is: one uses sponge iron, ferroalloy, and a small amount of scrap steel as raw materials, called Roller A (Roller A); the other uses 58% waste high chromium cast iron The grinding plate is called Roller B. The final composition of the two rolls is shown in Table 1. The chemical composition of the two rolls is not much different. The biggest difference is that the carbon content of roll B is about 0.1% lower than that of roll A.

In order to study the difference in the heat treatment process between the two roll materials, the LINSEISL 78 dilatometer was used to measure the influence of the heating temperature and the cooling rate on the phase change of the cooling process. The sample size is a cylinder of 3 mm×10 mm; the austenitizing temperature is 1020 ℃, and the holding time is 0.5 h; the cooling rate is 10, 3, and 1 ℃/min, respectively. In order to simulate the influence of the actual heat treatment process on the structure and performance of the roll, the sample was quenched and tempered in a muffle furnace. The size of the sample was 10 mm × 10 mm × 8 mm. After the sample is austenitized at 1020 ℃ and held for 1 h, it is cooled to room temperature at a cooling rate similar to that of the actual roll quenching and cooling, and then tempered twice at 400, 450, 500 and 550 ℃ with a holding time of 10 h. After the sample was corroded by 5% nitric acid alcohol, the microstructure was observed with Axiovert 200 MAT optical microscope; the carbide morphology of the sample was observed with S-3400 thermal field emission scanning electron microscope (SEM); D/MAX 2500 PC type X was used The content of retained austenite is measured by XRD; the hardness of each sample is measured by HR-150 C Rockwell hardness tester, and each sample is tested at least 5 times, and the average value is taken.

Test results--Solidification group of rolls

Figure 1 shows the optical microstructure and SEM microstructure of the two rolls. It can be seen from Figures 1 (a) and 1 (b) that the microstructures of the two rolls are not much different. They are both typical hypoeutectic cast iron structures, namely primary austenite dendrites and eutectic ledeburite. There are flaky strips and irregular massive carbides and austenite in the tensite. The XRD diffraction analysis results show (Figure 2) that the two rolls are mainly composed of α-Fe, γ-Fe, M 7 C 3 and a small amount of M 23 C 6 phase. According to the analysis of the microstructure and the characteristics of high chromium cast iron, the carbides in the eutectic ledeburite are M 7 C 3 type carbides mainly composed of Cr, the primary austenite phase and the austenite in the eutectic ledeburite The structure after cooling is martensite + retained austenite11. Because the carbide and retained austenite in eutectic ledeburite are difficult to distinguish under an optical microscope, the relative content of eutectic carbides in colored gold was used for quantitative analysis, as shown in Figure 1 (c) and 1 (d) . The volume fraction of eutectic M 7 C 3 type carbide of roll A without waste high chromium cast iron is 23.1%, while the volume fraction of eutectic M 7 C 3 type carbide of roll B added with high chromium cast iron is It is 25.4%. The difference in the amount of eutectic carbides also affects the room temperature structure of the primary austenite phase and the austenite phase in the eutectic zone.

SEM observations (Figures 1e and 1f) show that there is only a small amount of martensite in and around the eutectic ledeburite zone, and no secondary carbides are precipitated, mainly retained austenite. In the primary austenite, the structure should be a large number of secondary carbides distributed on the martensite matrix, but there are obvious differences in the structure of the two rolls. There are two kinds of secondary carbide particles in the structure without the wear-resistant plate roll A: one is a shuttle-shaped particle with an orientation distribution with a length of about 1 μm; the other is a cubic particle with a size of 0.1 to 0. 3 μm; The carbides in the structure of the wear-resistant plate roll B are mainly square particles with a size of less than 0.5 μm, and the number is significantly less than that of the roll A. The results show that the alloy content of C, Cr, etc. in the primary phase of roll B should be lower than that of roll A, and low alloys affect its hardenability. Comparing the optical microstructures of the two rolls (Figure 1a and 1b), there are a small amount of black tissue regions in the optical microstructure of roll B (Figure 1b), and its microhardness is only 472 HV, which should be judged to be Pearlite tissue. In addition, combined with the quantitative analysis of the color metallographic eutectic carbides and the XRD analysis, the amount of retained austenite of the two rolls is also significantly different. The amount of retained austenite of roll A is about 26.7%, while that of roll B The amount of austenite is only 16.6%. But the hardness of the two is not much different, the hardness of roll A is 59.0 HRC; the hardness of roll B is 59.4 HRC.

Test results--The effect of cooling rate on M s point and hardness

Figure 3 shows the cooling curve of two high chromium cast iron roll materials after being austenitized at 1020 ℃ for 0.5 h and then cooled to room temperature at cooling rates of 10, 3, and 1 ℃/min. The two roll materials have no other transformations within the cooling rate range, only low-temperature martensite transformation, showing good hardenability. However, the Ms point of the two roll materials is slightly different. The Ms point of roll A is lower than that of roll B, as shown in Table 2. In addition, as the cooling rate decreases, the Ms point tends to increase. When the cooling rate is reduced from 10 ℃ / min to 1 ℃ / min, the Ms point of roll A increases from 263 ℃ to 327 ℃; roll B increases from 301 ℃ to 346 ℃. Different Ms points also have a certain influence on the hardness, as shown in Table 2. The hardness of roll A is higher than that of roll B, and with the decrease of the cooling rate, the hardness also decreases slightly, but the overall hardness remains above 58 HRC.

Test results--Simulate the structure and hardness of the roll after thermal quenching

Figure 4 shows the structure of the two rolls after quenching and cooling. Compared with the as-cast structure (Figures 1a and 1b), the structure of the ledeburite eutectic zone of the two rolls has little change, but how can the structure of the primary austenite zone change significantly (Figures 4a and 4) c). The structure of the primary austenite zone of roll A is composed of a large number of fine carbides and martensite matrix (Figure 4a); while the amount of carbides in the primary austenite zone of roll B is significantly reduced and coarsened (Figure 4c). This is confirmed by SEM observations (as shown in Figures 4b and 4d). There are two types of carbide particles in the primary austenite zone of roll A: one is larger in size and rod-shaped, and the other is fine. The granular shape of the carbide (Figure 4b); while the amount of carbide particles in roll B is less, the granular carbide particles and the short rod-shaped particles composed of the particles (Figure 4d). Compared with the as-cast structure (Figures 1e and 1f), the shuttle-shaped carbides in roll A disappeared, and the size of some carbides increased significantly, and the number tended to increase (compare Figure 1e and Figure 4b); The fine carbides of roll B disappeared completely and turned into larger carbides (compare Fig. 1f and Fig. 4d). The XRD analysis results show that the phase structure of the roll after simulated differential temperature quenching does not change much, mainly α-Fe, γ-Fe, M 7 C 3 type carbides and a small amount of M 23 C 6 type carbides, that is, the structure is Martensite Body and retained austenite and carbides. Combined with the results of the as-cast structure analysis, the retained austenite is mainly distributed in the eutectic austenite region and around the eutectic carbides. The hardness analysis results show that the hardness is slightly improved after quenching compared with the as-cast state. The hardness of roll A is increased from 59.0 HRC to 61.7 HRC; the hardness of roll B is increased from 59.4 HRC to 62.5 HRC.

Test results--Structure and hardness after tempering

Figures 5 and 6 show the microstructures of the two rolls treated by different tempering processes. The changes of the structure of the two rolls with the tempering temperature are basically the same. Under the condition of one tempering (Figure 5a~5d and Figure 6a~6d), when the tempering temperature is 400 ℃, there is basically no obvious change in the structure, but the austenite in the eutectic ledeburite Fine carbide particles precipitate in the zone; when the temperature reaches 450 ℃, the matrix of the primary austenite zone is tempered, and the quenched structure characteristics disappear; the austenite in the eutectic ledeburite also undergoes significant transformation, and the structure transformation is similar to quenching organization. Combined with the analysis results of the as-cast and quenched structure, there is a large amount of retained austenite in the eutectic austenite zone. Carbides are precipitated from the retained austenite during the tempering and holding process, which reduces the stability of the retained austenite and the tempering cooling process The retained austenite is transformed into martensite. When the tempering temperature is higher than 500 ℃, the structure of the austenite zone in the ledeburite is transformed into a structure similar to that of the primary austenite zone. After the secondary tempering (Figure 5e～5h and Figure 6e～6h), under the same temperature conditions, the tempering is more sufficient, but overall, at a temperature of 400 ℃, the secondary tempering structure changes still Incomplete; when the temperature is higher than 450 ℃, the retained austenite can be completely decomposed after tempering. Comparing the two rolls, the stability of retained austenite and martensite of roll B is higher than that of roll A. Under one tempering condition, when the temperature reaches 500 ℃, the quenched retained austenite in the eutectic zone of roll B can be basically transformed (Figure 6c). Under two tempering conditions, when the tempering temperature is 450 ℃, The retained austenite in the structure can be completely transformed, which is confirmed in the XRD analysis.

Test results--Structure and hardness after tempering

Figures 5 and 6 show the microstructures of the two rolls treated by different tempering processes. The changes of the structure of the two rolls with the tempering temperature are basically the same. Under the condition of one tempering (Figure 5a~5d and Figure 6a~6d), when the tempering temperature is 400 ℃, there is basically no obvious change in the structure, but the austenite in the eutectic ledeburite Fine carbide particles precipitate in the zone; when the temperature reaches 450 ℃, the matrix of the primary austenite zone is tempered, and the quenched structure characteristics disappear; the austenite in the eutectic ledeburite also undergoes significant transformation, and the structure transformation is similar to quenching organization. Combined with the analysis results of the as-cast and quenched structure, there is a large amount of retained austenite in the eutectic austenite zone. Carbides are precipitated from the retained austenite during the tempering and holding process, which reduces the stability of the retained austenite and the tempering cooling process The retained austenite is transformed into martensite. When the tempering temperature is higher than 500 ℃, the structure of the austenite zone in the ledeburite is transformed into a structure similar to that of the primary austenite zone. After the secondary tempering (Figure 5e～5h and Figure 6e～6h), under the same temperature conditions, the tempering is more sufficient, but overall, at a temperature of 400 ℃, the secondary tempering structure changes still Incomplete; when the temperature is higher than 450 ℃, the retained austenite can be completely decomposed after tempering. Comparing the two rolls, the stability of retained austenite and martensite of roll B is higher than that of roll A. Under one tempering condition, when the temperature reaches 500 ℃, the quenched retained austenite in the eutectic zone of roll B can be basically transformed (Figure 6c). Under two tempering conditions, when the tempering temperature is 450 ℃, The retained austenite in the structure can be completely transformed, which is confirmed in the XRD analysis.

Analysis and discussion

It can be seen from the above test results that although the two rolls in this test have little difference in chemical composition (Table 1), only the carbon and chromium content of roll A is slightly higher than that of roll B, which is about 0.1% higher. However, due to the raw material The difference causes a slight difference in the solidification structure of the two rolls (Figure 1 and Figure 2), and this structural difference affects the transformation of the roll during the heat treatment process (Figure 3) and the final structure (Figure 4 to Figure 8) And performance (Table 3). Figure 9 shows the quasi-equilibrium phase diagram of high chromium cast iron with 17.5% Cr calculated using the TCFE 7 database in the Thermal-Cale software. The solidification structure of high chromium cast iron containing 17.5% Cr is pro-eutectic primary austenite and ledeburite composed of eutectic M 7 C 3 and austenite. However, because roll B uses a large amount of waste hypereutectic high chromium cast iron wear-resistant plates, and because there are a large number of hypereutectic M 7 C 3 type carbides and eutectic ledeburite in the structure of the wear-resistant plate (Figure 10 ), in the smelting In the process, the dissolution of the eutectic and eutectic M 7 C 3 carbides requires a higher melting temperature and time to obtain a uniform liquid phase structure. Therefore, under normal smelting conditions, insufficient dissolution of the pro-eutectic M 7 C 3 carbides leads to an increase in the tendency of the uneven concentration of Cr and C in the liquid phase to fluctuate. In the subsequent cooling process, the degree of undercooling of the primary austenite and eutectic structure transformation is reduced, and the eutectic transformation is promoted, resulting in an increase in the amount of eutectic and eutectic M 7 C 3 carbides in the final structure (Figure 1) , Thereby reducing the carbon and alloying element content of austenite in the primary austenite and co-ledite, and the stability of austenite austenite is reduced. In the subsequent cooling process, a small amount of pearlite appears on the roll B (Figure 1 b), and the amount of retained austenite is reduced (Figure 2). The difference in alloys such as C and Cr in the primary austenite also affects the precipitation of secondary carbides during the cooling process. The primary austenite of roll A has two kinds of carbides, M 7 C 3 and granular M 23 C 6, while the primary austenite of roll B has only one kind of granular M 23 C 6 carbide (Figure 1 e And 1 f ). According to the equilibrium phase diagram of high chromium cast iron (Figure 9), during the cooling process after solidification of the high chromium roll, secondary M 7 C 3 carbides should be precipitated; and in the subsequent ferrite region, only M 23 C 6 type Carbides precipitate, but under low C and Cr conditions, M 23 C 6 carbides precipitate in the austenite region during cooling. Related literature studies on 18% Cr hypoeutectic high chromium cast iron have also confirmed that there are two types of secondary carbides in the matrix: one is rhombic and rhombic M 7 C 3 type carbide; the other is face-centered cubic M 23 C 6 type carbide. Under certain conditions, both carbides can become precipitated phases, and this precipitation depends on the content of Cr and C in the matrix. Therefore, there are fusiform M 7 C 3 carbides and granular M 23 C 6 carbides in the primary austenite of roll A (Fig. 1 e ); while there are only mainly granular M 23 in the primary austenite of roll B C6 type carbide (Figure 1e), it is also confirmed that the primary austenite content of roll A is higher than that of roll B. The retained austenite of roll A is also higher than that of roll B after cooling (Figure 2). It is precisely because the raw materials affect the solidification structure of the roll, which affects the subsequent heat treatment process characteristics and the final structure and performance of the roll. During the quenching and heating process of high chromium cast iron, austenitization only occurs in the primary phase and eutectic austenite. The content of alloying elements such as C and Cr in austenite directly affects the transformation of the cooling process. The large amount of hypereutectic carbides in the solidification structure of roll B will inevitably lead to a decrease in the alloy content in austenite. Therefore, the Ms of roll B is higher than that of roll A, and the hardness is also lower than that of roll A. In addition, as the cooling rate decreases, the Ms point of the roll increases and the hardness decreases (Table 2), indicating that carbides precipitate during the cooling process. In the actual heat treatment process of the roll, due to the large size of the roll, the air cooling method is adopted, and the cooling rate of the roll is slow cooling, and when the surface is cooled to about 500 ℃, it directly enters the tempering furnace for heat preservation and then slowly cools.

During this process, supersaturated carbon and alloying elements in the austenite will precipitate, and the precipitation of carbides depends on the degree of supersaturation of the austenite. It can be seen from Figure 4 that after simulated quenching, there are two sizes of carbide particles in roll A, one is a larger block or short rod, and the other is small particles; roll B is mainly granular and The particles constitute chain-like carbides, and the number of carbides is significantly less than that of roll A. High chromium cast iron is in the austenitizing temperature range of austenite and M 7 C 3 equilibrium phase (Figure 9 ), the coarse eutectic M 7 C 3 carbides remain unchanged, but the fine carbides precipitated in the primary austenite The substance dissolves, and the M 7 C 3 carbide spheroidizes and grows up. In high chromium cast iron, there are mainly two kinds of carbides: M 7 C 3 type carbide and M 23 C 6 type carbide. The M 23 C 6 type carbides have lower interfacial energy and can be precipitated as transition phases of the M 7 C 3 carbides. Under low Cr and C conditions, the M 7 C 3 carbides in roll B are formed into chains of particles (Figure 4d). Due to the different contents of C, Cr and other alloying elements in the primary austenite of the two rolls, under the condition of simulating the low cooling rate of the roll, the roll A precipitates fine M 23 C 6 type carbides at low temperature, which causes the roll A to form two sizes of carbonization Objects (Figure 4 b). The quenched structure of high chromium cast iron is undissolved carbide, martensite and retained austenite. In the tempering process, the martensite is tempered, and the retained austenite is decomposed and transformed into martensite in the subsequent cooling process. When the tempering temperature is 400 ℃, due to the low tempering temperature, the quenched structure does not change much, only a small amount of carbides are precipitated in the matrix (Figure 8a and 8c), and martensite tempering mainly occurs (Figure 5a, 5e) And Figure 6a, 6e), the hardness is slightly reduced (Table 3). As the tempering temperature increases, the martensite is tempered and the retained austenite is decomposed (Figure 5b, 5f and Figure 6b, 6f), and fine carbides are precipitated. After tempering and cooling, the retained austenite The body transforms into martensite (Figure 7). The precipitation of carbides and the transformation of martensite produce secondary hardening to increase the hardness (Table 3). When the tempering temperature rises to 500 ℃, the martensite is fully tempered (Figure 5 c ～ 5 d, 5 g ～ 5 h and Figure 6 c ～ 6 d,6 g ~ 6 h), the retained austenite transforms (Figure 7), and the precipitated carbides begin to grow (Figure 8b)And 8 d) to reduce the hardness (Table 3).

Compared with quenching, the number of carbides in the primary austenite matrix is ​​significantly increased, but the coarse block and rod-shaped carbides disappear, and the particles gradually become relatively uniform in size (Figures 8b and 8d). In the low temperature region, the stable phase of chromium carbides is M 23 C 6 type carbides (Figure 9). During the tempering process, on the one hand, M 23 C 6 type carbides, on the other hand, M 7 C 3 transforms to M 23 C 6. This transformation leads to the transformation of the larger M 7 C 3 carbides in the primary austenite matrix to the M 23 C 6 carbides, so that the coarse M 7 C 3 carbides disappear, and finally particles of relatively uniform size are formed in the structure. Shaped carbides (Figure 8 b and 8 d). According to the review, the addition of waste high-chromium cast iron wear-resistant plate rolls has a certain effect on the solidification structure and the structure transformation and performance during heat treatment. This effect is mainly related to the effect of adding high-chromium cast iron wear plate on the solidification structure. Therefore, In order to make reasonable use of high-chromium cast iron wear-resistant plates, it is necessary to thoroughly study the effect of addition amount and smelting temperature and time on the solidification structure.

1) The solidification structures of the two high chromium cast iron rolls are both primary austenite and ledeburite eutectic. The primary austenite and eutectic austenite transform into martensite and retained austenite in the subsequent cooling process. , Retained austenite is mainly distributed in the eutectic austenite and around the eutectic carbides. The raw materials have a certain influence on the solidification structure of the high chromium cast iron rolls. The amount of eutectic carbides in roll A is 23.1%; primary austenite The secondary carbides in the body matrix are shuttle-shaped and granular carbides; while the amount of eutectic carbides in roll B with added waste high chromium cast iron wear-resistant plates is higher than that of roll A, which is 25.4%, and the secondary carbides are Granular carbides, in addition there is a small amount of pearlite in the structure;

2) Under the same austenitizing conditions, the two rolls have a martensitic structure in the range of 10 ～ 1 ℃ / min, but the Ms point of roll A is lower than that of roll B, which is 20 ～ 40 ℃ lower;

3) The structure after quenching of the simulated roll is martensite, retained austenite and carbides. Compared with the as-cast state, the number and morphology of carbides in the primary austenite have changed significantly, and the number of fine carbides has been significantly reduced. However, there are certain differences between the two rolls. The carbides in the primary austenite of roll A are coarse rods and fine particles; while the carbides in the primary austenite with waste high chromium cast iron wear-resistant plate roll B are relatively large particles. , And the number is significantly less than that of roll A, compared with the as-cast state, the hardness after quenching is slightly increased, and the hardness of roll B is slightly higher than that of roll A;

4) After tempering, the two rolls both undergo secondary hardening at 450 ℃, but roll A appears in the primary tempering, and roll B appears in the secondary tempering. This phenomenon is related to the degree of analysis of retained austenite . During the tempering process, the coarse M 7 C 3 type carbides in the primary austenite matrix are transformed into fine M 23 C 6 type carbides. As the tempering temperature increases, the carbides aggregate and grow, and the two types of roll carbides The shape tends to be consistent.

Research and Application of Repairing Technology of Worn Roll Surface of Metallurgical Roll

 Abstract: The main form of failure in the rolling process of metallurgical rolls is roll surface wear. The repairing technologies of worn roller surfaces mainly include brush plating, thermal spraying, thermal spray welding, traditional surfacing, laser cladding, etc. The advantages and disadvantages of various repairing technologies are analyzed. In order to ensure the performance of the roll after repair, it is necessary to reduce the residual tensile stress of the roll repair layer. Reducing the residual tensile stress is mainly carried out from two aspects: the matching of the repair layer material and the linear expansion coefficient of the substrate, and the reasonable preheating and post-repair heat treatment. Measures to reduce the residual tensile stress during the repair of the worn roller surface are proposed.

Roller is a direct tool to deform metal during rolling. Its quality and service life are directly related to the production efficiency, product quality and production cost of rolling production. In the actual use process, the roll has to withstand great rolling cyclic stress, instantaneous high temperature and strong impact force, strong friction and squeezing force, which will inevitably cause the failure of the roll. If the roll fails, the entire roll will be scrapped, resulting in huge waste and huge economic losses to the enterprise. Roll surface wear is a major failure form of metallurgical rolls. How to repair the worn roll surface has always been a major concern in the roll industry. Through the introduction of brush plating technology, thermal spray technology, thermal spray welding technology, traditional surfacing technology, and laser cladding technology for the repair of worn roller surfaces, the advantages and disadvantages of various repair technologies are analyzed, and the repair of worn roller surfaces of metallurgical rollers is proposed. Measures to reduce residual stress during the process provide a theoretical reference for on-site repair of worn roll surfaces.

1. Failure form of worn roller surface

Metallurgical roll wear roll surface includes two forms of normal wear and abnormal wear.

Normal wear is that during the actual rolling process of the roll, with the extension of the rolling time, the surface of the roll and the rolled product grind and contact each other, resulting in the gradual separation of metal particles on the surface of the roll from the surface of the roll, resulting in a smaller roll diameter and wear resistance. reduce. When the roll diameter wear is small to a certain extent and the roll surface hardness drops to a certain value, it cannot be used even if there are no other defects. Because the roll diameter is small, after the hardness is reduced, the rolled product will not be able to meet the specified size and shape requirements.

The wear mechanisms of abnormal wear mainly include fatigue wear, adhesive wear, corrosive wear, abrasive wear, and fretting wear. In the actual rolling process, these several forms of wear exist mutually and alternately work together. The main form of action is the surface cracks of the roll, which can be divided into axial cracks, circumferential cracks, cracks, ring-shaped cracks and net-shaped cracks. According to statistics, the failure rate of surface cracks of cold work rolls can reach more than 60%, and that of hot work rolls can reach more than 20%. The cracks mostly occur in the contact parts of the roll and the rolled product. As the wear intensifies, cracks, ring-shaped and net-like cracks will spread from the outside to the inside along the grain boundary, and shallow peeling of the roll surface or large area deep peeling may occur. At this time, the roll surface can be repaired; but with As the rolling time is prolonged, roll breakage may occur further, and the roll cannot be repaired and can only be scrapped.

2. Repairing technology of worn roller surface

Before repairing metallurgical rolls with worn roll surfaces, mechanical processing must be used to remove crack defects and fatigue layers on the roll surface to prevent them from being the source of cracks and affecting the quality of the repaired roll. There are mainly the following techniques for repairing worn roller surfaces.

2.1 Brush plating technology

The brush plating technology was invented by the French "Dalic" Research Institute in 1938. It is a method of quickly electrochemically depositing a metal or alloy coating on the local surface of the roll at room temperature and without grooves. Wang Hongmei et al. brush-plated nano-composite coatings on the surface of the rolls. The coatings have excellent fatigue and wear resistance properties.

Brush plating technology has the advantages of simple equipment, flexible operation, fast plating speed, low surface roughness of the coating, and many types of coatings. However, this technology has serious environmental pollution in production, which restricts its application to a certain extent.

2.2 Thermal spray technology

Thermal spraying technology is to heat the sprayed material to melt or semi-melt, and then use high-speed gas to disperse and refine the sprayed material and hit the surface of the substrate at high speed to form a micro-metallurgical bond or mechanical bond coating preparation technology. Si Jian et al. used oxyacetylene flame spraying nickel-aluminum composite powder F 505 (transition layer) and nickel-based alloy G 112 powder (working layer) to repair cast iron Km TBMn 5 W 3 rolls. The porosity between the coating and the roll surface was 25%. The tensile bond strength of the coating and the substrate is 25 MP, and the shear bond strength is 130 MPa. The working coating has been subjected to 1500 h, and the wear after working is small, which meets the technical requirements. Japan Fujii M et al. conducted abrasion resistance friction test by thermal spraying AI 2 O 3-Ti O 2 composite coating on the surface of steel rolls. The results showed that the coating with a thickness of 0.2 mm has good wear resistance when resisting rolling contact fatigue. .

Thermal spraying technology repairs the surface of the roll with small matrix deformation and very shallow heat-affected zone. However, the disadvantage of this technology is that the bonding strength between the coating and the substrate is low, and there are pores and residual stress inside the coating, the toughness is poor, and the machinability is poor, which also limits its wide application to a certain extent.

2.3 Thermal spray welding technology

Thermal spray welding technology is a coating technology developed on the basis of thermal spray technology. It uses a heat source to re-melt or partially melt the coating material on the surface of the substrate to achieve the gap between the coating and the substrate and between the particles in the coating. Metallurgical combination eliminates pores. Jiang Fuhui and others used SPH-C spray welding remelting equipment to spray weld G 112 powder on the surface of the roll. The hardness of the spray welding layer is 58 ~ 62 HRC, and the bonding strength of the spray welding layer and the substrate has exceeded or approached the base material. Ni Zhenhang et al. used flame as the heat source to spray-weld nickel-based alloy Ni 60 A powder on the CSP conveyor roller. The spray-welded layer and the substrate have high bonding strength and low porosity. Thermal spray welding technology The spray welding layer has a dense structure and few metallurgical defects. The metallurgical bonding strength of the spray welding layer and the substrate is high, but the deformation and heat-affected zone of the substrate are larger than that of the thermal spray technology.

2.4 Traditional surfacing technology

Traditional surfacing technology is a technology of cladding an alloy layer with special properties such as heat resistance, wear resistance and corrosion resistance on the surface of the roll. Traditional surfacing welding technology is the most commonly used repairing technology for the worn surface of metallurgical rolls. The general process route of the surfacing repairing technology is shown in Figure 1.

There are three types of surfacing welding technology, including automatic submerged arc welding, manual arc welding and argon tungsten arc welding. See Table 1 for the repair characteristics of different surfacing welding technologies. Various wear-resistant welding materials have been developed at home and abroad to be used in the repair of worn surface of metallurgical rolls, such as Japan's MF-30 / US-H 600 N, HF-1000; Sweden's UTP-CDU R 600, SK-C 600 -O; Face weld 12 in the United States; D 667, D 687, GFH-423-S / GXH-82 in China, etc.

2.4.1 Automatic submerged arc welding

Submerged arc automatic welding is currently the most commonly used metallurgical roll surface surfacing repair technology. Usually, the roll defect area is first used for transition layer materials, and then used for working layer materials. This method is automated production and has the advantages of high production efficiency and good working conditions. At the same time, due to the protective effect of the molten slag on the molten pool, the intrusion of nitrogen, oxygen and hydrogen in the air into the molten pool is reduced, and the performance and quality of the surfacing metal is good. The submerged arc automatic surfacing technology has a large heat input and a high dilution rate to the roll. It usually requires multiple layers of surfacing to ensure the required surfacing metal properties. In order to prevent cracks from being excessively cooled during roll repair, measures such as preheating and slow cooling before welding are usually required. In order to reduce the residual stress of the surfacing welding and improve the performance of the surfacing material, heat treatment is required after welding.

Shi Qiuhong and others used H 2 Cr 13 submerged arc welding wire and flux SJ 260 to repair the 70 Mn low alloy high-strength steel roll by submerged arc welding. The surfacing layer can not only meet the quality requirements, but also the high hardness and high resistance of the surfacing layer. The grindability nearly doubles the service life of the roll. Niu Ben et al. used self-made cored welding wire and flux to perform surfacing repair tests on Cr 5 cold rolls. The surfacing process is stable and beautiful in shape. The surfacing layer metal is based on austenite structure, and the hard phase particles are dispersed in the matrix. Medium, the structure is uniform and small; the average hardness of the surfacing layer is 59 HRC, and the wear resistance is better than that of Cr 5 steel.

2.4.2 Manual arc welding

Manual arc welding is a method in which the manually operated electrode and the workpiece to be welded are treated as two electrodes, and the arc heat between the electrode and the workpiece is used to melt the metal for welding. This technology is mainly used for surfacing repair of local defects on the surface of rolls. Japan invented a continuous casting roll surfacing type 1 Cr 16 Ni 4 Cu 4 Nb electrode with high strength and corrosion resistance. Lu Cheng et al. developed a wear-resistant surfacing D 600 electrode. The surfacing metal has a higher hardness value (about 58.8 HRC) and better wear resistance. Cheng Zhonggeng used self-made electrodes to perform manual arc surfacing on MC 5 cold-rolled work rolls. The metal hardness of the surfacing layer is 59.3 HRC, which is better than the performance of domestic D 322 electrodes.

The characteristics of manual arc welding are simple surfacing equipment, flexible operation, not limited by welding position and roller surface shape, but its production efficiency is low, the dilution rate is high, it is not easy to obtain a thin and uniform surfacing layer, and the working conditions are poor. .

2.4.3 Tungsten arc welding

Tungsten argon arc welding is a welding method that uses tungsten rods as electrodes and argon gas as shielding gas. During welding, argon gas is continuously sprayed from the nozzle of the welding torch to form a gas protection layer around the arc to isolate the air and prevent oxygen in the air from affecting the air. Oxidation of the tungsten electrode, the molten pool and the adjacent heat-affected zone to obtain a beautiful weld metal. This technology is mainly used for local defect areas on the surface of metallurgical rolls. Compared with manual arc welding technology, the heat input is easier to control, the gas protection effect is good, and the surfacing layer metal performance is excellent, but the working conditions are poor and the production efficiency is low.

2.5 Laser cladding technology

Laser cladding technology is a new type of surface modification technology with the most development prospects in roll repair. It uses preset powder or synchronous powder feeding to place selected cladding materials on the surface of the roll substrate, and make it through laser irradiation. It melts at the same time with the thinner layer on the surface of the substrate, and quickly solidifies to form a surface cladding layer with extremely low dilution and metallurgical bonding with the substrate material. Different cladding layer materials have different surface properties. This technology has the characteristics of small heat-affected zone, small roll deformation, compact structure, high bonding strength between the cladding layer and the substrate, and it is not restricted by the welding position and the shape of the roll surface.

The cladding materials used in laser cladding technology are generally powders, mainly iron-based alloy powders, nickel-based alloy powders, and cobalt-based alloy powders, as well as ceramic materials, pure metal powders, and so on. Iron-based alloy powders are inexpensive and widely used, and are suitable for parts that require local wear resistance and easy to deform; nickel-based alloy powders are suitable for parts that require local wear resistance, heat corrosion resistance and thermal fatigue resistance; cobalt-based alloy powder prices Expensive, generally suitable for parts requiring high hardness, high temperature wear resistance, high temperature corrosion resistance and thermal fatigue resistance; ceramic material powder has high strength at high temperatures, good thermal stability, and high chemical stability, generally suitable for Parts requiring wear resistance, corrosion resistance, high temperature resistance and oxidation resistance. Yan Kai et al. used a cross-flow CO 2 laser to cladding 50% Cr 3 C 2 and 50% Ni-Cr alloy powder on the surface of high chromium cast iron rolls. The surface structure of the cladding layer is Cr 3 C 2 and M 7 C 3 type carbides. , The hardness is significantly increased to 1100 HV, which is about twice the hardness of the substrate, and the wear resistance of the cladding layer is also improved. Zhang Hui and others prepared Ti VC 2 reinforced iron-based cladding on 42 Cr Mo roll substrates by using a mixed powder of ferro-vanadium, ferro-titanium, reduced iron powder, and graphite using a synchronous powder feeding method. Floor. Studies have shown that the cladding layer is well formed, compact, free of porosity and cracks, and has high metallurgical bonding strength with the substrate. Fu YM et al. analyzed the temperature field distribution on the surface of the continuous caster roll through finite element software, calculated the limit value of the load during the working process of the continuous casting roll, and then used laser cladding technology to coat the surface of the continuous casting roll with a thickness of The 3 mm Ni 45 alloy powder doubles the surface hardness of the roll. A factory installs a rectangular nozzle on a semiconductor laser robot, and uses a synchronous powder feeding method to cladding Fe Ni Cr BSi alloy powder on the support roller 70 Cr 3 Mo, as shown in Figure 2.

3. Analysis of repairability of worn roll surface

The metallurgical roll on the worn roll surface has a large mass and volume. During the repair process, the molten pool cools quickly and is easy to form a large temperature gradient. At the same time, there is a difference in the expansion coefficient between the repair layer material and the substrate, and it is easy to produce a large amount of The residual tensile stress causes cracks in the repair area of ​​the metallurgical roll and reduces the service life of the roll. Therefore, in order to ensure the service performance of the roll repaired, it is necessary to reduce the residual tensile stress of the roll repaired layer. Reducing the residual tensile stress is mainly carried out from two aspects: the matching of the repair layer material and the linear expansion coefficient of the substrate, and the reasonable preheating and post-repair heat treatment.

3.11 The matching of the repair layer material and the linear expansion coefficient of the substrate

One of the important reasons for the residual tensile stress in the repair layer is the difference between the expansion coefficient of the repair layer material and the base material. When the expansion coefficient of the repair layer is greater than the expansion coefficient of the substrate, tensile stress will be generated, otherwise, compressive stress will be generated. When the residual tensile stress is greater than the ultimate strength of the material, cracks are likely to occur, causing cracking and peeling of the repair layer. The expansion coefficient of the repair layer is not as small as possible for the matrix, and it needs to have a certain range limit. Therefore, selecting a repair layer material close to the expansion coefficient of the substrate is one of the effective methods to reduce the residual tensile stress of the repair layer and reduce the cracking sensitivity. 

3.22 Reasonable preheating and post-repair heat treatment

Preheating the substrate before the roll repair can reduce the temperature gradient and reduce the residual tensile stress. The heat treatment after the repair can reduce the residual stress, improve the performance of the repair layer, and ensure the quality of the roller after the repair. However, in the actual on-site repair of worn metallurgical roll surfaces, it is difficult to ensure that the roll substrate is preheated before the repair and the heat treatment after the repair. Preheating before repairing worn rolls and heat treatment after repairing will prolong the repairing time, increase costs, and worsen the working environment. The laser cladding technology can use a low-power laser to preheat the roll before repair, reduce the temperature gradient between the repair layer and the substrate, reduce the residual tensile stress, and improve the quality of the roll after repair.

4. Conclusion

What kind of technology is used to repair the worn surface of metallurgical rolls and improve the service life of the rolls has always been a major concern in the roll industry. Conventional wear roller surface repair technologies such as brush plating technology, thermal spray technology, thermal spray welding technology, automatic submerged arc welding, manual arc welding, and argon tungsten arc welding can not effectively improve the ability of the roller surface to resist high temperature wear and cracking. Therefore, it is of great significance to carry out laser cladding technology to repair the worn surface of metallurgical rolls and will be an important direction for future development. With the rapid development of laser cladding technology, composite laser cladding technologies have emerged on the market, such as laser cladding with ultrasonic, electromagnetic stirring, alternating magnetic field, mechanical vibration and other technologies. These technologies are beneficial to the internal structure of the cladding layer. The rate decreases, the grain size decreases, and the hardness and wear resistance of the cladding layer are greatly improved. In recent years, with the rapid development of nanomaterials, laser cladding technology can be used to cladding nanomaterials on the surface of rolls, which can increase the overall strength of the material to a certain extent, forming a new technology for nanometering the surface of metallurgical rolls, which is helpful for scientific research Workers' in-depth research on the overall performance of nanomaterials.