Ladle Furnace Essentials: Streamlined Steel Refining Process

 

The Ladle Furnace: Simplifying Steel Refining

The ladle furnace (LF), a secondary refining system, is indispensable in modern steel production. Positioned between primary steelmaking and continuous casting, this equipment enhances steel quality through three core functions: precise temperature control, targeted impurity removal, and exact alloy adjustments.

Three Pillars of LF Efficiency

1. Dual-Stage Impurity Removal

The LF combines deoxidation (oxygen removal) and desulfurization (sulfur reduction) through:

• Direct aluminum injection for rapid oxygen binding


• High-basicity slag (CaO/SiO₂ ≥2.5) that absorbs sulfur


• Argon gas stirring to accelerate reactions

This tandem approach achieves sulfur levels below 0.002% in specialty steels.

2. White Slag Optimization

The LF's signature low-oxidation slag system:

1. Reduces FeO+MnO content below 4%


2. Maintains a reducing atmosphere via argon shrouding


3. Enables 90% inclusion removal efficiency

3. Precision Temperature Control

Electric arc heating allows:

• 5°C/minute heating rates


• ±3°C temperature uniformity


• Optimal casting conditions

Why Argon Stirring Matters

Argon gas performs critical roles:

• Homogenizes steel chemistry in under 5 minutes


• Prevents slag foaming during heating


• Removes oversized inclusions (>20μm)

LF in Numbers

Key operational benchmarks:

• Refining time: 25-45 minutes per heat


• Argon consumption: 0.4-1.2 Nm³/ton


• Alloy recovery rates: 92-98%

ladle furnace refining basics、LF desulfurization techniques、steel temperature control in LF

Magnesita Refractories: Efficient Tundish Lining Solutions

 Magnesita Refractories: Smart Installation for Durable Tundish Linings

Core Installation Guidelines

Magnesita refractories combine organic/inorganic binders to create high-performance linings. Critical parameters include:

• Permanent layer temp: <100°C (ideal: ambient)
• Working layer thickness: 40-50mm (bottom), 45-60mm (walls)
• Minimum 55mm at slag line

3-Step Installation Process

1. Preparation & Base Layer

Install impact pads with ramming mix, spread magnesia dry vibratables evenly, and position forming molds with 45-60mm clearance from permanent walls.

2. Vibration & Curing

Layer material in 3-5min vibration cycles. Cure at 200-250°C for 60-90min, then cool below 100°C before demolding.

3. Final Assembly

Inspect for defects (>2mm cracks require repair), install flow control components, and backfill joints with matching material.

Optimized Baking Protocol

Maximize magnesita refractories' performance with:

• 30min ramp to 800°C
• 70min hold at 1100°C
• Total time: 70-180min

Key Advantages

Magnesia-based linings deliver:

• 12h+ operational lifespan
• 20% lower steel inclusion rates
• Reduced thermal shock risks

Pro Maintenance Tips

Extend magnesita refractory life with:

1. Post-cast laser wear scanning
2. Preventive repairs at 8h intervals
3. Controlled cooling between heats

Magnesita Refractories: Smart Installation for Durable Tundish Linings

Core Installation Guidelines

Magnesita refractories combine organic/inorganic binders to create high-performance linings. Critical parameters include:

• Permanent layer temp: <100 ambient="" ideal:="" li="">
• Working layer thickness: 40-50mm (bottom), 45-60mm (walls)
• Minimum 55mm at slag line

3-Step Installation Process

1. Preparation & Base Layer

Install impact pads with ramming mix, spread magnesia dry vibratables evenly, and position forming molds with 45-60mm clearance from permanent walls.

2. Vibration & Curing

Layer material in 3-5min vibration cycles. Cure at 200-250°C for 60-90min, then cool below 100°C before demolding.

3. Final Assembly

Inspect for defects (>2mm cracks require repair), install flow control components, and backfill joints with matching material.

Optimized Baking Protocol

Maximize magnesita refractories' performance with:

• 30min ramp to 800°C
• 70min hold at 1100°C
• Total time: 70-180min

Key Advantages

Magnesia-based linings deliver:

• 12h+ operational lifespan
• 20% lower steel inclusion rates
• Reduced thermal shock risks

Pro Maintenance Tips

Extend magnesita refractory life with:

1. Post-cast laser wear scanning
2. Preventive repairs at 8h intervals
3. Controlled cooling between heats

Key Factors Driving Magnesium Bricks Costs | Industry Analysis

 

What Determines Magnesium Bricks Pricing? 5 Critical Factors

1. Raw Material Costs: The Core Driver

Magnesia Quality Matters

High-purity fused magnesia (MgO ≥95%) costs 25% more than standard grades but delivers better thermal stability. Supply chain disruptions in major producing regions like China can cause price spikes exceeding 30%.

Graphite Market Pressures

Flake graphite (C ≥90%) enhances thermal shock resistance but competes with battery manufacturers. A 15% graphite price increase typically raises magnesium bricks costs by 7–9%.

2. Production Technology Impacts

Advanced Manufacturing

Isostatic pressing creates bricks with 98% density uniformity, enabling 20–25% price premiums. Automated mixing systems reduce material waste by 12% but require $1.5M+ investments.

Energy Efficiency

Modern kilns with AI-controlled combustion cut energy costs by 30%, saving $15–20 per ton. These technologies help offset rising raw material expenses.

3. Market Demand Fluctuations

Global steel production (1.95B tons in 2023) drives 65% of magnesium bricks demand. China’s green steel initiatives could boost premium brick requirements by 35% by 2030. Oversupply scenarios during industry downturns trigger price drops up to 18%.

4. Quality Specifications

Key Performance Metrics

• Thermal cycles: 25+ (1100°C ⇄ water)
• Compressive strength: ≥45 MPa
• Erosion resistance: ≤1.5 mm/hour

Nuclear-grade magnesium bricks cost 250% more than industrial grades due to strict certification requirements.

5. Strategic Purchasing Tips

Supplier Evaluation

Prioritize vendors offering:

• Third-party quality certifications (ISO 9001)
• Technical support teams
• 60–90 day inventory buffers

Cost Optimization

Implement JIT purchasing with 45-day safety stock. Predictive analytics can reduce inventory costs by 18% while maintaining 97% supply reliability.

Magnesia carbon brick: an excellent representative of high performance refractory materials

 

In many fields of modern industrial production, the operation of equipment in high temperature environments faces severe challenges, and refractory materials have become a key factor in ensuring the stable and efficient operation of these equipment.

As a refractory material with excellent performance, magnesia carbon bricks play an irreplaceable and important role in industries such as steel, non-ferrous metal smelting, and glass manufacturing with their unique advantages. This article will explore the advantages of magnesia carbon bricks in depth and show their important value in the field of high temperature industry.

1. Basic composition and structure of magnesia carbon bricks

Magnesia carbon bricks are mainly composed of two key components: magnesium oxide (MgO) and carbon ©. Magnesium oxide has an extremely high melting point (2800°C) and is a high melting point alkaline oxide, which gives magnesium carbon bricks excellent high temperature resistance and good corrosion resistance to alkaline slag. The carbon element usually exists in magnesium carbon bricks in the form of graphite. Graphite has excellent electrical conductivity, thermal conductivity, low expansion coefficient and poor wettability with slag. This unique combination makes magnesium carbon bricks have both the high melting point of magnesium oxide and the many excellent properties of carbon.

From the microstructure point of view, the magnesium oxide particles in the magnesia carbon brick are evenly distributed in the carbon matrix, forming a tightly interwoven composite structure. The magnesium oxide particles are connected to each other by a carbonaceous binder. This structure not only enhances the strength of the brick body, but also provides it with good thermal shock resistance and slag erosion resistance. The carbonaceous phase plays a role of bridge and buffer in the structure, which can effectively alleviate the stress caused by temperature changes and slag erosion, and ensure the stability of magnesia carbon bricks under complex working conditions.

2. Advantages of magnesia carbon bricks

(Ⅰ )Excellent high temperature resistance

Since both magnesium oxide and graphite have extremely high melting points, and the two do not undergo eutectic melting at high temperatures, magnesium carbon bricks have excellent high temperature resistance.

In high-temperature equipment such as converters and electric furnaces for steel smelting, the internal temperature is often as high as 1600℃ or even higher. Magnesium carbon bricks can maintain stable physical and chemical properties in such extreme high temperature environments, without softening or melting, providing reliable refractory protection for the furnace body and ensuring the smooth progress of the smelting process. Compared with some traditional refractory materials, magnesium carbon bricks have more outstanding structural stability and creep resistance at high temperatures, and can withstand long-term high temperature loads without obvious deformation or damage, greatly extending the service life of equipment such as furnace linings.

(II) Strong resistance to slag erosion

Magnesia has strong corrosion resistance to alkaline slag and high iron slag, while graphite has poor wettability with slag. The combination of these two characteristics makes magnesia carbon bricks have excellent slag corrosion resistance.

In practical applications, such as in the slag line of the converter, this area is in contact with high-temperature slag for a long time and is subject to strong slag corrosion. Magnesia carbon bricks can effectively resist the erosion of slag and slow down the loss rate of bricks due to their unique composition and structure. Compared with the old fired alkaline bricks, the penetration layer of magnesia carbon bricks is much shallower, which means that it is difficult for slag to penetrate into the interior of the brick body, thereby greatly improving the anti-corrosion life of the brick body.

In addition, magnesia carbon bricks have a strong ability to resist slag penetration, which can prevent slag from penetrating and accumulating in the pores of the brick body, and avoid the destruction of the brick structure and the reduction of strength caused by slag penetration.

(III) Good thermal shock stability

Graphite’s higher thermal conductivity, lower thermal expansion coefficient and lower elastic modulus give magnesium carbon bricks good thermal shock stability.

In the industrial production process, furnaces and other equipment often experience frequent temperature changes, such as furnace opening, furnace shutdown and temperature fluctuations during production. Such rapid temperature changes will cause thermal shock to refractory materials, which can easily lead to material cracking and peeling. Due to its advantages in thermal physical properties, magnesium carbon bricks can quickly conduct heat and reduce temperature gradients when the temperature changes sharply. At the same time, its own low expansion characteristics enable it to effectively buffer thermal stress and basically avoid tissue damage and peeling caused by thermal shock. For example, in the process of electric furnace steelmaking, frequent power-on heating and power-off cooling will cause the temperature of the furnace lining to change rapidly. The good thermal shock stability of magnesium carbon bricks ensures that it can still maintain its complete structure and performance under such conditions, providing a strong guarantee for the stable operation of the electric furnace.

(IV) High high temperature strength

Magnesium carbon bricks have high strength at high temperatures and can withstand the scouring, wear and mechanical stress of high-temperature materials and airflow in the furnace.

During the steel smelting process, the molten steel, slag and high-temperature airflow in the furnace will cause strong scouring and friction on the furnace lining. The high-temperature strength of magnesium carbon bricks enables them to resist these external forces and is not prone to wear and peeling.

This high-strength characteristic not only ensures the structural integrity of the brick body in a high-temperature environment, but also reduces the number of repairs and replacements of the furnace lining caused by brick damage, improves production efficiency and reduces production costs. At the same time, the high high-temperature strength also enables magnesium carbon bricks to adapt to some special working conditions that require stringent strength of refractory materials, broadening its application range.

(V) Good anti-peeling performance

In the past, alkaline refractory materials had poor spalling resistance and were prone to spalling during use, which affected the service life of the equipment.

Magnesium carbon bricks have effectively improved this shortcoming through reasonable raw material selection and structural design. Its carbon matrix can enhance the toughness of the brick body. When subjected to thermal shock, mechanical impact, etc., it can absorb and disperse stress, prevent the generation and expansion of cracks, and thus greatly improve the spalling resistance.

In parts such as the converter cap, due to the combined effects of rapid cooling and heating temperature changes and high-temperature airflow and dust scouring, the spalling resistance of refractory materials is extremely high. Magnesium carbon bricks, with their good spalling resistance, can serve stably in this part, reducing the workload of frequent repairs and replacement of furnace linings, reducing labor intensity, and also helping to improve the quality of molten steel and production efficiency.

(VI) Low production energy consumption

As an unfired product, compared with traditional refractory materials such as fired magnesia dolomite bricks, magnesia carbon bricks save at least 80% of fuel consumption in the production process.

This is mainly because magnesia carbon bricks do not need to go through a high-temperature firing process, avoiding a large amount of energy consumption during high-temperature firing. In today’s era of advocating energy conservation and emission reduction, the low-energy production characteristics of magnesia carbon bricks have significant advantages, which not only reduces the production costs of enterprises, but also conforms to the concept of sustainable development, and has made positive contributions to the green development of the industry. Lower production energy consumption also makes magnesia carbon bricks more economically feasible in large-scale production and application, and can meet the growing market demand.

3. The advantages of magnesia carbon bricks are reflected in various industries

(Ⅰ). Steel industry

In the steel industry, the advantages of magnesia carbon bricks have been fully reflected and widely used. In the converter, the furnace mouth is constantly impacted by cold and hot molten steel, and it also has to withstand the scouring of high-temperature slag and high-temperature exhaust gas. Magnesium carbon bricks have become the ideal refractory material for the furnace mouth due to their high temperature resistance, scouring resistance, and the characteristics of not easy to hang steel and easy to clean.

Due to the combined effects of severe slag erosion, rapid cooling and heating temperature changes, and high-temperature airflow and dust, the use of magnesia carbon bricks with strong slag erosion resistance and spalling resistance can effectively extend the life of the furnace lining. The charging side requires refractory materials to have high slag erosion resistance, high temperature strength and spalling resistance. High-strength magnesia carbon bricks with metal antioxidants can meet this demand well. The slag line is the junction of the three phases of furnace lining refractory materials, high-temperature slag and furnace gas, and is most severely slag-corroded. Magnesium carbon bricks with high carbon content are widely used in this area due to their excellent slag erosion resistance.

In electric furnaces, the furnace walls are almost all built with magnesia carbon bricks, and the life of magnesia carbon bricks directly determines the service life of electric furnaces. At present, by optimizing the raw material quality of magnesia carbon bricks, improving the production process and rationally adding antioxidants, the performance of magnesia carbon bricks in electric furnaces has been further improved, the consumption of refractory materials has been reduced, and the economic benefits of electric furnace steelmaking have been improved. In the clearance and slag line of the refining ladle furnace and ladle, magnesia carbon bricks have gradually replaced the magnesia-chromium refractory materials whose use has been reduced due to chromium pollution in the past, providing reliable refractory protection for the steel refining process.

(II) Nonferrous metal smelting industry

In the process of non-ferrous metal smelting, such as the smelting of copper, aluminum and other metals, it is also necessary to carry out in a high temperature environment, and there are various complex chemical substances and high-temperature melts in the furnace.

The advantages of magnesia carbon bricks such as high temperature resistance, slag erosion resistance and thermal shock stability make them widely used in non-ferrous metal smelting furnaces. For example, in copper smelting furnaces, magnesia carbon bricks can effectively resist the erosion of high-temperature copper liquid and slag in the furnace, ensure the stability of the furnace lining, and reduce production interruptions and maintenance costs caused by damage to the furnace lining.

In aluminum electrolytic cells, magnesia carbon bricks, as lining materials, can withstand the scouring and erosion of high-temperature electrolytes and aluminum liquids. At the same time, good thermal shock stability enables them to adapt to temperature changes during the electrolysis process, extending the service life of the electrolytic cell and improving production efficiency.

(III) Glass manufacturing industry

In the glass manufacturing process, the glass kiln needs to operate for a long time at high temperature, and the performance requirements of refractory materials are extremely high.

The high temperature resistance of magnesia carbon bricks enables them to withstand high temperatures of up to 1500℃ in glass kilns. At the same time, their slag erosion resistance can effectively resist various corrosive substances in glass liquid and kiln atmosphere. The use of magnesia carbon bricks in the heat storage chamber, pool wall and other parts of the glass kiln can significantly increase the service life of the kiln, reduce the downtime caused by kiln maintenance, and improve the continuity and output of glass production. In addition, the good thermal shock stability of magnesia carbon bricks can also adapt to the temperature changes of the glass kiln during the heating and cooling process, ensuring the integrity and stability of the kiln structure.

Magnesium carbon bricks have become an indispensable key refractory material in the modern high-temperature industry due to their excellent high-temperature resistance, strong resistance to slag erosion, good thermal shock stability, high high-temperature strength, outstanding anti-stripping performance and low production energy consumption.

In the steel, non-ferrous metal smelting, glass manufacturing and other industries, the application of magnesium carbon bricks not only improves the service life and production efficiency of equipment, but also reduces production costs, making an important contribution to the sustainable development of the industry. With the continuous advancement of science and technology and the growing demand for high-performance refractory materials in industrial production, it is believed that magnesium carbon bricks will show more excellent performance and broader application prospects through further technological innovation and performance optimization in the future, and continue to promote the development and progress of the high-temperature industry.

High temperature flexural strength of magnesia carbon brick

There are many factors that affect the high-temperature flexural strength of magnesia carbon brick, the most important of which is the purity of raw material, carbon content, binder, matrix composition and organizational structure of magnesia carbon brick. The purity of raw material is relatively simple, the purity of magnesia is high, the crystal scale is large, the low melting point phase content distributed in the periclase grain boundary is low, the direct bonding degree is high, the high-temperature flexural strength is better; the purity of graphite The research on matrix composition, microstructure and other aspects is relatively complex, and it is also the most concentrated research field to improve the high-temperature flexural strength of magnesia carbon brick, which is roughly divided into the following three directions.

1、Add metal powder

In the aspect of improving the flexural strength at high temperature, the metal powders mainly include A1, Si, etc

① Al4C3 and SiC are formed by the reaction of metal Al and Si with graphite and resin carbon in magnesia carbon brick, strengthening the combination of carbon and carbon, and improving the strength;

② whiskers and fibers are formed in MgO-C brick by metal Al and Si, which strengthen the material matrix;

③ The formation of magnesia alumina spinel and the improvement of ceramic bonding

2、In situ formation of carbide, nitride and other whiskers

The improvement of high temperature flexural strength of MgO-C brick is usually achieved by in-situ formation of carbide and nitride whiskers.

Whiskers are generally one-dimensional crystalline materials of nanometer or submicron scale, with few internal defects, and the strength and modulus are close to the theoretical value of crystal materials. At the same time, the net distribution of whiskers in the brick or the pinning and locking effect in the microstructure of MgO-C brick also endow the material with a better mechanical properties Good strength. For example, yijingguang et al. Found that with the increase of heat treatment temperature, the high-temperature flexural strength and residual flexural strength of MgO-C brick added with metal Si powder and Al powder increased, while the flexural strength of the sample after heat treatment at 1400 ℃ was larger.

Through the analysis of microstructure, it was found that there was not only needle like AlN formation in the brick, but also inlaid on the surface of magnesia particles at 1400 ℃, At the same time, there are a large number of SiC whiskers and acicular β – Sin whiskers. In such a microstructure, when the material is subjected to external force, the stress can be transferred from the matrix to the whisker through the interface layer, and the whisker disperses the stress on the matrix and reduces the damage effect.

When the crack size of the sample under the action of thermal stress is small, the whisker plays a bridging role, When the crack increases, the whisker at the crack tip will be further destroyed, and the whisker will be pulled out of the matrix to consume energy. At this time, the pull-out effect will give the magnesia carbon brick high temperature mechanical properties

3、Generation or addition of nano carbon in magnesia carbon brick

Carbon nanotubes are new materials which appear in recent years, and their mechanical properties are very outstanding. Therefore, in the aspect of improving the high-temperature flexural strength and microstructure of MgO-C brick, some scholars have formed carbon nanotubes in the material by introducing catalysts and other ways, and achieved good results.

For example, we ì and other scholars modified phenolic resin and prepared low-carbon MgO-C brick by introducing Fe nano sheets. It is found that doping 0 A large number of carbon nanotubes with a diameter of 50-100nm and a length of micrometer are produced by the MgO-C brick with a mass fraction of. 5%. Compared with the sample without doping Fe nano sheet, the high-temperature flexural strength increases from 8.29mpa to 10.29mpa with a amplitude of about 24%, reaching the highest value. The presence of a large number of carbon nanotubes firmly locks the MgO particles.

When the stress is applied to the blank sample, the For the 0.5% doped sample, when the crack passes through the MgO particles, the carbon nanotubes can absorb and release the stress at the crack tip through the bridging and crack deflection mechanism due to its high strength and toughness.

In addition to the formation of carbon nanotubes in MgO-C brick, nano carbon is also introduced to improve the microstructure of MgO-C brick and improve the high-temperature flexural strength of materials. For example, on the basis of 3% mass fraction of graphite, by introducing different proportions of nano carbon and graphite, the high-temperature flexural strength (hMOR) increases with the increase of nano carbon content, and its value increases from 2.5MPa When it reaches 4.5MPa (0.9% mass fraction) and keeps constant when the nano carbon is further increased, as shown in Figure 21. Further analysis shows that with the increase of the content of nano carbon, the filling and compaction effect is better. At the same time, the nano carbon has very high reactivity and can form carbides at a higher rate when contacting with the gold additive, with stronger binding force and higher strength.

LMM GROUP

The influence of mill rolls on product quality in the production of plate steel and strip steel

In the rolling process, the quality of the rolls is very important. Often due to the poor quality of the roll itself or improper operation, many rolling accidents occur, which bring losses to the steel mill. The following is a detailed analysis of the phenomena and causes of several rolling accidents that may occur.

What is the cause of mill rolls sticking?

The sticking mill roll is caused by excessive local pressure, broken strip fragments and folded strip steel entering the rolling mill. Generally, the slightly sticky mill roll can continue to be used after manual grinding with grindstone. When the strip surface require is high, the mill roll must be changed.

What are the material requirements for the cold mill rolls?

During the cold rolling process, the surface of the roll bears great squeezing and intense wear. Steel jamming and over-burning during high-speed rolling will cause cracks on the roll surface. Therefore, cold-rolling work rolls should have extremely high and uniform hardness, a certain depth of hardened layer, and good wear resistance and crack resistance. The roll has good resistance to over burning and crack resistance is the main factor to extend the life of the roll.

What are the effects of insufficient mill rolls hardness on the rolling process?

The roll hardness is not enough, the elastic flattening is large during rolling, and the contact area between the roll and the strip surface is increased. To obtain the same thickness of the product, the rolling pressure must be increased, but the large rolling pressure is not good for the adjustment of the plate shape. The roughness of the roll is large, and the friction coefficient between the roll and the strip steel surface increases during rolling, which causes the friction force and the rolling pressure to increase.

How to use bending rolls to eliminate “both sides waves” and “middle waves”?

When waves appear on both sides of the strip during rolling, it means that the rolling pressure on both sides of the strip is too large. At this time, positive bending rolls are used to eliminate the waves on both sides. When there is an middle waves, it means that the original crown or thermal crown of the roll is too large. At this time, use a negative bending roll to eliminate.

How to prevent the skewing when the strip passes through the gap of the roll

First of all, before the strip passes through the gap of the roll, it must be minimize the clearance between upper and lower rollers, given a standard roll gap, it looks like the quality of the material, whether there are edge waves, and observe the strip running condition. In the rolling process, the deviation of the strip generally occurs during the strip passes through the gap of the roll or tail flicking. The main reasons for the skewing of the strip are as follows:

1）Due to the shape of the incoming material is not good, and there are serious edge waves, so that the strip edge control device cannot be accurately and timely adjusted effectively, causing the strip to deviate in the first pass. The measure to be taken is that control the rolling speed don’t be too high! Control the clearance between upper and lower roller, swing adjustment in time or stop in time.

2) Operational reasons: The unreasonable adjustment of the swing due to the the clearance between upper and lower roller causes the strip to run out of direction.

3) For electrical reasons, the coiler tension suddenly decreases or disappears during the rolling process, causing the strip to run off and break.

4) Due to the serious taper of the roll after the roll is ground, the clearance between upper and lower roller is inaccurate. During the rolling, the reduction and swing of the operation increase the difficulty. The lighter one will produce serious side waves and cause the plate shape defect, and the heavy one will cause deviation and broken strip.

5) The strip edge control device failure, the deviation device, the lamp tube or the pollution of the receiving device, etc., make the deviation device failure and cause the first deviation.

What quality defects can occur in rolls grinding? What are the undesirable consequences in the rolling process?

1) The roll body has a taper: the reduction cannot be corrected, and it is easy to cause a side wave, and the plate shape is difficult to control. The roll body taper is required to be less than 0.1mm.

2) Grinding is not round: the roll body has ellipticity. Vibration occurs during the rolling process, the rolling pressure fluctuates, and the strip thickness varies along the length direction.

3) Crown: The roll is required to be a flat roll in the process of the unit. If the roll has a crown,In the rolling process, it is easy to produce the middle wave and the second rib wave of the strip steel.

4) The surface roughness of the roll is too large. During the rolling process, the rolling pressure increases, the strip shape is difficult to control, and the surface quality of the strip is affected.

5) The roll body cracks, because the cracks have not been ditched and ground. The rolls were not inspected for flaw detection, and protruding rolling marks with crack shapes were generated on the surface of the strip during the rolling process.

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