This paper studies and analyzes the application of high-speed steel rolls in the production of hot-rolled strips, and predicts the broad prospects of hss rolls with the help of wear resistance, chemical composition, heat resistance and mechanical properties. Solutions and good suggestions are put forward for the problems existing in the production of steel rolls in hot-rolled strips.
High chromium cast iron is generally used to cast the work rolls of the front-end stand of the finishing mill in the hot strip continuous rolling mill. It forms a layer of high chromium with high hardness and wear resistance on the surface of the work rolls through the contact between the rolls and the high-temperature strip steel. Oxide film is used to improve the service life of the roll. The process of forming this layer of oxide film is a dynamic process, and the quality of cooling conditions and rolling conditions will directly affect the density and thickness of the oxide film. Because the whole process is difficult to grasp, it is difficult to meet the conditions for the formation of the oxide film. Therefore, when high-speed steel rolls are produced in hot-rolled strips, the oxide film will fall off, which directly affects the surface quality of the strip steel and the service life of the rolling mill rolls.
Improvement of High Speed Steel Rolls
By changing the chemical composition of the roll and improving the matrix structure, the wear resistance of the roll can be improved. After more than ten years of updating and perfecting the technology, high-speed steel rolls have begun to be used in hot strip finishing mills. The application of this new technology in combination with the lubrication process not only improves the product quality to a certain extent, but also achieves a very obvious effect in reducing the production cost. The combination of the core of the high-speed steel roll and the outer layer of the roll is a defect-free metallurgical bond. The core of the high-speed steel composite roll has high tensile strength and the strength of the bonded layer is high, which can increase the bending load of the roll, so that the plate can be obtained more Good shape.
Good wear resistance
Through horizontal comparison, high-speed steel rolls exhibit good wear resistance under the same frame and the same use condition. Based on the good condition of the surface of the high-speed steel roll after being off the machine, we increase the number of times the roll is used after a single grinding. This not only reduces the workload of the grinding machine, but also reduces the production cost. Compared with the high-chromium steel, the millimeter rolling capacity of high-speed steel has been greatly improved, which is about 26 to 28 times that of the original, and the cost performance has been greatly improved. .
Good thermal cracking resistance
Due to its unique organizational characteristics, high-speed steel can effectively suppress the generation of cracks. In actual use, it is found that high-speed steel rolls do have better thermal cracking resistance than high-chromium cast iron rolls. In this way, if a general production accident occurs, the impact of the accident can be eliminated through constant grinding or adding a small amount of grinding, so that the processing process is simplified and the cost is saved.
The friction coefficient of high-speed steel rolls is 0.4 to 0.44, which is higher than that of high-chromium iron rolls on average. When the high-speed steel roll is arranged on the F stand, the biting state can be obviously changed, and the rolling force will be improved. We can combine the use of process lubrication to reduce the rolling force of high-speed steel rolls in use.
Optimization and detection of hss rolls use
Because the high-speed steel roll has good wear resistance, high hardness and friction coefficient, it directly brings certain difficulties to grinding and quality control. For example, the reduction of grinding efficiency, the vibration marks are easy to occur during grinding, the control of roll shape is difficult, and the roughness is re-determined. In this regard, the manufacturer can re-select the material of the grinding wheel, and by adjusting various parameters such as the hardness and particle size of the grinding wheel, the grinding efficiency can be greatly improved. In terms of controlling the grinding quality, by optimizing the grinding parameters, such as controlling the feed rate and grinding current during fine grinding, using periodic variable speed control technology and controlling the smooth grinding pass and smooth grinding current, etc., the high-speed steel roll The surface quality of the machine fully meets the production requirements.
Use of process lubrication
The purpose of rolling with lubricating oil in the finishing mill is to reduce rolling force, reduce rolling energy consumption, reduce roll wear, reduce roll consumption, improve roll surface condition, and improve strip surface quality. In order to improve the rolling state and improve the surface quality of the product, the process lubrication system should be invested. Process lubrication mixes oil and water, and sprays the mixed oil and water to the surface of the roll with a nozzle. A certain concentration of emulsion is formed as a lubricant. When the work roll is cooled and closed during use, the lubricant is sprayed on the surface of the work roll on the day-entry side, and a continuous, uniform, and firm lubricating oil film is formed when the roll is in contact with the strip to reduce work. The friction coefficient between the roll and the strip can reduce the rolling force, reduce the vibration of the rolling mill, and reduce the wear of the work roll. This technology is used in conjunction with the roll gap spray (anti-oxidation film shedding), which can effectively reduce the oxide film shedding of the work roll. , reduce the temperature of the surface of the work roll in the deformation zone, reduce the thermal cycle stress of the work roll, and thus prevent the occurrence of cracks.
In actual production, the combination of process lubrication and high-speed steel rolls not only eliminates the increase in rolling force caused by the high friction coefficient of high-speed steel rolls, but also improves product quality and reduces roll consumption and energy consumption. showed a very obvious effect.
Detection of high-speed steel rolls
In order to ensure the normal working condition of the high-speed steel roll, it must be strictly tested. The accidents of high-speed steel rolls generally come from two aspects,
Mechanical Collision: When a mechanical collision occurs. Mechanical cracks sometimes occur on the surface of the roll.
Production Accidents: When a steel stacking accident occurs, because the high-speed steel roll has good thermal crack resistance, if the operator responds quickly and handles it in time, generally no surface cracks will occur. However, sometimes the working layer is detached due to the impact of stacked steel. This necessitates confirmation of surface defect detection with eddy current testing after an accident. Once a crack is found, it must be ground, and the working layer is inspected by ultrasonic flaw detection to confirm that there are no defects or that the existing defects do not expand within the safe range. Another method is to use surface wave testing instead of eddy current testing. When cracks are detected, confirm the cracks with color penetrant inspection or magnetic particle inspection, and then use the angle probe to determine the depth, determine the appropriate grinding amount, and process the roll to ensure the normal operation of the roll.
Although high-speed steel rolls have good thermal crack resistance, they are very sensitive to mechanical cracks. Once mechanical cracks appear, they must be ground, otherwise there will be dangers of roll spalling, falling blocks or even broken rolls during production. Therefore, when a mechanical collision occurs to the roll, it is necessary to carry out eddy current flaw detection or surface wave flaw detection in time to ensure that there are no mechanical cracks and ensure the safety of production.
PC FC board shape control optimization
Since the physical and chemical properties of high-speed steel rolls are different from those of high-chromium rolls or ICDP rolls, adjustments to the roll shape must be made. The physical and chemical properties refer to thermal expansion coefficient, friction coefficient, elastic modulus and hardness. When the rolling ends, stop the water immediately, and record the water stop time, and then replace the high-speed steel roll. Measure the temperature after about 2ML from the time when the water is cut off. Take the middle of the roll body as the origin of the coordinates, take points on both sides, divide the roll body into 21 equal parts for every 10ML measurement point, and measure the temperature of each point. According to the measured value, the temperature distribution map of the roll body is drawn to optimize the temperature model: then the work roll is hoisted to the roll room for air cooling. After air-cooling to room temperature, the wear curve is measured by the grinding machine, and then fed back to PC FC to optimize its wear model.
Continuous application of new technologies to improve the quality and precision of rolled products and reduce production costs is the development direction of today’s rolling technology. High-speed steel rolls have good wear resistance and thermal crack resistance, which can improve product quality and reduce production costs. But there are also some disadvantages. Therefore, we must constantly summarize the experience of using high-speed steel rolls.
