The large hollow rollers of the semi-continuous rolling hot output roller table are made of 45 steel seamless steel pipes, with shaft heads hot-assembled at both ends. The technical requirements are: roller surface hardness ≥ 40HRC, roller surface deformation ≤ 1.00mm, and central shrinkage ≤ 0.70mm. The heat treatment uses medium frequency induction heating surface quenching. The equipment is a vertical medium frequency quenching machine tool. The oscillation frequency is 1-8KHZ. The single-turn inductor is continuously quenched and heated by water spray cooling. During production, it was found that the hollow rolls experienced large deformation after quenching, and it was very difficult to correct the workpieces with large rolls and the effect was not good, resulting in many workpieces being scrapped due to excessive deformation. It seriously affects product quality and normal production, and causes huge economic losses.
Tests and production have found that after the roller surface is quenched, the diameter of the roller surface decreases and the roller body elongates; when the surface of the hollow roller is quenched, the roller surface bending deformation also occurs. Analysis believes that the deformation that occurs during the heat treatment of the hollow roller is caused by induction heating. Thermal stress and ancestral stress cause uneven plastic deformation of the workpiece.
Analysis believes that this is because induction heating heats up quickly and the degree of superheat is large, so the austenitization temperature is 70-150°C higher than Ac3gao. When the 45 steel workpiece is heated to 840°C, austenitization has not yet been completed, and a complete martensite structure cannot be obtained after rapid cooling, so the phase transformation stress is not obvious. At this time, thermal stress plays a dominant role; when the quenching temperature increases, the workpiece After cooling, the amount of martensite transformation increases, and the phase transformation stress increases, which offsets part of the thermal stress effect and reduces the deformation. When the heating temperature rises to 870°C, the workpiece is completely austenitized, and all transforms into martensite during cooling. At this time, the phase change stress is the largest and the deformation of the workpiece is the smallest; as the quenching temperature increases, the phase change stress is the same as at 870°C and no longer increases, while the thermal stress increases due to the increase in temperature, and the thermal stress plays a dominant role. , the workpiece shows obvious thermal stress changes. By analyzing the monthly temperature relationship of the deformation of the hollow roller, it can be seen that the induction quenching heating temperature of 860-870°C is the best for the hollow roller, and its deformation is the smallest.
Process improvement measures to prevent deformation after quenching:
1. The heating temperature for induction quenching of the workpiece is 860-870°C.
2. The workpiece must not shake when rotating, and the tailstock spring must not be pressed too tightly. The workpiece and the sensor sprinkler should be concentrically aligned, and the sensor sprinkler must be horizontal and not skewed.
3. The linear speed of the spindle speed should be greater than the rising speed of the inductor, so that the workpiece can be cooled evenly and better, and the hardness of the workpiece can be more uniform and consistent after surface hardening. The spray holes of the water spray ring should be evenly distributed, and there should be no less than 3 water inlets to ensure stable and uniform water spray volume.
4. When tempering, the convex side of the workpiece should be upward and both ends should be padded to reduce bending deformation.
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GS-ZP-1200
