The overall dimension is a trapezoidal screw rolling wheel with a diameter of 186mmx130mm, which is installed on the WAN-DERERRM60X wire rolling machine imported from Germany. In order to meet the working requirements of the rolling wheel, we usually use high-frequency induction heating equipment for heat treatment. However, due to incorrect heat treatment and other processes, the service life of the wire rolling wheel is only a few hundred pieces. Many wire rolling wheels will have brittle tooth chipping after rolling 200-300 pieces. Some wheels will be repaired and then rolled after about 200 pieces. Scrapped, seriously affecting the normal production order. For this reason, a critical battle has been carried out to improve the life of the rolling wheel.
The production process of the original wire rolling wheel is forging - spheroidizing annealing - rough turning - finishing - quenching - grinding - aging - fine grinding. In order to improve the toughness, the process flow was adjusted, high-temperature quenching and tempering was added before finishing, and the quenching process parameters were adjusted.
1) Forging. Cr12MoV steel is a high-carbon, high-chromium cold work die steel with many eutectic carbides and severe segregation. This severe carbide segregation is detrimental to the final quenching of the mold or tool and the service life of the product. Especially when carbide segregation is distributed in a network, it is more harmful. To this end, a certain forging ratio is required, and three upsetting, drawing, and one forming processes are required to crush the carbides and improve their segregation state. After forging, it should be checked that the carbide segregation is less than level 3.
2) Spheroidizing annealing. Spheroidizing annealing is to improve the cutting performance and prepare the structure for subsequent heat treatment. High-frequency heating equipment is often used. The process is 860℃×3h heating, rapid cooling to 730℃×4h, and then furnace cooling to 500℃ and air cooling. The hardness after annealing is 207-255HBW, and the spheroidization level is 2-4.
3) High temperature quenching and tempering process. After annealing, the blank is roughed and drilled, and then high-frequency annealing equipment is used for high-temperature quenching and tempering. The process is 850℃x45min+1120℃x45min oil quenching, 760℃xlh tempering, and air cooling. The hardness after quenching and tempering treatment is 260-280HBW.
4)Quenching and tempering. The rolling wheel is mechanically processed after high-temperature quenching and tempering. After forming, high-frequency heating equipment is used for quenching heat treatment. According to the quenching characteristic curve of Cr12MoV steel, the highest hardness value can be obtained by quenching in the range of 1020-1040℃, that is, the largest amount of martensite is obtained, and the structure is ideal. After tempering at 400℃×2.5h×2 times, the final hardness is 57-58HRC.
Using a higher tempering temperature to reduce the hardness of the rolling wheel is based on further improving the toughness. Low-temperature tempering at 250°C was once used, and it was scrapped after about 1,100 pieces were rolled (brittle cracks propagated along the grinding cracks). The failure mode is still brittle cracking, that is, the edge is damaged due to the expansion of the wear crack. No crest depression was found. The fact shows that the toughness is still insufficient. Based on this fact, the tempering temperature is increased from 250°C to 400°C to avoid the 275-350°C temper brittleness zone of Cr12MoV steel and improve the toughness of the cutting tool.
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GS-ZP-1200
