Cr12MoV steel secant wire primary knife annealing heat treatment process

The initial secant knife on the textile machinery ring cutting machine is made of Cr12MoY steel, the knife thickness is 8Bmm, and the heat treatment requires a hardness of 63-65HRC. The tool processing process is: blanking (wire cutting), heat treatment, and grinding. The original heat treatment process is 98℃ x 15min oil quenching, 140℃ x 2h pit furnace tempering. After the grinding process, fine network cracks visible to the naked eye appeared on the entire grinding surface, and local areas were accompanied by a burnt yellow oxidation color. The surface cracks of the tool were analyzed using methods such as chemical composition analysis, metallographic analysis and hardness testing. The results show that the Cr12MoV steel tool is seriously insufficient in tempering, the eutectic carbides are distributed in a network, and the grinding is too intense, resulting in final grinding cracks. For this reason, the annealing heat treatment process is adjusted.

1) Preheat. Preheat twice at 500℃ and 850℃. The first time is done in a pit air furnace and the second time in a salt bath, the preheating time is twice the heating time.

2) Heating. Use 1000-1020 x 30s/mm for heating. There is no need to install a hanging device. Use thick iron wire to hang the workpiece. The position of the workpiece in the furnace must be appropriate and must not touch the furnace wall.

3) Cool down. Cool in quenching oil at 60 -80°C.

4) Tempering. Change the air furnace to nitrate tempering, and the tempering process is 160℃ x3h x2 times. Promote the transformation of quenched martensite into tempered martensite, fully eliminating the quenching internal stress. The hardness after tempering is 63-64HRC. When grinding, use a grinding wheel with good self-sharpening properties, reduce the feed amount, reduce the cutting speed, and use a lubricating cutting fluid as much as possible to prevent grinding cracks. The finished tool is further tempered with oil at 150°C x 2h to relieve stress. The improved technology has been tested for many years, with stable quality, improved service life and no wear and tear.