In the auto parts industry, cold forging is a kind of precision plastic forming technology, which has the advantages of energy saving and environmental protection. The mechanical properties of products are good, the production efficiency is high and the material utilization rate is high. The heat treatment before cold forging is particularly critical. Cold forging materials are often softened by spheroidizing annealing, so as to improve the plasticity of materials. Compared with hot forging, cold forging has high dimensional accuracy and small machining allowance. The implementation of cold forging process requires that the steel has low hardness and good fluidity. Because ferrite is a structure with excellent plasticity, it is a structure with the best plasticity and the lowest hardness in steel. Spheroidizing annealing is an effective means to improve the cold formability of steel. The structure obtained by spheroidizing annealing is spherical pearlite + ferrite matrix.
Cheng Weiwei and others studied the spheroidizing annealing process of 20MnCrS5 steel and developed cold forging materials with spheroidizing rate of more than 85% and hardness of about 140HBW. Xue gang and others studied the rapid spheroidizing annealing process of sks51 tool steel, which can effectively reduce the heat treatment time and save energy consumption. Wang et al. Studied the spheroidization process of 0.8% C ⁃ Fe steel pearlite under the condition of static spheroidization annealing at 700 ℃, computer-aided three-dimensional tomography and electron backscatter diffraction. The results show that the internal holes play an important role in the occurrence and development of pearlite spheroidization.
1) The elongation of 16mncrs5 steel is positively correlated with the spheroidization rate of the structure. The higher the spheroidization rate, the higher the elongation of the material and the lower the tensile strength. This is because the higher the spheroidization rate of the material and the greater the proportion of ferrite in the matrix, the better its plasticity.
2) Heat preservation at 760 ℃ for 4h, cool to 710 ℃ at the cooling rate of 12 ℃ / h, then heat preservation for 3h, and then cool to 680 ℃ at the cooling rate of 12 ℃ / h for 2h. After the furnace is cooled to 500 ℃, the spheroidization rate of 16mncrs5 steel is the highest, which can reach more than 95%, the tensile strength of the material is about 400MPa, and the hardness reaches 123hbw, The elongation is 39%, and the plasticity of the material is the best, which is better than that of conventional 16mncrs5 steel cold forging material. Therefore, this process can be used as a reference for 16mncrs5 gear steel for cold forging.
16MnCrS5 steel is a commonly used cold forged gear steel material, which has been widely used in engineering. In actual production, forging factories often feed back that the spheroidizing rate of the material is not high (about 80%) after conventional spheroidizing annealing, resulting in high hardness, 140hbw left and right, poor plasticity and other problems. In this paper, the effects of different spheroidizing annealing processes on the hardness, strength and elongation of 16mncrs5 steel are studied to find the best spheroidizing annealing process and provide guidance for the spheroidizing annealing process of cold forged gear steel.