Abstract
The production of fasteners from special alloy steels is an urgent need for Russian automotive companies. MMK-METIZ has implemented a comprehensive program for the production of high-strength fasteners using cold die forging (CDD) methods. The goal of the work is to develop a technology for the production of high-strength automotive fasteners from low-alloy steel grades 32CrB4, 36MnB4, 42CrMo4. When conducting the study, methods of light and scanning electron microscopy were used. The formation and evolution of the structural state of hot-rolled steel during the process of spheroidizing annealing was studied using industrial samples of round steel. During laboratory analysis, the possibility of obtaining a spheroidized ferrite-pearlite structure of rolled metal was established. The results of the study were implemented in the production of pilot batches of wheel bolts M16x125, M16x135, M22x85. The tests carried out confirmed the achievement of the required level of mechanical properties for strength classes 10.9 and 12.9. When analyzing the data obtained, it was concluded that it is necessary to form the properties of bolts not only through heat treatment, but also through plastic deformation. It is proposed to produce bolts with thread rolling after heat treatment. The results obtained can be used for the industrial production of automotive fasteners, which are in demand on the Russian market.
Keywords:
32CrB4 steel, 36MnB4 steel, 42CrMo4 steel, round bars, spheroidizing annealing, microstructure, globular pearlite, quenching and tempering, high-strength fasteners.