Effect of Composition and Heat Treatment Regime on Structural State and Capacity of Special Alloy Steel Round Rolled Product for Cold Upsetting

Resumo

On the basis of physicochemical prediction of the effect of component content on the phase and structural transformations, it is shown that in order to prepare a favourable ferrite-pearlite microstructure and to ensure the key capacity of round rolled product for cold upsetting, it is preferable to obtain in special alloy steels 40Х, 38KhGNM, 35KhGSA, 30G1R, and 12KhN an element content close to the lower grade limit. A study of the microstructure and hardness of round-rolled specimens from steels 35KhGSA, 38KhGNM, and 40Х establishes that isothermal annealing at 20–50°C below the А1 temperature and nonisothermal annealing at 1–30°C below the А1 temperature are the optimum for spheroidizing heat treatment. In this case, a different fraction of globular pearlite is obtained in the metal microstructure depending on the steel grade: 35KhGSA about 90%, 38KhGNM and 40Х about 30%, and in all cases there are favorable results for cold upsetting tests. The defining effect of surface defects and rolled product structural state on cold upsetting capacity is demonstrated.