Experiment and mechanism investigation on the effect of deep cryogenic treatment on residual stress and machining deformation of hydrogen-resistant steel

Abstract

Hydrogen resistant steel is widely used in various fields due to its numerous advantages, including high strength, toughness and excellent corrosion resistance. However, the presence of initial residual stress in the material is a significant factor contributing to machining deformation. To mitigate this problem, the contour method was used to determine the initial residual stress for various aging parameters. As a result, a set of optimal cryogenic treatment parameters (350 °C 2 h, −130 °C 10 h, 350 °C 2 h) was proposed to effectively reduce the initial residual stress. The results showed that under the optimal cryogenic treatment parameters, the residual stress reduction effect was most significant, with a value of 189 MPa. Compared to no aging treatment, the residual stress was reduced by 54.2 %. The effect of deep cryogenic treatment on the microstructure of hydrogen resistant steel materials was investigated by TEM. Compared to no aging treatment, the average dislocation density decreased by 51.5 % after treatment with the optimal cryogenic treatment parameter. In addition, the lattice spacing was reduced to 0.246 nm after deep cryogenic treatment, and two types of carbides were precipitated, i.e., spherical carbides (with a diameter of 24 nm) and rod carbides (with a length of 15 nm). The changes in grain size of the material after deep cryogenic treatment were further investigated by EBSD. The number of grains increased by 38.5 % after cryogenic treatment compared to no treatment. In addition, it was verified by non-contact material removal experiments that deep cryogenic treatment could reduce the machining distortion of thin-walled parts. Finally, for thin-walled parts used in engineering, a deep cryogenic treatment was interspersed during machining, resulting in a significant reduction in the overall deformation of the workpiece.