The features of residual stresses investigation in the hardened surface layer of die steels after diffusion boroaluminizing

Introduction. Diffusion boroaluminizing provides improved performance properties of the die steels’ surface such as wear resistance, high hardness, and corrosion resistance. Surface hardening can significantly contribute to the occurrence of technological residual stresses (TRS) on the surface. Currently, there are no studies on the topic of the stress state of diffusion boroaluminizing. The purpose of this work is to develop a method for determining the TRS and a nature of its distribution in the diffusion layers on the surface of 5CrNiMo and 3Cr2W8V die steels after boroaluminizing by a mechanical method. The paper considers the results of experimental studies on the determination of the normal components of TRS by the mechanical method in diffusion layers of die steels. The conducted studies showed that the formation of unfavorable tensile TRS occurs along the depth of the hardened layer in the case of the investigated TCT method and types of steels. Results and discussions. The main approaches for determining the TRS in the surface layer of 3Cr2W8V and 5CrNiMo die steels after TCT are considered. Problems in the determination of TRS by the mechanical method on the UDINON-2 unit are identified, and its solution is proposed. The efficiency of using the anodic dissolution method for the continuous removal of stressed layers during the TRS study by the mechanical method on the UDION-2 unit is shown. The optimal electrolyte composition is selected for the process of anodic dissolution consisting of: NaNO3 – 60 g/l; NaNO2 – 5 g/l; Na2CO3 – 5 g/l; C3H8O3 – 15 g/l; H2O – the rest. The distributions of the normal TRS components in the diffusion layer of die steel specimens are revealed. It is established that, during the TCT of these steels predominantly tensile TRS are formed in the surface layer. Further research will be aimed at developing measures to reduce tensile TRS during diffusion boroaluminizing of die steels.