Application of Laser Radiation for Intensification of Chemical Heat Treatment

Abstract

The processes of chemical heat treatment were analyzed. The areas of their application, productivity, energy intensity, advantages and disadvantages are highlighted. The surface nitrided layers with hardness up to 800–900 HV were obtained. In this case, nitriding thickness does not exceed 0.15–0.2 mm, which is insufficient, especially if the value of residual deformations exceeds the thickness of the diffusion layer. It is shown that to increase the efficiency of nitriding, it is advisable to pre-modify the microstructure of the layer of the sample by laser irradiation. Modeling of thermal processes occurring in steels under irradiation and experimental studies have determined the conditions under which highly dispersed, with a high dislocation density, disoriented in space structures are formed in the surface layers. Dislocations, located on the grain boundaries and having a complex configuration, form paths along which nitrogen atoms can move, forming nitrides with alloy elements. It was shown that in U8 tool carbon steel (AISI M2) after laser treatment and subsequent nitriding in ammonia at a temperature of 780–800 °К for 12 h, a nitrided layer is formed. The depth of the nitrided layer without prior laser treatment is 0.115 mm, on laser-treated it varies within 0.12–0.46 mm depending on the processing speed. The results of the combined nitriding of 40Cr13 stainless steels (AISI 420 Stainless Steel) and 12Cr18Ni10Ti (AISI 321 Stainless Steel), in which the thickness of the hardened layer with a hardness of 815.7–917.7 HV is 0.4–0.5 mm, with a significantly shorter (by 3–5 times) process time and its cost, are presented. The expediency of manufacturing discretely located nitrided zones on the working surfaces of products is discussed.