Surface modification of die steels by liquid boriding

Abstract

The research investigates the effect of liquid boriding on the microstructure, composition and microhardness of the surface layer on 5KhNM and 3Kh2V8F die steels. Boriding was carried out for 8 hours at 850 and 1000 °С in a melt based on sodium tetraborate and sodium salts. After high-temperature exposure during the boriding process, the samples were quenched in oil and tempered. Next, the samples were subjected to metallographic, X-ray spectral, X-ray diffraction and durometric analyses. As a result of processing, boride diffusion layers were obtained on the surface of 5KhNM and 3Kh2V8F steels up to 100 and 130 μm thick, respectively. It has been established that iron borides Fe2B and FeB are formed on the surface of both steels. In addition, chromium boride CrB is additionally formed on the surface of 5KhNM steel, increasing the maximum microhardness of the layer to 2130 HV. The maximum microhardness of 3Kh2V8F steel reaches 1709 HV due to the formation of borides and carbides in the layer. A study of the surface topography after boriding showed that the roughness parameter Ra of 5KhNM steel increased by 1.87 times, and of 3Kh2V8F steel by 1.78 times compared to the initial state.