Increasing the contact strength of Bohler K490 MicroClean steel parts by determining carbonitriding conditions

Abstract

The problem of increasing the service life of various devices and units operating under high loads on parts remains open to date. Increasing the service life of these mechanisms is possible by increasing the contact strength of the material. Various thermal and chemical-thermal treatment (CTT) methods are often used to improve this parameter. This work presents the results of an experimental study of the influence of CTT parameters on the contact strength of the surface layer of high-quality powder steel Bohler K490 MicroClean. The study’s relevance is due to the need to increase the wear resistance and durability of parts of tools and machines operating under challenging conditions. The primary purpose of the work was to determine rational temperature-time conditions of carbonitriding to ensure maximum surface hardness and effective depth of the hardened layer. The research methodology included sample preparation, heat treatment, machining using Tenifer-QPQ technology at 560, 580, and 610 °C, and holding for 1–6 h. The Vickers method measured the microhardness, the carbonitrided layer depth was determined, and metallographic analysis of the microstructure was performed. The results showed the best combination of high surface hardness (up to 1434 HV0.2) and sufficient hardening depth at a temperature of 580 °C and a holding time of 6 h. Pre-hardening positively affects the formation of a dense zone, strengthening the surface layer. On the contrary, an increase in temperature to 610 °C led to a deepening of the diffusion layer, but was accompanied by a decrease in the hardness of the core. The results of this study were implemented in the practice of a machine-building enterprise in the Sumy region of Ukraine, which specializes in thermal and CTT of parts of various types.