Influence of the Salt Bath Deoxidation Degree on Change in Hard Alloys Properties during Heat Treatment

Abstract

Performance characteristics of hard-alloy tools are largely depends on the structure. The hard-alloy tool structure can be influenced by various factors. The main factors influencing the structure and properties of hard alloys at heat treatment are ВаCl2 salt bath deoxidation degree, heating temperature, holding time, rate of cooling and cooling medium, temperatures and holding time. Oxidation at temperatures more than 500-600оС and relatively low thermal conductivity of λ = 27.214 W/(m×K) are characteristic for hard alloys under heating.In this regard, it became necessary to study the salt baths deoxidation processes occurred in the course of heat treatment. Insufficient study of hard alloy heat treatment processes is associated with peculiarity of their structure and large assortment, difficulty of setting heat treatment modes.Research of hard alloy sample heating with the subsequent air cooling (normalization) was carried out in a salt baths in thermal area of tool shop.X-ray diffraction analysis was performed by Williamson-Hall method. In our experiments, coherent scattering regions size and WC phase micro-distortions magnitude were defined using MD-10 microdiffractometer. It was found out that phase structure of hard alloys is not change as a result of heat treatment. There are only reflections from carbide phase planes in the diffraction pattern. A quantitative analysis of diffraction reflection broadening using Williamson-Hall method showed that size of the coherent scattering regions for VK8 and T14K8 hard alloys subjected to hardening procedure is more than for sintered alloys.Relevance of the study is due to the fact that heat treatment involved heating in salt baths can be a promising method of improving mechanical and operational properties of hard alloys. This approach ensures necessary strength and performance characteristics of hard alloys without significant economic expenses.The purpose of this paper is to define effect of ВаCl2 salt bath deoxidation degree on physical and mechanical properties of VK8 and T14K8 hard alloys.