Investigation of effects of heat treatment parameters on mechanical properties and corrosion behavior in induction hardening of martensitic stainless steels

Martensitic stainless steels are widely used in industrial applications due to their high hardness and superior durability properties. The fundamental method that imparts these characteristics to these steels is the application of heat treatments. Traditionally conducted in heat treatment furnaces, these processes have long processing times and high energy consumption. To mitigate these drawbacks, alternative methods have been explored in recent years. Among these alternatives, induction heat treatment has emerged as a significant option due to its speed, energy efficiency, and suitability for automation. While induction heating has been predominantly utilized for surface hardening, recent advancements demonstrate that, when appropriate parameters are employed, it can also yield effective results in volumetric heat treatments. In the initial phase of this study, the objective was to determine the optimal induction heat treatment parameters that maximize hardness, corrosion resistance, and wear resistance for 440B martensitic stainless steel. To this end, the effects of austenitizing temperature, austenitizing duration, tempering, and cryogenic cooling processes were investigated. The tests and analyses revealed that a heat treatment conducted at 1110°C in 2 minutes, followed by cryogenic treatment and a single tempering cycle, resulted in a 30% improvement in wear performance and an 86% enhancement in corrosion resistance compared to conventional heat treatment methods, while also reducing the crystal grain size by 46%. Within the scope of this thesis, thermal cycling heat treatment applications were also conducted based on the optimized heat treatment parameters. The thermal cycling heat treatment process contributed to grain refinement in the austenitic phase and resulted in a more homogeneous martensitic microstructure. Additionally, thermal cycling reduced wear loss by 25%. Although corrosion loss showed a slight increase compared to single-cycle treatment, the pitting corrosion resistance improved by 60%. Considering the reliability analyses of the data obtained, the results indicate that the 4-cycle treatment is the most suitable heat treatment parameter.