Accelerated Carbide Spheroidization of 100CrMnSi6-4 Bearing Steel by Hot Rolling

摘要

Current industry trends include the search for cost and energy-saving procedures and technologies. Conventional methods of annealing steel stock to produce globular pearlite require long holding times, up to several tens of hours, due to the diffusional basis of the process. The presented experiment deals with accelerated carbide spheroidization of 100CrMnSi6-4 bearing steel during the final stage of hot rolling. The main purpose here was to achieve a microstructure consisting of globular carbides and ferritic matrix directly after hot forming. Thus it is possible to take out soft annealing completely from the production process because this operation is usually the longest operation in the whole process. Steel properties after accelerated carbide spheroidization and after conventional soft annealing enable machining and cold forming. Apparently, the structure after accelerated carbide spheroidization is significantly finer than after long duration soft annealing in terms of carbide particles and grain size. This enhances steel hardness and homogeneity of the structure in the final state after hardening. The accelerated carbide spheroidization process consists of forming a steel workpiece at temperature close to Ac1 temperature. The energy introduced causes the work-piece temperature to increase. The combination of a suitable forming temperature, an appropriate amount of deformation, and a possible reheating lead to globular carbide formation during austenite decomposition instead of cementite lamellae. This article describes the influence of thermo-mechanical treatment parameters on microstructure and mechanical properties of 100CrMnSi6-4 bearing steel. Deformation intensity, deformation rate, and temperature are discussed. This thermo-mechanical treatment could replace conventional hot forming and subsequent soft annealing with significant time saving.