Microstructures of SUS304 Stainless Steel after Long-Term Service in Vacuum Carburizing Quenching

Abstract

The microstructural changes and crack propagation in the carburized layer of SUS304 stainless steel due to repeated vacuum carburizing quenching as a heat treatment basket were investigated in this paper. As a result, beneath a graphite scale formed on the outermost surface, it was revealed that there were three types of carburized layers with different morphologies: M₇C₃ layer, M₇C₃/M₂₃C₆ mixed layer, and M₂₃C₆ layer (M = Cr, Mn, Fe). In addition, the surface was found to be uneven due to the occurrence of metal dusting. Besides, repeated heating and quenching caused the formation of voids in carbides and matrix in the carburized layer, and micro cracks appeared in the surrounding areas. Under the loading stress during vacuum carburizing quenching, these voids, micro cracks, and the uneven surface are considered to be the initial points for cracking.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 87 (2023) 211–218.

Fig. 3 EPMA quantitative mapping and line analysis result of carbon and chromium concentration in vacuum-carburized SUS304 stainless steel. (online color)