Mechanical properties and cracking behavior of low-temperature gaseous carburized austenitic stainless steel

Abstract

In the present paper, in order to study the effect of low-temperature gaseous carburization (LTGC) on the mechanical properties of AISI 316 L stainless steel, uniaxial tension tests were performed on carburized specimens with different thickness. Cracking behavior of carburized layer at different depths was investigated by using scanning electron microscope (SEM). After carburizing, a ~30 μm thick carburized layer with ~ −2.2 GPa residual stress is formed on the surface region. Correspondingly, tensile stress in the non-carburized core compensating the surface residual compressive stress occurs. The yield strength (YS) of carburized specimen determined from tensile test reduces due to the existence of the pre-tensile stress in the core. Because of high hardness of carburized layer, ultimate tensile strength (UTS) of carburized specimen increases. After carburization, the ductility of the outmost carburized layer is significantly reduced and the cracking behavior of the carburized layer is dependent on layer depth. During the uniaxial tension process, the brittle surface layer (<10 μm) firstly cracks perpendicular to the loading direction at a low strain (≤ 4.3%), then cracks along different directions. Besides, intergranular cracking also occurs because of the carburization-induced lattice rotation. The cracking strain at the carburized layer depth of ~10 μm and ~20 μm increases to ~25% and ~56%, respectively.