A study on thermal-induced phase transformation behavior and deterioration mechanism of 310S stainless steel

In this study, cold drawing 310 S stainless steel was selected as the raw material and employed two heat treatment methods, isothermal treatment (900°C for 12 hours) and thermal cycling processes (900°C-1 h↹room temperature-1 min-12 cycles and 900°C-1 min↹room temperature-1 min-100 cycles), to investigate the effects of heat treatment on the microstructural characteristics and mechanical properties. The results indicate that after isothermal treatment (900°C for 12 hours), the microstructure of AISI 310 S stainless steel transforms into a single-phase equiaxed grain structure. The strength decreases while the ductility increases. After thermal cycling treatment, the grain size is refined, resulting in increased strength but decreased ductility. Through FIB (Focused Ion Beam), WDS (Wavelength Dispersive Spectroscopy), and EPMA (Electron Probe Microanalysis) analyses, it was revealed that in a high-temperature, long-term environment, silicon (Si) tends to diffuse to the surface and aggregate with carbon (C) and oxygen (O) to form eutectic SiCO phase. These eutectic SiCO phase, upon melting at high temperatures and subsequent solidification after the experiment, result in the formation of shrinkage cavities in subsurface. Therefore, leads to the deterioration of tensile properties. On the other hand, after thermal cycling tests (900°C-1 min↹room temperature-1 min-100 cycles), due to thermal expansion and contraction inducing shear-induced defects in the lattice, the material exhibits recrystallization behavior, resulting in grain refinement and an increase in tensile mechanical properties. Additionally, conducting tensile strain analysis on the specimens after thermal cycling (two strain levels: 16%, 32%), it was observed that tensile cracks continue to propagate and grow along the surface cracks generated during the original thermal cycling, confirming the failure mechanism of thermal cycling.