Abstract
The heat treatment solution annealing was used on austenitic stainless steel (ASS) 316L to examine the influence of microstructure modifications in various situations on mechanical properties. The samples were held at temperatures of 1050 and 1200°C for three hours. The heated samples were cooled in a variety of conditions, including the furnace, air, oil, and water. Before the heat treatment of the ASS 316L, the thermodynamic assessment was employed to illustrate the equilibrium conditions of possible phases stimulated to develop. For phase predictions in the Fe-Cr-Ni-Mo-Mn-C-Si-Cu-Al-P-S multicomponent system, the Thermo-Calc loaded with the TCFE8 database was utilized. The results showed that solid ferrite dendrites formed at 1400 °C in the ferritic-austenitic solidification mode. The ferritic phase fraction continues to dissolve rapidly into the austenite matrix below this temperature until 1130 °C when the matrix becomes totally austenitic down to 1050 °C. Ferrite, on the other hand, reaches its maximum value of 71% in the microstructure at 420 °C. Sigma phase formation is only feasible after hundreds of hours of aging.
The prediction of the phases is supported by microstructural examination of the heat-treated ASS 316L. The Vickers analysis test was used to evaluate the microhardness test at the same time. The results of the experiments demonstrated that these ASS 316L microstructures altered dramatically after being exposed to varying temperatures and cooling rates. As a result, heat treatment (heating and cooling) improves the desired ASS's microstructural and mechanical properties, allowing it to improve functional properties. The samples heated to 1050 °C and quenched in oil had an optimal microstructure of ASS 316L with well-alternating grain size and mechanical properties. In these conditions, the grain size variation of the ASS 316L was somewhat greater than that of the as-received material. The heat-treated samples displayed a well recrystallised microstructure. The results revealed that the average grain size was 42 ± 3.0 μm for oil-quenched at 1050 °C compared to 30 ± 3.4 μm for the as-received sample. The hardness was (174 ± 6.3 HV), ultimate tensile strength (595.27 MPa), and yield strength (219.23 MPa) for oil-quenched at 1050 °C; while the hardness of the as-received sample was (182 ± 9.2 HV), ultimate tensile strength (600.67 MPa), and yield strength (227.68 MPa). Based on the lattice strain results, the highest strain percentage was found in the samples heat-treated at 1050 °C compared to the hot-rolled sample, while the lowest strain percentage was found in the samples heat-treated at 1200 °C.