Abstract: Microstructure and mechanical properties of super-martensitic stainless steel SMSS 00Cr13Ni5Mo quenched at 880 ℃ and tempered at different temperatures (530, 580, 630 ℃) were studied. The changes in microstructure during tempering were analyzed using electron backscatter diffraction analysis (EBSD) and scanning electron microscopy (SEM), and the tensile properties were tested using an electronic universal testing machine. The results show that the tempered microstructure of the tested steel consists of a ferrite-like phase derived from the decomposition of tempered martensite, along with a small amount of austenite. As the tempering temperature increases, the ferrite-like phase evolves from a granular to a banded structure, eventually forming continuous bands. The grain size also increases from 25.76 μm to 29.45 μm. When the tempering temperature increases to 580 ℃, Ni enrichment leads to the formation of reversed austenite, reducing the martensite phase content from 88.7% to 75.8%. Further increasing the tempering temperature to 630 ℃ causes excessive Ni content in the Ni-rich phase, which inhibits the formation of reversed austenite, resulting in a recovery of martensite phase content to 79.6%. As the tempering temperature is increased, the change in reversed austenite leads to a decrease in the microhardness and yield strength initially, followed by an increase (hardness: 274.19 HV0.1→239.16 HV0.1→242.45 HV0.1; yield strength: 857.63 MPa→792.91 MPa→823.51 MPa). The elongation first increases, then decreases (20.67%→22.87%→20.80%). When the tempering temperature is 580 ℃, the steel exhibits the highest austenite content, which results in the best plasticity of the tested steel.

Key words: super-martensitic stainless steel, lath martensite, reversed austenite, tempering, mechanical properties