Effect of Vanadium Nitride Precipitation on Martensitic Transformation and Mechanical Properties of CrMnNi Cast Austenitic Steels

The microstructural evolution and mechanical properties of two cast Fe-15Cr-6Mn-3Ni-0.5Si-0.2N-0.1C (concentrations in wt pct) steels containing no vanadium and 0.65 wt pct vanadium were investigated under uniaxial tensile loading for room temperature (RT) and 373 K (100 °C). The alloy development was focused on the formation of nanosized vanadium nitride precipitates in the austenite to serve as obstacles to dislocation motion. The austenitic steels exhibited transformation- and twinning-induced plasticity (TRIP/TWIP) effects and the planar glide of dislocations in the austenite. The triggering stress for the RT strain-induced σ ^γ→α′ formation increased by 190 MPa, and the transformation occurred at higher strain levels due to the presence of VN precipitates. The occurrence of the TWIP effect during tensile testing at 373 K (100 °C) of both steels resulted in engineering strains above 50 pct. The yield strength (YS) of the VN-containing steel was 420 MPa at RT, 52 MPa higher than the vanadium-free alloy. The difference increased to 59 MPa at 373 K (100 °C) with the VN-containing alloy exhibiting a YS of 311 MPa.