Physical simulation of the heat-affected zone in nickel-free high-nitrogen stainless steel weld at various peak temperatures and cooling rates

Abstract

Nickel-free high-nitrogen stainless steel (NFHNSS) stands out for its remarkable strength, ductility and toughness making it a preferred choice for applications demanding robust structural integrity. Physical simulations of NFHNSS heat-affected zone under different peak temperatures and cooling rates were studied. Based on the phase diagram simulated from Thermo Calc, physical simulations were carried out on 16 specimens with varying peak temperatures ( 800 °C, 900 °C, 1000 °C and 1250 °C) and various cooling rates (CR) as (25 °C/s, 15 °C/s, 5 °C/s and 2 °C/s). The specimens were grouped and characterised based on peak temperature under varying cooling rates. The microstructural changes, precipitates, hardness and tensile properties of the base metal and heat-affected zone (HAZ), were investigated. HAZ subzones are very sensitive to peak temperature and cooling rate lead to variation in grain size. The test results showed significant refinement in HAZ grain size and significant improvement in strength with a fast cooling rate. Furthermore, transmission electron microscopy analysis showed Cr2N formation with respect to the cooling rate. Yield and tensile strength increased with an increase in CR and ductility reduced slightly. Whereas, with an increase in peak temperature yield strength, tensile strength reduced and ductility increased due to grain coarsening