Effects of Ni content on the microstructures, mechanical properties and thermal aging embrittlement behaviors of Fe-20Cr-xNi alloys

The effects of Ni content on the microstructures, mechanical properties and thermal aging embrittlement behaviors of Fe-20Cr-xNi alloys were investigated in the model alloys of Fe-20Cr, Fe-20Cr-5Ni and Fe-20Cr-10Ni, corresponding to ferritic stainless steel, duplex stainless steel and weld of austenitic stainless steel, respectively. Addition of Ni element will significantly change the solidification process and the microstructures of model alloys. Thermal aging at 400 °C for 3000 h leads to different degrees of hardening in ferrite of alloys, and a ductile-brittle transition in Fe-20Cr-5Ni alloy. It is well-known that Ni will accelerate the decomposition kinetics of ferrite. The thermodynamic calculation for Fe-Cr-Ni alloy indicates that addition of Ni will reduce the fraction of Cr-rich phase in the equilibrium phase diagram.