Effect of Mn/N ratio on microstructure and mechanical behavior of simulated welding heat affected zone in 22% Cr lean duplex stainless steel

Abstract

The effect of Mn/N ratio on microstructural evolution, mechanical and fracture properties in welding heat affected zone (HAZ) of 22% Cr lean duplex stainless steel (DSS) were investigated. At comparative low heat inputs for low nickel tested DSS, the reformed austenite evolution of HAZ was mainly controlled by N content, and increasing Mn/N ratio promoted the growth of widmanstatten austenite (WA) and inhibited Cr2N precipitates formation in HAZ, and then significantly reduced its strength and elongation due to weakened strengthening effect and the decrease of austenite fraction. The tensile and yield strength of HAZ for 17.80 Mn/N ratio DSS are higher than that of 2205 DSS, but the obstruction of dislocation movement resulted in a sharp decrease of plasticity at high heat input of 2.935KJmm-1. The impact fracture of HAZ changed from ductile to brittle mode with the increase of Mn/N ratio, and for 17.80 Mn/N ratio DSS with high nitrogen content, the widening gaps of hardness and elastic moduli between two-phases in HAZ increased crack tendency, and significantly reduced its toughness. More grain boundary austenite (GBA) and WA formation for 51.14 high Mn/N ratio DSS segmented and refined the ferrite matrix in HAZ and improve impact toughness at higher heat input, while the coarsening of WA and (Cr, Mn) O oxides adversely reduced it to a lesser extent.