An Investigation on the Microstructure Evolution and Tensile Property in the Weld Heat-Affected Zone of Austenitic FeMnAlC Lightweight Steels

Abstract

IMicrostructure evolution and tensile property in the weld heat-affected zone (HAZ) of austenitic Fe-30Mn-9Al-0.9C lightweight steels were investigated. Five alloys with different V and Nb content were prepared by vacuum induction melting and hot rolling process. The HAZ samples were simulated by a Gleeble simulator with welding condition of 300kJ/cm heat input and HAZ peak temperatures of 1150°C and 1250°C. Micro-structures of base steels and HAZ samples were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their mechanical properties were evaluated by tensile tests.The addition of V and Nb formed fine V and/or Nb-rich carbides, and these carbides increased tensile and yield strength of base steels by grain refinement and precipitation hardening. During thermal cycle for HAZ simulation, the grain growth occurred and the ordered carbide (κ-carbide) formed in the HAZs. The yield strength of HAZ samples (HAZ 1) simulated in 1150°C peak temperature was higher as compared to the base steel due to the formation of κ-carbide, while the yield strength of the HAZ samples (HAZ 2) simulated in 1250°C decreased as compared to HAZ 1 due to the excessive grain growth. Key words: Lightweight steel, Heat-affected zone, Grain growth, κ-carbide, Yield strength