Embrittlement and toughening in CGHAZ of ASTM4130 steel

Abstract

In the present investigation, a thermal welding simulation technique was used to investigate the mechanical properties and microstructure features of the coarse-grained heat-affected zone (CGHAZ) of ASTM4130 steel. The effect of post welding heat treatment (PWHT) and welding heat inputs on the toughness of CGHAZ was also analyzed. The results show that CGHAZ has the lowest toughness, which is only 5.5%–7.1% of the base metal. CGHAZ is mainly composed of dislocation martensite, upper and lower bainite, and M-A constituents. But after PWHT, carbides precipitate from non-equilibrium microstructures of CGHAZ accompanying some retained austenite which transforms into low bainite, thereby enhancing toughness over the base metal. Therefore, the key microstructure factors affecting fracture toughness are lathlike non-equilibrium microstructure and lowered supersaturation before and after PWHT respectively. When welding heat input is between 12 kJ/cm and 28 kJ/cm, the mechanical properties in CGHAZ of ASTM4130 with single-pass welding can satisfy the requirements when PWHT is applied.