Effect of heat input on microstructure and properties of FCAW joints of high strength weathering steel

Flux-cored arc welding of high strength weathering steel was carried out at three different heat input. Microstructures of weld metal and heat-affected zone（ HAZ） were observed by optical microscope（ OM） and scanning electron microscope（ SEM）. And the strength,hardness and impact toughness at-40 ° were analyzed. The results indicate that the microstructure in weld metal is mainly consisted of fine-grain acicular ferrite and that in HAZ is composed of lath bainite and granular bainite. With increase of heat input,microstructures become certainly coarser. At the lower heat input of 0. 74 kJ/mm and middle heat input of 0. 96 kJ/mm,the strength and plasticity of weld metal are matched with base metal. At the higher heat input of 1. 19 kJ/mm,embrittlement occurs in weld metal. At three different heat input,impact absorbing energy of HAZ is lower than that of weld metal. Fracture mode is tough/brittle hybrid fracture in both weld metal and HAZ.