Causes of bending brittle fracture of ER70S－6 welding wire

The bending test of ER70S－6 welding wire after cold drawing was carried out, and the brittle fracture phenomenon of welding wire was found. The causes of bending brittle fracture of welding wire were analyzed by means of macroscopic observation, chemical composition analysis, metallographic examination and microanalysis after different heat treatment processes. The results show that the main reason for the bending brittle fracture of ER70S－6 welding wire was the existence of pale yellow martensite and bainite composite structure (M－B), and the work hardening during cold deformation also promoted the occurrence of bending brittle fracture. The pale yellow M－B non－equilibrium microstructure was caused by the controlled cooling process that did not meet the conditions of ER70S－6 steel wire rod after finishing rolling. In the controlled cooling stage, when the temperature of the wire rod in the insulation cover was cooled to A₁ point (700 ℃), controlled and adjusted the opening rate of the fan to improve the supercooling degree, reduced the pearlite lamellar spacing and ensured that the temperature of the cover was not more than 600 ℃,the plasticity of the material could be improved and the generation of M－B could be prevented.