Welding Process Of 420MPa Grade Weathering Bridge Steel And Microstructure Performance Of Heat Affected Zone

High-strength weather-resistant bridge steel has excellent mechanical properties and better environmental corrosion resistance,and has broad application prospects in bridge steel During welding process of weather-resistant bridge steel,the microstructure and mechanical properties of welded joints have npt been studied.In this paper,the welding process of 420 MPa weathering bridge steel and the microstructure and performance of heat affected zone are systematically studied.The research results are as follows:(1)Compared with the heating rate of 0.05 ?/s,the temperature was increased between Ac1 and Ac3 when the heating rate was 120?/s.With the increase of cooling rate,polygonal ferrite,granular bainite,lath bainite and lath martensite was appeared of microstructure.The phase transition temperature was measured and the SHCCT curve was plotted of the experimental steel.(2)When the heat input was 13?30kJ/cm,with the increase of line energy,the microstructure was in the order of lath bainite structure and granular bainite structure,grain coarsening of CGHAZ.Proportion of large angle grain boundary was reduced.The toughness and tensile strength were gradually reduced.When the heat input was 18kJ/cm,impact energy of CGHAZ was 156J at-20?,tensile strength of 821 MPa,an elongation of 17.7%,and hardness of 273HV,which has the best comprehensive mechanical properties.(3)Research findings on different heat affected zones with heat input of 28 kJ/cm,the roughened grains and lath bainite in CGHAZ caused the most severe toss of impact toughness.The granular bainite in FGHAZ was fine and the toughness was increased;the coarse grain and pearlite of ICHAZ slightly reduced the impact toughness.Small and medium-sized M-A cementite and ferrite increased the toughness of SCHAZ.CGHAZ and FGHAZ havd relatively high hardness values,and the hardness values of ICHAZ and SCHAZ were low.Hardening and softening are not obvious of all specimens.(4)The weld zone,fusion zone and fine grain zone of the experimental steel submerged arc welded joint were softening zone,the softening rate was 3.1?8.8%;the coarse grain zone was the hardening zone,and the hardening rate was 11.6-12.0%.The hardness change rate of the whole welded joint was?12.0%,the hardness of the welded joint was not changed obviously,and the hard performance was stable.When heat input was 30kJ/cm and 38kJ/cm,the minimum impact energy in the fusion zone,coarse grain zone and fine grain zone was 128J and 92J of-20?,respectively.when heat input was 30kJ/cm and 38kJ/cm,the yield strength and tensile strength of the weiding joint were 530 MPa and 635 MPa respectively.Although the mechanical properties of the welded joints were reduced,the requirements for use can still be met,and the performance of the experimental steel welded joint was great when heat input Was larger.