Microstructure And Mechanical Properties Of A514 Steel Controlled By Heat Treatment And Welding Heat Simulation

Because of the depletion of oil and gas resources,the national investment has been gradually increased in offshore platforms and marine equipment.In order to meet the requirments of deep water and low temperature environments,it is necessary to improve the performance and thickness specifications of offshore engineering steels.This study focuses on the research on the microstructure,mechanical properties and heat treatment process of A514 steel,and discusses the impact toughness of the coarse grain region resulted from welding heat.Tensile test and Charpy impact test were used to test the mechanical properties.Meanwhile,the optical microscopy(OM),scanning electron microscope(SEM),Backscattered electron microscopy(EBSD),and transmission electron microscope(TEM)were used to observe the microstructure of A514 steel The main research results are as follows:A514 steel was quenched and tempered(QT)heat treated to study the effect of austenitizing temperature on microstructure and mechanical properties.Yield strength of the unheated sample at the core position was 715 MPa,the tensile strength was 1049 MPa,and impact energy was 46 J(0?).On the other hand,yield strength at the near surface position was 854 MPa,tensile strength was 1160 MPa,and impact energy was 39 J(0?).After quenching and tempering(800? austenitizing for 1 h+600? tempering for 2 h),yield strength was 705 MPa,tensile strength was 880 MPa,and impact energy was 230 J(0?)at the core position.However,yield strength was 745 MPa,tensile strength was 882 MPa,and impact energy was 209 J(0?)at the top layer.The hot-rolled steel consisted of granular bainite,and the M-A islands distributed on the bainite ferrite to reduce the toughness,In contrast,after quenching and tempering,the formation of is tempered martensite and sorbite was useful for improving toughness.Explore the influence of welding line energy on the microstructure and properties of Coase-Grain Heat Affect Zone(CGHAZ)by changing the welding line energy input When the welding line energy was 50 kJ/cm,Coarse-grained heat affected zone(CGHAZ)consisted of lath martensite,and impact energy is 52 J(0?).When the welding line energy was 100 kJ/cm,CGHAZ consisted of bulky martensite.And granular bainite,and impact energy was 25 J.When the welding line energy was 150 kJ/cm,CGHAZ mainly consisted of granular bainite,and impact energy was 7 J.The reason for the decrease in impact toughness was because austenite grain size increases from 50 ?m to 69 ?m with increasing input of line energy,and the coarsening grains reduces the toughness;...