Heat Input. E40 Steel Welded Joint Performance Studies

40mm plates of E40steels were welded with60kJ/cm,122kJ/cm,158kJ/cm heat inputs by Dual Wire Arc Welding. Welded joints without developing any defects were obtained through different heat input welding. Mechanical properties (tensile strength, toughness,) and Microstructures of Welds and Heat Affected Zone were studied by means of Tensile and Impact Tests, Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Based on above analysis, strength and toughness of the welds were investigated.With the heat inputs increasing, microstructures of welds were main Acicular Ferrite (AF), litter Pro-eutectoid Ferrite(PF) and Ferrite Side Plate(FSP).Weld columnar grain width showed increasing trend from450μm,700μm to850μm,the Area Percentage of Proeutectoid Ferrite showed5.2%,3.23%,2.5%decline.feerite lath width were1～3μm,and a large umber of dislocations in the ferrite lath, density of high angle grain boundaries between Acicular Ferrite are similar.The grain boundary angle distribution were mainly between50°and60°. There were two typical uniform distribution of fine inclusions which were oxide of Si,Ti,Mn,Al,Ca,Mg and MnS covered,the size of inclusions were less than3μm, and the average diameters were increased, the number reduced.Fine and homogenous distribution M-A constituent of welds increased form0.463%,0.799%to1.361%, mean chord length were less than2μm,such M-A constituent didn't have a negative impact on the toughness.Welding pass reduced from6,3to2,weak zone in the welds produced by thermal cycling were reduced.With the heat inputs increasing, hardness of welds were between190HV and230HV, strength of welds increased,it was related to the increasing of Acicular Ferrite and the content of alloying elements. Impact toughness of welds increased, it was related to increasing of width of columnar grains and percentage of Acicular Ferrite, reducing of the oxygen content of welds and the number of inclusions, weak zone of welds produced by thermal cycling.With the different heat inputs welding, heat affected zone (HAZ) can be divided into Coarse Grain HAZ (CGHAZ), Fine Grain HAZ (FGHAZ),Incomplete Recrystallization HAZ (ICHAZ). With the heat inputs increasing, austenite grain size in the coarse grain zone increased, Pro-eutectiod Ferrite increased, Intragranular ferrite were Acicular Ferrite.Microstructures of FGHAZ were Fine Ferrite, and ICHAZ were partly fine and coarse ferrite and little Perlite. With the heat inputs increasing, hardness of HAZ showed the first decrease and then increase with the increase of distance from weld interface, the minimum hardness value were180HV5,145HV5and165HV5,respectively. Because there were softening zone. Due to the microstructure of HAZ were non-uniform, low temperature impact toughness high but unstable.