Optimization Of 30CrMnMoRe Steel Multi-layer And Multi-pass Welding Sequence And Analysis Of Heat-affected Zone Microstructure

The 30 CrMnMoRe high-strength steel welding heat-affected zone(HAZ)is prone to martensite transformation,which is not conducive to joint performance.Especially in the multilayer and multi-pass welding of 30 CrMnMoRe thick plates,the HAZ undergoes multiple thermal cycles,which will cause its structure to be complex and difficult to control mechanical properties.Research on the evolution of HAZ structure of 30 CrMnMoRe steel multi-layer multi-pass welding,revealing the internal structure response behavior of typical HAZ under multiple thermal cycles,is of great significance for controlling the mechanical properties of30 CrMnMoRe multi-layer multi-pass welding joints.In addition,the welding of 40mm30 CrMnMoRe butt joints requires a multi-layer multi-pass welding process with 4 layers and10 passes on each side.The welding sequence and direction have an impact on the residual stress and deformation of the joint,and the welding sequence of the multi-layer multi-pass welding is also required to be systematic Sexual inquiry.This article uses OM,SEM,EBSD and other methods to characterize the joints in the single-pass welding and multi-layer multipass welding processes of flat plate butt welding,and uses a variety of numerical simulation software to analyze the microstructure and mechanical properties of the welded joints.Based on the finite element method,the temperature field,stress and deformation of X-shaped weld joints under different welding sequences are explored.For the 30 CrMnMoRe high-strength steel base metal,the flat plate butt single-pass welding and the multi-layer multi-pass welding test were carried out.For single-pass welding,the joints obtained under different welding parameters all fracture at the weld,and all are ductile fractures.The hardness of the HAZ of the joint is the highest,the base metal is the second,and the weld is the lowest.The microstructures of the weld seam are austenite and a small amount of ferrite,and its average grain size is 87.8?m.The average grain size of HAZ coarse grain zone is 2.87?m,and the average grain size of HAZ fine grain zone is 2.36?m.The microstructures of the two zones are mainly lath martensite with a small amount of bainite,ferrite and retained austenite.Since experienced different welding thermal cycles,there are differences in the grain size and microstructure of the HAZ coarse-grain zone and fine-grain zone in different layers of the multi-layer multi-pass welded joint.The main microstructure of the coarse-grained zone in the lower three layers is tempered sorbite,accompanied by a small amount of martensite,bainite,fine granular pearlite and retained austenite.The main microstructure of the fine-grained region of the lower three layers is granular pearlite,accompanied by a very small amount of ferrite and base metal phase(tempered sorbite).Compared with the first three layers,the coarse-grained region of the surface layer newly formed tempered troostite.Compared with the first three layers,the fine-crystalline area of the surface layer has flaky pearlite remaining.There are a small amount of recrystallized grains in each layer of coarse-grained regions and fine-grained regions,and the nucleation of the grains is formed by the rotation of sub-crystals to gradually transform the small-angle grain boundaries into large-angle grain boundaries.Based on the calculation results of the material performance simulation software,the calculation results of the HAZ structure and hardness are consistent with the actual situation.Based on the finite element numerical simulation,the near seam area and the far seam area of the multilayer multi-pass welded joint have undergone different thermal cycles,which brings about different microstructure changes.The different welding sequence has almost no effect on the temperature.The stress and deformation of joints with reciprocating welding sequence on both sides can be significantly reduced.Adopting different welding sequence of adjacent layers slightly reduces stress and deformation.If the two are combined,the stress and deformation of the welded joint are minimized.