| S620Q thick plate of low carbon quenched and tempered was widely used in machinery,mining and other fields, welding is used as the main connection mode of the application of it,and the weld ability is directly related to the safe operation of equipment components. Recently,the method of combining experiment with numerical simulation is used for the research of theweld ability of low carbon quenched and tempered steel, which has been paid more and moreattention. The weld ability experiments of the thickness of40mm S620Q thick plate Multi-passWelding were carried out by GMAW and FCAW. Micro-structural characteristics andmechanical properties of welded joint were investigated by means of scanning electronmicroscope, tensile test and other methods. In order to better study on S620Q thick plate multi-pass welding, the distribution of S620Q multi-pass welding temperature field was obtained byANSYS finite element analysis software using the double ellipsoid heat source model in thispaper, and meanwhile the HAZ width of thick plate each welding layer is predicted. Thedistribution of welding residual stress fields are got by heat-structure coupling method againstthe practical measurement of residual stress on the basis of the temperature fields.The weld ability experiments show that acicular ferrite (AF) and Granular bainite (GB) iscreated in GMAW weld, while GB and a small amount of AF are formed in FCAW weld. Thestrength and hardness of flux-cored wire weld is higher than solid wire weld. When the heatinginput is small, the microstructure of GMAW grained heat affected zone (CGHAZ) is lathbainite (LB), and the FCAW CGHAZ for GB, with the increase of heating input, themicrostructure is coarse LB in GMAW CGHAZ, and FCAW CGHAZ for GB. The solid wireweld has a higher impact value compared to flux-cored wire weld, while the impact value ofthe FCAW fusion zone and the coarse heat grain zone is a slightly higher than GMAW. Theirregular, granular M-A islands and bainite ferrite are created in the boundaries of CGHAZbecause of the influence of second thermal cycle, only GB are distributed in the boundaries ofpartial quenching zone. The irregular, granular M-A islands along the grain boundary of CGHAZ have little effect on toughness.The distribution of S620Q thick plate multi-pass welding temperature field and stress filedwere obtained by the numerical simulation; the simulation calculation of HAZ of thermal cyclecurve can be well matched with practical measurement, the highest peak temperature comparedto the measured values, relative error is around14%. Width curve of each region in HAZ bythe simulation calculation is basically consistent with the actual measurement width of eachregion in HAZ. Thick plate residual tensile stress mainly distributed in the weld and its nearbyregion after welding, the maximum equivalent residual tensile stress is437MPa. X groovewelding seam root with large transverse residual tensile stress is500MPa. Angular distortion isoccurred outside the plane in the thickness direction, the largest displacement is0.968mm. thecurve of simulating residual stress is consistent with the actual measurement, welded joint partsof the welding residual stress are predicted well by using the finite element method, these canprovide reliable guidance for practical welding.GMAW and FCAW welding experiments and numerical simulation result of S620Q highstrength thick plate provide the experimental basis for the selection of appropriate welding methodand process parameter and the improvement of high strength steel plate weld ability in the practicalwelding ofS620Q thick plate. |
