Effect Of Prior Deformation On Welding Microstructure Of Steel Q235 And 304L

This subject, raised by an automotive company and based on the welding design on the curved surface, studies the effect of prior deformation on the welding structure and a proper welding procedure on pieces deformed. Q235 and 304 L, widely used steels with different microstructure are studied and MAG robot is used. The type of T-joint is used as non-deformed welding, and beads welded with a certain distance away from the deformed area are studied as welding after deforming. Essays are made to find the proper welding parameters in two joints, and observations of microstructure in the base metal, non-deformed weld bead and weld bead with a prior deformation are done. Experiments are carried out to determine the distribution of strain on the curved surface and it’s decided to weld with a distance of 5mm and 8mm away from an area of 30% prior strain to make sure the weld toe and the heat affected zone are in this area. The results show that, two types of Q235 joints both have typical features of welding microstructure in low carbon steel and the samples welded with a prior deformation have a smaller partially melted zone and a wider fine-grained zone however the grains fined have slightly grown, and which is more evident in the sample of 8mm. Two types of 304 L joints have similar microstructure while the welds with a prior deformation have smaller fusion zones and partially melted zones, and the quantity of carbide precipitation and intergranular ferrite decrease.To sum up, the welds with a prior deformation have more uniform microstructures, so a certain prior deformation can improve the welding microstructure.