Study On Welding Quality Control On The AH36Steel Plate

Submerged Arc Welding (SAW), Flux Cored Arc Welding (FCAW) and combined SAWwith FCAW on the AH36steel plate with thickness of6mm were done in this project. Theeffect of three different welding methods, welding parameters and cooling condition on themicrostructure, mechanical properties, residual deformation and stress in the joints werestudied.The results showed that both the unique FCAW and the combined FCAW with SAWproduced qualified joints with the different but satisfied tensile strength, bending and impacttoughness of CCS. The Difference on the tensile properties may be attributed to the amountof ferrite, pearlite, widmanstatten and quenching structure in the molten metal and theadjacent heat affected zone (HAZ). The real-time atomization with water-cooling at the backof weld bead can promote the formation of refined microstructure by controlling thecolumnar grains, decreasing the ferrites while increasing the amount of pearlites, and finallyincreased the tensile strength on the joints. On the other hand, although the multi-passwelding decreased the welding heat in the single pass, and refined the grain size, it did notwork on the vertical position welding on the AH36steel. The unique SAW with steelbacking accelerated the cooling rate of welding, refined the grain growth andcorrespondingly increased the impact toughness on the HAZ, but did not work on the centerof molten metal.With ANSYS, the temperature field and stress-strain field of AH36steel plate withthickness of6mm were studied. The finite element method (FEM) results showed thattrailing intensive cooling not only reduced temperature of specimen but also made weldingtemperature field distorted. The cooling effects on the second weld pass less than the firstweld pass with two-pass welding method. With distorted temperature field, trailing intensivecooling obviously decreased the longitudinal contraction deformation, but did not work onthe higher weld heat input. The distance between heat input and cooling output affected theresidual deformation in the joints. In order to verify the accuracy of the finite elementsimulation results, an experiment using the same parameters was done. The experimentalresults were consistent with the numerical results, and showed that the rules of residualdefomation with different parameters were different when layers changed, and longitudinaldistortion and angular deformation changed dramatically with different welding method. The residual stress using hole-drilling method showed that not only the unique FCAW butthe combined FCAW with SAW, the distribution of residual stress was consistent basicallyin both normal cooling and water-cooling condition. A high residual stress was existed in thejoints with the combined FCAW with SAW and ceramic backing, and reached338MPaduring normal cooling.ANSYS simulation also showed a reduction on the residual stresswith the help of atomization with water-cooling. With the same welding heat input, thelongitudinal residue stress can be decreased by increasing the cooling rate and decreasingthe distance between heat input and cooling output.