| The dissimilar metal materials have a great differences in chemical and physical properties and chemical composition, it will may exist chemical element segregation and the large of dilution rate in the process of welding.As a result,the welding of dissimilar metal materials is more difficult than the same metal material welding. Because the dissimilar steel weldment of316L stainless steel and Q345low-alloy steel is often applied in the structural design and manufacture.Based on these,the welding technology and the microstructure and properties of welded joint between316L stainless steel and Q345low-alloy steel are studied in this paper.The dissimilar steels welding were welded respectively by the tungsten electrode argon arc welding with ER309L welding wire and tungsten argon arc welding with ER308L welding wire and shielded metal arc welding with A042welding electrode. In order to determine the microstructure and properties of welded joints whether to meet the practical engineering requirements, the microstructure,mechanical properties,and corrosion resistance of welded joints under three different conditions were evaluated respectively.The analysis of microstructure, chemical compositions and phase structure of the dissimilar welded joints results showed that in the316L-weld metal interface,the fusion zone was small and acicular ferrite discontinuously distributed on the matrix of austenite.In the Q345-weld metal interface, there was a decarburization layer near the fusion line at the side of of Q345material and a black carbon layer at the side of of weld metal.There were different levels of carbon migration phenomenon in the welded joints under three kinds of welding process.The analysis of element line scanning and energy spectrum showed that the variations of CrsNi,Mn alloy contents presented the different gradient distribution, but there was not element segregation and M23C6s a phase precipitation in the interface. There was bone shape or worm-like ferrite distributed on the matrix of austenitic in the three kinds of weld metal, and the weld metal had a reasonable duplex organization.The results of mechanical properties tests showed that the tensile fracture position of three different welding joints had occurred at the side of Q345steel material. The average tensile strength of three different welded joints are533.4MPa MPa,525.1MPa and511.MPa respectively, all of which were higer than the Q345metal.And they can meet the tensile strength requirements of engineering structure. The impact toughness tests showed that the impact toughness of welded joints and316LHAZ and Q345HAZ were higher than the standard requirement under the test temperature. Three kinds of joint fracture mechanism was microporous polymerization mechanism of ductile fracture.Microhardness test results showed that the hardness distribution of the three kinds of joint change rules are basically identical.The results of intergranular corrosion showed that the intergranular corrosion resistance of three kinds of welded joints were relatively good.Through chemical immersion method and electrochemical test method to evaluate the pitting corrosion resistance of welded joints, the results showed that the pitting corrosion resistance of three kinds of welded joints were different.The joint welded by GTAW with ER309L welding wire had the best capability of pitting corrosion resistance.To sum up, under experimental conditions, the welded joint of316L stainless steel and Q345low-alloy steel can be successfully welded to some extent with higher levels by the choice of welding technology. |
PDF Full Text Request