Study On Microstructure,Mechanical Properties And Electrochemical Behavior Of Welded Joints Of High Strength Steel For Marine Engineering

The application environment of Marine engineering equipment is very strict,and the comprehensive properties of Marine engineering steel such as strength,hardness,corrosion resistance and weldability are increasingly required.The welding of thick plate steel has become one of the technical difficulties and research emphases in the construction of Marine engineering equipment.In view of the lack of research both at home and abroad to study,this project takes Q690 high-strength steel for offshore platform and EH36 high-strength steel for offshore ship as the research object.Combining with thermal simulation technology and micro-area electrochemical test method,the structure,mechanical properties and electrochemical behavior of welded joints are studied and analyzed.For high strength steel in different thermal cycling Q690 thermal simulation joint research,the microstructure of different joint mechanical properties and the electrochemical behavior of different soaking time in 3.5%Na Cl solution are analyzed.The study found that the microstructure with heat cycle times of 4 are a lot of number of granular and blocky bainite dispersed on ferrite,and the structures are finer than the thermal cycling times 3 joint.At the same time,the joint has good mechanical properties and corrosion resistance.The microstructure,mechanical properties and electrochemical behavior of the joints of Q690 high strength steel at different peak temperatures were studied.The results show that the microstructure of the thermal simulation peak temperature at 950 °C joint are a large number of granular and blocky bainite dispersed on ferrite,and the mechanical properties and corrosion resistance of the joint under are better than other states.After optimizing the process parameters according to the tests of thermal simulation welded joints,Q690 of 110 mm thick plate steels were welded by the narrow gap submerged arc welding technology.The tensile test results of welding joints show that stress corrosion has a significant effect on the mechanical properties of narrow gap welded joints in 3.5% Na Cl,leading to the loss of mechanical properties,but still welded joint can meet the requirements of the base metal yield strength.EH36 of 40 mm thick plate steels were welded by gas-electric vertical welding process Through the study on the welding seam,heat affected zone and base metal of EH36 welded joints welded,it is found that there are some differences in the microstructure and performance of EH36 welded joints in the top,middle and bottom layers.On the whole,the results of both traditional electrochemical tests and micro-area electrochemical tests show that the microstructure of the bottom weld zone has the best corrosion resistance,while the top layer has the worst corrosion resistance far away from the weld zone.The research results of this paper are helpful to promote the progress of welding technology of high strength steel for Marine engineering and provide important reference for the design and manufacture of Marine equipment.