Research On Welding Procedure Of Induction Heating-assisted Wet Welding Of Q345Steel

Along with the implementation of national strategy for "marine powers", largemarine engineering technology and equipment is listed as priority development status.The technology of underwater wet welding, as an important part of marine engineeringequipment technology, plays an extremely important support role for marine resourcesdevelopment and construction. However, due to the water quenching effect and richhydrogen environment, susceptibility to cold cracking is the main problem inunderwater wet welding of Q345steel.On account of water environment adverse effect, induction heating-assisted wetwelding was adopted to reduce the cooling rate of welding process in this paper. Theinduction heating auxiliary can reduce the cooling speed of the weld joint, avoid thegeneration of hard and brittle martensite and upper bainite microstructure. Therefore,the susceptibility to cold cracking was reduced and the mechanical properties of weldwas improved.Firstly, the basic principle of the induction heating-assisted wet welding isanalyzes by the heat affected zone CCT diagram. The effect of parameters L(thedistance between welding torch and center of induction coil), H(the height between theinduction coil and the bottom of plate), V(welding speed),I(output current of induction)on the welding temperature field is studies in this paper. The results show that theparameters H and I mainly determines the maximum temperature and heating rate ofthe welding temperature field, the parameters V mainly determines the retention timeof the maximum temperature, the parameters L determines the superposition of the twotemperature field.Secondly, the effect of parameter I on weld appearance, form factor,microstructure of Q345steel is studied in bead-on-plate welding configuration. It canbe concluded that increasing parameter I was equal to increasing the welding heatinput. As the parameter I increases, the microstructure of weld metal changes from lathmartensite and upper bainite to proeutectoid ferrite and acicular ferrite. As theparameter I is45A, proeutectoid ferrite is coarsening. Subsequently, the effect ofparameter I on tensile property and impact property of Q345steel is studied in buttwelding configuration. The results show that the tensile strength of welded joint increase gradually with the parameter I increasing. As the parameter I is45A, the jointefficiency increases to almost100%. The impact toughness of weld metal increasesfirstly and then decreases with the parameter I increasing.Finally, gas chromatographic method is chosen to measure the content of diffusiblehydrogen of weld joint. The effect of parameter I and H on the content of diffusiblehydrogen is studied. The content of diffusible hydrogen is mainly determined byhydrogen escape velocity and hydrogen dissolution velocity. The results show that thecontent of diffusible hydrogen of weld joint increase gradually with the parameter Iincreasing. The content of diffusible hydrogen increases firstly and then decreases withthe parameter H increasing. Subsequently, susceptibility to cold cracking wasevaluated using a Y-slit self-restrained cracking test. It can be concluded that thesection crack rate decreases gradually with the parameter I increasing. The resultsindicated that the susceptibility to cold cracking of Q345wet welding is improved.