Study On Weldability And Welding Process Of 1200MPa Grade HSLA Steel

The current domestic studies on the welding of HSLA steel are mainly focused on steels that the strength is 1000MPa grade and below.While the strength of HSLA steel increases,the strengthening and toughening of weld metal and the deterioration of heat affected zone are the problems during welding.In this paper,according to the characteristic of a 1200MPa grade HSLA steel,the weldability of tested steel was evaluated through welding thermal simulation test,maximum hardness test and Y-groove cracking test.And the welding test of tested steel under three different heat imputs,two kinds of interpass temperature and three different post heating temperature,to select proper welding material and process for the new HSLA steel,was conducted based on undermatching principle with GHS50NS wire.The test steel is wear resistant steel plate for mining machinery,the welded joint is not the major load-carrying part.It can meet the strength requirement while the tensile strength of welded joint reachs 600?700MPa.This strength grade tested steels are welded with"undermatched" ER307Si austenitic welding materials by conventional scheme.Welding with this GHS50NS tested welding wire can improve the strength of welded joint,and saving about 40%of welding materials cost.The study results have certain reference value and guidance significance for the study on the weldability of steels with this strength grade and the establishing welding process that based on“under-matching"principle during the practical welding engineering application.The main conclusions of this paper are summarized as follows:(1)The SH-CCT curve of tested steel was drawn by welding thermal simulation.When the cooling time t8/5 is 600?2000s,the microstructure of CGHAZ is granular bainite.As the cooling time t8/5 is shorter than 20s,it shows a microstructure of lath martensite.The hardness of CGHAZ decreases gradually with the increase of cooling time t8/5,and the maximum hardness was 477HV5.When t8/5 is 60s,the hardness of CGHAZ is lower than that of the base metal,and the microstructure was softened.During welding,the welding heat input should be controlled,and the cooling time t8/5 should be less than 30s to obtain the microstructure of lath martensite or lath martensite and lath bainite.It is necessary to take measures such as preheating and post weld heat treatment to avoid cold crack while the hardenability and cold crack sensitivity of tested steel is high.(2)The welding process test results indicate that:The mechanical properties of the weld metal first increase and then decrease with the increase of heat input,and increase with the increase of interpass temperature.The heat treatment temperature has no significant effect on the microstructure and properties of the welded joint.When the tested steel is welded with GHS50NS wire,while the heat input is 20KJ/cm,the interpass temperature is 140?150? and the hydrogen-eliminating treatment is150?×2h,the welded joint has good strength-toughness matching and low temperature impact toughness,and a welded joint with high comprehensive mechanical property can be obtained.The welding matching performance of GHS50NS welding wire and test steel is good.