| Tunnel Boring Machines(TBM)have been widely used in constructing tunnels of roadsand rails.Recently,with the growing impacts of TBM on other fields,they began to be employed in roadway projects of coal mines.Because of variations on geological conditions,the workload of a TBM changes frequently,demanding strict requirements about the strength of materials in a TBM.Therefore,Q460 D steel sheets are used in a TBM's structural part,instead of the conventional Q345 D steel sheets.For example,Q460 D steel sheets are applied to cutter heads,excessive sliding shoes,and their supporting beams on TBMs.However,Q460 D steel sheets were not adequately studied or not commonly applied to TBMs as well as other heavy machines.Meanwhile,as steel sheets of low alloy high strength steel such as Q460 D are becoming famous,it is crucial to study their welding characters nowadays.To study the Q460 D of low alloy high strength steel weld,we used gas for shielded arc welding and selected welding material as solid wire JM-60 and TWE-81K2.Considering adaption to the international market of TBMs,the European standard EN15614 welding process evaluation criteria were adopted in this study.The welding process evaluation and welding performance of Q460 D steel were also studied and analyzed to obtain the welding process that is suitable for production.Steel weldability is an important factor to be evaluated and is assessed by the carbon equivalent calculation method,the welding hot cracking susceptibility indices,and the oblique y-Groove cracking susceptibility test.Other factors to be analyzed are mechanical properties of such Q460 D HSLA steel according to different weld heat input,where tensile tests and bending tests are conducted.Also,the hardness of a welded joint is obtained by the Vickers hardness test.Finally,the organization of joint form of welded joints was assessed by observations and metallurgical tests,based on which the relationship between microstructure and mechanical properties of the joint can be analyzed.Results reveal that welding joint with 18-20 kj/cm weld heat input is optimal and the strength of welded joint matches with the base metal,and the bending and impact test performance meets the application requirements.To be specific,although Q460 D steel sheets haves slight tendencies to cold cracking,their thermal cracking tendency are not obvious,which is viewed as good weldability in general.Results from metallographic test show that the microstructure of welding joints' base metal are mainly massive ferrite,Pearlite and a small amount of granular Bainite,weld joints weld parts of acicular ferrite and Pre eutectoidferrite.The welding joint of base metal grain size is larger,because the steel rolling effect of grain is banded,the ferrite are massive,and the grain size of the weld zone of the welding joint is relatively small,the microstructure is mainly acicular ferrite.Research results show that Q460 D steel with good weldability,by selecting the proper welding process welding Q460 D of welded joints of steel can meet the requirements of Tunnel Boring Machine and other mechanical equipment.Q460D study on weldability of steel has been used in Huainan mining project of shield machine,shield in the Anhui Huainan mining zhangji coal mine of high level suction roadway,rock roadway operations,functioning well;it has realized the significant breakthrough of coal mine rock tunneling technology and equipment. |
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