| Hydraulic support is a critical part of coal mine machinery, which controls and supports the roof of working face reliable and effective using together with coal mining machine. Now, the hydraulic support developing direction for great resistance, high retaining strength and stability, and adopting high strength structural steel is the best way to achieve this objective. However, one of the problems is how to guarantee the mechanical property and crack resistance of welded joint meeting the requirements when the high strength structural steel widely used.Combined with the current actual situation that eliminate hydrogen is a necessary process after welding Q690high strength structural steel in some companies, the welding butt joint experiments with two different strength solid weld wires are carried out which adopting the actual welding process and canceling the hydrogen eliminated treatment in this paper, and analyzing the matching of strengthen and toughness of welding joint. Then the feasibility of canceling hydrogen eliminated treatment after welding is investigated with the weld process and cooling condition which has been changed. We can get the following main conclusions:(1) The microstructure of GHS75H weld metal is consisting of fine lath bainite and its tensile strength is higher than base metal. Weld joint of GHS75H presents high strength matching and has good plasticity and toughness. The microstructure of MK-GHS70-G weld metal is mainly consisting of lath bainite and some acicular ferrite, and its strength lower than base metal. Weld joint of MK-GHS70-G presents low strength matching and has excellent plasticity and toughness.(2) There are keeps low content of diffusible hydrogen which has different escape characteristic in deposited metal of GHS75H and MK-GHS70-G. The diffusible hydrogen of GHS75H deposited metal has big escape speed in initial stage and the amount of escape nearly same with later stage. The diffusible hydrogen of MK-GHS70-G deposited metal has low escape speed and a small amount of escape in initial stage, then the escape of diffusible hydrogen depends on later stage by low speed.(3) The theoretical calculations show that the Pcm of Q690high strength structural steel is0.274and the maximum hardness of heat affected zone is381.76HV, which illustrate the Q690high strength structural steel has tendency of cold cracking and needs preheat before welding. Signal weld bead cracking test show that MK-GHS70-G sample has better crack resistance than GHS75H. High stress concentration and diffusible hydrogen content in root fusion zone are the main reasons for cold crack emerging.(4) Window type restraint cracking test panel and large-scale rigid cracking test panel are in a state of quenched microstructure, high stress concentration and diffusible hydrogen content when canceling the hydrogen eliminated treatment and adopting repid cooling after welding, but the final results show that the two weld joints have no cold crack no matter high strength matching or low strength matching, which instructions that hydrogen eliminated treatment after welding Q690high strength structural steel is a conservative process. |
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