Research On The Microstructure And Tensile Properties Of The High Strength Steel Of The Laser-Arc Hybrid

The laser-arc hybrid which is the emerging technology of the laser welding technologies has strong competitiveness and broad application market at home and abroad, But the research of the laser-arc hybrid welding technology in domestic is very later, opposed to some developed countries, our country is relatively backward in this area. Therefore, this paper use a laser-arc hybrid welding method to analysis the microstructure and mechanical properties of the low-alloy high strength quenched and tempered steel welded.(1) First of all, using the laser-arc hybrid to weld the low-alloy high strength quenched and tempered steel under the laboratory conditions,and making it a standard sample after polishing and other treatment. Secondly, detailing the mechanical structure and main functions of the equipment and measuring instruments involved in the testing process. Finally, studying three areas of the distribution of the Vickers hardness, microstructure morphology and tensile properties, and giving the different research methods on the different aspects.(2) Firstly of all, the analysis of the Vickers hardness of the sample. Through the study we can find :the hardness has the tend to decrease near the center of the weld zone, the hardness remains at a relatively stable level between the weld area and thermal area,and began to decrease from the normal grain Reap area, and is the lowest in the softening zone. Hardness of the base metal at about 400 HV, in addition to some individual points, and the hardness of the weld heat affected zone is substantially between 500 HV to 600 HV, the width size of the softening zone which is the lowest hardness is in the 0.6 ~ 0.7mm. Secondly, the analysis of the microstructure morphology of the specimen. Microstructure morphology is observed by optical microscopy and scanning electron microscope and find: no new molding of ferrite in the heat affected zone, and all is the lath marten site from a position near the base to a position near the fusion line. Again, the analysis of the sample by X-ray diffraction shows that: the weld zone, the heat-affected zone or matrix organization is marten site. Finally, the analysis of the weld zone by EDS analysis, finds: the main elements of the weld zone,including Mn, Cr, Ni,do not change. that means, the composition of weld zone is more consistent and the hardness does not change.(3) Doing the tensile test on the specimen. The study finds that during stretching, the specimen fracture occurred in the weld zone, while tensile fracture morphology is related to the tensile strength: the strength of 573 MPa, the defect of the fracture is the crack of the crystalline; the strength of 806 MPa, the defect of the fracture is the crack of the crystalline and the defect of pores; the strength of 941 MPa, the defect of the fracture is the form of dimple fracture and the defect of pores; the strength of 1073 MPa, the defect of the fracture is the form of dimple fracture.