Study On Process Characteristics,microstructure Properties Of MAG And Laser Welding For 22MnB5 Hot Formed Steel

With the rapid development of the transportation industry,the requirements for light weight,safety and stability of vehicles have gradually increased.As one of the advanced high-strength steels,hot-formed steel is widely used in the manufacture of structural parts of vehicles to ensure the safety of vehicles while reducing the thickness of parts to achieve the purpose of lightweight body.High-strength steel can be processed by various welding methods,among which gas shielded welding and laser welding have greater application advantages due to the advantages of good welding quality and high efficiency.However,for the assembly gap problem of butt joints,it is necessary to fill the wire during laser welding to ensure the weld formation and welding quality.In this paper,for 3 mm thick uncoated 22 Mn B5 hot forming steel,MAG welding(melting electrode gas shielded welding),laser self-fusing welding and laser wire filling welding methods were used for butt joint welding,and the influence of key welding process parameters on the quality of the welded joint formation of 22 Mn B5 hot forming steel MAG welding and laser self-fusing welding was investigated and the welding process parameters were optimized.Analysis of different welding process parameters or assembly gap on the mechanical properties of welded joints,the study of different welding methods to obtain the microstructure characteristics of welded joints and their formation mechanism.For the MAG welding head,the study of welding current,welding voltage,welding speed on the weld overall and its cross-sectional forming law,analysis of the MAG welding head different regional microstructure characteristics and its formation mechanism,the study of three different process parameters under the microhardness,tensile strength of the law of change,the use of orthogonal tests to optimize the MAG welding process parameters,the results show that: MAG welding head forming is better,the No obvious defects,the welded joint can be divided into the weld zone,heat-affected zone,the base material zone.Weld zone microstructure is mainly granular bainite,martensite-austenite group consisting of massive tissue and a small amount of ferrite,the overall columnar growth.The heat affected zone can be divided into coarse crystal zone,fine crystal zone,incomplete quenching zone and tempering zone,different areas have different microstructure.the weakest area of mechanical properties of MAG welded head is located in the center of the weld,the highest tensile strength of789 MPa,tensile fracture is ductile fracture mode.Orthogonal test results show that the optimal process parameters for MAG welding head: welding current 130 A,welding voltage 18 V,welding speed 400 mm / min.For laser self-melting welding joints,the study of laser power,welding speed,the amount of defocus on the weld as a whole and its cross-sectional forming law,analysis of the laser self-melting welding joints in different areas of microstructural characteristics and their formation mechanism,the study of three different process parameters under the microhardness,tensile strength of the law of change,the use of orthogonal tests to optimize the laser self-melting welding process parameters,the results show that: laser self-melting welding joints forming More straight,narrow weld seam,no obvious defects,the welded joint can be divided into the weld zone,heat-affected zone,the base material zone.The microstructure of the weld zone is a coarse slate-like martensite tissue growing in columnar austenite grains.Heat affected zone can be divided into complete quenching zone,incomplete quenching zone and tempering zone,different areas have different microstructure.The weakest area of the mechanical properties of laser self-fusion welded joints is located in the tempering zone,with the highest tensile strength of 1206 MPa,and the tensile fracture gradually changes from ductile fracture mode to brittle fracture mode with increasing heat input.Orthogonal test results show that the optimal process parameters for laser self-fusion welding: laser power of 1600 W,welding speed of 0.8 m / min,the amount of defocus 0mm.For laser filler welding head,the study of different gaps on the weld as a whole and its cross-sectional forming law,analysis of different areas of the laser filler welding head microstructure characteristics and its formation mechanism,the study of different gaps under the microhardness,tensile strength change law,the results show that: the laser filler welding head shows a fish scale,no obvious defects.The welded joint can be divided into the weld zone,heat-affected zone,the base material zone.As the gap increases,the martensite content in the microstructure of the weld zone gradually decreases,and the ferrite content gradually increases.The tensile strength is 980 MPa when the gap is 1.0 mm.