The Research Of Experiment And Numerical Simulation For Fiber Laser Welding 304 Austenitic Stainless Steel Thin Sheet

Laser welding is widely used in the welding of 304 austenitic stainless steel because of its high power density, high speed, narrow weld and small deformation. Compared with traditional CO2 laser welding and YAG laser welding, fiber laser welding is more and more concerned by people due to its high power, high beam quality, good controllability and long service life. To improve and enhance the welding properties, the microstructure and properties of welded joints for 304 austenitic stainless steel in fiber laser welding are studied. In addition, weld profile morphology is one of the important criteria to evaluate weld quality. Weld profile morphologies are simulated by the numerical simulation of temperature field, it play an important role for pre-selected process parameters and reduce the number of tests.500 W fiber laser is used to weld 304 austenitic stainless steel with 1mm thick in surfacing welding and butt welding. When laser power, welding speed and defocusing distance are 400 W, 1.4 m/min and-1 mm, respectively, microstructure and mechanical properties of welded joints are studied. The effect of laser powers, welding speeds and defocusing distances on morphologies and mechanical properties of welded joints are discussed. Combined with Fortran and MARC, a new combination heat source model is established to study temperature field and simulate weld profile morphologies in different welding situations.When laser power, welding speed and defocusing distance are 400 W, 1.4 m/min and-1 mm, respectively, the process of solidification for welded joint are as follows: initial precipitation phase is ferrite, austenite has formed before the end of solidification(FA mode), after solid phase transformation, the final microstructure are austenite and ferrite in room temperature; The microhardness of welded joint are higher than base metal; The fracture mode of tensile specimen is ductile fracture, the fracture mechanism is microvoid accumulation fracture.When the other conditions are same, there are no defects and oxidation in 400–500 W. With the increase of welding powers, penetration depth increase significantly, but the increased degree of bead width, waist width and waist depth are not larger than penetration depth. With the increase of laser powers, the average microhardness of the weld are also increasing. When laser powers are 400-500 W, the fracture of tensile specimens are in the base metal, it is typical ductile fracture; When the other conditions are same, there are no defects and oxidation in 1.0–1.4 m/min. With the decrease of welding speeds, penetration depth, bead width, waist width and waist depth increase obviously. With the increase of welding speeds, the average microhardness of the weld increase at first, then decrease with the increase of welding speeds. When welding speeds are 0.8–2 m/min, the fracture of tensile specimens are in the base metal, it is typical ductile fracture; When the other conditions are same, there are no defects and oxidation in 0 mm. With the increase of defocusing distances, penetration depth decrease obviously, but the change of bead width, waist width and waist depth are little. With the increase of defocusing distances, the average microhardness of the weld increase at first, then decrease with the increase of defocusing distances. When defocusing distances are-1–0.5 mm, the fracture of tensile specimens are in the base metal, it is typical ductile fracture; In addition, the change of welding speeds have influence on the upper part morphplpgy parameters(bead width, waist depth, waist width) of the nail morphology, the change of laser powers and defocusing distances have influence on the penetration depth.Combined with actual weld profile morphologies, a new cylindrical+cylindrical combination heat source mode is established. In different welding situations, the simulation results show that the match of experimental and simulation results for the weld profile morphologies are well; With the change of welding situations, the change trends on experimental and simulation results for weld profile morphology parameters are similar; The error analysis show that the maximum error values of penetration depth, bead width, waist depth and waist width are 6.4%, 7.7%, 25.0% and 25.6% in different welding situations, respectively. The errors are within an acceptable range. The errors of penetration depth and bead width are smaller, but the errors of waist depth and waist width are more larger; Except that, with the decrease of welding speeds, the interior convex for the upper part of the simulated weld profile morphologies are more and more inconspicuous.