Study On Dynamic Mechanical Behavior Of GP1 Stainless Steel Made By Laser Additives Manufacturing

Additive manufacturing technology is to make parts by stacking layer by layer.The application range is wider and wider.Due to the unique production principle,it is valued by the industry all over the world.In this paper,GP1 stainless steel uniaxially stretched slab specimens,three-point bending specimens and spallation of disc specimens were prepared by selective laser melting additive manufacturing technology,and the materials were heat treated and microstructured.The dynamic tensile mechanical tests of GP1 stainless steel and heat-treated GP1 stainless steel were carried out by one-dimensional stress tensile test,three-point bending test and one-dimensional strain plate impact test.The following conclusions were obtained:(1)With the Zwick-HTM5020 high-speed tensile testing machine combined with the digital image correlation full field strain measurement technology,the experimental study on the axial tensile mechanical properties of GP1 stainless steel and heat treated GP1 stainless steel was carried out,and different strains were obtained.The tensile stress-strain curve of the material shows that the tensile mechanical response of GP1 stainless steel has a significant strain-strengthening effect.This phenomenon is more obvious after heat treatment.Austenite occurs in GP1 stainless steel under tensile load.Martensitic transformation;the fraction of martensite in the material increases after heat treatment,and the phase transformation also occurs during the stretching process;the yield stress increases with the strain rate before and after the heat treatment,and the yield stress at high strain rate The deformation increases rapidly and the strain at break decreases.The tensile fractures of the two materials are characterized by microscopic characterization.The results show that the GP1 stainless steel grains are obviously elongated under the tensile load,and the fracture mode is microcavity aggregation.(2)Three-point bending test of GP1 stainless steel before and after heat treatment was carried out by Zwick-HTM5020 high-speed stretching machine and MTS810 universal testing machine.The impact load-displacement curve was obtained.The results show that in the quasi-static threepoint bending experiment,before and after heat treatment The peak load of GP1 stainless steel increases with the increase of impact speed.In the dynamic three-point bending experiment,the peak load of GP1 stainless steel does not change,and the load of heat-treated GP1 stainless steel increases with the increase of impact speed.Through the microscopic characterization of the fracture,it is found that there are a large number of dimples on the surface of the fracture surface of GP1 stainless steel,and the size is large.The surface of the fracture surface of the heat-treated GP1 stainless steel is distributed with a large number of cleavage surface steps and river patterns,and there are a few small-sized dimples.In summary,the fracture mode of GP1 stainless steel is ductile fracture,and the phenomenon of micro-hole accumulation is obvious.The fracture mode of heat-treated GP1 stainless steel is quasi-cleavage plane fracture.Therefore,the ability of GP1 stainless steel to resist impact fracture is higher than that of heat treated GP1 stainless steel.(3)Using the first-stage light gas gun experimental device and laser interference particle velocity measurement technology,the layer cracking experiment of additive manufacturing GP1 stainless steel was carried out,and the free surface velocity time history curve was obtained.The results show that GP1 stainless steel is used before and after heat treatment.The spalling strength decreases slightly as the impact velocity of the flyer increases.The delamination strength of GP1 stainless steel and heat-treated GP1 stainless steel is calculated by comparison.It is found that the delamination strength of heat-treated GP1 stainless steel is slightly larger,indicating that the heat treatment can increase the ability of GP1 stainless steel to resist crack damage;through the metallographic and fracture of the section The micromorphology analysis shows that the GP1 stainless steel crack damage is easy to nucleate at the intersection of the laser molten pool boundary line.The fracture dimple morphology is obviously different from the uniaxial tensile fracture,and the fracture mode and damage evolution of the specimen after heat treatment The damage patterns of traditionally processed test pieces are similar.