Stress State Of 316L Stainless Steel Cladding Layer By Laser Cladding

Laser cladding can provide good surface strengthening effect on mechanical parts,enhance surface strength and hardness of base material,and increase wear resistance and corrosion resistance.At present,this technology has been widely used in the field of surface modification,new material preparation,and components remanufacturing.Laser energy is used to achieve local high-density energy input during cladding process.Under rapid heating and cooling rate,the melting and solidification process are completed in a short period of time,resulting in a large temperature gradient.Large residual tensile stress remains inside the cladding layer as well,which could cause deformation,delamination,cracking and other adverse effects of the workpiece easily.Therefore,residual stress is an important problem that can't be ignored in engineering applications.The characteristic of rapid heating and cooling of laser cladding makes the residual stress unavoidable.The best way is to minimize the regulation or eliminate the post-processing to ensure the performance of the workpiece.The process parameters are the main controllable factors in the cladding process.Therefore,it is very necessary to study the influence of process parameters on the distribution of residual stress.It is also worthwhile to study the stress by changing the state of stress distribution.In this paper,the hole-drilling method is used to systematically investigate the influence of different cladding parameters on the residual stress state distribution of 316 L stainless steel laser cladding layer,the effect of laser remelting and heat treatment on the residual stress are studied as well.The effects of various stress state changing methods on the microstructure properties of the cladding layer are investigated by optical microscopy(OM),Vickers hardness tester,X-ray diffractometer(XRD),etc.Research indicates:(1)The 316 L stainless steel cladding layer has no defects such as macroscopic cracks,and the apparent quality is good.The cladding layer is composed of uniform austenite phase,with dense and uniform equiaxed grain structure with partial columnar dendrites.The average hardness of the cladding layer is 289 HV,while the matrix hardness is 114 HV.The longitudinal residual stress of the cladding layer is greater than the transverse residual stress.The average longitudinal residual stress is 233.07 MPa,and the average transverse residual stress is 120.55 MPa,both of which are tensile stresses.The initial overlapping area of the cladding layer and the substrate has the largest residual stress,and the residual stress of the matrix away from the cladding region is the smallest.(2)In a certain range,the residual stress raises with the increase of laser power,powder feeding speed,number of cladding layers,and cladding area.While the scanning speed decreases could also cause the increase of residual stress.The residual stress of long-edge scanning is significantly larger than that of short-edge scanning.Gap scanning and average scanning cannot effectively improve the residual stress distribution.(3)Both laser remelting and heat treatment processes can effectively eliminate residual stress without substantially changing the properties of the structure.The residual stress value of the cladding layer sample with the laser power of 1200 W and the scanning speed of 4 mm/s was the lowest.The residual stress improvement effect was more obvious when the relationship between the remelting path and the cladding path was changed from parallel to vertical.The heat treatment after cladding can minimize the residual stress.The higher the heat treatment temperature,the more obvious the effect of eliminating the residual stress of the cladding layer.After heat treatment at 800 °C,the longitudinal residual stress and the transverse residual stress decreased by 83.8% and 73.6%,respectively.