Effect Of Low Temperature Ultrasonic Impact Treatment On The Microdtructure And Properties Of 316L Stainless Steel

Ultrasonic impact technology(UIT)can effectively improve the surface properties of materials.Current research is limited to the influence of instrument parameters on materials,while ignoring external temperature factors.The movement of material dislocations is difficult at low temperatures,and the work hardening is remarkable.If combined with low-temperature process and ultrasonic impact technology,it can not only enrich the ultrasonic impact surface nanometerization system,but also provide a new method for preparing ultrafine crystal materials;in addition,studying the high strain rate plastic deformation behavior of metal nano-block materials can Deepen people's understanding of the deformation mechanism of nanomaterials.This article firstly carried out 4 experimental studies on ultrasonic shock of 316L stainless steel at different temperatures(25?,-20?,-80?),combined with X-ray diffraction analysis(XRD),optical microscope(OM)and transmission electron microscope(TEM)The impact on the nanometerization mechanism of ultrasonic impact surface,and reflect the performance of the material through hardness test,corrosion test and friction and wear test.In addition,the bulk nano-austenite is prepared by ultrasonic impact technology and recrystallization annealing,which is characterized by ultrasonic impact treatment at different temperatures(25?,-25?,-196?),combined with microstructure observation and hardness test to characterize the bulk Plastic deformation behavior and mechanism of nanomaterials.According to the two-part experimental analysis,the conclusion is as follows:(1)After the UIT of 316L stainless steel,a nanocrystalline layer and a plastic strengthening layer with a certain thickness are formed on the surface.As the impact temperature decreases,the thickness of the nanocrystalline layer increases with the decrease in the thickness of the plastic strengthening layer;the low temperature environment is prone to martensite nucleation,and the deformation induces an increase in the content of martensite.When the impact temperature is-20?,the sample obtains a finer microstructure than the room temperature impact,and the average grain size of the surface layer is about 20nm;(2)Low temperature UIT can reduce the surface roughness of the material,improve the surface hardness of the material and damage the inherently excellent corrosion resistance of the material.In addition,the wear resistance of 316L stainless steel after low temperature ultrasonic impact treatment has been improved,and the wear mechanism has also changed,from the original adhesion+oxidation wear to oxidation+fatigue wear;(3)The optimal recrystallization annealing temperature of the UIT 2 pass sample is 600?,and the nano-austenite grains obtained at this time tend to be equiaxed,with an average grain size of about 80nm;bulk nano-austenite The original surface microhardness is 350HV.As the impact temperature decreases,the microhardness of bulk nano-austenite is improved,but the grain size shows a growing trend.(4)Combined with metallographic and transmission analysis,the plastic deformation mechanism of nano-austenite can be obtained:the dislocation motion and twins cut together to refine the grains,as the impact temperature decreases,the twin interface migration and grain rotation promotes the grains grow up.