Surface Nanocrystallization And Alloying Of 20 Steel

Failures of engineering structure material in service occur on the surface in most occasions.To optimize the surface microstructure and properties is going to be an effective strategy to improve overall performance and enhance the working duration of materials.The surface nanocrystallization technology and surface alloying were combined to realize the surface modification of 20 steel in this paper.It can improve the corrosion resistance and wear resistance of materials.It has a broad prospect at present time.We processed a nanostructured surface layer of 304 stainless steel and aluminum on 20 steel sample by means of ball milling in this work.Microstructure and property of the surface layer of samples befor and after annealing was characterized by using optical microscope,X-ray diffraction(XRD),transmission electron microscopy(TEM),and scanning electron microscopy(SEM),and micro-hardness tester.The main results are as follows:Experimental evidences show that a nanocrystallization layer of 304 stainless steel is obtained in the surface of 20 steel sample by ball milling.The thickness and the hardness of the layer increase with increasing treatment time.The thickness of the surface layer of 304 stainless steel can be 40?m after ball milling for 60min.And the hardness is as high as 600HV,which is 3 times as high as 20 steel's.The average grain size on the top nanostructure layer is in the range of 55-65nm with random crystallographic orientation.The grain size increases with the increasing depth from the surface.A smooth and uniform nanocrystallization layer of aluminum is obtained in the surface of 20 steel sample by ball milling.The thickness of the layer is about 35 ?m.The nanocrystallization layer is formed by ball's pounding.Fe-Al intermetallic which is homogeneous,with a high density and free of porosity formed by faster diffusion of atom.This technique reduced the annealing temperature and duration significantly.This technique produced layer of Al-rich phase ?-FeAl3 annealing at 600? and ?-Fe2Al5 with small amounts of P-FeAl at 650? by fast interdiffusion of Fe and Al.And the hardness is as high as 930HV,which is 5 times as high as 20 steel's.