Study On Microstructure And Properties Of Martensitic Stainless Steel Laser Cladding Layers With High Strangth And Ductility

Martensitic stainless steel（MSS）has been extensively utilized in aerospace,bridge construction and other industrial fields,due to its good comprehensive mechanical properties,corrosion resistance and processability.In order to obtain high-performance MSS cladding layer,two types of MSS laser coating including martensite/ferrite（M/F）and martensite/austenite（M/A）were designed and fabricated in this research.V element microalloying and post-cladding heat treatment were carried out respectively.The microstructure and properties of coatings were investigated by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,microhardness tester,universal material testing machine and electrochemical workstation.The main work and conclusions as follows:（1）A novel M/Fss coating without defects has been prepared by laser additive manufacturing technology,and the effects of V microalloying on the cladding layer was investigated.The results show that the M/Fss coating is mainly composed of martensite/ferrite（M/F）and M23（B,C）6 carbide（the M represent Fe,Cr,etc.）.The tensile strength,elongation and microhardness is 1500 MPa,9.84% and 448.96 HV,respectively.The V element microalloying refines the martensite structure in the cladding layer.With the increase of V element content,the ferrite and precipitates in the cladding layer increase gradually.The optimum comprehensive mechanical properties were obtained with the V content of 0.25 wt.%,the tensile strength,elongation and microhardness is1580 MPa,10.45% and 472.67 HV,respectively.The mechanical properties of the cladding layer decrease with the further increase of V content（0.5%²wt.%）.The electrochemical corrosion tests indicate that the cladding layer without V exhibits the optimum corrosion resistance,and the corrosion resistance of the cladding layers decreases by V element microalloying.（2）The M/Ass laser cladding layers was treated by a post-cladding heat treatment,and the effects of heat treatment temperature on the microstructure and properties of the coating has been studied.The results show that the cladding layer is mainly composed of martensite（M）,a small amount of austenite（A）and nano-sized carbides(Fe₃C and M₂₃C₆).The phase constituent of the cladding layer remain after tempering at200 ℃ and 400 ℃ for an hour,but the reversed austenite is formed in the cladding layer,and martensite was decomposed into carbide and finer tempered martensite.After the heat treatment at 600 ℃ for an hour,a portion of martensite in the cladding layer is decomposed into ferrite and carbide.The mechanical properties test results show that after tempering at 200 ℃ and 400 ℃ for 1 hour,the cladding layer maintains high strength（>1700 MPa）and high hardness（>500 HV）,and the elongation is improved significantly（from 6% increase to 11.2% and 14.1%,respectively）.After tempering at 600 ℃ for 1 hour,the microhardness and strength of the cladding layer decreased significantly（reduced by20% and 25%,respectively）.The electrochemical corrosion tests show that the corrosion resistance of the cladding layer decreases with the increase of heat treatment temperatures.