Study On Solidification Mode And Microstructure Of 316 Stainless Steel By Laser Additive Manufacturing

The advantage of manufacturing freedom offered by additive manufacturing and the advantage good corrosion resistance and superior high/low temperature performance of 3x austenite stainless steels,made additive manufacturing of 3x austenite stainless steel a promising method for the development of innovative products for oil,metallurgy,chemistry,automobile and nuclear applications.However,current additive manufacturing of 3x austenite stainless steel is limited in the areas of the usage of different additive manufacturing technologies and the fabrication of high strength and high ductility materials with selective laser melting.There is rare report on how the compositions of the nominal composition affect the solidification mode.And it is still unclear if direct energy deposition is able to break the strength-ductility trade-off.In view of the above two challenges,this work focuses on the following aspects.6 different 316 L stainless steels and 1 304 L stainless steel are used for direct energy deposition by laser.The change of the solidification mode is predicted with the Delong1973(Cr)eq/(Ni)eq.It is found that the solidification mode is primary austenite(A mode)when(Cr)eq/(Ni)eq<1.3 and while switches to primary ferrite-secondary austenite(FA mode)when(Cr)eq/(Ni)eq>1.5.The hierarchical macro-scale melt pool,micro-scale grain and dendrite sub-microscale oxide inclusion and nano-scale dislocations are analyzed.The grain size is decreased,the segregation is alleviated,and the dislocation is enhanced for FA mode than A mode.A mode is more susceptible to hot cracking due to the impurity element of S and P.The strengthening mechanism is analyzed for samples fabricated both A and FA solidification modes.It is found that dislocation strengthening and compositional strengthening contribute the most for A mode.Compared A mode,more dislocation strengthening and less compositional strengthening contribute to the strengthening effect.The overall strengthening is increased for FA mode.The above finds could contribute the understanding of how compositions affect the solidification mode during additive manufacturing of 3x austinites and offer an innovative approach to break the strength-ductility trade-off.