Process Strategy And Mechanism Of Manufacturing High Strength And Ductility 316L Stainless Steel By Laser Additive

In this paper,based on Laser Direct Energy Deposition（LDED）technology,a new process strategy of laser additive manufacturing high strength and high ductility stainless steel was proposed and designed,that is,strengthening and toughening 316L stainless steel via doping titanium.By mixing 1%～3%pure titanium powder into 316L stainless steel printing powder,the microstructure of 316L stainless steel printing can be refined to a great extent,and its corresponding mechanical properties can be improved.The yield strength and ductility of 316L ware 450MPa and 42%respectively,while when titanium content is 1%it increased to 600MPa and 53%and when titanium content is 2%which are 750MPa and 25%.Based on this,firstly,we explored the mechanism of the effect of titanium doped on the microstructure and mechanical strengthening and toughening of 316L stainless steel prints in detail.The addition of titanium into 316L changed its Cr、Ni equivalent ratio(₀)/4)₀))and promoted the change of the solidification mode of 316L microstructure（A→F）.At the same time,a large number of dispersed fine Ti（N,C,O）particles were formed in situ which plays an effective heterogeneous nucleation role under the corresponding solidification mode（F）.In addition,the component undercooling increases with the addition of titanium,which is the main reason why titanium doping can refine 316L microstructure.The grain refinement,particle dispersion strengthening and high dislocation density in the printing microstructure make the titanium doped 316L stainless steel have higher strength.At the same time,the low stacking fault of titanium doped 316L can easily form stacking fault and nano-twins in the microstructure,so that it can maintain a good elongation in the tensile process.In addition,it was found that not only the mechanical properties of 316L stainless steel can be greatly improved by titanium doping process,the thermal stability of 316L stainless steel printed doped with titanium also show certain advantages,especially 316L stainless steel printed with nano particle titanium powder doped.A large number of in-situ Ti（N,C,O）particles ware generated at 600℃,which improves the high-temperature thermal stability of 316L stainless steel,it is possible to expand the application range of 316L stainless steel to high temperature.Moreover,when using different laser processes to print titanium doped 316L stainless steel,its strength and toughness also have different characteristics,especially the laser power and quasi-continuous-wave laser frequency have a great influence.Based on this,this paper summarized and gave the process window of LDED to prepare high strength and high ductility titanium doped stainless steel,and provide a further process reference for laser additive manufacturing of high strength and high ductility titanium doped stainless steel.