Study On Process And Properties Of 316L Stainless Steel By Laser Additive Manufacturing

316L stainless steel is a workhorse material of our society owing to its excellent corrosion and oxidation resistance,mechanical properties and is used in such diverse applications to Aerospace Engineering,medical implants,and nuclear power plants.However,the strength of 316L can not be enhanced by heat treatment.316L is usually enhanced by strain hardening.But using this method,elongation of 316L will be reduced,furthermore thermostability will be droped because of recrystallization.One longstanding challenge,however,is overcoming the strength–ductility trade-off that exists ubiquitously in pure metals and alloys,which is hampering their structural applications.In recent years316L with an exceptional combination of strength and ductility was produced by laser additive manufacturing（LAM）.LAM of metal parts and components has the features of complex-sturcture forming,high-percision forming and high-performance forming.It uses high-energy laser beam to melt the synchronized metal powder,and the melted powder overlap to form parts.At present,a lot of investigations of processing parameters on performance of part merely are focused on energy density like line energy,surface energy,but it is lack of universality.In this paper,dimensionless parameters,orthogonal design and analysis of variance are used.Dimensionless parameters have following advantages:1)It can reduce the number of parameters that need to be investigated in a multi-variable and complex system.2)It can compare results from different researches.3)Dimensionless parameters have physical meanings and are useful for different metal materials.Orthogonal design have following advantages:orthogonal design is an important,mathematical method to study multi-factor experiment,and it can reduce test errors.For the results of orthogonal design experiments,variance analysis and range analysis can usually be used.The advantages of variance analysis are as follows:1)It can distinguish the data fluctuations caused by test errors in the experiments.2)Accurate estimation can be made of the importance degree of factors.In this paper,normalized quantities,such as E₀^*,q^*,v^*,etc.,and a dimensionless group of process variables are firstly derived to determine a processing window of laser metal deposition（LMD）.Orthogonal experiment is used to optimize the settings of processing parameters.The effect of laser power q,scanning speed v,hatch spacing h on hardness（HV₁）and density（ρ）was evaluated by Analysis of Variance（ANOVA）.The following hardness（HV）,density（ρ）,Microstructure and cooling rate was measured with Optical Microscopy（OM）and Vickers.The effect of E₀^*on density,hardness（HV₁）,microstructure and cooling rate was evaluated.It is shown that the 316L samples have a high density beyond than 99.7%for fabricated by E₀^*in 4.31-5.79.the density first rises then descends with increase of E₀^*,meanwhile hardness decreases.The max of hardness is 393.7HV₁,when E₀^*=3.49.The microstructure of 316L is consisted of columnar dendrites,cell crystals and equiaxed dendrites.With the rising of E₀^*,the cooling rate of molten pool decreases and the microstructure changes from equiaxial dendrites to cell crystals and columnar dendrites.Because of the Coarse grains,the hardness should drop.This paper provides a new research method for exploring the LMD process of 316L high-performance parts.