Effect of Process Parameters on Defects,Melt Pool Shape,Microstructure,and Tensile Behavior of 316L Stainless Steel Produced by Selective Laser Melting

Previous studies have revealed that laser power and energy density are significant factors affecting the quality of parts manufactured by selective laser melting(SLM).The normalized equivalent density E_(0)^(*) and dimensionless laser power q^(*),which can be regarded as a progress on the understanding of the corresponding dimensional quantities,are adopted in this study to examine the defects,melt pool shape,and primary dendrite spacing of the SLM-manufactured 316 L stainless steel,because it reflects the combined effect of process parameters and material features.It is found that the number of large defects decreases with increasing E_(0)^(*) due to enough heat input during the SLM process,but it will show an increasing trend when excessive heat input(i.e.,utilizing a high E_(0)^(*))is imported into the powder bed.The q^(*) plays an important role in controlling maximum temperature rising in the SLM process,and in turn,it affects the number of large defects.A large q^(*) value results in a low value of absolute frequency of large defects,whereas a maximum value of absolute frequency of large defects is achieved at a low q^(*) even if E_(0)^(*) is very high.The density of the built parts is greater at a higher q^(*) when E_(0)^(*)remains constant.Increasing the melt pool depth at relatively low value of E_(0)^(*) enhances the relative density of the parts.A narrow,deep melt pool can be easily generated at a high q^(*) when E_(0)^(*) is sumciently high,but it may increase melt pool instability and cause keyhole defects.It is revealed that a low E_(0)^(*) can lead to a high cooling rate,which results in a refined primary dendrite spacing.Relatively low E_(0)^(*) is emphasized in selecting the process parameters for the tensile test sample fabrication.It shows that excellent tensile properties,namely ultimate tensile strength,yield strength,and elongation to failure of 773 MPa,584 MPa,and 46%,respectively,can be achieved at a relatively low E_(0)^(*) without heat treatment.

Effect of Annealing Temperature and Strain Rate on Mechanical Property of a Selective Laser Melted 316L Stainless Steel

In the present work,316 L stainless steel specimens are fabricated by selective laser melting(SLM)via optimized laser process parameters.The effects of two extrinsic factors,i.e.,strain rate and annealing temperature,on the mechanical performance of SLM-processed parts are studied.The two intrinsic factors,namely strain rate sensitivity m and work hardening exponent n,which control the tensile properties of the as-built samples,are quantified.Micro structure characterizations show that cellular structure and crystalline grain exhibit apparently different thermal stability at 873 K.Tensile testing reveals that the yield strength decreases from 584±16 MPa to 323±2 MPa,while the elongation to failure increases from(46±1)%to(65±2)%when annealing temperature varies from 298 K to 1328 K.The n value increases from 0.13 to 0.33 with the increase in annealing temperature.Due to the presence of fine cellular structures and high relative density achieved in as-printed 316 L samples,a strong dependence between tensile yield strength and strain rate is observed.In addition,the strain rate sensitivity of the SLM-produced 316 L part(m=0.017)is much larger than that of conventional coarse-grained part(m=0.006),whereas the n value increases slightly from 0.097 to 0.14 with increasing strain rate.

Correction to:Effect of Process Parameters on Defects,Melt Pool Shape,Microstructure,and Tensile Behavior of 316L Stainless Steel Produced by Selective Laser Melting

In the Original Publication of the article,some reference numbers in the Figs.1,5,14 and Appendixes B,C,D are mismatched.The corrected reference numbers in the figures and appendixes are given below.