Effect of heat treatment on fatigue crack initiation of laser powder bed fusion stainless steel 316L

Laser powder bed fusion (L-PBF) is an emerging additive manufacturing technique for building structural components. L-PBF processing defects, such as lack of fusion pores, promote fatigue crack initiation and shorten the fatigue life. With well-controlled processing, critical pores can be avoided such that the microstructure-driven intergranular crack initiation mode becomes operative. In this work, the fatigue crack initiation behaviours of as-built and solution annealed L-PBF stainless steel 316L were studied. Crack initiation of the as-built samples is driven by de-bonding of the dendritic grain boundaries. High temperature annealing results in the formation of thermally-induced defects, possibly via the reheat cracking mechanism and the nucleation of pre-existing gas pores. As heat treating could have led to recrystallization and annihilation of the original grain boundary defects, the thermally-induced defects became the new sites for crack initiation. In addition, heat treatment incurred significant reduction in yield strength, such that the interaction of fatigue and ratcheting strain accumulation dominated the deformation behaviour of the material. The resulting fatigue strength in the finite life regime was reduced by about 13% but the fatigue endurance limit was not affected.

[1]  B. Van Hooreweder,et al.  Crack propagation and fracture toughness of Ti6Al4V alloy produced by selective laser melting , 2015 .

[2]  T. Mower,et al.  Mechanical behavior of additive manufactured, powder-bed laser-fused materials , 2016 .

[3]  J. Kruth,et al.  Selective laser melting of biocompatible metals for rapid manufacturing of medical parts , 2006 .

[4]  Tomáš Kroupa,et al.  The Influence of Processing Parameters on the Mechanical Properties of SLM Parts , 2015, Procedia Engineering.

[5]  J. Kruth,et al.  Residual stresses in selective laser sintering and selective laser melting , 2006 .

[6]  D. Gu,et al.  Influence of processing parameters on laser penetration depth and melting/re-melting densification during selective laser melting of aluminum alloy , 2016, Applied Physics A.

[7]  Meng Zhang,et al.  Fatigue and fracture behaviour of laser powder bed fusion stainless steel 316L: Influence of processing parameters , 2017 .

[8]  W. Hwang,et al.  Determination and controlling of grain structure of metals after laser incidence: Theoretical approach , 2017, Scientific Reports.

[9]  Frank Walther,et al.  Effects of Defects in Laser Additive Manufactured Ti-6Al-4V on Fatigue Properties , 2014 .

[10]  Y. Zhong,et al.  Hardened austenite steel with columnar sub-grain structure formed by laser melting , 2015 .

[11]  Yang Liu,et al.  A study on the residual stress during selective laser melting (SLM) of metallic powder , 2016 .

[12]  H. Bhadeshia,et al.  Residual stress. Part 2 – Nature and origins , 2001 .

[13]  Ming Gao,et al.  Effects of processing parameters on tensile properties of selective laser melted 304 stainless steel , 2013 .

[14]  Galina Kasperovich,et al.  Improvement of fatigue resistance and ductility of TiAl6V4 processed by selective laser melting , 2015 .

[15]  Y. Zhong,et al.  Intragranular cellular segregation network structure strengthening 316L stainless steel prepared by selective laser melting , 2016 .

[16]  Ahmed Hussein,et al.  Evaluations of cellular lattice structures manufactured using selective laser melting , 2012 .

[17]  Xiao Huang,et al.  Effect of homogenization heat treatment on the microstructure and heat- affected zone microfissuring in welded cast alloy 718 , 1996 .

[18]  Thomas Tröster,et al.  On the fatigue crack growth behavior in 316L stainless steel manufactured by selective laser melting , 2014 .

[19]  P. C. Goh,et al.  Elucidating the Relations Between Monotonic and Fatigue Properties of Laser Powder Bed Fusion Stainless Steel 316L , 2018 .

[20]  Defect Formation Mechanisms in Selective Laser Melting: A Review , 2017 .

[21]  Petr Lukáš,et al.  Effect of mean stress on cyclic stress-strain response and high cycle fatigue life , 1989 .

[22]  Thomas Tröster,et al.  On the fatigue properties of metals manufactured by selective laser melting — The role of ductility , 2014 .

[23]  R. P. Skelton,et al.  Factors affecting reheat cracking in the HAZ of austenitic steel weldments , 2003 .

[24]  A. Dhooge,et al.  Reheat cracking in welded structures during stress relief heat treatments , 1979 .

[25]  Michael Gorelik,et al.  Additive manufacturing in the context of structural integrity , 2017 .

[26]  Christopher J. Sutcliffe,et al.  Convective heat transfer and pressure losses across novel heat sinks fabricated by Selective Laser Melting , 2009 .

[27]  Mohsen Seifi,et al.  Metal Additive Manufacturing: A Review of Mechanical Properties , 2016 .

[28]  C. Colin,et al.  Microstructural and mechanical approaches of the selective laser melting process applied to a nickel-base superalloy , 2012 .

[29]  Tobias Melz,et al.  Fatigue performance of additive manufactured TiAl6V4 using electron and laser beam melting , 2017 .

[30]  D. Masaylo,et al.  Impact of heat treatment on mechanical behaviour of Inconel 718 processed with tailored microstructure by selective laser melting , 2017 .

[31]  Khalil Abdelrazek Khalil,et al.  Processing and mechanical properties of porous 316L stainless steel for biomedical applications , 2007 .

[32]  Ian A. Ashcroft,et al.  Understanding the effect of laser scan strategy on residual stress in selective laser melting through thermo-mechanical simulation , 2016 .