Subgrain-controlled grain growth in the laser-melted 316 L promoting strength at high temperatures

Abstract

Stainless steel 316 L prepared by laser melting consisted of a hierarchical austenitic microstructure with micrometre-sized (10–25 µm) grains containing fine 1 µm subgrains with a cellular structure. At high-temperature thermal treatments (greater than or equal to 1100°C), merging and growth of the 1 µm subgrains into bigger subgrains restricted the rapid grain growth and microstructure coarsening. Partial phase transformation of austenite to ferrite at temperatures greater than or equal to 1100°C, in combination with gradual and steady growth of subgrains inside the micrometre-sized grains and nucleation of the sigma phase, has promoted the tensile strength of stainless steel 316 L to 300 MPa at 1100°C compared with that of conventionally made 316 L counterparts (approx. 40 MPa). The grain growth mechanism of the laser-melted microstructure can change the application criteria for 316 L and expand the application fields for 316 L.

Microstructure and mechanical properties of 316L austenitic stainless steel processed by different SLM devices

“…However, the low Young's modulus here has to be discussed with respect to the higher dislocation density and the previously described segregation effect in addition to the porosity and the effect of grain orientation. The higher dislocation density in SLM-processed samples is attributed to the high cooling rates, which is consistent with the work of Saeidi et al, who conducted TEM investigations on SLM-compacted samples made of 316L steel [53]. They found a high dislocation density at the outer areas of the cell structure on the microscale.…”

Compositionally-tailored steel-based materials manufactured by electron beam melting using blended pre-alloyed powders

“…There is a significant number of publications describing different AM approaches to its manufacturing [2,[20][21][22][23][24], specifics of laser-and electron-beam based PBF manufacturing processes used for SS316L, characteristic microstructure of additively-manufactured SS316L and its mechanical properties [21,[25][26][27][28][29][30][31][32][33][34][35]. In many cases, authors are comparing the properties of AM-manufactured SS316L samples with the ones reported for the same material manufactured by more traditional methods.…”

“…A number of researchers reported on SS316L manufacturing by laser-based AM methods, in particular by laser-based PBF (L-PBF) [2,21,22,24,28,31,34,36]. Characteristic microstructure of the achieved materials is predominantly hierarchical and austenitic with 10 to 25 μm sized grains containing fine 1 μmsized subgrains with a cellular microstructure [2,21].…”

“…A number of researchers reported on SS316L manufacturing by laser-based AM methods, in particular by laser-based PBF (L-PBF) [2,21,22,24,28,31,34,36]. Characteristic microstructure of the achieved materials is predominantly hierarchical and austenitic with 10 to 25 μm sized grains containing fine 1 μmsized subgrains with a cellular microstructure [2,21]. Partial phase austenite to ferrite transformation at high temperatures characteristic to L-PBF melt pool cooling dynamics combined with the growth of subgrains inside the micronsized grains and nucleation of the sigma phase can promote the tensile strength of SS316L to 300 MPa at 1100° C compared with approximately 40 MPa of conventionally manufactured 316L.…”

Microstructure-Tailored Stainless Steels with High Mechanical Performance at Elevated Temperature

“…The presence of abnormally large grains is detrimental to the mechanical properties of polycrystalline structures [46]. Mechanical properties of SLM 316L at 1100 and 1200°C is listed in Table 5 and compared to conventional 316L materials at the same temperature [47].…”