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

Stainless steel 316 L prepared by laser melting consisted of a hierarchical austenitic microstructure with micrometresized (10-25 mu m) grains containing fine 1 mu m subgrains with a cellular structure. At high-temperature thermal treatments (greater than or equal to 1100 degrees C), merging and growth of the 1 mu m 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 degrees 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 300MPa at 1100 degrees 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.