Control of Solidification Structure of Stainless Steel in Additive Manufacturing Process

Additive metal manufacturing-has been attracting attention for various applications such as aircraft parts. However, the parts manufactured exhibit anisotropy characteristics due to the columnar crystal structure induced by rapid melting and solidification. In this work, an equiaxed solidification structure is obtained by adding Zr to promote nucleation. Samples were fabricated by additive manufacturing using Zr-added SUS304L powder. Their microstructures were observed by scanning electron microscopy and transmission electron microscopy. The mechanical and corrosion resistance properties were evaluated by comparison with samples fabricated by additive manufacturing using SUS316L. The microstructure observation revealed that the formation of columnar crystals in the SUS304L-Zr-3DP samples was suppressed compared with the SUS316L-3DP samples and that the average grain size was reduced to 1/3 or less. The transmission electron microscopy revealed a ZrN crystallized substance, which may have contributed to the suppression of columnar crystal formation. Tensile test results showed that the SUS304L-Zr-3DP exhibited isotropic mechanical properties. Corrosion resistance tests using electrochemical methods showed that they exhibited higher corrosion resistance than the SUS316L-3DP. These results demonstrate that the solidification structure formed during additive manufacturing can be controlled by adding Zr into the alloy matrix as nucleation sites.