周惠久论坛 | Mingxing Zhang教授做客周惠久论坛开展主题讲座

The complicated thermal history of additive manufacturing (AM) leads to different microstructures of steels from their counterparts made by conventional processing. AM of 316 stainless steel is associated with coarse columnar structures, causing anisotropic properties. AM of H13 tool steel leads to the formation of elongated, high-carbon retained austenite films between martensite laths, resulting in high brittleness of the as-built H13 steel. To overcome this problem, we identified TiN as an effective inoculant for steel AM based on crystallographic calculation. The addition of 0.5 wt.% TiN nanoparticles not only eliminates property anisotropy, but also simultaneously increases the strength (tensile strength of 2051 ± 48 MPa) and ductility (elongation of elongation of 7.4 ± 0.7%) of laser AM-fabricated H13 steel. However, AM of 4340 steel produces equiaxed grains with isotropic properties comparable to forged steel.

In addition, AM of plain carbon steels can achieve tensile and impact properties comparable to, or even superior to, those of ultra-high-strength steels, including expensive maraging steels. This is attributed to the sequential micro-scale melting and solidification within AM melt pools, which provides sufficient cooling to directly form finer martensite or bainite. This process strengthens the steel while ensuring microstructural and property homogeneity without dimensional limitations, avoiding heat-treatment distortion and cracking typical of conventional production. This is equivalent to increased hardenability of plain carbon steels during AM.