Synergistic improvement of strength and elongation in laser-melting-deposited 18Ni300/316 heterostructured dual-phase steel by heat treatment

Abstract

18Ni300 maraging steel has an ultra-high strength above 2000 MPa after aging, but the elongation is compromised. Herein, a heterogeneous lamellar structure and solution-aging heat treatment are designed to overcome the trade-off between strength and elongation. Laser melting deposition using a synchronous feeder is employed to fabricate the heterostructured materials (HSM), and the powder delivery rates are optimized to prepare high-quality materials. The ultimate tensile strength and total elongation of the 18Ni300 maraging steel are improved to 1051 MPa and 10.4 %, respectively. The hetero-structure composed of a sandwiched layer of the 316L soft phase in the 18Ni300 hard phase exhibits high strength and elongation due to hetero-deformation-induced (HDI) strengthening, which obtain the trade-off between strength (reduction of 6.7 %) and elongation (increase of 62.3 %) when the austenitic layer thickness is optimized. Solution-aging treatment is performed to adjust the microstructure, including Ni-(Mo, Ti) nano-precipitates, second-phase diffusion, and refined grains relative to as-fabricated sample. The excellent tensile characteristics stem collectively from a synergistic strengthening effect of HDI strengthening, nanoscale precipitation, refined grains, grain boundaries, and dislocations. The HSM have the advantage of restraining sudden fracture, and the results reveal an innovative strategy to improve the properties of bearings and engineering materials.