3D printing of new martensitic stainless steel
Ultra-high-strength martensitic stainless steel has excellent mechanical properties (stronger than austenitic stainless steel) and corrosion resistance (stronger than maraging steel), making it widely used in transportation, machinery, molds, and other fields. Our team has developed a new type of ultra-high-strength martensitic stainless steel, 10Cr13Co13Mo4Ni2NbW, using LPBF and cryogenic + aging heat treatment. The material achieves an ultimate tensile strength of 2.1 GPa while maintaining an elongation at break of 9.2%.
化学組成：
In this study, stainless steel powder with a particle size of 15 to 53 μm was dried at 120°C for 4 hours and then prepared by LPBF. The laser power was 200 W, the scanning speed was 1000 mm/s, the layer thickness was 0.03 mm, the scanning pitch was 0.07 mm, the spot diameter was 0.07 mm, and the rotation per layer was 67°. The prepared samples were cryogenically treated at -196°C for 8 hours and then aged at 550°C for 10 hours.
SEM photo of Truer martensitic stainless steel
The as-printed stainless steel contained half austenite (47.7%), but after cryogenic and heat treatment, only 3.52% remained. After heat treatment, the stainless steel exhibited a higher number of low-angle grain boundaries and dislocation density due to the transformation of large-scale metastable austenite to martensite. The average grain size decreased from 3.75μm to 2.73μm.
Microstructure of printed stainless steel
After heat treatment, the martensitic matrix and precipitated phases provide high strength, but the elongation is significantly reduced. Because austenite is a soft phase, the strength of martensitic stainless steel increases significantly after heat treatment as the austenite content decreases. Retained austenite in martensitic stainless steel can improve its plasticity by preventing crack propagation and altering crack paths. Furthermore, the TRIP effect occurs during deformation of retained austenite, delaying fracture and increasing both strength and plasticity. Consequently, stainless steel exhibits increased strength and decreased plasticity after heat treatment.
Mechanical property comparison
The fracture pattern after heat treatment is a mixed fracture, with cleavage planes and pits.
The transformation of austenite into martensite during cryogenic and heat treatment further increases the dislocation density. Dislocations promote the nucleation of second phases, leading to ultra-high strength through second-phase strengthening. Theoretical calculations show that the increase in yield strength is primarily due to grain boundary strengthening, dislocation strengthening, and second-phase strengthening.
Fracture pattern
結論
This study developed a new ultra-high-strength martensitic stainless steel with excellent toughness, produced through laser powder bed fusion and cryogenic-aging heat treatment.
After cryogenic-aging, a large amount of austenite transforms into martensite, with dislocation density comparable to that of forging and rolling. This results in the formation of Laves phase and carbide precipitation.
The martensitic stainless steel produced by the research team exhibits excellent mechanical properties, with an ultimate tensile strength of up to 2.1 GPa and an elongation at break of 9.2%.
The new martensitic stainless steel developed in this study offers significant advantages in mechanical properties and effectively avoids the trade-off between strength and toughness.
