Process Parameter Optimization for Selective Laser-Melted High-Nitrogen Steel and the Effects on Microstructure and Properties

Abstract

Chromium nitride powder is blended with pre-alloyed powder to make an overmatched powder with a high nitrogen concentration in order to manufacture high-nitrogen steel by selective laser melting. By employing a wider range of process parameters, the impact of process parameters on the relative density, nitrogen concentration, microstructure, and mechanical properties of high-nitrogen steel is investigated. In simulated human body fluid conditions, the corrosion resistance of high-nitrogen steel, pure titanium, and 316L was compared and evaluated. The findings demonstrate that the relative density of high-nitrogen steel initially rises and then falls with the increase in energy density, reaching a high value of 98.8% at 148.8 J/mm3. With rising energy density, the nitrogen concentration falls. The microstructure of high-nitrogen steel is mainly composed of columnar and cellular grains. Both grain sizes steadily grow, but their mechanical characteristics initially rise and then fall as the energy density rises from 83.3 to 187.3 J/mm3. With yield strength, tensile strength, and elongation reaching 921.9 MPa, 1205.1 MPa, and 27%, respectively, the alloy exhibits outstanding mechanical characteristics when the laser power is 250 W, the scanning speed is 700 mm/s, and the associated energy density is 148.8 J/cm3. The high-nitrogen steel at an energy density of 148.8 J/mm3 has the lowest corrosion rate when compared to pure titanium and 316L steel, which suggests that the HNS alloy will have good corrosion resistance in human body fluid conditions.

Keywords

• overmixed powders
• selective laser melting
• high-nitrogen steel
• corrosion resistance