Characterizing alloy additions to carbon high-nitrogen steel

Abstract

Alloy compositions are designed for specific industrial needs and applications. In this study, alloying elements that are known to enhance specific material properties of commercial Fe-Cr-Ni stainless steels were found to be similarly successful when added to Fe-15Cr-15Mn stainless steels. Unique to this study is the alloy addition of both carbon and nitrogen in excess of approximately 0.4 wt%. The nitrogen and carbon remained as interstitials without the formation of nitride or carbide precipitates even in carbon and nitrogen concentrations as high as 2wt%. Nitrogen and carbon alloying increased hardness, strength (σYIELD 850 MPa and σTMAX 2 GPa), toughness and wear resistance. Precipitate formers such as niobium and solid solution additives such as silicon and molybdenum enhanced σYIELD but to a much smaller extent than interstitial alloying. Additions of silicon and molybdenum significantly improved oxidation protection at all temperatures and are necessary to prevent spallation at temperatures above 800 K. In corrosion tests, alloys form a passive region, but small concentrations of nickel are necessary to ensure repassivation.