Characterizing Alloy Additions to High Nitrogen Steels

Abstract

Numerous articles of individual high nitrogen stainless steel compositions or alloys with near identical alloy compositions have been published characterizing the properties the alloy or the improvement which an individual element contributes to the base alloy's properties. In this study a series of high nitrogen steels alloys were prepared with the intent of characterizing the advantages and limitations of different alloy chemistry on the base alloy's material properties such as: microstructure, mechanical properties, environmental interactions (corrosion and oxidation), and wear. A base composition of Fe-15Cr-15 Mn was chosen. Alloys of similar basic compositions are austenitic and often used as a starting composition as a substitute or replacements for Fe-Cr-Ni stainless steel alloys. Mn is less expensive than Ni, is a strong austenizer, enhances nitrogen solubility, and has no allergenic effects. To this base alloy composition additions of C, N, Si, Mo, and Nb was added. Nitrogen (and carbon) alloys as interstitials and have been shown to enhance strength and reduce corrosion. Niobium (or similar elements) is often added to produce intergranular carbide precipitates that further enhance strength. Molybdenum and silicon are added to improve corrosion-oxidation properties. This study was designed to evaluate the action and interaction of these different alloysmore » and suggest what alloys compositions are best used under different engineering requirements. The results of the experimental alloys are compared with that of two experimental higher-nitrogen commercial alloys steels with further alloy addition of Ni and Cu were also studied. Alloy evaluation included: (1) microstructure: optical, SEM, and X-ray diffraction, (2) mechanical properties: yield, tensile, elongation, hardness (room temperature and hot), and energy to failure, (3) oxidation and corrosion, and (4) abrasive wear: scratch, pin-on-drum, and pin-on-disk.« less