Analysis of the Mechanical Properties of N-Added CMn Structural Steel by the Impulse Internal Friction Technique

Abstract

The presence of substitutional solutes has a strong influence on the Snoek effect of interstitial atoms in body-centered cubic (bcc) Fe alloys, such as the structural CMn steel grades produced in hot strip mills. In the current study, bcc Fe-Mn-N alloys were analyzed using the impulse technique and the results were correlated to their mechanical properties and the AlN precipitation characteristics. The broadened Snoek peak related to the octahedral interstitial N could be resolved into three distinct Debye peaks related to the arrangement of Mn atoms surrounding the N atoms. The simulation results suggest that precipitation of AlN occurred mainly during coiling and that the precipitation kinetics was enhanced at higher coiling temperatures. Alloys isothermally held at high temperatures had a yield strength and tensile strength linearly proportional to the difference between the nominal N content and the interstitial N content. The observations point to the pronounced precipitation strengthening effect of AlN after high-temperature coiling simulations. The result also reveals that interstitial N increases both the yield strength and the tensile strength in steels coiled at low temperatures.