High Strength and Retained Ductility Achieved in a Nitrided Strip Cast Nb-Microalloyed Steel
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The current study investigates the strengthening of an Nb-microallyed CASTRIP steel at 798 K (525 C) by nitriding in a KNO3 salt bath. Nitriding up to 1 hour dramatically increased the yield strength of the steel by 35 pct (from 475 to 645 MPa) with no sacrifice of ductility (16 pct). Further nitriding led to brittle fracture. Hardness profiles of the nitrided steels through the thickness reveal hard surfaces and a relatively softer core. The hardening of the shell in the nitrided steels is thought to be the combined effect of solid solution strengthening from nitrogen and dispersion strengthening from clusters and precipitates. The retained ductility is attributed to the hard-shell-soft-core structure through nitriding. 2012 The Minerals, Metals & Materials Society and ASM International.