Nitriding of niobium steel and product made thereby

A nitrided thin cast coiled steel strip comprising, by weight, less than 0.25% carbon, between 0.20 and 2.0% manganese, between 0.05 and 0.50% silicon, less than 0.01% aluminum, niobium between 0.01 and about 0.20%, and between 0.01 and 0.075% nitrogen, and having a majority of the microstructure comprised of bainite and acicular ferrite, having more than 70% niobium in solid solution prior to nitriding and having yield strength between about 600 MPa and about 722 MPa, tensile strength between about 673 MPa and about 797 MPa, and having a total elongation of at least 10% where the steel strip is less than 3 mm in thickness and has fine oxide particles of silicon and iron distributed through the steel microstructure having an average particle size less than 50 nanometers.