Influences of Nitrogen Addition and Annealing on the Microstructure and Corrosion Resistance of Fe-Cr-Mn-W Stainless Steels(I)

Influences of Nitrogen addition and annealing heat treatment on the properties of Fe-Cr-Mn-W Stainless Steels for the low activation material of a fusion reactor component were studied. OM, TEM, VSM, and XRD analyses wee used to study the microstructural changes of the alloys. Mechanical properties were investigated by means of a tension test and a Vickers hardness test, and corrosion resistance was evaluated using an anodic polarization test, 6% FeCl3 immersion test, 65% boiling nitric acid immersion test, and hydrogen embrittlement test. Increasing nitrogen content in Fe-Cr-Mn-W alloys reduced ferrite content and improved partitioning coefficient of chromium between austenite and ferrite. The microstructures of the alloys observed by OM were in accordance with the thermodynamically calculated phase diagram, but ε martensite was formed by water quenching when the stable phase at annealing temperature was austenite. With increasing annealing temperature, corrosion resistance was improved, and anodic polarization resistance of high nitrogen bearing Alloy 6 was better than that of STS 304. The results of the corrosion tests showed that corrosion resistance of Fe-Cr-Mn-W alloys was affected by not only alloying elements but also the presence of the 2' nd phase