Effect of Enhancement in Surface Nitrogen Concentration on the Corrosion and Fatigue Properties of Austenitic Steel Wire Rod

Abstract

Austenitic steel rod for wire production with a nitrogen content of 0.23% has been nitrided to produce an enhanced nitrogen surface layer. The level of nitrogen and depth of penetration is controlled by the temperature, gas potential and the residence time in the furnace. The cooling rate from the nitriding temperature is also shown to be important in control of the nitrogen distribution. The alloys were then subjected to thermal treatments and the effect of those on the microstructure of the rods was assessed. Measurements of the strength, fatigue resistance, corrosion resistance and corrosion fatigue resistance in salt-water were made and these are interpreted in terms of the nitrogen distribution in the alloys. The consequences of these effects for production and use of wire from such rod is discussed and suggestions are made for a production sequence for improved high-nitrogen alloy wire.