Effects of metal composition and temperature on the yield strength of nitrogen strengthened stainless steels

Abstract

Solid solution strengthening of low-carbon stainless steel alloys with interstitial nitrogen greatly increases yield strength, and the maximum amount of interstitial nitrogen in an alloy is compositionally dependent. This study explores the effect of varying the alloy composition on yield strength and tries to separate the interstitial nitrogen strengthening contributions from the substitutional solution strengthening. Statistical analysis was conducted on the yield strength of stainless steel compositions with significantly different chromium, nickel, and manganese concentrations as a function of nitrogen concentration and temperature. Two different nitrogen strengthening mechanisms have previously been reported: (i) matrix strengthening due to the presence of interstitial nitrogen; (ii) dislocation drag resulting from nitrogen being carried along with the dislocation as it moves through the lattice. Both strengthening mechanisms were found to be a strong function of nitrogen concentration but were essentially independent of the character and the amount of metallic elements in the alloy. The principal effect of varying the chromium, manganese, and nickel concentration in the stainless steel compositions was to increase the nitrogen solubility. Varying the composition did little to improve strength.