EFFECTS OF METAL COMPOSITION AND TEMPERATURE ON THE YIELD STRENGTH OFNITROGEN STRENGTHENED STAINLESS-STEELS

Solid solution strengthening of low-carbon stainless steel alloys with interstitial nitrogen greatly increases yield strength, and the maxim um amount of interstitial nitrogen in an alloy is compositionally depe ndent. This study explores the effect of varying the alloy composition on yield strength and tries to separate the interstitial nitrogen str engthening contributions from the substitutional solution strengthenin g. Statistical analysis was conducted on the yield strength of stainle ss steel compositions with significantly different chromium, nickel, a nd manganese concentrations as a function of nitrogen concentration an d temperature. Two different nitrogen strengthening mechanisms have pr eviously been reported: (i) matrix strengthening due to the presence o f interstitial nitrogen; (ii) dislocation drag resulting from nitrogen being carried along with the dislocation as it moves through the latt ice. Both strengthening mechanisms were found to be a strong function of nitrogen concentration but were essentially independent of the char acter 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 solubil ity. Varying the composition did little to improve strength.