Dependence of Carbon and Nitrogen Content on Grain Refinement Strengthening in Austenitic Stainless Steel

The effects of C and N on solid solution strengthening and grain refinement strengthening were quantitatively evaluated using various austenitic stainless steels in which C and N were added independently to Fe -18 mass%Cr-12 mass%Ni alloys. As a result of evaluating the amount of solid solution strengthening from the intercept value in the Hall-Petch relationship, it was confirmed that N has a stronger solid solution strengthening capacity than C. On the other hand, the addition of C and N increased the slope of the Hall-Petch relationship, the so-called Hall-Petch coefficient, and the amount of grain refinement strengthening increased. Comparing the effects of C and N, there was no significant difference in the effect of increasing the Hall-Petch coefficient between the two elements at the same amount of addition. The critical grain boundary shear stress measured by nanoindentation tests and the Hall-Petch coefficient corresponded well for both steels, demonstrating that the increase in critical shear stress due to the addition of C and N results in increased grain refinement strengthening. However, the amount of grain boundary segregation was calculated to be considerably higher for C than for N, suggesting that N is more effective than C in increasing the critical grain boundary shear stress.