Effect of Low Temperature Aging on Hall-Petch Coefficient in Ferritic Steels Containing a Small Amount of Carbon and Nitrogen

Abstract

Effect of aging treatment at 373 K on Hall-Petch coefficient (k_y) was investigated in consideration of the change in friction stress associated with carbide/nitride precipitation in ferritic steels containing 60 ppm carbon or nitrogen (C60 and N60). Tensile tests revealed that the k_y was monotonously increased with increasing aging time in both steels, and also, C60 exhibited a larger k_y value than that of N60 under the same aging time. As a result of 3DAP analysis and theoretical calculation for grain boundary segregation of carbon and nitrogen, the k_y corresponded to the amount of carbon and nitrogen existing at grain boundary. There was no difference in the effect on k_y increment between both elements. The larger k_y in C60 under the same aging condition was due to the larger amount of segregated carbon compared with nitrogen.