Effect of titanium on the tensile ductility of 30 mass% chromium ferritic steels

The effect of titanium on the ductility of 30% chromium ferritic steels was investigated by tensile testing at low temperatures. Carbon content is 0.023 +/- 0.002 mass%. Titanium content is varied from 0.051 to 0.26 mass%. The ratio of titanium content to carbon content, Ti/C, ranges from 2.1 to 12.4. Two kinds of heat treatment with or without solution treatment were adopted to obtain different types of morphology of carbide precipitates. Aging after solution treatment gives rise to grain boundary precipitation of coarse Cr carbides and numerous fine Ti carbides, depending on Ti/C ratio, while annealing without solution treatment produces coarse globular carbide particles within the grains. The Effect of Ti/C ratio on the ductile-brittle transition temperature (DBTT) determined by the tensile tests is not as remarkable as that on the DBTT determined by Charpy impact tests. In the case of specimens containing globular carbide particles within the grains, there is no noticeable influence of varying Ti/C ratio on fracture modes, while in the case of specimens containing grain boundary carbides, the effect of Ti/C ratio on fracture modes is remarkable and the amount of intergranular fracture first decreases with increasing Ti/C ratio up to 8 and then increases with the ratio at testing temperatures above 200 K.