2003 Volume 67 Issue 4 Pages 165-168
The effect of morphology of titanium carbides on the toughness of 30% chromium ferritic steels containing carbon and titanium was investigated by a Charpy impact test at low temperatures. Carbon and titanium contents vary from 0.011 to 0.071 mass% and from 0.094 to 0.60 mass%, respectively. Ti/C ratio is about nine times. Two kinds of heat treatments including with or without solution treatment were adopted to obtain different types of morphology of numerous fine grain boundary titanium carbides under 0.1 μm in diameter and uniformly dispersed coarse globular titanium carbides in the 1 μm size range.
The results obtained are summarized as follows:
(1) Ductile-brittle transition temperatures (DBTTs) increased with increasing titanium carbides independent of the morphology of titanium carbides.
(2) Numerous fine grain boundary Ti carbide precipitates led to an increase in the DBTTs more than uniformly dispersed coarse globular Ti carbide particles.
(3) In case of titanium carbides less than 0.25 vol%, DBTTs estimated for the specimens having grain size of 80 μm are also higher in the specimen with the grain boundary carbides than in the specimen with the uniformly dispersed ones.
(4) Initiation of microcracks for brittle fracture is considered to be caused by the intergranular fracture cracks which are brought about by the decohesion at the interfaces between the matrix and many grain boundary Ti carbide precipitates.
