V鋼の焼戻微細組織変化の直接観察

抄録

An investigation was carried out to examine the changes in the hardness and microstructures of steels containing up to 0.5%V during tempering. The nucleation sites, the process of growth and changes in shapes of vanadium carbide during tempering were observed systematically. The results are as follows; (1) Climbing of dislocations was strongly surpressed, and the rate of softening was lowered by the addition of 0.07∼0.5%V at temperatures between 300° and 500°C. (2) In the steels containing vanadium higher than 0.1%, a secondary hardening occurred above 550°C. The peak hardness was attained by tempering for 1 hr at 625°C. The amount of the secondary hardening was approximately proportional to the vanadium content of specimens. (3) At the onset of secondary hardening, fine particles of vanadium carbide were observed along dislocation lines and on tangled dislocation nodes within the matrix. (4) It was observed that vanadium carbides grew into platelets parallel to the {100}_α planes by tempering for 1∼10 hr at 700°C, then spheroidized gradually at subboundaries. (5) The orientation relationship between vanadium carbide and ferrite matrix was as follows:
{100}_V₄C₃ \varparallel{100}_α-Fe, ⟨010 ⟩_V₄C₃ \varparallel⟨011 ⟩_α-Fe.