Nb 첨가 고장력 저합금강의 냉연 후 열처리에 따른 기계적 성질 = Mechanical Properties of Nb-Microalloyed HSLA Steel After Cold Rolling and Heart Treatment

다국어 초록 (Multilingual Abstract)

Mechanical properties of cold rolled 0.12C-1.36Mn-0.08Nb HSLA steel have been studied after annealing followed by water quenching. The degrees of cold work were 25% and 50%, and the annealing temperatures were in the range of 500-780℃.
By increasing the heat treating temperature, strength of the specimens has increased at first stage and then decreased. After annealing treatment at the temperature range of 600-720℃, 50% cold worked specimens have shown lower strength than the 25% cold worked specimens. This strength reversion is caused by more accelerated growth of the precipitates in the ferrite matrix in the specimens subjected to the heavier cold work.
When compared the specimens which heat treated at different temperatures in the intercritical temperature (α+γ) range, the specimens heat treated at lower temperature (720℃) have shown higher strength than the specimens heat treated at higher temperature (780℃). Martensite volume fraction of the former specimens is lower but it contains more fine precipitates than the latter specimens. Therefore it is concluded that the strength of intercritically annealed specimens is strongly influenced by the distribution of the fine precipitates than the martensite volume fraction. The fine precipitates are analyzed to be the NbC by the electron diffraction pattern.