アルミキルド軟鋼の降伏強度におよぼすCrおよびZrの影響

抄録

A systematic study has been made of the effects of Cr and Zr on the yield strength of steels in order to develop super mild steels. The steels studied have almost the same chemical composition as commercial Al-killed mild steels except for the addition of Cr and Zr.
The yield strength of the hot rolled steels decreases with Cr content and becomes the lowest at about 0.35wt%Cr. It also decreases with Zr content up to 0.12wt%.
The relation of grain size and yield strength (σ_y) of the steels has been investigated in order to determine the parameters of σ₀ and Ky in Hall-Petch relation expressed as σy=σ₀+Kyd^-1/2, where σ₀, Ky and d have usual meanings. σ₀ and Ky have been discussed in terms of Cr and Zr contents.
Cr addition continuonsly increases Ky but decreases σ₀. In contrast, Zr addition decreases Ky and provides little effect on σ₀. The variations of σ₀ and Ky can be attributed to the carbon and nitrogen contents in solution and to the area fraction of pearlite formed at the grain boundaries, respectively.
It has been concluded that the proper combination of Cr and Zr decreases both σ₀ and Ky and results in a super mild steel with an extremely low yield strength of about 10kg/mm².