「ストリップキャスティング低炭素鋼材の集合組織と塑性異方性」

超鉄鋼研究センター　冶金グループ　徐平光

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キーワード：鋳片、塑性異方性、集合組織、低炭素鋼、結晶粒径

Plastic anisotropy is an important mechanical property that affects the formability of steel sheet. Based on the empirically established relationship between plastic anisotropy and the crystallographic texture, the stronger {111} grains oriented parallel to the sheet plane, i.e. the gamma fiber texture, is responsible for the higher normal anisotropy and superior deep drawability. The processes applied to produce steel sheets will influence the ultimate texture features, especially the cold-rolling and recrystallization treatment processes.


Recently, strip casting process, characterized of a low consumption of time and energy, has been applied to the production of near-net-shape strips. The texture and formability of strip cast low carbon steels in the as-cast condition were scarcely reported.
In order to characterize the texture and the formability of the as-cast steel sheets, the plastic anisotropy of the strip-cast low-carbon steels was investigated, in comparison with that in the homogenization treated condition. The compositions of the investigated low-carbon Si-Mn steels are 0.05 mass% C with low impurity and 0.08 mass% C with high impurity, respectively.


The as-cast strip steels possess a tensile strength of 360MPa and a total elongation of 33%.
The good balance between strength and ductility of the as-cast strips is comparable with that of the cold-rolled and recrystallized strips, and the homogenized strips processed following the strip casting. It is quite instructive that the as-cast strips show the better normal anisotropy and planar anisotropy than the post-treated strips.


Although the texture in the as-cast strips are quite weak on the whole, three characteristic orientation lines, i.e. gamma, alpha, {114}-fiber, can be observed in the phi2=45°section of orientation distribution function (ODF). The orientation imaging microscope (OIM) analysis shows that the average grain size of gamma-fiber oriented ferrite in the as-cast strips is apparently larger than that in the post-treated strips, which is considered beneficial for the improvement of the normal anisotropy.


In addition, as an important parameter to affect the earring tendency during deep drawing of steel sheets, the better planar anisotropy in the as-cast strips can be attributed to the proper orientation compensation of the scattered components in {114}-fiber texture.

Reference:

1. P.G. Xu, F.X. Yin and K. Nagai, 埼玉工業大学若手研究フォーラム 第1回研究フォーラム--21世紀の新しい創造性を支えるハイテクノロジー. pp.87-90.
   
   
2. P.G. Xu, F.X. Yin and K. Nagai, submitted to Materials Transactions.