低炭素鋼の初析フェライトの生成挙動および 2 相域での延性

概要

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Hot ductility of low carbon steels containing small amount of Nb or B was investigated with a Gleeble tensile machine. Special emphases were placed on the relation between the formation behavior of proeutectoid ferrite and the ductility in (α+γ) two phase region in the specimens with different austenite grain sizes (100μm and 350μm). The morphology of statically precipitated ferrite changed with an austenite grain size. In the case of coarse austenite grains, film-like ferrite was formed along austenite grain boundaries, whereas globular ferrite was formed in the specimen with small austenite grain size. Even when the specimen was single phase austenite before tensile testing, ferrite was formed during tensile testing at a certain temperature range below Ae_3. This dynamically precipitated ferrite exhibited very thin film-like network along austenite grain boundaries, irrespective of austenite grain size. These morphology and distribution of ferrite affected the hot ductility in (α+γ) two phase region. The ductility became minimum under the condition in which the network structure of very thin film-like ferrite was formed. Such a structure was commonly obtained by the occurrence of dynamic precipitation of ferrite. The ductility in (α+γ) two phase region was markedly influenced by austenite grain size, namely, it decreased with increase in austenite grain size.
社団法人日本鉄鋼協会の論文
1985-08-01