変態組織を利用した固溶強化 IF 鋼の低降伏比化

概要

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The employment of the transformation structure by the (α+γ) intercritical annealing was investigated for achieving advantageous decrement of yield ratio (yield strength/tensile strength) in TS 440MPa grade extra low carbon IF steel with the solution hardening by preferential P addition. The transformed microstructure obtained from dual phase annealing induced remarkable low yield ratio even in the high P-added steel (0.10%P-1.5%Mn-0.5%Si). This phenomena, associated with decrease of yield point elongation of as-annealed steel is attributable to the formation of the low temperature transformed phase, which is classified as the granular bainitic ferrite (α_B) or bainitic ferrite (α^O_B) with high dislocation density. It can induce the much movable dislocation in ferrite matrix around the second phase. Low yield ratio was obtained even in the high Mn steel (0.04%P-2.2%Mn-0.4%Si). However, progress of γ transformation exhibited considerable increase of both yield and tensile strengths predominantly, which is caused by extremely high distribution of Mn in γ phase. Addition of B also affects the yielding behavior in the intercritically annealed steel. This can be explained by the contribution of B addition on the Mneq. formula.
社団法人日本鉄鋼協会の論文
1997-09-01