低合金高張力鋼のオーステナイト結晶粒微細化と超塑性

概要

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Austenite grain refinement of low carbon steels prepared with and without addition of minor amount of niobium was attained by a thermomechanical processing in order to obtain the materials with (α+γ) microduplex structure in the intercritical temperature field. Such materials showed superplastic behavior during high temperature tensile deformation. The largest elongation to failure value of 738% and high value of strain rate sensitivity exponent, m, (>0.6) were obtained by tensile deformation at 790℃ and at strain rate of 5×10^<-3> min^<-1> in the Nb-bearing steel. Moreover, elongation to failure value of about 300% was obtained by tensile deformation at around 800℃ and at strain rate of 5×10^<-1> min^<-1> which may be applicable for practical forming process. The largest elongation to failure value and the highest m-value were, as a whole, obtained at around the temperature where the specimens are composed of nearly equal volume fraction of α and γ phase. A minor addition of niobium presumably promoted superplasticity of low carbon steel through a suppressive effects of finely dispersed precipitates of niobium-carbide (or-carbonitride) on grain growth during high temperature deformation.
社団法人日本鉄鋼協会の論文
1985-02-01