Transformation-Induced Plasticity of Pre-Deformed Austenite in Fe-Cr-Ni Alloy

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  • Fe-Cr-Ni 合金における前加工をうけたオーステナイトのマルテンサイト変態誘起塑性
  • Fe-Cr-Ni ゴウキン ニ オケル ゼン カコウ オ ウケタ オーステナイト ノ マルテンサイト ヘンタイ ユウキ ソセイ

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The martensitic transformation-induced plasticity (TRIP phenomenon) of pre-deformed austenite in Fe-15% Cr-12% Ni alloy (Ms<room temperature) was investigated by means of tensile test at various temperatures between -196°∼+120°C. As pre-deformation, the reduction of 0∼80% was given by rolling at 200°C. Since the rolling temperature was above Md temperature of the specimen, all specimens consisted of austenitic single phase even after rolling at 200°C. The TRIP was observed in the pre-deformed austenite as well as in the non-predeformed one, and the maximum elongation appeared at a certain temperature between Md and Ms. The Ms temperature decreased with increasing the degree of pre-deformation. Accordingly, as the degree of pre-deformation increases, the range of temperature showing the TRIP phenomenon became narrower and the temperature at which the maximum elongation appeared shifted toward the lower temperature. While the strength of austenite (especially the 0.2% proof stress) at 120°C was markedly increased by rolling, at the same time the elongation became smaller. However, the elongation of pre-deformed austenite was enhanced when the TRIP occurred. For example, the elongation of the specimen given a pre-deformation of 80% was only 5% at 120°C (above Md), but it was increased to 57% by TRIP at -196°C. It was found that the amount of increase in elongation by TRIP, which is the difference between the elongation value at the temperature showing maximum TRIP and that at the temperature of austenitic state, was almost constant (about 50%) independently of the degree of pre-deformation of austenite. Therefore, it is possible to obtain the optimum condition that the alloy shows high strength and ductility by TRIP after pre-deformation of austenite.<br>The yield point and plateau stage similar to Lüders strain were observed in the stress-strain curves of pre-deformed specimens. These phenomena became to appear more distinctly with increasing the degree of pre-deformation and with decreasing the test temperature.

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