Abstract
The influence of austenitising temperature on the tensile properties of low temperature bainitic steel was investigated. With the increasing austenitising temperature, a significant change of elongation was found between 850 and 950 °C, which was changed from 1.0 ± 0.5 to 10.7 ± 2.0%; while there was a slight increase between 950 to 1050 °C (11.2 ± 1.5%). By characterising the retained austenite at necking and matrix, we found that the elongation is obviously correlated with the retained austenite content, and also determined by the volume change of retained austenite during the tensile test. The transformation induced plasticity (TRIP) effect, which contributes to the improve elongation, almost did not occur at 850 °C due to the relatively low volume percentage of retained austenite and its high carbon concentration, which resulted in a very low martensite transformation temperature. With the austenitising, the temperature was increased up to 950 and 1050 °C, and a large volume percentage of retained austenite was observed in the matrix. Meanwhile, a considerable amount of retained austenite has occurred by the TRIP effect because of a moderate carbon content.
Highlights
Bainitic steels are a kind of steel used in armor, bearing, and wear-resistant plates owing to their ultra-high strength, good ductility, and toughness properties [1,2]
The film-like retained austenite, which promotes the elongation in the transformation induced plasticity (TRIP) steel, are more stable, and less likely to transform into martensite, because of their relatively high carbon content [8]
The aim of this study is to explore the retained austenite content and its carbon concentration influence on the elongation of low temperature bainitic steels treated at different austenitising temperatures
Summary
Bainitic steels are a kind of steel used in armor, bearing, and wear-resistant plates owing to their ultra-high strength, good ductility, and toughness properties [1,2]. The microstructure of bainitic steel contains a mixture of fine bainitic ferrite plates, retained austenite, and some martensite [3,4]. The strength is mainly determined by bainitic ferrite (harder phase) and its dislocation density; and the ductility is controlled by the retained austenite, which is a softer phase compared with bainitic ferrite and martensite [5,6]. Retained austenite with a different stability contributes to the transformation induced plasticity (TRIP) effect at different strain stages until necking or damage occurs. It is found that the carbon concentration in retained austenite has the strongest influence on the ductility of bainitic steel. The film-like retained austenite, which promotes the elongation in the TRIP steel, are more stable, and less likely to transform into martensite, because of their relatively high carbon content [8]
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