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Effect of Grain Size on Mechanical Properties of Dual Phase Steels Composed of Ferrite and Martensite

Published online by Cambridge University Press:  28 March 2016

Myeong-heom Park*
Affiliation:
Department of Materials Science and Engineering, Kyoto University, Sakyo-Ku, Kyoto, 606-8501, Japan
Akinobu Shibata
Affiliation:
Department of Materials Science and Engineering, Kyoto University, Sakyo-Ku, Kyoto, 606-8501, Japan Elements Strategy Initiative for Structural Materials (ESISM), Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan
Nobuhiro Tsuji
Affiliation:
Department of Materials Science and Engineering, Kyoto University, Sakyo-Ku, Kyoto, 606-8501, Japan Elements Strategy Initiative for Structural Materials (ESISM), Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan
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Abstract

It is well-known that dual phase (DP) steels composed of ferrite and martensite have good ductility and plasticity as well as high strength. Due to their excellent mechanical properties, DP steels are widely used in the industrial field. The mechanical properties of DP steels strongly depend on several factors such as fraction, distribution and grain size of each phase. In this study, the grain size effect on mechanical properties of DP steels was investigated. In order to obtain DP structures with different grain sizes, intercritical heat treatment in ferrite + austenite two-phase region was carried out for ferrite-pearlite structures having coarse and fine ferrite grain sizes. These ferrite-pearlite structures with coarse and fine grains were fabricated by two types of heat treatments; austenitizing heat treatment and repetitive heat treatment. Ferrite grain sizes of the specimens heat-treated by austenitizing and repetitive heat treatment were 47.5 µm (coarse grain) and 4.5 µm (fine grain), respectively. The ferrite grain sizes in the final DP structures fabricated from the coarse-grained and fine-grained ferrite-pearlite structures were 58.3 µm and 4.1µm, respectively. The mechanical behavior of the DP structures with different grain sizes was evaluated by an uniaxial tensile test at room temperature. The local strain distribution in the specimens during tensile test was obtained by a digital image correlation (DIC) technique. Results of the tensile test showed that the fine-grained DP structure had higher strength and larger elongation than the coarse-grained DP structure. It was found by the DIC analysis that the fine-grained DP structure showed homogeneous deformation compared with the coarse-grained DP structure.

Type
Articles
Copyright
Copyright © Materials Research Society 2016 

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References

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