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Article

Microstructure and Mechanical Properties of Cast and Hot-Rolled Medium-Carbon Steels under Isothermal Heat-Treatment Conditions

1
Department of Materials Science and Engineering, Inha University, Incheon 22212, Korea
2
Department of Mechanical and Materials Engineering, Portland State University, Portland, OR 97207-0751, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Lucia Morales-Rivas
Metals 2021, 11(12), 1950; https://doi.org/10.3390/met11121950
Received: 27 October 2021 / Revised: 25 November 2021 / Accepted: 30 November 2021 / Published: 3 December 2021
(This article belongs to the Special Issue Advanced High-Strength Bainitic Steels)
In this study, the changes in the microstructure and mechanical properties during isothermal heat treatment of cast steel before and after hot deformation were investigated using medium-carbon steel with low alloy content. The microstructural characteristics of the cast and hot-rolled medium-carbon steel under isothermal heat-treatment conditions were examined using optical microscopy and scanning electron microscopy in conjunction with electron backscatter diffraction. The variation in the mechanical properties was evaluated using Rockwell hardness and tensile tests. After maintaining an austenitizing condition at 1200 °C for 30 min, an isothermal heat treatment was performed in the range 350–500 °C, followed by rapid cooling with water. Both the cast steel and hot-rolled steel did not completely transform into bainitic ferrite during isothermal heat treatment. The partially untransformed microstructure was a mixture of martensite and acicular ferrite. At 500 °C, the prior austenite phase changed to Widmanstätten ferrite and pearlite. At 450 °C, bainitic ferrite and cementite were coarsened by the coalescence of ferrite and subsequent diffusive growth. The mechanical properties increased as the isothermal heat-treatment temperature decreased, and the hardness of the cast steel was generally higher than that of the hot-rolled steel. Hardness and strength showed similar trends, and overall mechanical properties tend to decrease as the isothermal heat-treatment temperature increases, but there are slight differences depending on complex factors such as various phase fractions and grain size. View Full-Text
Keywords: medium-carbon low-alloy steel; isothermal heat treatment; phase fraction; bainite; degenerated upper bainite; bainitic ferrite; multiphase steel medium-carbon low-alloy steel; isothermal heat treatment; phase fraction; bainite; degenerated upper bainite; bainitic ferrite; multiphase steel
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MDPI and ACS Style

Shin, B.; Kim, K.; Yi, S.; Choi, S.; Hyun, S. Microstructure and Mechanical Properties of Cast and Hot-Rolled Medium-Carbon Steels under Isothermal Heat-Treatment Conditions. Metals 2021, 11, 1950. https://doi.org/10.3390/met11121950

AMA Style

Shin B, Kim K, Yi S, Choi S, Hyun S. Microstructure and Mechanical Properties of Cast and Hot-Rolled Medium-Carbon Steels under Isothermal Heat-Treatment Conditions. Metals. 2021; 11(12):1950. https://doi.org/10.3390/met11121950

Chicago/Turabian Style

Shin, Byungsue, Kwangyuk Kim, Sung Yi, Sanggyu Choi, and Soongkeun Hyun. 2021. "Microstructure and Mechanical Properties of Cast and Hot-Rolled Medium-Carbon Steels under Isothermal Heat-Treatment Conditions" Metals 11, no. 12: 1950. https://doi.org/10.3390/met11121950

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