ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Effect of Molybdenum Content on the Hardenability and Precipitation Behaviors of Boron Steel Austenitized at High Temperatures
Kyohei Ishikawa Masaaki FujiokaManabu HoshinoJun TakahashiRyuichi HommaKohsaku Ushioda
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JOURNAL OPEN ACCESS Advance online publication

Article ID: ISIJINT-2023-473

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Abstract

The effect of molybdenum (Mo) contents on hardenability and precipitation behaviors in Mo-B simultaneously added steels were investigated placing a focus on high austenitizing temperature. The hardenability of 0.5 % Mo - 11 ppm B steel austenitized at 1150°C was decreased compared with that austenitized at 950 °C, whereas 1.0 % Mo - 10 ppm B and 1.5 % Mo - 9 ppm B steels were less affected by high austenitizing temperature than 0.5 % Mo - 11 ppm B steel. The Fe23(C, B)6 precipitation by increasing austenitizing temperature was also revealed to be suppressed in 1.5 % Mo – 9 ppm B steel. These results indicate that the improved effect of the Mo addition on hardenability by retarding the precipitation of Fe23(C, B)6 still appear in B-added steels austenitized at high temperature. Furthermore, Fe23(C, B)6 precipitation start temperature was increased in Mo–B added steels austenitized at 1150 °C. This result implies that non-equilibrium B segregation mechanism during cooling from high austenitizing temperature enhances the amount of segregated B on grain boundaries leading to the promotion of the borides precipitation at high austenitizing temperature region. However, Mo is presumed to fix a part of thermal vacancies as Mo-V complex resulting in the suppression of non-equilibrium B segregation to grain boundaries during cooling, which is speculated to inhibit the Fe23(C, B)6 precipitation. Thus, the effect of Mo-B combined addition on hardenability was presumably maintained even in high austenitizing temperature region.

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© 2024 The Iron and Steel Institute of Japan

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