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Metals 2017, 7(7), 253; doi:10.3390/met7070253

High-Temperature Tempered Martensite Embrittlement in Quenched-and-Tempered Offshore Steels

1
Department of Materials Science and Engineering, National Taiwan University, Roosevelt Road, Taipei 10617, Taiwan
2
Iron and Steel R&D Department, China Steel Corporation, Chung Kang Road, Kaohsiung 81233, Taiwan
*
Author to whom correspondence should be addressed.
Received: 31 May 2017 / Revised: 23 June 2017 / Accepted: 3 July 2017 / Published: 6 July 2017
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Abstract

Embrittlement induced by high-temperature tempering was investigated in two quenched-and-tempered offshore steels. Electron backscattering diffraction and analysis of Kernel average misorientation were applied to study the coalescence of martensite; transmission Kikuchi diffraction coupled with compositional mapping was used to characterize the martensite/austenite (M/A) phases. It is suggested that the formation of lenticular martensite along prior austenite grain boundaries or packet boundaries primarily explains the embrittlement in conventional S690Q steel, which has a higher carbon content. This embrittlement can be cured by additional heat treatment to decompose martensite into ferrite and cementite. In a newly designed NiCu steel with reduced carbon content, new lath martensite formed along interlath or inter-block boundaries of prior martensite. This microstructure is less detrimental to the impact toughness of the steel. View Full-Text
Keywords: tempered martensite embrittlement; lenticular martensite; offshore steels; electron backscattering diffraction; Kernel average misorientation; transmission Kikuchi diffraction tempered martensite embrittlement; lenticular martensite; offshore steels; electron backscattering diffraction; Kernel average misorientation; transmission Kikuchi diffraction
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Yen, H.-W.; Chiang, M.-H.; Lin, Y.-C.; Chen, D.; Huang, C.-Y.; Lin, H.-C. High-Temperature Tempered Martensite Embrittlement in Quenched-and-Tempered Offshore Steels. Metals 2017, 7, 253.

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