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Effects of Mo Content on Low‐Angle Misorientation Microstructure and Mechanical Properties of YS 550 MPa‐Grade Steels for Offshore Structures
Author(s) -
Kim In,
Lee Myungjin,
Choi Yoonsuk,
Kang Namhyun
Publication year - 2018
Publication title -
steel research international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.603
H-Index - 49
eISSN - 1869-344X
pISSN - 1611-3683
DOI - 10.1002/srin.201700278
Subject(s) - charpy impact test , microstructure , acicular ferrite , materials science , misorientation , bainite , metallurgy , austenite , ultimate tensile strength , martensite , ferrite (magnet) , volume fraction , toughness , pearlite , elongation , composite material , grain boundary
This study investigates the effects of Mo content on the low‐angle misorientation microstructure and the mechanical properties of high strength steels of YS 550 MPa grade. Steels of various Mo contents (0.08, 0.15, and 0.25 wt%) are fabricated by controlled rolling and accelerated cooling. The Mo steels consist of acicular ferrite (AF), granular bainite (GB), a low‐angle misorientation microstructure, that is, bainitic ferrite (BF), and a secondary phase of martensite‐austenite (MA), regardless of the Mo content. Degenerated pearlite (DP) is observed only in the 0.08 wt% Mo steel. As the Mo content increases from 0.08 to 0.25 wt%, the microstructure and mechanical properties are described as follows: (i) the volume fraction of AF decreases and that of BF increases, (ii) the yield and tensile strengths increase and the elongation decreases, and (iii) the Charpy toughness at −60 °C decreases owing to the decrease in AF and increase in BF.