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Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

Microstructural Characterization And Mechanical Property Of 420MPa Class Steel Plate
Used For Marine Structure
Xiaoshu Wang1, PengZhang1*, Huiyong Pang1, Baojun Zhao2(1HBIS, Wuyang Iron and Steel Co., Ltd; Wugang, Henan, China)(2Jiangxi University of Science and Technology, Ganzhou, Jiangxi, China)

ABSTRACT

toughness; 4-excellent weldability; and 5-strong corrosion and fatigue
resistance in the future.
Currently, marine engineering steel with yield strength of lower than
355 MPa has mature technologies, contributed 90% market share in
China. However, steel plates with 420MPa or even higher yieldstrength are needed to meet future marine equipment. In the paper,
420MPa yield strength steel under proper rolling and heat treatment
technology was designed with maximum thickness of 100 mm. The
characteristic values of CTOD are more than 0.59, which presents
strong cracking resistance ability and can fulfill multiple marine
equipment utilization.

In this paper, a 420MPa grade marine structure steel used for offshore
platforms was developed. The content of C was reduced to improve thelow-temperature toughness and weldability. Microalloying elements Nb
was added and rolling technology was designed. Submerged arc
welding (SAW) and flux-cored arc welding (FCAW) were used toevaluate the weldability of the steel plate with thickness of 100mm. The
mechanical properties of the welded joints and matrix materials aretested. The experiment of crack tip opening displacement (CTOD) was
carried out at -10℃. The results show that the steel plate has the mixed
microstructure of fine bainite and quasi-polygonal ferrite, with grain
size up to 10.0 grade, which is beneficial to high strength and toughness.
The yield strength of the steel plate is more than 420MPa and the lowtemperature impact toughness is more than 200J at -40℃. The
characteristic values of CTOD are more than 0.59, which shows highcracking resistance due to appropriate alloy design and production
technology. This improves the safety factor of offshore engineering use
due to the excellent crack arrest properties.

PERFORMANCE REQUIREMENTS
The chemical composition and main mechanical properties for this420MPa steel plates are listed below (Table 1-2). The steel plate
requires high strength and low temperature (-40 ℃) impact toughness,and large thickness is needed at the same time for the future offshore
structure platform. Methods such as getting better shatter crystal,
uniform microstructure, and higher temperature cooling speed areneeded to achieve the desired strength and toughness. This means much
more precise requirements for heat treatment equipment and moredifficulty to tackle with thick plates.

KEY WORDS: Marine structure steel; cracking resistance; CTOD;
Weldability

INTRODUCTION

Table 1 Chemical composition of test steel (wt/%)

Marine engineering equipment and facilities support the developmentof the offshore oil industry, energy industry, and marine resources,
which are crucial to national energy resources safety. Increasing anddiversified marine engineering applying further drives steel R&D andtech-renew, correspondingly. Today, it was also noted (Zhang ZL, 2015;
Gao XH, 2019) that the main parameters for the function of marine usedsteel plates are increasing to tackle with brittle and fatigue challenge,
which is supposed to focus on: 1-high strength; 2-thicker; 3-strong*Corresponding author, email zhangpengysu@126.com

2873

CMn

PS

Si

Ni

≤
0.12

1.151.60

≤
0.03

≤
0.006

0.050.50

≤
1.00

Cr
≤
0.25

Mo
≤
0.15Cu
≤
0.35

Nb
≤
0.03

N
≤
0.009

B
≤
0.0005Ti
N≤0.005，Ti:0.0030.020；
N>0.005，Ti:0.0070.020
Alt
0.02-0.06