Effect of Austenite Grain Refinement on Microstructure and Properties of Ultra‑Heavy EH47 Crack Arrest Steel

doi:10.12068/j.issn.1005-3026.2024.05.005

Abstract

Abstract:

The degree of austenite grain refinement in steel for ultra‐heavy ships is limited by conventional processes， resulting in the effect of very small?size austenite grains on the organization and properties of the steel plate being unclear. The effect of austenite grain refinement on the microstructure evolution and mechanical properties of ultra‐heavy EH47 crack arrest steel was investigated by using the secondary austenitization method and thermo mechanical control process. The results showed that the prior‐austenite grain size increased from 14 μm to 28 μm， with the reheating temperature of the test rolled steels rising from 890 ℃ to 1 050 ℃； the decrease of ferrite content reduced the proportion of large angle grain boundary from 57.4% to 40.5%； the volume fraction of martenite/austenite（M/A） islands increased from 2.0% to 6.5%； the yield strength of the steels increased from 440 MPa to 488 MPa. The effective interfacial area per unit volume of 890 ℃ rolled steel was 269.0 mm^-1， which was the key reason for its microstructure refinement， homogenization， and 241 J impact energy at -100 ℃.

Key words: EH47 crack arrest steel, prior‐austenite grain, microstructure, M/A islands, impact energy

CLC Number:

TG 142.1

Jiu-xin ZHANG, Xiao-jian REN, Dong-zheng JIN, Yong TIAN. Effect of Austenite Grain Refinement on Microstructure and Properties of Ultra‑Heavy EH47 Crack Arrest Steel[J]. Journal of Northeastern University(Natural Science), 2024, 45(5): 643-651.

Figures/Tables 12

Table 1 Chemical composition of the EH47 continuous

C	Si	Mn	P	S	Nb+Ti	Ni+Cr+Cu
0.05	0.15	1.95	0.008	0.002	0.052	1.03

Fig.1 Microstructures at 1/2 thickness of test rolled steels

Table 2 Parameters of the M/A island of test rolled steels

编号	平均弦长/μm	最大尺寸/μm	体积分数/%
T890	1.4	5.5	2.0
T970	2.5	6.3	5.5
T1050	3.5	9.9	6.5

Fig.2 Inverse pole figure， grain boundary figures and dislocation distribution figures at 1/2 thickness of test rolled steels

Fig.3 Statistical results of EBSD at 1/2 thickness of test rolled steels

Fig.4 Orientation distribution and volume fraction of <110>//RD and <001>//RD at 1/2 thickness of test rolled steels

Fig.5 Prior‐austenite grain morphology and the volume fraction of different grain sizes for test rolled steels

Fig.6 Impact energy and test temperature curves of test rolled steels

Fig.7 Engineering stress‐strain curves of test rolled steels

Table 2 Tensile test results of test rolled steels

编号	屈服强度	抗拉强度	延伸率/%	屈强比
编号	MPa	MPa	延伸率/%	屈强比
T890	440	587	26.1	0.75
T970	467	610	26	0.76
T1050	488	636	23.3	0.77

Fig.8 Effective interfacial area per unit volume of test rolled steels

Fig.9 Morphology and EDS energy spectra of precipitated phases at different austenitization temperatures

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