An Integrated Study on the Evolution of Inclusions in EH36 Shipbuilding Steel with Mg Addition: From Casting to Welding

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An Integrated Study on the Evolution of Inclusions in EH36 Shipbuilding Steel with Mg Addition: From Casting to Welding XIAODONG ZOU, DAPENG ZHAO, JINCHENG SUN, CONG WANG, and HIROYUKI MATSUURA Inclusion evolution behaviors, in terms of composition, size, and number density, and associated inﬂuence on the microstructures of the as-cast slabs, rolled plates, and simulated welded samples of plain EH36 and EH36-Mg shipbuilding steels have been systematically investigated. The results indicate that the inclusions in the as-cast plain EH36 are almost Al-Ca-S-O-(Mn) complex oxides with sizes ranging from 1.0 to 2.0 lm. After Mg addition, a large amount of individually ﬁne MnS precipitates and Mg-containing Ti-Al-Mg-O-(Mn-S) complex inclusions are generated, which signiﬁcantly reﬁne the microstructure and are conducive to the nucleation of acicular ferrite in the rolled and welded sample. Moreover, after rolling and welding thermal simulation, the number of individual MnS decreases gradually due to its precipitation on the surface of Ti-Al-Mg-O oxides. https://doi.org/10.1007/s11663-017-1163-x The Minerals, Metals & Materials Society and ASM International 2017

I.

INTRODUCTION

DURING steelmaking and casting, non-metallic inclusions are inevitably generated due to active elements in steel contacting and reacting with refractory materials and slags. In addition, impurity elements in the solidiﬁcation process will also incur segregation and secondary reactions to generate inclusions. According to traditional views and experiences, inclusions are harmful to steel properties such as toughness, fatigue, and strength.[1,2] Therefore, various attempts have been exercised to remove inclusions in steels. However, with improved understanding of inclusions, particularly their positive inﬂuences on steel microstructures, it generally comes to a consensus to enable full utilization of particular groups of inclusions during pertinent metallurgical processes, which is coined as Oxide Metallurgy.[3] Recently, high heat input welding has gained engineering signiﬁcance for improving welding eﬃciency and lowering construction cost.[4] However, high heat input welding usually involves longer residence at high temperature and lower cooling rate, which invariably leads XIAODONG ZOU, DAPENG ZHAO, JINCHENG SUN, and CONG WANG are with the School of Metallurgy, Northeastern University, Shenyang 110819, China. Contact e-mail: [email protected] HIROYUKI MATSUURA is with the Department of Materials Engineering, The University of Tokyo, Tokyo 113-8656, Japan. Manuscript submitted August 15, 2017.

METALLURGICAL AND MATERIALS TRANSACTIONS B

to signiﬁcant coarsening of austenite grains and formation of brittle microstructures such as ferrite side plate (FSP), upper bainite (Bu), and coarsening grain boundary ferrite (GBF), resulting in the reduced toughness of Heat-Aﬀected Zone (HAZ).[5,6] Therefore, it is imperative to investigate alternative techniques that can uphold high heat input welding while keeping the outstanding issues minimal. For low

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