Quantifying MnS Inclusion Evolution Behaviors During 1473 K Heating in EH36 Shipbuilding Steel with Zr Addition
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is a common non-metallic inclusion in steels, which usually exerts negative effects on ductility and deformability.[1] Moreover, further investigations reveal that, under the influence of certain types of active oxides, such as Ti2O3 and ZrO2, MnS could be effective for the nucleation of acicular ferrite (AF).[2,3] In general, AF dominating microstructure is considered as combining good strength and excellent toughness due to its fine effective grain size and interlocking characteristics so as to inhibit the propagation of cracks.[4–6] These advantageous features are particularly needed for low-carbon low-alloy steels, such as shipbuilding steels, for which fracture toughness is a major concern but can be improved via the adoption of oxide metallurgy under high heat input welding. MnS prefers to form on the surfaces of oxide inclusions. Yuki et al.[7] investigated in situ MnS formation behavior of Fe-Ni alloy and found that
XIAODONG ZOU is with the School of Metallurgy, Northeastern University, Shenyang 110819, China. HIROYUKI MATSUURA is with the Department of Materials Engineering, The University of Tokyo, Tokyo 113-8656, Japan. CONG WANG is with the School of Metallurgy, Northeastern University and also with the Shenyang NEU New Industrial Technology Research Institute Co. LTD, Shenyang 110819, China. Contact e-mail: [email protected] Manuscript submitted February 8, 2019. METALLURGICAL AND MATERIALS TRANSACTIONS B
MnS phases were formed at the surfaces of Al2O3 particles. Ueshima et al.[8] concluded that MnS could nucleate on the surfaces of a variety of oxide particles and that the Mn-depleted zones around such particles were likely to nucleate on sites of AF. Wu et al.[9] showed that the complex structures of Al2O3-TiOx-MgO oxides and the precipitation of MnS on their surfaces were important to the nucleation of interlocking AF in Mg-treated low-carbon low-alloy steel. In our previous studies, it was also found that the addition of Mg or Zr to EH36 shipbuilding steel could induce plenty of individual MnS to precipitate, while the amount of individual MnS was significantly reduced and that of MnS/complex oxide inclusions was enhanced from casting to rolling.[10,11] EH36 slabs are often reheated at 1473 K for 2 hours for homogenization and subsequently hot rolled into plates with desired thicknesses. The number density, composition, or morphology of inclusions including MnS may vary during the reheating process. Nevertheless, direct in situ observation of the behavior of inclusions during such heating process remains far from complete. The present study is undertaken to more accurately investigate the evolution of inclusions during the heating at 1473 K in EH36 shipbuilding steel with Zr addition. In particular, in situ high-temperature confocal scanning laser microscopy (CSLM),[12,13] is utilized to document and quantify resulting behaviors, with an emphasis on MnS particles. The composition of materials used in the experiment is shown in Table I. Zr was added into the EH36 shipbuilding steel to form Zr oxides, a
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