Regular Article

Mechanism of improving transverse corner cracks of peritectic steel slab based on control of inclusions and microstructures with magnesium treatment

¹ State Key Laboratory of Advanced Special Steel, School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China
² Shanghai Meishan Iron and Steel Co., LTD, Nanjing 210039, China

^* e-mail: yang_jian@t.shu.edu.cn

Received: 3 July 2022
Accepted: 29 August 2022

Abstract

In this paper, in order to clarify the mechanism of improving the transverse corner crack of peritectic steel slab with Mg treatment, the inclusions and microstructure characteristics at the slab corner of Al deoxidized (S-Al), (Al+Ca) deoxidized (S-Ca) and (Al+Mg) deoxidized (S-Mg) peritectic steels were studied. The inclusions in S-Al sample are mainly Al₂O₃, Al₂O₃· MnS and MnS inclusions. The S-Ca sample mainly contains Al₂O₃ inclusions and their complex inclusions. In the S-Mg sample, the number of Mg containing inclusions increase sharply. The S-Mg sample has the smallest average size of inclusions and the largest number of inclusions with the size smaller than 1 µm. The brittle structures are dominant in S-Al sample, which basically disappear in S-Ca sample and S-Mg sample. Mg treatment refines the size of grains at the slab corner, reduces the size of the proeutectoid ferrite films, and restrains the crack propagation along the grain boundary. More IAF microstructures are formed in S-Mg sample. IAFs take MgO · Al₂O₃· MnS, MgO · Al₂O₃· TiN · MnS and other complex inclusions as the nucleation cores, which diverge and grow outward from the inclusions. Thus, IAFs form a fine crack resistant microstructure, improving the microstructure at the slab corner to prevent the occurrence of transverse corner cracks.