Abstract
Calcium sulfide (CaS) inclusion with large and irregular shape is detrimental to the properties of steel. Understanding the shape and distribution of CaS inclusions in a continuous casting (CC) slab is of significance for improving the rolling properties. In this study, CaS inclusions were extracted from CC slab of Ni20Mn6 steel using the electrolytic extraction and investigated by scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX). The CaS inclusions morphologies vary with their locations in the CC slab and, thus, are classified into five categories. The thermodynamics calculated results showed that CaS inclusions precipitated at the end of solidification due to the microsegregation of sulfur and calcium in the interdendrite liquid and finally precipitated along the austenite grain boundary. The macrosegregation degree of solutes in different regions is one of the reasons that affect the size of CaS inclusion. The morphologies of CaS inclusion are affected by the solidification structure of slab and austenite grain boundary.
Highlights
Ni20Mn6 high-alloy steel, a precision alloy defined in national standard GB/T 37797-2019, is a functional alloy with controllable thermal expansion properties, low thermal conductivity, and high plasticity [1]
The rate of liquid flow in the Position C was lower than Position D, the grain boundaries played a main factor on the morphology, resulting in the higher percentage of sheet-like Calcium sulfide (CaS) inclusions in position C, while the higher percentage of rod-like CaS inclusions is in position D
The following conclusions were obtained by investigation of the CaS morphology in the cross-section of Ni20Mn6 steel slab: (1)
Summary
Ni20Mn6 high-alloy steel, a precision alloy defined in national standard GB/T 37797-2019, is a functional alloy with controllable thermal expansion properties, low thermal conductivity, and high plasticity [1]. Sulfide inclusions have been found a critical issue for Ni20Mn6 high-alloy steel, since the sulfide inclusions morphology, size, and distribution significantly affect the alloy properties [2,3,4,5]. Studies on the connection of solidification structure and sulfide inclusions still focused on the size of dendrite structures instead of the macrostructure. Imagumbai et al [21,22] studied the relationship between solidification conditions and the morphologies of sulfide inclusion in dendrite structure. The connection between sulfide inclusion and macrostructure of the whole transverse section of slab has not been intensively studied yet, especially in the columnar-to-equiaxed transition zone. This work firstly describes the morphology and distribution of CaS inclusions on the cross-sectional of the slab firstly.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
