Analysis of Non-metallic Inclusions in Continuously Cast Low-Carbon Steel

Abstract

In the present research, the physics and chemistry tests were conducted, and microstructural analyses were made on the cracked regions of the bar after cold forging by using a SUPRA 35 scanning electron microscope (SEM) equipped with a Oxford energy dispersive spectrometry (EDS) microanalysis. The formation of nonmetallic inclusions during metallurgical process is investigated. The results have shown that the internal defects such as shrinkage porosity and square segregation, etc do not result in cracking phenomenon occurring during cold forging. Nonmetallic inclusions lead to significant stress concentration. The presence of them in continuously cast low-carbon cold forging steel is the basic reason for the cracks. Some of film non-metallic inclusions consisted of MnS and CaS. They are related to the desulphurization of hot metal. A lot of film non-metallic inclusions are mainly composed of magnesia alumina spinel (MgO·A12O3). Magnesia alumina spinel (MgO·A12O3) is considered to be from the tundish lining collapse, which results in exogenous inclusions. It is necessary for low-carbon cold forging steel during continuous casting to strengthen the tundish quality.