Regular Article

Effect of composition and morphology of non-metallic inclusions on fracture toughness in as-cast AHSS

¹ School of Materials Science and Engineering, Northeastern University, Shenyang 110819, Liaoning, PR China
² National Engineering and Research Center of Continuous Casting Technology, Central Iron & Steel Research Institute, Beijing 100081, PR China
³ China Iron & Steel Research Institute Group, Beijing 100081, PR China

^* e-mail: wuzhanfang1122@hotmail.com

Received: 5 August 2019
Accepted: 19 September 2019

Abstract

A set of water-cooling copper-chill mold equipment is designed to study the precipitation behavior of different inclusion types in test steel under different cooling conditions, as well as its effects on the steel mechanical properties. As the results reveal, slow cooling treatment near the solidus temperature of test steel is conducive to forming more MnS + Al₂O₃ composite inclusions. The impact energy (−16 °C) of slow-cooled cast ingots at the core position is 28% higher than that of the air-cooled ingots. Scanning electron microscopy analysis of the specimens shows that small cracks are formed around single Al₂O₃ inclusions, but no cracks were found around composite inclusions. A calculation model of the tessellated stress of composite inclusions in steel is introduced to verify this phenomenon. The calculation demonstrates that, with a cover of ductile MnS, stress concentration around the composite inclusion is significantly decreased as compared with the single Al₂O₃ inclusion in the test steel.