Scale Formation on HSLA Steel during Continuous Casting Part I: The Effect of Temperature–Time on Oxidation Kinetics

Rosa Maria Pineda Huitron,Pavel Ernesto Ramírez López,Leonardo Pelcastre,Pooria Nazen Jalali,Maija Kärkkäinen,Esa Vuorinen

doi:10.3390/met10091243

Rosa Maria Pineda Huitron, Pavel Ernesto Ramírez López + Show 4 more

Open Access

https://doi.org/10.3390/met10091243

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Abstract

The findings in this work enhance the understanding of oxidation mechanisms and scale growth at high temperatures of a high strength low alloy (HSLA) steel for improving surface quality during continuous casting. The oxidation phenomenon was investigated under dry air and water vapor atmospheres by heating specimens at 1000, 1100, and 1200 °C at different holding times. Temperature and time had great effects on the kinetics, where faster (i.e., parabolic) oxidation rates were present under water vapor when compared with the dry air condition. Temperature strongly influenced the number of defects, such as pores, voids, gaps and micro-cracks, formed in the oxide scale. A phase analysis confirmed the presence of FeO as the first phase formed at the steel surface, Fe3O4 as the middle and thicker phase, and Fe2O3 as the last phase formed in the oxide/air interface. The micromechanics of the oxides demonstrated that a combination of phases with high (wüstite) and low plasticity (magnetite and hematite) could also have been the reason for the uneven cooling during Continuous Casting (CC) that resulted in the undesired surface quality of the steel slabs. This work gives a good look at the oxide scale effect on the surface quality of steel slabs through an understanding the kinetics during oxidation.

Highlights

The present work was focused on the analysis of oxidation kinetics occurring at temperatures relevant to continuous casting process
Even though the oxidation process under dry and water vapor conditions occurred via the same mechanisms, the interaction between the number of oxygen atoms from the environment and the steel substrate significantly differed from one case to another
The importance of oxidation phenomena occurring at high temperatures under dry air and water vapor conditions was investigated for temperatures relevant to the secondary cooling zone

Summary

Introduction

The present work was focused on the analysis of oxidation kinetics occurring at temperatures relevant to continuous casting process (e.g., secondary cooling below the mold). This investigation sought to address the gaps of knowledge regarding the effect of oxide scale formed under dry and water vapor conditions, as well as its impact on the surface quality of a high strength low alloy (HSLA) steel slab. The experimental setup was designed to simulate the thermal gradients and environment experienced by a surface throughout the casting process, with special focus on the oxidation behavior after the mold exit where the strand is in direct contact with the environment including the water flow from the submerged entry nozzles (SENs).

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Discussion

Conclusion