The Influence of Mg-Based Inclusions on the Grain Boundary Mobility of Austenite in SS400 Steel

Chih-Ting Lai,Fei-Ya Huang,Chi-Kang Lin,Hwa-Teng Lee,Hsuan-Hao Lai,Jui-Chao Kuo,Yen-Hao Su

doi:10.3390/met9030370

Chih-Ting Lai, Fei-Ya Huang + Show 5 more

Open Access

https://doi.org/10.3390/met9030370

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Journal: Metals	Publication Date: Mar 22, 2019
Citations: 2	License type: CC BY 4.0

Affiliation: National Cheng Kung University

Abstract

In this study, the effects of the addition of Mg to the grain growth of austenite and the magnesium-based inclusions to mobility were investigated in SS400 steel at high temperatures. A high-temperature confocal scanning laser microscope (HT-CSLM) was employed to directly observe, in situ, the grain structure of austenite under 25 torr Ar at high temperatures. The grain size distribution of austenite showed the log-normal distribution. The results of the grain growth curves using 3D surface fitting showed that the n and Q values of the growth equation parameters ranged from 0.2 to 0.26 and from 405 kJ/mole to 752 kJ/mole, respectively, when adding 5.6–22 ppm of Mg. Increasing the temperature from 1150 to 1250 °C for 20 min and increasing the addition of Mg by 5.6, 11, and 22 ppm resulted in increases in the grain boundary velocity. The effects of solute drag and Zener pinning on grain boundary mobility were also calculated in this study.

Highlights

Both medium and thick steel plates are used in the building of high-rise buildings, bridges, and in ships
TiN inclusions were first applied to improve the toughness of heat-affected zone (HAZ), which serve as potential nucleation sites for acicular ferrite (AF) formation [2,3,4]
We investigated the effect of the addition of Mg on austenite grain growth in SS400 low-carbon steel using a high-temperature confocal scanning laser microscope (HT-CSLM)

Summary

Introduction

Both medium and thick steel plates are used in the building of high-rise buildings, bridges, and in ships. Mizoguchi et al [10] first proposed oxide inclusions to improve the impact toughness of HAZs under high-heat-input welding. The pinning efficiency against grain growth for grain coarsening was determined by the particle size [21]. The chemical composition of steel, the cooling rate at temperatures ranging from 800 to 500 ◦ C, the size of austenite grains, and the inclusion parameters affect the formation of intragranular AF in metal [31]. We investigated the effect of the addition of Mg on austenite grain growth in SS400 low-carbon steel using a high-temperature confocal scanning laser microscope (HT-CSLM). The pinning effect of the magnesium-based inclusions on the mobility of austenite was studied

Materials and Experiments

Parameters of Grain Growth Equation

Effects

Zener Pinning Effect of Inclusions on the Austenite Grain Mobility

Effect of Solute Drag on the Grain Mobility of Austenite

Conclusions