Anisotropic Pinning-Effect of Inclusions in Mg-Based Low-Carbon Steel

Area of Science:

• Materials Science
• Metallurgy
• Physical Metallurgy

Background:

• Acicular ferrite (AF) formation is a critical microstructural feature in low-carbon steels, influencing mechanical properties.
• Controlling AF nucleation is essential for tailoring steel performance.
• Austenite grain size and inclusions play significant roles in AF nucleation and grain growth.

Purpose of the Study:

• To investigate the effect of austenite grain size on acicular ferrite nucleation in low-carbon steel with 13 ppm Mg.
• To determine the pinning ability of different inclusion types on austenite grain boundary migration in low-carbon steel with 22 ppm Mg.
• To establish the relationship between austenite grain size, carbon diffusion, and microstructure evolution.

Main Methods:

• Calculation of average austenite grain size using OM Leica software.
• In situ observation using confocal scanning laser microscopy (CSLM) for micro-analysis of inclusion pinning ability.
• Calculation of grain mobility for various inclusion types.

Main Results:

• An optimal austenite grain size (164 µm) maximizes acicular ferrite nucleation probability; excessively small or large sizes inhibit AF formation.
• Mg-based inclusions exhibit strong pinning ability on austenite grain boundaries.
• MnS inclusions are the least effective in pinning austenite grain boundary migration.

Conclusions:

• Austenite grain size is a critical factor influencing acicular ferrite nucleation in low-carbon steels.
• The type of inclusion significantly impacts its ability to inhibit austenite grain migration, with Mg-based inclusions being most effective.
• Understanding these factors allows for better control over steel microstructure and properties.