Correlation of Heterogeneous Local Martensite Tetragonality and Carbon Distribution in High Carbon Steel

Abstract

A novel approach for the correlation of local martensite tetragonality determined by electron backscatter diffraction and carbon distribution by atom probe tomography (APT) is presented. The two methods are correlated by site-specific sample preparation for APT based on the local tetragonality. This approach is used to investigate the local carbon distribution in high carbon steel with varying local martensite tetragonality. Regions with low tetragonality show clear agglomeration of carbon based on statistical nearest neighbour (NN) analysis, while regions with high tetragonality show only small elongated agglomerations of carbon and no significant clustering using NN analysis. The APT average bulk carbon content shows no quantitative difference between regions with low and high tetragonality, indicating that no significant long-range diffusion of carbon has taken place.

Evolution of Martensite Tetragonality in High-Carbon Steels Revealed by In Situ High-Energy X-Ray Diffraction

“…A separate investigation of the local correlation of c/a values with the carbon distribution determined by APT for the 15 C/s and 0.5 C/s C74 samples showed clear autotempering effects with carbon segregation. [47] The carbon segregation was more pronounced for low c/a regions compared to high c/a [47] probably due to a stronger autotempering after formation at higher temperatures or slower cooling. The effect of autopartitioning can be estimated from the austenite peak position at room temperature and a small shift of the 311 austenite peak to lower 2h values is observed for the 0.5 C/s C54 sample compared to the faster cooling rates in Figure A.2(c).…”