Abstract
As-quenched low-carbon martensitic steels (<0.2 wt.% C) contain auto-tempered carbides. Auto-tempering improves the work hardening and upper-shelf impact energy; however, an efficient characterization method to determine the degree of auto-tempering has not been available. This paper demonstrates an efficient image processing tool that calculates the relative auto-tempered carbide fraction by analyzing scanning electron microscope micrographs. By the process of image segmentation, the qualitative volume fraction of auto-tempered carbides can be determined, and an associated color map produced, which distinguished the levels of auto-tempering. This image processing tool could become useful for the optimization of new low-carbon steel’s mechanical properties.
Highlights
High strength, excellent toughness, and good weldability are three steel properties that are highly desirable for mechanical applications [1]
This paper demonstrates an image processing methodology to qualitatively analyze the auto-tempered carbides formed in as-quenched low-carbon steels
The microstructure consisted of (1) coarse with a high-volume fraction of carbides relative to the other features in the microstructure, (2) thin martensite laths with a high-volume fraction of carbides relative to the other features in the martensite laths without carbides, and (3) dark islands with minimal or no carbides [8]. These results microstructure, (2) thin martensite laths without carbides, and (3) dark islands with minimal or no were consistent with the observations made by Morsdorf et al [4]
Summary
Excellent toughness, and good weldability are three steel properties that are highly desirable for mechanical applications [1]. In the automobile industry, low-carbon high-strength structural steels offer the possibility of weight reduction while maintaining or increasing component strength [3]. The microstructure of martensite is a major contributor to the attainment of these desirable properties [4]. Martensite is formed by a diffusionless shear mechanism when austenite is cooled rapidly to room temperature [5]. In the case of low-alloy steels, this rapid cooling normally requires water quenching. The morphology of martensite in low-carbon low-alloy steels are lath like [5,6]. The diffusionless shear mechanism produces martensite that is supersaturated with carbon when compared with the equilibrium ferritic state of the steel
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