Observations on the Relationship between Crystal Orientation and the Level of Auto-Tempering in an As-Quenched Martensitic Steel

Shashank Ramesh Babu,David Porter,Sakari Pallaspuro,Antti Järvenpää,Matias Jaskari,Tuomo Nyyssönen,Thomas Paul Davis,Jukka Kömi

doi:10.3390/met9121255

Shashank Ramesh Babu, David Porter + Show 6 more

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https://doi.org/10.3390/met9121255

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Journal: Metals	Publication Date: Nov 24, 2019
Citations: 18	License type: CC BY 4.0

Affiliation: University of Oulu, Outotec (Finland), University of Oxford

Abstract

Auto-tempering is a feature of the technologically important as-quenched low-carbon martensitic steels. The focus of this paper is on the morphology of the martensite and the orientation of the last forming untempered regions in relation to the earlier formed auto-tempered martensite in both small and large austenite grains. A low-carbon martensitic steel plate was austenitized for 24 h and quenched to room temperature. The resulting microstructure was characterized using electron microscopy and electron back scattered diffraction (EBSD) imaging. It was found that all the untempered regions in the martensitic microstructure were oriented with the plane normals {100} close to the thickness, or normal, direction of the plates. Variant analysis revealed that the untempered regions and the auto-tempered regions are part of the same packet.

Highlights

High-strength low-carbon martensitic steels provide low-cost environmentally efficient materials for weight critical engineering
The first objective of this study is to investigate the martensite morphology in both large and small grains in a low-carbon steel using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD)
The grain boundary pinning effects caused by the presence of VC and AlN at the prior austenite grain boundaries has caused the abnormal distribution in the prior austenite grain sizes

Summary

Introduction

High-strength low-carbon martensitic steels provide low-cost environmentally efficient materials for weight critical engineering. Low-carbon steels are commonly used as structural materials as they have good weldability. Using such steels in the quenched martensitic condition provides both good weldability and high strength making them attractive materials for structural applications [2,3]. Martensite is formed by a diffusionless transformation at low temperatures when austenitized steel is quenched [2,3]. In low-carbon steels, martensite has a lath morphology [2,3,4]. The carbon atoms that are fully soluble in austenite prior to the transformation to martensite become supersaturated in the bcc matrix after the formation of martensite. As the solubility of C in ferrite in equilibrium with cementite is only

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