Understanding the microstructure-properties relationship of low-temperature carburized austenitic stainless steels through EBSD analysis
Journal article, 2017

The present article is dedicated to the microstructural characterization of the surface layer of two different austenitic stainless steels, 304L and 904L, subjected to a low-temperature carburizing process (Kolsterising®,Bodycote) and a subsequent annealing at high-temperature. The carburizing treatment forms a hard expanded austenite in both materials. However, thermal decomposition occurs at high temperatures through precipitation of chromium-carbides, hence compromising the surface hardness of the treated materials. The purpose of this paper is to explore the potential applicability of electron backscatter diffraction (EBSD) technique to reveal the correlation between phase transformation and hardness. First of all, EBSD was used to create kernel average misorientation (KAM) maps of the modified surface layers to identify the internal strains. Moreover,the preferential sites for precipitation of chromium-compound during annealing were identified. We prove here that EBSD can provide useful information to distinguish the main hardening mechanisms within modified surface layers at different annealing conditions. When combined with nano-indentation, X-ray diffraction(XRD) and glow discharge optical emission spectrometry (GDOES), an effective bridge between macro and microanalysis can be obtained. Solid solution hardening was found to be the dominant mechanismin as-carburized materials, with pre-existing strain promoting a higher supersaturation. In the annealed materials, the alloy composition and surface finish can also dictate the preferential sites of precipitation and can therefore affect the residual hardening.

Expanded austenite

Austenitic stainless steel

Kolsterising

EBSD

Surface modification

S-phase

Kernel average misorientation

Author

Giulio Maistro

Chalmers, Materials and Manufacturing Technology, Surface and Microstructure Engineering

Christos Oikonomou

Chalmers, Materials and Manufacturing Technology, Surface and Microstructure Engineering

Lina Rogström

Linköping University

Lars Nyborg

Chalmers, Materials and Manufacturing Technology, Surface and Microstructure Engineering

Yu Cao

Chalmers, Materials and Manufacturing Technology, Surface and Microstructure Engineering

Surface and Coatings Technology

0257-8972 (ISSN)

322 141-151

Subject Categories

Materials Engineering

Areas of Advance

Materials Science

DOI

10.1016/j.surfcoat.2017.05.036

More information

Latest update

2/28/2018