Quantification of the carbon content of single grains in martensite-ferrite dual phase steel by UHV-EDXS

Description

Ferrite and martensite in dual phase steel differ in hardness, local dislocation density and in the carbon content. A conventional method for the distinction of the two phases is electron back scatter diffraction (EBSD). Even though martensite and ferrite show a similar crystal structure, the quality of electron back scatter pattern differs for the phases. Hence, we estimated the martensite volume fraction, which determines the hardness of the grains, with the help of EBSD. The carbon content of the steel grains were obtained by measurements with a scanning Auger electron microscope. While Auger electron spectroscopy did not lead to satisfactory results, chemical mappings of carbon obtained by novel ultra high vacuum energy dispersive X-ray spectroscopy (UHV-EDXS) showed a clear correlation to the distribution of ferrite and martensite. The ultra high vacuum of the scanning Auger microscope in combination with a customized windowless EDXS detector resulted in a minimization of hydrocarbon contamination and maximization of the sensitivity for the detection of light elements. These conditions resulted in a measurement which even enabled us to quantify the carbon content of individual grains. Furthermore, nano-hardness tests were performed on the exact same grains which were evaluated with UHV-EDXS and EBSD for samples with varying martensite volume fraction. An increase of hardness of the ferrite grains and decrease of hardness of martensite grains with increasing martensite fraction could be observed. We were able to confirm that the decrease of the hardness of the martensite grains is associated with the carbon content of the grains.

Period	06 Oct 2021
Event title	Conference on Surface and Solid State Analytics
Event type	Conference
Location	GermanyShow on map