Estimation of Phase Ratio in Bulk, Textured TWIP/TRIP Steels from Pole Figures.

Marton Benke,Ferenc Kristaly,Adrienn Hlavacs,Valeria Mertinger,Mate Sepsi

doi:10.3390/ma14154132

Abstract

The volume fraction of austenite (γ), ε martensite and α′ martensite is of key importance in the research of TWIP/TRIP steels. When mechanical loading is involved, the crystallographic texture also develops, which complicates X-ray diffraction-based phase ratio determination. The problem is more pronounced when only a couple, or only one Bragg-reflection can be measured. A solution for such cases is to determine the ratio of the phases based on the pole distribution function of a selected Bragg-reflection of the present phases. In this manuscript, this method is reconsidered for and applied to non-transmittable bulk specimens for the first time in the reflection mode of XRD pole figure measurements. First, the method was applied to a series of γ–α′ powder mixtures. The results were compared to those obtained by the Rietveld method. Afterwards, the technique was applied to strongly textured, bulk TWIP/TRIP steel specimens which were tensile tested at different temperatures. It was shown that the results of the presented method were close to those of the Rietveld technique in the case of powder mixtures. The results of the tensile-tested steels revealed that the α′ content increases with decreasing test temperatures, and the variation of the α′ ratio correlates very well with the ultimate tensile strength versus the temperature, confirming the contribution of the α′ content to the strength of TWIP/TRIP steels.

Highlights

X-ray diffraction (XRD) provides more comprehensive information about the texture compared to Electron backscattered diffraction (EBSD)
The phase ratio estimation method based on the incomplete pole distribution function of one Bragg reflection of each phase was presented
The method was validated on texturefree powder samples and applied to three steels undergoing both twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effects

Summary

Introduction

Electron backscattered diffraction (EBSD) is an effective technique to provide information about both [3,4,5,7,9,11,12]. The determination of the phase ratio by means of XRD is generally associated with the Rietveld method, which was originally developed for powders and samples with only a weak texture [14,15]. This method provides accurate data for texture-free cases and samples with a relatively weak texture, its accuracy is questionable if the crystallographic anisotropy is strong. There are two ways to deal with the effect of texture

Results

Discussion

Conclusion