Elemental Mapping of Nanoscale Boron-Containing Phases in Steel

QUANTAX WDS has a high sensitivity for light elements making it ideal for the microanalysis of boron-containing phases in special steel grades.

Boron is used in the steel industries as an alloying element in certain special steels: Boron-induced precipitation hardening can lead to the desired increase in yield strength and strength in some austenitic Cr-Ni-steels. Furthermore, the strength properties of high-temperature steel grades are improved at higher temperatures with the help of boron-induced precipitation. Steels alloyed with boron are also used in nuclear technology, as boron has a high effective cross-section for neutron absorption.

The example shown here of combined WDS/EDS mapping of a boron steel demonstrates that light element distributions can be mapped very well by QUANTAX WDS, even when concentrations are in the trace element range and phases of interest are extremely small.

The results show that relative boron enrichments are related to sub-micron size cementite phases (Fe₃C) that are characterized by relative enrichment of carbon, manganese, chromium and boron. Boron contents in cementite determined by WDS are 0.4 wt% as compared to 0.2% in the steel matrix. Mapping the trace element distribution with a pixel resolution of 14 nm was done at 5 kV, 17 nA in 120 minutes using diffractor BRML200.

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QUANTAX WDS

QUANTAX WDS is a parallel-beam wavelength-dispersive X-ray spectrometer that is optimized for light element determination. The system is fully integrated in the ESPRIT software, allowing simultaneous acquisition and combined quantification with EDS.

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Composite element distribution map from a simultaneous EDS/WDS measurement acquired at 5 kV, 17 nA. Sub-micron size cementite (Fe3C) inclusions in green, matrix steel in orange. B content in B-”rich” phase is 0.4 wt% only! Sample courtesy of Dr. Murugaiyan Amirthalingam, IIT Madras.

Single element distribution maps of the same field of view as shown in the above image for boron (WDS, upper left), carbon (EDS, upper right), iron (EDS, lower left) and manganese (EDS, lower right).

X-ray intensity maps for selected elements presented in palette colors (heat maps) on SE image underlay. From upper left to lower right: B (WDS), C (EDS), Fe (EDS) and Mn (EDS).

Phase map derived from mapping results of combined WDS/EDS measurement on boron steel. The cementite phase is shown in green, the steel matrix in red. The inset table presents the deduced modal proportions of the phases.