Accurate and fast elemental analysis during the production process of steel and its base materials is a critical requirement, not only as a quality control procedure to conform to standards, but also to enable the steel producer to obtain cost savings in an ever increasing competitive environment.
The Axios FAST is ideally suited for many applications, where speed and accuracy are factors of prime importance. This application note demonstrates the performance of the Axios FAST XRF spectrometer for the analysis of low- alloy, ferritic and austenitic steels.
Measurements were performed using an Axios FAST simultaneous X-ray fluorescence spectrometer equipped with a 4 kW Rh SST-mAX X-ray tube, set at 60 kV/66 mA for optimal measurement conditions.
A 300 µm brass filter and a brass beam stop were mounted. Further it was equipped with:
- Rh reference plate for sample holders with a 37 mm opening
- Flow counter detector window: 1 µm polypropylene for carbon analysis.
Twenty-three standards were used to set up the calibration, including 11 low- alloy steel standards from CKD plus 4 ferritic and 8 austenitic steel standards from BAS. The standards were surfaced (for 5 seconds) with a 60 grit Al2O3
grinding disk, prior to measurement. A sample holder with a 37 mm opening was used.
The X-ray intensities for 19 elements were measured for 10 seconds at the peak. Calibration was performed using the theoretical alphas and Fundamental Parameters (FP) regression model incorporated in the SuperQ software package. FP allows for the analysis of elements with wide concentration ranges, with a single program, thus saving both on the time to set-up and to maintain numerous calibrations as well as on the number of standards required. During the calibration, line- overlap corrections (12 in total) and gamma-corrections (for Ni and Fe) were determined by multiple-regression by the software. No other corrections were applied.
The analysis speed is usually determined by the element with the lowest sensitivity (carbon in this case) and/ or the lowest concentration. Despite the short counting time of 10 seconds, excellent results are obtained for all elements, including carbon and nickel (see examples Figures 1 and 2). Table 1 gives an overview of the elements with their concentration range, their respective values for the ‘root mean square’ (RMS) error, for K and for the lower limit of detection (LLD) based on a 100 second counting time. The values for RMS and K are absolute and relative indications respectively, of the magnitude of the differences between the measured concentration and the supplied chemical concentration. A lower value for K indicates a more accurate calibration. Since the RMS value relates to the whole concentration range, a better estimate for the absolute error of a specific element with a known concentration can be obtained by using a formula based on the K value:
For example, error estimates for Ni determinations of 1.0 and 10.0 wt% based on the calibration detailed in Table 1 (where K = 0.0088) would be 0.009 wt% and 0.044 wt%, respectively.
Table 1. Values for K, RMS and LLD for wide-range calibrations of alloyed steels
The Axios FAST is well suited for analyzing an extended range of concentrations of various types of steel within one analytical program by using the Fundamental Parameter (FP) model in SuperQ. Accurate results are obtained, even for carbon, within a counting time of only 10 seconds. Without measuring carbon, a counting time of 4 seconds would be sufficient to obtain these results for the resulting elements.