Faster analysis of high-alloy steel with Zetium and SumXcore technology

Zetium 

Introduction

Stainless steel is a family of special grades of iron-based alloys containing a minimum 10.5% of chromium in their composition. The high chromium content in combination with other alloying elements determines the high corrosion resistance of these grades of steels. Depending on the final usage, stainless steel compositions are carefully controlled to obtain specific corrosion-resistant characteristics and crystalline structure, which in turn affect their hardness and strength. This makes stainless steel the ideal base material for applications  such as automotive and aerospace bodies, construction material, industrial equipment as well as major appliances and surgical equipment. In order to ensure the desired properties, it is crucial to perform rapid and accurate elemental analysis at each step of the production, from process control to quality control.

Integration of the  revolutionary  ED core into the Zetium X-ray fluorescence (XRF) spectrometer combines two technologies, namely wavelength dispersive (WD) and energy dispersive (ED) XRF, converging to form a unique and powerful analytical heart called SumXcore technology. It  delivers specific benefits for metals applications, such as:

• Reduced measurement times
• Identifying and flagging of unexpected elements in production
• Fast sample screening
• Spectrum archiving

This data sheet demonstrates the time savings achieved with SumXcore technology for the analysis of high- alloy steel by XRF.

Table 1. Elemental and concentration ranges analyzed with their calibration results

Instrumentation and software 

Measurements were  performed  using a Zetium XRF spectrometer configured with a 2.4 kW Rh SST R-mAX X-ray tube, a WD core, which is made up of the appropriate collimators, crystals and detectors for WDXRF analysis, and an ED core, which is a fixed EDXRF channel capable of capturing a complete EDXRF spectrum simultaneously with WDXRF measurements. All measurements were conducted using the state-of-the-art SuperQ software package.

Sample preparation

Twenty-one certified reference materials from the Bureau of Analyzed Standards (BAS) and the Iron and Steel Institute of Japan (JSS) - SS 461/1 – SS 468/1, SS 469 – SS 474 and JSS 650/11 – JSS 655/11 - were used to set up a calibration for 13 elements. Full elemental and concentration ranges are listed in Table 1. Standards were freshly surfaced prior to analysis with a Herzog grinding machine using 60 grit Al2O3 sandpaper.

Measurement conditions

One application was set up using the optimum combination of both technologies where certain elements were measured using the WD core and others using the ED core. This was done without compromising the analytical requirements for accuracy and precision. Measurements were performed using a 27 mm mask size. Elements analyzed using simultaneous ED and WD cores were measured using a Al 200 micron filter, while a 0.8 mm attenuator for the ED channels was used for all elements. Calibration RMS values (root mean square error), K-factors (weighted standard deviation), as well as lower limits of detection are shown in Table 1. The measurement times for the novel combination of WD and ED measurements in one are compared to a classical WD core-only setup in Table 2, showing a significant time reduction of 44%.

Table 2. Measurement times for the WD core and SumXcore applications 

To determine the optimum combination of analytical conditions such that the analytical performance remains uncompromised, a comparison between the WD core and ED core setups was made for all elements of interest. An example of this comparison is shown in Figure 1 which shows the difference between certified values and measured values for all standards used to perform the analysis of Cr on both WD and ED optical paths.

The optimization of the analytical conditions resulted in an application where Si, P, S, Ti and Co were measured on the WD core and all other elements on the ED core. Since elements are measured simultaneously on the ED core, the analysis time is determined by the element with the lowest sensitivity and/or the lowest concentration (As in this case). This resulted in an analysis time of 60 s for the ED condition. The same time can be used to measure elements showing low concentrations – in this case Co - longer compared to the WD core application, with the benefit of improving LLD and precision without increasing the total measurement time

Figure 1. Comparing WD and ED core performance on Cr analysis: differences between theoretical and calculated values for Cr concentrations measured using WD and ED core

Accuracy and precision

Table 3 demonstrates the achievable accuracy and precision (repeatability) of the combined application when measuring a certified stainless steel standard SS 474 as routine sample. The obtained results confirm the accuracy of the combined application, delivering concentration values close to the certified values. It can also be seen that the application delivers consistent results, with excellent repeatability values.

Table 3. Accuracy and precision of the SumXcore application (SS 474)

Conclusions

The results clearly demonstrate that the combination of WD- and EDXRF incorporated in the Zetium spectrometer delivers faster measurement times for the analysis of high-alloy steels. The increase in speed is achieved without a loss in analytical performance and the stability of the Zetium spectrometer ensures repeatability close to the theoretical limit. These two factors allow improved sample throughput, which is highly desirable where fast analytical response is required, for example during steel manufacturing.