Retained austenite measurements with Xstress DR45 and Xstress G2R systems

The case: Comparing the results and measurement time between systems

The Xstress DR45 system utilizes two-dimensional area detectors, while the Xstress G2R system uses traditional line detectors. The 2D detectors have numerous advantages compared to the line detectors. For this application the most important advantage is the shorter measurement time and the capability to automate the measurements thanks to the motorized detector movement. Measuring the diffraction peaks of the austenitic phases using X-ray diffraction (XRD) requires long exposure times when using the more traditional line detectors. This application was done to compare the results and the measurement times between the Xstress DR45 and Xstress G2R systems when measuring samples with different retained austenite contents.

xstress G2R x-ray diffractometer — Xstress G2R

The testing method: X-ray diffraction

Austenite is a crystallographic phase of iron, and it is formed in steel as the steel is heat treated at high temperatures. When the steel is quenched after heat treatment, the austenite is transformed into martensite, a much harder phase of iron. Retained austenite content is the volume fraction of austenite which did not undergo the transformation to martensite during quenching. For many applications a certain retained austenite level is required for the final product.

In this application retained austenite measurements were performed on certified powder samples with known austenite contents ranging from 2 % to 80 %. These powder samples are usually used for validating the equipment before retained austenite measurements are done on other samples.

The retained austenite measurements were performed on the powder samples using X-ray diffraction (XRD) with the four-peak method. The measurement setups are shown in Figure 1 and Figure 2.

Figure 1. Retained austenite measurement setup on Xstress G2R.

Figure 2: Retained austenite measurement setup on Xstress DR45. — Figure 2: Retained austenite measurement setup on Xstress DR45

The Results

Xstress G2R results plotted against Xstress DR45 results. Correlation coefficient r2 =0.9999. — Figure 3: Xstress G2R results plotted against Xstress DR45 results. Correlation coefficient r² =0.9999.

The results were in very good agreement between the Xstress DR45 and Xstress G2R systems as can be seen in Figure 3. They also matched the certificate values provided for the powder samples. Results are tabulated in Table 1.

Table 1: Retained austenite measurement results for the Xstress G2R and Xstress DR45 systems.

Xstress G2R results		Xstress DR45 results
Retained austenite content (%)	±	Retained austenite content (%)	±
82.6	1.8	82.9	0.8
67.3	2.6	67.6	1.9
49.7	2.2	50.1	2.2
28.5	2.3	28.8	0.8
15.1	2.2	16.2	0.3
7.3	1.2	8.8	0.5
1.7	0.2	2.0	1.0

Measurement time for the whole sample set consisting of seven samples was approximately 120 minutes with the Xstress G2R and 10 minutes with the Xstress DR45. We can see that with the two-dimensional area detectors that the Xstress DR45 utilizes the measurement time was reduced to one twelfth compared to that of the G2R system. The difference in measurement time is especially high on samples that have low retained austenite content. Also, for the Xstress DR45 the whole measurement set was automated, while with the Xstress G2R the detectors needed to be manually moved between measuring the ferritic and austenitic phases for each sample. Examples of the fitted data with both Xstress DR45 and Xstress G2R are shown in Figure 4 and Figure 5.