PSI - Issue 54

Liese Vandewalle et al. / Procedia Structural Integrity 54 (2024) 180–187 Liese Vandewalle/ Structural Integrity Procedia 00 (2019) 000 – 000

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furnace. After tempering the samples were water quenched and immediately tested. Additional details regarding the gaseous charging set-up and sample preparation are described by Vandewalle et al. (2023). Comparison is also made with generic Fe-C-Ti alloys with varying C contents (0.2wt% and 0.3 wt%), for which the results have been published in an earlier study of Vandewalle et al. (2023). The Fe-C-Ti materials were subjected to similar treatments as the Fe-C-V. Austenitization was done at one temperature, i.e. 1250°C, since the higher stability of the TiC results in a dissolved C and Ti content of only 0.060 wt% and 0.238 wt%, respectively.

Table 1: chemical composition of the generic Fe-C-V alloy, given in wt% C Ti V Al N

Impurities

Fe-C-V 0.286

0

1.670 0.02-0.03 0.0015-0.0020 0.0005-0.0010 S 0.0010-0.0020 P

The materials microstructures were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was used to characterize the carbides. TDS and hot extraction were used to evaluate the H interactions. During hot extraction samples were subjected to a constant temperature of 950°C and the amount of desorbed H was measured using a TCD detector. As such, the total H content of the samples could be determined. Analysis of the different active trapping sites was done based on the TDS spectra. In this case, the specimens were heated at a constant rate from room temperature up to 900°C while the H desorption rate is measured using a mass spectrometer. Both TDS and hot extraction measurements were performed with a Galileo G8 setup and calibration was performed daily using the gas calibration method. More information regarding the TDS/hot extraction equipment and analysis can be found in the paper of Vandewalle et al. (2023). 3. Results and Discussion SEM images of the Fe-C-V alloy austenitized at 1250°C and 950°C after tempering at 600°C are shown in Figure 2. The Fe-C-V alloy austenitized at 1250°C consisted out of a coarse martensitic matrix. No vanadium-based precipitates could be observed by SEM. Even TEM investigation could not clearly visualize any vanadium carbides. While white cuboidal shapes could be observed in some TEM images, as can be seen in Figure 3a, no enrichment of vanadium could be detected by EDX, nor of any other elements. Hence, these features might originate from cube shaped particles (possibly AlN) which were removed by the sample preparation. On the other hand, hardness measurements (see Figure 4) clearly showed secondary hardening upon tempering. Thus, significant precipitation of vanadium carbides should have taken place. Possibly, the coherent precipitated carbides were too small to clearly visualize them as vanadium carbides have indeed been reported to precipitate as very small plate-like particles with a maximum thickness of around 5 nm (Speich and Leslie (1972)), De Seranno et al. (2020), Lee et al. (2016), and Takahashi et al. (2012)).

a) b) Figure 2: SEM image of the Q&T Fe-C-V alloys austenitized at a) 1250°c and b) 950°C with corresponding EDX elemental maps.