PSI - Issue 13

T. Depover et al. / Procedia Structural Integrity 13 (2018) 1414–1420 Author name / Structural Integrity Procedia 00 (2018) 000–000

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3. Results and discussion 3.1. Materials Characterization

Optical microscopy images revealed a martensitic (as-Q) and Q&T microstructure (cf. related publications). However, the Fe-C-Ti as-Q material still contained large incoherent TiC since austenitizing at 1250°C was not sufficient to dissolve all the carbides present from processing. Their presence is illustrated by TEM in Fig. 1(a). For Fe-C-V, all particles were dissolved during the austenitizing step and the as-Q condition did not contain any V based precipitates. Next, carbides were introduced for both materials during tempering, i.e. the Q&T condition. TEM bright field images for the Q&T samples were also taken to confirm their presence, as shown in Fig. 1 (b) and (c). For the Q&T condition, small nano-sized carbides of less than 10 nm were identified in both Fe-C-Ti and Fe-C-V. Additional microstructural details and a comprehensive TEM analysis comprising the study of diffraction patterns for the identification of the different carbide morphologies (TiC and V 4 C 3 ) can be found in the related publications.

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(a) (c) Figure 1: TEM bright field images for Fe-C-Ti as-Q (a) and for Fe-C-Ti Q&T (b) and Fe-C-V Q&T (c). (b)

3.2. Hydrogen trapping ability deliberated by thermal desorption spectroscopy The available traps were evaluated by performing TDS for both the as-Q and Q&T condition. The TDS spectra together with their deconvoluted peaks are presented in Fig. 2. For the as-Q conditions, only one peak was present for both materials with E a ’s of about 27 – 30 kJ/mol. This first peak was therefore associated to H trapped by the martensitic lath boundaries (Thomas et al. (2002)).

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Figure 2: TDS curves of Fe-C-Ti and Fe-C-V in the as-Q and Q&T condition, at a heating rate of 600°C/h.