PSI - Issue 82

L.F. Guedes et al. / Procedia Structural Integrity 82 (2026) 199–205 Guedes et al. / Structural Integrity Procedia 00 (2026) 000–000

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Fig. 1. Thermal cycles in the plasma ion nitriding processing.

3. Results and discussion Fig. 2(a-b) shows the hardness profiles of N350, N400 and N570. The hardness peaks in the nitride layers were found to increase slightly with the nitriding temperature, 1420 HV0.01 for N350, 1470HV0.01 for N400, and 1520HV0.01 for N570.

Fig. 2. Microhardness profiles of N350, N400 and N570 specimens.

Fig. 3(a-c) shows the SEM images of the nitride layers, in which microcracks can be observed. The thicknesses of the nitride layers of N350, N400 and N570 were ~ 20 µ m, ~ 38 µ m, and ~ 130 µ m, respectively. Analyzing the nitride layer of N570 in detail, it is composed of two sublayers (Fig. 4(a)). The first and external sublayer has higher Cr and Mo contents (as determined by EDS analysis, not shown), and contains sub-microcracks in the dark areas (Fig. 4(b)), besides the microcracks. Some regions of the internal sub-layer were damaged during preparation, due to the chemical etching with Vilela’s reagent, which provoked intergranular attack (Fig. 4(c)). Figs. 5(a,b), 6(a,b) and 7(a,b) show the comparison of the tensile curves ( s x e ) of the nitride specimens (N350, N400 and N570) with the specimens only heat treated following the same thermal cycle employed in the nitriding (C350, C400 and C570). The ductility parameters, total and uniform elongations ( e Total and e Unif ), were reduced with nitriding. The toughness parameter, represented by the area of the s x e curve (A s x e ), also decreased with the nitriding process.