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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(a)

(b)

Fig. 6. Tensile curves: (a) N400; (b) C400.

(a)

(b)

Fig. 7. Tensile curves: (a) N570; (b) C570.

Table 2 shows the calculated R e Total , R e Unif , RA s x e . These indexes shows that the embrittlement effect increased with the nitriding temperature and was found to be much more pronounced in the specimen nitrided at 570 o C. The observation of the profile of the fractured specimens (Fig. 8(a-c)) revealed that specimens N350 and N400 still present ductile fractures, but the nitride layer was damaged in the region of plastic deformation. The nitride layers are brittle and many cracks initiate in the external surface of specimens N350 and N400 (Fig. 9(a-b)). The profile of the fractured specimen N570 is different because it contains many secondary cracks. Fig. 10(a) shows the secondary cracks being stopped in the bulk material. These brittle cracks are periodic and coincident with the passes of machining by turning (Fig. 10(b-c)).

Table 2. Embrittlement indexes. Nitriding temperature ( o C)

R e

R e Unif

RA s x e

Total

350 400 570

0.80 0.63 0.21

0.60 0.20 0.34

0.78 0.58 0.20