Issue 56

D. Pilone et alii, Frattura ed Integrità Strutturale, 56 (2021) 56-64; DOI: 10.3221/IGF-ESIS.56.04

The results of the tensile tests are summarized in Tab. 2 for various castings both in the as-cast and in the forged state after heat treatment. The results obtained for the commercial alloy are also reported for comparison. For all the castings, even in the forged state, the obtained mechanical properties are lower than the ones characterizing the commercial alloy, but they abundantly meet the design requirements. As far as the differences with the commercial alloy are concerned, we can make the following considerations. The commercial alloy has been forged and drawn in the form of a bar, undergoing significant plastic deformations, while for the satellite we need to produce a sphere. It is being assessed whether to produce it by casting or by casting and forging, but with low deformations. Our study considered different types of castings whose properties meet the physical and mechanical requirements. It is apparent that forging treatment with a 15% reduction improves the mechanical properties of the alloy and that casting mechanical behavior is affected by the presence of microshrinkage cavities that decrease strength and toughness of the alloy as well as its density. By examining the behavior of the samples, we can observe that as the aging time increases, the mechanical strength increases and the ductility decreases and then increases again after 120 hours treatment. The alloy cast in air is generally less ductile. Some significant σ - ε curves characterizing the forged alloy (Fig. 5) are reported and compared with the one of the commercial alloy (Fig. 6). For all the tested specimens the plastic behavior is tendentially linear with a work hardening exponent of about 0.24.

Figure 5: Stress-strain curves of the forged Haynes 242 alloy after solubilization and heat treatment.

Figure 6: Stress-strain curve of the commercial Haynes 242 alloy aged for 48 h.

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