Effect of R Phase Formation on the Impact Toughness of a 25%Cr-7%Ni-3%Mo Duplex Stainless Steel.

Degradation of Impact Toughness due to Formation of R Phase in High Nitrogen 25Cr-7Ni-Mo Duplex Stainless Steels.

“…The previous results indicate that the aging stage for the significant loss of the impact toughness corresponds to the stage, where the R phase is formed but the s phase is not yet formed. 7) Figure 3 also indicates that alloys 25Cr-7Ni-N and 25Cr-7Ni-Mo show a large decrease in the impact toughness after the aging for 18 and 10.8Ϫ36 ks, respectively.…”

“…1(a) and 1(b). Figure 2 indicates the aging time dependencies of the Vickers hardness for alloys 25Cr-7Ni and 25Cr-7Ni-N at 873 K. Our previous results 7) show that, after an incubation time of about 30 ks, the Vickers hardness of alloy 25Cr-7Ni gradually increases with increasing aging time t and that this gradual increase is caused by the formation of s phase. A significant increase in the Vickers hardness after tϭ 3.6ϫ10 2 ks is attributed to the formation of a large volume of bulky s phase.…”

“…3. Solid squares, circles and triangles in this figure indicate the results of alloys 25Cr-7Ni, 7) 25Cr-7Ni-N and 25Cr-7Ni-Mo, respectively. A significant loss of the impact toughness for alloy 25Cr-7Ni occurs after the aging for tϭ3.6 ks.…”

“…The chemical compositions of these steels as well as that of the steel in a previous study 7) are listed in Table 1. In this table, alloy 25Cr-7Ni is a commercial steel containing 2.8 mass% of Mo and 0.14 mass% of N utilized in a previous study, whereas alloy 25Cr-7Ni-N is a commercial steel containing 3.8 mass% of Mo and 0.27 mass% of N. On the other hand, alloy 25Cr-7Ni-Mo is a…”

“…The relationship between the impact toughness and the microstructural change was experimentally studied by the present authors 7) using a commercial steel containing 24.7 mass% of Cr, 6.8 mass% of Ni, 2.8 mass% of Mo, 0.14 mass% of N and 0.017 mass% of C. The steel was aged at 873K for various times and then metallographically observed by transmission electron microscope. According to the observation, however, the R phase is formed much earlier than the precipitation of the s phase during the aging and the formation of the R phase results in remarkable degradation of the impact toughness at early stages of the aging.…”