CB2 cast steel is 9CrMoVNbB steel, and its trial produced steel castings have an extrapolated endurance strength of 85mpa at 625 ℃ for 100000 hours. The high temperature endurance strength is better than that of GX12CrMoWVNbN10-1-1 steel used in the previous generation of steam turbine steel castings, and the maximum service temperature can reach 625 ℃ (Fig. 1).
The conventional mechanical properties of CB2 cast steel and GX12CrMoWVNbN10-1-1 steel are shown in Figure 2.
By comparing the conventional mechanical properties of the two, it is found that the tensile strength of CB2 cast steel at room temperature is about 100MPa higher than that of GX12CrMoWVNbN10-1-1 steel, and the tensile strength at high temperature above 600 ℃ is basically the same; The impact toughness of CB2 cast steel at room temperature is lower than that of GX12CrMoWVNbN10-1-1 steel, and the ductile brittle transition temperature is higher than that of GX12CrMoWVNbN10-1-1 steel.
This is because CO and B elements are added to CB2 cast steel to further improve its high-temperature strength, and the interstitial solid solution strengthening effect of B element will reduce the impact toughness of B-containing cast steel. Therefore, the room temperature impact property of CB2 cast steel is significantly lower than that of GX12CrMoWVNbN10-1-1 steel.