Conditions of stability of the structure of Ni-resist alloys

Conclusions

• 1. Heating of Ni-resist samples to 550–950° leads to considerable reduction of the stability of austenite with regard to the martensitic transformation, the largest rise of M_S occurring at temperatures around 800°, while the maximum rate of the destabilization of austenite occurs at 500–700°. Destabilization of austenite is associated with the precipitation of carbides from it.

• 2. M_S is affected by the concentration of carbon dissolved in austenite, which increases with temperature above 550°, and the mechanical condition of austenite, which is determined mainly by the quantity and size of carbide particles precipitated within austenite grains; when the temperature is raised from 550 to 1000° the number of carbides decreases and the size increases.

• 3. Overheating of engines leading to heating of Ni-resist cylinder sleeves to 550–900° cannot be tolerated, especially at low ambient temperatures, since the stability of austenite with regard to the martensitic transformation decreases in this case.