The Impact of Metal Micro-Damages on the Lifetime of Cast Casing of the Valve

Abstract

Dependence of the residual resource on the amount of micropores formed in conditions of prolonged aging of cast steel 15Kh1M1FL under stress conditions and high degree of damage with micropores is determined. Two series of cylindrical specimens are also tested for long-term strength: circumferentially notched and smooth specimens. The resource factor K_t is determined for operation conditions [stress (50 - 80 MPa) and temperatures (520 - 560°C)] by comparison of the calculated durability of the notched specimens of other series with a lower depth of the notches than that in tested specimens and durability of the smooth specimens. Using the results of studying pore formation we revealed a quantitative correlation between the impact of the microdamage severity on the lifetime and relative damage of the section of a circumferentially notched cylindrical specimen. Temperature and stress dependence of K_ô in the working range of loading conditions is studied for notched specimens. The type of damage at which further operation should be terminated is determined. It is found that the same stage of damage of steel 15Kh1M1FL must be simulated by a deeper notch than that in steel 12Kh1MF.