Abstract
A large scatter normally occurs in the properties of 1Cr–1 Mo–0·25V high-temperature steam turbine rotors. On the basis of linear regression analysis of 35 production rotors and 12 laboratory heats of controlled composition and heat treatment, it has been shown that significant improvements in properties can be achieved by better control of alloying elements, strength, and residual elements. The fracture appearance transition temperature can be decreased by lowering the phosphorus content and the ultimate tensile strength (UTS) and raising the Cr and Mo contents. The rupture strength increases with higher UTS and lower Mn, Mo, Ni, and P contents. Creep ductility improves with higher Mn and Mo and lower Sn, As, Sb, and S contents, V/C ratio, UTS, and rupture time. Metallographic and fractographic examination of broken rupture specimens showed that a higher impurity content and a greater UTS resulted in greater cavitation and intergranular fracture. Additional work is required to understand more fully the complex interactions between properties, residuals, alloying elements, and strength.
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