低りん・低硫13Cr-4Ni鋳鋼製水車ランナー

抄録

  While 13Cr-4Ni cast steels are widely used for hydraulic turbine runner castings, it had been difficult to reduce phosphorus and sulfur content of these steels because of their high chromium content. Recent advanced ladle refining process and Duplex process have enabled one to obtain heats with P and S less than 0.01 percent. Effects of the two elements on mechanical properties were investigated using specimens taken from a hydraulic runner casting with the following results. (1) Ductility and shelf energy are improved with a decrease of S content, whereas mechanical strength and FATT depend on tempering conditions regardless of S and P content. (2) Lowering P content retards the precipitation of M₂₃C₆ carbide in austenite range and consequently suppresses the carbide-induced grain boundary brittleness. (3) Superior toughness and fatigue properties of the 13Cr-Ni steel resulting from low P and S content greatly contribute to safety and reliability of hydraulic runner castings.