Abstract
A286 iron-base superalloy has been planned to be applied to rotor material of ultra-super critical steam turbine in which main steam temperature is 649°C, because of its high strength at high temperatures. In this case, a large ESR ingot weighing about 40 t is necessary. However, in the large ESR ingot of this material, "A" segregation is easily formed which may deteriorate the properties of the forgings.
Therefore, characteristics of "A" segregation and mechanical properties of the segregated region, comparing with the normal region, in large A286 alloy forgings made from the 1 0001350 mm diameter ESR ingots with different Ti contents have been investigated. The following results are obtained;
1)Lowering Ti content is favorable for reducing "A" segregation.
2) Tensile properties, creep rupture properties, high and low cycle fatigue strength except tensile ductilities below 200°C and low cycle fatigue strength in higher strain than 1.0% are not deteriorated by "A" segregation in A286 alloy with 1.9% Ti.
3) Lowering Ti content improves the tensile ductility and low cycle fatigue strength in higher strain range.
4) Influence of "A"segregation on mechanical properties can be well explained by the difference in hardness between normal and segregated regions after work hardening by each test.
