Abstract
Effects of lowering Si and impurities on temper embrittlement and creep rupture strength in Cr-Mo-V steel were investigated, using specimens with various amounts of Si (0.020.26 wt%) and embrittlementfactor X (4.3-25.4).
(1) Microstructure of samples with a heat treatment corresponding to the center position in a large rotor was completely bainitic without ferrite, even though with reducing Si content to 0.02 wt%.
(2) Temper embrittlement susceptibility decreased with lowering Si content and X. Low Si low X steelwas not embrittled by the step-cooling treatment.
(3) Creep rupture strength of low Si and low X steel remarkably increased beyond that of high Si and high X steel.
(4) A low Si and low X turbine rotor of actual size (32t) was manufactured as a trial based on the above basic investigation, and it was proved that this had higher creep rupture strength than that of commercial one, and was not embrittled by aging at elevated temperature.
