The eutectic carbides and creep rupture strength of 25Cr20Ni heat-resistant steel tubes centrifugally cast with different solidification conditions

The eutectic carbides and creep rupture strength of 25Cr20Ni heat-resistant steel tubes centrifugally cast with different solidification conditions were investigated in detail. The results reveal that the eutectic carbides precipitated primarily at the dendrite and grain boundaries show various morphologies from the outer wall to the inner wall along radial direction of the cast tubes, consisting of the thin film-like carbides, the blocky carbides, the lamellar carbide clusters resembling the pearlite and the skeleton-like carbides. The initial solidification conditions have significant influences on the grain morphologies and the distribution of the eutectic carbides in the cast tubes. Increasing the cooling rate markedly promotes the development of the columnar grains and restrains the precipitation of the eutectic carbides, while an applied electromagnetic field during the centrifugal solidification induces a notable grain refining and a marked change of the precipitation zones of the eutectic carbides from the dendrite boundaries to the grain boundaries. The applied electromagnetic markedly improves the creep rupture strength of the centrifugal cast 25Cr20Ni heat-resistant steel tubes. The relationships between the initial solidification conditions and the solidification processes as well as the creep rupture strength were discussed at length.