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 we re investigated in detail. The results reveal that the eutectic carbides pr ecipitated primarily at the dendrite and grain boundaries show various morp hologies from the outer wall to the inner wall along radial direction of th e cast tubes, consisting of the thin film-like carbides, the blocky carbide s, the lamellar carbide clusters resembling the pearlite and the skeleton-l ike carbides. The initial solidification conditions have significant influe nces on the grain morphologies and the distribution of the eutectic carbide s in the cast tubes. Increasing the cooling rate markedly promotes the deve lopment of the columnar grains and restrains the precipitation of the eutec tic 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 stee l tubes. The relationships between the initial solidification conditions an d the solidification processes as well as the creep rupture strength were d iscussed at length. (C) 2000 Elsevier Science S.A. All rights reserved.