Centrifugal casting of bimetallic tubes - using nickel barrier layer to prevent carbon diffusion between metal layers

摘要

In the centrifugal casting of bimetallic tube blanks by successive casting of a base layer with flux and a cladding layer, a layer of Ni, in amt. 2-3% (by wt. of the base layer), is cast on the surface of the base layer when it has cooled to about 100-200 degrees C below its solidus temp. and then the cladding layer is cast onto the Ni layer, the Ni content of the cladding metal being 11-18% of that in the cladding layer after casting. From the start of casting the Ni, the rotational speed of the mould is controlled to be 30-40% of its starting speed. The method allows tubes of length to-dia. ratio >8-10 to be cast in different steel types, and gives a base layer/cladding weld joint of improved notch ductility without post-treatment. This improvement is due to the presence of Ni which acts as a diffusion barrier for C.