Automotive engine parts composed of heat resistant ferritic cast steel having excellent thermal fatigue resistance

摘要

A heat-resistant ferritic cast steel having excellent thermal fatigue resistance, consisting, by weight, of 0.25 to 0.45% C, 0.3 to 2.0% Si, not more than 1.0% Mn, 17 to 22% Cr, at least one kind selected from the group consisting of not more than 6% Co and not more than 1.5% Ni, the amount of %Co + 3 %Ni being in the range of 1 to 6%, 0.001 to 0.1% of at least one kind selected from the group consisting of Y and rare earth elements, and the balance Fe and incidental impurities, the ferritic cast steel being composed of a structure in which a ferrite (c) and M₂₃C₆ carbide (b) are dispersed in δ ferrite (a). With this specific composition, even at high temperatures, there can be maintained the structure which has the a ferrite (c) and the M₂₃C₆ (b) dispersed in the δ ferrite (a), with the result that there is obtained an excellent thermal fatigue resistance, and in this structure, the transformation under heating will not occur even at a temperature of about 1,000°C. The steel of the present invention is particularly suited for a turbo rotor casing, an exhaust manifold, etc., of an automobile.