Low‐temperature annealing and graphitizing of white‐solidified low‐alloy cast irons

Abstract Hypoeutectic iron‐carbon and iron‐carbon‐silicon model alloys as well as conventional cast irons GJL‐250 mod and EN‐GJS‐600‐3 have been produced and processed by different solidification techniques, i. e. mold casting, electron beam surface remelting and melt spinning. The white‐solidified alloys exhibit different degrees of microstructural refinement indicated by a secondary dendrite arm spacing of 0.3 μm–12 μm. The effects of microstructural refinement and silicon content on the hardness as well as on coarsening of cementite and graphitizing at temperatures of 540 °C to 670 °C have been investigated. The hardness of the as‐solidified alloys increases with decreasing secondary dendrite arm spacing and increasing silicon content. High silicon content effectively retards coarsening of pearlitic cementite, and thus is beneficial to retain the hardness at small thermal load. On the downside, high degree of microstructural refinement and high silicon content promote and accelerate graphitizing at temperatures > 600 °C. The results are discussed in terms of the applicability of a recently developed two‐step surface treatment for cast irons, i. e. electron beam remelting followed by nitriding.