구상흑연주철(球狀黑鉛鑄鐵)의 3상혼합조직(相混合組織)의 변태거동(變態擧動)에 관(關)한 연구(硏究)

A Study on the Transformation Behaviors of a Multi-phase (Ferrite-Bainite-Martensite) in Ductile Cast Iron

Ductile cast iron(DCI) with a multi-phase(ferrite-bainite-martensite) structures was produced by various special heat treatment. Intercritical heat treatment(I. C.), intermediate heat treatment(I. M.) and step quenching(S. Q.) were used to strengthen and toughen the fracture initiation sites such as graphite-marix interfaces and eutectic cell boundaries in DCI. The purpose of this study was to investigate of DCI by the special heat treatment. (I. C., I. M., and S. Q.) At a result, bainite nucleation rate at higher temperature was higher than that of at lower temperature, and shapes of bainite and martensite became bar /spheroidal type with increase of isothermal transformation time.