A recent literature review of available data for the bainitic creep strength enhanced ferritic steel grade 23 revealed significant variations among available continuous cooling transformation (CCT) diagrams. Substantial differences in these diagrams were noted with respect to the observed transformation products, reported transformation temperatures and the data provided with the CCT diagram. While it is recognised that grade 23 is a complex material exhibiting up to three transformations on-cooling from austenitisation, there does not seem to be a standardised or uniform procedure for the development of CCT diagrams for such metallurgically diverse materials. This paper details development of a CCT diagram for this material through integration of results from thermal analysis, hardness measurements and microstructural observations.

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Eglin steel is a new ultrahigh strength steel that has been developed at Eglin Air Force Base in the early 2000 s. This steel could be subjected to a variety of processing steps during fabrication, each with its own thermal history. This article presents a continuous cooling transformation diagram developed for Eglin steel to be used as a guideline during processing. Dilatometry techniques performed on a Gleeble thermomechanical simulator were combined with microhardness results and microstructural characterisation to develop the diagram. The results show that four distinct microstructures form within Eglin steel depending on the cooling rate. At cooling rates above ,1uC s 21 , a predominately martensitic microstructure is formed with hardness of y520 HV. Intermediate cooling rates of 1 to 0?2uC s 21 produce a mixed martensitic/ bainitic microstructure with a hardness that ranges from 520 to 420 HV. Slower cooling rates of 0?1 to 0?03uC s 21 lead to the formation of a bainitic microstructure with a hardness of y420 HV. The slowest cooling rate of 0?01uC s 21 formed a bainitic microstructure with an apparent carbide constituent at the prior austenite grain boundaries.

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