Mechanical Property - Microstructure Relations in Iron-Carbon Alloys from 1.0 to 5.2% Carbon

Mechanical property studies of Fe-C alloys, from 1.0 to 5.2 wt.% carbon, became of commercial interest because of their superplastic properties. Optimal superplasticity was achieved with carbon contents in the range of 1.0 to 2.0 wt % carbon. These steels are known as ultrahigh carbon steels (UHCSs). The basis for this success is the creation of a two-phase structure of ultrafine ferrite grains containing fine iron carbide particles. Similar superplastic behavior is achieved with iron-carbon steels in the carbon range from to 2.1 to 4.2% C (white cast iron and ductile iron) and even up to 5.2% C (iron carbide). A number of commercially viable components were successfully formed. However, high-strain-rate superplasticity could not be achieved in the UHCSs and production of commercial components was postponed. Current studies on UHCS-based materials center on optimizing processing steps for manufacture of strong and tough UHCS products involving modem continuous-casting and metal working procedures. Creation of ultra-fine pearlite in UHCS by simulated production processing has shown remarkable mechanical properties at ambient temperatures. A divorced eutectoid transformation, coupled with associated deformation (DETWAD), is used to develop fully spheroidized structures of ultra-fine ferrite grains in UHCS. The modem studies on UHCSs has a fascinating relation to the history of ancient Damascus steel and Japanese swords that are known to contain an ultra high amount of carbon.