4. Conclusions
The eutectoid reaction of a hypereutectoid high manganese steel was investigated. The steel samples underwent solution heat treatment at 1373 K, followed by isothermal holding at low temperatures. Various forms of proeutectoid cementite exist in the austenite as either grain boundary precipitates or Widmanstätten plates at temperatures below 1048 K. The Widmanstätten plates feature either side-plates from the grain boundary allotriomorphs or intragranular plates in the austenite. At temperatures below 1023 K, in addition to the proeutectoid carbide, lamellar ferrite plates accompany M3C Widmanstätten plates to form complex Widmanstätten plates. Complex Widmanstätten plates are product phases from the eutectoid reaction. Thus, the upper temperature limit for the eutectoid reaction of the Fe–C–Mn alloy is between 1023 K and 973 K. Besides the complex Widmanstätten plates, pearlite nodules composed of lamellar ferrite and cementite are involved in the eutectoid reaction at temperatures below 973 K. Normally Widmanstätten plates appear before pearlite nodules. Complex Widmanstätten plates are similar to the Widmanstätten (cementite + ferrite) in inverse bainites of hypereutectoid steels. However, Complex Widmanstätten plates appear just below the eutectoid temperature. Thus, two types of product phases from the eutectoid reaction are discovered in the austenite. One is pearlite of lamellar ferrite and cementite, and the other is complex Widmanstätten plates of (cementite + ferrite).