Formation of Widmanstatten Ferrite and Grain Boundary Ferrite in a Hypereutectoid Pearlitic Steel

Accompanied by the formation of pearlite, Widmanstatten ferrite (WF), grain boundary ferrite and cementite are often found to nucleate at the prior austenite grain boundary during isothermal heat treatment. A hypereutectoid pearlitic steel transformed isothermally at temperatures ranging from 607 to 707 degrees C was investigated to clarify the evolution of different phases. At 607 degrees C, WF grains, which had a Kurdjumov-Sachs orientation relationship with the remaining austenite, were found to be aligned with the grain boundary. At 707 degrees C, lath WF grains, which were arranged parallel to each other, were at a certain angle to the grain boundary. The formation of pearlite showed two-stage kinetics in the dilatometer curve, and the grain boundary's abnormal structure was suppressed.