Effects of Mn, Si and Cr addition on reverse transformation at 1073 K from spheroidized cementite structure in Fe-0.6 mass% C alloy

The effects of addition of Si, Mn and Cr on the kinetics of reverse transformation at 1073 K from the spheroidized cementite structure obtained by heavy tempering of high carbon martensite are investigated. The rate for reverse transformation is the fastest in the Fe-0.6 mass% C binary material, and becomes slower with the addition of Mn, Si and Cr. In particular, the retarding effect of Cr addition is remarkable, and holding times orders of magnitude longer than for other alloys are necessary to complete the reverse transformation. Based on thermodynamics and TEM/EDS analyses, it is supposed that austenite growth is controlled by carbon diffusion in specimens with Si and Mn added, as well as the Fe-0.6 mass% C binary material, while a decrease in the carbon activity gradient with the addition of these elements results in slower reversion kinetics. However, in the Cr-added specimen, Cr diffusion is necessary for austenite growth, yielding extremely sluggish reaction kinetics.