Mitigating the hardness loss due to divorced eutectoid transformation in pearlitic steels: influence of the cooling rate and austenitization temperature.

Divorced eutectoid transformation (DET) in pearlitic steels results in spheroidized cementite morphology instead of characteristic lamellar structure of pearlite. In case of welding, spheroidized areas in the heat affected zone exhibit significantly lower hardness than surrounding pearlite potentially acting as weak spots that compromise mechanical reliability. This study investigates strategies to mitigate the detrimental effects of DET by examining the influence of cooling rate on transformation kinetics, cementite morphology, and final hardness in a hypereutectoid steel austenitized at 740, 770, and 800 °C. It is demonstrated that at lower austenitization temperatures, DET dominates across all cooling rates until the formation of martensite starts to take place. For the austenitization temperature of 800 °C the fraction of lamellar cementite grows with increasing cooling rate allowing to partially compensate the hardness loss. However, a highly inhomogeneous cementite morphology is observed, with fully lamellar grains occurring adjacent to fully spheroidized ones. The findings are summarised in two continuous cooling transformation diagrams, followed by a discussion of potential strategies for minimizing the hardness loss associated with DET.