Effect of Hot Forging on Microstructural Evolution and Impact Toughness in Ultra-high Carbon Low Alloy Steel

The effect of a hot forging ratio on the microstructural variation and tensile properties of ultra-high carbon low alloy steel was investigated. Scanning electron microscopic analyses depict that with an increase in the hot forging ratio, the thickness of the network and acicular proeutectoid cementite decreased. Moreover, the lamella spacing and thickness of the eutectoid cementite decreased and broke up into particle shapes, which then became spheroidized as the hot forging ratio increased. Furthermore, when the forging ratio exceeded 65%, the network and acicular shape of the as-cast state disappeared. By increasing the hot forging ratio, the tensile strength and elongation remained below 50%, but they increased rapidly with an increase in the forging ratio. Strength and elongation were not affected by the thickness of the proeutectoid and eutectoid cementites, but were greatly affected by the shape of the proeutectoid cementite. Due to the decrease in the austenite grain size, as well as the spheroidization of the cementite, the tensile strength and elongation sharply increased.