Investigation on the effects of microstructure on the impact and fracture toughness of a C–Mn steel with various microstructures

A C–Mn steel was heat-treated to exhibit three types of microstructures with different sizes of ferrite grains and carbide particles. The effects of microstructures on the impact and fracture toughness were studied through comparing the critical events and the local fracture stresses for cleavage fracture which were determined by the morphology and sizes of the grains and the carbide particles. The mechanism was analyzed why the microstructure with coarse grain and coarse carbide presents the inferior impact toughness while the comparable fracture toughness comparing with the microstructure with fine grain and coarse carbide.