Mechanical Properties and Fracture Characteristics of Ultra-Microduplex Structure in High Carbon Steel

The ultra-microduplex structure was fabricated in the high carbon steel with a fully pearlitic structure after severe plastic deformation. The sizes of ferrite grains and cementite particles were about 0.4 μm and 0.1~0.2 μm, respectively. The mechanical properties of the ultra-microduplex structure were investigated using mini-tensile tests and the morphologies of fracture surfaces were observed with scanning electron microscopy (SEM). The results show that the tensile strength of the ultra-microduplex structure and the lamellar pearlite are almost at the same level, but after warm deformation, the yield strength was obviously increased and correspondingly, the elongation and the reduction of area were 19.2%, 32.1%, respectively, which are markedly higher than those of the lamellar pearlite. The tensile fracture of the ultra-microduplex structure is typical ductile fracture, however the fracture of original lamellar pearlite appears a mixture of cleavage fractures and quasi cleavage fractures.