FRACTURE-TOUGHNESS OF HETEROGENEOUS MARTENSITE IN LOW ALLOYED STEELS

On the experimental low alloyed MnSiCrMoV steels with various carbon content (0,30, 0,54 and 0,76 % C) the influence of heterogeneous martensitic structure gained by rapid austenitizing of the initial ferritic-carbidic and/or martensitic structure with subsequent quenching and low temperature tempering on strength and fracture properties was investigated. In comparison to homogeneous martensite, the structure of low carbon martensite containing remainders of undissolved carbides in all the steels investigated manifests a substantial increase of fracture toughness without greater loss of strength. In the steel with 0.3 % C the martensitic structure containing microregions with increased content of carbide-forming elements results, in comparison to homogeneous martensite, in the increase of both strength and fracture toughness. The structure of hereditarily modified martensite manifests a substantial increase of strength properties by about 150 MPa without greater loss of toughness, at the same time the transition temperature of impact energy is lower by about 50-degrees-C.