NATURE OF EUTECTIC CARBIDES IN CARBON STEELS LEDEBURITE CLASS

Stages of formation troostite carbide structure in carbon steels ledeburite class У22А (Russia) obtained by vacuum melting was developed. At the first stage of the technological process, a solid carbide shell is formed along the boundaries of austenitic grains, which in its morphology resembles the inclusion of ledeburite. At the second stage of the technological process, large carbide formations of eutectic type are compacted and cut. At the third stage of the technological process, a threefold matrix is formed with unevenly distributed in the direction of deformation faceted eutectic carbides ranging in size from 5 µm to 20 µm under the conditions of forging production. It was found that the stoichiometric composition of faceted eutectic carbides is in the range of 34 < C < 36 (atom %), which corresponds to -carbide type Fe2C with hexagonal close-packed lattice. The mechanism of transformation of metastable ledeburite into faceted eutectic -carbides of Fe2C type is considered. It was revealed that the duration of isothermal exposure during heating to the eutectic temperature, is an integral part of the process of formation of new excess carbides type Fe2C with a hexagonal close-Packed lattice. It is shown that troostite-carbide structure carbon steel ledeburite class У22А (Russia), with volume fraction of excess -carbide more than 20 %, fully consistent with the highest grades of Indian steels type Wootz. Alloy У22А (Russia) can be described as non-alloy tool steel of ledeburite class, with similar structural and morphological characteristics of die steel type X12 (Russia) or Cr12 (China) and high-speed steel type P6M5 (Russia) or W6Mo5Cr4V2 (China), differing from them only in the nature of excess carbide phase.