The structure, mechanical and functional properties of ultrafine-grained low-carbon steels
have been studied after severe plastic deformation (SPD) by high pressure torsion (HPT) and equalchannel
angular pressing (ECAP). It is revealed that HPT of low carbon steels at a temperature
below 0.3 Tm leads to the formation of nanocrystalline structure with a grain size of <100 nm or a
mixture of oriented substructure and nanograins. ECAP under similar conditions leads to the
formation of submicrocrystalline structure with a grain size of 200-300 nm. The initial martensitic
state compared with the initial ferritic-pearlitic state of the low-carbon steels results in formation of
finer structure after SPD and less intense grain growth upon heating, i.e., results in a higher thermal
stability. Low-carbon low-alloy steels after ECAP are characterized by high strength (UTS > 1000
MPa) and plasticity (EL = 10-15%). The high-strength state after ECAP is retained upon tensile test
testing up to a temperature of 500°C. The submicrocrystalline low-carbon steels after ECAP
processing and subsequent heating is characterized by an increased impact toughness at test
temperatures down to -40°C.
Heat Treatment Effect on Lath Martensite
