Achievement the strength level of 2400-2500 MPa in the ХН3МФС-type steels with different carbon contents

The possibility of obtaining high strength of about 2400-2500 MPa is studied on the samples of high-purity steels 45ХН3МФСА, 55ХН3МФСА and 65ХН3МФСА melted in a  vacuum induction furnace. Research efforts suggests that it is not possible to receive  high strength of the steel 45ХН3МФСА even after high-temperature thermomechanical treatment (HTMT). It is possible to receive the strength level of 2400-2500 MPa on the steels 55ХН3МФСА and 65ХН3МФСА after tempering at 150 and 200 oC each after quenching and HTMT. In this case the impact strength and plasticity steels after HTMT are at on quite a satisfactory level (δ = 9-13%, ψ = 28-42%, KCU = 0,40-0,46 MJ/m2). The study of the destruction mechanisms undertaken on the fractures of the impact samples showed that the reduction of impact strength of the samples after quenching and tempering at the temperatures in excess of 250 ° C is explained by activation of intergranular fracture, which is associated with the manifestation of irreversible temper brittleness. HTMT reduces the tendency of high-strength steels to irreversible temper brittleness, so after tempering at 300 ° C in the fractures of the samples subjected to HTMT facets of quasi-chip and pits are observed.

high-strength state, HTMT.