Improving the impact toughness of the Hy-Tuf steel by austempering

The microstructure and mechanical properties of the high-strength Hy-Tuf steel are studied after different heat treatment modes – conventional oil quenching and tempering, austempering in the bainite transformation temperature range. It is shown that the tempering embrittlement of the Hy-Tuf steel can be observed at temperatures ranging between 400 and 500 °C. The highest impact toughness of the studied steel for the case of conventional oil quenching and tempering (1.2 MJ/m2) can be achieved after high temperature tempering (600 °C), which also leads to the deterioration of tensile strength down to 800…900 MPa. The unique combination of high tensile strength (above 1300 MPa), elongation (up to 15%) and impact toughness (1.1 MJ/m2) is obtained after austempering at a low transformation temperature.