Increase in Impact Strength During Bainite Structure Formation In HY-TUF High-Strength Steel

The high-strength structure and properties of silicon-containing steel HY-TUF used in the aerospace industry and engineering for the manufacture of heavy-duty components is studied, including a dilatometric study of austenite transformation during continuous cooling in the range of constant cooling rates of 0.025–75°C/sec and during isothermal exposure in the bainitic range. The mechanical properties of HY-TUF steel after traditional quenching and tempering and isothermal quenching are determined. It is shown that during the isothermal exposure at 370–430°C and above low toughness upper bainite is formed, containing residual austenite with reduced carbon content. The relationship between the toughness of the bainitic structure and the reduction of area is shown, which is explained by the stability of residual austenite under load. It is substantiated scientifically that the best combination of toughness and strength of HY-TUF steel may be achieved after isothermal quenching in the lower bainite formation temperature range.