Effect of titanium microalloying on microstructure and mechanical properties of vanadium microalloyed steels for hot forging

Effect of titanium microalloying on the microstructure and mechanical properties of vanadium microalloyed steels for hot forging was studied. Titanium microalloying improves the mechanical properties mainly through refining the austenite grains. When the heating temperature is in the range of 1050–1300 °C, the austenite grain diameter is decreased from 77–133 to 26–68 μm by titanium microalloying. With the decrease in austenite grain diameter, the final microstructure is refined significantly, and the high misorientation boundaries are increased. After the steel is heated at 1200 °C (the common hot forging temperature) and cooled slowly, titanium microalloying decreases the yield strength from 548.4 to 519.4 MPa, and the tensile strength decreases from 842.7 to 808.7 MPa. However, the elongation increases from 19.0% to 21.4%, and the impact energy increases from 9.8 to 38.2 J. V–Ti steel has a better combination of strength, plasticity and toughness than V steel. In addition, the nucleation of intragranular ferrite idiomorphs is promoted by titanium microalloying, which may have a beneficial effect on the property of steels with coarse microstructure caused by the critical deformation in hot die forging.