Improved toughness in a bainitic 38MnV7 steel

Abstract

High toughness can be obtained in médium carbón microalloyed bainitic stee (38MnV7) after a careful control of the chemistry and heat treatment. A specific chemical composition of 38MnV7 steel has been developed , providing impact energies after Charpy-V tests at room temperatura as high as 40J (the steel in bainitic state). Present work is oriented to an optimization of the above chemical composition by control of the Transformation Time Temperature (TTT) curves as well as the Precipitation Time Temperature (PTT) curves of the present microalloyings elements. To attain this purpose six different casting were prepared, ranging the chemical composition as follows %C:0.35-0.46, %Mn: 1.33-1.84, %V: 0.066-0.14 and Ti: 0.010-0.025. To appropriate design the thermal cycle , TTT curves were determined for each steel at two austenitization conditions , in order to promote fine and large initial grain sizes. Additionally, the PTT curves of each Steel were also determined. Results are finally discussed in terms of the chemical composition , initial microstructure and precipitates interaction with the bainite nucleation.