Thermo-mechanical treatment of forged products of Ti-V-B microalloyed steel

The work presents research results of the influence of thermo-mechanical treatment via forging on microstructure and mechanical properties of newly elaborated microalloyed steel containing of 0.31 %C, 1.45 %Mn, 0.033 %Ti, 0.008 %V and 0.003 %B. Conditions of forging with the method of thermo-mechanical treatment were developed basing on the analysis of precipitation kinetics of MX interstitial phases in a solid solution, plastometric examinations and investigations of the kinetics of supercooled austenite phase transformations. Applied thermo-mechanical treatment allows obtaining fine-grained microstructure of austenite during hot-working and production of forged parts, which acquire advantageous set of mechanical properties and guaranteed crack resistance after controlled cooling from finishing plastic deformation temperature and successive tempering. Forgings produced with the method of thermo-mechanical treatment, consecutively subjected to tempering in the temperature range from 550 to 650°C, reveal the values of YS0.2 equal from 954 to 878 MPa, UTS from 1040 to 939 MPa, KV ^-40 from 50 to 69 J and hardness ranging from 330 to 300 HB.