THERMOMECHANICAL TREATMENT OF Ti-Nb-V-B MICRO-ALLOYED STEEL FORGINGS

The work presents the research results of the influence of thermomechanical treatment through forging on the microstructure and mechanical properties of newly elaborated micro-alloyed steel containing 0.28 % C, 1.41 % Mn, 0.028 % Ti, 0.027 % Nb and 0.019 % V. The applied thermomechanical treatment makes it possible to obtain a fine-grained microstructure of austenite during the hot working and the production of forged parts that acquire an advantageous set of mechanical properties and a guaranteed crack resistance after controlled cooling from the finishing plastic-deformation temperature and the successive tempering. The forgings produced with the method of thermomechanical treatment, consecutively subjected to tempering in the temperature range from 550 degrees C to 650 degrees C, have YS0.2 from 994 MPa to 939 MPa, UTS from 1084 MPa to 993 MPa and KV-40 from 77 J to 83 J.