INFLUENCE OF MICROALLOYING ON THE MECHANICAL-PROPERTIES OF MEDIUM-CARBON FORGING STEELS AFTER A NEWLY DESIGNED POST FORGING TREATMENT

For more than twenty years the classical quench and tempering of mediu m carbon Cr-alloyed steels has been substituted in the production of d rop-forged parts for the automotive industry by a direct continuous co oling of less expensive V-microalloyed steels with lower carbon conten t. However, this simplified treatment has serious limitations concerni ng the yield strength and ductility if compared with the properties af ter quench and tempering. On a group of such V-bearing steels addition ally microalloyed with Ti and Nb and with different N contents, an alt ernative two-step-cooling (TSC) strategy after forging, combined with an additional annealing (AN), has been applied. This new post forging treatment results in a significant improvement of the final mechanical properties. The paper is focused on the particular contributions of a different microalloying in the optimized deformation schedules to imp rove mechanical properties after TSC + AN. The aim of this additional microalloying is to achieve a more homogeneous distribution of ferrite in the final multi-phase microstructure due to a proper austenite con ditioning as well as to make a full use of the strengthening potential of vanadium in these forging steel grades.