Influence of microalloying on the mechanical properties of medium carbon forging steels after a newly designed post forging treatment

Abstract

For more than twenty years the classical quench and tempering of medium carbon Cr‐alloyed steels has been substituted in the production of drop‐forged parts for the automotive industry by a direct continuous cooling of less expensive V‐microalloyed steels with lower carbon content. However, this simplified treatment has serious limitations concerning the yield strength and ductility if compared with the properties after quench and tempering. On a group of such V‐bearing steels additionally microalloyed with Ti and Nb and with different N contents, an alternative 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 improve 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 conditioning as well as to make a full use of the strengthening potential of vanadium in these forging steel grades.