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.

Static Recrystallization Behavior of Non-Quenched and Tempered Steel 38MnSiVS

“…Where X SRX is the static recrystallization volume fraction ; t is the delay time between two passes (s); n is the constant related to experimental material , and the value is not more than 1 [8] ; t 0.5 is the time when the recrystallization volume fraction reaches 50% (s), and it can be expressed:…”

“…Dynamic recovery and dynamic recrystallization occur when the metal reaches critical strain during thermal deformation. In the case of multi-pass deformation, the critical strain condition is not reached in the first deformation, and static recovery and static recrystallization occur between the passes [7,8] . For non-quenched and tempered steels, static softening and grain refinement of the static recrystallization process play a key role in improving performance.…”

Thermomechanical Treatment of Steels - A Real Disruptive Technology Since Decades

“…Meanwhile, the TMCP principle to get fine microstructures has also been used for low and medium carbon bainitic steels, high strength bainitic steel, Dual Phase steel, precipitation hardened ferritic‐pearlitic steel, TRIP‐Steel, medium carbon steels, Spring steels, eutectoid and bearing steels, Mn‐Hadfield‐steel, over‐eutectoid steel, Creep resistant 9%Cr‐steel, and stainless steels . Automotive sheet metals are also TM‐rolled to obtain fine microstructures before cold rolling and annealing, but they will be treated in another paper of this issue.…”