Application of thermomechanical treatment on medium‐carbon microalloyed steels continuously cooled from forging temperature

Abstract

In the high‐production‐drop‐forging of parts for automobile and truck engines the classical quench and tempering (QT) of low‐alloyed steels is nowadays ‐ in a lot of plants in Europe ‐ substituted by direct continuous cooling (CC) of microalloyed steels without the necessity of additional heat treatment and expensive straightening as well as stress relieving cycles. Nevertheless, there are some limitations on strength and toughness achievable by this technique. On two commercial medium‐carbon (0.3%C) steels microalloyed with vanadium or vanadium and titanium, modified deformation parameters were applied. The mechanical properties, determined by the tensile test, can be improved by decreasing the deformation temperature. Nevertheless, the values of yield strength (resp. 0.2%‐proof stress) as well as reduction of area remain inferior to those after QT of the same steels.

Enhancing the Mechanical Properties of Vanadium-Microalloyed Medium-Carbon Steel by Optimizing Post-Forging Cooling Conditions

“…Of the three aforementioned factors, the variation of post-forging cooling conditions could obtain different microstructural characteristics and thus has an extraordinary influence on the final mechanical properties of MA steels [2][3][4][5][8][9][10]. Increasing cooling rate enhances grain refinement and increases the proportion of hard phase of pearlite or the formation of high hardness phases such as bainite and martensite.…”

“…For MA steels, it also significantly influences the precipitation hardening effect of microalloying elements [4]. Therefore, different post-forging cooling methods have been used to optimize the mechanical properties of MA steels [1,2,[11][12][13]. Initially, direct continuous cooling after finish forging was utilized to improve mechanical properties [1,2,13].…”

“…MA forging steels are usually characterized by a small addition of microalloying elements to a basic C-Mn composition, and then the desired strength levels and other properties of hot-forged components could be obtained by controlled cooling after thermomechanical forging. The forging parameters, post-forging cooling strategies as well as compositions of MA steels have a significant effect on the microstructural characteristics, and thus the final mechanical properties of forged components, and therefore, many researches have been conducted [2][3][4][5][6][7][8][9][10].…”

Fatigue behavior of a multiphase medium carbon V-bearing microalloyed steel processed through two thermomechanical routes

“…Recently, a two-step cooling and annealing (TSCA) treatment following controlled forging was developed to produce multiphase (ferrite-bainite-martensite, F-B-M) microstructures that displayed tensile properties similar to those of Q&T steels. It was reported that a decrease in the final deformation temperature led to a finer grain size (beneficial for toughness) and also promoted the formation of ferrite , 1998Kaspar et al, 1997). As part of a detailed investigation to develop better fatigue resistant and cost effective MA steels through process control, the processing parameters of the TSCA treatment (finish forging temperature, quenching temperature, annealing temperature and time) were optimized to get the desired microstructure and tensile properties in the medium carbon microalloyed steel 38MnSiVS5 (Sankaran et al, 2003a).…”

Static and dynamic fracture toughness of a medium carbon microalloyed steel of three different microstructures

“…It was reported that a decrease in the final deformation temperature led to a finer grain size (beneficial for toughness) and also promoted the formation of ferrite. [3,4,5] The present investigation forms a part of an attempt to improve the tensile properties and the fatigue resistance of the automotive grade microalloyed steel 38MnSiVS5 through thermomechanical processing to produce a F-B-M microstructure. [6][7][8][9] Here an attempt was made to optimize the parameters (finish forging temperature, quenching temperature, annealing temperature and time) of the TSCA treatment.…”