New post forging treatment of medium carbon microalloyed steels

Abstract

In drop forging of parts for the transport industry the classical quench and tempering (QT) of alloyed steels is nowadays substituted by direct continuous cooling (CC) of microalloyed steels with elimination ofquench cracking and expensive straightening and 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 forging parameters and a new two-step cooling (TSC) strategy combined with an additional annealing were applied. Some increase in manufacturing costs, when compared to CC, can be justified by a significant increase in strength and ductility. The improvements attainable through such a modified treatment give evidence of the large potential of multi-phase ferrite-containing microstructures as a substitute ofa tempered martensite. Neuartige Schmiedenachbehandlung von mikrolegierten Stahlen mit mittlerem Kohlenstoffgehalt. Beim Gesenkschmieden von Kraftfahrzeugteilen wird heutzutage die klassische VergOtung (QT) von legierten Stahlen durch eine direkte kontinuierliche AbkOhlung (CC) von mikrolegierten Stahlan ersetzt. Dadurch kennan die RiBbiidungsgefahr eliminiert und das SpannungsarmglOhen und das Richten eingespart werden. Mit dieserTechnologie lassen sich allerdings nicht immer zufriedenstellende Festigkeits-und Zahigkeitseigenschaften erreichen. Auf zwei handelsObliche mit Vanadium oder mit Vanadium und Titan mikrolegierte Stahle mit mittlerem Kohlenstoffgehalt (0,3% C) wurden modifizierte Umformparameter und eine neuartige zweistufige AbkOhlung (TSC) in Kombination mit einem nachtraqllchan GIOhen angewendet. Diese im Vergleich zurCCaUfwendigere Behandlung kann durch eine bemerkenswerte Verbesserung von Festigkeit und Duktilitat gerechtfertigt sein. Die erreichten Ergebnisse verdeutlichen das Potential von mehrphasigen ferrithaltigen GefOgen, die als Ersatz fOr einen angelassenen Martensit eingesetzt werden kennan,Figure 1. Two designs for the manufacturing of crankshafts by drop forging. Quench and temper (QT) operation (a) requiring expensive straightening and stress relieving cyclesand -as a substitute-continuous cooling (CC) from the forging temperature (b)

On a New Two‐Step Air Cooling Method Following Thermomechanically Controlled Rolling: Microstructural Evolution and Mechanical Properties of a High‐Strength Multiphase Medium Carbon Microalloyed Steel

“…It is noticed that the average grain size of PF is approximately the same in both the FAC (%9 μm in FAC1 and FAC2) and both the CAC (%15 μm in CAC1 and CAC2) steels as presented in Table 3. According to Kasper et al, [37] due to a low start cooling temperature, a larger fraction of ferrite develops as a result of a longer ferrite transformation time. Simultaneously, the prolonged formation time leads to a large fraction of V (C, N) precipitates in ferrite when compared with a high start temperature.…”

Critical Assessment 22: bainitic forging steels

“…In the 1980s, precipitation hardened ferriticpearlitic steels were developed, which needed fast cooling to about 600°C followed by an isothermal transformation and precipitation of V(C,N)-carbonitrides. [4][5][6][7][8][9] A typical reference steel is the grade 38MnVS6 having about 0.1 wt-% V, others can be found in ISO-standard ISO 11692. Some improvements have been achieved using microalloying with small amounts of Ti and Nb.…”