On four grades of medium carbon V‐bearing steels with additional Ti and Nb microalloying hot deformation tests were conducted as a simulation of hot forging. The aim of the study was to suggest general guidelines for the design of deformation patterns and cooling conditions of austenite. Both the resulting flow stresses and the strengthening/softening behaviour were taken into consideration. The maximum flow stresses appear to be insensitive both to the variation of microalloying and to the design of the deformation schedule over the range tested. Nevertheless, large differences can be achieved regarding austenite strengthening, especially its residual value at the begin of the γ‐α‐transformation which is decisive for the subsequent transformation process. A substantial effect of the final deformation temperature and the type of microalloying was ascertained.

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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.

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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)