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A new microalloyed, multi-phase low carbon steel has been developed as an alternative to the QT steels which have traditionally been used in the fabrication of high strength cold forged products. The benefits of this new steel include: (1) the elimination of spheroidize annealing prior to cold forming; (2) the elimination of the QT heat treatment after the deformation; and (3) the ability to achieve in the final component yield strengths of desired levels, high fatigue resistance and very high notch toughness. The excellent properties exhibited by this steel are a direct result of the advanced thermomechanical or controlled processing of the austenite during bar and/or rod rolling. This paper will first briefly review the physical metallurgy of this steel as it pertains to cold forming. This will be followed by a review of industrial trials where various components have been cold forged from this steel.

High strength fasteners and cold forgings are typically produced from carbon or low alloy steel. While the final components usually exhibit adequate mechanical properties such as strength, toughness and fatigue resistance, the cost of producing components using these conventional steels is unattractively high. A large portion of these costs originate in the nature of the steel chosen for fabrication. The cumulative cost of total material-related processing, e.g. spheroidize annealing required before cold forging plus that of the QT and stress relieving heat treatments following cold forging, renders the total process rather cost ineffective. An ideal steel for cost-effective cold forging must exhibit the following characteristics: (i) Good bulk formability in the hot rolled bar or rod form, (ii) Should be capable of generating high strengths during the cold forging process, and (iii) Should retain good toughness in the final component.

Forged components to be used in high strength applications have traditionally been heat treated after forging. This processing route unfortunately suffers from many technical and economical shortcomings. The first attempt to overcome these difficulties led to the development of medium carbon microalloyed steels for bar applications in the early 1970's. While these steels did not require heat treatment, their strengths were limited. Furthermore, the notch toughness of these steels was rather poor. The limitation on strength and toughness have hindered their acceptance as a substitute for the conventional QT steels, especially in safety critical components. In addition, these shortcomings eliminate the possibility of downsizing through redesign. Since the tempered martensite and the microalloyed ferrite-pearlite steels have obvious limitations, an alternative microstructure had to be developed.