Applications of steels for new forged automotive components require a complete understanding of material properties and design requirements. Today there are many potential combinations of steel bar compositions and surface hardening methods that can be employed. Generally plain carbon steels, alloy steels, and microalloyed steels are used for forged bar applications and nitriding, induction hardening, or fillet rolling are applied to selected highly-stressed areas to produced optimum performance. At the preliminary stage in the design of a new model several factors must be considered. Cost, infrastructure requirements, and lead time are considered together to ensure proper selection of material alloy and hardening method. Currently many crankshaft forging companies have eliminated quenching and tempering (Q&T) heat-treatment facilities from their shops, and thus in the production of crankshafts it is not easy to apply alloy steels that require Q&T processing. The use of microalloyed steels in crankshafts have been shown to be a viable alternative to Q&T steels, particularly in engines that require significant improvements in performance (1). High strength of microalloyed bar steels develop desired properties through additions of microalloying elements such as V, Ti, Nb (2) in conjunction with control of processing which may include direct cooling. For specific applications, the use of microalloy additions provides the optimum method to tailor the material properties for a specific crankshaft application. In this paper, the development and choice of steel for a new crankshaft application are used to illustrate the stages in the process of selecting materials for new applications. The major processes required in the production of new prototype crankshafts were investigated and highlights of the results demonstrate a methodology for material selection. The goal of this study is to optimize selection of the appropriate microalloyed bar steel that simultaneously satisfies strength requirements to meet the criteria in specific areas listed below for high performance as well as achieves the required properties, i.e. hot formability and machinability, required to successfully and economically produce the parts. Specific mechanical properties that must be met include high fatigue strength in fillets and high surface hardnesses on journal surfaces to prevent abrasive wear at high contact forces. For reference, Figure 1 summarizes the steps involved in evaluating materials for new crankshaft applications.
Application of high strength microalloyed steel in a new automotive crankshaft
Anwendung des hochfesten mikrolegierten Stahls in einer neuen Fahrzeugkurbelwelle
2006
8 Seiten, 11 Bilder, 2 Tabellen, 7 Quellen
Conference paper
English
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