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The bending fatigue performance of high temperature (1050 °C) vacuum carburized Nb modified 8620 steel, with niobium additions of 0.02, 0.06 and 0.1 wt pct, was evaluated utilizing a modified Brugger specimen geometry. Samples were heated at two different rates (20 and 114 °C min-1) to the carburizing temperature resulting in different prior austenite grain structures that depended on the specific Nb addition and heating rate employed. At the lower heating rate, uniform fine grained prior austenite grain structures developed in the 0.06 and 0.1 Nb steels while a duplex grain structure with the presence of large (>200 μm grains) developed in the 0.02 Nb steel. At the higher heating rate the propensity for abnormal grain growth was highest in the 0.02 Nb steel and complete suppression of abnormal grain growth was achieved only with the 0.1 Nb steel.

Air disc brakes have been under development in Europe now for many years, and have reached the stage where the technical demands of energy capacity, disc and pad life, and general durability are being met. The focus of development in European brakes has now moved more towards the cost of installation and ease of assembly and service, as the technology matures. Achieving reduced costs, while maintaining the technical capability of the product, has led to the use of new methods of integration of design and industrial engineering such as “Design for Assembly” and Quality Function Deployment, which in turn have demanded changes in organisation. This paper discusses the application of these new techniques, and highlights the benefits of their usage.

Hydraulic disc brakes are now well established in production on both front and rear axles of commercial vehicles up to 11 tonnes (24250-lb) in Europe. Last year saw the introduction of mechanical air disc brakes at 19 tonne (41900-lb) GVM on Renault's flagship, the R420, and more recently their AE500 (using the Mack EE9.503 8 cylinder engine), heralding the imminent widespread adoption of air mechanical disc brakes on many of Europe's premium trucks and buses. This paper discusses the experience gained during testing of these vehicles, highlighting the benefits to be gained from the use of disc brakes, through comparisons of performance, wear, and durability.