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Today, most bearings for automotive transmission operate in an environment of severe debris contaminated lubrication. Thus, to develop the bearings that have a long life under the lubrication environment, micro-alloyed forging steel with a vanadium element based on medium-carbon steel and a carbonitriding heat-treatment process have been developed. Initially, the variation of grain size caused by an amount of aluminum and nitrogen was investigated. The hot deformation behavior was evaluated by means of a Gleeble tester. In general, it is extremely difficult to obtain sufficient nitrogen in the case-hardened layer by a conventional carbonitriding process. However, the application of the newly developed steel has not only the increment of nitrogen content in the case-hardened layer, but also the additional benefit that heat treatment costs could be cut effectively. In addition, we have investigated the retained austenite and precipitation behavior of V(CN), and the evaluated rolling contact fatigue life of a heat-treated specimen. As a result, we identified that the fatigue life of developed steel samples, under contaminated lubrication environment, is about five times better than comparative steel. The micro-structural degradation mechanism during fatigue testing was elucidated.
An experimental investigation was made to evaluate two vanadium-base sheet alloys for aerospace applications in the 1,800 F to 2,400 F (1,260 K to l,590 K) temperature range. The investigation consisted of mechanical property tests both at room and elevated temperatures and oxidation tests on coated and uncoated material. Three silicide diffusion coatings were evaluated by continuous and cyclic oxidation testing to determine their protective qualities. An X-ray study, a metallographic examination, and hardness measurements were made to identify and locate the elements and compounds present in the coating and substrate before and after elevated-temperature exposure. Fabrication and joining of the alloys are discussed. A description of the equipment and procedures utilized in performing the evaluation tests is included.
The average operation temperature of rolling element bearings in standard applications is rising. Due to this advancing demand, the chemical composition of martensitic bearing steels like 100Cr6 (DIN 1.3505; SAE 52100) and 100CrMnSi6-4 (DIN 1.3520) has to be adapted. To enhance the tempering resistance of these steels several alloying approaches concerning the contents of silicon and manganese were tested. The central point of interest in the presented investigation was the influence of the new alloy concept on the lifetime of ball bearings. It could be shown that the lifetime of artificially damaged bearings containing 1.5 % silicon is significantly higher compared to alloys with lower silicon contents. At test temperatures of 120°C and Hertzian contact stresses of approximately 3200 and 3400 MPa, the L50 lifetime was about three times higher with 1.5 % silicon alloyed steels. The further characterization of the investigated alloys consisted of soft turning and hard grinding tests, of stress-strain tests, fatigue tests, and bearing tests with ball bearings type 6206. The results of the turning and grinding tests showed no significant influence of the alloying elements up to 1.5 % silicon and 1.1 % manganese. The parameters of the stress-strain curves showed a small influence of the silicon content, which is dominated by the influence of the heat treatment parameters. The change in the retained austenite content and therewith in the mechanical properties due to different tempering procedures is characteristically reduced with the high silicon content of 1.5 %.
Results indicate the preliminary feasibility of these alloys from all viewpoints under examination and suggest the desirability of studying fabrication problems of alloys and improved reduction methods for vanadium metal.