发明申请
US20060225814A1 Crankshaft and method for manufacturing same 审中-公开
曲轴及其制造方法

Crankshaft and method for manufacturing same
摘要:
A surface of a steel, as a material for a crankshaft, is nitrocarburized. The steel contains, as alloy elements C having a content 0.10 mass % or more 0.30 mass % or less, Si having a content 0.5 mass % or more and 0.3 mass % or less, Mn having a content 0.3 mass % or more and 1.5 mass % or less, Mo having a content 0.8 mass % or more and 2.0 mass % or less, Cr having a content 0.1 mass % or more and 1.0 mass % or less, and V having a content 0.1 mass % or more and 0.5 mass % or less, with a remainder consisting of Fe and inevitable impurities. The contents of the alloy elements fall within ranges: 2.0 mass %≦Mn+Cr+Mo≦3.0 mass %, 2.3 mass %≦C+Mo+5V ≦3.7 mass %, and 2.7 mass %≦2.16 Cr+Mo+2.54V≦4.0 mass %. If a steel sample extracted from a central portion of the nitrocarburized steel free from an influence of the nitrocarburizing treatment is austenitized at 1200° C. for one hour, and cooled to a room temperature so that a cooling rate at which the steel sample passes through a temperature range between 900° C. and 300° C. is 0.5° C./second, then an area percentage of a bainite structure in steel structures is 80% or more and a Vickers hardness measured at a cross section is 260 Hv or more and 330 Hv or less. A surface hardness of a nitrocarburized layer is 650 Hv or more, a formation depth of the nitrocarburized layer is 0.3 mm or more, and a hardness of the central portion is 340 Hv or more. Thereby a crankshaft which is excellent both in the machinability and in fatigue strength, even after nitrocarburizing treatment on the surface, is provided.
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