【作者】

Ryota Yakura，Tomoya Shinozaki

【摘要】

论文已在中国上海举行的2013年CIMAC大会上发表。论文的版权归CIMAC所有。With recent trend toward higher output and compactness in marine and power generator engines, the solid type crankshaft used for the 4cycle diesel engine is demanded to have higher fatigue strength. It is well known that fatigue strength is influenced by non-metallic inclusions responsible for the fatigue crack initiation, fatigue strength can be improved by reducing the amount and size of nonmetallic inclusions. The non-metallic inclusions are mainly sulfide and oxide. Therefore, ’super clean steel making process’ that is the way to reduce sulfur and oxygen by vacuum ladle refining furnace has been developed. In order to confirm the material qualities of the steel manufactured by ’super clean steel making process’, the fatigue test on RR-forged crankshaft was carried out. As a result, it is confirmed that fatigue strength of super clean steel has been improved at least 10% higher than that of conventional steel. In the conventional steel, as for K factor in the fatigue strength calculation formula specified in IACS UR M53, K=1.05 is given for CGF (Continuous Grain Flow) forging crankshaft. By reducing the amount and size of non-metallic inclusions, fatigue strength has been improved 10% or more to conventional steel. This result shows that safety margin would be maintained at the same level with present state after K-factor raises up to 1.15 for super clean steel. Therefore, designed fatigue strength may be improved about 10%. On the other hand, in the fatigue of high strength steel, some cases in very high cycle (more than 10,000,000 cycles) fatigue region are reported in recent literatures. Nevertheless study for very high cycle fatigue behavior of low alloy steel used for solid type crankshaft is not enough. Therefore, the investigation for very high cycle fatigue property of super clean and conventional steel has been carried out. In very high cycle fatigue test up to 1,000,000,000 cycles, fatigue fracture did not occur in both steels. It was confirmed that the difference of fatigue strength between super clean steel and conventional steel is maintained in very high cycle region. From this result,it became clear that super clean steel has high fatigue strength and high reliability in both conventional (less than 10,000,000 cycles) fatigue region and very high cycle (more than 10,000,000 cycles) fatigue region.

【会议名称】

第27届CIMAC会议

【会议地点】

上海

【下载次数】

1

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