Gigacycle fatigue behavior of 60Si2CrVA high strength spring steel was investigated by ultrasonic fatigue test machine. Fatigue fractography was observed by scanning electron microscopy （SEM）. Maximum inclusion size...Gigacycle fatigue behavior of 60Si2CrVA high strength spring steel was investigated by ultrasonic fatigue test machine. Fatigue fractography was observed by scanning electron microscopy （SEM）. Maximum inclusion sizes and fatigue strength in different volumes were estimated by statistics of extreme values （SEV） and generalized Pareto distribution （GPD） methods. The results showed that S N curves of 60Si2CrVA spring steels for two rolling processes were not horizontal asymptotes but a gradient in a regime of 109 cycles, and traditional fatigue limits were eliminated. Surface machined topography and inclusions in steel were major factors that led to elimination of fatigue limit for 60Si2CrVA spring steel. The SEV and GPD methods could effectively predict size of the maximum inclusion and fatigue strength in different volumes of 60Si2CrVA spring steel. Predicted fatigue strength was in accordance with experimental results by ultrasonic fatigue testing.展开更多
The vermicular graphite iron is an important material with excellent combination properties for cylinder heads of diesel engines,and the high-temperature oxidation is a crucial problem during service of the component....The vermicular graphite iron is an important material with excellent combination properties for cylinder heads of diesel engines,and the high-temperature oxidation is a crucial problem during service of the component.In this study,the oxidation experiment of RuT400 vermicular graphite iron was performed at 500 ℃,and the oxidation time was chosen as 100 h,200 h,300 h,400 h,and 500 h,respectively.Meanwhile,the corresponding microstructure evolution,oxidation kinetics,and oxidation mechanism were discussed.It is found that oxidation pores and oxide layer often appear at the vermicular graphite on the specimen surface;the vermicular graphite plays the role of oxidation channel,and it tends to diff use along the adjacent pearlite and then connect with each other to form oxidation bridges as the oxidation time prolongs.A linear relationship between oxidation weight gain and the thickness of the oxide layer was established and verifi ed well.These results will give a more comprehensive understanding on the oxidation mechanism of vermicular graphite iron and provide certain guidance for design and preparation of anti-oxidation cast irons.展开更多
基金Sponsored by National Basic Research Program(973 Program)of China(2004CB619100)
文摘Gigacycle fatigue behavior of 60Si2CrVA high strength spring steel was investigated by ultrasonic fatigue test machine. Fatigue fractography was observed by scanning electron microscopy （SEM）. Maximum inclusion sizes and fatigue strength in different volumes were estimated by statistics of extreme values （SEV） and generalized Pareto distribution （GPD） methods. The results showed that S N curves of 60Si2CrVA spring steels for two rolling processes were not horizontal asymptotes but a gradient in a regime of 109 cycles, and traditional fatigue limits were eliminated. Surface machined topography and inclusions in steel were major factors that led to elimination of fatigue limit for 60Si2CrVA spring steel. The SEV and GPD methods could effectively predict size of the maximum inclusion and fatigue strength in different volumes of 60Si2CrVA spring steel. Predicted fatigue strength was in accordance with experimental results by ultrasonic fatigue testing.
基金the National Natural Science Foundation of China (NSFC) under Grant.No.51871224the Natural Science Foundation of Liaoning Province under Grant.No.20180550880。
文摘The vermicular graphite iron is an important material with excellent combination properties for cylinder heads of diesel engines,and the high-temperature oxidation is a crucial problem during service of the component.In this study,the oxidation experiment of RuT400 vermicular graphite iron was performed at 500 ℃,and the oxidation time was chosen as 100 h,200 h,300 h,400 h,and 500 h,respectively.Meanwhile,the corresponding microstructure evolution,oxidation kinetics,and oxidation mechanism were discussed.It is found that oxidation pores and oxide layer often appear at the vermicular graphite on the specimen surface;the vermicular graphite plays the role of oxidation channel,and it tends to diff use along the adjacent pearlite and then connect with each other to form oxidation bridges as the oxidation time prolongs.A linear relationship between oxidation weight gain and the thickness of the oxide layer was established and verifi ed well.These results will give a more comprehensive understanding on the oxidation mechanism of vermicular graphite iron and provide certain guidance for design and preparation of anti-oxidation cast irons.
