• Journal of Korea Foundry Society
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• v.11 no.3
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• pp.217-227
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• 1991

The present study was conducted to estimate the fatigue crack growth rate of the Mo-Ni alloyed ductile cast iron for the influence of austempering temperature and time. The fatigue crack growth rate was affected by retained austenite. Retained austenite volume were higher with the ductile cast irons which were austempered at $360^{\circ}C$ than austempered at $260^{\circ}C$, and the fatigue crack growth rate of the former was lower than that of the latter. Also, the fatigue growth rate of the former was the lowest at austempering for 1 hour and that of the latter was the lowest at austempering for 3 hours.

• Journal of Korea Foundry Society
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• v.10 no.3
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• pp.235-246
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• 1990

This study has been carried out to investigate into the rolling wear characteristics of austempered ductile iron under unlubricated dry rolling condition by Amsler type test with 9.09% sliding ratio. Wear amount is increased with increasing of ferrite and retained austenite and it has been found that the amount of rolling wear is decreased when the hardness of matrix are higher. The rolling life up to generation of abnormal condition is conspicusly increased and amount of rolling wear is increased asrolling revolutionis increased and wear of austempered ductile ironunder dry rolling condition. Matrix has been obtained to upper bainite, low bainite at heat treatment, obtained to bull`s eye structure at as cast. It has been found that the amount of rolling wear is decreased when the tensile strength of the casting are increased and then the rolling life up to generation of abnormal wear in conspicuously increased and amount of wear was intend to graphite content.

• Journal of Mechanical Science and Technology
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• v.14 no.10
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• pp.1021-1027
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• 2000

In this study, fatigue tests were performed to examine the effects of micro drill hole on fatigue limit of as cast and austempered ductile cast iron (ADI) using the rotary bending fatigue tester. As results, micro drill holes ($diameter{\leq}0.4mm$) did not influence the fatigue limit of ADI, compared to annealed ductile cast iron; the critical defect size of crack initiation, in ADI was larger than as cast. If the ${\sqrt{area}}$ of micro drill hole and graphite nodule in ADI are comparable, crack initiates at the graphite nodule. When the ruggedness developes through austempering treatment process, microstructure on crack initiation at micro drill hole is tougher than that of as cast ductile cast iron.

• Journal of Korea Foundry Society
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• v.8 no.spc1
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• pp.115-124
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• 1988

• Journal of the Korean Society for Precision Engineering
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• v.13 no.7
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• pp.36-44
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• 1996

Drilling tests were carried out austempered ductile cast iron(ADI) to clarify the factors influencing the drilling characteristics of ADI material. The machinability of material was evaluated using high speed steel drill and cobalt contained drill of 6mm diameter. The spheroidal graphite cast iron materials were austemized at 900 .deg. C for 1 hour and then wear was kept at 375 .deg. C for 2 hours. Austempered ductile cast iron contains a great deal of retained austenite which contribustes to an improvement of impact strength. In this paper, machinability of ADI was invastigated by drilling experimentation. The results obtained are as follows:a) Flank wear incresses logarithmically with the increases of cutting time and proportionally with the increases of cutting force. b) Drilling hole number of about 2 times can be educed more step feed than ordinary feed due to the high hardness of ADI material and hardness increasing ascribed to the martensite of retained austenite.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.6
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• pp.90-96
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• 1998

The ductile cast iron is austempered at 300, 350 and 40$0^{\circ}C$ temperature in order to investigate the basic factors for monitoring drill wear in automatic production process, and cutting force and AE RMS signals are measured with changing cutting condition for ADI(Austempered Ductile Cast Iron) with different mechanical properties. The signals of cutting force were influenced by cutting speed and feedrate greatly. On the other hand AE RMS signals are influenced by cutting speed where as it is not related with feedrate. As the depth of drilling increases, cutting force shows a slow increase and the value of AE RMS increases until the range of h/d=4. But over the range it increases greatly due to an amount of chip discharge and friction with inner wall of drilling hole, etc. As the drill diameter increases at a constant depth of drilling. Cutting force increases linearly, but the level of AE RMS does not increases linearly due to circumferential velocity and great influence of h/d.

• Journal of Korea Foundry Society
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• v.14 no.1
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• pp.52-61
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• 1994

The effect of Ni addition, on the mechanical properties and fracture characteristics of Mo-Cu and Mo-Ni-Cu alloyed ductile iron austenitized at $900^{\circ}C$ and austempering temperatures of $250^{\circ}C$, $300^{\circ}C$ and $350^{\circ}C$. The tensile strength, yield strength and hardness are decreased and elongation and impact value are increased in both Mo-Cu and Mo-Ni-Cu alloyed austempered ductile iron, with increased austempering temperature. According to the austempering temperature are increased, the amount of retained austenite are increased. Maximum value of fracture toughness is obtained at $350^{\circ}C$ austempering temperature at this condition, the amount of retained austenite came to 40% in Mo-Ni-Cu alloyed ADI and 34% in Mo-Cu alloyed ADI. The fracture surface of ADI which had represented high toughness are showed a quasi-cleavage pattern and a dimple pattern with micro void. Comparing the fracture characteristics of Mo-Cu alloyed ADI with that of Mo-Ni-Cu alloyed ADI, the latter was superior to the former.

• Journal of Korea Foundry Society
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• v.11 no.3
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• pp.228-235
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• 1991

The Effects of the matrix structures and the amount of the retained austenite in austempered ductile iron(ADI) which contains Ni, Cu and Mo on fracture characteristics were inverstigated. The structures were changed from lower bainite to mixture of Lower and upper bainite, and then to upper bainite as austempering temperature increased. A higher austempering temperature yielded lower tensile strength and hardness, but higher impact valve and $K_{IC}$. In addition, the amount of the retained austenite increased with the austempering temperatures. Fracture surface showed a fibrous pattern and a dimple pattern with increasing the retained austenite amount.

• Journal of Korea Foundry Society
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• v.22 no.2
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• pp.97-104
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• 2002

• Journal of Korea Foundry Society
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• v.29 no.6
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• pp.251-256
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• 2009

The effect of austempering treatment on mechanical properties of nodular indefinite chilled iron(NICI) and ductile cast iron(DCI) was investigated. In microstructural observation, matrix phase(pearlite and ferrite) was changed to ausferrite after austempering treatment both DCI and NICI. In case of NICI, decomposition of cementite($Fe_3C$) during austempering treatment was induced. After austempering treatment, mechanical properties such as hardness, tensile strength and impact toughness was improved in NICI and DCI. The wear resistance is slightly decreased because of decomposition of cementite during austempering treatment in NICI but impact toughness and strength is dramatically increased.