• 한국생산제조학회지
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• 제8권1호
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• pp.81-88
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• 1999

This paper was carried out to know the influence of advanced austempered ductile cast iron (ADI) on the tool life and mechanical properties of drilling machinability. For manufactured method of ADI, the spheroidal graphite cast iron were austenized at 90$0^{\circ}C$ for 1 hour and then austempered for 2 hour at 37$0^{\circ}C$ in the salt bath. And interrelationship has been investigated between tool life and mechanical characteristics of specimen material on drilling condition when the ordinary and step-feed drilling are carried out to drill holes of specimens. Tensile strength and hardness of ADI decrease and elongation of ADI increases with the increase austempered temperature. It is known that about 2 times of tool life in the case of step-feed decreases compared with ordinary feed due to the high hardness of ADI and hardness ascribed to the fact that retained austenite became to martensite state due to cutting heat in drilling. Under the constant feed rate 0.1mm/rev relation between hardness and length of end tip after drilling can be formularized to Hv=$788.46L^{-0.096}$ for the cutting speed 6.1m/min.

• 대한기계학회논문집
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• 제12권6호
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• pp.1296-1302
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• 1988

The study has been carried out under various experimental conditions to investigate mechanical properties by the transformation conditions of austempered low-alloy ductile cast iron. The amount of retained austenite and bainite after quenching was determined by the X-ray diffractometer and the point counting method and which the microstructure was investigated by the S.E.M. The mechanical properties of austempered low-alloy ductile cast iron can be varried over a comparatively wide range by changing the transformation conditions. During isothermal transformation of austenite in the bainite region, low-alloy ductile cast iron austempered at holding time of 40 minute has the maximum volume fraction(24%) of retained austenite in the cast iron matrix and which optimum values of mechanical properties correspond to the maximum amount of retained austenite, which falls with decreasing transformation temperature. The low values of both tensile strength and elongation in the initial stage of bainite transformation can be explained by premature fracture of tensile specimens and the tensile strength, hardness and elongation do not change considerably after a certain period. With a decreasing transformation temperature the tensile strength increase while the elongation decrease, especially the elongation has the maximum value at temperature $370^{\circ}C$.

• 동력기계공학회지
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• 제11권4호
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• pp.86-91
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• 2007

This study was investigated to know the effect of subzero treatment in austempered ductile cast iron. Retained austenite transformed to martensite by subzero treatment. With decreasing subzero treatment temperature, more volume fraction of retained austenite transformed to martensite and transformed to martensite above 30% by subzero treatment temperature at $-196^{\circ}C$. With decreasing subzero treatment temperature, the value of strength and hardness increased but the value of elongation and impact value decreased. In case of subzero treatment at $-196^{\circ}C$, hardness value increased about 18% and impact value decreased by above 20%. We could find that subzero treated specimens had a little of effect on the tensile properties but had very much effect on the hardness and value of the impact.

• 동력기계공학회지
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• 제12권1호
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• pp.47-52
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• 2008

This study was investigated the effect of subzero treatment in austempered ductile cast iron. Retained austenite transformed to martensite by subzero treatment and strain. With decreasing subzero treatment temperature and increasing strain, retained austenite transformed more to martensite and transformed 30% above by subzero treatment at $-196^{\circ}C$. With decreasing subzero treatment temperature, the value of strength and ratio of increasing of strength, hardness and ratio of increasing of hardness increased but the value of elongation and ratio of decreasing of elongation decreased. With decreasing subzero treatment temperature, impact value and ratio of decreasing of impact value decreased. In case of subzero treatment at $-196^{\circ}C$, hardness value increased about 18% and impact value decreased above 20%. We could find that in subzero treated specimens had a little of effect on the tensile properties but had very much effect on the hardness and value of the impact.

• 대한금속재료학회지
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• 제47권3호
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• pp.169-174
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• 2009

The effect of sub zero treatment on the damping capacity in austempered ductile cast iron investigated. Austenite transformed in to martensite by subzero treatment, and with the decrease of subzero treatment temperature, volume fraction of martensite increased. Damping capacity of austempered ductile cast iron was highly increased by subzero treatment, with the decrease of subzero treatment temperature, damping capacity was slowly increased. With the decrease of subzero treatment time, damping capacity was rapidly increased to 30 min. and then slowly increased. With the increase of volume fraction of martensite, damping capacity rapidly increasing to 5% and then slowly increased.

• 한국주조공학회지
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• 제10권5호
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• pp.408-416
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• 1990

The application of this new design approach called fracture mechanics allow one to determine the maximum allowable stress from the knowledge of the largest expected flow size and the plane strain fracture toughness of a material. In this study we examined the relation between retained austenite, mechanical property and fracture toughness accompanied by austempering heat treatment. Fracture toughness values and retained austenite volume were higher with the ADI(austempered ductile iron) which were austempered at $380^{\circ}C$ than austempered at $320^{\circ}C$. Additionally, fracture toughness values were increased for 1~2 hour austempering time but it was slowly decreased for 5 hour ADI maintaining the predominant fracture toughness($K_{IC}:83MPa{\sqrt{m}}$) is obtained following condition, namely, austempering temperature and time ($380^{\circ}C$ and 1 hour).

• 비파괴검사학회지
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• 제9권1호
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• pp.90-97
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• 1989

Austempered ductile cast iron (ADI) which has been recently developed shows good mechanical properties. These properties are related to the microstructure which is greatly affected by processing variables such as austempering time and temperature. In this study, the relationships between mechanical properties from impact test, and hardness test and the results from ultrasonic velocity measurement and electrical resistivity measurement are studied on the ADI samples which are heattreated at different austempering temperature and time. From the results, we conclude the followings. The ultrasonic velocity measurement could be used for the study of austempering reaction mechanism. The electrical resistivity measurement could be used as quality assurance technique for the ADI.

• 동력기계공학회지
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• 제12권3호
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• pp.72-77
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• 2008

This study was investigated to know the effect of Cu addition on austempered ductile cast iron at various temperatures and times. Test results showed that the volume fraction of retained austenite and the carbon contents of retained austenite showed the greatest value at $400^{\circ}C$. Also, in case of specimens having more Cu contents, the volume fraction of retained austenite and the carbon contents of retained austenite showed the lower value. After austempering treatment, tensile strength and Impact value increased, but elongation decreased. With increasing austempering treatment temperature, tensile strength, elongation, and impact value decreased. In case of specimen having more Cu contents, tensile strength showed the higher value, but elongation showed the lower value. Damping capacity was decreased by austempering treatment and was not affected on austempering temperature and time. In case of specimen having more Cu contents, damping capacity showed the higher value.

• 한국안전학회지
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• 제11권1호
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• pp.3-10
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• 1996

The mechanical properties and fatigue crack growth rate fracture toughness of permanent mould cast austempered gray cast iron(AGI) were compared to those of sand cast AGI. Specimens prepared for tensile, impact and fatigue test were austenitized at $900^{\circ}C$ and austempered at $270^{\circ}C$, $320^{\circ}C$, $370^{\circ}C$ and $420^{\circ}C$ for 1 hour. The strength, impact and fatigue crack propagation behavior of permanent mold cast AGI were found to be superior to those of sand cast AGI. Maximum values in tensile strength, BHN, Charpy impact energy, were obtained at the austempering temperature of $270^{\circ}C$. Samely, the slowest fatigue crack growth rate was appeared at the austempering temperature of $270^{\circ}C$. But ductility of AGI was not improved by permanent mould casting.

• 한국주조공학회지
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• 제11권4호
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• pp.323-330
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• 1991

The relationships between the microstructure changes, retained austenite volume and elevated temperature tensile properties of Mo-Ni-Cu ADI corresponding to various austempering temperatures and time were investigated, After the $250^{\circ}C$ tensile test for the test piece austempered at $270^{\circ}C$ the accicular bainite structure was observed blunted under room temperature microscope. In the case of $370^{\circ}C$ austempering, the feathery bainite lath spacing was observed broadened. But after the $450^{\circ}C$ tensile test, bainitic features could not be observed. As the testing temperature increased, retained austenite volume tested at room temperature decreased. Especially, after the $450^{\circ}C$ tensile test retained austenite volume approached nearly to zero. A little higher tensile properties appeared at $250^{\circ}C$ testing than those at room temperature.