• Journal of Power System Engineering
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• v.11 no.4
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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.

• Journal of Korea Foundry Society
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• v.16 no.6
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• pp.503-512
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• 1996

Austempered ductile irons(ADI) are characterized by their relatively high retained austenite content which has a significant effect on mechanical properties and performance, such as ductility, toughness, wear resistance and machinability. Austenitising treatment at $900^{\circ}C$ for $1{\sim}2hours$, and austempering treatment within the temperature range $240{\sim}400^{\circ}C$ on ductile cast iron alloyed with Cu and Mo were carried out, and the effects of retained austenite content on the mechanical properties and wear resistance were investigated. In consequence, the amount of retained austenite was found to be 13.5% at the austempering temperature of $240^{\circ}C$, and was increased 28% at $400^{\circ}C$. Tensile strength and hardness of austempered ductile iron were decreased as the retained austenite content increased, but elongation was increased. The retained austenite content at the austenitising time of 2hours was more than at 1hour. The amounts of rolling wear loss were increased as the retained austenite content increased, and the wear surface was become to be rough.

• Journal of Korea Foundry Society
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• v.10 no.5
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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).

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.1
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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.

• Journal of Advanced Technology Convergence
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• v.2 no.2
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• pp.9-14
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• 2023

This study is shown the result of the first year to develop an export 1050MPa-class lightweight ductile iron castings Austempered control arm through the research process to obtain the following results. First, the structure of the optimal design Layout design and development of the component, and then achieve them through the Control Arm rigidity and optimal structure design and robust design of the focus areas of the expected stress Control Arm. Second, to develop a Control Arm reflects the high rigidity and high performance lightweight structures. Control Arm them developed to meet the design and rigidity as required by the consumer through the hollow, and to develop a process for the Core. Third, through optimum alloy composition and heat treatment methods will be derived to derive the amount of iron alloy (Cu, Ni, Mo) and Austempered heat treated and tempered condition. Fourth, through the development of optimum molding technology development component to develop the optimum ADI for the low-stiffness, high-rigidity component development, it attempts to develop a high-strength casting forming technology..

• Journal of Korea Foundry Society
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• v.8 no.3
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• pp.310-321
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• 1988

This study is aimed to investigate the effects of the multi-phase(ferrite-bainite-martensite) on the strengthening and toughening in ductile cast iron. All the specimen were austenitized at eutectoid transformation temperature range(${\alpha}+{\gamma}$) for 1hr and austempered at $300^{\circ}C$ and $400^{\circ}C$ for various holding time, and then quenched in iced water for multi - phase (${\alpha}-B-M$). When the volume fraction of martensite is below 15%, excellent maximum fracture load can be obtained due to strengthening by the fine martensite, but, with increasing of volume fraction over 15%, it was decreased drastically. The martensite size became finer and the shape of it changed from bar to spherical type with increasing of austempering holding time. The higher the austenitizing temperature is, the more preferential is the formation of austenite phase around the graphite nodules improving strength and toughness of austempered ductile cast iron.

• Journal of Korea Foundry Society
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• v.13 no.1
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• pp.50-61
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• 1993

Retained austenite in matrix of austempered ductile iron has been well-known as a parameter in controlling mechanical properties, but investigation to obtain quantitative relationship with mechanical properties lack. Therefore, this study executed austempering treatment at various temperatures on ductile iron alloyed with Mo, Ni, Cu. In consequence, microstructure of retained austenite transformed coarse, and quantity increased according as austempering temperature increased. After heat-treatment, microstructure of specimen alloyed with Ni was fine, and toughness improved. At austempering temperature up to $400^{\circ}C$, carbide precipitation started in retained austenite. In consequence, afforded cause of hardness increase, a lot of increase did not arise for coarse structure.

• Journal of the Korean Society for Heat Treatment
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• v.15 no.6
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• pp.255-259
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• 2002

Effect of martensite on the mechanical properties of austempered ductile cast iron was investigated after obtained the martensite by subzero treatment. Retained austenite was transformed to martensite by subzero treatment, and with decreasing subzero treatment temperature, volume fraction of martensite was increased. With increasing of the volume fraction of martensite, tensile strength was increased and elongation was decreased, ratio of increasing of strength and decreasing of elongation was higher in case of specimens with lot's of Cu contents. With increasing of the volume fraction of martensite, hardness slowly increased until only about 5% and it rapidly increased in a straight proportion when it is above 5%, while impact value was rapidly decreased until about 7% but it had a little change when it is above 7%.

• Journal of Korea Foundry Society
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• v.19 no.1
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• pp.24-32
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• 1999

A series of investigations for Austempered Ductile Iron (ADI) castings were carried out by using the specimens with various chemical compositions and heat treatment conditions. The rolling wear characteristics of alloyed austempered ductile irons under an unlubricated dry rolling condition was evaluated by the Amsler type test with 9.09% sliding ratio. Generally, the wear amount was increased with the austempering temperature and decreased when the hardness of the matrix was higher. The alloying elements also influenced the austempering reaction, the microstructure and the mechanical properties. In this study, the mechanical properties (i.e.) ultimate tensile strength (UTS), hardness, elongation) and the wear resistance are analysed to show the relationship between the alloying elements and the austempering temperatures. Mo, Cu and Ni are alloyed individually or in combination. It has been found that when Cu and Ni alloyed individually to a casting, the wear amount is increased than others with elements alloyed in combination. The amount of rolling wear loss was decreased when Mo was alloyed in cast iron, individually or in combination.

• Journal of Korea Foundry Society
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• v.32 no.6
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• pp.284-288
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• 2012

The effects of Si content on the variation of microstructure and processing window of austempered ductile cast iron were investigated. Four different Si contents between 2.42 and 3.37 wt.% were used. The influence of silicon on the microstructure and processing window of these materials were studied. Austenitizing was performed at $900^{\circ}C$ for 60min and austempering temperature were both $340^{\circ}C$ and $360^{\circ}C$ and austempering time were for 4min upto 119min and for 5min upto 160min respectively. After heat treatment, the evolution of stage I and stage II were performed by optical metallography, XRD, hardness test. The results showed that $t_2$ was delayed as Si contents was increased due to the fact that Si retarded the formation of cementite ($Fe_3C$). The high silicon content promoted the stability of the metastable two-phase combination of austenite and ausferrite.