• 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.17 no.3
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• pp.286-291
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• 1997

Influence of Si contents on the mechanical properties and microstructure of austempered ductile iron was investigated. Four different Si contents between 2.0 and 2.9% were used. Austenitizing was performed at $890^{\circ}C$ for 2 hrs and austempering temperatures were both 340 and $380^{\circ}C$ for 0.5, 1, and 2 hrs. Nodule content was more than $300/mm^2$ and nodularity was more than 90%. Microstructure was revealed using nital and retained austenite was measured by x-ray diffractometer. Tensile test, no-notch Charpy impact test and wear test were performed. Tensile strength was improved as Si content increased and both elongation and impact toughness had peak at 2.6%Si. The specimen austempered at $380^{\circ}C$ showed lower tensile strength than that of $340^{\circ}C$, but showed higher elongation. However, austempering temperature of $380^{\circ}C$ was desirable because that of $340^{\circ}C$ was close to lower bainite transformation. As austempering time increased, tensile strength and elongation were improved and optimum condition was obtained for 2 hrs heat treatment.

• 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 the Korean Society for Heat Treatment
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• v.11 no.4
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• pp.333-341
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• 1998

The study was investigated on the effect of austenitizing and austempering conditions on retained austenite amount and carbon contents in retained austenite and simultaneously the effect of these variation on hardness, tensile and impact properties. A material of as-cast condition is composed of bull's eye structure with ferrite surrounding spheroidized graphite having about $5-10{\mu}m$ size and matrix structure of pearlite. Then, the contents of spheroidized graphite was about 5%. The retained austenite and carbon contents in the retained austenite were increased with the increasing of austenitizing and austempering temperatures, while the retained austenite showed the peak value and is decreased with increasing of austempering time. With increasing of austenitizing temperature, tensile strength, elongation and impact absorb energy increased and hardness was almost not changed, while with increasing of austempering temperature, tensile strength and hardness decreased, whereas elongation and impact absorb energy was increased. With increasing of retained austenite amount, the tensile strength is slowly decreased but elongation was increased with direct proportion. Also, Impact absorb energy is shown identity value untile about 18%, but rapidly increased above it. Elongation and Impact absorb energy are strongly controlled by the amount of retained austenite, but tensile strength is affected with various factors such as retained austenite amount and bainitic morphology.

• Journal of the Korean Society of Safety
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• v.11 no.1
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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.

• 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.15 no.3
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• pp.291-297
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• 1995

The mechanical properties and fracture toughness of permanent mold cast austempered gray cast iron(AGI) were compared to those of sand cast AGI. The iron was melted to eutectic composition in order to get better castability especially in permanent mold casting. Specimens prepared for tensile, impact and fracture toughness test were austenitized at $900^{\circ}C$ and austempered at $270^{\circ}C$ and $370^{\circ}C$ for 1 hour. The strength, impact and fracture toughness of permanent mold cast AGI were found to be superior to those of sand cast AGI. The maximum value of 836 MPA in tensile strength, was obtained at the austempering temperature of $270^{\circ}C$. But ductility of AGI was not improved by permanent mold casting.

• Journal of Korea Foundry Society
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• v.14 no.6
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• pp.548-557
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• 1994

Grey iron containing a small amount of Cu and Mo to improve the effect of heat treatment and microstructures were poured in to the mold and them austenized at $900^{\circ}C$. After austenitizing the specimens of castings were austempered $210^{\circ}C$, $250^{\circ}C$, $300^{\circ}C$ and $350^{\circ}C$. The effects of matrix structures, mechanical properties and wear characteristics were investigated by austempering temperatures. Tensile strength and hardness of austempered grey iron are increased and the amount of retained austenite is decreased as austempering temperature is lower even though the amount of retained autenite in it only 4%. The amount of rolling wear loss are increased as rolling revolution is increased and wear loss of austempered grey iron under dry rolling condition is characterized by three models; initial wear, stationary wear and abnormal wear. It has been found that the amount of wear loss was increased with increasing maxium compressive stress and rolling revolution.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.32-38
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• 1998

For the purpose of monitoring the abnormal state in proportion to cutting in automatic production process, the 3 kinds of specimens different from mechanical properties by austempering through temperature variation were manufactured, and the effects of tool wear on thrust and AE RMS was analyzed with sequential drilling in in-process. When the ADI specimens were drilled, the relationship of thrust and AE RMS with flank wear was studied through experiments, and it is confirmed that the reliable wear state is able to be monitored by using these signals. It was shown that thrust and AE RMS increased slowly till flank wear reached to V$_{B}$ = 0.25mm, and they increased steeply over the value. The effective tool exchange time was able to be pre-estimated by using this fact. It was validated that the tool breakage was able to be detected on the real time by monitoring in in-process.s.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.1
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• pp.1-9
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• 1997

The variation of the mechanical properties and the formation of retained austenite with heat treatment conditions in austempered Si bearing carbon steels has been investigated. In the case of a steel containing 0.35C-1.48Si-0.95Mn, it has been found that a feather shape bainite structure of lath are obtained under a isothermal treated condition at just below the Ms temperature, and the martensite, bainitic ferrite and retained austenite of second phase particles on the ferrite matrix for a isothermal treated steels after intercritical annealing are precipitated in a linked shape. The retained austenite with $2{\mu}m$ size induced as TRIP is found to increase with increasing the formation rate of retained austenite for the intercritical annealing and high Si containing steels. The tensile strength is increased as austempering temperature increases in all isothermal treatment temperature, whereas the elongation is shown to roughly decrease as the tensile strength increases. The values of tensile strength-elongation balance have showed a marked dependence upon the elongation rather than the tensile stregth, and their values are increased for high Si containing steels and intercritical annealing condition. The most optimum result has been shown to be the tensile stregth-elongation balance of $2882.4kgf/mm^2.%$ and the elongation of 33.3% for a "B" steel in the heat treating temperature range of $780{\sim}370^{\circ}C$.