• 산업기술연구
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• 제24권A호
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• pp.3-8
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• 2004

This study was performed to investigate the effect of two step austenitized treatment on the mechanical properties and fracture characteristic of the ductile cast iron and austempered ductile cast iron(ADI). The obtained results of this study were as follows. The matrix structures of specimens were changed differently by austenitizing heat treatment. Microstructure of austempered ductile cast iron obtained by two step austenitized treatment was bainitic ferrite and retained austenite. With two step austenitized treatment, vield strength, tensile strength and hardness decreased, while the elongation increased.

• 한국주조공학회지
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• 제28권6호
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• pp.273-281
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• 2008

Effects of alloying elements on the mechanical properties of hardened and austempered 3.60wt%C - 2.50wt%C ductile cast iron were investigated. Strength and hardness were increased and ductility was decreased as the amount of alloying element increased. The increasing effect of copper addition on the strength was the most pronounced. The strength and hardness were greatly increased and ductility was decreased by hardening. The effect of alloying element on the mechanical properties of the hardened ductile cast iron was not so pronounced due to the high contents of C and Si. The strength and hardness of austempered ductile cast iron were greatly increased, meanwhile the difference of strength from that of hardened one was not so big. The ductility of the former was higher than that of the latter. The strength and ductility of austempered ductile cast iron with 0.25%Mn were the maximum of all Mn added ones. The maximum strength of that was obtained with the addition of 0.80wt%Cu or 2.00wt%Ni along with this amount of Mn added.

• 대한기계학회논문집A
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• 제29권3호
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• pp.462-469
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• 2005

Single phase bainite structure which is obtained by the conventional austempering treatment reduces the ductility of ductile cast iron. Because of the reduction of ductility it is possible to worsen the fatigue properties. Therefore, semi austempered ductile iron which is treated from ${\alpha}+{\gamma}$ is prepared to investigate the static strength and fatigue properties in comparison with fully austempered ductile iron (is treated from ${\gamma}$). In spite of semi austempered ductile iron shows the $86{\%}$ increase of ductility. Also, semi austempered ductile iron shows the higher fatigue limit and lower fatigue crack growth rate as compared with fully austempered ductile iron. By the fractographical analysis, it is revealed that the ferrite obtained by semi austempering process brings about the plastic deformation(ductile striation) of crack tip and gives the prior path of crack propagation. The relatively low crack growth rate in semi austempered specimen is caused by above fractographical reasons.

• 한국주조공학회지
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• 제10권2호
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• pp.144-153
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• 1990

Ductile cast iron has good ductility and toughness, for the graphite morphology is spheroidal. It has been reported that the strengthening and toughening of the ductile cast iron was resulted from the modification of matrix structure by the heat treatment or the addition of alloying elements. In this study, effects of various special heat treatments (cyclic heat treatment and intermediate heat treatment) and Ni addition on the toughness and strength of the austempered ductile cast iron were studied. The results obtained from this study were as follows : 1. The amount of fine pearlite was increased with the Ni content and the number of cycle in cyclic heat treatment. 2. When the specimens treated and not by special heat treatment at 820 was austempered, in the former the austenite was formed on grain boundary entirely, but in the latter on grain boundary partially. 3. The impact energy was decreased with the Ni content, because the coarisen austenite pools formed with the Ni content was transformed into martensite during quenching. 4. The mechanical properties of austempered ductile cast iron containing 2%Ni treated cyclic heat treatment(5 cycles)was very excellent in handness 99(HRB), impact energy 12(kg-m) maximum fracture load 1500(kg-f).

• 한국주조공학회지
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• 제6권4호
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• pp.290-297
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• 1986

Austempered ductile cast iron has been well known for their good toughness and strength. Generally these properties were improved by the various heat treatments and alloying elements. In this study, the effects of prior heat treatment history(near ferrite, near pearlite, near martensite) on the toughness and strength of the austempered ductile cast iron were studied experimentally and theoretically. All of the test specimens was austenitized at $900^{\circ}C$ for 1 h and austempered at $300^{\circ}C$, $350^{\circ}C$, $400^{\circ}C$, $450^{\circ}C$, respectively. The prior structure of near martensite in austempered ductile cast iron was not good in term of toughness and strength because the carbon content was apt to high in austenite during ausnitizing. It was found, on the other hand, that the ferrite matrix as prior structure had good combination of toughness and strenght. The best tensile strength and good toughness were obtained at $300^{\circ}C$, austemper in the prior structure of near ferrite, while $400^{\circ}C$ austemper in that of near pearlite and martensite.

• 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 $370^{\circ}C$.

• 한국주조공학회지
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• 제29권2호
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• pp.86-94
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• 2009

The effect of austenitizing temperature and time on the processing window of 3.60wt%C - 2.50wt%Si - 0.80wt%Cu ductile cast iron and that of the amount of copper added were investigated. The second stage reaction at 400oC was retarded with increased austenitizing temperature. The widest processing window was obtained at the lower austempering temperature with the increased time at the same austenitizing temperature. The width of the widest processing window was decreased with the increase of time at the same austenitizing temperature. The width of processing window was increased with the increased amount of copper added.

• 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.

• 열처리공학회지
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• 제26권5호
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• pp.219-224
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• 2013

In this study, we investigated effect of Mo addition on mechanical properties of Cu added ADI. Ductile cast iron specimens were austenitized at $900^{\circ}C$ for 150 min and then austempered at $380^{\circ}C$ for the various time periods from 15 min to 480 min. Mo added ADI had a higher volume fraction of retained austenite, and the volume fraction of retained austenite was determined by XRD analysis. As decreasing volume fraction of retained austenite, the elongation was also decreased as expected. But the UTS and yield strength were not decreased.

• 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.