• 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.12 no.5
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• pp.390-396
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• 1992

In this study, we investigated effect of austempering factors and Mn addition on mechanical properties of ADI with ferrite-bainite matrix by pearlite-bainite transformation treatment. Ductile cast iron specimens containing various of Mn were austenitized at 875$^{\circ}C$ for 350 sec or 925$^{\circ}C$ for 160 sec and then austempered at 300$^{\circ}C$ or 400$^{\circ}C$ for the various periods(5 to 30 min). Manganese increased pearlite volume fraction in as cast ductile cast iron. The obtained results are as follows ; 1) In austenitizing, hardness of sepecimens austenitized at 875$^{\circ}C$ for 350 sec was higher than that of 925$^{\circ}C$ for 160 sec. 2) In effect of austempering temperature, tensile strength and handness of specimens austempered at 300$^{\circ}C$ was higher than that of 400$^{\circ}C$. However, elongation had reverse tendency. 3) Increasing austempering time decreased hardness due to the increment of bainite and retained austenite fractions. However, toughness are increased.

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.1
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• pp.89-94
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• 2015

This study was conducted to compare the laser weldability of boron steel and hot-stamped steel. In general, boron steel is used in the hot-stamping process. Hot-stamping is a method for simultaneously forming and cooling boron steel in a press die after heating it to the austenitizing temperature. Hot-stamped steel has a strength of 1500 MPa or more. Thus, in this study, the laser weldability of boron steel and thet of hot-stamped steel were investigated and compared. A continuous wave disk laser was used to produce butt and lap joints. In the butt welding, the critical cooling speed at which full penetration was obtained in the hot-stamped steel was lower than that of boron steel. In the lap welding, the joint widths were similar regardless of the welding speed when full penetration was obtained.

• Journal of Korea Foundry Society
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• v.18 no.4
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• pp.340-348
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• 1998

C/V graphite iron has superior tensile strength, toughness and ductility than grey iron, and better castability than ductile iron. The retained austenite content of C/V graphite iron by austempering treatment affects on the mechanical properties such as ductility, hardness, wear properties and machinability. C/V graphite iron alloyed with Cu and Mo were carried out on the austenitizing at $900^{\circ}C$ for 1 hour, and the austempering at $240{\sim}400^{\circ}C$ for 1 hr. And then the mechanical and wear properties of austempered C/V graphite iron have been investigated by the retained austenite content. In consequence, the retained austenite content was found to be 18.2% in austempering temperature at $240^{\circ}C$, and was increased 39.2% at $400^{\circ}C$. Tensile strength and hardness of austempered C/V graphite iron were decreased as the retained austenite content increased, but elongation was increased. The rolling wear loss were increased as the retained austenite content increased. The wear surface of as-cast became to be rough. The microstructure of austempered C/V graphite iron was became to be acicular ausferrite in austempering at $240^{\circ}C$, and feathery ausferrite at $400^{\circ}C$.