• Journal of the Korean Society for Heat Treatment
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• v.5 no.1
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• pp.23-31
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• 1992

It is investigated that Fe-C-N compound layer, defusion layer, and induction hardened layer produced by nitrocarburizing blend heat treatment in austenitic temperature with high frequency induction heating of mild steel specimen sprayed sursulf salt-bath. As the temperature of blend-heat treatment got increased, the thickness and hardness of compound layer and diffusion layer were increased. Compound layer(max. $35{\mu}m$), diffusion layer (max. 2.5mm) and induction hardened layer were gained in the shortest time 10 sec and in the case of $1000^{\circ}C$ total hardness depth of those was about 3.5mm. When the blend-heat treated specimen was reheated, maximum hardness of compound layer was dropped more than that of the reheated compound layer after sursulf treated, whereas hardness of diffusion layer was increased.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.3
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• pp.429-436
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• 2013

This study considers how the fatigue behavior and probabilistic properties of SAE1055 steel are related to its hardness level. SAE1055 steel was heat-treated using induction hardening. Five types of specimens were prepared (A: base material, B: through hardened material with HV390, C: through hardened material with HV510, D: through hardened material with HV700, and E: surface hardened material with HV700). Fatigue tests were performed under a stress ratio of R = -1 using a 4-point rotary bending fatigue tester. The fatigue behaviors were greatly influenced by the hardness, but the fatigue limit did not increase over a hardness of HV510. In addition, the effect of the hardness level on the failure mechanism was evaluated using a scanning electron microscope. The probabilistic properties of the fatigue life were investigated using a probabilistic S-N approach, and the effect of the hardness level on these properties was evaluated using a residue analysis.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.6
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• pp.1-8
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• 1994

To enhance the strength of gears for transmission, Generally caburizing heat treatment is applied. But there are some problems in this technology the distortion of gears during heat treatment process, and the discontinuity of manufacturing process. For these reasons, the high frequency induction hardening process is widely used. This method is one of the surface hardening process to improve the wear resistance and fatigue life of the machine components. In this study, to compare the bending fatigue strength of caburized gear with that of induction hardened gear, bending fatigue testing of gears with two different cases was performed by using an electrohydraulic servo-controlled fatigue testing machine and double tooth bending fatigue test fixture. Fatigue life distributions at constant stress levels were established directly from fatigue data. For gear design, the fatigue strength distribution at specified life is more important. This distribution is obtained by statical transformation from fatigue life distribution. Reliability of bending fatigue strength was estimated by P-S-N curves and Weibull distribution.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.1
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• pp.78-84
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• 2012

Mold may experience deterioration of molding quality as the abrasion of mold occurring due to friction between mold and molded product works as allowance in the course of press process. Therefore, to improve the wear-resistance of mold, methods like nitriding, carburizing, flame and induction surface hardening treatment etc have been applied. However, as such methods are accompanied by problems like shape limitation or product deformation etc, laser surface treatment technology is under review as surface treatment method that can solve such problems. Therefore, in this study, mold material cast iron was surface-treated by using high power diode laser. In previous report 1 and report 2, the heat treatment characteristics were compared by the differences of die materials and shapes, then this paper observed microstructure by using optical microscope and scanning electronic microscope to analyze the structural difference of hardened zone, interface area and base metal after heat treatment. And the structural condition was grasped through EDS. As a result of microstructure, hardened zone showed formation of acicular martensite.

• Journal of the Korean Society for Nondestructive Testing
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• v.11 no.1
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• pp.38-43
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• 1991

The relationship between eddy current response and case hardening depth has been studied on SM40C(KS D-3752) and SCM440(KS D-3711) steels which were surface hardened by high frequency induction hardening. The results obtained in this study were as follows ; 1) Case hardening depth was successfully measured by observing the eddy current impedance changes of each steel. The impedance decreased linearly with increasing case hardening depth. 2) For large impedance gradient between the hardened surface and core metal, the eddy current response was more sensitive to case hardening depth than for low impedance gradient.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.3
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• pp.165-171
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• 1997

Laser hardening for the piston ring groove of ductile cast iron was tried. Mechanical and microstructural investigation for the hardened area indicated that the laser heating technique could replace conventional induction hardening process completely and further showed that post grinding process would be eliminated by minimizing bulging of heat treated area. In laser hardening, the volume increase caused by martensitic phase transformation proved to be less than $10{\mu}m$, which insures no post machining on the hardened surface. As expected, the depth of hardening was inversely proportional to the beam scanning velocity and the highest surface hardness was obtained at the beam velocity of 0.75m/min. Heat treatment using phosphate coating demonstrated quite comparable result to the case of graphite suscepter.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.645-649
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• 2010

Induction hardening has been used to improve the torsional strength and characteristics of wear for axle shaft that is used to transmit driving torque from the differential to the wheel in automobiles. After the rapid heating and cooling processes of induction hardening are carried out, the shaft has residual stress and material properties change; this affects the allowable transmitted torque. The objective of this study is to predict the distribution of residual stress and estimate the torsional strength of induction-hardened axle shafts with residual stress. In this study, the finite element method is used to study the thermomechanical behavior of the material, and the results are compared with experimental results. The results indicate that the torsional strength of the axle shaft depends on the surface hardening depth and distribution of residual stress.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.10
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• pp.74-79
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• 2006

In this study, the tempering effect on the wear characteristics of induction-hardened SPS5 steel was investigated. For this purpose, three tempering conditions were applied to control the hardness of heat-treated SPS5 steel. Ball-on-disk wear tests have been performed using zircornia balls on the tempered specimens to determine the variation of wear characteristics. The results showed that friction coefficient decreased with increasing hardness for induction hardening conditions. This seems to occur because real contact area between specimen and mating ball was affected by the specimen hardness.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.409-410
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• 2006

In this study, the tempering effect on the wear characteristics of induction-hardened SPS5 steel was investigated. For this purpose, three tempering conditions were applied to control the hardness of heat-treated SPS5 steel. Ball-on-disk wear tests have been performed using zircornia balls on the tempered specimens to determine the variation of wear characteristics. The results showed that friction coefficient decreased with increasing hardness for induction hardening conditions. This seems to occur because real contact area between specimen and mating ball was affected by the specimen hardness.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1103-1108
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• 2010

We fabricated flanged outer races for wheel bearing units using 0.52%C clean steels, and then characterized and studied the transformation behavior. The outer races produced by hot forging and high frequency induction hardening in this study were analyzed through microstructural characterization using OM, SEM, TEM, and X-ray diffractometer and their microhardness depth profiles of the raceway contacted by balls were measured using MVH tester. The surface hardened layers with a uniform hardness profile in the raceway consisting of very fine martensite with sub-micron sized retained austenite could be formed for very short time during high frequency induction hardening after hot forging. The very fine martensite may be transformed on rapid cooling, from the inhomogeneous austenite nucleated on rapid heating in small particles of pearlitic cementite fragmentated by hot forging. On the other hand the sub-micron sized retained austenite may be chemically stabilized due to their extremely small size, from the small austenite nucleated at the grain boundaries.