• Journal of the Korean Society for Heat Treatment
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• v.3 no.2
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• pp.10-19
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• 1990

The tempering behavoirs of 0.45% carbon steel treated by automatic progressive high frequency induction hardening equipment have been investigated. In order to examine the correlation of hardness with both tempering temperature and time, simple regression analysis has been made using the statistical quality control package. The maximum surface hardness value of induction hardened zone and its effective hardening depth have been determined to be Hv 810 and 0.76mm, respectively. The hardness obtained after tempering has been shown to vary lineary with tempering time at six different temperatures. The activation energies during tempering have been calculated to be 25.34kcal/mole, 32.73kcal/mole and 49.24kcal/mole for HRcs 60, 50 and 40, respectively, showing that tempering process occurs by a complex mechanism, The tempering hardness equation of $H=90.113{\sim}4.531{\times}10^{-3}$ [T(11.996+log t)] has proved to be in a reasonably good agreement with experimently determined data and it is also expected to be useful for the determination of tempering treatment conditions to obtain a required hardness value.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.11
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• pp.243-247
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• 1999

Carbon nitride coatings on the substrates of 0.55wt% C - 1.68wt% Mn induction-hardened rolling elements were prepared by ion beam assisted deposition. It was found through metallographic observation that the carbon nitride coatings appeared lamellar-type repeated layers parallel to the surface of substrate. Surface roughness of the coated specimens was improved in comparison with that of the substrates. Wear resistance of the coatings was evaluated using Polymet RCF-1 machine with a constant supply of lubricant followed by Weibull statistical analysis and scanning electron microscopy. the results indicated failure due to old-age wear-out of the coatings was mainly caused by numerous micropits formed on the wear track during repeated rolling contact.

• Journal of Welding and Joining
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• v.25 no.3
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• pp.78-84
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• 2007

Laser Material Processing has been replaced the conventional machining systems - cutting, drilling, welding and surface modification and so on. Especially, LTH(Laser Transformation Hardening) process is one branch of the laser surface modification process. Conventionally, some techniques like a gas carburizing and nitriding as well as induction and torch heating have been used to harden the carbon steels. But these methods not only request post-machining resulted from a deformation but also have complex processing procedures. Besides, LTH process has some merits as : 1. It is easy to control the case depth because of output(laser power) adjustability. 2. It is able to harden the localized and complicated a.ea and minimize a deformation due to a unique property of a localized heat source. 3. An additional cooling medium is not required due to self quenching. 4. A prominent hardening results can be obtained. This study is related to the surface hardening of the rod-shaped carbon steel applied to the lathe based complex processing mechanism, a basic behavior of surface hardening, hardness distribution and structural characteristics in the hardened zone.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.776-780
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• 2002

This paper describes the concept and the characteristics of hyper interfacial bonding developed as a new concept joining process for UFG (ultra-fine grained) steel. Hyper interfacial bonding process is characterized by instantaneous surface melting bonding which involves a series of steps, namely, surface heating by high frequency induction, the rapid removing of heating coil and joining by pressing specimens. UFG steels used in this study have the average grain size of 1.25 ${\mu}{\textrm}{m}$. The surface of specimen can be rapidly heated up and melted within 0.2s. Temperature gradient near heated surface is relatively steep, and peak temperature drastically fell down to about 1100K at the depth of 2~3mm away from the heated surface of specimen. Bainite is observed near bond interface, and also M-A (martensite-austenite) islands are observed in HAZ. Grain size increases with increasing heating power, however, the grain size in bonded zone can be restrained under 11 ${\mu}{\textrm}{m}$. Hardened zone is limited to near bond interface, and the maximum hardness is Hv350~Hv390.

• Journal of Power System Engineering
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• v.21 no.3
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• pp.37-44
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• 2017

In this study, failure analysis of the angular pin for molding machines to aluminum component molding was carried out. SM45C steel was used for the angular pin, it was surface hardened by the induction surface hardening heat treatment. The cross section of damaged angular pin was observed, and micro Vickers hardness value from the fractured part was measured. Brittle fracture was occurred from the fracture surface of angular pin, therefore, impact toughness value was evaluated by V-notch Charpy impact test. It was confirmed that the impact absorption energy was high when was tempered at a high temperature for a long time, and the toughness was slightly increased. Also, 2-parameter Weibull statistical analysis was investigated in order to evaluate the reliability of the measured micro Vickers hardness values and absorbed energy. The micro Vickers hardness and absorbed energy well followed a two-parameter Weibull probability distribution, respectively. The reverse design against angular pin was proposed as possible by using test results.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.5
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• pp.355-359
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• 2000

Ion beam assisted deposition system was used to deposit CNx coatings with various thickness on the substrates of high-frequency induction hardened steels. Rolling contact fatigue tests were performed using Polymet RCF-1 machine with a constant supply of lubricant. Rolling contact fatigue life was substantially different in the steels with various thickness of CNx coatings. The optimum thickness of CNx coating was found to be $8.9{\mu}m$, showing the longest fatigue life, mainly caused by higher resistance to initiation of cracks and protective overcoat remaining to the surface failure during rolling contact fatigue. Cracks were initiated in the substrates under the surface of wear track and propagated to the surface, which eventually resulted in the failure. The reduction of fatigue life observed in the specimen with elimination of CNx coating during rolling contact fatigue was explained by the substrates deformation.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.6
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• pp.139-144
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• 2012

In the automobile industry, the various efforts to lower their industrial cost and enhance fuel efficiency have been made through process improvement or weight saving of automobile parts. Gear is one of significant parts of transmission, which is made by cast iron or alloy steel. It is expensive due to complex processing, inferior materials and large machining allowance. In this study, alternative gear cars oil which is based on fluid applications materials is produced by reducing surface induction hardening and carburizing hardened in production. And then, wear characteristic and mechanical properties such as hardness of the sintered alloy which is used as a substitute for small machining allowance is investigated.

• Korean Journal of Materials Research
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• v.19 no.9
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• pp.457-461
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• 2009

Recently, metal molding has become essential not only for automobile parts, but also mass production, and has greatly influenced production costs as well as the quality of products. Its surface has been treated by carburizing, nitriding and induction hardening, but these existing treatments cause considerable deformation and increase the expense of postprocessing after treatment; furthermore, these treatments cannot be easily applied to parts that requiring the hardening of only a certain section. This is because the treatment cannot heat the material homogeneously, nor can it heat all of it. Laser surface treatment was developed to overcome these disadvantages, and, when the laser beam is irradiated on the surface and laser speed is appropriate, the laser focal position is rapidly heated and the thermal energy of surface penetrates the material after irradiation, finally imbuing it with a new mechanical characteristic by the process of self-quenching. This research estimates the material characteristic after efficient and functional surface treatment using HPDL, which is more efficient than the existing CW Nd:YAG laser heat source. To estimate this, microstructural changes and hardness characteristics of three parts (the surface treatment part, heat affect zone, and parental material) are observed with the change of laser beam speed and surface temperature. Moreover, the depth of the hardened area is observed with the change of the laser beam speed and temperature.