• Journal of the Korean Society for Heat Treatment
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• v.12 no.2
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• pp.166-173
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• 1999

Commercial carbon steels containing 0.2~0.55 wt.----C were plasma-nitrided or plasma nitrocarburized at $550^{\circ}C$ for 21.6Ks using $H_2-N_2$ or $H_2-N_2$-CO mixed gas respectively. The characteristics of hardening and wear-resistance of each treatment were studied and compared. And also microstructure of nitrided layer and nitrides formed in compound layer near surface were studied. All plasma-nitrided steels investigated showed remarkable increase of surface hardness with the increase of carbon content. But nitrocarburized steels resulted in higher surface-hardness than plasma-nitrided steels, which means that nitrocarburized has higher surface-hardening effect. Plasma-nitrided steels showed hardness increase in through-thickness direction near surface. And also nitrocarburized steels showed similar hardness distribution in through-thickness direction to that of plasma-nitrided steel. However, nitrocarburized steels had higher cross-sectional maximum-hardness than plasma-nitrided steels as much as 100Hv. Wear test showed that the amount of specific wear was reduced by both plasma-nitriding and nitrocarburized, showing that the amount of specific wear was not related to the hardness. But non-treated specimen showed that the amount of specific wear was related to the hardness.

• Journal of Power System Engineering
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• v.20 no.4
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• pp.5-11
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• 2016

This study analyzed the damage to a slitting knife after cutting steel sheets. Damages to the structure were observed and wear tests were conducted. In addition, the degradation on the damaged and undamaged parts was compared with a micro Vickers hardness test. Weibull statistical analysis was carried out in order to evaluate the reliability of the micro Vickers hardness measured data. Spalling of the edge portion occurred by degradation during use over a long period. Rough parts in the specimens were caused by damage because the slitting knife was used for 1 year. The friction coefficient and wear loss at the damaged parts of the knife edge were slightly larger from shock due to repetitive cutting operation. The micro Vickers hardness followed a two-parameter Weibull probability distribution.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.205-210
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• 2002

This article presents an integrated modeling approach for coupled analysis of heat transfer and microstructure evolution in welding carbon steel. The modeling procedure utilizes commercial [mite element code ABAQUS/Standard as the platform for solving the equation of heat conduction. User subroutines that implement computational thermodynamics and kinetics models are integrated with the FEA code to compute the transient microstructure evolution. In this study, the integrated models are applied to simulate the hot-tap repair welding of carbon steel pipeline. Microstructural components are treated as user output variables. Based on the predicted microstructure and cooling rates, hardness distributions in the welds were also predicted. The predicted microstructure and hardness distribution were found in good agreement with metallographic examinations and hardness measurements. This study demonstrates the applicability of computational models for the development of welding procedure for in-service pipeline repair.

• International Journal of Korean Welding Society
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• v.2 no.2
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• pp.1-6
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• 2002

This article presents an integrated modeling approach for coupled analysis of heat transfer and microstructure evolution in welding carbon steel. The modeling procedure utilizes commercial finite element code ABAQUS/Standard as the platform for solving the equation of heat conduction. User subroutines that Implement computational thermodynamics and kinetics models are integrated with the FEA code to compute the transient microstructure evolution. In this study, the integrated models are applied to simulate the hot-tap repair welding of carbon steel pipeline. Microstructural components are treated as user output variables. Based on the predicted microstructure and cooling rates, hardness distributions in the welds were also predicted. The predicted microstructure and hardness distribution were found in good agreement with metallographic examinations and hardness measurements. This study demonstrates the applicability of computational models for the development of welding procedure for in-service pipeline repair.

• Journal of the Korean Society for Heat Treatment
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• v.35 no.2
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• pp.66-73
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• 2022

Partial-hardened hot stamping has been well known to be very effective to absorb more energy in automotive lateral crash. Hardness distribution and dimensional change after partial-hardened hot stamping have been studied to find out effect of thermal deformation of the heated hot stamping die on dimensional accuracy of automotive center pillar. Soft zone of commercial center pillar showed 275~345 in Vickers hardness, indicating bigger non-uniformity which resulted from thermal deformation of heated die. Dimensional changes in soft zone of the commercial center pillar measured by three dimensional scanner were much bigger than that in hard zone. It has been found that hot stamping die compensation considering thermal deformation in soft zone causes a significant decrease in hardness deviation in the soft zone, corresponding to 20 percent of commercial center pillar and subsequently leads to much higher dimensional accuracy.

• Transactions of Materials Processing
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• v.19 no.1
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• pp.25-31
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• 2010

To achieve desired microstructure and mechanical property of a manufacturing product, heat treatment process is applied as a secondary process after forging. Especially, quenching process is used for improving strength, hardness, and wear resistance since phase transformation occurs owing to rapid heat transfer from the surface of the specimen. In the present paper, a study on surface temperature measurement for water quenching of eutectoid steel was investigated. In order to determine the temperature history in experiments, three different measuring schemes were used by varying installation techniques of K-type thermocouples. Depending on the measured temperature distribution at the surface of the specimen, convective heat transfer coefficients were numerically determined as a function of temperature by the inverse finite element analysis considering the latent heat generation due to phase transformation. Based on the inversely determined convective heat transfer coefficient, temperature, phase, and hardness distributions in the specimen after water quenching were numerically predicted. By comparing the experimental and computational hardness distribution at three different locations in the specimen, the best temperature measuring scheme was determined. This work clearly demonstrates the effect of temperature measurement on the final mechanical property in terms of hardness distribution.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.3
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• pp.376-381
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• 2012

This paper deals with application of instrumented indentation technique for quality inspection methodology for automobile component. For this, the instrumented indentation tests were performed the normal and cracked compressor journal, which is made from spheroidal graphite cast iron and utilized in air-conditioning system. And the Brinell hardness was estimated using the unloading slope and maximum indentation force. With the aid of Normal distribution, this Brinell hardness was statistically compared and analyzed with hardness measured by indentation hardness tests. Also, application possibility of reliability-based quality inspection criteria for compressor journal was evaluated through the probabilistic analysis for the Brinell hardness estimated by instrumented indentation technique.

• Journal of Welding and Joining
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• v.30 no.2
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• pp.76-80
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• 2012

In this study, the effect of the welding current on the hardness characteristics and microstructure in the resistance spot welding of 1GPa grade cold-rolled DP steel was investigated, Also, correlation between the hardness and microstructure was discussed. In spite of the change in the welding current, the hardness distributions near weld was similar. the hardness in the HAZ and the fusion zone was higher than that of the base metal and the hardness in the fusion zone was variated with the location. Especially, the hardness of HAZ adjacent to the base metal showed maximum value, and softening zone in the base metal adjacent to HAZ was found. With the increasing of welding current, there were no difference in maximum hardness and average hardness in the fusion zone were, but the hardness of the softening zone reduced. The difference in the hardness in each location of weld due to grain size of prior austenite. The softening of the base metal occurred by tempering of the martensite.

• Journal of Power System Engineering
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• v.20 no.5
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• pp.5-13
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• 2016

This study is on wear damage of the material for a molding machine that be used at finally cutting of metal beam made in roll forming process of vehicle bump beam process line. SKD11 steel was used with the material for cutting mold jig. In the cutting mold jig, Ti diffusion heat treatment after vacuum heat treatment was carried out for upgrade of surface hardness and anti-wear. Also, the heat treatments by various methods were performed to compare the wear damage degree against above the existing heat treatment. Wear loss and friction coefficient were obtained from wear test. And, micro Vickers hardness values were compared with damaged parts or not of cutting mold jig. Micro Vickers hardness value appeared higher at the undamaged part by Ti diffusion heat treatment. The micro Vickers hardness well followed a two-parameter Weibull probability distribution.

• Proceedings of the KWS Conference
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• 1996.10a
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• pp.3-15
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• 1996

The formation of a thicker hard alloyed layer have been investigated on the surface of aluminum cast alloy (AC2B) by PTA overlaying process with Cr, Cu and Ni motel powders under the condition of overlaying current 125-200A. overlaying speed 150 mm/min and different powder feeding rate 5-20 g/min. In addition the characteristics of hardening and wear resistance of alloyed layer here been examined in relation to the microstructure of alloyed layer. Main results obtained were summarized as follows: 1) There was an optimum overlaying condition to get a good alloyed layer with smooth surface. This good layer became easy to be formed as increasing overlaying current and decreasing powder feeding rate under a constant overlaying speed. 2) Cu powder was the most superior one in metal powders used due to a wide optimum overlaying condition range, uniform hardness distribution of Hv250-350, good oar resistance and freedom from cracking in alloyed layer with fine hyper-eutectic structure. 3) On the contrary, irregular hardness distribution was usually obtained in Cr ar Ni alloyed layers of which hardness was increased as Cr or Ni contents and reached to maximum hardness of about Hv400-850 at about 60wt%cr or 40wt%Ni in alloyed layer. 4) Cracking occurred in Cr or Ni alloyed layers with higher hardness than Hv250-300 at mere than 20-25wt% of Cr or Ni contents in alloyed layer. Porosity was observed in all alloyed layers but decreased by usage of spherical powder with smooth surface.