• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.91-97
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• 2004

The drawbead is one of the most important factors in sheet metal forming for automotive parts. So clarifying the friction characteristics between sheets and drawbead is essential to improve the formability of sheet metal. Therefore in this study, drawbead friction test was performed at various bead materials(FC300, HC891, FCD550, HD700, HK600, HK700, SKD11) and surface treatment of beads(Base, induction hardening, Cr plating, ion nitriding, Toyoda diffusion process, TiCN, TiN, CrN). Circular shape bead has been used for the test. The results show that friction and drawing characteristics were mainly influenced by surface treatment.

• Korean Journal of Metals and Materials
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• v.47 no.2
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• pp.71-78
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• 2009

The precipitation behavior of solute carbon and nitrogen strongly affects the mechanical properties of low-carbon automotive panel. In the present study, the effects of aluminum and solute nitrogen on the bake hardenability and strain aging of extremely low-carbon steel with carbon content below 15 ppm has been investigated. The ferrite grain size and distribution of precipitates were varied with the amount of aluminum content of 0.003 to ~ 0.100 wt% in a constant solute carbon and nitrogen. With increasing the aluminum content, the ferrite grain size is increased and strain aging is delayed. The strain aging is also delayed by increasing the annealing temperature, although the ferrite grain size is not much changed.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.5
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• pp.499-506
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• 2013

Heat-treatment is one of the core technologies to enhance various characteristics such as strength, hardness, toughness, abrasion resistance and fatigue resistance for the mold material. This paper focuses on characteristics of the laser heat-treatment according to the cylindrical bar diameter variation in case of the SM45C. From the results of the experiments, it has been observed that the maximum hardness is 744Hv when the power is 1630W and the travel of laser is 0.5m/min. And then, the hardness width, depth and microstructure were observed for characteristics. Finally, when the cylindrical bar diameter size grow, the hardness width decrease whereas hardness depth increase.

• Tribology and Lubricants
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• v.13 no.2
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• pp.39-45
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• 1997

The shot peening treatment were conducted for improving the strength of rolling contact fatigue of machine element like a gear. This paper was undertaken to analyze the influence of shot peening treatment for inner race of ball bearing on the rolling contact fatigue. Shot peening treatment were applied to the full hardened and the carbonitrided bearing. And the rolling contact fatigue life test and X-ray diffraction test were carried out. The results of this study showed that the fatigue life of ball bearing in the clean and the contaminated oil could be improved by shot peening treatment. This effect was found to be more pronounced to the full hardened bearing. These facts might be due to the generation of compressive residual stress and the strain hardening of surface layer by shot peening treatment. The failure of the shot peened bearing were presumed to initiate at surface.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.2
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• pp.275-282
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• 2010

The improved properties of surface layer can be achieved by so-called "new salt bath nitriding(NSBN)", which has been developed by a domestic company. This process based upon modified traditional salt bath nitriding process, increased hardenability with minimum toughness deterioration. This process also offers not only less white layer surfaces but also more eco-friendly one. That is, NSBN is the new eco-friendly surface treatment technology removing harmful $CN^-$ and toxic gas. According to the research of applying NSBN to Cr-Mo-V steel which has been used in defense industry, showed the improved result of wear resistance and surface hardening than non-coated condition. In further, we expect NSBN to curtail expenses and productivity improvement applied to the various defense industry parts.

• Journal of Industrial Technology
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• v.26 no.A
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• pp.69-73
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• 2006

Mach peening treatment is one of the various kinds of techniques to improve the fatigue properties. The mach peening process gives high-level work hardening and compressive residual stress near the surface layer, improving the fatigue strength. In addition, this treatment reduces slip bands that initiate the fatigue cracks near the surface. During impingement, a plastic indentation surrounded by a plastic zone is formed. Mach peening treatment characteristic is less energy consumption and is an environmental friendly processing methods that is not accompanied by pollution. It is machining process that can prevent fatigue fracture beforehand in structure using already as well as process of production. The test results showed that fatigue crack propagation delay appeared by drilling type 43%, mach peening type 110%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.9
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• pp.5460-5466
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• 2014

In this study, mainly for kitchen knives and small swords, cutlery, etc. STS420J2 used material used for the experiments. In order to cure the surface of the test piece after the rough grinding and fine grinding was performed in order polishing. Perform the surface hardening of STS420J2 local area by using a diode laser. The output of the laser diode and the feed rate to the process variable. Micro-hardness testing, microstructure testing, scanning electron microscope testing(SEM), the heat input to the analysis. After analyzing the experiment to compare the mechanical properties of the material. When using a diode laser to assess the soundness of the surface hardening. Accordingly, the process for deriving the optimum demonstrate the feasibility.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.1620-1625
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• 2015

In this study, a variety of industrial gears, shafts, chains, rollers, mold, etc. are widely used inautomotive steel carbon steel for machine structural SM45C typical material used for the experiments. In order to cure the surface of the test piece after the rough grinding and fine grinding was performed in order polishing. Perform the surface hardening of SM45C lacal area by using a diode laser. The output of the laser diode and the feed rate to the process variable. Micro-hardness testing, microstructure testing, scanning electron microscope testing(SEM), the heat input to the analysis. After analyzing the experiment to compare the mechanical properties of the material. When using a diode laser to assess the soundness of the surface hardening. Accordingly, the process for deriving the optimum demonstrate the feasibility.

• Journal of the Korean institute of surface engineering
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• v.39 no.2
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• pp.49-56
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• 2006

In this study, the movable flame hardening process of 12Cr steel for a uniform hardness and desirable residual stress have been investigated. For this, the temperature cycles have been controlled accurately as a function of the three processing variables, the flame intensity $I_f$, the scanning velocity $V_s$, and the initial flame holding time $t_h$, where the standard surface temperature $T_{s,\;max}$, was maintained at $960^{\circ}C$. The optimized conditions were $V_s=0.68mn/s\;and\;t_h=67sec$ for the $C_3H_8:O_2\;=\;5:20l/min,\;V_s=0.80mm/s$ and $t_h=56sec$ for the $C_3H_8:O_2=6:24l/min,\;V_s=1.01mm/s\;and\;t_h=48sec$ for the $C_3H_8:O_2=7:28l/min,\;and\;V_s=1.15mm/s$ and $t_h=39sec$ for the $C_3H_8:O_2$=8:32 l/min. The optimally flame-hardened surface exhibited uniform distributions of the hardness and residual compressive stress over the treated area with moderate levels of $470{\sim}490HV_{0.2}$in hardness and $-300{\sim}-450MPa$ in residual stress, which were acceptable on the basis of the acceptance criteria of Siemens AG-KWU and GE Power Generation Engineering.

• Journal of the Korean Society for Heat Treatment
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• v.8 no.3
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• pp.169-181
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• 1995

This study has been performed to investigate some effects of the power density and traverse speed of laser beam on the optical microstructure, hardness and fatigue resistance of gray cast iron treated by laser surface hardening technique. Optical micrograph has shown that the dissolution of graphite flakes and the coarsening of lath martensite tend to increase with a small amount of retained austenite as the power density increases under the condition of a given traverse speed. Hardness measurements have revealed that as the power density increases, hardness values of outermost surface layer increases from Hv=620 to Hv=647 in case of traverse speed of 2.0m/min at gray cast iron. Fatigue test has exhibited that the fatigue strength of laser surface hardened specimen is superier compared to that of untreated specimen, showing that values for the fatigue strength at $N_f=10^7$ of gray cast iron laser-surface-hardened at a low power density of $4076w/cm^2$ and a high power density of $8153w/cm^2$ under the condition of a given traverse speed of 2.0m/min are $15kg_f/mm^2$ and $20kg_f/mm^2$, respectively, whereas the fatigue strength of untreated specimen is $11kg_f/mm^2$. Under high stress-low cycle condition a noraml brittleness fracture appears, whereas a ductile fracture with beach mark is observed in the specimen tested under low stress-high cycle condition.