• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1041-1047
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• 2011

In this study, two types of die material cast iron was treated for surface hardening by using high power diode laser to improve mechanical properties of die which is using as essential production technology in the parts manufacturing in virtually all the infrastructure industries now. First of all, the heat treatment characteristics of FCD550 material which is spheroidal graphite cast iron, and through the heat treatment of HCI350 material which is flake graphite cast iron, the heat treatment characteristics of the two materials were compared. The hardness of hardened zone increased over 3 times over base material for both specimens, but as for required heat input, HCI350 was higher than FCD550 material depending on the heat conductivity of the materials by the content amount and shape of graphite contained in the material.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.921-924
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• 1995

Case hardening behavior of carbon tool steel(SK5) was investigated after pulsed YAG laser irradiation. In the case od beam passes,martensite formed in the melt zone and in former pearlite regions of the austenitization zone exhibits vary high Vickers hardness values. The molten depth and width decrease as the beam power density increase. The influence of depth and width of color painted specimen was also investigated. The molten zone of the black painted specimen was the largest. The were loss of the black painted specimen was smaller than any other painted or raw material.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.5
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• pp.67-74
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• 2004

Laser heat treatment is an effective technique used to improve the tribological properties and also to increase the service life of automobile components such as camshafts, crankshatfs, lorry brake drums and gears. High power $CO_2$ lasers and Nd:YAG lasers are employed for localized hardening of materials and hence are of potential application in the automobile industries. The heat is conducted rapidly into the bulk of the specimen causing self-quenching action to occur and the formation of matrensitic structure. In this investigation, the microstructrual features occurring in Nd:YAG laser hardening SM45C and $STD_11$ steel are discussed with the use of optical microscopic and scanning electron microscopic analysis. Moreover, This paper describes the optimisation of the processing parameters for maximum hardened depth of SM45C and $STD_11$ steel specimens of 10mm thickness by using CW:YAG laser.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.75-81
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• 2016

This study applied laser surface melting process using CW(Continuous wave) Yb:YAG laser and cold-work die steel SM45C and investigated microstructure and hardness. Laser beam speed, power and beam interval are fixed at 70 mm/sec, 2.8 kW and $800{\mu}m$ respectively. Depth of Hardening layer(Melting zone) was a minimum of 0.8 mm and a maximum of 1.0 mm that exceeds the limit of minimum depth 0.5 mm applying trimming die. In all weld zone, macrostructure was dendrite structure. At the dendrite boundary, Mn, Al, S and O was segregated and MnS and Al oxide existed. However, this inclusion didn't observe in the heat-affected zone (HAZ). As a result of interpreting phase transformation of binary diagram, MnS crystallizes from liquid. Also, it estimated that Al oxide forms by reacting with oxygen in the atmosphere. The hardness of the melting zone was from 650 Hv to 660 Hv regardless of the location that higher 60 Hv than the hardness of the HAZ that had maximum 600 Hv. In comparison with the size of microstructure using electron backscatter diffraction(EBSD), the size of microstructure in the melting zone was smaller than HAZ. Because it estimated that cooling rate of laser surface melting process is faster than water quenching.

• Proceedings of the KWS Conference
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• 1994.05a
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• pp.145-147
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• 1994

• Journal of the Korean Society for Heat Treatment
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• v.2 no.1
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• pp.21-26
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• 1989

• 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 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.

• Journal of Welding and Joining
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• v.33 no.3
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• pp.54-61
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• 2015

In this study, effect of laser power on hardness and microstructure of SKD61 Hot Die steel of which surface was melted and hardened with Yb:YAG disk laser was investigated. Beam speed was fixed at 70 mm/sec and distance between them was 0.8 mm about Laser surface melting. The only thing that was changed laser power. Laser powers were 2.0, 2.4 and 2.8 kW. No defect was found under all conditions. As the laser power increased, the penetration depth were deepened and the bead width was also widened. There was no hardness deviation of fusion zone at same laser power and it was higher than that of heat affected zone. In addition, the more laser power increased, the more hardness in fusion zone decreased. Fusion zone was macroscopically dendrite structure. However, core matric in dendrite was lath martensite of 100 nm size. There were $M_{23}C_6$ of 500 nm and the VC and $Mo_2C$ of a nano meters on boundary of dendrite.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.4
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• pp.289-299
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• 1996

This study has been performed to investigate into some effects of power density and traverse speed of laser beam on the microstructure, hardness and residual stress of AISI 4140 treated by laser surface hardening technique. Optical micrograph has shown that large martensite and a small amount of retained austenite in outermost surface layer and fine lath martensite in inner surface hardened layer are formed under the condition of a given power density and traverse speed. Hardness measurements have revealed that as the power density increases at a given 2.0m/min of the traverse speed, the maximum hardness values of outermost surface hardened layer is increased from Hv=635 to Hv=670. X-ray analysis for residual stress has exhibited that low compressive residual stress values are obtained in center point of the cress section of surface hardened layer with in mid point between the edge and the center point, about 1.5mm from the center point, due simply to a difference in self-quenching rate. It has been shown that the higher the power density at a given traverse speed and the olwer the traverse speed at a given power density, the more the compressive residual stress values are increased due to an increase in the input heat of laser beam.