• Journal of the Korean Society for Precision Engineering
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• v.16 no.7
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• pp.188-195
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• 1999

Cutting edge plays an important role in generating machined surface. In order to consider the geometric effects of the cutting edge on mechanical states, the concept of ploughing force and stagnation point was introduced which explains the generating mechanism of machined surface during cutting. The effects of edge radius and nose radius of cutting tool on the distribution of residual stresses of the machined surface having several hardness were studied. Good machined surface having high compressive residual surface stresses can be achieved if cutting tools having large edge radius and small nose radius are used for cutting work materials having high hardness with high depth of cut. The magnitude of edge radius and the hardness of work material also affected the shape of the chip in orthogonal cutting.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.427-432
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• 1995

Surface heat treatment using a laser beam or an electron beam is studied through numerical analyses and experiments. For the surface heat treatment process, a theoretical model is developed to predict the effects of laser beam power, travel speed and properties of a workpiece on the depth and width of the heat affected zone(HAZ). The shape of HAZ and the hardness of heat-treated surface are experimentally obtained using an electron beam. Three materials(SS41, S45C and S55C) are selected as workpiece materials. The hardness of HAZ is increased up to 3 times for materials of a low carbon content. The results of the numerical analysis are compared with those of experiments. The comparison shows that the numerical model predicts larger depths and widths.

• Journal of Korea Foundry Society
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• v.30 no.4
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• pp.142-146
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• 2010

To elucidate the characteristics of cavitation erosion of super duplex stainless steel, a cavitation erosion test, an optical microstructure, a hardness test, and a transmission electron microscope (TEM) analysis were conducted. As aging time at $475^{\circ}C$ increased, the hardness of ferrite phase increased whereas that of austenite phase was nearly constant. The reason why the cavitation erosion resistance increased with an increase of aging time was due to the formation of W-rich phases (${\alpha}$') of a nanometer scale with the high hardness that were precipitated within ${\alpha}$-grains and at ${\alpha}$-grain boundaries during aging, compared with that of the solution annealed alloy.

• Journal of the Korean institute of surface engineering
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• v.31 no.5
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• pp.266-277
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• 1998

The effects of $H_2S$ gas ratio, temperature and time on the case depth, hardness, and sulfide and nitride formation on the surface of sulfnitrided SCM440 steel have been studied by micro-pulse plasma technique. The thickness of compound layer of sulfide and nitride increased with the increase of time, temperautre and $H_2S$ gas ratio. But surface hardness decreased with the increase of soft sulfide layer because the hard nitride layer formed beneath the sulfide. The thickness of sulfide layer was about 10$\mu\textrm{m}$ abpve 0.0088% of $H_2S$ gas. The highest surface hardness of the compound layer was Hv835 at $530^{\circ}C$, 1hr and 0.06% of $H_2S$ gas. X-ray diffraction indicated that the surface products were $Fe_{1_x}S$, $Fe_{2.5}N$ and $Fe_4N$. It was confirmed by EPMA that sulfide only existed in the surface.

• Journal of Welding and Joining
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• v.32 no.4
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• pp.34-38
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• 2014

Carburizing treatments are the important way to developing fatigue strength and wear resistance. It is well known that the case depth is one of the most significant parameters determining fatigue strength. In this study, 3-point bending fatigue test was conducted to evaluate fatigue strength for the carburized depth with 18CrNiMo7-6 steel. As a result, fatigue strength increased with effective case depth decreased. It is shown that hardness in case hardened layer played principal role in the fatigue strength.

• Journal of the Korean Professional Engineers Association
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• v.25 no.4
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• pp.102-108
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• 1992

This study was carried to find out the soil characteristics of landslide site and to develope landslide prediction method by seismic refraction prospecting. For these aims, landslide condition and travel time were investigated at 68 Landslide sites over the country during 1990 to 1991. The results were as follows. 1. The surface of rupture was included mainly in C layer. Its Hardness was less than 3kg / $\textrm{cm}^2$ at the upper pare of landslide. 2. When the profile line length was 20m, the range of travel time was 40 to 90 msec. The travel time did not differ between bedrocks. 3. Refraction distance ranged from 1 to 7m and mean of that was 2.5m. Travel time was increased according to receiving distance without large variance in the refraction distance but that was appeared large variance out of the refraction distance on slope that has shallow soil depth and discontinuous ground surface. Therefore, the spread distance must be shorten to 10-l5m. 4. The seismic velocity at the first layer(layer of rupture) was less than 500m1sec by degree of weathering and the velocity at the second layer decreased in order of Granite> Granitic gneiss >Sedimentary rock. 5. The first layer observed by seismic refraction was contained C layer that has parent material and weathered rocks of hardness 10-20kg/$\textrm{cm}^2$. 6. Among the range of seismic velocity was less than 200m/sec in 63% of the total plots, 200-300m/sec in 34% and 300-500m /sec in 3%. 7. There was a proportional relationship between seismic prospecting soil depth and executive soil depth, and seismic propection soil depth was about 10 to 20cm deeper than the order.

• Journal of Environmental Science International
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• v.16 no.6
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• pp.677-682
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• 2007

This study was performed to provide the basic information on characteristics of groundwater pollution in Gyeongsan city. Forty two groundwater samples were collected, and pH, DO, COD, $NH_3-N,\;NO_3^--N$, T-N, $PO_4^{3-}-P$, Cl, Ca, Mg, hardness, evaporate residues and others were investigated. And, ANOVA analyses were carried out to reveal the differences in water pollution indicator values of by industry, commerce/residence and agriculture areas. The results were as follows. 1. The mean values of pH, DO, COD, $NH_3-N,\;NO_3^--N$, T-N, $PO_4^{3-}-P$, Cl, evaporate residues, Ca and hardness were 6.9, $7.9mg/\ell,\;0.4mg/\ell,\;2.44mg/\ell,\;2.73mg/\ell,\;6.06mg/\ell,\;0.82mg/\ell,\;32.72mg/\ell,\;381.67mg/\ell,\;41.53mg/\ell,\;177.17mg/\ell$, respectively. 2. As groundwater became deeper, the values of Cl, Ca, Mg, Na, hardness and evaporate residues remarkably increased, but those of COD, $NH_3^--N,\;NO_3^--N,\;NO_2^-N$, T-N decreased. 3. The values of COD, Cl, Ca, Mg, Na, hardness and evaporate residues were very high in industrial area, and those of $NH_3-N,\;NO_2^--N$, T-N were very high in commercial/residential area, and those of $NO_3^--N$ were a little high in agricultural area. 4. The correlations between depth and each value of Mg, Na, Fe, hardness and evaporate residues were highly positive, and those between DO and each value of Mg, Cu, Fe, hardness and evaporate residues were highly negative. 5. According to ANOVA analyses, the differences in three area groups (industry, commerce/residence and agriculture) on the values of $NH_3-N$, T-N, evaporate residues, hardness, Ca, Mg, K and Fe were significant at 1% level.

• 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.2
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• pp.130-138
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• 1996

It has been investigated that the ion nitriding effects of a STD61 steel in various time conditions of 3 to 9 hours, and the microstructure of compound and diffusion layers of the ion nitrided specimen for 6 hours and subsequently reheated for 1 hour at various temperatures of $400{\sim}800^{\circ}C$ As the nitriding time increased, the thickness of compound and diffusion layers was increased, but the hardness of surface was not considerably increased (Max Hv=1045 at 9hrs). Some of the nitrogen was denitrided out of the surfac and diffused into the core, and also the oxides ($Fe_3O_4$, $Fe_2O_3$) were formed on the surface of the specimen during reheating. The compound layer was partially decomposed at about $600^{\circ}C$ but the diffusion layer was increased up to $800^{\circ}C$. With increasing reheated temperture, the hardness of the surface was decreased, whereas the hardness depth of diffusion layer (0.25mm) was increased up to $600^{\circ}C$ more than that of ion nitrided (0.18mm). The blend-heat treated STD61 steel by ion nitriding is therefore expected to hold on the characteristics of ion nitriding up to $600^{\circ}C$.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.2
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• pp.216-223
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• 2010

The general way to process the surface by means of the laser was heat treatment for strengthening the surface hardness. They have used the laser for changing the property of the surface, especially for metal. Generally, it is recent increasing tendency to use the thin plate panel for making things smaller and lightweight. However, thin plate should be strengthened or let the thin plate panel have moment of inertia by means of engraving the groove or wave on them for lightweight and strengthening. Therefore it is expected that the thin plate panel can be harder and more stable through processing the metal surface by laser beam irradiation and the hardness of thin plate possibly can be also changed how many parts of them are harden. Through this research, it can be grasped how the hardness and mechanical characteristic changes according to width and depth of groove by laser affect the max stress by the ratio of $A_H/A_T$ (hardening area/total area) and characteristic of displacement and structural characteristic for making the thin plate harder by the strengthening metal surface of thin plate by laser through the experiment and analysis of FEA can be presented.