• 열처리공학회지
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• 제25권3호
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• pp.115-120
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• 2012

It has been known that the ferritic stainless steel can be changed to martensitic stainless steel when nitrogen is added. However the high hardness of martensitic stainless steel prevents the plastic deformation. In this study, instead of martensite, the surface microstructure was changed into nitrogen pearlite to increase the plastic deformation easily by isothermal heat treatment after high temperature gas nitriding (HTGN) the AISI 430 ferritic stainless steel. The isothermal treatment was carried out at $780^{\circ}C$ for 4, 6, and 10 hrs, respectively, after HTGN treatment at $1100^{\circ}C$ for 10 hrs. The surface layer of isothermal-treated steel appeared nitrogen pearlite composed with fine chromium nitride and ferrite. Hence, the interior region that was not affected by nitrogen permeation exhibited ferrite phase. When quenching the isothermal treated steel at 1100oC, martensitic phase formed at the surface layer. The hardness of surface layer of isothermal-treated steel and quenched steel measured the value of 150~240 Hv and 630 Hv, respectively.

• 한국레이저가공학회지
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• 제3권1호
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• pp.29-37
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• 2000

For a development purpose of thick metal / metal Graded-Boundary Materials(GBM), a basic research on the fabrication of Ni-Cr/steel GBM was carried out by a laser beam and its mechanical properties and thermal characteristics were investigated. In order to produce a compositionally graded boundary region between substrate steel and added Ni-Cr alloy, a series of surface alloying treatments was performed with a high power CO$_2$ laser beam. Ni-Cr sheet was placed on a low carbon steel plate(0.18%C), and then a CO$_2$ laser beam was irradiated on the surface to produce a homogeneous alloyed layer. On this first surface-alloyed layer, another Ni-Cr sheet was placed and then the CO$_2$ laser beam was irradiated again to produce second surface-alloyed layer. Sequential repetitions of laser surface alloying treatment 4 times resulted in a graded-boundary region with the thickness of about 1.4mm. Simultaneous concentration profiles of different kinds of alloying elements(Ni and Cr) showed from 42%Ni, 45%Cr and 13%Fe on surface region to 0%Ni, 0%Cr and 99%Fe in substrate region. Also a thermal conductivity gradient resulted in graded-region and its value changed from 0.03㎈/cm s$\^{C}$ in surface region to 0.1㎈/cm s$\^{C}$ in substrate region. Microstructural observation showed that any visible root porosities and solidification shrinkage cracks were not formed in graded region between alloyed layer and substrate region during rapid cooling.

• 한국표면공학회지
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• 제47권5호
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• pp.221-226
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• 2014

A low temperature plasma nitrocarburizng was implemented on the duplex stainless steel to achieve the enhancement of surface hardness without degradation of its corrosion resistance. Attempts were made to investigate the influence of Pulse frequency and Duty factor of pulsed power in a high Pulse frequency regime on the surface characteristics of the hardened layer. The hardened layer (S-phase) was formed on all of the treated surfaces. Surface hardness reached up to 1300 $HV_{0.1}$ which is about 4.6 times higher than that of the untreated material (280 $HV_{0.1}$). The thickness of the hardened layer tends to increase lightly with the higher Pulse frequency and the higher Duty factor. The corrosion resistance of nitrocarburized duplex stainless steel was almost similar to that of the untreated material. Both the Pulse frequency and the Duty factor do not have a significant influence on the corrosion property of plasma treated duplex stainless steel.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.179-180
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• 2002

In this study. the friction transition diagram based on the effect of oxide layer formation on contact surface between TiN coated steel ball and uncoated steel disk was constructed. From the diagram. it can be seen that as the contact load increases. the contact number of cycle at the beginning of oxide layer formation decreases linearly and as the coating thickness increases and the surface roughness of steel disk increases under same contact load. that increases. For the coated ball specimen, a AISI 52100 steel ball was used and AISI 1045 steel was used for the disk counter part.

• 한국주조공학회지
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• 제23권2호
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• pp.86-93
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• 2003

It has been a major concern in the foundry that steel castings manufactured by the evaporative pattern casting process encounter the carbon pick-up problem. A carbon rich layer at the evaporative pattern cast surface is a result of interactions between the gaseous products from foamed polystyrene and the molten metal. The carburized layer with a high hardness makes it difficult to machine the casting. In this study, the influence of the density of EPS pattern and coatings on carbon pick-up phenomena of S25C and S45C commercial carbon cast steel were investigated. As the density of EPS pattern is increased, the carbon concentration of decomposed pattern is increased and the thickness of carburized layer at the surface of steel castings is increased. Also as the density of coatings is increased, the permeability of coatings is decreased and the thickness of carburized layer at the surface of steel castings is increased. S25C steel which has lower original carbon content compared to S45C steel exhibited severe carburization.

• 열처리공학회지
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• 제16권5호
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• pp.253-259
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• 2003

In this study, to find out the reason of deterioration in surface roughness of steel and cast iron after Tufftride, it has been investigated on the relation between the surface roughness and various factors such as the evolution of compound layer, surface morphology, and surface hardness, and change of pore ratio in the compound layer during Tufftride at $580^{\circ}C$. It is found that the surface roughness was increased with the evolution of compound layer during Tufftride of steel and cast iron. The change of surface roughness after Tufftride was reduced with decreasing tho content of carbon and cementite ($Fe_3C$) in the materials. in the cast irons, the various shaped graphites that was exposed to the surface should induce the discontinuous growth of the compound layer, and this resulted in the incoherent interfaces between matrix and compound layer and the deterioration of surface roughness. In the steels, the existence of cementites in the matrix resulted in the incoherent interfaces between matrix and compound layer. It is considered that during Tufftride the surface roughness must be mainly influenced by the formation of the incoherent interface between compound layer and matrix that is affected by some factors such as the microstructure, the composition, and the hardness of the matrix.

• 한국표면공학회지
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• 제31권5호
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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.

• 한국표면공학회지
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• 제17권1호
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• pp.7-13
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• 1984

Carburizing of a 12%Cr steel containing 0.6%Si was performed at 950$^{\circ}C$ for various times, and the microstructure, hardness and the water characteristics of the carburized chromium steel were examined. The results obtained in this study are as follows: 1. Carbide-dispersed layer (CD layer) with fine dispersion of $Cr_7C_3$ in martensite matrix was formed by carburizing. The radius and amount of the carbides in the surface region of CD layer were about 0.3${\mu}m$ and 35% by volume, respectively. 2. Chromium steel carburized and quench-tempered showed better wear resistance and hardness than ordinary high chromium tool steel. It is concluded from these results that fine dispered carbides are very effective in improving wear resistance and hardness.

• 한국정밀공학회지
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• 제11권5호
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• pp.153-160
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• 1994

In this study, residual stress and surface roughness were investigated experimentally to evaluate surface integrity on surface layer machined by CBN, ceramics and WC cutting tools. When machining difficult-to-cut material (hardened STD11 steel $H_{R}$C 60), residual stresses remaining in machined surface layer were mainly compressive. The increase of flank wear caused a shift of the compressive residual stress maximum to greater workpiece depths, but the changes did not penetrate the workpiece beneath a depth of 300 .mu. m. Surface roughness was influenced considerably by variations of the cutting speed and feed. In machining hard material, CBN and A1$_{2}$ $O_{3}$ ceramics cutting tool materials proved significantly superior to mixed ceramics A1$_{2}$ $O_{3}$-TiC and WC in evaluation of surface integrity.y.

• 대한기계학회논문집A
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• 제28권2호
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• pp.196-205
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• 2004

The cutting characteristics and the deformed layer of nitrogen(N)-added type 316LN stainless steel were comparatively investigated to type 316L stainless steel. The cutting force, the surface roughness(Ra) and the tool wear in face milling works were measured with cutting conditions, and the deformed layers were obtained from micro-hardness testing method. The cutting resistance of type 316LN was similar to type 316L in spite of its high strength. The surface roughness of type 316LN was superior to type 316L for all the cutting conditions. In particular, in the high cutting speed above 345m/min, the surface roughness of the two stainless steels was closely same. The deformed layer thickness of the two stainless steels was generated in the 150$\mu\textrm{m}$-300$\mu\textrm{m}$ ranges, and its value of type 316LN was lower than that of type 316L. This is due to the high strength properties by nitrogen effect. It was found that type 316LN was higher in the tool wear than that type 316L, and flank wear was dominant to crater wear. In face milling works of type 316LN steel, tool wear is regarded as a important problem.