• 한국해양공학회지
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• 제25권1호
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• pp.56-60
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• 2011

A low temperature plasma carburizing process was performed to AISI 304L austenitic stainless steel to achieve the enhancement of surface hardness without a compromise in their corrosion resistance. Attempts were made to investigate the influence of the processing temperatures on the surface-hardened layer during low temperature plasma carburizng in order to obtain the optimum processing conditions. The expanded austenite (${\gamma}C$) was formed on all the treated surfaces. Precipitates of chromium carbides were detected in the hardened layer (C-enriched layer) only for the specimen treated at $500^{\circ}C$. The hardened layer thickness of ${\gamma}C$ increased up to about $35\;{\mu}m$, with increasing treatment temperature. The surface hardness reached about 1000 $HK_{0.05}$, which is about 4 times higher than that of the untreated sample (250 $HK_{0.05}$). Minor loss in corrosion resistance was observed for the specimens treated at temperatures of $310^{\circ}C-450^{\circ}C$ compared with untreated austenitic stainless steel. Particularly, the precipitation of chromium carbides at $500^{\circ}C$ led to a significant decrease in the corrosion resistance.

• 열처리공학회지
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• 제11권4호
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• pp.247-257
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• 1998

In order to evaluate the relation between prior structure and fatigue strength on a induction surface hardened medium carbon steel(SAE1050M) for automotive drive shafts, torsional fatigue test were conducted with various cases of different hardened depths and applied loads. Prior structures of the steel such as pearlite, fine pearlite and spheroidal pearlite were prepared by conventional nomalizing, tempering after quenching and spheroidized annealing, respectively. Maximum torsional fatigue strength can be obtained when the case depth is 18~25% diameter of the bar in each prior structure. The effect of case depth on the torsional fatigue strength was different depending on applied load to specimen, but the most good fatigue life was shown in the case of pearlitic structure when the case depth was 4.0~5.5mm(18~25% of bar diameter). Among three different prior structures, energy consumption, to obtain high strength or to get the same case depth, was the most saved in the case of pearlitic structure.

• 대한기계학회논문집
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• 제3권3호
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• pp.116-123
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• 1979

On the basis of optical microscope and electro microscope observation for the fatigue fracture process of medium corbon martensitic structure produced by rapid heat treatment, mainly the abstracts of the studied results for the morphology of fatigue crack initiation process of high hardened steel are summarized as follows. Fatigue crack initiated from inclusion on the surface or subsurface. Above all the crack which initiated from inclusion exposed on the surface in as follows. (1) fatigue crack initiated from the boundary of the matrix and inclusion. (2) fatigue crack initiated at surrounding of small pit by drop out of inclusion.

• 열처리공학회지
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• 제13권4호
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• pp.224-230
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• 2000

Garbon steel(SM35C) was gas nitrocarburized at $580^{\circ}C$ in $55%N_2-40%NH_3-5%CO_2$ mixed gas atmosphere, and then the steel was induction hardened at $850^{\circ}C$. The microstructure of gas nitrocarburized surface layer was observed by optical microscope and SEM. The phase analysis was carried out by X-ray diffraction method. The mechanical properties of gas nitrocarburized SM35C steel was evaluated by hardness, wear and fatigue test. The thickness of compound and diffusion layer were increased with increasing the gas nitrocarburizing time and the densest compound layer was obtained at 3 hours gas nitrocarburizing time. In case of 15sec induction hardening after gas nitrocarburizing, the surface hardness was decreased from 800Hv to 630Hv owing to the decomposition of compound layer, but wear resistance was increased because of increased hardness of diffusion layer. The fatigue strength of induction hardened steel after gas nitrocarburizing, $58kgf/mm^2$, was higher than $41.5kg/mm^2$ of gas nitrocarburized steel and $45kg/mm^2$ of induction hardened steel, respectively.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표대회 논문집(III)
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• pp.791-796
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• 1998

Air voids existed in hardened concrete have an important influence on concrete deterioration such as carbonation, freezing and thawing, and corrosion of embedded steel in concrete. Therefore it is very significant to investigate the pore structure of system(size, number and continuity of air voids) to solve the reason caused concrete deterioration. The purpose of this study is to develop the standard method of measuring air voids which affect properties in hardened concrete using image analyzing system. This paper presents the settlement of rapid and exact experimental method which extracts fine bubbles, calculates the number of air voids, and determines air-void distribution using image analyzing system with computer.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.245-250
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• 2003

This research conducted milling tests to study effects of cutting environment conditions of ball end mills on the characteristics of hard milling process. KP4 steels and STD11 heat treated steels were used as the workpiece and WC-Co ball end mill tools with TiAIN coated were utilized in the cutting tests. Dry cutting without coolant and semi-dry cutting using botanical oil coolant were conducted and MQL (Minimum Quantity Lubricant) device was used to spray coolant. Cutting forces, tool wear and surface roughness were measured in the cutting tests. Results showed that dry cutting of KP4 and hardened STD11 specimens produced better surface quality and wear performance than MQL spray cutting did.

• 한국정밀공학회지
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• 제18권9호
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• pp.122-130
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• 2001

Induction surface hardening is widely used to enhance local strength and hardness. However, most research is only to have a focus on fatigue life and fatigue behavior is not so much studied. So, in this study, Cr-Mo steel alloy(SCM440) was used to show the effect of residual stress and micro hole on the fatigue strength fur base metal and induction surface hardened specimen. In addition, the fatigue characteristic between surface hardened and fully hardened steel is somewhat different. It is caused by hardness distribution, residual stress and inclusions etc.. The modification of prediction equation of fatigue strength is proposed and predicted results show very good accuracy. A $textsc{k}$, which is calculated 1.46, is introduced to consider the effect of stationary crack with defect. A new method of modifying residual stress is proposed to examine the mean stress effect under fatigue loading.

• 소성∙가공
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• 제13권1호
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• pp.45-52
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• 2004

This research conducted milling tests to study effects of cutting environment conditions of ball end mills on the characteristics of hard milling process. KP4 steels and STD11 heat treated steels were used as the workpiece and WC-Co ball end mill tools with TiAlN coated were utilized in the cutting tests. Dry cutting without coolant and semi-dry cutting using botanical oil coolant were conducted and MQL(Minimum Quantity Lubricant) device was used to spray coolant. Cutting forces, tool wear and surface roughness were measured in the cutting tests. Results showed that dry cutting of KP4 and hardened STD11 specimens produced better surface quality and wear performance than MQL spray cutting did.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 추계학술대회논문집
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• pp.238-244
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• 2004

This research conducted milling tests to study effects of cutting environment conditions of ball end milts on the characteristics of high speed milling cutting process. KP4 steels and STD11 heat treated steels were used as the workpiece and WC-Co ball end mill tools with TiAIN coated were utilized in the cutting tests. Dry cutting without coolant and semidry cutting using botanical oil coolant by the MQL(Minimum Quantity Lubricant) device were conducted. Cutting forces, tool wear and surface roughness were measured in the cutting tests. Results showed that MQL spray cutting of KP4 and hardened STD11 specimens produced better surface quality and wear performance than dry cutting did.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.287-290
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• 2005

Once hot forgings for automotive parts such as wheel bearing flange to which cyclic asymmetric bending stress is continuously applied are produced, it is necessary to control their microstructure to obtain superior mechanical properties. It is however hard to control the microstructure uniformly because the strength is reduced as coarsening of ferrite grains. To investigate the microstructural alteration according to process variables during hot working, the variation of the ferrite grain size was studied by utilizing of the computer aided servo-hydraulic Gleeble tester which is hot deformation behavior reproduction equipment. In addition, the effect of the ferrite grain size of raw material on the austenite grain behavior of hot forgings was also examined. The rolling contact fatigue resistance of the induction hardened SAE 1055 steel was compared with the occasion of the same condition of SAE52100 bearing steel. As a result, it was confirmed that the ferrite grain sizes of the forgings depend on the heating temperature and cooling start temperature during hot forging and cooling processes. The induction hardened SAE1055 steel showed a superior rolling contact fatigue resistance to the induction hardened SAE52100 steel. The reason is that SAE1055 steel is freer from the material defect such as segregation than the comparative steel.