Quenching한 SCM 440 강에서 초음파 전파특성에 미치는 템퍼링온도의 영향

이계완,김문일,박은수 ( K . W . Lee,M . I . Kim,U . S . Park ) 한국열처리공학회 1991 熱處理工學會誌 Vol.4 No.3

The effect of tempering temperature on the ultrasonic propagation velocity at SCM 440 steel quenched from 870℃ and 1000℃ has been studied by metallurgical and crystallographical observation. The measurements of ultrasonic velocity were made on the specimen by appling an immersion ultrasonic pulse-echo technique with a constant frequency of 10㎒. The quenched microstructure of this steel was a lath martensite. As the tempering temperature was increased, the martensite was transformed into the tempered martensite composed of cementite and carbide. The ultrasonic velocity increased with increasing the tempering temperature. It was thought that these were resulted from the microstructural transformation. The change of ultrasonic propagation velocity with quenching and tempering heat treatment was resulted from microstrain due to the change of internal stress. Considering these results concerning to the change of ultrasonic propagation velocity, the phenomena of microstructural transformation were estimated. Consequently, it was thought that the degree of quenching and tempered heat treatment of steel could he nondestructively evaluated with the change of ultrasonic propagation velocity.

생형순환사의 품질평가

김봉완,이계완 ( B . W . Kim,K . W . Lee ) 한국주조공학회 1992 한국주조공학회지 Vol.12 No.5

Al-Cu 공정합금의 일방향응고에 따른 현미경조직의 변화에 관한 연구

김창범,이계완 ( Chang Beom Kim,Kye Wan Lee ) 한국주조공학회 1985 한국주조공학회지 Vol.5 No.1

The eutectic composite to primary deudritic transition in Al-Cu alloys near eutectic composition has been studied at various solidification conditions. Structures produced upon solidification of the eutectic composition (33.0wt% Cu) of Al-Cu alloy have been studied as a function of solidification rate. The results obtained from this study were as follows; 1. As solidifiation rate increased, the range of eutectic composite zone had been extended to aluminum-rich compositions. 2. At the rapid solidification rates, primary Al was formed at rod-shaped colonies, whereas primary CuAl₂formed at fine lamellar composite zone. The primary CuAl₂was aligned parallel to the direction of heat flow. 3. The lamellar composite of Al-CuAl₂eutectic was arranged in the form of rod-shaped colonies at rapid solidification rates. The colonies were aligned parallel to the direction of heat flow, whereas the lamellar within the colonies aligned at various angles, as high as 90 deg. to the direction of heat flow. 4. A duplex dendritic structure was produced at slow solidification rates. 5. The colony spacing, lamellar spacing and the ratio of colony spacing to lamellar spacing increased with a decrease in the solidification rats.

고 Mole 비 규산소다를 이용한 CO2 주형의 (鑄型) 고온특성에 관한 연구

김봉완,이계완 ( Bong Wan Kim,Kye Wan Lee ) 한국주조공학회 1988 한국주조공학회지 Vol.8 No.1

In this study the elevated temperatures properties of CO₂sands bonded with high mole ratio sodium silcates were investigated and following results obtained. 1) The CO₂sand has peaks of the compression strength at the temperatures of 200℃ and 500℃ and its strength decreases to 2㎏/㎠ at 690℃. The higher mole ratio binder shows strength at the region of overall temperatures and the sodium silicate with 3.3 mole ratio appears very low strength of under 2.5㎏/㎠ at the peak point. 2) The dehydration reaction of sodium silicate continues up to 500℃ and at the temperatures higher than that, the dehydration does not take place. Near the temperature of 600℃, the silica sand diminishes in its grain sizes with the phase transformation occurred. 3) among organic additives, polyol increases Strength at the temperatures up to 400℃ and has the contrary influence at the temperature higher than hat. The bonding strength of sodium silicate at the temperature region of up to 400℃ is affected by the retained moisture and by the sponge structure changes of formed silica gel. And the addition of polyol has an affect of maintaining higher retained moisture within silica gel. 4) The bonding strength of high mole ratio sodium silicate increases with its content, and for the binder with 3.3 mole ratio, it is necessary to add 6% of sodium silicate for the enough strength. 5) The high temperature compression deformation of CO₂sand decreases gradually at the temperatures below 400℃ and has a linear increase at the temperatures up to 700℃. But the sand has a tendency of sligt increase in deformation at the temperatures above 700℃. With silicate bond softening by fusion, the silicate forms a viscous glass and the rise in compressiveness occurs. 6) The higher mole ratio silicate has a lower deformation. Organic addition produces a lower deformation, though depending upon its material. 7) The expansion of CO₂ sand forms a peak near the temperature of 600℃ with the phase transformation of silica and has the maximum value near 1,100℃. But the sand boned with 3.3 mole ratio sodium silicate decreases gradually its value and comes to a null value at 600℃. 8) when the mole ratio of the binder increases, the expansion of CO₂sand decreases on the contrary. And polyol additive has a considerable effect of absorbing the sand expansion. In conclusion, the addition of polyol to the CO₂sand bonded with high mole ratio sodium silicate causes a good effect of improving the mold strength, which is requested at the region of low temperature of up to 500℃ and of decreasing deformation and expansion.

고 MOLE 비의 규산소다를 사용한 CO2 주형의 (鑄型) 강도개선에 관한 연구

김봉완,이계완 ( Bong Wan Kim,Kye Wan Lee ) 한국주조공학회 1987 한국주조공학회지 Vol.7 No.4

The influences of some factors on the variation of compression strength of CO₂process were investigated with an attention given to use of high SiO₂/Na₂O silicate, addition of organics and gassing operation. 1) Higher ratio binder offers faster rates of hardening with lower CO₂consumption requiring more concentration for a good strength development. A mixture containing 4 percent of 2.7 : 1 ratio silicate produces the strength above 8㎏/㎠ after 80 seconds gassing, but 5% and 6% respectively of 3.0 : 1 and3.3 : 1 ratio silicate are necessary to achieve equivalent levels of strength. 2) The correct water content in sand mixtures containing higher ratio silicates is necessary for the better strength properties to be obtained. The addition of 1% water to the sand mixtures bonded with 5%, 3 : 1 ratio and 6%, 3.3 : 1 ratio silicates maintains near-maximum strength on extended gassing. 3) When higher ratio silicates with 3 : 1 and 3.3 : 1 ratios are used,the addition of organic additives such as oil, sucrose and polyol results in considerable changes in strength. The presence of 1.0 to 1.5 percent of polyol produces a noticiable improvement 4) Gas diluted with air raises the efficiency of gas utilization. When gas contains 50 percent CO₂, the efficience is significantly increased with the best strength in the silicates having high ratios of 3 : 1 and 3.3 : 1. 5) The strength of molds is liable to change on storage with the reduction in water content. The magnitude of the strength change is determinded with the mole ratio. The presence of polyol in the mixture with 3.3 : 1 ratio silicate has a pronounced effect on maintaining the gassed strength.

주강의 탈산기술 (2)

김봉완,이계완 ( B . W . Kim,K . W . Lee ) 한국주조공학회 1992 한국주조공학회지 Vol.12 No.3

주강의 탈산기술 (1)

김봉완,이계완 ( B . W . Kim,K . W . Lee ) 한국주조공학회 1991 한국주조공학회지 Vol.11 No.6

유도로의 주철용해에 있어서 에너지 절감 ( 유도로의 설계 및 용해작업 )

김봉완,이계완 ( B . W . Kim,K . W . Lee ) 한국주조공학회 1991 한국주조공학회지 Vol.11 No.1

고 Mole 비 규산소다를 사용한 CO2 주형의 (鑄型) 잔류강도와 (殘留强度) 반응생성물의 성상에 (性狀) 관한 연구

김봉완,남태운,이계완 ( Bong Wan Kim,Tae Woon Nam,Kye Wan Lee ) 한국주조공학회 1988 한국주조공학회지 Vol.8 No.2

N/A The study was carried out to investigate the changes of retained strength and reaction products in the CO₂ sands obtained are as follows. 1) Higher mole-ratio sodium silicates have the lower retained compression strength. 2) Organic liquid additives make a notable decrease in the retained strength and, in case of when use the 2.7 mole-ratio sodium sillicate, the effect is remarkable at the range of temperature to 600℃. 3) Sodium silicate binder forms silica gel with very high bonding force, accompaning an exothemic reaction at the temperatures of around 200℃, and dehydrated brittle silica gel and hydrated sodium silicate glass with sands transformed at the temperature of ahout 600℃. 4) It forms dehydrated glass with sintering of the sand gain surfaces, at the temperatures of around 800℃ and has a value of high retatined strength. 5) The decreases in the retaired strength of CO₂sands are accelerated with the lots of defects resulted from the porosity and cracks in sodium silicate bond films which are caused by the evaporation or combustion of the organic additives.

CV 흑연주철의 응고특성에 관한 연구

김철진,김수영,이계완 ( C . C . Chun,S . Y . Kim,G . W . Lee ) 한국주조공학회 1985 한국주조공학회지 Vol.5 No.3

Many researchers have studied the eutectic solidification of CV Graphite Cast Iron qualitatively. However quantative studies have not been done. The type of eutectic solidification of CV Graphite Cast Iron treated with CG Alloy (Fe-Si-Mg-5Ti-Ca-Ce) was studied quantitatively through M.D.E. value (Mushy Degree of Eutectic Solidification) = t₂/t₁), where t₁is the difference of the eutectic solidification starting time between surface and center part of the casting sample, and t₂is the time of eutectic solidification of the center part. Following results were obtained. (1) The M.D.E. value of CV graphite cast iron lies between that of spheroidal graphite and that of flake graphite cast iron but is closer to that of Flake graphite cast iron. (2) The M.D.E. value of CV graphite cast iron depends upon CV ratio. (3) The time required for eutectic solidification increases as graphite form is changed from Flake, CV. to spheroidal graphite. (4) The M.D.E. value increases as cooling rate increases.