저탄소강의 미세조직과 집합조직에 대한 탄소의 영향

정우창 ( Woo Chang Jeong ) 한국열처리공학회 2014 熱處理工學會誌 Vol.27 No.2

The effect of carbon on the microstructure and texture of low carbon steels was investigated in a series of 1.6 Mn-0.3Cr-0.2Mo-0.001B steels with carbon ranging from 0.021 to 0.048%. Intensity of {111} orientation increased with decreasing the carbon content, resulting in the increase in rm value. The highest rm value of1.30 was obtained in 0.021%C steel annealed at 820~850oC according to the typical galvannealing heat cycle. Marten site volume fraction was not substantially affected by the annealing temperature. It was found that the fine and uniformly distributed marten site particles which were present in amounts of about 5% volume fraction were desirable for the highest rm value. The other factor affecting the high rm value was the preferred epitaxial growth of retained ferrite with {111} orientation into austenite during cooling.

논문: 0.015% C - 1.5% Mn - 0~0.5% Mo 강의 어닐링과정에서 미세조직과 집합조직의 변화

정우창 ( Woo Chang Jeong ) 한국열처리공학회 2011 熱處理工學會誌 Vol.24 No.5

The changes in microstructure and texture during annealing were examined in a series of 0.015% C-1.5% Mn cold-rolled sheet steels with 0~0.5% Mo. Orientation distribution function data were calculated from the (110), (200), (211) pole figures determined on the rolled plane of cold-rolled and annealed steel sheets. Regardless of Mo content and annealing conditions, martensite volume fraction was less than 1.0 %, not affecting the texture evolution. Textural change at the cooling stage after heating at 820oC for 67 sec was not observed. Increasing the Mo content and annealing temperature markedly strengthened the intensities of γ-fiber texture, resulting in the increase in r(m) value. The desirable texture evolution for deep drawability in the 0.5% Mo steel may be mainly caused by the grain refining effect of Mo carbide in the hot-rolled steel sheet.

구상흑연주철의 열처리에 따른 미세조직 및 경도 변화

정우창 ( Woo Chang Jeong ) 한국열처리공학회 2008 熱處理工學會誌 Vol.21 No.2

도시지역을 관통하는 홍수파의 특성에 관한 수치적 연구 (1) : 수치모형의 개발 및 검증

정우창,이진우,조용식,Jeong,Woo-Chang,Lee,Jin-Woo,Cho,Yong-Sik 한국방재학회 2009 한국방재학회논문집 Vol.9 No.6

본 연구에서는 도시지역을 관통하는 댐 붕괴파의 전파특성을 모의하고 분석하기 위한 선행 작업으로 천수방정식과 well-balanced HLLC 기법에 근간을 둔 2차원 비구조적 유한체적모형을 개발하였다. 개발된 모형은 다양한 1차원과 2차원의 댐 붕괴파 해석과 관련된 문제에 대해 검증되었으며, 검증결과 해석해 및 수리모형실험을 통한 실측자료와 매우 일치하는 경향을 나타냈다. 본 연구에서 개발된 수치모형은 현장에서 그리고 수리모형실험을 통해 관측된 수위자료와 잘 일치하였으며, 기존의 모형으로부터 계산된 수위결과에 비해 비교적 보다 정확한 결과를 나타내었다. In this study, a two-dimensional unstructured finite volume model based on the shallow-water equations and well-balanced HLLC scheme is developed. The model is verified by applying to various one- and two-dimensional problems related to the analyses of dam-break wave. The predicted numerical results agree very well with available analytical solutions and laboratory measurements. The model provides slightly more accurate results compared with the existing models.

0.27% C-1.0% Si-1.5% Mn 강의 미세조직과 기계적성질에 미치는 Cr의 영향

정우창 ( Woo Chang Jeong ) 한국열처리공학회 2016 熱處理工學會誌 Vol.26 No.2

The variation in microstructure and mechanical properties during heat treatment was examined in a series of 0.27% C-1.0% Si-1.5% Mn steels with chromium contents in the range of 0 to 1.0 wt%. It was found that chromium decreased the martensite packet size through the austenite grain refinement and increased tensile strength in the as-quenched steel, about 70 MPa per 1.0 wt%. The 0.27% C-1.0% Si-1.5% Mn-1.0% Cr steel showed tensile strength of 1700 MPa in the as-quenched steel. The 0.27% C-1.0% Si-1.5% Mn-1.0% Cr steel revealed a full martensitic structure after air cooling from 900℃ to room temperature, showing air hardening characteristics. Tempering at 150℃ slightly decreased the tensile strength and increased elongation, which is in a good agreement with impact toughness result. (Received June 9, 2016; Revised July 13, 2016; Accepted July 22, 2016)

실험실 규모의 Tankless 정수처리 시스템의수리학적 안정성 평가에 관한 연구

정우창 ( Woo Chang Jeong ),김관엽 ( Kwan Yeop Kim ) 한국수처리학회 2014 한국수처리학회지 Vol.22 No.6

In this study, the hydraulic stability of lab scale tankless water treatment system was evaluated. This system consists of dummy membrane filtrations, AC filter, backwashing pump, air compressor, supply pump, pressure and flow-rate control valves, water supply tank. The experiments were carried out with 4 cases related to the set-up of pressure, in-going flow-rate and closing status of upper valves of dummy membrane filtration. As the results of experiments, in the case of relatively low preset in-going flow-rate of 10 l/min. the pressure preset from 2.0 bar to 3.0 bar is increased, the flow-rate in the system was stable during the period of experiment but the pressure was very unstable. In the case of the in-going of 20 l/min, the flow-rate and pressure were slightly more stable than the case of the in-going of 10 l/min. In the partially closed case of upper valves of membrane filtrations, the fluid in the system flows with bigger pressure than in the completely opened case.

0.27% C-1.5% Mn-1.0% Cr 강의 미세조직과 기계적성질에 미치는 Si의 영향

정우창 ( Woo Chang Jeong ) 한국열처리공학회 2017 熱處理工學會誌 Vol.30 No.3

The variation in microstructure and mechanical properties during heat treatment was examined in a series of 0.27% C-1.5% Mn-1.0% Cr steels with silicon contents in the range of 0 to 1.0 wt%. It was found that addition of 0.5%~1.0% silicon increased both tensile strength and impact toughness through solid solution strengthening and microstructural refinement. 0.27% C-1.0% Si-1.5% Mn-1.0% Cr steel showed tensile strength of 1,700 MPa in the as-quenched condition and the steel revealed a full martensitic structure even after air cool-ing from 900℃ to room temperature, showing air hardening characteristics. Tempering at 150℃ which corre-sponds to the typical paint-baking temperature after painting of body in white, slightly decreased the tensile strength and increased elongation, but substantially increased the impact toughness compared to the as-quenched steel. (Received April 10, 2017; Revised April 21, 2017; Accepted April 27, 2017)

0.27% C-1.0% Si-1.5% Mn 강의 미세조직과 기계적성질에 미치는 Cr의 영향

정우창,Jeong, Woo Chang 한국열처리공학회 2016 熱處理工學會誌 Vol.29 No.4

The variation in microstructure and mechanical properties during heat treatment was examined in a series of 0.27% C-1.0% Si-1.5% Mn steels with chromium contents in the range of 0 to 1.0 wt%. It was found that chromium decreased the martensite packet size through the austenite grain refinement and increased tensile strength in the as-quenched steel, about 70 MPa per 1.0 wt%. The 0.27% C-1.0% Si-1.5% Mn-1.0% Cr steel showed tensile strength of 1700 MPa in the as-quenched steel. The 0.27% C-1.0% Si-1.5% Mn-1.0% Cr steel revealed a full martensitic structure after air cooling from $900^{\circ}C$ to room temperature, showing air hardening characteristics. Tempering at $150^{\circ}C$ slightly decreased the tensile strength and increased elongation, which is in a good agreement with impact toughness result.

인장강도 1200 MPa 급 자동차 서브 프레임의 합금성분 최적화 및 열변형 거동 연구

정우창 ( Woo Chang Jeong ) 한국열처리공학회 2020 熱處理工學會誌 Vol.33 No.3

Four air hardening steels with carbon, silicon, manganese, chromium, and molybdenum variations have been used in this study to find out the optimal chemical compositions of steels with over 1200 MPa tensile strength for automotive subframe. The dimensional changes after heat treatment were determined for two automotive parts with open and closed cross sections using 3D scanner. When four steels were austenitized at 900℃ for 30 seconds, cooled at 3℃/s, reheated to 450℃ for 10 seconds followed by air cooling to simulate hot-dip galvanizing treatment showed ultra high tensile strength over 1200 MPa. Rear floor cross member with open cross section revealed much bigger dimensional changes than subframe with closed cross section after heat treatment at 900℃ for 20 minutes followed by air cooling. (Received April 16, 2020; Revised April 27, 2020; Accepted April 28, 2020)

고장력 냉연강판에서 미세조직에 대한 연속어닐링 조건의 영향

정우창 ( Woo Chang Jeong ) 한국열처리공학회 2004 熱處理工學會誌 Vol.17 No.5

N/A The effect of the annealing parameters on microstructures were examined in a cold-rolled high strength steel containing 0.1% C, 0.5% Si, 1.5% Mn, and 0.04% Nb. It was impossible to avoid martensite in the microstructure even though the continuous annealing parameters were controlled. This indicates that the alloying elements such as silicon and manganese contributing to manganese equivalent (Mn_(eq)) should be reduced to pro-duce the ferrite-pearlite microstructure for the solid solution and precipitation hardened steel. It was found that a decrease in the rapid cooling temperature to 520℃ was effective to change the microstructure from ferrite-martensite to ferrite-pearlite-martensite. Typical dual-phase properties exhibiting a low yield ratio and a continuous yielding behavior were obtained when the rapid cooling temperature was in the range of 680℃ to 600℃. The critical volume fraction of martensite for the typical properties of dual-phase steel was about 11 percent.