• 열처리공학회지
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• 제19권5호
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• pp.270-279
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• 2006

The effects of eight types of spheroidizing annealing conditions including annealing temperature, annealing time, cooling rate, and furnace atmosphere on the microstructure and hardeness were determined in SCM440 steel which has been widely used for automotive parts. The well-spheroidized structure and minimum hardness were obtained when the steel was heat-treated at $770^{\circ}C$ for 6 hours, cooled to $720^{\circ}C$ at a cooling rate of $24^{\circ}C/h$, and then kept for 7 hours at the $720^{\circ}C$ followed by air cooling. In order to increase the productivity and to save the manufacturing cost, it is desirable to apply a faster cooling rate to the spheroidizing annealing. It was found that a cooling rate of $100^{\circ}C/hr$ was the fastest cooling rate applicable to the SCM440 steel among the four cooling rates used in this study. The microstructure consisted of ferrite and very fine spheroidized cementite when the steel was annealed for 13 hours at $720^{\circ}C$ below $A_{C1}$ temperature. This was caused by the short annealing time and the retarding effect of Cr and Mo on both the dissolution of pearlite to cementite and coarsening of spheroidized cementite. The steel heat treated in air showed the decarburized layer of about $125{\mu}m$ in thickness at the surface.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제30회 추계학술대회
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• pp.257-262
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• 1999

The economic loss arisen from the abrasion wear have been increasing at every industrial field. To reduce the economic loss we developed a new process, which is named MAHa process(Metallic Adhesives for HArdening). MAHa process is a process to weld tungsten carbide(WC) to the surface of a plain carbon steel so that it may stay longer under the severe abrasive environment. The depth of the WC layer ranges from 0.5 mm to 5 m. Compared with the conventional technology, arc-augmented welding which bonds WC on the flat surface only, MAHa process has the merits that it can make a robust WC layer on the round or wave- shaped surface also. How to turn the WC powder into a flexible mat is the key technology of the MAHa process. We invented new polymer materials to accomplish such a goal and both the MAHa process and the invented materials were applied for patents. For the application, the inner wall of elbow of Concrete Pump Truck(CPT) was maharized(MAHa process-treated) and the new WC layer on the inner wall was made successfully. The elbow was equipped to a CPT.

• 열처리공학회지
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• 제19권3호
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• pp.149-155
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• 2006

The effects of eight types of spheroidizing annealing conditions including annealing temperature, annealing time, cooling rate, and gas atmosphere in the annealing furnace on the microstructure were determined in SM45C steel which has been widely used for automotive parts. The well-developed spheroidized structure and minimum hardness were obtained when the steel was heat-treated 6 hours at $740^{\circ}C$, cooled to $710^{\circ}C$ at a cooling rate of $24^{\circ}C/h$, and then kept for 7 hours at the $710^{\circ}C$ followed by air cooling. In order to increase the productivity and to save the manufacturing cost, it is desirable to apply a faster cooling rate in the spheroidizing annealing. It was found that air cooling was the fastest cooling rate applicable to the SM45C steel. The steel heat treated in air showed the decarburized layer of about $110{\mu}m$ in thickness at the surface of the specimen, resulting in serious problems in the quality of the quenched product.

• Corrosion Science and Technology
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• 제10권3호
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• pp.80-86
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• 2011

Welding was widely used in shipbuilding industries as a joining method. In present study, the effects of welding fume contaminated on steel surface on corrosion protection were examined by water ballast simulation test and condensation chamber test. Pull-off adhesion test, blistering test and cathodic disbondment test were carried out to evaluate the effects of residual welding fume. Consequently, it was clearly indicated that the residual welding fume didn't affect the corrosion protection of epoxy coated on steel when surface was treated by light sweep blasting to heavy sweep blasting which was applied in this study.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2022년도 봄 학술논문 발표대회
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• pp.43-44
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• 2022

In this study, the optimum amount of chloride ions is used to collaborate with hybrid corrosion inhibitor for carbon steel rebar treatment in simulated pore concrete (SCP) solution is discovered. The corrosion inhibition performance of hybrid inhibitors is carried on by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PP). The highest corrosion inhibition resistance is found in case of LP-C2 after 240 h exposure. Surface studies including scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to figure out the surface morphology of the steel rebar treated with hybrid inhibitors in order to collaborate well with electrochemical studies. Anodic type inhibition action was confirmed by potentiodynamic polarization study.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 가을 학술논문 발표대회
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• pp.65-66
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• 2021

In this study, the optimum amount of hybrid inhibitors i.e. L-Arginine (LA) and sodium phosphate tribasic dodecahydrate (SP), applied for carbon steel rebar in simulated pore concrete (SCP) solution contaminated with 3.5 wt.% NaCl, was discovered. The corrosion inhibition performance of hybrid inhibitors was investigated by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization. The highest corrosion inhibition efficiency was found as 99.52% corresponding to 2% LA and 0.25% SP after 210 h exposure. Anodic type inhibition action was confirmed by potentiodynamic polarization study. Surface studies including scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to figure out the surface morphology of the steel rebar treated with hybrid inhibitors in order to collaborate with electrochemical studies.

• 소성∙가공
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• 제23권6호
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• pp.345-350
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• 2014

The current study elucidates the effects of cementite spheroidization and pro-eutectoid ferrite on the sliding wear resistance in medium carbon (0.45wt%C) and high carbon (1wt%C) steels. Both steels were initially heat treated to obtain a fully pearlite or ferrite + pearlite microstructure. Spheroidizing heat treatments were performed on both steels to spheroidize the pearlitic cementite. Sliding wear tests were conducted using a pin-on-disk wear tester with the steel specimens as the disk and an alumina ($Al_2O_3$) ball as the pin. The sliding wear tests were carried out at room temperature in air with humidity of $40{\pm}2%$. Adapted sliding distance and applied load was 300m and 100N, respectively. Sliding speed was 0.1m/s and the wear-track radius was 9 mm. Worn surfaces and cross-sections of the wear track were examined using an SEM. Micro Vickers hardness of the wear-track subsurface was measured as a function of depth from the worn surface. Hardness and sliding-wear resistance of both steel decreased with increased spheroidization of the cementite. The decrease was more significant in the fully pearlitic steel (1wt%C steel). The steel with the pro-eutectoid ferrite showed relatively higher wear resistance compared to the spheroidized pearlitic steel.

• 열처리공학회지
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• 제3권2호
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• pp.10-19
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• 1990

The tempering behavoirs of 0.45% carbon steel treated by automatic progressive high frequency induction hardening equipment have been investigated. In order to examine the correlation of hardness with both tempering temperature and time, simple regression analysis has been made using the statistical quality control package. The maximum surface hardness value of induction hardened zone and its effective hardening depth have been determined to be Hv 810 and 0.76mm, respectively. The hardness obtained after tempering has been shown to vary lineary with tempering time at six different temperatures. The activation energies during tempering have been calculated to be 25.34kcal/mole, 32.73kcal/mole and 49.24kcal/mole for HRcs 60, 50 and 40, respectively, showing that tempering process occurs by a complex mechanism, The tempering hardness equation of $H=90.113{\sim}4.531{\times}10^{-3}$ [T(11.996+log t)] has proved to be in a reasonably good agreement with experimently determined data and it is also expected to be useful for the determination of tempering treatment conditions to obtain a required hardness value.

• 한국재료학회지
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• 제3권3호
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• pp.292-299
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• 1993

본 연구에서는 탄소/탄소복합재료의 마모특성에 대한 탄소섬유 길이의 영향을 고찰하였다. 매트릭스 precursor로 레졸형의 페놀수지와 강화재로 표면처리를 하지않은 PAN계 단섬유형 탄소섬유를 사용하여 액상함침법으로 1회의 고온열처리 공정과 4회의 탄화공정을 통하여 탄소/탄소복합재료를 제조하였다. Disk-on-disk형의 마모시험기를 통하여 상대 마찰재로 AISI 304 stainliss steel을 사용하여 0.6MPa(61 ${\times}{10^3}$Kg/$m^2$)의 압력과 0.71m/sec의 미끄러짐 속도하에서 측정된 탄소/탄소복합재료의 마찰계수는 0.2-0.3이었다. 마찰계수에 대한 섬유의 길이의 영향은 크게 나타나지 않았지만, 마모 속도는 섬유의 길이가 증가함에 따라 증가하는 경향이 나타났다. 본 실헙 결과를 섬유 강화 플라스틱의 마모 모델을 적용하여 고찰하여 본 결과, 섬유의 길이가 증가함에 따라 탄소/탄소복합재료의 마모 속도가 증가되는 경향은 생성된느 마모조각의 크기가 커기기 때문에 나타난 현상으로 판단되었다.

• 열처리공학회지
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• 제19권2호
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• pp.90-95
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• 2006

Nitriding or carburizing of carbon steels results in good mechanical properties such as high surface hardness and wear resistance but it has no affection on the corrosion resistance. Corrosion properties of nitriding and carburizing steels could be deteriorated. So, recently, there have been great demand for oxi-nitriding to enhance both mechanical properties and corrosion resistance. In this study, the corrosion resistance of carbon steel, S35C, and free cutting steel, SUM222, are prepared by vacuum nitriding and vacuum post-oxidation were compared with those treated by nitriding. After vacuum post-oxidation, $5{\mu}m$ oxide layer was formed on the nitride layer with $20{\sim}30{\mu}m$ depth. Potentio-dynamic polarization curve in corrosion test showed that the corrosion potential after post oxidation was increased from 200 mV to 800 mV in S35C and from 600 mV to 1200 mV in SUM222. SEM analyses showed that pores was increased and surface roughness became rougher with post oxidation. However, the formation of $Fe_3O_4$ resulted in the enhanced corrosion resistance of steels.