• 한국기계연구소 소보
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• 통권9호
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• pp.83-93
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• 1982

The influence of different heat treatment conditions on microstructure, mechanical and fatigue properties of Spheroidal Graphite cast Iron with 0.4-0.6% Mn was investigated. 1) Maximum tensile strength was arrived by tempering at about $450^{\circ}C$after quenching. Tempering at higher than $600^{\circ}C$ was changed martensitic structure to ferritic structure and secondary graphites were precipitated. 2) The relationship between matrix hardness and total hardness of the specimens are as following. [HB]$T$=0.7[HB] [HB]$M$+35 Maximum tensile strength was arrived at the total hardness of HB400-450. 3) Endurance ratio decreases with increasing total hardness, and fatigue limits can be presumed from as following. $\sigmaf$=$\sigmat$

• 한국기계가공학회지
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• 제5권4호
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• pp.46-52
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• 2006

From the past, most of the studies about thermoplastic elastomers(TPEs) have been conducted for theirs compounded materials and morphology. However these studies do not directly affect on injection molding processing. Therefor this study is focus on the variation of mechanical properties on TPEs moldings by increasing injection molding conditions which included injection molding conditions include injection pressure, holding pressure, melt temperature, mold temperature. The used experimental TPEs is a group of styrene(TPS). Injection pressure slightly affected on tensile strength, shrinkage and hardness. Holding pressure only affected on hardness. The melt temperature was the most affective condition on tensile strength.

• 한국정밀공학회지
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• 제29권1호
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• pp.96-102
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• 2012

The current establishment of car engineering plastic piping polyethylene (PE) tube used as bonding state or part of the health or safety of fusion is very important. A part of these fusion methods to determine the soundness of the short-term trials and long-term tests can be largely classified. Typical tests included short-term strength, tensile strength, impact strength, compressive strength, resiliency and compression. Polyethylene (PE) pipes installed in the domestic terms of overall penetration rate of 45% has been used. However, polyethylene (PE) pipes have reliability problems, and these occurs mostly in part by defective welding. Therefore, the test is necessary for safety. Non-destructive methods (ultrasonic testing) are difficult to be used. Therefore, Polyethylene (PE) pipe are used. Fusion of thses materilas is necessary in these field however, its technical, and basic research has not been studied well. In this research, short-term strength of welding parts, its tensile strength, hardness, fatigue, and microstructure have been analyzed to find the optimum process conditions to improve mechanical properties.

• 한국생산제조학회지
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• 제20권5호
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• pp.564-569
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• 2011

The current establishment of city gas piping polyethylene (PE) tube used as bonding state or part of the health or safety of fusion is very important. A part of these fusion methods to determine the soundness of the short-term trials and long-term tests can be largely classified. Typical tests include short-term strength, tensile strength, impact strength, compressive strength, resiliency and compression. Polyethylene (PE) pipes installed in the domestic terms of overall penetration rate of 45% has been used. However, polyethylene (PE) pipes have reliability problems, and these occurs mostly in part by defective welding. Therefore, the test is necessary for safety. Non-destructive methods (ultrasonic testing) are difficult to be used. Therefore, Polypropylene copolymer (PP-C), polypropylene homopolymer (PP-H), and polyethylene (PE) pipe are used. Fusion of these materials is necessary in these field however, its technical, and basic research has not been studied well. In this research, short-term strength of welding parts, its tensile strength, hardness, fatigue, and microstructure have been analyzed to find the optimum process conditions to improve mechanical properties.

• Korean Chemical Engineering Research
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• 제50권5호
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• pp.783-788
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• 2012

스턴튜브베어링(Stern tube bearing))은 축계장치에서 축 회전 시 마찰을 줄이고 축의 무게를 지지하는 주요한 역할을 하는 부품임에도 불구하고 국산화가 이루어지지 않아 전량 수입에 의존하고 있어 국산화 개발이 요구되고 있다. 이에 국산화를 위한 스턴튜브 베어링용 폴리우레탄 수지를 개발할 목적으로 경도, 인장강도, 신장률에 미치는 첨가제의 영향을 조사하였다. 기본적으로 경화제 종류에 따라 MOCA Type과 Non-MOCA Type으로 구분하여 각각 폴리우레탄을 합성하고, 기본적 물성을 확인한 결과, Non MOCA Type은 경도 23 D, 인장강도 4.3 Mpa로 본 연구의 목표치에 훨씬 미치지 못하는 것으로 나타났으며, 반면에 MOCA Type의 폴리우레탄 수지는 기계적 강도가 높은 것으로 나타나 전반적으로 MOCA Type의 폴리우레탄수지를 기본 수지로 사용하여 연구를 진행하였다. 기본적인 폴리우레탄 수지의 합성은 폴리올에 MOCA를 23.0 wt%로 첨가하고, 1차 경화는 $110^{\circ}C$에서 1시간 경화하고, $110^{\circ}C$에서 15시간 2차 경화를 하여 수지를 제조하였다. 첨가제로는 그래파이트, 칼슘카보네이트, 카본블랙, 실리카를 각각 사용하여, 이들 첨가제의 종류와 첨가량에 따라 경도, 인장강도, 신장률에 미치는 효과에 대한 실험을 수행하여 실리카를 첨가한 폴리우레탄 수지는 경도, 인장강도가 비교적 우수하면서도 신장률도 다소 증가하는 폴리우레탄 수지를 제조할 수 있었다.

• 한국재료학회지
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• 제21권6호
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• pp.303-308
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• 2011

The effect of heat treatment on the micro-structures and the mechanical properties of 0.002% boron added low carbon steel was investigated. The tensile strength reached the peak at about $880-890^{\circ}C$ with the rising quenching temperature and then the hardness decreased sharply, but the tensile strength hardly decreased. The tensile and yield strength decreased and the total elongation increased with a rising tempering temperature, but the tensile and yield strength sharply fell and the total elongation prominently increased from above a $400-450^{\circ}C$ tempering temperature. Tempered martensite embrittlement (TME) was observed at tempering condition of $350-400^{\circ}C$. In the condition of quenching at $890^{\circ}C$ and tempering at $350^{\circ}C$, the boron precipitates were observed as Fe-C-B and BN together. The hardness decreased in proportion to the tempering temperature untill $350^{\circ}C$ and dropped sharply above $400^{\circ}C$ regardless of the quenching temperature.

• 한국재료학회지
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• 제28권7호
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• pp.391-397
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• 2018

This study deals with the microstructure and tensile properties of 700 MPa-grade high-strength and seismic reinforced steel bars. The high-strength reinforced steel bars (600 D13, 600 D16 and 700 D13 specimens) are fabricated by a TempCore process, while the seismic reinforced steel bar (600S D16 specimen) is fabricated by air cooling after hot rolling. For specimens fabricated by the TempCore process, the 600 D13 and 600 D16 specimens have a microstructure of tempered martensite in the surface region and ferrite-pearlite in the center region, while the 700 D13 specimen has a microstructure of tempered martensite in the surface region and bainite in the center region. Therefore, their hardness is the highest in the surface region and shows a tendency to decrease from the surface region to the center region because tempered martensite has a higher hardness than ferrite-pearlite or bainite. However, the hardness of the 600S D16 specimen, which is composed of fully ferrite-pearlite, increases from the surface region to the center region because the pearlite volume fraction increases from the surface region to the center region. On the other hand, the tensile test results indicate that only the 700 D13 specimen with a higher carbon content exhibits continuous yielding behavior due to the formation of bainite in the center region. The 600S D16 specimen has the highest tensile-to-yield ratio because the presence of ferrite-pearlite and precipitates caused by vanadium addition largely enhances work hardening.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 추계학술대회(한국공작기계학회)
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• pp.172-178
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• 2001

Titanium alloys have lightness, high strength and good corrosion resistant characteristics, and broadly used in manufacturing parts for military and aerospace industries. And these alloys also are recognized for organism materials comparatively and used as fixing ones in the human body. Nevertheless thess alloys have excellent properties such as corrosion resistance, heat resistance, and good tensile strength, it is difficult to machine by traditional methods because of high hardness and chemically activated property. So higher tool wear is expected when cutting by tools. Therefore, it is required nontraditional machining process. And the mechanical characteristics such as surface structure and shape, hardness and bending strength are studied for wire electrical discharge machined and surface ground titanium alloys for various heat-treated conditions.

• 열처리공학회지
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• 제11권4호
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• pp.333-341
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• 1998

The study was investigated on the effect of austenitizing and austempering conditions on retained austenite amount and carbon contents in retained austenite and simultaneously the effect of these variation on hardness, tensile and impact properties. A material of as-cast condition is composed of bull's eye structure with ferrite surrounding spheroidized graphite having about $5-10{\mu}m$ size and matrix structure of pearlite. Then, the contents of spheroidized graphite was about 5%. The retained austenite and carbon contents in the retained austenite were increased with the increasing of austenitizing and austempering temperatures, while the retained austenite showed the peak value and is decreased with increasing of austempering time. With increasing of austenitizing temperature, tensile strength, elongation and impact absorb energy increased and hardness was almost not changed, while with increasing of austempering temperature, tensile strength and hardness decreased, whereas elongation and impact absorb energy was increased. With increasing of retained austenite amount, the tensile strength is slowly decreased but elongation was increased with direct proportion. Also, Impact absorb energy is shown identity value untile about 18%, but rapidly increased above it. Elongation and Impact absorb energy are strongly controlled by the amount of retained austenite, but tensile strength is affected with various factors such as retained austenite amount and bainitic morphology.

• 소성∙가공
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• 제27권5호
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• pp.281-288
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• 2018

This study deals with the microstructure and tensile properties of 600 and 700 MPa-grade high-strength seismic reinforced steel bars. High-strength seismic resistant reinforced steel bars (SD 600S and SD 700S) were fabricated by TempCore process, especially the SD 700S specimen was more rapid cooled than the SD 600S specimen during the TempCore process. Although two specimens had microstructure of tempered martensite in the surface region, the SD 600S specimen had ferrite-degenerated pearlite in the center region, whereas the SD 700S specimen had bainite-ferrite-degenerated pearlite in the center region. Therefore, their hardness was highest in the surface region and revealed a tendency to decrease from the surface region to the center region because tempered martensite has higher hardness than ferrite-degenerated pearlite or bainite. The SD 700S specimen revealed higher hardness in the center region than SD 600S specimen because it contained a larger amount of bainite as well as ferrite-degenerated pearlite. On the other hand, tensile test results indicated the SD 600S and SD 700S specimens revealed continuous yielding behavior because of formation of degenerated pearlite or bainite in the center region. The SD 600S specimen had a little higher tensile-to-yield ratio because the presence of ferrite and degenerated pearlite in the center region and the lower fraction of tempered martensite enhance work hardening.