• 산업기술연구
• /
• 제21권B호
• /
• pp.341-348
• /
• 2001

The effect of initial ${\alpha}^{\prime}$ in STS 304 Stainless Steel on fatigue resistance, and fatigue crack propagation behavior was studied with using C-T specimens. Higher ${\Delta}K_{th}$ was observed in the specimens with the content of 0% initial ${\alpha}^{\prime}$ than in the contents of 2% and 33% initial ${\alpha}^{\prime}$. The difference of da/dN at the same level of ${\Delta}K$ was distinctive in low and intermediate level of ${\Delta}K$ however became less different as the level of ${\Delta}K$ increased. It is because the formation of strain induced martensite occurred readily in lower ${\alpha}^{\prime}$ at the vicinity of the fatigue crack tip, which causes compressive residual stresses resulting in the enhancement of crack closure. In general fatigue cracks propagated transgranular mode and many segments of ridges were observed on the fracture surfaces. At the higher contents of initial ${\alpha}^{\prime}$ appeared the smaller size of ridge segments. Slips in austenite were blocked more frequently by the martensite colonies formed in austenite.

• 한국재료학회지
• /
• 제24권8호
• /
• pp.401-406
• /
• 2014

In this study, we investigated the precipitation behavior of the R-phase precipitated at the initial stage of aging and its effects on the mechanical properties of 25%Cr-7%Ni-2%Mo-4%W super duplex stainless steel. The R-phase was mainly precipitated at the interface of ferrite/austenite phases and inside of the ferrite phase during the initial stage of aging. It was transformed into the ${\sigma}$-phase with an increase of the aging time. The ferrite phase was decomposed into a new austenite(${\gamma}_2$)phase and the ${\sigma}$-phase by an aging treatment. The R phase was an intermetallic compound showing higher molybdenum and tungsten concentrations than the matrix and also showed higher molybdenum and tungsten concentrations than the ${\sigma}$ phase. In the initial stage of aging, precipitation of the R-phase did not change the hardness, the strength and the elongation. The hardness and the strength increased upon a longer aging time, but the elongation rapidly decreased. These results show that the R-phase did not significantly affect the hardness and the strength, though it did influence the elongation.

• 대한치과교정학회지
• /
• 제15권2호
• /
• pp.163-174
• /
• 1985

The requirements of orthodontic wire should include chemical stability, non-discoloration and non-corrosion in oral environment. Ability to be soldered, ease of fabrication and elasticity should be also considered. The purpose of this study was to compare and analyze the physical properties of Tru-chrome wire and manufactured E.S.S. (Experimental Stainless Steel) wire similar to Tru-chrome. The results were as follows: 1. Tru-chrome wire and E.S.S. wire were SUS 304 which was 18 Cr-8Ni austenite stainless steel. There was not significant difference in each composition between two wires. 2. There were not significant differences in ultimate tensile strength, yield strength, elongation and modulus of elasticity between Tru-chrome and E.S.S. wires. 3. There was not significant difference between flexuree modulus of elasticity of Tru-chrome and E.S.S. wires. 4. Micro-hardness value of E.S.S. wire was more than that of Tru-chrome wire and they were softened significantly by solution heat reatment. 5. Micro-structure of Tru-chrome and E.S.S. wires showed fibrous interlocking grains, and an austenite structure after solution heat treatment. 6. There was significant difference between corrosion rate of Tru-chrome and E.S.S. wires.

• 대한금속재료학회지
• /
• 제49권3호
• /
• pp.197-202
• /
• 2011

This study was carried out to investigate the precipitation behavior of ${\chi}$ phase and effect of ${\chi}-phase$ which precipitated at the initial stage of aging on mechanical properties of 25%Cr-7%Ni-4%Mo-0.2%N super duplex stainless steel. ${\chi}-phase$ was precipitated mainly at the interface of ferrite / austenite phases and inside of the ferrite phase at the initial stage of aging, and it was transformed into ${\sigma}-phase$ with an increase of aging time. The ferrite phase was decomposed into new $austenite({\gamma}_2)phase$ and ${\sigma}-phase$ by aging treatment. The hardness and tensile strength of the initial stage of aging when ${\chi}-phase$ was precipitated did not changed considerably, while elongation rapidly decreased. Accordingly, it is considered that ${\chi}-phase$ didn't affect the hardness and strength significantly, but it affected the elongation.

• 한국재료학회지
• /
• 제16권9호
• /
• pp.584-591
• /
• 2006

To enhance the machinability of the austenite stainless alloys, Mn and S were added to form MnS in the austenite matrix. Recently, Ca is also added to increase machinability. The alloying elements, such as C, Mn, S, Ca, and Al, are known to affect machinability, but those roles are not well understood. In this study, the ingots, controlled of alloying elements, C, Mn, S, Ca, Al, were prepared in the 304 stainless steel. The relationship between microstructure and machinability was compared to understand the role of alloying elements. It was proved that Mn and S enhanced machinability but C reduced it by analyzing cutting force on machining in the lathe. The alloying elements, Ca and Al, made a complex oxide compound of Mn-S-Ca-Al-Si-O, which results in increasing tool life. The ferrite volume fraction was changed with alloying elements and the effect of the ferrite fraction on machining was also discussed.

• 한국표면공학회지
• /
• 제54권3호
• /
• pp.102-111
• /
• 2021

The corrosion behaviors of laser-welded super duplex stainless steel tubes with post-weld heat treatment(PWHT) conditions(950, 1000, 1050, 1100 ℃ for 5 and 30 min) were evaluated by electrochemical potentiodynamic polarization and critical pitting temperature measurements. This study showed that the critical metallurgical factors affecting the degradation of corrosion resistance of a steel tube in as-welded condition were the unbalanced phase fraction(ferrite:austenite = 94:4), Cr₂N precipitation, and phase transformation from the austenite phase to ɛ-martensite(via stress-induced phase transformation). The improvement in the corrosion resistance of the welded specimen depends greatly on the PWHT conditions. The specimens after PWHT conducted below 1000 ℃ showed inferior corrosion resistance, caused by precipitation of the sigma phase enriched with Cr and Mo. At 1100 ℃ for a longer duration in PWHT, the ferrite phase grows, and its fraction increases, leading to an unbalanced phase fraction in the microstructure. As a result, pitting can be initiated primarily at the interface between the ferrite/austenite phase, particularly in base metal.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2006년도 춘계학술대회 논문집
• /
• pp.421-424
• /
• 2006

High nitrogen steels (HNS) exhibit both high strength and ductility during tensile deformation. In the present study the Fe-18Cr-14Mn-4Ni-0.9N high nitrogen steel was heat treated at $1000^{\circ}C$ and $1100^{\circ}C$ to produce $Cr_2N$ precipitates in austenite matrix and full austenite microstructures, respectively. Tensile tests of the heat treated specimens were performed at two different strain rates of 0.05/sec and 0.00005/sec. Each tensile curve of the specimens could be well characterized by the the modified Ludwik equation. Plastic deformation of the steel was adequately represented by the four parameters of the modified Ludwik equation. At 0.05/s strain rate, the specimen with the $Cr_2N$ precipitate exhibited higher strength than the full austenite specimen, while the full austenite specimen showed better mechanical properties at 0.00005/s strain rate. It was found that the $Cr_2N$ precipitates influences deformation behavior of the high nitrogen steel significantly.

• 한국표면공학회:학술대회논문집
• /
• 한국표면공학회 2013년도 춘계학술대회 논문집
• /
• pp.92-94
• /
• 2013

우수한 기계적 강도 및 내식성을 가지고 있는 F51(Duplex Stainless Steel)에 저온 plasma Carburizing처리를 적용하여 온도 및 Ar농도에 따른 표면특성을 조사하였다. 플라즈마 처리된 시편은 표면에 탄소가 과포화된 S-phase 또는 Expanded austenite가 형성되어 미처리 시편에 비해 경도 및 내식성 모두 증가하였다.

• 한국강구조학회 논문집
• /
• 제18권2호
• /
• pp.271-278
• /
• 2006

오스트나이트계 STS 304 스테인리스강의 응력도-변형도 곡선을 전 영역에 걸쳐 연구하는 것을 본 논문의 목적으로 한다. 실험적, 이론적 연구를 통하여 비교분석하였고, 개선된 곡선을 제안한다. 0.2% 강도까지 Ramberg-Osgood 곡선은 유용하지만, 이 영역을 초과하는 한계상태의 경우 그것은 원칙적으로 일치하지 않는다. Rasmussen 곡선은 Ramberg-Osgood 곡선의 원리에 기초하여 0.2% 강도를 초과하는 영역에 대하여 개발되었다. 실험과 비교한 결과 잘 일치하지 않기 때문에 실험결과를 분석하여 개선된 식을 제안하며 응력도-변형도 관계를 전 영역에 걸쳐 비교 평가한다.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 1999년도 추계학술강연 및 발표대회 강연 및 발표논문 초록집
• /
• pp.23-24
• /
• 1999