• 제목/요약/키워드: Austenite grain growth

검색결과 30건 처리시간 0.035초

저합금강 소재의 열처리해석 기술개발 (Heat Treatment Analysis on Low-Alloy Steel)

  • 최영심;곽시영;최정길;김정태
    • 소성∙가공
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    • 제14권3호
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    • pp.215-223
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    • 2005
  • A numerical analysis program is developed by FDM scheme for the prediction of microstructural transformation during heat treatment of steels. In this study, multi-phase model was used fur description of diffusional austenite transformations in low-alloy hypoeutectoid steels during cooling after austenitization. A fundamental property of the model consisting of coupled differential equations is that by taking into account the rate of austenite grain growth, it permits the prediction of the progress of ferrite, pearlite, and bainite transformations simultaneously during quenching and estimate the amount of martensite also by using K-M eq. In order to simulate the microstructural evolution during tempering process, another Avrami-type eq. was adopted and method for vickers hardness prediction was also proposed. To verify the developed program, the calculated results are compared with experimental ones of casting product. Based on these results, newly designed heat treatment process is proposed and it was proved to be effective for industry.

합금원소와 소성변형이 22Cr 마이크로 듀플렉스 스테인리스강의 미세조직에 미치는 영향 (Effect of Alloying Composition and Plastic Deformation on the Microstructure of 22Cr Micro-Duplex Stainless Steel)

  • 박준영;안용식
    • 대한금속재료학회지
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    • 제50권11호
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    • pp.793-800
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    • 2012
  • The effect of cold rolling on the microstructural evolution in 22Cr-0.2N micro-duplex stainless steel was investigated. The 22Cr-xNi-yMn-0.2N duplex stainless steel plates with various Ni and Mn contents were fabricated. The steels were vacuum induction melted and hot rolled, followed by annealing treatment at the temperature range of $1000-1100^{\circ}C$, in which both the austenite and ferrite phases were stable. The volume fraction of the ferrite phase depending on the alloy compositions of Ni and Mn increased with an increase in the annealing temperature. Grain growth in the ferrite phase occurred markedly after cold rolling followed by annealing, while fine recrystallised grains were still found in the austenite phase. A large number of martensite laths was found in the microstructure of cold rolled steels, which should be formed by strain-induced martensite from the austenite phase. The intersections of stacking faults were revealed by TEM observation. The volume fraction of the martensite phase increased with an increase of the reduction ratio by cold rolling.

SM40C 강의 열처리가 피로균열전파속도에 미치는 영향 (The Effect of Heat Treatment on the Fatigue Crack Propagation in SM40C Steel)

  • 금창훈;권숙인
    • 열처리공학회지
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    • 제3권2호
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    • pp.37-44
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    • 1990
  • The effect of the microstructural change on the near threshold fatigue crack growth rate in SM40C steel has been studied using the ${\Delta}K$ decreasing method. Below the total strain amplitude of 0.56%, cyclic softening occured, whereas above this value cyclic hardening occurred in the pearlitic lamellar structure. However, in the spherodized structure the cyclic hardening solely occurred. The crack growth rate in the near-threshold region was decreased with increasing prior austenite grain size and this was due to surface roughness. The crack growth rate of the spherodized structure was lower than that of the pearlite lamellar structure and the ${\Delta}K_{th}$ of the former was higher than that of the latter. It was understood that the crack propagates preferentially through the ferrite phase. The intergranular facets in the near-threshold region appeared in the spherodized structure.

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DEVELOPMENT OF HYPER INTERFACIAL BONDING TECHNIQUE FOR ULTRA-FONE GRAINED STEELS

  • Kazutoshi Nishimoto;Kazuyoshi Saida;Jeong, Bo-young;Kohriyama, Shin-ichi
    • 대한용접접합학회:학술대회논문집
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    • 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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    • pp.776-780
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    • 2002
  • This paper describes the concept and the characteristics of hyper interfacial bonding developed as a new concept joining process for UFG (ultra-fine grained) steel. Hyper interfacial bonding process is characterized by instantaneous surface melting bonding which involves a series of steps, namely, surface heating by high frequency induction, the rapid removing of heating coil and joining by pressing specimens. UFG steels used in this study have the average grain size of 1.25 ${\mu}{\textrm}{m}$. The surface of specimen can be rapidly heated up and melted within 0.2s. Temperature gradient near heated surface is relatively steep, and peak temperature drastically fell down to about 1100K at the depth of 2~3mm away from the heated surface of specimen. Bainite is observed near bond interface, and also M-A (martensite-austenite) islands are observed in HAZ. Grain size increases with increasing heating power, however, the grain size in bonded zone can be restrained under 11 ${\mu}{\textrm}{m}$. Hardened zone is limited to near bond interface, and the maximum hardness is Hv350~Hv390.

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압력용기강 용접 열영향부에서의 미세조직 및 기계적 물성 예측절차 개발 및 적용성 평가 (Development and Evaluation of Predictive Model for Microstructures and Mechanical Material Properties in Heat Affected Zone of Pressure Vessel Steel Weld)

  • 김종성;이승건;진태은
    • 대한기계학회논문집A
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    • 제26권11호
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    • pp.2399-2408
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    • 2002
  • A prediction procedure has been developed to evaluate the microtructures and material properties of heat affected zone (HAZ) in pressure vessel steel weld, based on temperature analysis, thermodynamics calculation and reaction kinetics model. Temperature distributions in HAE are calculated by finite element method. The microstructures in HAZ are predicted by combining the temperature analysis results with the reaction kinetics model for austenite grain growth and austenite decomposition. Substituting the microstructure prediction results into the previous experimental relations, the mechanical material properties such as hardness, yielding strength and tensile strength are calculated. The prediction procedure is modified and verified by the comparison between the present results and the previous study results for the simulated HAZ in reactor pressure vessel (RPV) circurnferential weld. Finally, the microstructures and mechanical material properties are determined by applying the final procedure to real RPV circumferential weld and the local weak zone in HAZ is evaluated based on the application results.

CrMoV 터빈로터강에서 모의 열영향부 시험편을 이용한 재열균열 민감도평가 (Evaluation of Reheat Cracking Susceptibility with Simulated Heat Affected Zones in Cr-Mo-V Turbine Rotor Steel)

  • 김광수
    • Journal of Welding and Joining
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    • 제13권1호
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    • pp.89-102
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    • 1995
  • The evaluation of reheat cracking susceptibility in CrMoV turbine rotor steel was performed using thermally simulated heat affected zones. The examinations were carried out in terms of microstructural characterization, microhardness measurement and a Charpy type notch opening three point bend test. It was found that reheat cracking susceptibility increased as the peak temperature increased. This effect was due to the combined effects of the carbide dissolution and unrestricted grain growth at 1350.deg. C peak temperature. Reheat cracking susceptibility was estimated based on microhardness measurement and prior austenite grain size. It was established that for this particular material, reheat cracking in coarse grained heat affected zone can be eliminated if the microhardness is below about 360DPH and the grain size is below about 30.mu.m. It is evident that reheat cracking susceptibility can be eliminated or reduced by carefully controlling the welding parameters such that a refined structure is produced in the coarse grained heat affected zone.

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초고탄소강의 제어압연에 의한 세멘타이트의 구상화와 냉각중 마르텐사이트의 핵발생과 성장의 현상론적 고찰 (Study on the Spheroidization of Cementite by Controlled-Rolling and Martensitic Nucleation and its Growth during Cooling in Ultra High Carbon Steel)

  • 최종술;윤진국
    • 열처리공학회지
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    • 제6권2호
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    • pp.98-106
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    • 1993
  • Ultra high carbon steel (Fe-1.4%C) was prepared by means of a high frequency induction furnace. The preferred nucleation site of martensite was observed. The changes of hardness and impact thoughness due to tempering temperatures, and the spheroidization of cementite by controlled -rolling were also studied for the steel. The preferred nucleation site of martensite in the ultra high carbon steel is prior austenite grain boundary. The hardness of the steel is slightly increased up to about $300^{\circ}C$, and then decreased with further tempering temperature. However, the impact energy keeps a almost constant value, independent of the tempering temperature. The spheroidization of cementite is accelerated as the reduction in thickness per rolling pass is increased and the number of the rolling passes becomes greater.

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Ti 첨가 저합금강에서의 용접 열영향부 석출물 거동 및 오스테나이르 결정립 성장 예측 모델 (Prediction model for particle behavior and austenite grain growth in Ti added low alloyed steel HAZ)

  • 문준오;엄상호;이창희;안영호;이종봉
    • 대한용접접합학회:학술대회논문집
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    • 대한용접접합학회 2004년도 추계학술발표대회 개요집
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    • pp.130-132
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    • 2004
  • 석출물의 용해 온도보다 낮은 온도에서의 석출물의 야금학적인 거동을 예측하였다. 평균 사이즈 석출물의 지속적인 성장만을 고려하는 기존의 모델과 달리, 본 연구에서 제안된 모델의 경우에는, Gibbs-Thomson equation으로부터 유도되는 critical particle size를 고려하였다. 제안된 모델을 이용해서 TiN석출물의 거동을 예측하였으며, 이를 실험 결과 및 기존의 모델에 의한 예측 값과 비교하였다. 석출물들의 분포는 전형적인 log-normal 분포를 따르는 것으로 관찰되었으며, 본 연구에서 제안된 모델이 기존의 모델에 비해서 실험결과와 잘 일치함을 확인할 수 있었다.

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페라이트계 스테인리스강의 마찰교반접합 (Friction Stir Welding of Ferritice Stainless Steel)

  • 안병욱;최돈현;연윤모;정승부
    • Journal of Welding and Joining
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    • 제32권2호
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    • pp.14-17
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    • 2014
  • Ferritic stainless steels are widely used in the construction industry and in exhaust manifolds due to their low cost and relatively superior stress corrosion cracking resistance and pitting corrosion resistance compared to austenite stainless steels. Ferritic stainless steels are currently welded by various welding process including gas tungsten arc welding (GTAW), electron resistance welding (ERW) and laser beam welding. However, when these stainless steels are welded by fusion welding, some problems occur in the fusion zone (FZ) and heat affected zone (HAZ). First, the ductility of the weld is reduced due to the grain growth in the FZ and HAZ. Second, as its HAZ is frequently sensitized during welding, corrosion resistance deteriorates in this region due to the Cr depletion zone. To prevent these problems, it is recommended that ferritic stainless steels be welded with a low heat input. In this study, recent researches in the view of friction stir welded ferritic stainless steels are briefly reviewed.

TMCP강의 용접 공정별 입열량에 따른 용접부 물성 평가 및 비교 (Evaluation and Comparison of Weldabilities with Various Welding Processes on TMCP Steels)

  • 최철영;지창욱;김형찬;남대근;김정돈;김순국;박영도
    • Journal of Welding and Joining
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    • 제32권1호
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    • pp.6-14
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    • 2014
  • This paper has an aim to evaluate microstructure and fracture toughness of TMCP steel weldment applied for off-shore wind tower with the focus on the effect of heat input on the weldment with various welding processes; FCAW(13kJ/cm and 30kJ/cm), SAW(62kJ/cm), and EGW(177kJ/cm). Based on experimental results developed from this study, it was found that the impact toughness of top side for TMCP steel weldments with heat input up to 62 kJ/cm satisfied the required minimum value except the EGW(177kJ/cm). The heat input and microstructure are the main factors of impact toughness. The heat input of 13kJ/cm on back side with low heat input increased the amount of grain boundary ferrite which has low impact toughness, and heat input of 177kJ/cm on top side is significant enough to produce the austenite grain growth. The compositions and sizes of inclusions which are the dominant factors for the formation of acicular ferrite were analyzed by OM and EDS. As the heat input increased, the inclusions also grew and a nucleation site decreased. The size of nonmetallic inclusions and the crack width was nearly similar, therefore the inclusions were related with the crack propagation.