• 제목/요약/키워드: Coarse-Grained Austenite

검색결과 16건 처리시간 0.023초

대입열 EH36-TM강의 Tandem EGW 용접부 미세조직 및 기계적 성질 (Mechanical Properties and Microstructures of High Heat Input Welded Tandem EGW Joint in EH36-TM Steel)

  • 정홍철;박영환;안영호;이종봉
    • Journal of Welding and Joining
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    • 제25권1호
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    • pp.57-62
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    • 2007
  • In the coarse grained HAZ of conventional TiN steel, most TiN particles are dissolved and austenite grain growth easily occurrs during high heat input welding. To avoid this difficulty, thermal stability of TiN particles is improved by increasing nitrogen content in EH36-TM steel. Increased thermal stability of TiN particle is helpful for preventing austenite grain growth by the pinning effect. In this study, the mechanical properties and microstructures of high heat input welded Tandem EGW joint in EH36-TM steel with high nitrogen content were investigated. The austenite grain size in simulated HAZ of the steel at $1400^{\circ}C$ was much smaller than that of conventional TiN steel. Even for high heat input welding, the microstructure of coarse grained HAZ consisted of fine ferrite and pearlite and the mechanical properties of the joint were sufficient to meet all the requirements specified in classification rule.

초미세 결정립 TRIP 강의 미세조직 변화 (Microstructural evolution of ultrafine grained TRIP low-carbon steel)

  • 이철원;고영건;남궁승;신동혁
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2009년도 추계학술대회 논문집
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    • pp.263-266
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    • 2009
  • Transformation induced plasticity (TRIP) steel consisting of ferrite, austenite, and bainite phases was regarded as an excellent candidate for automotive applications due to the good combination of ductility and strength. The aim of the present study was to understand the microstructural characteristics of ultrafine grained (UFG) TRIP low-carbon steel fabricated via equal channel angular pressing accompanied with intercritical- and isothermal-annealing treatments. When compared to coarse grained counterpart, only the volume fraction of austenite phase in UFG TRIP steel remained unchanged, but all other microstructural variables such as size and morphology were different. It was found that UFG TRIP steel showed the homogeneous distribution of each constituent phase, which was discussed in terms of annealing treatments done in this study.

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3Cr-1Mo강/STS-309L 오버레이 용접부의 천이영역 조직에 미치는 용접조건의 영향 (Effect of Welding Condition on Microstructure of Transient Zone in Overlay Weld of 3Cr-1Mo Steel/STS-309L)

  • 김동진;김병훈;지병하;김정태;김성곤;강정윤;박화순
    • Journal of Welding and Joining
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    • 제18권2호
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    • pp.176-176
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    • 2000
  • Recently developed Austenite stainless steel,309L was to overlay on 3Cr-1Mo-V-Ti-B steels, using Electroslag welding process, which wide electrodes were adopted. Transition region in welding interlayer relating to disbonding crack was investigated. Also. the effect of welding condition on the width of transition region and coarsening grains of the austenite were studied.1) With increasing welding speed the width of martensite at transient region was increased, but the amount of delta ferrite in weld metal was reduced, being fine grained.2) The form of martensite at the transition region was occured by reversible transition region, leading to increasing Ms point.3) With increasing welding speed, the grain of austenite formed at the welding interface was finer. With increasing welding current under the same welding speed, the grain size of the austenite was finer. At high current, original grain size of the austenite is coarse, but the austenite has fine grains because the austenite was transformed to martensite during cooling.4) In the case of high welding speed, the width of martensite at the welding interface was increased, but the grain size of austenite at the welding interface was finer. This indicates that the inhibition of disbonding crack may be achieved through dispersening fine carbides in the grain boudary.(Received August 3, 1999)

3Cr-1Mo강/STS-309L 오버레이 용접부의 천이영역 조직에 미치는 용접조건의 영향 (Effect of Welding Condition on Microstructure of Transient Zone in Overlay Weld of 3Cr-1Mo Steel/STS-309L)

  • 김동진;김병훈;지병하;김정태;김성곤;강정윤;박화순
    • Journal of Welding and Joining
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    • 제18권2호
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    • pp.49-56
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    • 2000
  • Recently developed Austenite stainless steel, 309L was used to overlay on 3Cr-1Mo-V-Ti-B steels, using Electroslag welding process, which wide electrodes were adopted. Transition region in welding interlayer relating to disbonding crack was investigated. Also, the effect of welding condition on the width of transition region and coarsening grains of the austenite were studied. 1) With increasing welding speed the width of martensite at transient region was increased, but the amount of delta ferrite in weld metal was reduced, being fine grained. 2) The form of martensite at the transition region was occurred by reversible transformation during cooling since the interdiffusion of Cr and Ni from weld metal and Fe and C from base metals at the transition region, causes to lowering the concentration of Cr and Ni at the transition region, leading to increasing Ms point. 3) With increasing welding speed, the grain of austenite formed at the welding interface was finer. With increasing welding current under the same welding speed, the grain size of the austenite was finer. At high current, original grain size of the austenite is coarse, but the austenite has fine grains because the austenite was transformed to martensite during cooling. 4) In the case of high welding speed, the width of martensite at the welding interface was increased, but the grain size of austenite at the welding interface was finer. This indicates that the inhibition of disbonding crack may be achieved through dispersening fine carbides in the gain boundary.

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Ti-Nb첨가 저합금강 용접열영향부에서의 열-응력 이력이 미세조직 및 기계적 성질에 미치는 영향에 관한 연구 (Microstructure Evolution and Its Effect on Strength during Thermo-mechanical Cycling in the Weld Coarse-grained Heat-affected Zone of Ti-Nb Added HSLA Steel)

  • 문준오;이창희
    • Journal of Welding and Joining
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    • 제31권6호
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    • pp.44-49
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    • 2013
  • The influence of thermo-mechanical cycling on the microstructure and strength in the weld coarse-grained heat affected zone (CGHAZ) of Ti-Nb added low carbon HSLA steel was explored through Vickers hardness tests, nanoindentation experiments, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Undeformed and deformed CGHAZs were simulated using Gleeble simulator with different heat inputs of 30kJ/cm and 300kJ/cm. At high heat input of 300kJ/cm, the CGHAZ consisted of ferrite and pearlite and then their grain sizes were not affected by deformation. At low heat input of 30kJ/cm, the CGHAZ consisted of lath martensite and then the sizes of prior austenite grain, packet and lath width decreased with deformation. In addition, the fraction of particle increased with deformation and this is because the precipitation kinetics was accelerated by deformation. Meanwhile, the Vickers and nanoindentation hardness of deformed CGHAZ with 30kJ/cm heat input were higher than those of undeformed CGHAZ, which are due to the effect of grain refinement and precipitation strengthening.

극 저탄소강의 Intercritical coarse grained HAZ에서의 M-A상과 인장특성 간의 상관관계 (Correlation Between M-A Constituents and Tensile Properties in the Intercritical Coarse Grained HAZ of an Ultra Low Carbon Steel)

  • 이윤기;문준오;김상훈;이창희
    • Journal of Welding and Joining
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    • 제28권3호
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    • pp.99-103
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    • 2010
  • It is well known that martensite-austenite (M-A) constituents are formed in the intercritically reheated coarse grained heat affected zone (ICCGHAZ) of a multipass weld and they act on the local brittle zone (LBZ) in the welded structures. To investigate the effect of M-A constituents on the tensile properties of ICCGHAZ, specimens with M-A constituents of different volume fraction and size were prepared through the multipass welding cycles simulated by a Gleeble simulator and then tensile test was carried out. The results indicated that finely distributed M-A constituents contributed to decrease the yield ratio, which is mainly due to the increased tensile strength.

저탄소 미량합금강의 미세조직에 미치는 고온변형의 효과 (Effects of Austenitization Temperature and Hot Deformation on Microstructure of Microalloyed Low Carbon Steels)

  • 김새암;이상우
    • 열처리공학회지
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    • 제16권2호
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    • pp.83-89
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    • 2003
  • As a research for developing fine-grained high strength low carbon steels, the effects of austenitization temperature and hot deformation on microstructure was investigated in 0.15 wt.% carbon steels with microalloying elements such as Nb and Ti. When the steels were reheated at $1250^{\circ}C$, Nb containing steel showed very coarse austenite grain size of $200{\mu}m$ whereas Nb-Ti steel did fine one of $70{\mu}m$ because Ti carbonitrides could suppress the austenite grain growth. In case of 50% reduction at $850^{\circ}C$, the austenite grains in the Nb steel partially recrystallized while those in the Nb-Ti steel fully recrystallized probably due to finer prior austenite grains.For the Nb-Ti steel, ferrite grain size was not sensitively changed with austenitization temperature and compression strain and, severe deformation of 80% reduction was not essentially necessary to refine ferrite grains to about $3{\mu}m$ which could be obtained through lighter deformation of 40% reduction.

MODELING OF THE BAINITE TRANSFORMATION KINETICS IN C-MN-MO-NI STEEL WELD CGHAZ

  • Sangho Uhm;Lee, Changhee;Kim, Joohak;JunhwaHong
    • 대한용접접합학회:학술대회논문집
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    • 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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    • pp.276-281
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    • 2002
  • A metallurgical model for bainite transformation kinetics in the coarse-grained heat affected zone(CGHAZ) on the basis of an Avrami-type equation was studied. Isothermal transformation tests were carried out to obtain the empirical equations for incubation time and Avrami kinetic constants for C-Mn-Mo-Ni steel. The effect of prior austenite grain size(PAGS) on the reaction rate of bainite was also investigated. Compared with experimental transformation behavior of bainite, the predicted behavior was in good agreement. It was also found that a smaller grain size retard the bainite reaction rate, contrary to the classical grain size effect and this is considered to be caused by constraint of grain size to bainite growth.

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스테인레스강 Overlay용접부의 수소취화 균열감수성에 관한 연구 1 (Study on the hydrogen embrittlement crack susceptibility of stainless steel overlaid weld metal (1))

  • 이영호
    • Journal of Welding and Joining
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    • 제8권3호
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    • pp.39-52
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    • 1990
  • The research is to insure the soundness of the stainless steel overlaid weld metal(21/4Cr-IMo steel + SUS 309L) for a pressure vessel application. Detail studies were conducted for the PWHT influence on the micrstructure and intergranular corrosion characteristics of the overlaid weld metal as well as initiation of hydrogen embrittlement crack(or Disbonding) when welded metal are exposed to the hydrogen atmosphere. Hydrogen was experimentally charged to the overlaid weld metal in order to study PWHT effect on the susceptibility of hydrogen embrittlement crack. The results of this research are as follows: 1. At the bond region, austenite grain of the stainless steel side became coarsed and Cr23C6 type carbide was precipitated at the coarsed austenitic grain boundaries. Intergranular Corrosion width(by Straiss test) increased with increasing PWHT temperature and PWHT time.

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Modeling of the Bainite Transformation kinetics in C-Mn-Mo-Ni Steel weld CGBAZ

  • Uhm, S.;Lee, C.;Kim, J.;Hong, J.
    • International Journal of Korean Welding Society
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    • 제2권1호
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    • pp.11-14
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    • 2002
  • A metallurgical model for bainite transformation kinetics in the coarse-grained heat affected zone(CGHAZ) on the basis of an Avrami-type equation was studied. Isothermal transformation tests were carried out to obtain the empirical equations for incubation time and Avrami kinetic constants for C-Mn-Mo-Ni steel. The effect of prior austenite grain size(PAGS) on the reaction rate of bainite was also investigated. Compared with experimental transformation behavior of bainite, the predicted behavior was in good agreement. It was also found that a smaller grain size retard the bainite reaction rate, contrary to the classical grain size effect and this is considered to be caused by constraint of grain size to bainite growth.

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