• 제목/요약/키워드: Austenite grain growth

검색결과 32건 처리시간 0.021초

The Effects of TiN Particles on the HAZ Microstructure and Toughness in High Nitrogen TiN Steel

  • Jeong, H.C.;An, Y.H.;Choo, W.Y.
    • International Journal of Korean Welding Society
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    • 제2권1호
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    • pp.25-28
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    • 2002
  • In the coarse grain HAZ adjacent to the fusion line, most of the TiN particles in conventional Ti added steel are dissolved and austenite grain growth is easily occurred during welding process. To avoid this difficulty, thermal stability of TiN particle is improved by increasing the nitrogen content in steel. In this study, the effect of hlgh nitrogen TiN particle on preventing austenite grain growth in HAZ was investigated. Increased thermal stability of TiN particle is helpful for preventing the austenite grain growth by pinning effect. High nitrogen TiN particle in simulated HAZ were not dissolved even at high temperature such as 1400'E and prevented the austenite grain growth in simulated HAZ. Owing to small austenite grain size in HAZ the width of coarse grain HAZ in high nitrogen TiN steel was decreased to 1/10 of conventional TiN steel. Even high heat input welding, the microstructure of coarse grain HAZ consisted of fine polygonal ferrite and pearlite and toughness of coarse grain HAZ was significantly improved.

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THE EFFECTS OF TiN PARTICLES ON THE HAZ MICROSTRUCTURE AND TOUGHNESS IN HIGH NITROGEN TiN STEEL

  • Jeong, Hong-Chul;An, Young-Ho;Choo, Wung-Yong
    • 대한용접접합학회:학술대회논문집
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    • 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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    • pp.217-221
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    • 2002
  • In the coarse grain HAZ adjacent to the fusion line, most of the TiN particles in conventional Ti added steel are dissolved and austenite grain growth is easily occupied during welding process. To avoid this difficulty, thermal stability of TiN particle is improved by increasing the nitrogen content in steel. In this study, the effect of high nitrogen TiN particle on preventing austenite grain growth in HAZ was investigated. Increased thermal stability of TiN particle is helpful for preventing the austenite grain growth by pinning effect. High nitrogen TiN particle in simulated HAZ were not dissolved even at high temperature such as 1400 C and prevented the austenite grain growth in simulated HAZ. Owing to small austenite grain size in HAZ the width of coarse grain HAZ in high nitrogen TiN steel was decreased to 1/10 of conventional TiN steel. Even high heat input welding, the microstructure of coarse grain HAZ consisted of fine polygonal ferrite and pearlite and toughness of coarse grain HAZ was significantly improved.

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용접 열영향부 미세조직 및 재질 예측 모델링 : III. 석출물 - Free 저합금강의 초기 오스테나이트 결정립크기의 영향을 고려한 용접 열영향부 오스테나이트 결정립성장 예측 모델 (Prediction Model for the Microstructure and Properties in Weld Heat Affected Zone: III. Prediction Model for the Austenite Grain Growth Considering the Influence of Initial Austenite Grain Size in Weld HAZ of Precipitates Free Low Alloyed Steel)

  • 엄상호;문준오;정홍철;이종봉;이창희
    • Journal of Welding and Joining
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    • 제24권4호
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    • pp.39-49
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    • 2006
  • The austenite grain growth model in low alloyed steel HAZ without precipitates was proposed by analyzing isothermal grain growth behavior. Steels used in this study were designed to investigate the effect of alloying elements. Meanwhile, a systematic procedure was proposed to prevent inappropriate neglect of initial grain size (D0) and misreading both time exponent and activation energy for isothermal grain growth. It was found that the time exponent was almost constant, irrespectively of temperature and alloying elements, and activation energy increased with the addition of alloying elements. From quantification of the effect of alloying elements on the activation energy, an isothermal grain growth model was presented. Finally, combining with the additivity rule, the austenite grain size in the CGHAZ was predicted.

용접열영향부 호스테나이트 결정립 크기 예측 모델링 (Prediction model for prior austenite grain size in low-alloy steel weld HAZ)

  • 엄상호;문준오;이창희;윤지현;이봉상
    • 대한용접접합학회:학술대회논문집
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    • 대한용접접합학회 2003년도 춘계학술발표대회 개요집
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    • pp.43-45
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    • 2003
  • The empirical model for predicting the prior austenite grain size in low-alloy steel weld HAZ was developed through examining the effect of alloying element. The test alloys were made by vacuum induction melting. Grain growth behaviors were observed and analyzed by isothermal grain growth test and subsequent metallography. As a result, it was found that the grain growth might be controlled by grain boundary diffusion and the empirical model for grain growth was presented.

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A Study on the Melting Morphology of Graphite in Cast Iron

  • Lim, Chang-Hee;Ra, Hyung-Yong
    • 한국주조공학회지
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    • 제5권4호
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    • pp.243-257
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    • 1985
  • Many authors have studied the solidification process of cast iron and the effect of grain boundaries in austenite shell on the growth of spheroidal graphite. But, the studies on the melting morphology of cast iron are rare and the effect of grain boundaries in austenite shell on the melting procedure of spheroidal graphite cast iron is unknown. Therefore, in this work, the melting procedure of cast iron and the role of grain boundaries in austenite shell on the melting of spheroidal graphite have been studied. The main results are summarized as follows. 1. In white cast iron containing silicon, melting initiates at the interface between austenite matrix and temper carbon which was decomposed from $Fe_3C$ during heating. 2. In gray cast iron, melting initiates at the boundary of eutectic cell where elements with low melting temperature are condensed. The dissolution of kish graphite is difficult. 3. In spheroidal graphite cast iron containing little phosphor, melting initiates at the outer region of austenite shell in which silicon is condensed. In this case, grain boundaries in austenite shell give little effect on the melting procedure of spheroidal graphite. 4. In spheroidal graphite cast iron containing phosphor above 0.3 wt%, its melting phenomena are changed with heating rate due to the existence of steadite. In this case, it can be concluded that liquid phase of steadite, which segregated on outer region of austenite shell, moves to spheroidal graphite-austenite interface along the grain boundaries in austenite shell.

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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.

베이나이트강의 미세조직과 저온 충격 인성에 미치는 바나듐과 보론의 영향 (Effect of Vanadium and Boron on Microstructure and Low Temperature Impact Toughness of Bainitic Steels)

  • 황원구;이훈;조성규;서준석;권용재;이정구;신상용
    • 한국재료학회지
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    • 제31권3호
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    • pp.139-149
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    • 2021
  • In this study, three kinds of bainitic steels are fabricated by controlling the contents of vanadium and boron. High vanadium steel has a lot of carbides and nitrides, and so, during the cooling process, acicular ferrite is well formed. Carbides and nitrides develop fine grains by inhibiting grain growth. As a result, the low temperature Charpy absorbed energy of high vanadium steel is higher than that of low vanadium steel. In boron added steel, boron segregates at the prior austenite grain boundary, so that acicular ferrite formation occurs well during the cooling process. However, the granular bainite packet size of the boron added steel is larger than that of high vanadium steel because boron cannot effectively suppress grain growth. Therefore, the low temperature Charpy absorbed energy of the boron added steel is lower than that of the low vanadium steel. HAZ (heat affected zone) microstructure formation affects not only vanadium and boron but also the prior austenite grain size. In the HAZ specimen having large prior austenite grain size, acicular ferrite is formed inside the austenite, and granular bainite, bainitic ferrite, and martensite are also formed in a complex, resulting in a mixed acicular ferrite region with a high volume fraction. On the other hand, in the HAZ specimen having small prior austenite grain size, the volume fraction of the mixed acicular ferrite region is low because granular bainite and bainitic ferrite are coarse due to the large number of prior austenite grain boundaries.

C-Mn-Mo-Ni강 용접열영향부의 석출물을 고려한 오스테나이트 결정립 성장 거동 예측 (Austenite Grain Growth Prediction Modeling of C-Mn-Mo-Ni Steel HAZ Considering Precipitates)

  • 서영대;엄상호;이창희;김주학;홍준화
    • Journal of Welding and Joining
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    • 제20권5호
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    • pp.78-86
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    • 2002
  • A metallurgical model for the prediction of prior austenite grain size considering the dissolution kinetics of M$_3$C precipitates at the heat affected zone of SA508-cl.3 was proposed. The isothermal kinetics of grain growth and dissolution were respectively described by well-known equation, $dD/dT=M({\Delta}F_{eff})^M$ and Whelan's analytical model. The isothermal grain growth experiments were carried out for measure the kinetic parameters of grain growth. The precipitates of the base metal and the specimens exposed to thermal cycle were examined by TEM-carbon extraction replica method. The model was assessed by the comparison of BUE simulation experiments and showed good consistencies. However, there was no difference between the model considering and ignoring $M_3C$ precipitates. It seems considered that pinning force exerted by $M_3C$ Precipitates was lower than driving force for grain growth due to large size and small fraction of precipitates, and mobility of grain boundary was low in the lower temperature range.

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.

Fe-27%Ni-0.27%C 합금의 마르텐사이트 변태온도와 형태에 관한 연구 (Study on the Martensitic Transformation Temperature and Morphology in Fe-27%Ni-0.27%C Alloy)

  • 손인진;김환철;김학신
    • 열처리공학회지
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    • 제9권3호
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    • pp.198-204
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    • 1996
  • This work was carried out in order to investigate the effect of grain size on martensitic transformation temperature and morphology of Fe-27%Ni-0.27%C alloy. The martensitic transformation temperature was raised with increasing the austenitizing temperature within the range from $750^{\circ}C$ to $1200^{\circ}C$, owing to the grain growth, vacancy concentration. It was observed that the larger was the austenite grain, the higher was the martensitic transformation temperature. The influence of the austenite grain size was similar to that of the austenitizing temperature. The morphology of martensite in Fe-27%Ni-0.27%C alloy changed from lath to lenticular with the variation of grain size. From the above results, it was concluded that the martensitic transformation temperature and morphology was mainly dependent upon the austenite grain size.

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