• Title/Summary/Keyword: Lath width

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Effect of Hardness and Substructure on Long-term Creep Behavior of Mod.9Cr-1Mo Steel (개량 9Cr-1Mo 강의 장시간 크리프거동에 미치는 경도와 하부조직의 영향)

  • 박규섭;이근진;정한식;김정호;정영관;엔도타카오
    • Journal of the Korean Society for Precision Engineering
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    • v.21 no.2
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    • pp.168-176
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    • 2004
  • Interrupted creep tests were carried out on the Mod.9Cr-1Mo steel in order to investigate the structural degradation during creep. The ranges of creep stress and temperature were from 71 to 167MPa and 873 to 923k, respectively. The change of hardness and tempered martensitic lath width were measured in the grip and gauge parts of interrupted specimens. The lath structure was thermally stable in static conditions, but was not stable during creep, and the structural evolution was enhanced by creep strain. The relation between the change in lath width and strain was described in the from, $\delta$W= a ($W_s-W_o$)$cdot;varepsilon$, where $\varepsilon$ is the strain, $W_o$is the initial lath width, $W_s$ is the final lath width depending solely on stress, and a is the constant of the magnitude of 0.67 $\mu$m /strain. The change in Victors hardness was expressed by a one-valued function of creep life consumption ratio. Based on the empirical relation between strain and lath width, a model was proposed to explain the relation between change in hardness and creep life consumption ratio. The model revealed that about 65$%$ of dislocations in lath structures were eliminated by the migration of subboundaries.

EFFECT OF HARDNESS CHANGES AND MICROSTRUCTURAL DEGRADATION ON CREEP BEHAVIOR OF A Mod.9Cr-1Mo STEEL

  • PARK K. S.;CHUNG H. S.;LEE K. J.;JUNG Y. G.;KANG C. Y.;ENDO T.
    • International Journal of Automotive Technology
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    • v.6 no.1
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    • pp.45-52
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    • 2005
  • Interrupted creep tests for investigating the structural degradation during creep were conducted for a Mod.9Cr-1Mo steel in the range of stress from 71 to 167 MPa and temperature from 873 to 923 K. The change of hardness and tempered martensitic lath width was measured in grip and gauge parts of interrupted creep specimens. The lath structure was thermally stable in static conditions. However, it was not stable during creep, and the structural change was enhanced by creep strain. The relation between the change in lath width and creep strain was described quantitatively. The change in Vickers hardness was expressed by a single valued function of creep LCR(life consumption ratio). Based on the empirical relation between strain and lath width, a model was proposed to describe the relation between change in hardness and creep LCR. The comparison of the model with the empirical relation suggests that about 65% of hardness loss is due to the decrease of dislocation density accompanied by the movement of lath boundaries. The role of precipitates on subboundaries was discussed in connection with the abnormal subgrain growth appearing in low stress regime.

Effect of Transformation Cycles(α' ↔ γ')on Microstructures and Mechanical Properties of Lath and Lenticular Martensites in Fe-Ni Alloys (Fe-Ni 합금에서 래쓰 마르텐사이트와 렌즈상 마르텐사이트의 반복변태사이클(α' ↔ γ')에 따른 미세조직과 기계적 성질)

  • Seo, Seong-Bok;Jun, Joong-Hwan;Choi, Chong-Sool
    • Journal of the Korean Society for Heat Treatment
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    • v.13 no.2
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    • pp.85-90
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    • 2000
  • The influence of transformation cycles (${\alpha}^{\prime}{\leftrightarrow}{\gamma}^{\prime}$) on the microstructure and mechanical properties of lath and lenticular martensites has been studied in Fe-Ni alloys. The width of lath in Fe-15%Ni alloy decreased with increasing the number of transformation cycles, while no appreciable change in dislocation density inside the lath was observed. In case of Fe-31%Ni alloy, a number of dislocations were additionally introduced into the martensite plate after the transformation cycling. Tensile strength and Vickers hardness of lath martensite decreased with the increase in number of transformation cycles, whereas those of lenticular martensite increased up to 1 cycle and then remained constant. Elongation of two alloys was deteriorated after 1 transformation cycling, corresponding to the tensile strength. But the decrement of elongation in Fe-31%Ni alloy was smaller than that in Fe-15%Ni alloy.

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The Effects of Fe and V on the Characteristics of $\beta$to$\alpha$ Transformation for Zr-0.8Sn Alloys (Fe와 V이 Zr-0.8Sn 합금의 $\beta{\rightarrow}\alpha$ 상변태 특성에 미치는 영향)

  • O, Yeong-Min;Kim, Seon-Jin
    • Korean Journal of Materials Research
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    • v.10 no.9
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    • pp.636-641
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    • 2000
  • The effects of Fe and V content on the characteristics of $\beta$ to $\alpha$ phase transformation for Zr-0.8Sn alloys were studied by optical and transmission electron microscopy. With increasing V content, $\beta{\rightarrow}\alpha+\beta$ transformation temperature decreased, thus allowing the width of $\alpha$-lath to be fine air-cooled Zr-0.8Sn-xV alloys. The width of $\alpha$-lath, however, was slightly increased with Fe content. While the $\beta$ to $\alpha$ transformed microstructures of water-quenched Zr-0.8Sn, Zr-0.8Sn-0.1Fe, Zr-0.8Sn-0.2Fe, Zr-0.8Sn-0.4Fe, Zr-0.8Sn-0.1V and Zr-0.8Sn-0.2V were mainly slipped martensite, that of water-quenched Zr-0.8Sn-0.4V was predominantly twinned martensite. The transition of slipped martensite to twinned martensite in Zr-0.8Sn-Xv was thought to be due to the decrease of $M_S$ temperature.

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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 (Ti-Nb첨가 저합금강 용접열영향부에서의 열-응력 이력이 미세조직 및 기계적 성질에 미치는 영향에 관한 연구)

  • Moon, Joonoh;Lee, Changhee
    • Journal of Welding and Joining
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    • v.31 no.6
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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.

The effect of cooling rates on carbide precipitate and microstructure of 9CR-1MO oxide dispersion strengthened(ODS) steel

  • Jang, Ki-Nam;Kim, Tae-Kyu;Kim, Kyu-Tae
    • Nuclear Engineering and Technology
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    • v.51 no.1
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    • pp.249-256
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    • 2019
  • The 9Cr-1Mo ferritic-martensitic ODS steel is a promising structural material for the next generation nuclear power plants including fast reactors for application in reactor vessels and nuclear fuel. The ODS steel was cooled down by furnace cooling, air cooling, oil quenching and water quenching, respectively, after normalizing it at $1150^{\circ}C$ for 1 h and then tempering at $780^{\circ}C$ for 1 h. It is found that grain size, a relative portion of ferrite and martensite, martensitic lath configuration, behaviors of carbide precipitates, and hardness of the ODS steel are strongly dependent on a cooling rate. The grain size and martensitic lath width become smaller with the increase in a cooling rate. The carbides were precipitated at the grain boundaries formed between the ferrite and martensite phases and at the martensitic lath interfaces. In addition, the carbide precipitates become smaller and more widely dispersed with the increase in a cooling rate, resulting in that the faster cooling rate generated the higher hardness of the ODS steel.

Microstructural Evolution and Magnetic Property of Creep-Fatigued Ferritic 9Cr Heat-Resisting Steel (크리프-피로 손상된 페라이트기 9Cr 내열강의 미세조직 발달과 자기적 특성)

  • Kim, Chung-Seok;Kwun, S.I.;Park, Ik-Keun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.27 no.5
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    • pp.417-425
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    • 2007
  • The ferritic 9Cr-1Mo-V-Nb heat-resisting steel was experimentally studied in order to characterize its microstructural evolution during creep-fatigue by coercivity measurement. The creep-fatigue test was conducted at $550\;^{\circ}C$ with the tensile holding time of 60s and 600s, respectively. The coercivity decreased until the failure and the hardness monotonously decreased for the whole fatigue life. As the life fraction of creep-fatigue increased, the $M_{23}C_6$ carbide coarsened following the Ostwald ripening mechanism. However, the MX carbonitrides did not grow during creep-fatigue due to so stable at $550\;^{\circ}C$. The width of martensite lath increased because of the dislocation recovery at the lath boundaries. The magnetic coercivity has an influence on the microstructural properties such as dislocation, precipitates and martensite lath boundaries, which interpreted in relation to microstructural changes. Consequently, this study proposes a magnetic coercivity to quantify the level of damage and microstructural change during the creep-fatigue of ferritic 9Cr-1Mo-V-Nb steel.

The Characteristics of the ${\beta}\;to\;{\alpha}$ Transformation for Zr-Sn and Zr-Nb Alloys (Zn-Sn 및 Zr-Nb 합금의 ${\beta}{\to}{\alpha}$ 상변태 특성)

  • O, Yeong-Min;Jeong, Heung-Sik;Jeong, Yong-Hwan;Kim, Seon-Jin
    • Korean Journal of Materials Research
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    • v.9 no.12
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    • pp.1222-1228
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    • 1999
  • The effects of Sn and Nb content on the characteristics of ${\beta}$ to ${\alpha}$ phase transformation for Zr were studied by optical microscopy and transmission electron microscopy. The basketweave structures consisted of fine ${\alpha}$-laths were shown in all the air-cooled specimens. As the Nb content increased, the ${\beta}{\to}{\alpha}$+${\beta}$ transformation temperature decreased thus allowing the width of ${\alpha}$-lath, however, did not change with Sn content. While water-quenched pure Zr and Zr-xSn alloys were found to be mailny slipped martensite, water-quenched Zr-xNb alloys showed predominantly a twinned martensite. The transition of slipped martensite to twinned martensite was contributed to the decrease of Ms temperature.

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Effect of V and Sb on the Characteristics of β to α Transformation in Zr-0.84Sn Alloy (V과 Sb 첨가가 Zr-0.84Sn 합금의 β→α 상변태 특성에 미치는 영향)

  • O, Yeong-Min;Jeong, Yong-Hwan-Jeong;Kim, Seon-Jin-Kim
    • Korean Journal of Materials Research
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    • v.12 no.4
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    • pp.317-323
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    • 2002
  • Effect of V and Sb content on characteristics of ${\beta}\;to\;{\alpha}$ phase transformation in Zr-0.84Sn alloy has been studied using optical microscopy and transmission electron microscopy. As V content increased, the ${\beta}{\to}{\beta}+{\alpha}$ transformation temperature was lowered, thus allowing the width of $\alpha$-lath in air-cooled Zr-0.86Sn-0.40V alloy to be fine. The width of ${\alpha}$-lath in air-cooled Zr-0.84Sn-xSb, however, was rarely changed with Sb content. The ${\beta}\;to\;{\alpha}$ transformed microstructures of water-quenched Zr-0.84Sn, Zr-0.84Sn-0.10V and Zr-0.84Sn-0.19V alloys were mainly slipped martensite. On the other hand, those of wafter-quenched Zr-0.86Sn-0.40V and Zr-0.85Sn-0.05Sb alloys were predominantly twinned martensite. In case of water-quenched Zr-0.85Sn-0.12Sb and Zr-0.84Sn-0.17Sb alloys, basketweave structure was observed. The transition of slipped martensite to twinned martensite in Zr-0.84Sn-xV alloys and the transition of twinned martensite to basketweave structure in Zr-0.84Sn-xSb alloys were due to the decrease of $M_s$ temperature.