• 제목/요약/키워드: tempered hardness

검색결과 97건 처리시간 0.024초

Al 2013-T8 합금에서 Zr 첨가에 따른 기계적 특성 분석 (Analysis of Mechanical Properties with Addition of Zr in Al 2013-T8 Alloy for Galvanizing Equipment)

  • 백민숙;조사현;박만복;윤동주;허기복
    • 한국재료학회지
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    • 제26권8호
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    • pp.444-448
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    • 2016
  • In this study, the recently developed Al 2013 alloy was T8-tempered and, to improve the strength and corrosion-resistance, slight amounts of Zr of 0.2 wt% and 0.5 wt%, respectively, were added and the mechanical properties were analyzed. For microstructure and precipitate analysis, OM observation, XRD analysis, and TEM analysis were performed, and for the mechanical property analysis, hardness and tensile strength tests were done. Also, in order to determine the corrosion rate according to the Zr content, a potentiodynamic polarization test was performed and the properties were compared and analyzed. The size of the precipitate varied with the content of Zr and was finest at Zr content of 0.2 wt%; it grew larger at 0.5 wt%, at which point the hardness value accordingly showed the same trend. On the other hand, as calculated from the aspect of chemical bonding among atoms, it was confirmed that the tensile strength and the corrosion-resistance increased with the same trend.

Microstructural Evolution of Grade 91 Steel upon Heating at 760~1000℃

  • He, Yinsheng;Chang, Jungchel;Lee, Je-Hyun;Shin, Keesam
    • 한국재료학회지
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    • 제25권11호
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    • pp.607-611
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    • 2015
  • The microstructural evolution of Grade 91 tempered martensite ferritic steels heat treated at $760{\sim}1000^{\circ}C$ for two hours was investigated using scanning electron microscopy(SEM), energy disperse spectroscopy(EDS), electron backscattered diffraction (EBSD), and transmission electron microscopy(TEM); a microhardness tester was also employed, with a focus on the grain and precipitate evolution process as well as on the main hardening element. It was found that an evolution of tempered martensite to ferrite($760{\sim}850^{\circ}C$), and to fresh martensite($900{\sim}1000^{\circ}C$), occurred with the increase of temperature. Simultaneously, the parabolic evolution characteristics of the low angle grain boundary(LAGB) increased with the increase of the heating temperature(highest fraction of LAGB at $925^{\circ}C$), indicating grain recovery upon intercritical heating. The main precipitate, $M_{23}C_6$, was found to be coarsened slightly at $760{\sim}850^{\circ}C$; it then dissolved at $850{\sim}1000^{\circ}C$. Besides this, $M_3C$ cementite was formed at $900{\sim}1000^{\circ}C$. Finally, the experimental results show that the hardness of the steel depended largely on the matrix structure, rather than on the precipitates, with the fresh martensite showing the highest hardness value.

Cr-Mo계 금형강의 기계적 성질에 미치는 합금원소 및 템퍼링의 영향 (Effects of Alloying Element and Tempering on the Mechanical Properties of Cr-Mo Plastic Mold Steels)

  • 김남규;김병옥;이오연
    • 열처리공학회지
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    • 제25권4호
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    • pp.196-205
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    • 2012
  • The purpose of this study is to enhance the hardenability and the mechanical properties by the addition of alloying elements such as Ni, Cr, Mo and B for the development of Cr-Mo plastic mold steel with uniform hardness and microstructure. The ingots were prepared by vacuum induction melting and forged to ${\Phi}35mm$ round bar. Forged bars were quenched and tempered at $200{\sim}600^{\circ}C$ for 1.5 hour. Jominy test, boron distribution observation, microstructual observation, tensile test and charpy impact test were conducted. It was confirmed that the hardenablity of these steels was improved by increasing of alloying elements and further promoted by the addition of boron. The critical rate of cooling required to obtain the bainitic structure for 0.27C-1.23Cr-0.28Mo-B steel was $0.5^{\circ}C/sec$. Hardness and strength of Cr-Mo steels decreased with increasing tempering temperature, but elongation and reduction of area increased with increasing tempering temperature. However, impact energy tempered at $400^{\circ}C$ showed the lowest value in the range $200{\sim}600^{\circ}C$ due to the temper embrittlement.

Mo계 고속도 공구강의 오스템퍼렁에 따른 기계적 성질에 관한 연구 (Study on the Mechanical Properties of Mo Series High Speed Tool Steel Austempered)

  • 최문성;이해우;노용식;김영희;김한군;이상윤
    • 열처리공학회지
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    • 제4권1호
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    • pp.1-12
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    • 1991
  • This study has been performed to find out the effect of austenitizing temperature, austempering temperature and its holding time, and tempering cycle on the mechanical properties such as impact resistance, hardness etc. of AISI $M_2$ Mo series high speed tool steel austempered or tempered after austempering treatment. The results obtained from the experiment are as follows ; (1) Optical micrograph has revealed that the transformation rate of bainite is delayed as the austenitizing temperature increases and that bainite is most apparently transformed at an austempering temperature of $290^{\circ}C$. (2) The amount of retained austenite during austempering has been analysed to be increased by the X-ray diffraction technique as the transformation product of bainite is increased. It has also been shown that the longer the holding time of austempering, the more the transformation quantity of bainite is formed, exhibiting, however, that the rate of bainitic transformation is considerably retarded after a certain period of holding time elapses. (3) Hardness measurement has shown that hardness values obtained after austempering increase with decreasing the amount of retained austenite. (4) The austempering and then tempering cycle has been formed to give hardness values which are more greatly improved as austenitizing temperature is increased. (5) The mechanical property of the specimen primary-tempered for 1 hour at $550^{\circ}C$ after austempering for 2 hours at $290^{\circ}C$ from the austenitizing temperature range of $1180^{\circ}C$ to $1210^{\circ}C$ have been estimated to be good values.

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구상화 열처리된 고탄소강의 미끄럼 마멸 거동에 미치는 시멘타이트 형상과 페라이트 기지조직의 영향 (The Effect of Cementite Morphology and Matrix-ferrite Microstructure on the Sliding Wear Behavior in Spheroidized High Carbon Steel)

  • 허하리;권혁우;구본우;김용석
    • 소성∙가공
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    • 제25권2호
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    • pp.96-101
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    • 2016
  • The current study was conducted to elucidate the effect of cementite morphology and matrix-ferrite microstructure on sliding wear behavior in spheroidized high carbon (1wt. % C) steel. The high carbon steel was initially heat treated to obtain a full pearlite or a martensite microstructure before the spheroidization. The spheroidizing heat treatment was performed on the full pearlitic steel for 100 hours at 700℃ and tempering was performed on the martensitic steel for 3 hours at 650℃. A spheroidized cementite phase in a ferrite matrix was obtained for both the full pearlite and the martensite microstructures. Sliding wear tests were conducted using a pin-on-disk wear tester with the heat treated steel as the disk specimen. An alumina(Al2O3) ball was used as the pin counterpart during the test. After the spheroidizing heat treatment and the tempering, both pearlite and martensite exhibited similar microstructures of spheroidized cementite in a ferrite matrix. The spheroidized pearlite specimens had lower hardness than the tempered martensite; however, the wear resistance of the spheroidized pearlite was superior to that of the tempered martensite.

Mod. 9Cr-1Mo강에서의 $550^{\circ}C$ 부근에서 템퍼링시 발생하는 취성에 관한 연구 (Study on the Embrittlement of the Mod. 9Cr-1Mo Steel Tempered at $550^{\circ}C$)

  • 구지호;신종호;허성강
    • 열처리공학회지
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    • 제23권3호
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    • pp.156-162
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    • 2010
  • The modified 9Cr-1Mo steel (P91 steel) is very popular as a boiler tube material of the USC (Ultra-Supercritical) power plants. The steels were tempered in the temperature range of 400 to $650^{\circ}C$ and the mechanical tests, such as impact and hardness tersts were performed at the room temperature for the tempered steels. A drop in the impact value (embrittlement) and the hardeness increase were simultanously observed in the range of temperature between $475^{\circ}C$ and $600^{\circ}C$, particularly at $550^{\circ}C$. TEM observation shows the hardening was caused by $M_2C$, resulting in the embrittlement. And the maximum volume fraction of $M_3C$ was also observed at $550^{\circ}C$, Therefore, the embrittlement seems to be caused by both the $M_2C$ and $M_3C$.

700 MPa급 고강도 내진 철근의 미세조직과 기계적 특성에 미치는 템프코어 공정의 영향 (Effect of TempCore Processing on Microstructure and Mechanical Properties of 700 MPa-Grade High-Strength Seismic Resistant Reinforced Steel Bars)

  • 신승혁;김승규;임휘강;황병철
    • 소성∙가공
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    • 제30권2호
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    • pp.91-98
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    • 2021
  • The present study deals with the microstructure and mechanical properties of 700 MPa-grade high-strength seismic resistant reinforced steel bars fabricated by various TempCore process conditions. For the steel bars, in the surface region tempered martensite was formed by water cooling and subsequent self-tempering during TempCore process, while in the center region there was ferrite-pearlite or bainite microstructure. The steel bar fabricated by the highest water flow and the lowest equalizing temperature had the highest hardness in all regions due to the relatively fine microstructure of tempered martensite and bainite. In addition, the steel bar having finer microstructures as well as the high fraction of tempered martensite in the surface region showed the highest yield and tensile strengths. The presence of vanadium precipitates and the high fraction of ferrite contributed to the improvement of seismic resistance such as high tensile-to-yield strength ratio and high uniform elongation.

평면연삭에 있어서 숫돌의 입도와 표면거칠기와의 관계 (On the Relation between Grain Size of Grinding Wheel and Surface Roughness in Surface Grinding)

  • 국정한;김성천
    • 한국정밀공학회지
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    • 제2권2호
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    • pp.60-68
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    • 1985
  • The Surface roughness is affected by the factors such as elements of grinding wheel, grinding conditions, and so on. Of all these factors, we studied surface roughness variation in accordance with grain size of grinding wheel and grinding depth of cut on the surface grinding. Tempered, annealed, quenched, and non-heat treated materials were used as specimen. The results obrained in these experiments are as follows: 1) The smaller the hardness is, the better the grinding surface roughness becomes. 2) Tempered materials after quenching shows the finest finished surface on grinding.

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합금강(ASTM A387 Gr. 91) - 탄소강(ASTM A516 Gr.70) 이종금속의 FCA 다층 용접부 특성 평가 : Part. 1 (A Study of Characteristics on the Dissimilar Metals (Alloy Steel : A387 Gr. 91 - Carbon Steel : A516 Gr. 70) Welds Made with FCA Multiple Layer Welding : Part 1)

  • 신태우;장복수;고진현
    • Journal of Welding and Joining
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    • 제34권3호
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    • pp.61-68
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    • 2016
  • Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E91T1-B9C wire. Post-weld heat treatment was carried out at $750^{\circ}C$ for 2.5 h. Based on microstructural examination, tempered martensite and lower bainite were formed in first layer of weld metal. The amount of tempered martensite was decreased and the amount of lower bainite was increased with increasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered Martensite and lower Bainite. Tensile strengths of dissimilar welds decreased with increasing heat inputs. Dissimilar welds seemed to have a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals showed that the corrosion rate increased with increasing heat inputs due to the increase of the amount of lower Bainite.

12%-Cr 강의 $CO_2$ 레이저 표면경화에서 금속조직과 경도분포 (Microstructure and Hardness Distributions of $CO_2$ Lser Hrdened 12%-Cr Seel)

  • 김재도
    • 대한기계학회논문집
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    • 제16권10호
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    • pp.1861-1868
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    • 1992
  • 본 연구에서는 발전소의 터빈 블레이드는 물방울에 의해서 부식이 발생한다는 사실은 널리 알려져 있다. 부식을 방지하기위해서 보통 12%-Cr 강으로 만들며 표면 을 고주파 유도경화법에 의해서 표면을 경화시킨다. 고주파유도 경화법은 경화층 깊 이가 마모 특성을 가장 좋게 하는 깊이보다 훨씬 깊게 경화되며, 열응력이 과대하게 생기고, 처리시간이 많이 걸리며, 표면경화 처리후 기계가공이 필요하다. 12%-Cr 강 의 레이저 표면경화를 연속파 3kw CO$_{2}$ 레이저로 실험하여 금속조직과 경도분포에 대해서 연구하여 레이저 표면경화 가능성을 고찰하였다.