• Title, Summary, Keyword: yield-to-tensile strength ratio

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Effect of Austenitizing and Quenching·Tempering Temperatures on Tensile and Impact Properties of AISI 51B20 (AISI 51B20강의 인장 및 충격특성에 미치는 오스테나이트화 온도와 퀜칭·템퍼링 온도의 영향)

  • Kim, Heon-Joo
    • Journal of the Korean Society for Heat Treatment
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    • v.24 no.6
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    • pp.327-337
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    • 2011
  • Effects of microstructural change, tensile properties and impact property according to the change of austenitizing temperature and tempering temperature of AISI 51B20 steel were examined. Regardless of austenite grain size, lath martensite with needle and packet shapes was found at tempering temperature of $300^{\circ}C{\sim}400^{\circ}C$. The needles of lath martensite changed to parallel packet at tempering temperature of $450^{\circ}C{\sim}600^{\circ}C$. As tempering temperature increased, tensile strength, yield strength and hardness decreased, while elongation, ratio of reduction area and Charpy impact energy increased. Grain size increased when quenching temperature was $930^{\circ}C$. Grain size had prominent effect on the mechanical properties of AISI 51B20 steel. Ratio of tensile strength/yield strength and yield strength autenitized at $880^{\circ}C$ followed by tempering at $350^{\circ}C{\sim}450^{\circ}C$ showed higher values than that of autenization at $930^{\circ}C$ due to fine grain size.

Ultimate Compressive Strength Analysis of TMCP High Tensile Steel Plates with HAZ Softening(2nd Report) (HAZ 연화부를 가진 TMCP형 고장력강판의 압축최종강도에 관한 연구 - 제 2 보)

  • 백점기;고재용
    • Journal of Welding and Joining
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    • v.9 no.2
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    • pp.44-50
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    • 1991
  • The use of high tensile steel plates is increasing in the fabrication of ship and offshore structures. The softening region which has lower yield stress than base metal is located to prevent cracking in the conventional high tensile steel. Also, thermo mechanical control process(TMCP) steel with low carbon equivalent has the softening region which occurs in the heat affected zone when high heat input weld is carried out. The softening region in the high tensile steel gives rise to serious effect on structural strength such as tensile strength, fatigue strength and ultimate strength. In order to make a reliable structural design using high tensile steel plates, the influence of the softening on plate strength should be evaluated in advance. In the previous paper, the authors discussed the ultimate compressive strength of 50HT steel square plates with softening region. In this paper, the ultimate compressive strength with varying the yield stress of softening region and the aspect ratio of the plate is investigated by using the elasto-plastic large deformation finite element method.

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Advanced Indentation Studies on the Effects of Hydrogen Attack on Tensile Property Degradation of Heat-Resistant Steel Heat-Affected Zones

  • Choi, Yeol;Jang, Jae-il;Lee, Yun-Hee;Kwon, Dongil;Kim, Jeong-Tae
    • Corrosion Science and Technology
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    • v.2 no.6
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    • pp.266-271
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    • 2003
  • Safety diagnosis of various structural components and facilities is indispensable for preventing catastrophic failure of material by time-dependent and environment accelerating degradation. Also, this diagnosis of operating components should be done periodically for safe maintenance and economical repair. However, conventional standard methods for mechanical properties have the problems of bulky specimen, destructive procedure and complex procedure of specimen sampling. So, a non-destructive and simple mechanical testing method using small specimen is needed. Therefore, an advanced indentation technique was developed as a potential method for non-destructive testing of in-field structures. This technique measures indentation load-depth curve during indentation and analyzes the mechanical properties related to deformation such as yield strength, tensile strength and work-hardening index. In this paper, we characterized the tensile properties including yield and tensile strengths of the V-modified Cr-Mo steels in petro-chemical and thermo-electrical plants. And also, the effects of hydrogen-assisted degradation of the V-modified Cr-Mo steels were analyzed in terms of work-hardening index and yield ratio.

Effect of Microstructural Factors on the Strength and Deformability of Ferrite-Pearlite Steels with Different Mn and V Contents (Mn 및 V 함량이 다른 페라이트-펄라이트 조직강의 강도와 변형능에 미치는 미세조직 인자의 영향)

  • Hong, Tae-Woon;Lee, Sang-In;Shim, Jae-Hyeok;Lee, Junho;Lee, Myoung-Gyu;Hwang, Byoungchul
    • Korean Journal of Materials Research
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    • v.28 no.10
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    • pp.570-577
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    • 2018
  • This study examines the effect of microstructural factors on the strength and deformability of ferrite-pearlite steels. Six kinds of ferrite-pearlite steel specimens are fabricated with the addition of different amounst of Mn and V and with varying the isothermal transformation temperature. The Mn steel specimen with a highest Mn content has the highest pearlite volume fraction because Mn addition inhibits the formation of ferrite. The V steel specimen with a highest V content has the finest ferrite grain size and lowest pearlite volume fraction because a large amount of ferrite forms in fine austenite grain boundaries that are generated by the pinning effect of many VC precipitates. On the other hand, the room-temperature tensile test results show that the V steel specimen has a longer yield point elongation than other specimens due to the highest ferrite volume fraction. The V specimen has the highest yield strength because of a larger amount of VC precipitates and grain refinement strengthening, while the Mn specimen has the highest tensile strength because the highest pearlite volume fraction largely enhances work hardening. Furthermore, the tensile strength increases with a higher transformation temperature because increasing the precipitate fraction with a higher transformation temperature improves work hardening. The results reveal that an increasing transformation temperature decreases the yield ratio. Meanwhile, the yield ratio decreases with an increasing ferrite grain size because ferrite grain size refinement largely increases the yield strength. However, the uniform elongation shows no significant changes of the microstructural factors.

An Experimental Study on the Strengh and Ductility of High-Strength Flexural Members (고강도 휨재의 강도와 연성에 관한 실험적 연구)

  • Lee, Seung-Joon
    • Journal of Korean Society of Steel Construction
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    • v.13 no.1
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    • pp.19-28
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    • 2001
  • The strength and ductility of steel flexural members are investigated experimentally in this study. As for the performance evaluation of flexural members. experimental studies on the 9 test specimens were carried out. Four specimens were fabricated from SM490 and five specimens were fabricated from SM570. The experimental results of the specimens were analyzed with focus on the flexural strength and ductility. The experimental results exhibited that all the specimens provided sufficient flexural strengthes which exceeded the nominal flexural strengthes specified in the current Limit State Design Specification by average ratio of 1.22. However. the experimental results showed that the compact-section specimens fabricated from SM570 did not provide the required rotational ductility. The yield-to-tensile strength ratio(YR) of SM570 of about 0.9 might be the causes of such insufficient capacities.

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

  • Lee, Yoon-Ki;Moon, Joon-Oh;Kim, Sang-Hoon;Lee, Chang-Hee
    • Journal of Welding and Joining
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    • v.28 no.3
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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.

The Characteristics of Mechanical Properties and Fatigue Crack Propagation of Fire Resistance Steel for Frame Structure (구조용 내화강의 기계적 성질과 피로균열전파 특성에 관한 연구)

  • Kim, Hyeon-Su;Nam, Gi-U;Gang, Chang-Ryong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.1
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    • pp.54-60
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    • 2001
  • This study is to investigate the mechanical properties and the fatigue crack propagation of fire resistance steel for frame structure as the chemical composition was changed by addition of N, B and rolled end temperature was varied. We used two kinds of specimen, the one is parallel and the other is perpendicular to the rolling directions. As rolled end temperature increased, volume fraction of ferrite and pearlite decreased, but volume fraction of baintie and grain size increased. Micro-hardness decreased as rolled end temperature increased, but tensile and yield strength increased. Volume fraction of ferrite and pearlite decreased by addition of N. But volume fraction of bainite, tensile and yield strength increased. Microstructure was changed to martensite by addition of B, and tensile and yield strength increased. Fatigue life of TL direction specimen was shorter than that of LT direction specimen. There was no significant effect to fatigue crack propagation rate by addition of N and changing rolling condition, but fatigue life was increased by addition of B.

Local Buckling and Inelastic Behaviour of 800 MPa High-Strength Steel Beams (800MPa급 고강도강 보 부재의 국부좌굴 및 비탄성 거동)

  • Lee, Cheol-Ho;Han, Kyu-Hong;Kim, Dae-Kyung;Park, Chang-Hee;Kim, Jin-Ho;Lee, Seung-Eun;Ha, Tae-Hyu
    • Journal of Korean Society of Steel Construction
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    • v.24 no.4
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    • pp.479-490
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    • 2012
  • Flexural tests on full-scale H-shaped beams, built up from high-strength steels (HSB800 and HSA800) with a nominal tensile strength of 800 MPa, was carried out to study the effect of flange slenderness of high-strength steel on flexural strength and rotation capacity. The primary objective was to investigate the appropriateness of extrapolating current stability criteria (originally developed for ordinary steel) to high-strength steel. The performance of high-strength steel specimens was very satisfactory from the strength, but not from the rotation capacity, perspective. The inferior rotation capacity of high-strength steel beams was shown to be directly attributable to the absence of a distinct yield plateau and the high yield ratio of the material. Residual stress measurements reconfirmed that the magnitude of the residual stress is almost independent of the yield stress of the base metal.

Yield strength estimation of X65 and X70 steel pipe with relatively low t/D ratio

  • Kim, Jungho;Kang, Soo-Chang;Kim, Jin-Kook;Song, Junho
    • Steel and Composite Structures
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    • v.38 no.2
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    • pp.151-164
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    • 2021
  • During the pipe forming process, a steel plate undergoes inelastic behavior multiple times under a load condition repeating tension and compression in the circumferential direction. It derives local reduction or increase of yield strength within the thickness of steel pipes by the plastic hardening and Bauschinger effect. In this study, a combined hardening model is proposed to effectively predict variations of yield strength in the circumferential direction of API-X65 and X70 steel pipes with relatively low t/D ratio during the forming process, which is expected to experience accumulated plastic strain of 2~3%, the typical Lüder band range in a low-carbon steel. Cyclic tensile tests of API-X65 and X70 steels were performed, and the parameters of the proposed model for the steels were calibrated using the test results. Bending-flattening tests to simulate repeated tension and compression during pipe forming were followed for API-X65 and X70 steels, and the results were compared with those by the proposed model and Zou et al. (2016), in order to verify the process of material model calibration based on tension-compression cyclic test, and the accuracy of the proposed model. Finally, parametric analysis for the yield strength of the steel plate in the circumferential direction of UOE pipe was conducted to investigate the effects of t/D and expansion ratios after O-forming on the yield strength. The results confirmed that the model by Zou et al. (2016) underestimated the yield strength of steel pipe with relatively low t/D ratio, and the parametric analysis showed that the t/D and expansion ratio have a significant impact on the strength of steel pipe.

Earthquake Resistance Performance of Frames with High-Yield Ratio Steels (고항복비 강재를 이용한 내진구조시스템의 내진성능)

  • Oh, Sang-Hoon
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • pp.211-219
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    • 2005
  • Nowadays, various grades of high-strength steels are available. The application of ultra-high grades of steels for building structures, however, is limited only to the elements stressed under tension. The highest grade of steels generally used has a tensile strength of around 600N/mm2. Most research is focused on lower yield ratios of high strength steel in the inelastic range to ensure the stability of structures. In this paper, however, the possibility of an effective application of high strength steel with high yield ratio to building structures is discussed. An efficient structural system and a design method based on earthquake response analysis and experimental results are proposed.

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