• Title/Summary/Keyword: Hot-Rolled High Strength Steel

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Mechanical Properties of High Stength Sheet Steels for Auto-Body by Induction Heat Treatment (고주파열처리에 의한 자동차용 고강도 강판의 기계적 성질변화)

  • Lee, D.H.;Yoon, C.S.;Lim, J.D.
    • Journal of the Korean Society for Heat Treatment
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    • v.17 no.2
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    • pp.73-77
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    • 2004
  • The efforts which increase the strength of the auto-body structure and decrease its weight lead to develop a new concept of part production systems, such as Post-Form Strengthening by induction heat treatment. In this study, several cold and hot-rolled sheet steels were used to find out optimum induction heat treatment conditions. After induction heat treatment, strength of heat-treated sheet steels was increased significantly compared with that of as-rolled steels. From these results, auto-body structure which has more light and safe has been made by using this induction hardening method.

The Effects of Austempering Heat Treatment on the Processing Window and Mechanical Properties in Cast and Hot-rolled Fe-0.7wt%C-2.3wt%Si-0.3wt%Mn Steel (주조 및 열간 압연된 Fe-0.7wt%C-2.3wt%Si-0.3wt%Mn 강의 프로세싱 윈도우와 기계적 성질에 미치는 오스템퍼링 조건의 영향 비교)

  • Son, Je-Young;Hwang, Dong-Chan;Choi, Jae-Joo;Song, June-Hwan;Kim, Ji-Hun;Kim, Won-Bae;Ye, Byung-Joon
    • Journal of Korea Foundry Society
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    • v.30 no.2
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    • pp.60-65
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    • 2010
  • In this study, we investigate the effects of austempering heat treatment on the processing window and mechanical properties in cast and hot-rolled Fe-0.7 C-2.3 Si-0.3 Mn steel. Each specimens were austenitised at $900^{\circ}C$ for 7 min, and austempered at $260^{\circ}C,\;320^{\circ}C$, and $380^{\circ}C$ for the various periods of time from 2 min to 240 min. After heat treatment, the evaluation of stage I and stage II as performed by optical metallography, XRD, hardness test. Both cast and hot rolled specimens had similar processing window. So grain size effect is not important to the austempered high carbon high silicon cast steel. When the austempering temperature was $260^{\circ}C$, the microstructure consisted of the lower ausferrite while the upper ausferrite structure was formed at $380^{\circ}C$. As the austempering temperature increases from 260 to $380^{\circ}C$, the strength and hardness decreased, elongaton and volume fraction of austenite increased. In addition, there was no change of mechanical properties between cast and hot-rolled specimens.

Effect of Reverse Transformation Treatment on the Formation of Retained Austenite and Mechanical Properties of C-Mn TRIP Steels (C-Mn계 TRIP강의 잔류오스테나이트 생성과 기계적 성질에 미치는 역변태처리의 영향)

  • You J. S;Hong H;Lee O. Y;Jin K. G;Kim S. J
    • Korean Journal of Materials Research
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    • v.14 no.2
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    • pp.126-132
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    • 2004
  • The high strength steel sheets has been widely used as the automobile parts to reduce the weight of a vehicle. The aim of this research is to develop the TRIP aided high strength low carbon steels using reverse transformation process. The 0.15C-4Mn and 0.15C-6.5Mn steel sheets were reversely transformed by slow heating to intercritical temperature region and air cooling to room temperature. The stability of retained austenite depends on the enrichment of carbon and manganese by diffusion during the reverse transformation. The amount of retained austenite formed after reversely transformed at $645^{\circ}C$ for 12 hrs. was about 46vol.% in hot rolled 0.lC-6.5Mn steel. The change in volume fraction of retained austenite with a holding temperature was consistent with the changes in elongation and the strength-ductility combination. The tendency of tensile strength to increase with increasing the holding temperature was due to the decrease of retained austenite after cooling from the higher temperature of $670 ^{\circ}C$. The maximum strength-ductility combination was about 4,250 kg/$\textrm{mm}^2$ㆍ% when the hot rolled 0.lC-6.5Mn steel was reversely transformed at $645^{\circ}C$ for 12 hrs.

Finite Element Analysis of the Hot Rolled Cladding for the Ni-based Superalloy/steel Corrosion-resistant Alloy (CRA) Plate (니켈 기반 초합금 클래드 판재의 열간 압연 제조 공정 유한요소해석)

  • C. Kim;S.J. Bae;H. Lee;H.J. Bong;K.S. Lee
    • Transactions of Materials Processing
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    • v.33 no.3
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    • pp.208-213
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    • 2024
  • Ni-based superalloys have exceptional performance in high-temperature strength, corrosion resistance, etc, and it has been widely used in various applications that require corrosion resistance at high-temperature operations. However, the relatively expensive cost of the Ni-based superalloys is one of the major hurdles. The corrosion-resisted alloy(CRA) clad materials can be a cost-effective solution. In this study, finite element analysis of the hot rolling process for manufacturing of the Alloy 625/API X65 steel CRA clad plates is conducted. The stress-strain curves of the two materials are measured in compressive tests for various temperature and strain rate conditions, using the Gleeble tester. Then, strain hardening behavior is modeled following the modified Johnson-Cook model. Finite element analysis of the hot rolled cladding process is performed using this strain rate and temperature dependent hardening model. Finally, the thickness ratio of the CRA and base material is predicted and compared with experimental values.

Manufacturing Technologies and Applications of Steel Strip Products (철강 압연제품의 제조기술 및 응용)

  • 권오준
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1999.08a
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    • pp.10-21
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    • 1999
  • Recent progress in manufacture of hot and cold rolled steel strip products and their applications were reviewed. The main trend in the technological development has been to meet the customers' requests for quality improvement and cost reduction. The weight reduction to reduce the fuel consumption is the main issue in the automotive industry and, therefore, various steels have been developed to improve formability as well as strength. The steels include super-EDDQ steels, bainitic steels, TRIP steels, etc. In the oil industry, efforts have been focused to improve strength together with either low temperature toughness or HIC/SSCC resistance. The packaging industry is also a highly competitive market, and steel and canmaking companies have worked cooperatively to develop cost-effective canmaking processes as well as high performance steels. This type of cooperation has also been found important in other industries such as the appliance and electronic industries for the benefits of both steelmakers and customers.

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Hole Flangeability and Fracture Behaviors of Circular Flanges of High Strength Hot Rolled Steels (고강도 열연재의 Hole Flanging시 성형특성과 파단에 관한 연구)

  • Kim J. W.;Gong S. R.;Kim B. J.;Moon Y. H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2000.10a
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    • pp.49-52
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    • 2000
  • The hole flanging experiments are performed on a flat circular plates with a hole in the center and the flangeability and fracture behavior of TRIP steel and ferrite-bainite duplex steel were examined. Over the ranges of conditions investigated, the flangeability of ferrite-bainite duplex steel is better than TRIP steel and the term 'hole flanging capacity' introduced in this study. Fracture behavior of TRIP steel and ferrite-bainite duplex steel was characterized by petal formation at the edge of flange. In case of crack propagation, crack tip diversion that is supposed to be responsible for flangeability occurs more severely on HSLA Steel.

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Effect of Lip Shape on the Hole Flangeability of High Strength Steel Sheets (고강도 열연재의 홀 플랜징시 립 형상이 플랜정성에 미치는 효과)

  • Kim, Jeong-Un;Kim, Bong-Jun;Mun, Yeong-Hun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.1
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    • pp.147-152
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    • 2002
  • Effect of lip shape on the hole flangeability of high strength steel sheets is investigated. Circular plates of various hole sizes are tested and the variation of lip length as well as the variation of thickness on the sectional views of the finished lip were studied. The conventional hole flanging process is limited to a certain limit hole diameter below which failure will ensue during the hole expansion. The intention of this work is to examine the effect of lip shape on the flangeability of TRIP steel and Ferrite-Bainite duplex steel and find out major parameters which can affect flanging shape of high strength hot rolled steels. Over the ranges of conditions investigated, the minimum hole diameter of F+B steel is better than TRIP steel. while, the lip-shape accuracy of TRIP steel is better than that of F+B steel. although the tensile strength and elongation of %P steel are superior than those of Ferrite-Bainite duplex steel, the flangeability is found to be not so strongly sensitive to the tensile properties but sensitive to displacement on the circumferential direction of hole edge.

Development of a Prestressed Plate Girder Forming Hybrid Sections of Hot-rolled H Beam and High-Strength Steel Plates (H형강과 고강도 강판으로 복합단면을 구성하는 프리스트레스트 플레이트거더의 개발)

  • Kyung, Yong Soo;Ahn, Byung Kuk;Bang, Jin Hwan;Kim, Moon Young
    • Journal of Korean Society of Steel Construction
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    • v.17 no.5 s.78
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    • pp.637-648
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    • 2005
  • Innovative prestressed steel plate girders were presented in this study. Hot-rolled H beams were loaded first, then relatively high-strengthsteel plates were welded on the top and bottom flanges of preloaded H beams. Finally, high prestressed plate (HiPP) girder was manufactured by simply releasing prestresses of rolled beams. To verify prestress distributions induced in this girder, the experimental study was conducted and some guidelines to manufacture these girders effectively were addressed. In addition, methods to determine the allowable bending stress of HiPP girders and to check welding stresses were addressed for design of temporary bridges. The efficiency and effectiveness of the present girder were demonstrated through design examples of temporary bridges adapting the prestress-induced girder or the plate girder of the same section without prestresses. As a result, it has been found to be possible that the span length of HiPP girders for temporary bridges is longer than that of girders without prestresses.