Simulation of the controlled rolling and accelerated cooling of a bainitic steel using torsion testing

Cota, André Barros; Barbosa, Ronaldo; Santos, Dagoberto Brandão

doi:10.1016/s0924-0136(99)00467-7

Cited by 36 publications

(22 citation statements)

References 6 publications

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“…Recently, more emphasis is placed on developing acicular ferrite or bainite base steels for linepipe applications. [11][12][13] However, the toughness of these steels is often disappointing. Therefore new microstructures are needed to obtain the adequate combinations of strength, toughness and yield ratio.…”

mentioning

confidence: 99%

Effect of Microstructure on the Yield Ratio and Low Temperature Toughness of Linepipe Steels.

Kim²,

et al. 2002

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Linepipe steels, which transport oil and gas, should have high strength, high toughness, excellent corrosion resistance and superior weldability. [1][2][3] The current demand is towards the larger-diameter and higher-pressure linepipes to improve the efficiency of transmission, resulting in more stringent specifications for the linepipe steels. In addition to the above mentioned properties, the steels should have low yield ratio (yield strength/tensile strength) for the safety concern. The lower yield ratio means the higher resistance to deformation from yielding to plastic instability, 4,5) preventing the sudden decrease in the strength. According to the engineering specifications, API X-70 steels should have the yield strength higher than 480 MPa, impact energy larger than 100 J at Ϫ40°C and the yield ratio smaller than 85 %. It has been shown in the previous study that the achievement of low yield ratio (around 80 %) and high toughness (ductile-brittle transition temperature of around Ϫ100°C) is possible in the 440 MPa grade C-Mn steel by controlling the thermomechanical process.6) However, it becomes more difficult to maintain adequate values of yield ratio and toughness as strength increases to a higher level. The basic difficulty in optimizing these properties comes from the fact they are often inversely correlated, i.e. an increase in the strength is achieved at the expense of the yield ratio and toughness, and vice versa. Therefore to develop the high performance linepipe steels, the individual effect of microstructural features on these properties should be clearly understood.One of the ways of decreasing the yield ratio is the utilization of hard second phase in the microstructure. Numerous studies on so-called dual phase steels showed that these steels have low yield ratio due to the presence of hard martensite or bainite in soft ferrite matrix. 7,8) Shikanai et al.,9) analyzed the relationship between the volume fraction and morphology of second phase and the yield ratio by finite element method (FEM) and reported that the steel should have soft matrix with around 50 % volume fraction of hard second phase to obtain low yield ratio. It has also been suggested that the larger difference in the strength between the two phases is more desirable to obtain low yield ratio.9,10) However these dual phase steels generally have low yield strengths which do not meet the property requirement for X-70 linepipe steels. Moreover the large difference in the strength between the two phases might have a deleterious effect on toughness since cracks can easily nucleate at the hard second phase particles at low temperatures. Recently, more emphasis is placed on developing acicular ferrite or bainite base steels for linepipe applications.11-13) However, the toughness of these steels is often disappointing. Therefore new microstructures are needed to obtain the adequate combinations of strength, toughness and yield ratio. ISIJ International, Vol. 42 (2002) The present study aims at elucidating the effects of microstructu...

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mentioning

confidence: 99%

Effect of Microstructure on the Yield Ratio and Low Temperature Toughness of Linepipe Steels.

Kim²,

et al. 2002

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“…11) Third is the ram motion is forced to stop by a stop plate, whenever that plate engages against the cross stop at same position, and the reduction of the workpiece is adjusted a hydro/wedge system placed on the opposite side of the main ram. 9) We adopt third method, the main ram is force to stop the end of the cylinder of actuator and that the reduction of the workpiece is adjusted the sub-jack driven by trapezoidal thread, in stead of the hydro/wedge system, installed on the opposite side of the main ram. Figure 3 shows the motion of the ram and the sub-jack used to determine of reduction of the workpiece.…”

Section: Experiments On Velocity Control Of High-speedmentioning

confidence: 99%

“…These testing machines have the capability of freezing microstructure immediately after deformation by water quenching. Torsion test 8,9) have also been conducted, since they can be carried out under a wide range of thermomechanical processing condition with severe plastic deformation. However, the deformation rate is limited to less than 30 s -1 .…”

Section: Introductionmentioning

confidence: 99%

Multistage and High-speed Compression Testing Machine for Obtaining Flow Stress and Microstructure Evolution in Hot Forming of Steels

Yanagida

Ikeda²,

Komine

et al. 2012

ISIJ Int.

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A method of predicting the microstructure evolution and shape in the hot forming process is important for optimizing the process conditions. To develop a new analytical model that can be used to predict microstructure behavior in the actual process, a high-speed with multistage compression testing machine is required for physical simulation of the production process and to obtain material data for the prediction model. A high-speed uniform true strain rate (~300 s -1 ) was achieved by a servo-hydraulic computerdriven machine with a deviation control feedforward program. The effects of processing parameter and chemical composition of plane carbon and Nb alloyed steels on ferrite grain size were investigated. A grain size of about 1 μm was accomplished in this simulator by severe hot plastic deformation.KEY WORDS: hot compression test; flow stress; high strain rate; microstructure.

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“…Este aço contém 24 ppm de B e é microligado com Nb, Ti e V e foi fornecido na condição como laminado a quente pela indústria nacional. O monitoramento da temperatura dos corpos de prova tubulares foi feito através de um termopar chromel-alumel, de 1,5 mm de diâmetro, colocado no interior destes [12] . Um sistema de resfriamento a gás hélio foi utilizado com o objetivo de controlar a taxa de resfriamento após o ensaio de torção a quente [12] .…”

Section: Procedimento Experimentalunclassified

“…O monitoramento da temperatura dos corpos de prova tubulares foi feito através de um termopar chromel-alumel, de 1,5 mm de diâmetro, colocado no interior destes [12] . Um sistema de resfriamento a gás hélio foi utilizado com o objetivo de controlar a taxa de resfriamento após o ensaio de torção a quente [12] . Na Figura 1, estão indicados os ní-veis de deformação equivalente (ε eq ) utilizados nos ensaios de torção à temperatura de deformação de 810ºC, estabelecida a partir do conhecimento da temperatura de não recristalização, T nr =970ºC [12] , desse aço.…”

Section: Procedimento Experimentalunclassified

Influência da deformação na região de não recristalização da austenita sobre a transformação em resfriamento contínuo em um aço bainítico de baixo carbono

Cota

Rodrigues

Barbosa³

et al. 2005

Rem: Rev. Esc. Minas

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Estudaram-se os efeitos da deformação na região de não recristalização da austenita e da taxa de resfriamento sobre a temperatura Bi (temperatura de início de transformação bainítica) e sobre a microestrutura final, de um aço ARBL bainítico de baixo carbono submetido a resfriamento contínuo, usando ensaios de torção a quente e resfriamento a gás He. As amostras foram submetidas a quatro programas de ensaios de torção, sendo quatro taxas de resfriamento acelerado para cada um. A evolução microestrutural com a taxa de resfriamento foi estudada por microscopia eletrônica de varredura e por medição de dureza Vickers. Os resultados mostram que, para a taxa de resfriamento de 2ºC/s, a microestrutura é constituída de ferrita poligonal e bainita, independente do grau de deformação. Para taxas de resfriamento mais altas, a microestrutura é, predominantemente, bainítica, com uma pequena quantidade de ferrita poligonal fina. Verifica-se que, para um mesmo grau de deformação, uma maior taxa de resfriamento implica uma menor temperatura Bi, sendo esse efeito mais pronunciado para as amostras não deformadas; e que, para uma mesma taxa de resfriamento, uma maior deformação na região de não recristalização resulta em uma maior temperatura B i . Palavras-chave:Quantidade de deformação, temperatura de não recristalização, cinética de transformação bainíti-ca, temperatura Bi. AbstractThe influence of deformation in the nonrecrystallization region of austenite and cooling rates on the bainitic transformation temperature (Bi)

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Simulation of the controlled rolling and accelerated cooling of a bainitic steel using torsion testing

Cited by 36 publications

References 6 publications

Effect of Microstructure on the Yield Ratio and Low Temperature Toughness of Linepipe Steels.

Effect of Microstructure on the Yield Ratio and Low Temperature Toughness of Linepipe Steels.

Multistage and High-speed Compression Testing Machine for Obtaining Flow Stress and Microstructure Evolution in Hot Forming of Steels

Influência da deformação na região de não recristalização da austenita sobre a transformação em resfriamento contínuo em um aço bainítico de baixo carbono

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