Hot ductility of steels and its relationship to the problem of transverse cracking during continuous casting

Mintz, B.; Yue, Stephen; Jonas, J. J.

doi:10.1179/imr.1991.36.1.187

Cited by 339 publications

(539 citation statements)

References 69 publications

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“…[1][2][3] This correlates quite well with the observation that steels prone to transverse cracking exhibit very low ductilities (Ͻ20% reduction in area at fracture) at high temperatures. [3][4][5][6][7] With regard to transverse cracking, hot ductilities are usually determined by isothermal tensile test that includes melting and then cooling to the desired test temperature.…”

Section: Introductionsupporting

confidence: 73%

“…In general, the unbending operation, which takes place in the final stage of continuous casting process, coincides with this thermal region. [1][2][3][4][5][6][7] It is frequently reported that performing the unbending operation at the temperatures below or above the aforementioned thermal region has been moderately successful in improving the incidence of cracking in some problem grades because the temperature range of embrittlement has been avoided. 8) However, recent laboratory studies have shown that the thermal history itself has a pronounced effect on the hot ductility.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Thermomechanical Processing on the Hot Ductility of a Nb-Ti Microalloyed Steel.

Akhlaghi

Yue

2001

ISIJ International

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Many attempts have been made to understand the problem of transverse cracking in continuous casting process. Much of this research has involved the study of hot ductility using 'conventional' isothermal hot ductility testing. In these tests, the specimens were isothermally tensile tested to fracture, at temperatures achieved by cooling from a solutionizing temperature, close to the solidus, or above the liquidus. These studies showed that hot ductility at the test temperature is highly depended on the thermal path followed by the specimens. The thermal histories experienced by strands during continuous casting were found to be quite complex and invariably involve rapid cooling and heating cycles. This may therefore lead to high thermal gradients, which, in turn, can generate strains in the surface of the solidifying strand. This then may alter the microstructural evolution of the strand surface and the corresponding hot ductility, a possibility that has not been addressed in any previous studies. Thus, the purpose of this study was to consider the effect of the thermomechanical history on the hot ductility of steel.After in-situ melting and solidification, Nb-Ti microalloyed tensile specimens were subjected to a thermal history typical of a continuously cast billet. Different degrees of deformation were imposed on the specimens at selected stages of this thermal history, before tensile testing to fracture point at the time and temperature corresponding to the unbending stage of the billet casting. It was found that the hot ductility varied from 1 to 98 %, depending on the stage in the thermal history at which deformation was executed. The microstructural evolution during the thermomechanical profile was followed to study the effect of thermomechanical history on the hot ductility.

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Section: Introductionsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Effect of Thermomechanical Processing on the Hot Ductility of a Nb-Ti Microalloyed Steel.

Akhlaghi

Yue

2001

ISIJ International

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“…A Figura 9a foi adaptada para apresentar a localização dos 5 primeiros passes do desbaste do processo estudado, onde todos encontram-se dentro da zona de segurança. Mintz et al [13] …”

Section: Taxa De Deformaçãounclassified

Avaliação De Risco Sobre a Perda De Ductilidade a Quente De Barras De Aço Ca-50

Nascimento¹,

Ramos²,

Silva³

et al. 2017

Anais Do Seminário De Laminação E Conformação

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ResumoA capacidade de um determinado aço suportar as deformações ocorridas durante laminação sem fraturas ou trincas severas é denominada de ductilidade a quente, que é função de diversos parâmetros de processo dentre os quais: qualidade do tarugo, tipo de corte, ciclo térmico, temperatura de processo, layout do laminador, calibração, taxa de deformação e composição química. Diversos trabalhos abordam a ductilidade a quente enfatizando a influência isolada de uma variável como critério de qualidade como as conhecidas relações Mn/S e Ni/Cu através da determinação de valores mínimos. A globalização tem sido responsável pela crescente competitividade entre as siderúrgicas que, para se manterem competitivas no mercado, têm que buscar inovações, quebras de paradigmas, estratégias ousadas e assumir riscos. No presente trabalho realizou-se uma avaliação de risco com base no princípio ALARP (As Low As Reasonable Practical) através da análise conjunta das principais variáveis de processo responsáveis pela perda de ductilidade a quente de um aço utilizado para produção de barras de aço CA-50, objetivando-se uma solução otimizada de menor custo garantindo a competitividade e sustentabilidade da cadeia produtiva. Palavras-chave: Ductilidade a quente; Barras de aço CA-50; Avaliação de risco. RISK ASSESSMENT ON THE HOT SHORTNESS OF CA-50 REBARS AbstractThe ability of a particular steel withstand the deformations occurring during hot rolling without fractures or severe cracks is called hot ductility, which is a function of several process parameters among which: billet quality, cut type, thermal cycle, process temperature, roughing mill strand, pass design, strain rate, and chemical composition. Several works address the hot ductility emphasizing the isolated influence of a particular variable as a quality criterion as the known Mn/S and Ni/Cu ratios by determining minimum. Globalization has been responsible for increasing competition among steelmakers that, to remain competitive in the market, have to seek innovations, paradigms breaks, bold strategies and take risks. In this work we carried out a risk assessment based on the ALARP principle (As Low As Reasonable Practical) through the joint analysis of key process variables responsible by hot shortness of steel used for the production of rebars CA-50, aiming to an optimized solution for lower cost, ensuring the competitiveness and sustainability of the business.

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“…Such strains are generated in the spray chambers or by the straightening. The latter one appears to result in crack formation if the surface temperature is too low, particularly in the range of 700-900 °C corresponding to the low temperature zone of low ductility [5,23,24].…”

Section: Evaluation Of the Risk Of Transverse Crackingmentioning

confidence: 99%

“…In [15], the link between segregation, low ductility, oscillation mark formation and transverse cracking is clearly underlined. Mintz [23,24] realized a large review on hot ductility of steels and its relationship to the problem of transverse cracking in continuous casting. He demonstrated the importance of four variables that mostly control hot ductility: the strain rate, the grain size, the precipitation and inclusion contents.…”

Section: Fig 1: Sketch Of Continuous Casting Processmentioning

confidence: 99%

Finite element study of the effect of some local defects on the risk of transverse cracking in continuous casting of steel slabs

Pascon

Habraken

2007

Computer Methods in Applied Mechanics and Engineering

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This paper introduces a numerical 2.5D model of continuous casting of steel slabs. This model is based on the finite element method and it has been applied to the study of some local defects in a continuous caster, such as partial blockage of nozzles (leading to a local reduction of secondary cooling rate), locking or misalignment of rolls. The purpose of the study was the evaluation of the effect of such defects on the risk of transverse cracking during bending and unbending operations. To do so, the simulation at macro-scale of the complete process has been first performed in standard conditions to get reference values and then each defect has been introduced. Defining two indexes (indicators) of the risk of transverse cracking, it has been possible to classify the defects in terms of risk increase, helping steel producers to focus on the most critical problems.Keywords: Continuous casting; Transverse crack; Nozzle blockage; Roll locking; Misalignment; Finite element PROCESS PRESENTATION AND CHALLENGESContinuous casting has progressively replaced ingot casting over the years 70s and 80s. Nowadays it is the most common way to produce cast steel thanks to its advantages: better quality, higher yield and lower costs (in manpower and energy). The process is schematically drawn in Fig. 1: it consists in pouring a mould with molten metal, i.e. steel in the present case, that starts solidifying in contact with the walls of the mould (primary cooling). When the process is launched, the bottom of the mould is a dummy that is moving down at a constant speed, so-called casting speed, allowing a constant supplying of the process. When the dummy reaches the exit of the mould, the solidified skin of the strand should be thick and resistant enough to avoid breaking. At this moment, the core of the strand is still liquid. To keep on cooling, the surface of the strand is then sprayed with water at each roll interval (secondary cooling), so that solidification front finally reaches the core of the strand, which can be cut and generally sent to next process (rolling). Once the process has been launched, the caster is continuously supplied in molten steel and the production does not stop until the geometry (cross section) of cast product must be changed. Obviously, this short presentation of continuous casting remains simplified and partial and it does not introduce all the complexity of such a process. For further reading, a lot of information is available in literature as well as on the internet.The quality of continuously cast products is still increasing, thanks to the development and the improvement of the technique. To do so, many studies have been conducted by different teams. Among others, Brimacombe and co-workers are recognized to have helped going ahead in understanding the keys of the process, see [4][5][6]2,3,9,30]. Meanwhile, the growth of computer's potential progressively enabled the advent of powerful numerical models. Thomas and co-workers at University of Illinois have also developed many applications i...

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Hot ductility of steels and its relationship to the problem of transverse cracking during continuous casting

Cited by 339 publications

References 69 publications

Effect of Thermomechanical Processing on the Hot Ductility of a Nb-Ti Microalloyed Steel.

Effect of Thermomechanical Processing on the Hot Ductility of a Nb-Ti Microalloyed Steel.

Avaliação De Risco Sobre a Perda De Ductilidade a Quente De Barras De Aço Ca-50

Finite element study of the effect of some local defects on the risk of transverse cracking in continuous casting of steel slabs

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