Abstract
The authors have made an analysis of problems arising in the rolling of continuous-cast billets in the modern mini-metallurgical and rerolling plants. It is shown that the use of trio stands in rolling mills of these plants makes it necessary to obtain billets of multiple lengths from bars (most often of 12-meter length) produced in the rolling shop. The subsequent rolling of such multiple billets has revealed increased cracking of the front edge and, as a result, increased metal consumption. Analysis of the causes of these cracks has been made. It was indicated that this defect can appear as a result of a certain stress-strain state formed at the end of hot-rolled breakdown. It is caused by the presence of an uneven temperature field due to more intensive end cooling, to reduction mode in the trio stand and to the presence of axial defects in the continuous-cast billet. The study was conducted on the industrial medium-grade mill 500/370, as well as using mathematical modeling by finite element method. The influence of a set of technological factors, such as temperature of the billets heating before rolling, the time interval of their transportation on the site “heating furnace – first stand of the rolling mill” and parameters of the macrostructure of axial area of the metal were investigated. Calculations by the developed mathematical model have indicated the need to take into account the presence of a scale layer on the heated continuous-cast billet. It is shown that depending on the heating temperature and transport time, the temperature difference at the billet’s end compared to the heating temperature can be from 45 to 100 °C. It will lead to an uneven distribution of deformation resistance and unfavorable stress-strain state at the billet’s end. In addition, the presence of an axial defect can affect the cracking because of its shape and its transformation during reduction. Obtained experimental data allowed hypothesizing the mechanism of transformation of discontinuity defects into cracks at the billet’s end due to the conditions of continuous casting and cutting of billets during rolling in the reduction stand.
Highlights
The authors have made an analysis of problems arising in the rolling of continuous-cast billets in the modern mini-metallurgical and rerolling plants
It is shown that the use of trio stands in rolling mills of these plants makes it necessary to obtain billets of multiple lengths from bars produced in the rolling shop
It was indicated that this defect can appear as a result of a certain stress-strain state formed at the end of hot-rolled breakdown
Summary
Скляр В.А.1, к.т.н., доцент кафедры «Металлургия и металловедение им. С.П. Белевитин В.А.3, д.т.н., профессор кафедры автомобильной техники, информационных технологий и методики обучения техническим дисциплинам. Что использование в прокатных станах данных заводов клетей трио вызывает необходимость получения заготовок кратной длинны из штанг (чаще всего 12-ти метровой длины), которые производятся в условиях прокатного цеха. Что последующая прокатка таких кратных заготовок выявила повышенную растрескиваемость передних концов и, как следствие, повышенный расход металла. Строительство в последние годы ряда прокатных станов, оснащенных клетями «трио» [10], а также использование непрерывнолитой заготовки на действующих станах линейного типа [11] обусловило тот факт, что получение заготовок кратной длины из штанг (чаще всего 12-ти метровой длины), поставленных с МНЛЗ, производится в условиях прокатного цеха. Последующая прокатка кратных заготовок выявила повышенную растрескиваемость передних концов и, как следствие, повышенный расход металла [11]
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