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Influence of continuously cast bloom's heating strategy on cracks occurence in low-alloyed Cr-Mo based steel 25CrMo4

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The low-alloyed Cr-Mo based steel types are used for production of important technical equipment parts in the petrochemical industry, for transportation of the gaseous hydrocarbons, concentrated acids, and lyes. They are also used for rolling of seamless tubes, in the production of pressure bottles, steel bolts, etc. In the past, many researchers studied conditions which could possibly cause internal cracks formation and propagation. Among the potential reasons for creation of inhomogenities (pores, cavities, etc.) in the volume, the inappropriate casting conditions of the heat are particularly important, especially the extraordinarily high overheating temperature in a tundish and low casting speed [1, 2] which could cause central segregations of molybdenum [3], microalloying elements precipitation on austenite grain boundaries [4, 5] during continuously cast bloom straightening in temperature range 800÷1050°C (minimum ductility zone) [6]. The other mentioned reasons for cracks initiation and propagation are improper tensile strain caused by small contact between rolling mills and round continuously cast bloom [7] and low rolling temperatures [8]. Heating and preheating process before hot rolling is necessary to obtain proper plastic properties of steel. Continuously cast blooms are commonly heated up to 1300°C if there are no extensive differences in heat conductivity of steels and/or steels are not sensitive to cracks occurence it can be used wide varieties of heating strategy. In our paper it was statistically and mathematically studied influence of heating time (overall period which spent continuously cast bloom in soaking pit) and preheating time (time necessary to achieve through heating temperature - so called plateau) and heating strategy. In our paper it was mathematically and statistically analyzed influence of heating strategy on cracks occurence indicated by ultrasonic device. Main aim of our study was find out rel[...]

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