Wyniki 1-2 spośród 2 dla zapytania: authorDesc:"JAN MORÁVKA"

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[...]

Physical Modelling of Metal Bath Flow in the Tundish and Importance of Validation Experiments

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Accuracy and thus the applicability of physical modelling results in the field of metallurgical processes must respect the basic rules of similarity theory and practice between the two systems. The choice of model geometry (length) scale is one of the basic factors which must be very carefully determined. This paper deals with the assessment of the impact of the geometric scale of the physical model of a tundish on the coincidence of the simulation results. Two models of an identical operating tundish designed on the scales 0.2 and 0.25 (1:5 and 1:4) were used for the experimental study. Different boundary conditions, including changes in the geometry of the bottom without any kind of impact pad (e.g. “Turbostop") were used to study the correctness of the similarity theory betwe[...]

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