PRODUCTION METHOD OF DRILL STEEL Russian patent published in 2017 - IPC B21B19/00 

FIELD: metallurgy.

SUBSTANCE: method includes the bar cutting into measured lengths, heating, piercing in the screw rolling mill, rolling of the sleeve into the crude tube at the short movable mandrel in the screw rolling mill, reducing in the screw rolling mill, pipe calibrating in the rolling mill, cooling. The reducing in the screw rolling mill is carried out with the internal diameter reduction upto 40%, then the tube is cooled, mechanically processed along the inner surface, until the defects are removed, and then it is heated again upto the temperature of 900…950°C and reduced with the reduction of cross-sectional area, the limiting value of which, excluding the formation of defects in the form of cracks, is regulated by mathematical dependence, and the calibration is carried out with the internal diameter decrease, the allowable value of which for each stand, which does not lead to defects in the form of buckles and notches, is regulated by the mathematical dependence as well.

EFFECT: increase of the geometric dimensions accuracy at high quality of the tubes surface.

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