SU954153A1 - Steel continuous casting method - Google Patents

Description

(54) METHOD FOR CONTINUOUS STEEL CASTING

one

The invention relates to metapurgy, and more specifically to continuous drinking of metapp, and is intended for dapstating of billets in a continuous casting plant of vertical steel.

There is a known method of continuous casting of stage pi, which provides for a constant rate of drawing of the workpiece during the whole technopological process 1.

Thus, when otbivka varietal billets octagonal cross-section with dimensions according to axis of symmetry mm working speed of pulling is equal to 0.45 m / min.

The disadvantage of this method is the low yield of the suitable metapp. This is due to the large depth of the shrinkage shell.

In addition, with this method of continuous casting, in the axial zone of the formed blanks, internal grafts are formed. For example, when otbivka blanks section 270x370 mm of steel grade 4OHN (working speed

0.45 m / min) the number of blanks with central arachnoid cracks in the axial zone reaches 2.8%, and of hundred pi 38X2H2MA, 15.2%.

This is due to the fact that in the liquid metal hardening in the central zone, there is an increased content of nonmetallic inclusions (soups (ice, oxide-silicate inclusions), the melting temperature of which is lower than the melting temperature of steel by about 0 ° 4 ° C. Therefore, during the solidification of the metal, nonmetallic inclusions are still in a liquid state

, 5 tsam grains. When such a billet is deformed, for example, in the rollers of the stand stands, still non-metallic liquid inclusions break (due to the incompressibility of the liquid) the grain boundaries of the solidified

20 metal, the strength of which is still quite low, and that leads to the formation. central arachnid cracks. The central spider-like cracks are not completely welded and remain in 395 subsequent rolling, which is an unacceptable rejection defect in the microstructure of the car. There is also known a method for continuous casting of steel in b grade workpieces, which includes the supply of liquid metal to the crushing machine and drawing the formed workpiece out of it at a rate which is reduced by 2О -4О% 10-15 minutes before the end of the process. The application of this method allows to increase the yield of the metal by 1.0-1.2%. This is explained by the fact that reducing the speed of the billet drawing reduces the depth of the shrinkage shell at the end of the billet, which reduces the cut to 5OO-900 mm 2 ... However, although the prevalence of the workpieces with internal central arachnoid cracks is somewhat reduced, it still remains at a high level. Thus, the incidence of the indicated defect in the billet of 4OHN steel is 2, O and 38XNZMFA steel 10.2%. The chain of the invention is an increase in the quality of the workpiece. The goal is achieved by the method of continuous casting of steel into billet grades, including feeding liquid metal into a crystallizer and pulling out of a negated formed workpiece with an adjustable working speed, reducing the content of non-metallic inclusions in steel, and {Working speed of drawing a billet decrease by 5-10% for every 0, O02% content of non-metallic inclusions in excess of O, OO4%. Reducing the rate of stretching of the workpiece as compared to a working one of 51O% for every 0, O02% of the content of non-metallic inclusions in excess of 0.004% of L ensures the hardening of the latter c. the axial zone of the workpiece until it gets into the rolls of the best stands by increasing the time it takes for the workpiece to pass from the mold to the number of stands. As a result, when the workpiece is deformed in the rolls of the lower stands, there is no movement of nonmetallic inserts in the axial preparation zone, as a result of which there is no rupture of grain boundaries and the formation of central arachnoid cracks. A decrease in the draw rate of cooking by less than 5% for every 0, OO2% non-metallic content in excess of 0.004% does not give a positive effect. The damage to the preforms 3 by the central arachnoid fissures remains as high as in the preforms obtained using known methods. A decrease in the rate of stretching of the preform by more than 10% for every 0, ОО2% content of nonmetappic inserts in excess of 0, ОО4% leads to the formation of defects of defective nature on the blanks - and subcortical bubbles. This is explained by the fact that an increase in the duration of the casting cycle (up to 120–160 min for melting with a mass of 50 tons, section of 270x370 mm) leads to additional cooling of the metal in the pouring ladle and the need to use oxygen for cleaning (burning) the canal of the steamer and an intermediate device, resulting in the formation of the above defects. With this reduction in the rate of stretching of the workpiece by an amount greater than 0.002%, for example, for each O, 003% or more, the probability of the formation of central spider-like cracks in the workpieces. When the content of nonmetappic inserts in steel is 0, O04% and below and the cutting is done at the optimum working speed, the central arachnoid cracks do not form. Example, (in relation to steel grades 40HN and 38H2N2MA). Melting is made in the 70-ton open-hearth furnace by the CKJpan process. Casting of steel is carried out on a two-strand Bej continuous casting machine into blanks of non-equilateral octahedral cross section with axes of symmetry 27 O “370 mm. The metal is fed into the crystallizer floor level from the stapling bucket through a two-staged intermediate device. The protection of the metal mirrors in the fabricator is carried out with powdered graphite. The working speed of the billet drawing is 4oNH 0 45 n / min for steel, for 38Kh2N2MA steel 0.4O m / m n. The working speed of the workpiece exhausting with respect to each continuous machine and each section of the workpiece is established on the basis of experimental data for determining the ingot hardening coefficients in such a way that the workpiece falls into the driving stands of the hardened central zone. Before pouring, metal samples are taken from the ladle into the metal

glass. The content of non-metallic inclusions in steel is determined by meta-graphic (linear-transverse method). According to the obtained results, the working speed is adjusted by pulling the workpiece.

The test results are shown in the table.

As can be seen from the table, the application of the proposed method (2 and 3) allows to obtain a blank without central arachnoid cracks, while the use of known methods (4 and 5) leads to the formation of centering arachnoid cracks (4) or subcortical blisters and bubbles (5).

The application of the proposed method to improve the quality of plastic coatings excludes the formation of spider-like cracks in the axial zone of the ingot.

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Claims (2)

1.Technical Instructions No. HFC1-76 for different steel sizes on UN PC. 2. USSR author's certificate number 594647, cl. B 22 D 11/00, 1976.