RU2000167C1 - Continuously cast ingot secondary cooling method - Google Patents

Abstract

In the zone of water-air secondary cooling of continuously cast ingots, the ratio of the shares of water and air in the mixture is regulated depending on the carbon content in the metal, while in the area equal to 0.05 ... 0.5 of the length of the liquid phase, the ratio of the shares of water and air in the mixture is reduced within 1/50 ... 1/150, and the pressure ratio of these components in this section is set in the range of 0.6 ... 1.0. 2 ill.

Description

The invention relates to metallurgy, in particular to the continuous casting of square and bloom cross-section ingots.

In modern practice of continuous casting of steel in the secondary cooling zone of a continuous casting machine, a water-air mixture is widely used for secondary cooling of the surface of ingots and billets.

A known method of continuous casting of metals, comprising cooling the ingot in the secondary cooling zone with a water-air mixture, in which the ratio of the shares of water and air is changed according to a straightforward law from 1: 0 to 0: 1, while the water-air mixture is cooled 0.1-0.6 the length of the liquid phase of the ingot.

A disadvantage of the known method is the low quality of the internal structure of continuously cast billets. This is explained by the fact that with the known method, there is no ingot in the secondary cooling zone

the ability to control the ratio of the proportions of water and air in the air mixture depending on the specific carbon content of the cast steel. As a result, during continuous casting of ingots from steel with a higher carbon content, a decrease in ductility, an increase in thermal stresses in the crystallizing crust of the ingot, “this leads to the formation of internal cracks and concentrated axial friability, and, as a consequence, the rejection of workpieces.

The closest in technical essence and the achieved result to the proposed one is a method of secondary cooling of continuously cast billets, comprising supplying a water-air mixture in a secondary cooling zone to a forming billet with controlling the flow rate of the cooler and changing the proportion of water in the water-air mixture, in which from 0.5 to 1.5 m / min

to

WITH

the pressure drop is increased from 0.1 to 0.6 atm, and along the length of the zone is gradually reduced from 0.6 to 0.1 atm, while maintaining its value constant in each section.,

A disadvantage of the known method is the poor quality of the macrostructure of continuously cast billets, which does not satisfy the requirement for rolled products made from these billets. This is explained by the fact that when regulating the water and air pressures in the air-water mixture through the secondary cooling sections when changing the drawing speed of the billets, the required cooling rate of the ingots is not achieved, since the carbon content in the cast steel is not taken into account. As a result, temperature gradients and thermal stresses exceeding the allowable values appear in the crystallizing ingot. This leads to the formation of cracks and axial friability,

The aim of the invention is to improve the quality of the ingots by adjusting the cooling rate, eliminating crack formation and reducing axial friability.

This goal is achieved due to the fact that in the method of secondary cooling of continuously cast spits, which includes supplying an air-air mixture to its surface with regulation of its flow rate and changing the ratio of the shares of water and air and their pressures along the length of the liquid phase of the ingots, the ratio of the shares of water and air in the mixtures are regulated depending on the carbon content in the metal, while in the area equal to 0.05 ... 0.5 of the length of the liquid phase, the ratio of the proportions of water and air in the mixture reduces P within 1/50 ... 1/150 , and the pressure ratio of these components nts in this section are set within 0, b ... 1.0.

A comparative analysis of the claimed solution with the prototype shows that the claimed method differs from the known one in that it allows one to take into account the effect of a specific carbon content in the metal on the change in the property of steel during cooling of the ingot in the process of drawing it from the crystallizer.

The proposed method makes it possible to eliminate defects in the macrostructure of the workpieces by appropriately adjusting the ratio of the flow rate of air and air and the ratio of their pressures when the carbon content in the steel being machined changes, taking into account the appropriate casting speed.

0

5

0

5

0

5

0

5

0

As the carbon content increases, the thermophysical properties of the steel change. Calculations of the heat transfer coefficients for the secondary cooling zones of the workpieces carried out, ceteris paribus conditions for continuous casting of steel, show that for high-carbon steel compared to low-carbon steel, the forced cooling zone is reduced and less heat is required within this zone. At the exit from the forced secondary cooling zone, continuously cast billets of high carbon steel come with a colder surface. Therefore, it is necessary to control the cooling intensity of the workpieces in the secondary cooling zone depending on the carbon content of the cast steel in order to compensate for the faster cooling of the workpieces from high-carbon steel, which prevents the formation of these defects in the macrostructure of the workpieces.

When analyzing the patent and technical literature, no signs were found that are part of the proposed method, which allows us to conclude that the proposed method meets the criterion of significant differences.

In FIG. Fig. 2 shows the INLZ scheme with the secondary cooling zone of the workpieces; Fig. 2 shows the distribution of the cooler over the secondary cooling zones.

The proposed method for the secondary cooling of continuously cast billets can be carried out using a continuous casting machine, including a mold 1. from which a solidified billet 2 is drawn, a secondary cooling zone consisting of several sections (for example A and B) supporting rollers 3. between which are installed nozzles 4. mounted on secondary cooling manifolds 5.

Using nozzles, a sprayed oh-1g1digel, for example, an air-water mixture, is supplied to the surface of the solid billet in the secondary cooling zone. The regulation of the cooling intensity jcyi is controlled in each section due to a corresponding change in the ratio of the fractions of years and β-air indicated in this method, depending on the carbon content in hn of the steel being alloyed and along the length of the secondary cooling zone, as well as by correspondingly changing the pressure of these components in sections providing a given rate of expiration of the water-air 1st mixture, which is necessary to increase the cooling efficiency and, and the zone of the A and B sections, cooling of the surface of the ingots os / 1 solution -: tsch chozlmgnpi wednesday

The lengths of sections A and B in relative values with respect to the length of the liquid phase of the continuous ingot are adopted in accordance with the typical size of the roller section, i.e. the length of the first section (A) was 3.03 m, the second (B) - 6.06 m.

EXAMPLE 1. A process of continuous casting of billets with a cross section of 300 x 360 mm grade CT10% C 0.10 is carried out. The casting speed was 0.6 m / min, the length of the liquid phase at this speed was 20.2 m. The length of the first section was 3.03 m, the distance from the meniscus of the metal to the beginning of this section was 1.01 m. The ratio of soda to air flow rate in the first section was set to 1 / 50, while the ratio of water and air pressures is maintained at 1.0 (water pressure was 0.35 MPa, air pressure 0.35 MPa).

In section B, 6.06 m long, the distance from the meniscus of the metal to the beginning of the section with a liquid phase length of 20.2 m is 4.04 m, to the end of the section 10.1 m, which, respectively, is 0.2 and 0.5 of the length of the liquid phase . The water-air flow ratio in this section is set to 1/100, while the ratio of water and air pressures is 1.0 (water pressure and air pressure are 0.3 mPz).

EXAMPLE 2. The process of continuous casting of billets with a cross section of 300x360 mm from steel grade st. 40% from 0.41. The casting speed is 0.6 m / min, the length of the liquid phase at this speed is 20.2 m. The length of the first section is 3.03 m, the distance from the meniscus to the beginning and end of the section is 1.01 and 4.04 m, which is respectively 0.05 and 0.2 of the length of the liquid phase. The ratio of water and air flow rates in this section is set to 1:70, while the ratio of water and air pressures is maintained at 0.9 (water pressure 0.3 MPa and air pressure 0.33 MPa). In section B of a length of 6.06 m, the distance from the meniscus of the metal to the beginning and end of the section is 0.2 and 0.5 times the length of the liquid phase, respectively. The ratio of water and air flow is set to 1/120, the ratio of water and air pressures is maintained at 0.8 (water pressure 0.25 MPa, air pressure 0.31 MPa).

Example 3. A process of continuous casting of billets with a cross section of 300 x 360 mm made of steel grade 65 N (% s 0.65) is carried out. The casting speed is 0.6 m / min. the length of the liquid phase at this speed is 20.2 m. The length of the first section is 3.03 m, the distance from the meniscus of the metal to the beginning and end of the section is 0.05 and 0.2, respectively, of the length of the liquid phase. The ratio of water and air flow rates in this section is set to 1/100, while the ratio of water and air pressures is maintained at 0.8 (water pressure 0.25 MPa. Air pressure 0.31 MPa). In section B of a length of 6.06 m, the distance from the meniscus of the metal to the beginning and end of the section is 0.2 and 0.5 times the length of the liquid phase, respectively. The ratio of the flow rates of water and air is set to 10 1/150, the ratio of the pressures of water and air is 0.6 (water pressure 0.2 MPa. Air pressure 0.33 MPa).

The test results of the proposed method on bloom caster showed that 5 when cooling blooms with the specified limits, an increase in the yield of billets by 0.5-1.5% was achieved, especially from carbon and ball-bearing steel. A reduction in the trim 0 of the axial looseness of the workpieces was achieved and cracks at the ends of the workpieces made of alloyed steel grades were practically eliminated.

As the test results showed, the optimal limits of the ratios of the fractions of water and air in section A (corresponds to the first roller section) are 1/50 ... 1/100, and in the section in (second section) 1/100 ..1 / 150.

With an increase in the ratio of the flow rates 0 of water and air less than 1/50 in the section A and less than 1/100 in the section B, the workpiece cools, the yield of the workpieces decreases, and with a decrease in the ratio in the section A more than 1/100, by 5 section B more than 1/150 unreasonably overestimates the flow of compressed air with the same quality of the workpieces. In this case, the cooling rate drops sharply and does not ensure normal growth of the hardening 0 crust of the workpiece.

Optimum air / water pressure ratios in the area. A is 0.8 ..1.0, and in section B 0.6 ... 1.0. When the ratio of water and air pressures in section 5 of section A is less than 0.8, and in section B of less than 0.6, the cooling rate of the air-air mixture drops sharply, approaching the cooling rate in air, and this causes the billet to reheat, 0 which can cause the formation of internal cracks. With an increase in the ratio of water and air pressures of more than 1, the cooling mode becomes very rigid, causing the workpiece to be supercooling, while the axial friability of the workpiece is significantly increased, which leads to an increase in workpiece defects.

Variation in the ratio of water and air pressures in this method makes it possible to increase its efficiency by providing cooling of the preforms over the entire surface area of the preform, including sub-regions due to the spreading of iodine-air mist behind the rollers on the surface of the preform at the indicated air-to-air ratios. This leads to lower temperatures in the zone of contact between the flame and the workpiece and provides a milder cooling mode.

Claims (1)

1. The method according to claim 1. Characterized in that the ratio of the shares of water and air and their pressures in the area of 0.05-0.2 the length of the liquid phase is changed in the range of 1 / 50-1 / 100 and 0.8-1.0, respectively . id Figure 1 100.1 Phage 2 &