RU2487176C1 - Method to produce cold-rolled strip from low-carbon steel for cutting of coin blank - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes melting of steel, subsequent hot rolling of a slab blank, strip etching, cold rolling, recrystallisation annealing, dressing and slitting for the necessary width. At the same time hot rolled semi-finished products in the cross section has a circular arc profile with convexity of up to 0.04 mm, and prior to etching its slitting is carried out into narrow strips, cold rolling of which is done with pressing in the first stand of the continuous mill of cold rolling within 35-40%, and the setpoint of thickness in the last stand is selected depending on thickness of the finished tape. Besides, the ratio between thickness of hot-rolled semi-finished products and thickness of finished cold-rolled tape is regulated, and in process of dressing the value of relative pressing is regulated.

EFFECT: required high accuracy of manufacturing by thickness by formation of minimum gage interference in production of a cold-rolled tape produced from a previously slitted wide hot-rolled strip.

1 tbl, 1 ex

Description

The invention relates to rolling production and can be used in the production of cold-rolled strip of low-carbon steel grades, used, for example, for high-speed cold cutting of coin blanks.

The technologies for the production of cold-rolled strip obtained from a longitudinally expanded hot-rolled strip from a wide-band hot-rolling mill with a reduced surface hardness (HR15T 73 ÷ 76 units) with its low roughness (Ra≤0.8 μm) are becoming increasingly developed. At the same time, in the cold-rolled tape, high precision of manufacturing in thickness should be ensured. Deviation from a given narrow range of normalization of the thickness variation of the cold-rolled strip leads to the impossibility of its use for the manufacture of, for example, coin blanks, or to a significant decrease in the efficiency of this process.

Known methods for the production of cold-rolled strips of hot-rolled mild steel from low carbon steel, including descaling by pickling, cold rolling of the pickled strip in a continuous mill, subsequent recrystallization annealing and tempering of the annealed strip (see, for example, Rolling production technology. In 2 books. Kn. 2. Reference: M. Benyakovsky, K.N. Bogoyavlensky, A.I. Vitkin and others. M .: Metallurgy, 1991. - S. 619-630; Pat. RF №2374014, Pat. RF №2281338, Pat. Of the Russian Federation No. 2315118, Pat. Of the Russian Federation No. 2313584).

The most significant drawback of the known methods is the difficulty of providing in a narrow cold-rolled strip (steel tape) the required set of physico-mechanical properties, as well as high precision manufacturing across the thickness of the tape.

The closest analogue to the claimed object is a method of producing cold rolled steel for cold stamping from low carbon steel with a content of 0.001 ÷ 0.006% carbon and 0.05 ÷ 0.25% manganese, microalloyed carbonitride-forming elements (Nb, Ti), including steel casting, hot rolling at a temperature of rolling end of 850 ÷ 910 ° С, at a winding temperature of 540-730 ° С, removal of scale from the surface of hot-rolled steel by pickling, cold rolling in a continuous mill with a total compression of 65-88%, subsequent annealing at temperature 700-750 ° C, and temper rolling the annealed strip (see. Pat. RF №2277594).

The disadvantage of this method is the lack of regulation of the geometric parameters of the tackle, as well as thickness settings during its cold rolling, which, in turn, does not allow for high precision manufacturing of tape thickness. In addition, the known method does not allow to achieve high accuracy in the thickness of the rental in the conditions of its preliminary longitudinal dissolution.

The technical problem solved by the claimed invention is to provide the required high precision manufacturing in thickness, for example, 0 / -0.06 mm by forming a minimum thickness difference in the production of cold-rolled tape obtained from a pre-longitudinally unfurled wide hot-rolled strip.

где Н - толщина горячекатаной полосы, мм; h_л - толщина готовой ленты, мм, при этом перед травлением производят продольный роспуск широкой полосы на узкие полосы, холодную прокатку которых осуществляют с единичными обжатиями в первой клети стана 35-40%, причем уставку толщины в последней клети стана выбирают из выражения: $$h_{уст}=\mathrm{0,98}\cdot h_{л}^{\mathrm{1,026}}$$

, где h_уст - толщина готовой ленты, мм; h_л - толщина готовой ленты, мм, кроме того, при дрессировке величину относительного обжатия ε выбирают в зависимости от конечной толщины готовой ленты и заданной разнотолщинности из выражения: $$\epsilon =(-\mathrm{0,0114}\cdot \ln (h_{л}-\frac{\Delta h}{2})+\mathrm{0,017})\times 100\%$$

,The problem is solved in that in the known method for the production of cold rolled strip of low carbon steel for cutting a coin billet, 1.16 ÷ 1.84 mm thick, including steel smelting, hot rolling of a slab billet on a broadband mill, etching of the strip surface, cold rolling on continuous mill, recrystallization annealing, as well as training and longitudinal dissolution to the desired width, according to the invention; during hot rolling, a strip with a lenticular cross-sectional profile with a bulge up to 0.04 mm is produced, the thickness of which is determined depending on the final thickness of the finished tape from the expression: $$H=2.16\cdot e^{0.57\cdot h_l},$$

where H is the thickness of the hot rolled strip, mm; h _l is the thickness of the finished tape, mm, while before etching, longitudinal dissolution of the wide strip into narrow strips is carried out, cold rolling of which is carried out with single reductions in the first mill stand of 35-40%, and the thickness setting in the last mill stand is selected from the expression: $$h_{\mathrm{at}\mathrm{from}t}=0.98\cdot h_l^{\mathrm{1,026}}$$

where h _mouth - the thickness of the finished tape, mm; h _l is the thickness of the finished tape, mm, in addition, when training the value of the relative compression ε is selected depending on the final thickness of the finished tape and the given thickness difference from the expression: $$\epsilon =(-0.0114\cdot \ln (h_l-\frac{\Delta h}{2})+0.017)\times \mathrm{one\; hundred}\%$$

,

where h _l is the thickness of the finished tape, mm; Δh is the given thickness difference of the finished tape, mm

The invention consists in the following.

The peculiarity of the production of cold-rolled strip in the considered technical solution is that before etching, for the cold rolling of the strip, a wide hot-rolled strip is dissolved in narrow strips. In this case, the average strip widths have a transverse thickness difference of not more than 0.01 mm, and the extreme bands are characterized by a maximum transverse thickness variation of a wedge-shaped shape with a common, according to the claimed method, wedge-shaped hot-rolled wide strip, not exceeding 0.04 mm.

Thus, to ensure a minimum level of transverse thickness variation of the finished strip, it is necessary to carry out the total reduction of the hot-rolled strip during the cold rolling process depending on the final thickness of the strip according to the proposed dependence. The dependence presented in the claimed technical solution is empirical and is obtained as a result of numerous experimental rolling on a continuous five-stand cold rolling mill 630 of OJSC MMK. Exceeding the declared total deformations during rolling on a continuous rolling mill leads to the possibility of overloading the mill, cracking the edges of the strip and violating its flatness. On the other hand, during cold rolling of a strip of low carbon steel with total deformations lower than the declared ones, it is difficult to achieve the minimum values of the longitudinal-transverse different thickness and rollability of the tape to a given thickness.

The regulation of the relative compression in the first stand of a continuous cold rolling mill is associated with the following. From the practice of cold rolling of a tape, for example, for a coin blank in a continuous five-stand mill 630 of OJSC MMK, the level of optimal relative reductions in the first stand of the mill is established within 35-40%. Exceeding the relative compression in the first stand above the stated values contributes to insufficient loading of the subsequent stands of the continuous mill, which, in turn, leads to a decrease in the efficiency of automatic tension and thickness control systems and, accordingly, the whole mill. The result of exceeding the allowable level of relative reduction in the first stand of the continuous mill will be a significant longitudinal thickness difference. Rolling with reductions below the regulated level forms an increased transverse thickness difference due to the inability to equalize in the subsequent stands the thickness of the hardened in the first passes of the rental. With the declared deformation mode of rolling on a continuous mill, a minimum level of transverse and longitudinal thickness difference is ensured, which corresponds to a high precision of tape production in thickness, for example, 0 / -0.06 mm.

Considering that for the manufacture of, for example, a coin blank, it is necessary to ensure high accuracy in thickness, which does not lead out of the tolerance field, it is also necessary to regulate the amount of compression in the last stand of a continuous cold rolling mill while normalizing the relative compression during training. Numerous studies during rolling on a continuous five-cage and two-cage rolling and tempering mills 630 of OJSC MMK found that to ensure a given accuracy in the thickness of the tape, not displaying its value outside the tolerance band in thickness, the choice of setting when rolling the tape in a continuous mill, and also relative reductions in its training should be based on the given empirical dependencies.

Deviation from these values leads either to a significant decrease in the efficiency of the manufacturing process of high precision tape in thickness, or to increased thickness variation of the finished tape.

Based on the above analysis of known sources of information, we can conclude that for a specialist the inventive method for the production of cold-rolled tape with high precision manufacturing thickness of low-carbon steel does not follow explicitly from the prior art, and therefore meets the patentability condition of "inventive step".

An example implementation of the method.

As an example, the production technology of cold-rolled tape with dimensions of 1.16 × 200 mm, 1.54 × 200 mm, 1.56 × 236 mm, 1.56 × 193 mm and 1.84 × 214 mm with an accuracy of manufacturing in thickness of 0 / -0.06 mm, intended for subsequent high-speed cold cutting of coin blanks.

Steel with the chemical composition shown in Table 1 is smelted in a 350-ton converter. After the out-of-furnace treatment of the metal and the introduction of the required additives, the steel is continuously casted, followed by its crystallization and cutting into slabs. Next, hot rolling of slabs is carried out on a continuous broadband hot rolling mill 2000 (SHSGP 2000) of OJSC MMK into strips 4.2–6.2 mm thick. In this case, the hot-rolled tackle in cross section has a lenticular profile with a bulge up to 0.04 mm.

After hot rolling and winding the strip into a roll, a longitudinal dissolution of a wide hot-rolled tackle into narrow strips of 1.16 × 415 mm, 1.54 × 415 mm, 1.56 × 400 mm, 1.56 × 485 and 1.84 × 440 sizes is carried out mm (respectively). Next, the strip is etched in a continuous etching unit, after which the etched strip is rolled on a continuous five-stand cold rolling mill 630 of OJSC Magnitogorsk Iron and Steel Works. At the same time, rolling of a tape with a thickness of 1.16 mm is carried out from a tackle with a thickness of 4.2 mm, a tape with a thickness of 1.54 mm and 1.56 mm from a tackle with a thickness of 5.2 mm, a tape with a thickness of 1.84 - from a tackle with a thickness of 6.2 mm Moreover, to ensure high precision manufacturing of the tape in thickness, the relative compression in the first mill stand is maintained within 35-40%. Moreover, in the last stand of the cold rolling mill, the thickness setting is determined according to the claimed relationship. After rolling on a continuous five-stand mill, recrystallization annealing of the rolls of tape in bell furnaces is carried out. Then, the annealed tape is trained to a final thickness on a rolling and training mill with regulated reductions in accordance with the given dependence. Then produce longitudinal dissolution on the tape of the required widths, for example 193 mm, 200 mm, 214 mm and 236 mm.

Variants of technological parameters, according to which, according to the claimed method, cold rolled low-carbon steel strip of high precision manufacturing by thickness was produced for cutting a coin billet under continuous five-stand and two-stand rolling and training mills 630 of OJSC MMK, as well as the research results are presented in Table 1 and 2.

The inventive technology for the production of rolls on the example of the production of cold-rolled tape for cold cutting from a low-carbon steel grade provides a tape with high accuracy of its manufacture in thickness.

The selected set of features allows us to conclude that the claimed method is workable and eliminates the disadvantages that occur in the prototype.

The inventive method can be widely used in the production of cold-rolled tape with high precision manufacturing thickness for high-speed cold cutting, for example, coin blanks. Therefore, the inventive method meets the condition of patentability "industrial applicability".

Claims (1)

A method of manufacturing a cold rolled strip 1.16 ÷ 1.84 mm thick from low carbon steel for cutting a coin billet, including steel smelting, hot rolling of a slab billet on a broadband mill, strip surface etching, continuous cold rolling, recrystallization annealing, tempering and longitudinal dissolution to the required width, characterized in that during hot rolling a strip is produced with a lenticular cross-sectional profile with a convexity of up to 0.04 mm and a thickness which is determined depending on the final thickness of the finished tape h _l from the expression: H = 2.16 · e ^{0.57 · h} , where H is the thickness of the hot-rolled strip, mm; h _l is the thickness of the finished tape, mm, while before etching, longitudinal dissolution of the wide strip into narrow strips is carried out, cold rolling of which is carried out in the first mill stand with single compressions of 35-40%, and the thickness setting in the last mill stand is selected from the expression: $$h_{\mathrm{at}\mathrm{from}t}=0.98\cdot h_l^{\mathrm{1,026}}$$

, and the value of the relative compression ε during training is selected depending on the final thickness of the finished tape and the given thickness difference Δh from the expression:
$$\epsilon =(-0.0114\cdot \ln (h_l-\frac{\Delta h}{2})+0.017)\cdot \mathrm{one\; hundred}\%,$$

where Δh is the given thickness difference of the finished tape, mm