RU2147943C1 - Process of production of low-carbon cold-rolled strip steel - Google Patents

Abstract

FIELD: production of rolled stock, specifically, cold-rolled coil strip from low-carbon steel. SUBSTANCE: proposed process includes cold rolling with specified reduction in passes and interstand tension of strip and cutting of its side edges by circular shears. While rolling strips with minimal cross-section with initial yield point σ_y=215-415, MPa and summary reduction of four passes within limits of 68-72% reduction of first pass should be equal to 32-33%. After first pass lateral displacement of rolled strips is limited by concave surfaces of rolls. Interstand tension is set depending on average design quantity of yield point

, MPa after n-th pass with n=

. Tension of strips for cutting of edges is assumed to be equal to σ_c= (0.34- 0.46)

. Circular shears are set with radial overlapping Δ=0.5h, where ξ is summary relative reduction in n-th pass, % equal to 0.30-0.32 with proportionality factor

, mean quantity of yield point of metal to be cut

Description

 The invention relates to rolling production and can be used in the manufacture of low-carbon strip steel on continuous cold rolling mills.

To produce such steel, four-six-quarto quarto mills are currently being used, rolling strips of various thicknesses and widths from hot-rolled billets. The applied cold rolling modes are characterized, first of all, by the values of the relative reductions in one pass and the total reductions in all passes, as well as the values of inter-stand tension (most often, specific, i.e. per 1 mm ^{2 of} the cross-sectional area of the rolled strip in the corresponding inter-stand gap ) The modern technology of continuous cold rolling of carbon steel is described in sufficient detail, for example, in the book of S.P. Efimenko and V.P. Sledneva "Roller of sheet rolling mills", M., "Metallurgy", 1980, p. 230 - 241.

 For each cold rolling mill and its assortment, there are norms for the values of reductions (per pass and total) and absolute (or specific) inter-stand tension.

 The final operation for the production of cold rolled strip steel is the trimming of the side edges, which is usually carried out using disc shears on cutting units.

A known method of cold rolling thin strips (tin) on a continuous mill with uniform compression across the stands, in which the strip between the 1st and 2nd stands is stretched with a specific tension equal to 0.7 - 0.9 yield strength (σ _t ) of the metal (see USSR AS N 1044347, class B 21 B 1/26, 07/10/81, published in BI N 36, 1983). There is also a known method for the production of cold-rolled strips, in which rolling and training of metal is carried out with a mismatch of the speeds of the rolls, depending on the relative compression in the stand (see A.S. USSR N 1093369, class B 21 B 1/28, from 11.04.83 published in BI N 19, 1984).

 The disadvantage of these methods is the inability to obtain with their use on a broadband mill high-quality cold-rolled strips with a minimum cross section for its assortment.

 The closest analogue to the claimed method is the production technology of cold-rolled strip steel, described in the book of V.F. Zotova and V. I. Elina "Cold rolling of metal", M., "Metallurgy", 1988, p. 64, 65, 70, 71, 165 - 172.

 This technology includes continuous cold rolling with predetermined compressions along the aisles and inter-stand tension of the strip and cutting of its side edges and is characterized in that the rolling process is controlled by tensioning the rolled strip taking into account the constant of the continuous mill. A disadvantage of the known technology is the lack of specific parameters (values of compression, tension, etc.) necessary to obtain high-quality low-carbon steel with a minimum cross-section on a broadband continuous mill (for example, mill 2500).

 Indeed, for cold-rolled sheet mills, the production of strips of minimum thickness and width is always the most difficult, since this leads to an increase in the relative deflection of the work rolls, the absolute value of the intercellular tension is limited, and the compression modes for wider strips become unacceptable, as a result of which the metal flatness worsens and its mechanical properties. The winding of such strips (especially low-carbon ones) after trimming their edges on the cutting unit often leads to ellipsoid rolls (after removing them from the winder).

 The technical task of the invention is to expand the technological capabilities of continuous cold rolling mills by improving the quality of low-carbon strip steel of minimal cross sections.

МПа, после n-го прохода, равным

при этом натяжение полос при обрезке кромок принимают равным

а дисковые ножи устанавливают с радиальным перекрытием Δ = 0,5h, где ε - суммарное относительное обжатие в n-м проходе, %

коэффициент пропорциональности,

средняя величина предела текучести обрезаемого металла, МПа, h - толщина полосы, мм.To solve this problem, in a method that includes cold rolling with predetermined compressions along the aisles and intercellular tension of the strip and cutting its lateral edges with disc scissors, when rolling strips of minimal cross sections with an initial yield strength σ _t = 215 - 415 MPa and a total relative compression of 68 - 72% compression in the first pass is taken equal to 32 - 33% and after it the lateral displacement of the rolled strips is limited by the concave surface of the rolls, and the interstand tension is set, depending on the average design yield strength values

MPa, after the n-th pass, equal to

while the tension of the strips when trimming the edges is taken equal

and circular knives are installed with a radial overlap Δ = 0.5h, where ε is the total relative compression in the nth passage,%

coefficient of proportionality

the average yield strength of the metal being cut, MPa, h is the strip thickness, mm

 The above mathematical dependences were obtained during the processing of experimental data and are empirical.

 The essence of the proposed technical solution is to determine some parameters of the processes of cold rolling and cutting strips, providing high-quality sheet steel with minimum dimensions for the mill.

In the course of research performed during the experimental rolling (see below) of such steel it was found:
1) the maximum reduction (higher than the commonly used values for the mill 2500: ε ₁ = 15 - 20% - see Yu.V. Konovalov "Directory of the distributor", M., "Metallurgy", 1977, p. 105) should be in the first aisle;
2) the work rolls in subsequent passes should have a concave barrel forming them;
3) interstand stresses are established with a decrease in their ratio "K" to the changing (ie, after deformation) average yield strength σ _{t of} steel, and the value of K = 0.38 - 0.22;
4) to obtain a roll of the required shape and with the proper quality of the strip edges, it is necessary to establish a certain radial overlap of the circular knives and create tension between the scissors and the coiler depending on the yield strength of the steel being cut.

брали по средним их значениям для полос одной плавки и одной партии (т.е. с одинаковым химсоставом стали).An experimental verification of the proposed method was carried out on a 4-stand continuous cold rolling mill 2500 of OJSC Magnitogorsk Iron and Steel Works in the production of low-carbon strip steel grades 08Y and 08ps with a cross section of 0.6x1030 mm ² (after trimming the edges, the width of the strips is 1000 mm). For this purpose, during cold rolling and on the cutting unit, individual process parameters were varied, fixing the sorting of the rolled products and its yield by rolling accuracy and category of drawing (after appropriate tests). Quantities

were taken according to their average values for strips of one heat and one batch (i.e., with the same chemical composition of steel).

 The best results (the yield of rolled products of increased accuracy A according to GOST 19904 is up to 94%, the rest is B; up to 65% of the strips of high flatness of PV according to GOST 19904, the rest is PU and PN; the categories of extracts of WWS and SV according to GOST 9045 are about 90%, the rest is VG; the number of ellipsoid rolls - not more than 1%) was obtained using the inventive technology. Deviations from optimal parameters worsened the quality level.

So, for example, reducing the amount of compression in the 1st pass (ε ₁ ) to 20 - 30% reduced the yield of steel of the WWS and CB. The use of cylindrical and rolls with a convex generatrix in the II ... IV passes led to the appearance of a unilateral undulation on a considerable part of the stripes.

см. упомянутую книгу Ю.В.Коновалова, с III - ухудшило точность и плоскостность прокатки. Снижение величины σ_o на агрегате резки повысило выход дефектных рулонов, а ее повышение за рекомендуемые пределы привело к необходимости изменения величины Δ, что ухудшило качество реза (заусенцы и волнистость по кромкам).The use of other tension during rolling, for example for all passes

see the mentioned book of Yu.V. Konovalov, since III - it worsened the accuracy and flatness of rolling. The decrease in σ _o at the cutting unit increased the yield of defective rolls, and its increase beyond the recommended limits led to the need to change the Δ value, which worsened the quality of the cut (burrs and waviness along the edges).

 The technology chosen as the closest analogue (see above) has not been tested due to the lack of specific recommendations on the parameters for rolling low-carbon strips of minimum size on a 4-stand broadband mill and trimming its edges.

 Thus, an experimental verification confirmed the acceptability of the technical solution found for the implementation of the task. The inventive object can be used on any mill, similar to mill 2500.

 Feasibility study of the proposed method consists in increasing profits from the implementation of more expensive thin and high-quality sheet steel in the domestic and foreign markets. According to the Central Control Laboratory of OJSC MMK, the use of the proposed technology for the production of the above-mentioned strip steel will increase the total profit from the sale of rolled products from mill 2500 of the plant by at least 8%.

 An example of a specific implementation.

08ps steel strip with a size of 0.6x1030 mm ^{2 is} rolled from a hot-rolled billet of 2x1030 mm ² on a 4-stand mill. The value of σ _t = 315 MPa; reduction mode: 2.0 ---> 1.35 ---> 0.95 ---> 0.75 ---> 0.6 mm.

а в первом проходе

После 1 прохода (в клетях II - IV) используются рабочие валки с вогнутой образующей: величина прогиба - 0,15 мм.Total

and in the first pass

After 1 pass (in stands II - IV), work rolls with a concave generatrix are used: the deflection value is 0.15 mm.

после первого прохода:

после II прохода:

после III прохода:

Величины К: для n = 1

для n = 2 К = 0,27 и для n = 3 К = 0,23.Value

after the first pass:

after pass II:

after the third pass:

K values: for n = 1

for n = 2 K = 0.27 and for n = 3 K = 0.23.

Абсолютные натяжения при прокатке:

217•1,35•1030 ≅ 301,7 кН≈30,6 тс;
T₂=183•0,95•1030 ≅ 179,1 кН≈18,2 тс;
T₃=164•0,75•1030 ≅ 126,7 кН≈12,9 тс.Values of σ _n after passes I-III:

Absolute tension during rolling:

217 • 1.35 • 1030 ≅ 301.7 kN≈30.6 tf;
T ₂ = 183 • 0.95 • 1030 ≅ 179.1 kN≈18.2 tf;
T ₃ = 164 • 0.75 • 1030 ≅ 126.7 kN≈12.9 tf.

после отжига и дрессировки - 185 МПа):

0,4•185=74 МПа, а
T₀=74•0,6•1000=44,4 кН≈4,5 тс.Strip tension when trimming their edges (

after annealing and training - 185 MPa):

0.4 • 185 = 74 MPa, and
T ₀ = 74 • 0.6 • 1000 = 44.4 kN≈4.5 tf.

 Radial overlap of circular knives: Δ = 0.5h = 0.5 • 0.6 = 0.3 mm.

Claims (1)

A method for the production of low-carbon cold-rolled strip steel, including cold rolling with predetermined reductions along the aisles and inter-stand tension of the strip and cutting its side edges with disc scissors, characterized in that when rolling the strips of minimum cross sections with the initial yield strength σ _t = 215 - 415 MPa and total relative compression in four passes within 68 - 72%, the compression in the first pass is taken to be 32 - 33% and after it the lateral displacement of the rolled strips with a concave surface is limited rolls, and interstand tension set depending on the average calculated value of the yield strength

MPa, after the n-th pass equal

while the tension of the strips when trimming the edges is taken equal

and circular knives set with a radial overlap Δ = 0.5h,
where ε is the total relative compression in the nth passage. %;

coefficient of proportionality;

the average yield strength of the cut metal, MPa;
h - strip thickness, mm.