RU2191645C1 - Method for cold rolling of low-carbon strip steel - Google Patents

Abstract

FIELD: manufacture of rolled products. SUBSTANCE: method involves compressing metal movable along succession of passes with predetermined compression value while applying tensile force to rear and front sides of strip. During rolling of strips through three passes at strip width to final thickness ratio within the range of 2,400-2,700, compression values in first and second passes are set to be equal to, respectively: ε₁=41-45% and ε₂=38-40%. Specific front tension values for each pass are selected to be within the range of 0.22-0.25 of maximal flowability of deformed strip. In first pass, tensile force is applied only to front strip side. Method provides for manufacture of rolled low-carbon steel strips of quality allowing following zincing thereof. EFFECT: increased quality of zinced strips due to improved planeness and by preventing development of defects on strip edges.

Description

 The invention relates to rolling production and can be used in the manufacture of low-carbon strip steel with a sufficiently large ratio of its width to thickness and intended for subsequent galvanizing.

(где

- предел текучести металла), т.е. в долях от

Различают переднее натяжение (т.е. усилие, прикладываемое к прокатываемой полосе после конкретного прохода) и заднее (прикладываемое к полосе перед этим же проходом). Так как натяжение снижает давление металла на валки, то до недавнего времени стремились прикладывать к полосе максимально возможное натяжение. Однако в последнее время наблюдается стремление к снижению величин натяжений при холодной прокатке.Such steel is rolled in continuous cold rolling mills. The modern technology of cold rolling of sheet steel is described in sufficient detail, for example, in the reference book edited by V.I. Zyuzina and A.V. Tretyakova "Technology of rolling production", Prince. 2, M., "Metallurgy", 1991, p. 640-664. Very important parameters of the cold rolling process that affect the geometry of the strips (in particular, their flatness) are the values of compressions and tensions along the aisles, moreover, they are usually set by the values of specific tensions (σ = T / F, where T is the absolute value of the tension, F - the cross-sectional area of the strip, which take in the form of:

(Where

- yield strength of metal), i.e. in shares from

Distinguish between front tension (i.e. the force applied to the rolled strip after a specific passage) and rear (applied to the strip before the same passage). Since the tension reduces the pressure of the metal on the rolls, until recently they tried to apply the maximum possible tension to the strip. Recently, however, there has been a tendency to reduce the values of tension during cold rolling.

 There is a known method of cold rolling, in which a predetermined value of the metal pressure is maintained by adjusting the interstand tension, which is controlled by controlling the number of revolutions of the rolls (see Japanese Pat. 50-17352, class. 21 V from 06/20/75).

There is also a known method for the production of steel strips, in which the strips are wound into a roll with a tension equal to 0.4-0.9 of the yield strength of steel after cold rolling, and in the rolled state, the strip is tempered at 370-440 ^o C (see ed. St. USSR 1423610, class C 21 D, published in BI 34, 1988).

 The disadvantage of these methods is the uncertainty of the reductions and tension during rolling, which makes them unacceptable for the production of strip steel with a large ratio of its width to thickness, intended for subsequent galvanizing.

 The closest analogue to the claimed object is a method of cold rolling sheet metal on a continuous mill according to ed. St. USSR 1044377, class In 21 In 1/26 of 07/10/81 (published in BI 36, 1983).

 This method consists of sequentially compressing metal passes with predetermined relative compressions and applying back and forward tension to the strip and is characterized in that the compression is evenly distributed over the mill stands and to improve the quality of the strip by increasing the durability of the rolls between the 1st and 2nd -th stands stretch the strip with a specific tension of 0.7-0.9 of its yield strength. The disadvantage of this method is its unacceptability for obtaining in three passes of high-quality wide and thin strips for galvanizing.

 Indeed, the well-known technology is implemented on a five-stand mill (i.e., rolling in five passes), where it is possible to uniformly compress (approximately 1/5 of the total strain) the metal along the aisles and use high specific tension, since the width of the rolled strip is relatively small (up to 800 mm).

 When rolling wide and thin strips in three passes, it is necessary to establish sufficiently high relative reductions in the 1st and 2nd passes and a low compression in the last pass, in order to ensure both the required properties of the steel and its satisfactory flatness, and, moreover, high specific tension at this is not required (the larger their value, the greater the energy consumption and wear of the rolls).

 An object of the present invention is to improve the quality of galvanized strips by improving their flatness and preventing defects at the edges.

To solve this problem in a cold rolling method, which includes sequentially compressing metal through passages with specified relative compressions ε and applying back and front tension to the strip, when rolling strips in three passes with a ratio of strip width to their final thickness within 2400-2700 magnitude reductions in first and second passes are set equal, respectively, ε ₁ = ε and 41-45% ₂ = 38-40%, with values of the specific tension to the front of each passage receiving 0.22-0.25 equal yield stress of the deformed TVOC and the first pass is applied thereto only front tension.

 The given values were obtained during the processing of experimental data and are empirical.

 The essence of the proposed technical solution is to establish the optimal values of compression and specific tension in the aisles, as well as in the annex to the strip after the first pass only the front tension. Since the front tension in the nth passage is the back in the (n + 1) th passage, it is sufficient to indicate the magnitudes of only the front tension.

 The application to the strip in the first pass only front tension due to the following. The rear tension in this passage is created due to braking (operation in the generator mode) of the unwinder engine. This causes a “densification” of the coil winding and, as a result, mutual slippage of individual turns, increasing from the center to the periphery of the coil. The roll strip is set on the cold rolling mill (after etching) with trimmed side edges, i.e. with the inevitable presence of burrs and metal chips on them. With mutual slippage of the turns, the strip surface is injured, and the crumb can roll (especially with a large reduction in the first pass) into the strip surface, causing irreparable defects during subsequent galvanizing. It should also be noted that braking of the unwinding roll significantly complicates and increases the cost of the unwinder unwinding.

 An experimental verification of the proposed rolling technology was carried out on a 1450 3-stand mill of OJSC Magnitogorsk Iron and Steel Works.

 For this purpose, when rolling low-carbon strips (mainly st. 08 sp) 1250 • 1.8 mm to final thicknesses of 0.52-0.47 mm, the values of relative compressions along the aisles and specific front tensions varied. The experimental results were evaluated by the flatness of the finished strips and the presence of the indicated defects and gaps on their edges. The values after deformation in the experiments were determined by the formulas for st.08 (see A.V. Tretyakov et al. "Mechanical properties of steels and alloys during plastic deformation (reference)". M., "Engineering", 1971).

The best results (the thickness difference is within the norms of GOST 19904 and up to 95% of the bands with normal and improved flatness) was obtained when implementing the proposed method. A decrease in ε ₁ and ε ₂ led to the need to increase ε ₃ (in the third pass), which worsened the flatness of the strips (mainly due to waviness along their edges), and an increase in ε ₁ and ε ₂ above the optimal values caused "(wave in the middle of the width) of the strips are above normal.

 An increase in the specific forward tension in some cases led to stretching of the edges (with the appearance of waviness), and their decrease increased the thickness of the strips, which brought their thickness beyond the tolerances in accordance with GOST 19904. The application of back tension in the first pass led to the rejection of up to 8% of strips in defects of their edges.

 Test rolling of these strips according to the technology described in ed. St. 1044377 (see above), led to rejection by non-flatness and edge defects of up to 12% of the metal.

 Thus, the experiments confirmed the acceptability of the proposed method for solving the problem and its advantages over the known technology.

 According to the Central Control Laboratory of the Magnitogorsk Iron and Steel Works, the use of the proposed method for cold rolling of low-carbon steel subjected to galvanization reduces the marriage of galvanized sheets 1250 • 0.52-0.47 mm by almost 3 times, which accordingly increases the yield of products and increases the profit from it implementation.

Concrete example
A low-carbon steel strip (st. 08 ps) 1250 • 1.8 mm is rolled in three passes to a thickness of 0.5 mm. The values of the relative reductions: ε ₁ = 43%, ε ₂ = 39%.

(предела текучести стали после деформации). В первом проходе к полосе прикладывается только переднее натяжение.The values of the specific front tension in each passage:

(yield strength of steel after deformation). In the first pass, only the front tension is applied to the strip.

Claims (1)

The method of cold rolling of low-carbon strip steel, comprising sequentially compressing the passages of metal with predetermined relative compressions and applying back and front tension to the strip, characterized in that when rolling strips in three passes with a ratio of strip width to their final thickness within 2400- 2700 values of reductions in the first and second passes are set equal to ε ₁ = 41-45% and ε ₂ = 38-40%, respectively, while the values of the specific front tension for each pass are taken equal to 0.22-0.25 fluid limit There is a deformed strip and in the first pass only front tension is applied to it.