RU2268097C1 - Cold rolled steel sheets making method - Google Patents

Abstract

FIELD: metallurgy, namely rolled stock production, possibly manufacture of cold rolled steel sheets and strips for further forming them.

SUBSTANCE: method comprises steps of hot rolling of strips at normalized temperature of rolling process termination; cooling strip by water; coiling it, etching and subjecting to multi-pass cold rolling till final thickness. Hot rolling of strip is realized till strip thickness determined according to relation H = 15h² - 20,5h + 10 where H, h - thickness of hot rolled and cold rolled strip respectively. Temperature of rolling process termination is equal to 820 - 865°C. Strip is cooled by water till temperature 515 -585°C.

EFFECT: lowered factor of metal consumption, production of rolled products having no cracking, ruptures and s other flaws in its lateral edges.

6 ex, 1 tbl

Description

The invention relates to the field of metallurgy, specifically to rolling production, and can be used in the manufacture of cold-rolled steel sheets and strips for stamping.

A known method for the production of cold rolled low carbon sheet steel, including heating slabs to a temperature of 1150-1280 ° C, rolling in a rough and finish group of stands with a total degree of reduction of 80-90%, cooling with water, winding into coils, pickling and cold rolling. In this case, the total degree of deformation in the finishing group of the stands of the hot rolling mill of each strip is preliminary determined, and depending on its value equal to 80-85, 86-92, 93-98%, the total degree of compression in the cold rolling mill is set to 75-80, 65-70, 55-60% [1].

The disadvantages of this method are that during the rolling process on the strips formed defects along the edges. Trimming the edges of hot-rolled and cold-rolled strips increases the expenditure coefficient of the metal. In addition, after cold rolling with reductions from 55 to 80% of the strip have unstable mechanical properties and low formability.

There is also known a method of manufacturing cold rolled sheets for deep drawing from steel deoxidized by aluminum. The method includes heating the slab to a temperature of 950-1200 ° C, hot rolling with a rolling finishing temperature above Ar ₃ point, the cooling water strips to a temperature not exceeding 600 ° C and coiling. Hot rolled strips are subjected to etching, multi-pass cold rolling to a final thickness with compression of 70-80% and bell-shaped recrystallization annealing [2].

With this rolling method, defects are present at the edges of the hot rolled and cold rolled strips. Trimming the edges to remove defects increases the expenditure coefficient of the metal for the production of rolled products.

The closest in its technical essence and the achieved results to the proposed invention is a method for the production of cold rolled sheet steel (automobile sheet), which includes hot rolling of slabs into strips with a regulated rolling end temperature of 860-900 ° C, water cooling to a temperature of 550-580 ° C, winding into coils, etching of hot-rolled strips with trimming of the side edges and multi-pass rolling to a final thickness of 0.9 mm [3] - prototype.

The disadvantage of this method is that the edges of the strips after hot rolling are affected by defects and small tears, which increase during the subsequent cold rolling. To eliminate these defects, the edges of the hot-rolled strips are cut, which increases the expenditure coefficient of the metal.

The technical problem solved by the invention is to reduce the expenditure coefficient of the metal by eliminating the need for trimming the edges of the hot rolled strips.

The stated technical problem is solved by the fact that in the known method for the production of cold rolled sheet steel, which includes hot rolling of strips with a regulated temperature of the end of rolling, water cooling, winding into coils, pickling and multi-pass cold rolling to a final thickness, according to the proposal, hot rolling of the strips leads to thickness, determined by the ratio:

H = 15h ² -20.5h + 10,

where H, h are the thickness of the hot-rolled and cold-rolled strip, respectively, while the temperature of the end of rolling is maintained equal to 820-865 ° C, and the cooling of the strips with water is carried out to a temperature of 515-585 ° C.

The invention consists in the following. Temperature-deformation regimes for the production of cold-rolled sheet steel for stamping should simultaneously provide both the formation of high exhaust properties and defect-free edges after hot and cold rolling. It was experimentally established that for each thickness of the cold-rolled strip there is a value of the thickness of the hot-rolled strip at which the development of defects along the edges during cold rolling does not occur, and the formability remains high. The combination of these values forms on the graph (see drawing) a curved line, the shape of which analytically describes the dependence H = 15h ² -20.5h + 10.

It should be noted that this dependence was determined experimentally only for cold-rolled strips with a thickness of 0.7-1.0 mm, and the absence of defects at the edges of the strips while maintaining high formability was achieved only at a temperature of rolling end equal to 820-865 ° C and cooling of the strips water to a temperature of 515-585 ° C. When all these conditions are met, no defects are formed on the edges, the need for trimming the edges of hot-rolled strips is excluded, the expenditure coefficient of the metal is reduced while maintaining high formability of cold-rolled steel sheets and strips.

It follows from the experiments that when the thickness of the hot-rolled strip is greater than that calculated from the proposed analytical dependence (i.e., for all points above the curve of the line on the graph), the edges of the strips are affected by defects, which requires trimming and increases the expenditure coefficient of the metal. A decrease in the thickness of the hot-rolled strip less than the value calculated from the analytical dependence leads to overcooling of the edges during hot rolling, a local loss of their ductility, and ruptures.

At a temperature of the end of rolling above 865 ° C, a coarse-grained, uneven microstructure of the ferrite matrix is formed, which affects the formability of the cold-rolled strips. A decrease in the temperature of the end of rolling below 820 ° C leads to a loss of ductility of the supercooled edges, the formation of defects. As a result, trimming of the edges is required, which increases the expenditure coefficient of the metal.

When the strips are cooled with water to a temperature above 585 ° C, the growth of microstructure grains in the roll, the deterioration of the mechanical properties and their uniformity across the width of the strip are not excluded. This causes a rupture of the edges during cold rolling, increases the expenditure coefficient of the metal. The cooling of the strips with water to a temperature below 515 ° C prolongs the cooling period and reduces the productivity of the rolling mill, which is unacceptable.

Method implementation examples

Parts of the hood of a car are stamped from cold-rolled sheet steel of 08Y grade with a thickness of h = 0.8 mm. The thickness of the hot-rolled strip N (rolled) for subsequent cold rolling is determined by the ratio:

H = 15h ² -20.5h + 10 = 15-0.8 ² -20.5-0.8 + 10 = 3.2 (mm).

Continuously cast slabs with a thickness of 250 mm from mild steel of the 08Y grade are heated in a methodical furnace of a continuous broadband mill 2000 to an austenitization temperature of 1230 ° C and rolled to the required thickness H = 3.2 mm with a temperature of rolling end T _kn = 845 ° C. Laminated strips are cooled on the discharge roller of the mill by laminar water jets to a temperature of T _cm = 550 ° C, and then wound into rolls.

To remove scale, the hot-rolled strips are subjected to sulfuric acid etching in the line of a continuous pickling unit and again wound into rolls. The side edges of the hot-rolled strips are not trimmed in the line of a continuous pickling unit. Hot rolled pickled strips are rolled on a 5-stand quarto cold rolling mill to a final thickness h = 0.8 mm. During the cold rolling process, there is no formation of defects along the unedged edges of the strips, because the edges have high ductility and were not affected by tears during hot rolling.

Cold-rolled strips in a final thickness h = 0.8 mm are subjected to recrystallization annealing at a temperature of 710 ° C in a bell-type furnace with a protective hydrogen atmosphere, training on a single-chamber quarto 1700 mill, cutting into sheets and rolls and packaging.

By selecting optimal thickness H of hot-rolled and the temperature T _kp and T _refer avoids the formation of defects on the edges of the strip and eliminating the need for trimming the hot-rolled strips in line continuous pickling line, thereby reduces consumable Q metal coefficient of rolling repartition with 32 kg / t up to 7 kg / t. At the same time, high formability of cold-rolled metal is achieved.

Variants of the method and the consumption rate of the metal for rolling redistribution are presented in the table.

Table
Cold Rolled Sheet Steel Production Modes No. p / p Thickness of hot rolled strip (rolled) T _kp , ° C T _cm , ° C Trimming Edges Q, kg / t one. H <15h ² -20.5h + 10 815 510 is necessary 32 2. H = 15h ² -20.5h + 10 820 515 no 8 3. H = 15h ² -20.5h + 10 845 550 no 7 four. H = 15h ² -20.5h + 10 865 585 no 8 5. H> 15h ² -20.5h + 10 870 590 is necessary 32 6. H ≠ 15h ² 20.5h + 10 890 580 is necessary 32 (prototype)

From the data given in the table, it follows that when implementing the proposed method (options No. 2-4), a reduction in the expenditure coefficient of the metal is achieved. If the proposed ratio between the thicknesses of the hot-rolled and cold-rolled strips and the transcendental values of temperatures (options No. 1 and No. 5) is not fulfilled, as well as when implementing the prototype method (option No. 6), it becomes necessary to trim the defective edges of the hot-rolled metal, which increases the specific metal consumption for rolling redistribution.

The technical and economic advantages of the proposed method consist in the fact that it provides defect-free lateral edges of hot-rolled strips having a sufficient margin of ductility for subsequent cold rolling to a predetermined thickness without the formation of cracks and tears. This eliminates the need for trimming the side edges of the hot rolled strips, and the specific metal consumption will decrease. Cold rolled sheets are highly formable.

The prototype method is adopted as the base object. Using the proposed invention will increase the profitability of the production of cold rolled sheet steel by 3-5%.

Literary sources

1. Autosvid. USSR No. 1384350, IPC B 21 V 3/00, 1988

2. Japan application No. 59-13030, IPC C 21 D 9/48, C 21 D 8/04, 1984

3. M. A. Benyakovsky and others. Production of automobile sheet. M., Metallurgy, 1979, S. 78-79, 117-119, 158 - prototype.

Claims (1)

Method for the production of cold rolled sheet steel, including hot rolling of strips with a regulated temperature of the end of rolling, water cooling, winding into coils, etching and multi-pass cold rolling to a final thickness, characterized in that the hot rolling of the strips is carried out to a thickness determined by the ratio H = 15h ² -20.5h + 10, where H, h are the thickness of the hot-rolled and cold-rolled strips, respectively, while the temperature of the end of rolling is maintained equal to 820-865 ° C, and the cooling of the strips with water is carried out to a temperature of 515-585 ° C.