RU2493923C1 - Method of producing thin hot-rolled sheet steel - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: proposed method comprises slabs austenitising heating, multipass roughing of strips, finishing and reeling. Possibility of steel reduction in two-phase austenite-ferrite state is ensured by roughing at 1290-800°C. Then, strips are subcooled and subjected to finish rolling at 620-750°C and total relative reduction of at least 50% while reeling is conducted at 400-740°C. It allows 3-10 outer and inner strip layers to be reeled at the temperature 30-70°C higher than that of mid layers. Besides, hot-rolled strips are additionally subjected to recrystallisation annealing at 660-770°C.

EFFECT: better drawing properties of hot-rolled steel sheet from low- and medium-carbon (IF) steels.

3 cl, 1 tbl, 3 ex

Description

The invention relates to rolling production and can be used to produce hot rolled sheet steel with a thickness of 1.0 mm or less from low carbon and ultra low carbon (IF) steels.

A known method for the production of thin hot rolled sheet low carbon steel with a thickness of 2-4 mm, including heating the slabs to an austenitizing temperature, rough rolling of strips with a rolling start temperature T _np = 1150-1230 ° C, continuous finishing rolling with compression in the last pass by 8-17% with a temperature of the end of rolling T _kn = 800-930 ° C, cooling of the strips with water to a temperature of T _cm = 500-780 ° C and winding into rolls [1].

The disadvantage of this method is that thin hot-rolled sheet steel has low exhaust properties. This significantly reduces the scope of its application. In addition, the method does not allow rolling strips with a thickness of less than 1.2 mm at a temperature T _kp = 800-930 ° C, which limits the lower limit of the dimensional assortment of metal products.

There is also a known method of rolling low-carbon steel, in which the workpieces are subjected to austenitic heating, rough rolling, sheathing and finishing rolling with a degree of deformation of at least 60% in the temperature range from 0.4 T _pl to 0.5 T _pl [2].

The disadvantages of this method are that it does not provide high exhaust properties of thin hot-rolled sheet steel.

The closest analogue to the present invention is a method for the production of low-carbon sheet steel, comprising heating slabs to an austenitizing temperature, rough rolling of strips, finishing rolling to a thickness of 2.3-4.0 mm, which is carried out with compression in the last two passes of at least 35% and complete at a temperature T _kn = 858-900 ° C, cooling the strips to a temperature T _cm = 600-735 ° C and winding into rolls [3].

The disadvantage of this method is that thin hot rolled sheet steel has low exhaust properties.

The technical problem solved by the invention is to increase the exhaust properties.

To solve the technical problem in the known method for producing thin hot rolled sheet steel, including heating slabs to austenitizing temperature, multi-pass rough rolling of strips, finishing rolling and winding into coils, according to the invention, rough rolling is carried out in a temperature range of 1290-800 ° C, after which the strips are cured and subjected to finish rolling in the temperature range of 620-750 ° C with a total relative compression of at least 50%, and the strip winding into coils is carried out at a temperature of 400-740 ° C.

In embodiments of the method, 3-10 external and internal coils of coils are wound at a temperature of 30-70 ° C higher than that of medium coils, and the hot-rolled strips are further subjected to recrystallization annealing at a temperature of 600-770 ° C.

The invention consists in the following. In the process of hot rolling of strips originally having an austenitic structure, they are continuously cooled. Simultaneously with a decrease in the strip thickness and an increase in its area, heat losses increase. For this reason, strips with a thickness of 1 mm or less from low-carbon and ultra-low-carbon steels undergo compression during the last finishing passes in a two-phase austenitic-ferritic state, which leads to a sharp drop in elongation properties: an increase in the tensile strength, a decrease in the relative elongation δ ₄ , and the depth of the hole E at Eriksen test, reducing the proportion of the component favorable for drawing the texture component {111}.

Rough rolling of strips of low-carbon and ultra-low-carbon steels in the temperature range of 1290-800 ° C occurs in the austenitic region, which ensures their high technological ductility. In the process of subsequent reinforcing, the process of phase γ → α transformation of austenite to ferrite and removal of phase hardening proceeds and is completed in strips; therefore, subsequent finishing rolling in the temperature range of 620-750 ° C is guaranteed in the single-phase ferrite region.

The exclusion of the possibility of the existence of a two-phase state of steel during finish rolling provides an increase in the exhaust properties of the finished sheet steel with a thickness of 1.0 mm or less. With a total reduction of at least 50% in the temperature range of 620–750 ° C, a texture is formed in the steel strips with a predominant orientation of the {111} grains, as well as the processes of recrystallization of deformed ferrite grains. The winding of strips into rolls at a temperature of 400-750 ° C contributes to the completion of recrystallization processes, the removal of thermal and phase stresses in steel.

The winding of 3-10 external and internal turns of coils with a temperature of 30-70 ° C is higher than that of medium coils, which are cooled more intensively in the coil, which makes it possible to increase the stretching properties of the front and rear ends of the strips, to align the mechanical properties along their length. An additional recrystallization annealing at a temperature of 600-770 ° C also allows to increase the exhaust properties and their uniformity along the length of the strips.

Thus, the combined effect of all the proposed features of the invention provides an increase in the exhaust properties of thin hot-rolled sheet steel.

It has been experimentally established that rough rolling at temperatures above 1290 ° C requires an increase in energy consumption for heating the slabs and the duration of the stripping of strips before finishing rolling, which is irrational. At the same time, rough rolling at temperatures below 800 ° C increases the metal resistance to deformation and energy consumption for rolling, reduces the technological plasticity of steel, which requires a reduction in single-time crimping and an increase in the total number of passes.

When finishing rolling at temperatures above 750 ° C in low-carbon and ultra-low-carbon steels, residual austenite is retained, which leads to a decrease in elongation properties. At temperatures below 620 ° C, the rate of recrystallization slows down, hot hardening of ferrite accumulates, and the exhaust properties of sheet steel decrease.

With a total relative reduction of less than 50%, the development of the ferritic microstructure of steel deteriorates, the grain size increases, and the exhaust properties decrease.

Winding strips into rolls at temperatures above 740 ° C leads to the appearance of collective recrystallization, which degrades the stretching properties. Lowering the winding temperature of less than 400 ° C does not ensure the removal of residual stresses in the coiled strip and the achievement of maximum exhaust properties.

When winding less than three external and internal turns of the roll with a temperature exceeding the temperature of the middle turns of less than 30 ° C, the exhaust properties of the end sections of the strips are reduced. When winding more than 10 external and internal turns of a roll with a temperature exceeding the temperature of the average turns by more than 70 ° C, instability of mechanical properties along the length of the strips appears, which is unacceptable.

Recrystallization annealing of hot-rolled strips at temperatures below 600 ° C does not increase the exhaust properties. An increase in the annealing temperature above 770 ° C does not lead to a further increase in the exhaust properties, but only increases the resource costs for annealing, which is impractical.

Method implementation examples

Example 1. Slabs of low-carbon steel grade 08Yu are heated in a methodical furnace to an austenitizing temperature of Т _нч = 1190 ° C and subjected to rough rolling in an austenitic state in a reversing group of stands of a semi-continuous broadband mill 1700 into a strip with an intermediate thickness of H ₀ = 20 mm. In the process of rough rolling, the temperature of the strip decreases to a value of T _cc = 900 ° C.

After rough rolling, the strip on the intermediate roller table of the rolling mill is cooled to a temperature of T _n = 740 ° C, due to which the phase transformation of austenite to ferrite proceeds in steel. Then the strip in the ferritic state is subjected to finish rolling in a continuous 6-stand group of quarto stands to a final thickness H ₁ = 0.7 mm with a total relative compression ε equal to:

$$\epsilon =\frac{H_0-H_{\mathrm{one}}}{H_0}\cdot \mathrm{one\; hundred}\%=\frac{\mathrm{twenty}-0.7}{\mathrm{twenty}}\cdot \mathrm{one\; hundred}=96.5\%$$

In the process of finish rolling, adiabatic (due to the work of deformation) heating of the strip and its controlled cooling with water in the inter-cleavage spaces occur. The temperature in the last finishing pass is maintained equal to T _kn = 660 ° C.

The rolled strip is cooled on a discharge roller table and on a coiler to a temperature of T _cm = 570 ° C, after which it is rolled up. The coiled coil is subsequently cooled in air, etched and trained.

Example 2. All the same operations as in example 1, only cooling of the first N = 6 internal and last N = 6 external turns of the roll lead to a temperature of T _smk = 620 ° C, which is ΔT = T _smk -T _cm = 620 ° C-570 ° C = 50 ° C exceeds the temperature at which the middle part of the strip is wound.

Example 3. All the same operations as in example 1, only the hot-rolled coil is additionally loaded into the charging bell furnace and recrystallization annealing of the strip at a temperature of T _about = 685 ° C.

Implementation options of the proposed method and indicators of their effectiveness are shown in the table.

From the data presented in the table, it follows that when implementing the claimed method (options No. 2-4, No. 7-9, No. 12-14), an increase in the exhaust properties of thin hot-rolled sheet steel is achieved: according to the set of mechanical properties, thin hot-rolled sheet corresponds to the category “Especially high drawing” (OSV), GOST 9045, and can be used instead of cold-rolled annealed sheet steel for the manufacture of stamping products.

With exorbitant values of the declared parameters (options No. 1, No. 5, No. 6, No. 10, No. 11, No. 15), as well as the implementation of the known method (option No. 16, [3]), there is a deterioration in the exhaust properties of hot-rolled sheet steel.

The technical and economic advantages of the proposed method consist in the fact that the hot finish rolling of the strips in the region of ferrite existence under regulated temperature-deformation conditions makes it possible to obtain thin hot-rolled sheet steel with enhanced exhaust properties. This, in turn, allows the use of hot-rolled pickled steel for stamping instead of cold rolled.

Table. Production Modes and Properties of Hot Rolled Sheet Steel 0.7 mm Thick No. p / p Production Modes Characteristics of exhaust properties T _low , ° C T _cd , ° C T _n , ° C ε,% T _kp , ° C T _cm , ° C N pcs ΔT, ° C T _o , ° C σ _t , MPa δ ₄ ,% E mm The proportion of component {111},% According to example 1 one. 1300 1000 770 49.0 760 750 - - - 210 28-30 9.31 25-35 2. 1290 800 750 50,0 620 740 190 36-37 11.5 85-88 3. 1190 900 740 96.5 660 570 180 37-38 12.0 90-93 four. 1100 850 750 85,4 620 400 195 36-38 11.9 85-89 5. 1050 790 720 87.9 610 390 230 29-32 9.9 22-43 According to example 2 6. 1300 1000 760 49.0 760 750 2 29th - 220 28-31 9,4 16-23 7. 1250 850 750 50,0 750 740 3 thirty 180 38 11.9 89 8. 1180 910 740 96.5 630 570 6 fifty 180 37 12.0 93 9. 1110 860 750 85,4 620 400 10 70 180 37 11.9 89 10. 1050 790 710 87.9 610 390 12 80 200 19-20 9.6 20-42 For example3 eleven. 1300 850 750 86.6 650 600 - - 590 220 32 10.0 24 12. 1210 870 730 50,2 630 740 600 180 39 12.0 89 13. 1230 800 740 75.7 620 500 685 180 39 12.0 94 fourteen. 1290 820 750 95.2 620 400 770 180 39 12.0 89 fifteen. 1200 790 740 96.5 610 390 780 210 32 10.1 41 16 1200 not regl. not regl. 40,0 870 620 - - - 280 14-23 7.5 20-36

From the data presented in the table, it follows that when implementing the claimed method (options No. 2-4, No. 7-9, No. 12-14), an increase in the exhaust properties of thin hot-rolled sheet steel is achieved: according to the set of mechanical properties, thin hot-rolled sheet corresponds to the category “Especially high drawing” (OSV), GOST 9045, and can be used instead of cold-rolled annealed sheet steel for the manufacture of stamping products.

With exorbitant values of the declared parameters (options No. 1, No. 5, No. 6, No. 10, No. 11, No. 15), as well as the implementation of the known method (option No. 16, [3]), there is a deterioration in the exhaust properties of hot-rolled sheet steel.

The technical and economic advantages of the proposed method consist in the fact that hot finish rolling of the strips in the region of ferrite existence under regulated temperature-deformation conditions makes it possible to obtain thin hot-rolled sheet steel with enhanced exhaust properties. This, in turn, allows the use of hot-rolled pickled sheet metal. for stamping instead of cold rolled.

In addition to increasing the exhaust properties, when implementing the proposed method, a side effect was obtained, which was expressed in a decrease in the hot wear of the work rolls of the finishing group, which is due to the lower temperature of the strip rolled in the ferrite region.

As a basic object in assessing the technical and economic efficiency of the proposed invention adopted the known technology [3]. Using the proposed invention provides an increase in the profitability of the production of thin hot rolled sheet steel by 40-50%.

Literature

1. Frantsenyuk I.V., Frantsenyuk L.I. Modern technologies for the production of metal at the Novo-Lipetsk Metallurgical Plant. - M., "Academic Book", 2003, p.52-53.

2. RF patent No. 2060847, IPC B21B 1/22, 1996.

3. RF patent No. 2288281, IPC C21D 8/04, C21D 9/48, 2006.

Claims (3)

1. A method for the production of hot-rolled low-carbon and ultra-low-carbon sheet steel with a thickness of not more than 1.0 mm, including heating slabs to austenitizing temperature, multi-pass rough rolling of strips, finishing rolling and winding into coils, characterized in that the rough rolling is carried out in the temperature range 1290-800 ° C, after which the strips are podstyzhut and subjected to finish rolling in the temperature range of 620-750 ° C with a total relative compression of at least 50%, and the winding of the strips in rolls is carried out at a temperature of 400-740 ° C. 2. The method according to claim 1, characterized in that 3-10 of the external and internal turns of the coils are wound at a temperature of 30-70 ° C higher than that of the average turns. 3. The method according to claim 1, characterized in that the hot-rolled strip is additionally subjected to recrystallization annealing at a temperature of 600-770 ° C.