RU2547389C1 - Method of production of hot-rolled metal sheets - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes strips hot rolling, their cooling to winding temperature, winding, etching and temper rolling. Hot rolling is finished at 840-900°C, winding is performed considering decreasing the specific tension of the strip by maximum 30 kg/mm² at 540-620°C. Difference between temperature of rolling completion and temperature of winding completion is set to minimum 220°C, at that cross-section profile of the hot-rolled strip with convexity 0.03-0.07 mm is ensured, and temper rolling is performed with relative cross-section reduction 1.2-2.5%.

EFFECT: production of hot-rolled metal rolls with cold-rolling properties of draught categories having high accuracy of thickness and flatness, with surface roughness 1,0-1,6 mcm.

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Description

The invention relates to the field of metallurgy and can be used in the production of hot-rolled sheets for the manufacture of structures, profiles, pipes, car parts by cold stamping.

A known method for the production of hot-rolled thin-sheet steel, including hot rolling of strips, their cooling, winding and pickling with training, according to which when the carbon content in the steel is in the range of 0.01-0.10%, the temperature of the end of rolling is taken equal to 780-800 ° C, cooling until the temperature of the winding is carried out at a speed of 9-13 ° C / s, etching is carried out at 60-80 ° C, and training is carried out with a relative compression of 0.5-1.0%. (RF patent No. 2164248, C21D 8/04, C21D 9/46, publ. 02/27/2001)

The disadvantage of this method is that at the end of hot rolling in the temperature range 700-800 ° C in hot-rolled steel, a structure with a mixed grain size of ferrite of 3-9 numbers can form, which is unacceptable for further use for cold stamping, in addition, even with the maximum relative compression during training 1.0%, the maximum deviations in the thickness of the hot rolled products will not decrease enough and will not meet the requirements of GOST 19904 for cold rolled products.

, при этом горячую прокатку завершают при температуре 885-915°C, охлаждение ведут до температуры 685-715°C, а затем полосы подвергают дрессировке с обжатием 0,8-1,2%. (Патент РФ №2202630, C21D 8/04, опубл. 20.04.2003 г.)There is also known a method for the production of hot rolled strips, including the smelting of ultra-low carbon steel with impurities of sulfur and nitrogen alloyed with titanium, satisfying the ratio $$\frac{Ti}{\mathrm{four}\cdot C+3.43\cdot N+\mathrm{1,5}\cdot S}=\mathrm{one}÷\mathrm{1,5}$$

while hot rolling is completed at a temperature of 885-915 ° C, cooling is carried out to a temperature of 685-715 ° C, and then the strip is subjected to training with compression 0.8-1.2%. (RF patent No. 2202630, C21D 8/04, publ. 04/20/2003)

The disadvantage of this method is the high cost of rolling through the use of evacuation of steel containing titanium.

The closest in technical essence and the achieved result is a method for the production of hot-rolled thin-sheet steel, which includes hot rolling of strips, their cooling to a winding temperature by section scrubbing with water, winding, etching in hydrochloric acid and tempering, according to which for strips of steel with carbon content up to 0 , 1 wt.% The temperature of the end of the rolling is taken equal to 860-890 ° C, the scuffing of the strips begins 7-9 s after the end of rolling, and the temperature of the winding is taken equal to 640-700 ° C, while training los to obtain their matte surface is carried out in rolls with the height of the microroughness of barrels R _a = 2.2-2.7 microns and to obtain surface roughness with R _a = 2.9-4.0 microns. (RF patent №2255990, C21D 8/04, publ. 07/10/2005)

The disadvantage of this method is the impossibility of obtaining with its help hot rolled sheet with high demands on the quality of the strip surface. When unwinding hot-rolled strips obtained by this method on a continuous etching unit, a temper mill, and also on cutting units, it is very likely that irreparable defects in the finished strips — “kink” and “kinks” - are unacceptable when using hot-rolled steel as cold-rolled. In addition, the lack of concretization of the cross-sectional profile of a strip with normalized transverse thickness difference and convexity does not allow for flatness and maximum thickness deviations corresponding to cold-rolled products on hot-rolled products.

An object of the invention is to obtain hot-rolled sheets with properties of cold-rolled categories of VG drawing (according to GOST 9045), G and H (according to GOST 16523), having high or high precision manufacturing in thickness, high flatness in accordance with GOST 19904 and surface roughness R _a = 1.0-1.6 microns.

To solve this problem in a method for the production of hot rolled thin-sheet products, including hot rolling of strips, their cooling to a winding temperature, winding, etching and training, according to the invention, hot rolling is completed at a temperature of 840-900 ° C, the winding is carried out taking into account a decrease in the specific tension of the strip more than 30 kg / mm ² at a temperature of 540-620 ° C, and the difference between the temperature of the end of rolling and winding is set at least 220 ° C, while providing a cross-sectional profile of the hot-rolled floor wasps with a bulge of 0.03-0.07 mm, and training is carried out with a relative compression of 1.2-2.5%.

The essence of the proposed technical solution lies in the optimal combination of technological parameters of hot rolling and tempering while providing a cross-sectional profile of the hot-rolled strip, which allows to obtain hot-rolled thin-sheet rolled products of the categories VG (according to GOST 9045), G and H (according to GOST 16523), satisfying all the requirements which are presented to cold-rolled steel. This eliminates the additional operations after etching of the hot rolled strip (cold rolling and recrystallization annealing), necessary for the production of cold rolled strip, which reduces the cost of finished steel.

Currently, the trend towards the production of hot rolled thin-sheet steel, which is used as cold-rolled, continues to intensify. The cost of such a rental is 15-20% lower than that of cold rolled steel. But in the process of processing hot-rolled steel, they are faced with the problem of large maximum deviations in thickness, flatness, inadequate mechanical properties, the absence of the necessary surface roughness and the presence of surface defects that are not allowed on cold-rolled steel. So, for example, for hot-rolled products with a thickness of 2.0 mm and a width of 1000 mm in accordance with the requirements of GOST 19903, the maximum deviations in thickness with increased manufacturing accuracy are ± 0.16 mm, deviations from flatness - 10 mm for high flatness. Moreover, the surface roughness is more than 2.5 microns. For cold-rolled steel with a thickness of 2.0 mm and a width of 1000 mm in accordance with the requirements of GOST 19904, these requirements are much more stringent: the maximum deviations in thickness with increased manufacturing accuracy are not more than ± 0.13 mm, deviations from flatness - not more than 8 mm for high flatness. For rolled products used for cold stamping, the roughness should be no more than 1.6 microns.

More stringent requirements for maximum deviations in thickness and flatness are necessary to ensure the accuracy of welding, stamping, and profiling. Typically, the manufacturing accuracy indicated for cold-rolled steel is achieved through the cold rolling operation, and the level of mechanical properties inherent in cold-rolled steel, due to recrystallization annealing. In order to exclude both of these operations, it is necessary to form a metal structure with ferrite of 6-8 numbers due to a combination of temperature conditions at the end of rolling and winding to ensure mechanical properties, and due to a certain temperature difference between the end of hot rolling and winding into coils, ensure the quality surfaces of a hot-rolled strip with the absence of such defects as “kinks” and “kink”. The temperature of the end of the rolling set within 840-900 ° C and the creation of a certain strip tension during winding ensure a good cross-sectional profile of the hot-rolled strip, which, after training, almost halves the maximum deviations in thickness and flatness.

An experimental verification of the claimed invention was carried out on a continuous broadband hot rolling mill "2000" and on a continuous pickling unit, followed by training on a mill "1700". At the same time, technological parameters were varied both during hot rolling and during training.

The best results were obtained for rolled products processed with the production parameters specified in the method. Deviation from these parameters leads to a mismatch of the technical result achieved: for example, at a temperature of rolling end T _kp <840 ° C, the plastic properties deteriorate due to grinding of ferrite grains and flatness of the hot rolled strip worsens, and at a temperature of the end of rolling T _kp > 900 ° C, the strength properties decrease due to the enlargement of ferritic grain. At a winding temperature T _cm <540 ° C, an increase in the temporary resistance of more than 410 MPa occurs. On rolls wound at a winding temperature of T _cm > 620 ° C, when unwinding on a continuous pickling unit, “kinks and kinks” defects are formed that are unacceptable for using hot-rolled steel as cold-rolled. For the same reason, the difference between the temperature of the end of rolling and the temperature of the winding should be at least 220 ° C. With a decrease in the specific tension values by more than 30 kg / mm ² , an increase in the convexity of the transverse profile occurs, which leads to a decrease in flatness of rolled products and an increase in the maximum thickness deviations during training. Providing a cross-sectional profile of a hot-rolled strip with a bulge in the range of 0.03-0.07 mm allows, after training with a relative compression of 1.2-2.5%, to have flatness and extreme deviations characteristic of cold-rolled steel on the strip.

With a relative compression of E _dr <1.2%, the maximum deviations in thickness exceed the requirements of the standard, with a relative compression of E _dr > 2.5% there is an increase in roughness, an increase in the yield strength and tensile strength of more than 410 MPa, and a decrease in elongation.

Method implementation examples

Smelted steels in an oxygen converter are continuously cast into slabs. Continuous cast steel slabs are heated and hot rolled in a continuous strip mill “2000” in stripes. Hot rolled strips are subjected to hydrochloric acid etching to remove scale. Etched strips are trained at the 1700 temper mill. Implementation options of the proposed method and indicators of their effectiveness are shown in table 1.

Table 1 N mm The convexity of the transverse profile, mm T _kp , ° C T _cm , ° C T _CP -T _cm , ° C E _dr ,% Mechanical properties Limit deviations in thickness (with a width of 1000 mm), mm Surface quality indicators σ _in , MPa σ _t , MPa δ,% Spherical hole depth mm R _a , μm The presence of a kink, duct, wave 1,50 0,045 846 600 246 1.7 280 380 34.5 11.55 ± 0.06 1.05 Absent. 1,50 0,03 840 611 229 1,6 290 390 33 11.55 ± 0.06 1,5 Absent. 2.00 0.05 847 596 251 1.9 232 368 34 12,2 ± 0.08 1,2 Absent. 3.00 0,07 872 613 259 2.1 300 382 30.5 not normal. ± 0.10 1.35 Absent.

In the case of the implementation of the proposed method, mechanical properties are achieved that meet the requirements of GOST 9045 for the VG hood categories and GOST 16523 for the G, N. hood categories. The surface roughness also met the requirements of the standards. The maximum deviations in the thickness of the rolled product corresponded to the standards of high precision manufacturing. The yield of surface quality was maximum.

Thus, the pilot test confirmed the acceptability of the technical solution found to achieve the goal and its advantages over the known technology.

Claims (1)

A method for the production of hot rolled thin-sheet products, including hot rolling of steel strips, cooling them to a winding temperature, winding, pickling and tempering, characterized in that the hot rolling is completed at a temperature of 840-900 ° C, the winding is carried out with a decrease in the specific tension value of not more than 30 kg / mm ² at a temperature of 540-620 ° C and the difference between the temperature of the end of rolling and the winding temperature of at least 220 ° C, while providing a cross-sectional profile of the hot-rolled strip with a convexity of 0.03-0.07 mm, and the dressing alignment is carried out with a relative compression of 1.2-2.5%.