CN110819877A - A method for producing decorative ultra-pure ferritic stainless steel by using a furnace coil mill - Google Patents

Abstract

The invention discloses a method for producing decorative ultra-pure ferritic stainless steel by using a furnace coil mill, which belongs to the field of stainless steel production and solves the problem of surface plate grain defects existing in the furnace coil mill rolling ultra-pure ferritic stainless steel. The invention comprises the following steps: smelting, continuous casting; grinding; heating in a heating furnace; hot rolling rough rolling; hot rolling finishing rolling; According to the characteristics of the furnace coil rolling mill, the invention adopts reasonable rolling temperature, rolling schedule and appropriately low thermal annealing temperature to eliminate the oriented grain clusters in the microstructure of the traditional cold-rolled product, and obtain the microstructure with randomly dispersed grain orientation. , and then effectively eliminate the defects of the macro surface of the cold-rolled 2B product along the rolling direction, and ensure that the product is qualified after grinding and wire drawing.

Description

A method for producing decorative ultra-pure ferritic stainless steel by using a furnace coil mill

technical field

The invention belongs to the field of stainless steel production, and in particular relates to a method for producing decorative ultra-pure ferritic stainless steel by using a furnace rolling mill.

Background technique

Ultra-pure ferritic stainless steel SUS443J1 has excellent corrosion resistance due to its extremely low C and N content, and the addition of a certain amount of stable elements Ti and Nb; its composition does not contain precious metal Ni, which greatly reduces its production cost. SUS443J1 is widely used in the field of architectural decoration for its economy and high corrosion resistance. In the field of decoration, the requirements for product surface defects are very strict. When there are defects on the surface that cannot be processed by wire drawing or require multiple wire drawing treatments, the promotion and use of products will be limited. The furnace coil rolling mill has heating furnaces on both sides of the reversing rolling mill, which can keep the slabs warm during the reciprocating rolling of the slabs. This feature is especially suitable for rolling stainless steel that is prone to edge cracks. In addition, the furnace coil mill also has the advantages of low investment and small footprint. However, the rolling speed of the furnace coil mill is slow, the high temperature residence time of the strip is long, and the thermal deformation energy storage is low. For the ferritic stainless steel with high chromium content, the final cold-rolled product is prone to "wrinkling", which is macroscopically manifested along the rolling direction. The strip-shaped plate grain defects, and such plate grain defects need multiple times of wire drawing to eliminate, which seriously affects the use of downstream customers.

At present, the production method of decorative stainless steel mainly achieves the purpose of good surface through the adjustment of steelmaking composition and cold rolling process. The effect of the "wrinkle" defect of rolled high-chromium ferritic stainless steels on decorative applications has not been considered. Therefore, the production process involved in the present invention is mainly to improve the "wrinkle" defect of the SUS443J1 ultra-pure ferritic stainless steel rolled by the furnace coil mill, thereby improving the grinding performance of the SUS443J1 ultra-pure ferritic stainless steel.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for producing decorative ultra-pure ferritic stainless steel by using a furnace coil mill, so as to solve the problem of surface plate grain defects existing in the furnace coil mill rolling SUS443J1 ultra-pure ferritic stainless steel.

In order to solve the above problems, the technical scheme adopted in the present invention is: a method for producing decorative ultra-pure ferritic stainless steel by using a furnace coil rolling mill, comprising the following steps:

A. Smelting and continuous casting slabs according to the conventional process of VOD-LF refining furnace;

B, carrying out full grinding treatment to the slab obtained in step A;

C, the slab after the grinding obtained in step B is heated to 750～800 ℃ in the preheating furnace, then enters the heating furnace and continues to be heated to 1160～1200 ℃, and the heating time is 210～240min;

D. The heated slab obtained in step C is rolled into an intermediate slab by 7 passes of rough rolling, and the rolling speed of the last pass is controlled at ≤ 2.5m/min, and the first two passes and the last two passes are rough rolling entrances Increase high-pressure water descaling, increase the swing residence time of the intermediate billet after rough rolling, swing 10~15s, the purpose is to further reduce the finishing rolling temperature;

E, carry out 7 passes of furnace rolling mill rolling on the intermediate billet obtained in step D after rough rolling, finish rolling opening temperature≤930 ℃, finish rolling temperature≤830 ℃, rolling into black coil;

F, the black coil after the finishing rolling obtained in step E is coiled, and the coiling temperature is 550～650 ℃, making SUS443J1 hot-rolled black coil;

G. The hot-rolled black coil obtained in step F is rolled by a six-high rolling mill, and the rolling reduction rate is 15-25%, and then the hot-rolled black coil is annealed and pickled in a thermal annealing and pickling line, and the annealing temperature is 900-950 ° C. .1 Products;

H, the No.1 product obtained in step G is rolled to the target thickness in a twenty-high cold rolling mill to make a hard-rolled product;

1, with step H gained rolling hard state product in cold annealing pickling line annealing and pickling, make 2D product;

J, the 2D product obtained in step 1 is smoothed and polished to improve the shape of the plate, and the final 2B cold-rolled product is made.

As a further improvement of the present invention, in step A, the slab composition is: C: ≤ 0.015%, Si: ≤ 0.40%, Mn: ≤ 0.40%, P: ≤ 0.030%, S: ≤ 0.0030%, Ni : ≤0.30%, Cr: 20.50~22.00%, Cu: 0.30~0.50%, Nb: 0.10~0.16%, Ti: 0.12~0.30%, N: ≤0.015%, the balance is Fe and residual elements.

As a further improvement of the present invention, in step A, the thickness of the slab is 220 mm, the width is 1250 mm, and the length is 8000-9000 mm.

As a further improvement of the present invention, in step B, the full grinding treatment is carried out with a 16# grinding wheel for two times, the grinding depth is 2.0~2.5mm, and then a 20# grinding wheel is used for grinding again, and the grinding depth is 0.5~ 1.0mm.

As a further improvement of the present invention, in step D, the thickness of the intermediate blank is 28-31 mm.

As a further improvement of the present invention, in step G, the pickling is pre-pickled with sulfuric acid, and then pickled with a mixed acid of nitric acid and hydrofluoric acid.

Compared with the prior art, the present invention has the following advantages:

1. Aiming at the characteristics of the furnace coil rolling mill, the present invention adopts reasonable rolling temperature, rolling schedule and appropriately low thermal annealing temperature to eliminate the oriented grain clusters in the microstructure of the traditional cold-rolled products, and obtain the random dispersion distribution of grain orientation. The microstructure of the cold-rolled 2B product can be effectively eliminated along the rolling direction of the plate grain defect of the cold-rolled 2B product, so as to ensure that the product is qualified after grinding and wire drawing;

2. In the present invention, high-pressure water is added to remove phosphorus in the first two passes and the last two passes of rough rolling, the rolling speed of the last pass of rough rolling is controlled to be ≤2.5m/min, and the swing residence time of the intermediate billet after rough rolling is increased. The measures delay the rolling rhythm, reduce the finishing rolling temperature, and no sticking defect occurs in the rough rolling stage;

3. The finishing rolling temperature of the present invention is ≤930°C, and the final rolling temperature is ≤830°C, which is 30-50°C lower than the conventional process, and no sticking defect occurs; the grain deformation coordination ability of different orientations is different. When the grain clusters of the same orientation lead to the inconsistency of deformation, thin linear wrinkles are generated on the surface of the steel sheet. The low finishing temperature of the present invention can weaken the grain clusters of the cold-rolled and annealed sheet, and eliminate the inconsistency of grain deformation caused by different orientations. The surface of the cold-rolled 2B product caused by the uniformity is along the rolling direction of the plate grain defect;

4. The present invention increases the six-high mill rolling of the hot-rolled black coil. After the six-high mill rolling, the deformation energy storage of the strip is increased, the recrystallization degree of the hot-rolled sheet is promoted, the grain clusters of the cold-rolled and annealed sheet are weakened, and the cold-rolled and annealed sheet is eliminated. The surface of the rolled 2B product has grain defects along the rolling direction;

5. The thermal annealing temperature of the present invention is 900~950°C, which is 30~50°C lower than that of the conventional process. Under the condition of ensuring complete recrystallization, the appropriately low annealing temperature can refine the crystal grain of the No.1 product and weaken the cold-rolled annealed sheet. The grain clusters are eliminated, and the surface grain defects along the rolling direction of the cold-rolled 2B product are eliminated.

Description of drawings

Figure 1 is a macro photo of a SUS443J1 cold-rolled 2B product produced by a conventional process;

Fig. 2 is the macro photo of SUS443J1 cold-rolled 2B product produced in Example 1 of the present invention;

Fig. 3 is the grain orientation distribution diagram of SUS443J1 cold-rolled 2B product produced by conventional process;

FIG. 4 is a grain orientation distribution diagram of a SUS443J1 cold-rolled 2B product produced in Example 1 of the present invention.

Detailed ways

The following examples may further illustrate the present invention, but do not limit the present invention in any form.

Because the furnace coil mill has the advantages of less investment, small footprint, and better effect on improving edge cracking, some steel mills use the furnace coil mill for the hot rolling process. However, the rolling speed of the furnace coil mill is slow, the high temperature residence time of the strip is long, and the thermal deformation energy storage is low. For the ferritic stainless steel with high chromium content, the final cold-rolled product is prone to "wrinkling", which is macroscopically manifested along the rolling direction. stripe defects. The hot rolling equipment used by the applicant is a furnace coil rolling mill. The applicant has developed a method for producing decorative ultra-pure ferritic stainless steel by using a furnace coil rolling mill through continuous process adjustment according to the characteristics of the equipment itself, eliminating the need for SUS443J1 Slab defects on the surface of cold-rolled finished products.

Embodiment 1. A method for producing decorative ultra-pure ferritic stainless steel using a furnace coil mill is characterized by comprising the following steps:

A. Smelting and continuous casting: smelting and continuous casting of SUS443J1 slab according to the conventional process of VOD-LF refining furnace, its specifications are: 220mm (thickness) × 1250mm (width) × 9000mm (length), and its composition mass percentage is: C: 0.015%, Si: 0.30%, Mn: 0.40%, P: 0.02%, S: 0.003%, Ni: 0.25%, Cr: 21.5%, Cu: 0.5%, Nb: 0.1%, Ti: 0.3%, N: 0.010%, the balance is Fe and residual elements;

B. Grinding: The slab obtained in step A is ground twice with a 16# grinding wheel with a grinding depth of 2.3mm, and once with a 20# grinding wheel with a grinding depth of 1.0mm;

C. Heating in the heating furnace: heating the polished slab obtained in step B to 800 °C in a preheating furnace, then entering the heating furnace and continuing to heat to 1160 °C, and the heating time is 240min;

D. Rough rolling by hot rolling: the heated slab obtained in step C is rolled into an intermediate billet by 7 passes of rough rolling, the thickness of the intermediate billet is 30 mm, and the rolling speed of the final pass is controlled at 2.5 m/min, and the first two passes High-pressure water descaling is added at the inlet of the first and last two passes of rough rolling, and the swing residence time of the intermediate billet after rough rolling is increased, and the swing is 12s;

E, hot rolling and finishing rolling: the intermediate billet after rough rolling obtained in step D is subjected to 7 passes of furnace rolling mill rolling, the finishing rolling opening temperature is 920 ° C, and the finishing rolling temperature is 830 ° C, and the rolling is 5.0mm thick black coil;

F. Hot rolling and curling: the black coil after finishing rolling obtained in step E is curled, and the curling temperature is 650° C. to make a 5.0mm thick SUS443J1 hot-rolled black coil;

G. Thermal annealing and pickling: the hot-rolled black coil obtained in step F is rolled by a six-high rolling mill, and the reduction rate is controlled at 25%. After rolling, it is annealed and pickled by a thermal annealing and pickling line. First, pre-pickling with sulfuric acid, and then pickling with mixed acid of nitric acid and hydrofluoric acid, wherein the concentration of sulfuric acid is 300g/l, the concentration of nitric acid is 80g/l, and the concentration of hydrofluoric acid is 30g/l. After rolling, annealing and pickling, No. 1 product (No.1 refers to stainless steel surface grade);

H, cold rolling: rolling the No.1 product obtained in step G into a 1.5mm specification rolled hard product in a twenty-high cold rolling mill;

1, cold annealing and pickling: the hard-rolled product obtained in step H is annealed and pickled in the cold annealing pickling line to make 2D products, and the annealing temperature is 950 ° C. The salt is sodium sulfate, the concentration is 200g/l, the mixed acid is nitric acid and hydrofluoric acid, the nitric acid concentration is 120g/l, and the hydrofluoric acid concentration is 15g/l;

J, flattening: the 2D product obtained in step 1 is flattened by a flattening machine to achieve the purpose of glazing to improve the shape of the plate, and finally make the 2B product of the 1.5mm specification without plate pattern defect on the surface.

Figure 1 is a macro photo of a SUS443J1 cold-rolled 2B product produced by a conventional process. From Figure 1, it can be seen that there are obvious striped "wrinkle" defects along the rolling direction; Figure 2 is a macro photo of a SUS443J1 cold-rolled 2B product produced in this embodiment. Photo, it can be seen from Figure 2 that the surface is smooth and flat, and there is no stripe "wrinkle" defect. Fig. 3 is the grain orientation distribution diagram of SUS443J1 cold-rolled 2B product produced by conventional process. It can be seen from Fig. 3 that grain clusters with the same orientation are obviously aggregated, and the length is along the rolling direction; Fig. 4 is produced in this embodiment. The grain orientation distribution diagram of SUS443J1 cold-rolled 2B product. It can be seen from Figure 4 that the grain orientation is randomly dispersed and the grain clusters are weak.

Embodiment 2. A method for producing decorative ultra-pure ferritic stainless steel by using a furnace coil mill, which is characterized by comprising the following steps:

A. Smelting and continuous casting: smelting and continuous casting of SUS443J1 slab according to the conventional process of VOD-LF refining furnace, its specifications are: 220mm (thickness) × 1250mm (width) × 8000mm (length), and its composition mass percentage is: C: 0.010%, Si: 0.40%, Mn: 0.30%, P: 0.03%, S: 0.002%, Ni: 0.3%, Cr: 22.0%, Cu: 0.3%, Nb: 0.16%, Ti: 0.12%, N: 0.015%, the balance is Fe and residual elements;

B. Grinding: The slab obtained in step A is ground twice with a 16# grinding wheel with a grinding depth of 2.5mm, and a 20# grinding wheel with a grinding depth of 0.5mm;

C. Heating in the heating furnace: heating the polished slab obtained in step B to 750°C in a preheating furnace, and then entering the heating furnace to continue heating to 1200°C, and the heating time is 210min;

D. Rough rolling by hot rolling: the heated slab obtained in step C is rolled into an intermediate billet by 7 passes of rough rolling, the thickness of the intermediate billet is 31 mm, the rolling speed of the final pass is controlled at 2.5 m/min, and the first two passes The first and last two passes of rough rolling are added with high-pressure water for descaling, and after rough rolling, the swing residence time of the intermediate billet is increased, and the swing is 10s;

E, hot rolling and finishing rolling: the intermediate billet after rough rolling obtained in step D is subjected to 7 passes of furnace rolling mill rolling, the finishing rolling opening temperature is 930 ° C, and the final rolling temperature is 830 ° C, and the rolling is 4.75mm thick black coil;

F, hot rolling and curling: the black coil after finishing rolling obtained in step E is curled, and the curling temperature is 550 ° C to make 4.75mm thickness SUS443J1 hot-rolled black coil;

G. Thermal annealing and pickling: the hot-rolled black coil obtained in step F is rolled by a six-high rolling mill, and the reduction rate is controlled at 22%. After rolling, it is annealed and pickled by a thermal annealing and pickling line. First, pre-pickling with sulfuric acid, and then pickling with nitric acid and hydrofluoric acid mixed acid, wherein the concentration of sulfuric acid is 310g/l, the concentration of nitric acid is 90g/l, and the concentration of hydrofluoric acid is 35g/l. After rolling, annealing and pickling, No. 1 product;

H, cold rolling: rolling the No.1 product obtained in step G into a 1.2mm specification rolled hard product in a twenty-high cold rolling mill;

1, cold annealing and pickling: the hard-rolled product obtained in step H is annealed and pickled in a cold annealing pickling line to make a 2D product, and the annealing temperature is 940 ° C. The salt is sodium sulfate, the concentration is 210g/l, the mixed acid is nitric acid and hydrofluoric acid, the nitric acid concentration is 110g/l, and the hydrofluoric acid concentration is 14g/l;

J, flattening: the 2D product obtained in step 1 is flattened by a flattening machine to achieve the purpose of glazing to improve the shape of the plate, and finally make the 2B product of the 1.2mm specification without plate pattern defect on the surface.

Embodiment 3. A method for producing decorative ultra-pure ferritic stainless steel by using a furnace coil mill, which is characterized by comprising the following steps:

A. Smelting and continuous casting: smelting and continuous casting of SUS443J1 slab according to the conventional process of VOD-LF refining furnace, its specifications are: 220mm (thickness) × 1250mm (width) × 8500mm (length), and its composition mass percentage is: 0.012%, Si: 0.35%, Mn: 0.20%, P: 0.01%, S: 0.002%, Ni: 0.15%, Cr: 20.5%, Cu: 0.4%, Nb: 0.12%, Ti: 0.18%, N: 0.012%, the balance is Fe and residual elements;

B. Grinding: The slab obtained in step A is ground twice with a 16# grinding wheel with a grinding depth of 2.0mm, and once with a 20# grinding wheel with a grinding depth of 0.8mm;

C. Heating in the heating furnace: heating the polished slab obtained in step B to 780°C in a preheating furnace, and then entering the heating furnace to continue heating to 1180°C, and the heating time is 225min;

D. Rough rolling by hot rolling: the heated slab obtained in step C is rolled into an intermediate billet by 7 passes of rough rolling, the thickness of the intermediate billet is 28 mm, and the rolling speed of the final pass is controlled at 2.5 m/min, and the first two passes High-pressure water descaling is added to the inlet of the first and last two passes of rough rolling, and the swing residence time of the intermediate billet after rough rolling is increased, and the swing is 15s;

E, hot rolling and finishing rolling: the intermediate billet after rough rolling obtained in step D is subjected to 7 passes of furnace rolling mill rolling, the finishing rolling temperature is 930 ° C, and the final rolling temperature is 820 ° C, and rolled into a black coil with a thickness of 4.0mm;

F. Hot rolling and curling: the black coil after finishing rolling obtained in step E is curled, and the curling temperature is 600 ° C to make a 4.0mm thick SUS443J1 hot-rolled black coil;

G. Thermal annealing and pickling: the hot-rolled black coil obtained in step F is rolled by a six-high rolling mill, and the reduction rate is controlled at 15%. After rolling, it is annealed and pickled by a thermal annealing and pickling line. First, pre-pickling with sulfuric acid, and then pickling with nitric acid and hydrofluoric acid mixed acid, wherein the concentration of sulfuric acid is 320g/l, the concentration of nitric acid is 95g/l, and the concentration of hydrofluoric acid is 40g/l. After rolling, annealing and pickling, No. 1 product;

H, cold rolling: rolling the No.1 product obtained in step G into a 1.0mm specification rolled hard product in a cold rolling twenty-high rolling mill;

1, cold annealing and pickling: the hard-rolled product obtained in step H is annealed and pickled in a cold annealing pickling line to make a 2D product, and the annealing temperature is 930 ° C. The salt is sodium sulfate, the concentration is 220g/l, the mixed acid is nitric acid and hydrofluoric acid, the nitric acid concentration is 100g/l, and the hydrofluoric acid concentration is 16g/l;

J, flattening: the 2D product obtained in step 1 is flattened by a flattening machine to achieve the purpose of improving the shape of the plate by glazing, and finally make the 2B product of the 1.0mm specification without plate pattern defect on the surface.

Claims (6)

1. a method for producing decorative ultra-pure ferritic stainless steel using a furnace coil mill is characterized in that comprising the following steps: A. Smelting and continuous casting slabs according to the VOD-LF refining furnace process; B, carrying out full grinding treatment to the slab obtained in step A; C, the slab after the grinding obtained in step B is heated to 750～800 ℃ in the preheating furnace, then enters the heating furnace and continues to be heated to 1160～1200 ℃, and the heating time is 210～240min; D. The heated slab obtained in step C is rolled into an intermediate slab by 7 passes of rough rolling, and the rolling speed of the last pass is controlled at ≤ 2.5m/min, and the first two passes and the last two passes are rough rolling entrances Increase high-pressure water descaling, increase the swing residence time of the intermediate billet after rough rolling, swing 10~15s; E, carry out 7 passes of furnace rolling mill rolling on the intermediate billet obtained in step D after rough rolling, finish rolling opening temperature≤930 ℃, finish rolling temperature≤830 ℃, rolling into black coil; F, the black coil after the finishing rolling obtained in step E is coiled, and the coiling temperature is 550～650 ℃, making SUS443J1 hot-rolled black coil; G. The hot-rolled black coil obtained in step F is rolled by a six-high rolling mill, and the rolling reduction rate is 15-25%, and then the hot-rolled black coil is annealed and pickled in a thermal annealing and pickling line, and the annealing temperature is 900-950 ° C. .1 Products; H, the No.1 product obtained in step G is rolled to the target thickness in a twenty-high cold rolling mill to make a hard-rolled product; 1, with step H gained rolling hard state product in cold annealing pickling line annealing and pickling, make 2D product; J, the 2D product obtained in step 1 is smoothed and polished to improve the shape of the plate, and the final 2B cold-rolled product is made. 2. a method for producing decorative ultra-pure ferritic stainless steel using a furnace coil mill according to claim 1, is characterized in that: in step A, the slab composition is: C:≤0.015%, Si : ≤0.40%, Mn: ≤0.40%, P: ≤0.030%, S: ≤0.0030%, Ni: ≤0.30%, Cr: 20.50~22.00%, Cu: 0.30~0.50%, Nb: 0.10~0.16%, Ti: 0.12~0.30%, N: ≤ 0.015%, and the balance is Fe and residual elements. 3. a kind of method that adopts furnace rolling mill to produce decorative ultra-pure ferritic stainless steel according to claim 1 and 2, is characterized in that: in step A, described slab thickness is 220mm, and width is 1250mm, The length is 8000-9000mm. 4. a kind of method that adopts furnace coil rolling mill to produce decorative ultra-pure ferritic stainless steel according to claim 3, it is characterized in that: in step B, the full grinding treatment first uses 16# grinding wheel to grind twice, The grinding depth is 2.0~2.5mm, and then use the 20# grinding wheel to grind it again, and the grinding depth is 0.5~1.0mm. 5 . The method for producing decorative ultra-pure ferritic stainless steel using a furnace coil mill according to claim 4 , wherein in step D, the thickness of the intermediate blank is 28-31 mm. 6 . 6. a kind of method that adopts furnace rolling mill to produce decorative ultra-pure ferritic stainless steel according to claim 5, is characterized in that: in step G, pickling is pre-pickled with sulfuric acid first, and then with nitric acid and hydrogen Fluoric acid mixed acid pickling.

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