A method for reducing the anisotropy of the r value of 439 cold-rolled sheet material

Abstract

The invention relates to a production method for reducing the anisotropy of the r value of a 439 cold-rolled plate material. The production process comprises smelting, casting, billet heating, hot rolling, hot rolling annealing, hot rolling pickling, cold rolling, cold rolling annealing, and cold rolling pickling; the annealing temperature of the hot rolling annealing is ≤900°C, and the annealing time is 1-4 minutes; the annealing temperature of the cold rolling annealing is 950-1030°C, and the annealing time is 1-4 minutes; the r value of the produced 439 cold-rolled plate steel strip in the 45° direction is increased by about 50% (increased from 1.1 to more than 1.6), and the Δr values ​​in the three directions of 0°, 45° and 90° are within 0.3, so that the anisotropy of the material is effectively reduced, the problem of cracking along the 45° direction during the material stamping process is improved, and the deep drawing forming performance of the material is improved.

Description

Technical Field

[0001] The invention relates to the technical field of metal processing, and in particular to a method for reducing the anisotropy of the r value of a 439 cold-rolled sheet material. Background Art

[0002] With the rapid development of the automobile industry, the sales volume of automobiles has increased year by year, and the consumption of stainless steel for automobile exhaust pipes has also gradually increased. As automobile exhaust emission standards become more and more stringent, the requirements for the stamping performance of materials are getting higher and higher, and the processing technology of stainless steel strips used to manufacture automobile exhaust pipes is becoming more and more complicated. In order to meet the complex processing technology of automobile exhaust pipe materials, the r value of the material is generally required to be as high as possible. The r value of the material can be improved by increasing the cold rolling reduction or cold rolling double rolling double annealing process, but there is a problem of large anisotropy of the r value of the material.

[0003] 439 material is mainly used to produce automobile exhaust pipe parts. The traditional production process of 439 material is: steelmaking - hot rolling - hot rolling annealing and pickling - cold rolling - cold rolling annealing and pickling. In the above production process, in order to make the 439 material have good surface quality and performance, high temperature and short time continuous annealing (annealing temperature is above 1000℃) is generally used for hot rolled plate annealing to eliminate the banded structure inside the material and make its structure grow to equiaxed crystal, and then cold rolling, annealing and pickling are carried out. The r value of the 439 material obtained by the above production process is generally the largest in the 90° direction, in the middle in the 0° direction, and the smallest in the 45° direction. The r value difference in the three directions, i.e., the Δr value, is generally between 0.8 and 1.5 (the calculation formula for Δr is: Δr = (r0° + r90° - 2 × r45°) / 2, where r0° is the r value in the 0° direction, r90° is the r value in the 90° direction, and r45° is the r value in the 45° direction). The r values ​​in the three directions are quite different, among which the r value in the 45° direction is the smallest. Therefore, during the stamping and forming process of the material, deformation often occurs along the 45° direction, leading to cracking. Summary of the invention

[0004] The present invention provides a method for reducing the anisotropy of the r value of a 439 cold-rolled plate material. The hot-rolled plate is subjected to short-time continuous annealing and pickling at a medium-low temperature, and then cold-rolled, annealed and pickled. The r value of the produced 439 cold-rolled plate steel strip in the 45° direction is increased by about 50% (from 1.1 to above 1.6), and the Δr values ​​in the three directions of 0°, 45° and 90° are within 0.3, thereby effectively reducing the anisotropy of the material, improving the problem of cracking along the 45° direction during the material stamping process, and improving the deep drawing forming performance of the material. Compared with the traditional production process, the plate surface texture of the produced cold-rolled 2B / 2D material has no obvious difference.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A production method for reducing the anisotropy of the r value of 439 cold-rolled sheet material, the production process includes smelting, casting, billet heating, hot rolling, hot rolling annealing, hot rolling pickling, cold rolling, cold rolling annealing, cold rolling pickling; the obtained product is a 439 stainless steel strip product with a 2B / 2D surface; wherein:

[0007] The hot rolling annealing process is: annealing temperature ≤ 900°C, annealing time 1 to 4 minutes, and annealing time is inversely proportional to annealing temperature and proportional to plate thickness; immediately water-cooling to room temperature after hot rolling annealing; grains of steel strip after hot rolling annealing are not fully grown;

[0008] The cold rolling annealing process is as follows: the annealing temperature is 950-1030°C, and the annealing time is 1-4 minutes; and the annealing time is inversely proportional to the annealing temperature and proportional to the thickness of the plate; after cold rolling annealing, the steel strip is immediately water-cooled to room temperature; the grain size level of the steel strip after cold rolling annealing is controlled at 6.0-8.0 levels.

[0009] Furthermore, the production process specifically includes the following steps:

[0010] 1) Molten steel is smelted and continuously cast to obtain a steel billet that meets the composition requirements;

[0011] 2) After the surface of the steel billet is ground, it is heated in a hot rolling heating furnace;

[0012] 3) The steel billet coming out of the hot rolling heating furnace is subjected to high-pressure water spraying for dephosphorization, rough rolling for at least 5 passes, and finish rolling for at least 7 passes, and then coiled to obtain hot-rolled black steel coil;

[0013] 4) The black steel coil is subjected to hot rolling annealing and hot rolling pickling to obtain a white steel coil;

[0014] 5) The white steel coil is rolled by a twenty-roll mill in multiple passes to obtain a hard plate steel coil;

[0015] 6) The hard plate steel coil is subjected to cold rolling annealing, electrolysis, cold rolling pickling, quenching and tempering rolling to obtain a 439 stainless steel strip product with a 2B / 2D surface.

[0016] Furthermore, in the step 2), the temperature of the steel billet entering the hot rolling heating furnace is ≥150°C.

[0017] Furthermore, in the step 3), the time of the steel billet in the furnace is ≥180 min, and the furnace temperature is controlled at 1130-1160°C.

[0018] Furthermore, in the step 3), the finishing rolling temperature is controlled at above 850°C, and the coiling temperature is controlled at below 700°C.

[0019] Furthermore, in step 4), the TV value of the annealing furnace is 100 to 200 mm. 2 / min.

[0020] Furthermore, in step 6), the TV value of the annealing furnace is 50 to 70 mm. 2 / min.

[0021] Furthermore, the chemical composition of the 439 cold-rolled sheet meets the 439 steel grade composition in the ASTM A240 standard.

[0022] Furthermore, the 439 stainless steel strip product with the 2B / 2D surface has an r value of greater than 1.6 in the 45° direction, and Δr values ​​in the 0°, 90°, and 45° directions are within 0.3.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) The hot-rolled plate is subjected to short-term continuous annealing and pickling at a medium-low temperature, and then cold-rolled, annealed, and pickled. During the continuous annealing and pickling of the hot-rolled plate, the annealing temperature is controlled below 900°C, and the annealing time is controlled within 1 to 4 minutes. The higher the temperature and the thinner the plate thickness, the shorter the annealing time. The hot-rolled plate obtained by the annealing process is in a semi-annealed state. The metallographic observation shows that the internal banded structure has not been eliminated and the grains have not grown completely. Then the hot-rolled plate is subjected to cold rolling, annealing, and pickling to obtain a 2B / 2D material. The grain size of the cold-rolled annealed plate is 6.0 to 8.0.

[0025] 2) The r value of the produced 439 cold-rolled steel strip in the 45° direction is increased by about 50% (from 1.1 to above 1.6), and the Δr values ​​in the 0°, 45° and 90° directions are within 0.3, which effectively reduces the anisotropy of the material, improves the problem of cracking along the 45° direction during the material stamping process, and improves the deep drawing performance of the material;

[0026] 3) Compared with the traditional production process, there is no obvious difference in the plate surface texture of the cold-rolled 2B / 2D material produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a steelmaking process flow chart described in an embodiment of the present invention.

[0028] Figure 2 It is a hot rolling process flow chart described in an embodiment of the present invention.

[0029] Figure 3 It is a process flow chart of hot rolling annealing and pickling according to an embodiment of the present invention.

[0030] Figure 4 It is a flow chart of the cold rolling process described in an embodiment of the present invention.

[0031] Figure 5 It is a process flow chart of cold rolling annealing and pickling according to an embodiment of the present invention.

[0032] In the figure: A. Alloy iron B. Scrap steel C. Stainless steel slab D. Black steel coil E. White steel coil F. Hard plate steel coil G. Stainless steel strip with 2B / 2D surface 1-1. Electric furnace 1-2. Converter 1-3. Ladle refining furnace 1-4. Vacuum refining furnace 1-5. Slab continuous casting machine 2-1. Heating furnace 2-2. Roughing mill 2-3. Finishing mill 2-4. Coiler 3-1. Uncoiler 3-2. Furnace area 3-3. Rust crusher 3-4. Sandblaster 3-5. Pickling area 3-6. Coiler 4-1. Uncoiler 4-2. Reciprocating multi-pass rolling mill 4-3. Coiler 5-1. Uncoiler 5-2. Furnace area 5-3. Neutral salt electrolysis area 5-4. Pickling area 5-5. Quenching and tempering rolling mill 5-6. Coiler DETAILED DESCRIPTION

[0033] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings:

[0034] The present invention discloses a production method for reducing the anisotropy of the r value of a 439 cold-rolled sheet material, wherein the production process includes smelting, casting, billet heating, hot rolling, hot rolling annealing, hot rolling pickling, cold rolling, cold rolling annealing, and cold rolling pickling; the obtained product is a 439 stainless steel strip product with a 2B / 2D surface; wherein:

[0035] The hot rolling annealing process is: annealing temperature ≤ 900°C, annealing time 1 to 4 minutes, and annealing time is inversely proportional to annealing temperature and proportional to plate thickness; immediately water-cooling to room temperature after hot rolling annealing; grains of steel strip after hot rolling annealing are not fully grown;

[0036] The cold rolling annealing process is as follows: the annealing temperature is 950-1030°C, and the annealing time is 1-4 minutes; and the annealing time is inversely proportional to the annealing temperature and proportional to the thickness of the plate; after cold rolling annealing, the steel strip is immediately water-cooled to room temperature; the grain size level of the steel strip after cold rolling annealing is controlled at 6.0-8.0 levels.

[0037] Furthermore, the production process specifically includes the following steps:

[0038] 1) Molten steel is smelted and continuously cast to obtain a steel billet that meets the composition requirements;

[0039] 2) After the surface of the steel billet is ground, it is heated in a hot rolling heating furnace;

[0040] 3) The steel billet coming out of the hot rolling heating furnace is subjected to high-pressure water spraying for dephosphorization, rough rolling for at least 5 passes, and finish rolling for at least 7 passes, and then coiled to obtain hot-rolled black steel coil;

[0041] 4) The black steel coil is subjected to hot rolling annealing and hot rolling pickling to obtain a white steel coil;

[0042] 5) The white steel coil is rolled by a twenty-roll mill in multiple passes to obtain a hard plate steel coil;

[0043] 6) The hard plate steel coil is subjected to cold rolling annealing, electrolysis, cold rolling pickling, quenching and tempering rolling to obtain a 439 stainless steel strip product with a 2B / 2D surface.

[0044] Furthermore, in the step 2), the temperature of the steel billet entering the hot rolling heating furnace is ≥150°C.

[0045] Furthermore, in the step 3), the time of the steel billet in the furnace is ≥180 min, and the furnace temperature is controlled at 1130-1160°C.

[0046] Furthermore, in the step 3), the finishing rolling temperature is controlled at above 850°C, and the coiling temperature is controlled at below 700°C.

[0047] Furthermore, in step 4), the TV value of the annealing furnace is 100 to 200 mm. 2 / min.

[0048] Furthermore, in step 6), the TV value of the annealing furnace is 50 to 70 mm. 2 / min.

[0049] Furthermore, the chemical composition of the 439 cold-rolled sheet meets the 439 steel grade composition in the ASTM A240 standard.

[0050] Furthermore, the 439 stainless steel strip product with the 2B / 2D surface has an r value of greater than 1.6 in the 45° direction, and Δr values ​​in the 0°, 90°, and 45° directions are within 0.3.

[0051] The 439 cold-rolled sheet material produced by the traditional process has a high proportion of processing cracks along the 45° direction during stamping. In view of the above problem, the present invention adjusts the sheet annealing process to achieve the following effects:

[0052] 1) The r value of 439 cold-rolled sheet material in the 45° direction was increased from the original 1.1 to above 1.6, which reduced the anisotropy of the material and increased the rm value of the material. The rm value = (r0° + r90° + 2×r45°) / 4.

[0053] 2) The deep drawing performance of the material is improved, and the defect rate of cracking along the 45° direction during stamping due to the low r value in the 45° direction during downstream processing is reduced.

[0054] The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0055] [Example]

[0056] In this embodiment, the composition of the produced 439 / 2B material meets the composition requirements of 439 steel grade in the ASTM A240 standard.

[0057] The specific implementation of this embodiment is further described below in conjunction with the accompanying drawings:

[0058] like Figure 1 As shown, in this embodiment, alloy iron A and scrap steel B are used as raw materials, which are first smelted through an electric furnace 1-1 and a converter 1-2, and then refined through a ladle refining furnace 1-3 or a vacuum refining furnace 1-4, and then continuously casted by a slab continuous casting machine 1-5 to obtain a stainless steel slab C.

[0059] like Figure 2 As shown, the stainless steel slab C is heated by a heating furnace 2-1, and then rough-rolled by a rough rolling mill 2-2, and fine-rolled by a fine rolling mill 2-3, and coiled by a coiler 2-4 to obtain a black steel coil D.

[0060] like Figure 3 As shown, after the black steel coil D is unwound by the unwinder 3-1, it is first subjected to heating annealing in the furnace area 3-2, rust crushing in the rust crusher 3-3, sandblasting in the sandblasting machine 3-4, and pickling in the pickling area 3-5, and then is rewound by the rewinder 3-6 to obtain the white steel coil E.

[0061] like Figure 4 As shown, the white steel coil E is uncoiled by the uncoiler 4-1, continuously rolled by the reciprocating multi-pass rolling mill 4-2, and then rolled by the coiler 4-3 to obtain the hard plate steel coil F.

[0062] like Figure 5 As shown, after the hard plate steel coil F is unwound by the unwinder 5-1, it is first heated and annealed in the furnace area 5-2, electrolyzed in the neutral salt electrolysis area 5-3, pickled in the pickling area 5-4, and tempered and rolled in the tempering rolling mill 5-5, and then coiled by the coiler 5-6 to obtain the stainless steel strip G with a 2B / 2D surface.

[0063] In this embodiment, the finishing rolling temperature of the hot rolling process is controlled at above 850°C, and the coiling temperature is controlled at below 700°C; the process of annealing the black steel coil (hot rolling annealing) is specifically: the annealing temperature is ≤900°C, the annealing time t is controlled at 1 to 4 minutes, and the annealing furnace TV value (annealing furnace TV value = steel strip thickness T × steel strip running speed V, the unit of steel strip thickness T is mm, and the unit of steel strip running speed V is mm / min) is 100 to 200 mm.2 / min, and then immediately water-cooled to room temperature. The specific process of annealing (cold rolling annealing) of hardened plate steel coils is: rapidly heating from room temperature to 950-1030°C, the heating time is 1-4 minutes, and the annealing furnace TV value is 50-70mm 2 / min, and then immediately water-cooled to room temperature. During hot rolling annealing and cold rolling annealing, the annealing time is inversely proportional to the annealing temperature and directly proportional to the thickness of the plate.

[0064] The specific process parameters are shown in Table 1:

[0065]

[0066] The 2B surface 439 cold-rolled stainless steel strip products produced in Examples 1 to 10 have an r-value anisotropy of less than 0.3, and their anisotropy is less than that of Control Examples 11 and 12, as shown in Table 2.

[0067] Table 2

[0068]

[0069]

[0070] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A production method for reducing the anisotropy of the r value of 439 cold-rolled sheet material, It is characterized in that The production process includes smelting, casting, billet heating, hot rolling, hot rolling annealing, hot rolling pickling, cold rolling, cold rolling annealing, cold rolling pickling; the obtained product is a 439 stainless steel strip product with a 2B / 2D surface; the chemical composition of the 439 cold-rolled sheet material conforms to the 439 steel grade composition in the ASTM A240 standard; the 439 stainless steel strip product with a 2B / 2D surface has an r value of 2.01 in the 45° direction, and a ∆r value of -0.03 in the 0°, 90°, and 45° directions; The production process specifically includes the following steps: 1) The molten steel is smelted and continuously cast to obtain a steel billet that meets the composition requirements; 2) After the surface of the steel billet is ground, it is heated in the hot rolling heating furnace; the temperature of the steel billet entering the hot rolling heating furnace is ≥150℃; the time of the steel billet in the furnace is ≥180min, and the temperature out of the furnace is controlled at 1130~1160℃; 3) The steel billet coming out of the hot rolling heating furnace is dephosphorized by high-pressure water spraying, rough rolled for at least 5 passes, finished rolled for at least 7 passes, and coiled to obtain hot-rolled black steel coil; the finishing rolling temperature is controlled at above 850℃, and the coiling temperature is controlled below 700℃; 4) The black steel coil is hot-rolled annealed and hot-rolled pickled to obtain a white steel coil; the hot-rolled annealing process is: the annealing temperature is 881°C, and the annealing furnace TV value is 100-200mm 2 / min; annealing time is 1.5min; water cooling to room temperature immediately after hot rolling annealing; grains of the steel strip after hot rolling annealing have not grown completely; 5) The white steel coil is rolled by a twenty-roll mill in multiple passes to obtain a hard plate steel coil; 6) The hardened plate steel coil is subjected to cold rolling annealing, electrolysis, cold rolling pickling, quenching and tempering rolling to obtain a 439 stainless steel strip product with a 2B / 2D surface; the cold rolling annealing process is: the annealing temperature is 974°C, and the annealing furnace TV value is 50-70 mm 2 / min; annealing time is 2.1min; cold rolling annealing is immediately cooled to room temperature; the grain size of the steel strip after cold rolling annealing is controlled at 6.0 to 8.0.

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