A method for improving the surface wave shape of parts after cold-rolled steel roll forming

Abstract

The present invention relates to a method for improving the surface wavy shape of parts after cold-rolled steel roll forming, and belongs to the technical field of steel smelting. Specifically, the method comprises the following steps: (1) sampling and analyzing parts; (2) adjusting the chemical composition of the material; and (3) adjusting process parameters. The preparation of the cold-rolled steel comprises steel smelting, continuous casting, hot rolling, pickling, annealing, leveling, and coiling. The present invention improves the mechanical properties of the material, thereby improving the surface wavy shape defects of the parts after forming, which is conducive to reducing the occurrence of surface wavy defects of the parts, improving the qualified rate of parts production, and improving the economic benefits of users.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a method for improving the surface wave shape of a part after cold-rolled steel is roll-formed. Background Art

[0002] Cold-rolled steel is produced by cold rolling, using hot-rolled steel as a base material and then rolling it below the recrystallization temperature. Cold rolling involves further thinning the steel sheet to a target thickness at room temperature. Compared to hot-rolled steel, cold-rolled steel offers superior surface quality, mechanical properties, and processability, making it widely used in industries such as automotive and home appliances. Automotive exterior panels require very high surface quality after forming. Surface defects such as wavy shapes can severely impact the appearance of parts after subsequent painting and other processes. Therefore, improving the surface wavy shape of cold-rolled steel parts is particularly important.

[0003] There are two main reasons for the wavy surface defects of parts after roll forming: (1) Improper mold parameter settings, such as pressure and clearance. (2) Inappropriate mechanical properties of the part material. Under national standards, the steel grades selected for part materials usually have a large performance range, which can lead to different surface quality of parts after roll forming even if the user purchases the same steel grade. Summary of the Invention

[0004] To address the aforementioned issues in the prior art, the present invention provides a method for improving the surface wavy appearance of cold-rolled steel parts after roll-forming. Based on the actual production process of the roll-forming die and the surface morphology of the roll-formed part, the invention adjusts the annealing temperature and flattening elongation of the steel strip to increase the material's yield strength, ensuring that the yield strength exceeds the longitudinal stress of the roll-forming process. This improves the surface morphology of the roll-formed part and ultimately determines a suitable performance range that meets user requirements. This method addresses the existing problem of wavy surface defects on roll-formed parts and improves the yield rate of part production.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for improving the surface wavy shape of a part after cold-rolled steel roll forming, comprising the following methods: (1) sampling and analyzing the part; (2) adjusting the chemical composition of the material; and (3) adjusting the process parameters.

[0007] The preparation of the cold-rolled steel includes processes such as steel smelting, continuous casting, hot rolling, pickling, annealing, skin pass, and coiling.

[0008] Preferably, the parts sampling and analysis is to perform sampling and analysis on the wavy curls of the parts of the user, and clarify that the reason for the wavy shape on the surface of the parts is that the longitudinal stress during roll forming exceeds the yield strength of the material.

[0009] Preferably, the composition of the adjusted part includes increasing the C content to 0.06% to 0.12%, the Mn content to 0.6% to 0.15%, the Nb content to 0.03% to 0.09%, controlling the Si content below 0.05%, controlling the Al content to 0.015% to 0.1%, and controlling the P and S contents below 0.025.

[0010] Preferably, the adjusted process parameters include lowering the soaking temperature to 750°C to 780°C.

[0011] Preferably, the adjusted process parameters include adjusting the flattening elongation to 1.1% to 1.2%.

[0012] Preferably, the hot rolling is as follows: slab heating temperature is 1200-1270°C, furnace time is 140-280min; seven-stand continuous rolling, rough rolling start temperature is 1050-1090°C, finishing rolling start temperature is 985-1060°C, finishing rolling final temperature is 870-920°C; after rolling, a rear-stage laminar cooling mode is adopted; U-type coiling is used, and the coiling temperature within 40 meters of the head and tail is 570-710°C, and the middle part is 540-680°C.

[0013] The pickling continuous rolling comprises: adding a pickling corrosion inhibitor with a concentration of 1‰ to 2‰ to the pickling tank 2 hours in advance, the pickling process speed is ≥100m / min, and checking at the process section exit to confirm that the steel plate surface is not over-pickled or under-pickled; five-stand continuous rolling, with a total reduction rate of 46.66% to 88.0%.

[0014] The continuous annealing is as follows: annealing speed ≤ 240 m / min, hydrogen content in the furnace 3% to 7%, oxygen content ≤ 10 ppm, furnace pressure 100 to 400 Pa; soaking temperature 750 to 780° C., slow cooling endpoint temperature 640 to 700° C., rapid cooling endpoint temperature 300 to 460° C., aging endpoint temperature 280 to 380° C., and final cooling furnace exit temperature ≤ 155° C.

[0015] The leveling is as follows: roller roughness (Ra) 2.0~4.0μm, working roller peak number (Pc) 90~100cm, leveling liquid concentration 3%, leveling elongation 1.1%~1.2%, strip surface roughness (Ra) 0.6~1.90μm. If it does not meet the requirements, the roller should be replaced online immediately.

[0016] The beneficial effects of the present invention are:

[0017] The present invention improves the mechanical properties of the material, thereby improving the wavy surface defects of the parts after forming, which is beneficial to reducing the occurrence of wavy surface defects of the parts, improving the qualified rate of parts production, and improving the economic benefits of users. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 It is a simplified schematic diagram of the roll forming process described in an embodiment of the present invention.

[0020] Figure 2 This is a physical picture of the wavy defect morphology on the surface of a cold-rolled structural steel part described in an embodiment of the present invention.

[0021] Figure 3 This is a physical picture of the surface morphology of parts after the cold-rolled structural steel process is improved as described in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0023] Example 1

[0024] A method for improving the surface wavy shape of a part after cold-rolled steel roll forming, comprising the following steps:

[0025] (1) Steel smelting

[0026] The steel composition after controlled smelting is as follows: C 0.066%, Mn 0.7%, Nb 0.031%, Si 0.02%, Al 0.036%, P 0.016%, S 0.008%, and the balance is Fe.

[0027] (2) Continuous casting

[0028] The liquid steel is rapidly solidified and crystallized, and after cooling and electromagnetic stirring, it is cut into slabs of a certain length, and the head and tail are peeled.

[0029] (3) Hot rolling

[0030] The slab heating temperature is controlled at 1210-1270°C and the furnace time is 240 minutes. The seven-stand continuous rolling is carried out, with the starting temperature of rough rolling at 1050-1090°C, the starting temperature of finishing rolling at 985-1060°C, and the final temperature of finishing rolling at 870-920°C. After rolling, the rear-section laminar cooling mode is adopted. U-type coiling is used, with the coiling temperature within 40 meters from the head to the tail at 600-670°C and 570-640°C in the middle.

[0031] (4) Pickling

[0032] A pickling corrosion inhibitor with a concentration of 1‰ to 2‰ is added to the pickling tank 2 hours in advance. The pickling process speed is ≥100m / min. An inspection at the process section exit confirms that the steel plate surface is not over-pickled or under-pickled. Five-stand continuous rolling is performed with a total reduction rate of 71.4%.

[0033] (5) Annealing

[0034] Annealing speed ≤ 240m / min, hydrogen content in the furnace 3% to 7%, oxygen content ≤ 10ppm, furnace pressure 100 to 400Pa; soaking temperature 750℃, slow cooling endpoint temperature 640 to 670℃, rapid cooling endpoint temperature 410 to 450℃, aging endpoint temperature 340 to 380℃, final cooling furnace outlet temperature ≤ 155℃.

[0035] (6) Leveling

[0036] The working roll is an ordinary roll with a roll roughness (Ra) of 3.0 μm, a working roll peak number (Pc) of 90-100 cm, a leveling liquid concentration of 3%, a leveling elongation of 1.1%, and a strip surface roughness (Ra) of 0.6-1.9 μm.

[0037] Example 2

[0038] A method for improving the surface wavy shape of a part after cold-rolled steel roll forming, comprising the following steps:

[0039] (1) Steel smelting

[0040] The composition of the steel after controlled smelting is as follows: C 0.064%, Mn 0.71%, Nb 0.029%, Si 0.02%, Al 0.036%, P 0.016%, S 0.006%, and the balance is Fe.

[0041] (2) Continuous casting

[0042] The liquid steel is rapidly solidified and crystallized, and after cooling and electromagnetic stirring, it is cut into slabs of a certain length, and the head and tail are peeled.

[0043] (3) Hot rolling

[0044] The slab heating temperature is controlled at 1210-1270°C and the furnace time is 240 minutes. The seven-stand continuous rolling is carried out, with the starting temperature of rough rolling at 1050-1090°C, the starting temperature of finishing rolling at 985-1060°C, and the final temperature of finishing rolling at 870-920°C. After rolling, the rear-section laminar cooling mode is adopted. U-type coiling is used, with the coiling temperature within 40 meters from the head to the tail at 600-670°C and 570-640°C in the middle.

[0045] (4) Pickling

[0046] A pickling corrosion inhibitor with a concentration of 1‰ to 2‰ is added to the pickling tank 2 hours in advance. The pickling process speed is ≥100m / min. An inspection at the process section exit confirms that the steel plate surface is not over-pickled or under-pickled. Five-stand continuous rolling is performed with a total reduction rate of 71.4%.

[0047] (5) Annealing

[0048] Annealing speed ≤ 240m / min, hydrogen content in the furnace 3% to 7%, oxygen content ≤ 10ppm, furnace pressure 100 to 400Pa; soaking temperature 750℃, slow cooling endpoint temperature 640 to 670℃, rapid cooling endpoint temperature 410 to 450℃, aging endpoint temperature 340 to 380℃, final cooling furnace outlet temperature ≤ 155℃.

[0049] (6) Leveling

[0050] The working roll is an ordinary roll with a roll roughness (Ra) of 3.0 μm, a working roll peak number (Pc) of 90-100 cm, a leveling liquid concentration of 3%, a leveling elongation of 1.2%, and a strip surface roughness (Ra) of 0.6-1.9 μm.

[0051] Example 3

[0052] A method for improving the surface wavy shape of a part after cold-rolled steel roll forming, comprising the following steps:

[0053] (1) Steel smelting

[0054] The composition of the steel after controlled smelting is as follows: C 0.067%, Mn 0.7%, Nb 0.03%, Si 0.03%, Al 0.046%, P 0.015%, S 0.006%, and the balance is Fe.

[0055] (2) Continuous casting

[0056] The liquid steel is rapidly solidified and crystallized, and after cooling and electromagnetic stirring, it is cut into slabs of a certain length, and the head and tail are peeled.

[0057] (3) Hot rolling

[0058] The slab heating temperature is controlled at 1210-1270°C and the furnace time is 240 minutes. The seven-stand continuous rolling is carried out, with the starting temperature of rough rolling at 1050-1090°C, the starting temperature of finishing rolling at 985-1060°C, and the final temperature of finishing rolling at 870-920°C. After rolling, the rear-section laminar cooling mode is adopted. U-type coiling is used, with the coiling temperature within 40 meters from the head to the tail at 600-670°C and 570-640°C in the middle.

[0059] (4) Pickling

[0060] A pickling corrosion inhibitor with a concentration of 1‰ to 2‰ is added to the pickling tank 2 hours in advance. The pickling process speed is ≥100m / min. An inspection at the process section exit confirms that the steel plate surface is not over-pickled or under-pickled. Five-stand continuous rolling is performed with a total reduction rate of 71.4%.

[0061] (5) Annealing

[0062] Annealing speed ≤ 240m / min, hydrogen content in the furnace 3% to 7%, oxygen content ≤ 10ppm, furnace pressure 100 to 400Pa; soaking temperature 760℃, slow cooling endpoint temperature 640 to 670℃, rapid cooling endpoint temperature 410 to 450℃, aging endpoint temperature 340 to 380℃, final cooling furnace outlet temperature ≤ 155℃.

[0063] (6) Leveling

[0064] The working roll is an ordinary roll with a roll roughness (Ra) of 3.0 μm, a working roll peak number (Pc) of 90-100 cm, a leveling liquid concentration of 3%, a leveling elongation of 1.1%, and a strip surface roughness (Ra) of 0.6-1.9 μm.

[0065] Comparative Example 1

[0066] A method for improving the surface wavy shape of a part after cold-rolled steel roll forming, comprising the following steps:

[0067] (1) Steel smelting

[0068] The steel composition after controlled smelting is as follows: C 0.067%, Mn 0.69%, Nb 0.032%, Si 0.03%, Al 0.043%, P 0.015%, S 0.005%, and the balance is Fe.

[0069] (2) Continuous casting

[0070] The liquid steel is rapidly solidified and crystallized, and after cooling and electromagnetic stirring, it is cut into slabs of a certain length, and the head and tail are peeled.

[0071] (3) Hot rolling

[0072] The slab heating temperature is controlled at 1210-1270°C and the furnace time is 240 minutes. The seven-stand continuous rolling is carried out, with the starting temperature of rough rolling at 1050-1090°C, the starting temperature of finishing rolling at 985-1060°C, and the final temperature of finishing rolling at 870-920°C. After rolling, the rear-section laminar cooling mode is adopted. U-type coiling is used, with the coiling temperature within 40 meters from the head to the tail at 600-670°C and 570-640°C in the middle.

[0073] (4) Pickling

[0074] A pickling corrosion inhibitor with a concentration of 1‰ to 2‰ is added to the pickling tank 2 hours in advance. The pickling process speed is ≥100m / min. An inspection at the process section exit confirms that the steel plate surface is not over-pickled or under-pickled. Five-stand continuous rolling is performed with a total reduction rate of 71.4%.

[0075] (5) Annealing

[0076] Annealing speed ≤ 240m / min, hydrogen content in the furnace 3% to 7%, oxygen content ≤ 10ppm, furnace pressure 100 to 400Pa; soaking temperature 780℃, slow cooling endpoint temperature 640 to 670℃, rapid cooling endpoint temperature 410 to 450℃, aging endpoint temperature 340 to 380℃, final cooling furnace outlet temperature ≤ 155℃.

[0077] (6) Leveling

[0078] The working roll is an ordinary roll with a roll roughness (Ra) of 3.0 μm, a working roll peak number (Pc) of 90-100 cm, a leveling liquid concentration of 3%, a leveling elongation of 1.0%, and a strip surface roughness (Ra) of 0.6-1.9 μm.

[0079] Test Case

[0080] The products manufactured in Examples 1 to 3 and the comparative example were subjected to relevant tests, and the test results are shown in Table 1 below:

[0081] Table 1 - Test results

[0082] Rel / Rp0.2 / MPa Rm / MPa A80 / ％ Example 1 380 463 30.2 Example 2 383 465 30.4 Example 3 377 461 30 Comparative Example 1 342 459 28.0

[0083] Through the mechanical properties results of Examples 1 to 3 and the comparative examples and the analysis of user usage, it can be seen that lowering the annealing temperature and increasing the flattening elongation in the examples can improve the strength of the finished product. Figure 2 and Figure 3 It can be seen that the use of cold-rolled steel under the new process can significantly improve the wavy defects on the surface of parts after roll forming, indicating that the mechanical properties of the steel coils after the modified process in Examples 1-3 are higher than the longitudinal stress during roll forming of the parts, meeting the user's usage needs. After multiple trials, the applicable performance range for specific user use was clarified, and no wavy defects on the surface of parts appeared in subsequent deliveries.

[0084] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person skilled in the art who can easily conceive of changes or substitutions within the technical scope disclosed in the present invention shall be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope of protection described in the claims.

Claims

1. A method for improving the surface wave shape of parts after cold-rolled steel roll forming, characterized in that: The following methods are included: (1) sampling and analyzing parts; (2) adjusting the chemical composition of materials; (3) adjusting process parameters; The preparation steps of cold-rolled steel include steel smelting, continuous casting, hot rolling, acid rolling, continuous annealing, tempering, and coiling; The composition of the adjusted parts includes increasing the C content to 0.06%~0.12%, the Mn content to 0.6%~0.71%, the Nb content to 0.03%~0.09%, controlling the Si content below 0.05%, the Al content to 0.015%~0.1%, and the P and S contents to below 0.025%; Continuous annealing is as follows: annealing speed ≤ 240m / min, hydrogen content in the furnace 3%~7%, oxygen content ≤ 10ppm, furnace pressure 100~400Pa; soaking temperature 750~780℃, slow cooling end temperature 640~700℃, rapid cooling end temperature 300~460℃, aging end temperature 280~380℃, final cooling furnace temperature ≤ 155℃; The leveling is: roller roughness 2.0~4.0μm, working roll peak number 90~100cm, leveling liquid concentration 3%, leveling elongation 1.1%~1.2%, strip surface roughness 0.6~1.90μm.

2. The method for forming a corrugated surface of a part after cold-rolled steel roll forming according to claim 1, characterized in that: Parts sampling analysis is to sample and analyze the wavy rolls on the parts of the user to clarify that the cause of the wavy surface of the parts is that the longitudinal stress during roll forming exceeds the yield strength of the material.

3. The method for forming a corrugated surface of a part after cold-rolled steel roll forming according to claim 1, characterized in that: The hot rolling process is as follows: slab heating temperature is 1200-1270°C, furnace time is 140-280 min; seven-stand continuous rolling, rough rolling start temperature is 1050-1090°C, finishing rolling start temperature is 985-1060°C, finishing rolling final temperature is 870-920°C; after rolling, a rear-stage laminar cooling mode is adopted; U-type coiling is used, with coiling temperatures of 570-710°C within 40 meters from the head to the tail and 540-680°C in the middle.

4. The method for forming a corrugated surface of a part after cold-rolled steel roll forming according to claim 1, characterized in that: The pickling continuous rolling process is as follows: a pickling corrosion inhibitor with a concentration of 1‰~2‰ is added to the pickling tank 2 hours in advance, the pickling process speed is ≥100m / min, and the exit of the process section is inspected to confirm that the steel plate surface is not over-pickled or under-pickled; five-stand continuous rolling is performed with a total reduction rate of 46.66%~88.0%.

Images