Surface special repair process for cold-rolled austenitic stainless steel

Abstract

A surface special repairing process of cold-rolled austenitic stainless steel, steps: determining the repairable coil material; shallow grinding process: the repairable coil is first subjected to shallow grinding process, the grinding belt needs to be subjected to brushing, rinsing and drying operations after being used for a certain time; repairing annealing process: the annealing temperature is controlled at 980-1020 DEG C, the annealing speed is 80-100 m / min, then air cooling is carried out, the cooling rate is <40 DEG C / S, then water cooling and drying are carried out; repairing pickling process: the strip steel then enters the neutral salt electrolysis section, the current is 3000A-4000A, then mixed acid pickling is carried out, then brushing, rinsing and drying are carried out; flattening operation. The application can repair the cold-rolled austenitic stainless steel products which do not meet the customer's requirements in part of the surface layer, the repaired products can meet the customer's use requirements, the product qualified rate is greatly improved, and the loss is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of stainless steel production and relates to a special surface repair process for cold-rolled austenitic stainless steel. BACKGROUND

[0002] In the process of stainless steel production, a special product is often developed according to the needs of customers, and the product is only suitable for a specific range of users. Due to the characteristics of stainless steel, more products are directly used without other surface treatment, which requires protection of the surface during cold rolling, and color, roughness, surface consistency and other aspects have higher control requirements. However, in the actual production process, a small amount of material surface cannot meet the use requirements of customers, and cannot be modified for use. Due to the particularity of the material, the part of the material will be downgraded or discarded, resulting in a large loss.

[0003] The process flow of cold-rolled strip steel production is as follows. The hot-rolled coil is welded on the CPL unit to reduce the consumption of non-rolled parts during cold rolling. Then the strip steel is softened and descaled on the HAPL of the hot-rolled strip steel continuous annealing and pickling unit. The strip steel is cold-rolled on the ZR20 roller or CR12 roller mill. Then it is recrystallized and softened on the CAPL of the cold-rolled strip steel continuous annealing and pickling unit. Then it is improved in shape and surface gloss on the SKP unit. Finally, it is delivered after being processed by the TLL unit (leveler) / STL unit (slitting line) / CTL unit (cross-cutting line), completing the production of cold-rolled strip steel.

[0004] In addition to ferritic stainless steel, the work hardening of stainless steel is relatively high, generally more than 2 times the room temperature strength. In order to cold roll stainless steel, a Sendzimir mill with a 20-roll integral rack or a CR12 roller mill is used. The work roll diameter of the multi-roll mill is only 45-120mm. Due to the small deformation area, the total deformation resistance is relatively small, so the total deformation rate can reach more than 85%, and thin gauge products can be produced. The rolling speed can reach 800m / min. These rolling mills have strong control ability on thickness size accuracy, have pre-set FF-AGC to control the specified gauge, have feedback FB-AGC to control the thickness tolerance, and have tension AGC and second flow AGC for thin gauge products.

[0005] The hot and cold rolled strip softening and recrystallization annealing and pickling are respectively in the form of continuous treatment, the equipment of the hot rolled strip comprises an inlet uncoiling section, a shear, a welding machine, an inlet loop, an annealing furnace, a cooling section, a scale breaking section, sulfuric acid electrolysis / neutral salt electrolysis, a cleaning section 1, mixed acid pickling, a cleaning section 2, an outlet loop, shearing, and an outlet coiling section, and the equipment of the cold rolled strip comprises an inlet uncoiling section, a shear, a welding machine, an inlet loop, an annealing furnace, a cooling section, neutral salt electrolysis, a cleaning section 1, mixed acid / electric acid pickling, a cleaning section 2, an outlet loop, a flattening section, shearing, and an outlet coiling section.

[0006] The finishing process is a post-process of the stainless steel production, and the size specification and quality of the product can meet the user's demand, and the finishing plays a great role, and the unit comprises an SPM (flattening) / TLL unit (leveling line) / STL unit (longitudinal cutting line) / CTL unit (transverse cutting line). In order to improve the glossiness of the strip surface or reduce the roughness, the strip is flattened, and the plate shape and the surface quality are improved.

[0007] The prior art cannot process the surface layer unqualified product, and can only be downgraded or discarded, and the conventional grinding and re-pickling cannot meet the consistency of the surface and thickness tolerance requirements of the customer, therefore, it is urgent to design a special surface repair process for cold rolled austenitic stainless steel to repair the product which does not meet the customer's requirements, and improve the product qualification rate. SUMMARY

[0008] The technical problem to be solved by the present application is to provide a special surface repair process for cold rolled austenitic stainless steel, which can repair the product which does not meet the customer's requirements, improve the product qualification rate, and reduce the loss.

[0009] The technical scheme adopted by the present application to solve the above technical problem is as follows: a special surface repair process for cold rolled austenitic stainless steel, characterized by comprising the following steps:

[0010] 1) determining the repairable coil material: after the recrystallization annealing APC, the surface quality is determined, and the defect coil which does not meet the user's requirements is determined by the quality inspector to determine the repairable coil;

[0011] 2) shallow grinding process: the repairable coil is first subjected to a shallow grinding process, and the grinding belt needs to be subjected to brushing, rinsing and drying operations after a certain period of use;

[0012] 3) Repair annealing process: annealing temperature is controlled at 980-1020℃, annealing speed is 80-100 m / min, then air cooling is carried out, cooling rate is <40℃ / S, then water cooling and drying are carried out;

[0013] 4) Repair pickling process: the strip steel then enters a neutral salt electrolysis section, current is 3000A-4000A, then mixed acid pickling is carried out, then brushing, rinsing and drying are carried out;

[0014] 5) The repaired steel coil is subjected to a tempering operation recently.

[0015] As an improvement, the surface defects of the repairable coil in step 1) include dirt, oil spots, oil stains, oil film rupture, pickling patterns, roller patterns, oil patterns, poor pickling, yellow spots and brush marks.

[0016] Preferably, the grinding belt in step 2) needs to be used for more than 500 minutes.

[0017] Further, the mixed acid for the mixed acid pickling in step 4) is HF concentration 18-25 g / l, nitric acid concentration 80-150 g / l, and metal ion concentration less than 45 g / l.

[0018] Finally, the process of the tempering operation in step 5) is: the tempering roll type is selected as 8 / 8 convexity, the rolling force is controlled at 260-320 tons, and the rolling unit tension is 6.5(±0.5) Kg.

[0019] Compared with the prior art, the advantages of the present application are that the product with surface defects is repaired by using a shallow grinding process, a repair annealing process and a repair pickling process, so that the surface can meet the use requirements of customers, and the thickness is within the tolerance range. The present application can repair the cold-rolled austenitic stainless steel product whose part of the surface layer does not meet the requirements of customers, and the repaired product can meet the use requirements of customers, greatly improving the product qualification rate and reducing the loss. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the surface photo of the unqualified product provided by example 1 of the present application;

[0021] Figure 2 is the surface photo of the repaired qualified product of example 1 and the surface photo of comparative example 1;

[0022] Figure 3 is the metallographic structure photo of the conventional qualified product of comparative example 1 (magnification 200 times);

[0023] Figure 4 is the metallographic structure photo of the repaired qualified product of example 1 (magnification 200 times). DETAILED DESCRIPTION

[0024] The application will be described in further detail below with reference to the drawings.

[0025] Firstly, the improved innovative idea of the application will be described in detail:

[0026] The conventional production technical route of the cold-rolled austenitic stainless steel is as follows:

[0027] 1) Hot coil annealing and pickling: the raw material is a 3-6mm hot-rolled black coil, which is softened by annealing at 900-1100 degrees, enters the scale breaking section, and the scale can be broken by adjusting the speed between the tension roller and the tension roller, and the elongation rate between 0-3% can be obtained, and then the shot blasting section, which includes four shot blasting machines, each of which includes an upper and lower shot blasting wheel, and then the acid pickling is carried out to obtain a relatively clean surface and a soft strip;

[0028] 2) Rolling: the strip from the previous process is rolled to a thickness of 0.6-1.0mm by a rolling mill to meet the requirements of a certain container customer, the rolling pass is 6-9 passes, the rolling speed is 400-600m / min, and the rolling tension is 20-40 tons;

[0029] 3) Recrystallization annealing and pickling: the annealing temperature is 1050-1110℃, the unit speed is 80-120m / min, the corresponding technical process parameters are executed according to the specifications, the performance requirements of the customer are met, and the surface scale is removed by pickling, and the strip surface is cleaned;

[0030] 4) Leveling: after recrystallization annealing and cleaning, the leveling operation is carried out, the leveling adopts 8 / 8 convex leveling roller, the rolling force is 200-300 tons, and the plate shape requirements of the customer are met;

[0031] 5) Finishing process: the strip is edge cut and divided into coils to meet the size and coil weight requirements of the customer;

[0032] 6) Packaging: according to the technical requirements, the steel coil is packaged to meet the packaging requirements of the customer.

[0033] The material is supplied to a certain container customer, and the customer's requirements are as follows:

[0034] 1) Material composition requirements:

[0035]

[0036] 2) Mechanical property requirements:

[0037]

[0038] The surface of the plate cannot have cracks, bubbles, stuttering, inclusions, folding and other defects, and obvious color difference is not allowed.

[0039] Thickness requirement: contract thickness ± 30 μm;

[0040] Ink test requirement: 38# dyne pen line on the surface of the steel plate, no shrinkage or aggregation within 5 seconds;

[0041] Other plate types, sizes, package weights and other requirements.

[0042] The product is currently about 90% of the finished product, 10% of the product is finally processed as a downgrade or a waste, and the special repair process is used to repair the 10% of the surface of the product that does not meet the customer's requirements. The defects are repaired to meet the customer's agreement requirements and do not affect the customer's use. After recrystallization annealing and pickling, the product is checked by the machine unit quality inspector, and the defects are classified and the degree is confirmed.

[0043] The prior art cannot process the unqualified product, and can only be downgraded or discarded, and the conventional grinding and re-pickling cannot meet the customer's requirements of consistent surface and thickness tolerance.

[0044] Treatment route:

[0045] After recrystallization annealing and pickling, the pickling uneven patterns on the surface of the strip steel and the uneven patterns in the rolling process are uniformly repaired by the CGL unit, the repair degree cannot exceed the customer's specification requirements, and the surface is uniform. The CGL uses a grinding belt to rub the surface of the strip steel under certain pressure and speed, and the grinding amount can be within 30 μm;

[0046] The surface color of the strip steel after grinding by the CGL unit is bright, which cannot meet the customer's product requirements, and needs to be annealed and pickled to achieve the product with the same color as the customer's requirements.

[0047] The following will be specifically described by three examples and three comparative examples, the materials of the examples and the comparative examples are selected from the same raw material manufacturer and the same batch production coil to ensure comparability, and the composition of the steel coil is shown in Table 1.

[0048] The surface special repair process of the present application is used in the example, and the specific process steps are as follows:

[0049] 1) Determine the repairable coil material: after the steel coil is recrystallized annealed APC, the quality inspection personnel make surface quality judgment according to the company's "appearance quality inspection standard" and "special product control standard", and the products with surface not meeting the user's demand are blocked, and the quality blocking unblocking disposal personnel make subsequent disposal according to the defect description of the quality inspector, and the surface defect coil with surface defects such as dirt, oil stain, oil stain, oil film rupture, pickling pattern, roller pattern, oil pattern, pickling defect, yellow spot, brush mark and the like is disposed by repair process again;

[0050] 2) Determine the repair process: the repairable coil is first subjected to shallow grinding process, the grinding belt needs to be used for a certain period of time, and the surface of the material is subjected to brushing, rinsing and drying operation; Then repair annealing operation, annealing process selects lower than recrystallization annealing temperature, repair annealing temperature is determined by experiment, to ensure that the performance of the material is not affected, and the surface of the material needs to be oxidized, so that the strip steel surface can be re-pickled after pickling, to achieve the same as before repair, and the pickling process needs to be adjusted compared with recrystallization annealing pickling control, so as to meet the use demand of customers.

[0051] 3) Shallow grinding process: the grinding belt needs to be used for more than 500 minutes, and the surface of the material is subjected to brushing, rinsing and drying operation;

[0052] 4) Repair annealing process: the annealing temperature is determined by experiment to be controlled in the range of 980-1020 degrees, the annealing speed is 80-100 m / min, then the air cooling cooling rate is <40℃ / S, then water cooling and drying are carried out;

[0053] 5) Repair pickling process: the strip steel then enters the neutral salt electrolysis section (current 3000A), mixed acid pickling (HF concentration 18-25g / l, nitric acid concentration 80-150g / l, metal ion concentration less than 45g / l), then brushing, rinsing and drying are carried out;

[0054] 6) Leveling operation: the steel coil is subjected to leveling operation, the leveling roll type is selected as 8 / 8 convexity, the rolling force is controlled at 260-320 tons, and the rolling unit tension is set at 6.5(±0.5)Kg.

[0055] Figure 1 The photos of the unqualified products before repair of example 1 can be seen that the surface has patterns, which are not flat.

[0056] Figure 2 The photos of the repaired products of example 1 and the photos of the products of comparative example 1 are compared, and the surface is smooth and has no pattern defect.

[0057] The repaired products of example and the comparative example are detected:

[0058] Table 1: The same raw material manufacturer and the same batch of steel coil are used for the selected comparative examples and examples, and the component deviation of each comparative example and example is about 5%, which is a normal fluctuation value.

[0059] Table 2: After the repair process, the thickness of examples 1-3 is slightly thinner than that of the conventional process, and the average thickness of the repaired steel strip is 10 μm, which is small and meets the customer's standard and use requirements.

[0060] Table 3: The performance values of the examples and comparative examples are compared, and the influence deviation is within 2%, which is smaller than the fluctuation in the example group and meets the customer's normal use.

[0061] Table 1: Chemical composition of hot-rolled stainless steel coil used in examples and comparative examples / wt%

[0062] Ingredients C Si Mn P S Cr Cu N Ni Standard requirements 0.07 1.0 5.5-7.5 0.045 0.03 16-18 2 0.3 3.5-5.5 Example 1 0.059 0.37 6.08 0.034 0.002 16.5 1.64 0.088 3.99 Example 2 0.055 0.35 6.1 0.036 0.003 16.07 1.61 0.09 4.08 Example 3 0.056 0.33 6.04 0.04 0.002 16.27 1.6 0.088 3.98 Comparative Example 1 0.057 0.35 6.18 0.04 0.004 16.23 1.63 0.114 3.95 Comparative Example 2 0.053 0.37 6.07 0.039 0.002 16.12 1.73 0.099 4 Comparative Example 3 0.054 0.38 6.05 0.035 0.005 16.26 1.61 0.104 4.15

[0063] Note: The components listed in Table 1 are maximum values except for the range indicated.

[0064] Table 2: Thickness change of examples and comparative examples

[0065]

[0066]

[0067] Table 3: Performance and head-tail deviation of examples and comparative examples

[0068]

[0069] From the data measured in Tables 2 and 3, it can be seen that the repaired steel coil products of examples 1, 2 and 3 meet the standard requirements in thickness and performance.

[0070] The above is only the preferred embodiment of the present application, and it should be noted that for ordinary skilled persons in the art, without departing from the technical principles of the present application, several improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A special surface repair process for cold-rolled austenitic stainless steel, characterized in that... Includes the following steps: 1) Determine the repairable coil material: After the steel coil is recrystallized and annealed (APC), the surface quality is judged. For defective coils whose surface does not meet the user's requirements, the quality inspector will judge and determine the repairable coil. The surface defects that can be identified as repairable rolls in step 1) include dirt, oil spots, oil stains, oil film cracks, pickling patterns, roller patterns, oil patterns, poor pickling, yellow spots, and brush marks. 2) Shallow grinding process: The repairable roll is first subjected to a shallow grinding process. The grinding belt needs to be used for a certain period of time before the material surface is brushed, rinsed and dried. The abrasive belt used in step 2) must have been used for more than 500 minutes. 3) Repair annealing process: The annealing temperature is controlled at 980-1020℃, the annealing speed is 80-100 m / min, then air cooling is performed at a cooling rate of <40℃ / S, followed by water cooling and drying; 4) Repair pickling process: The strip steel then enters the neutral salt electrolysis section with a current of 3000A-4000A, followed by acid pickling, then brushing, rinsing and drying; 5) The repaired steel coils have recently undergone leveling operations.

2. The special surface repair process according to claim 1, characterized in that: The mixed acid used in step 4) for acid washing has an HF concentration of 18-25 g / L, a nitric acid concentration of 80-150 g / L, and a metal ion concentration of less than 45 g / L.

3. The special surface repair process according to claim 1, characterized in that: The process for the leveling operation in step 5) is as follows: the leveling roll type is selected with an 8 / 8 crown, the rolling force is controlled at 260-320 tons, and the rolling unit tension is 6.5±0.5Kg.

Images