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Introduce the basic treatment process of stainless steel coils
source：www.p-t7.com | Release time：2025年10月14日1、 Core process 1: Surface treatment - solving "surface defects", optimizing appearance and corrosion resistance
Stainless steel coils (especially hot-rolled coils) may have surface problems such as oxide scale, oil stains, scratches, etc. when leaving the factory. Surface treatment is needed to remove defects and improve surface quality, laying the foundation for subsequent processing (such as welding, painting, bending) or direct application (such as decoration, food equipment). Common processes include:
1. Acid washing treatment (the most basic surface cleaning process)
Core function: Remove the oxide scale (black brown oxide layers such as Fe2O3 and FeO formed on the surface of stainless steel coils after high-temperature rolling), rust, and residual rolling oil, expose the stainless steel substrate, and form a "passivation film" (Cr ? O3) on the surface to enhance initial corrosion resistance.
Applicable scenarios: All stainless steel coils (especially hot-rolled coils, which must be pickled before subsequent processing; cold-rolled coils with slight oxidation or oil stains on the surface also need to be pickled).
technological process:
Degreasing: Soak or spray the coil with alkaline solution (such as NaOH solution) to remove surface rolling oil and dust;
Acid washing: Send the coil into an acid washing tank (usually a mixture of nitric acid and hydrofluoric acid, with low acid concentration for cold-rolled coils and high concentration for hot-rolled coils), soak for 5-15 minutes, and dissolve the oxide scale and rust;
Neutralization: Neutralize residual acid solution with alkaline solution (such as sodium carbonate solution) to avoid corrosion of the substrate;
Rinse: Rinse multiple times with clean water to remove neutralizing products;
Drying: Remove surface moisture through hot air or drying rollers to avoid secondary rusting.
Finished product effect: The surface appears as a "uniform gray white matte".
2. Passivation treatment (surface protection process to enhance corrosion resistance)
Core function: On the surface of the pickled stainless steel coil, a "passivation film" (Cr ? O3 layer) is chemically thickened to enhance its resistance to salt spray and weak acid corrosion (especially for austenitic stainless steels such as 304 and 316L), and to prevent rusting during subsequent processing or storage.
Applicable scenarios: Stainless steel coils that need to be used in humid and slightly corrosive environments (such as coils for food equipment and marine environment components).
Process characteristics:
Common passivators: nitric acid passivation (soaked in low concentration nitric acid solution), chromate passivation (gradually phased out due to hexavalent chromium pollution), environmentally friendly passivators (such as organic acid passivation solution, compliant with RoHS standards);
Simple process: It is often connected with acid pickling process (directly entering the passivation tank after acid pickling), with a processing time of 5-10 minutes, without the need for high temperature, and can be carried out at room temperature;
No thickness effect: The passivation film thickness is only 0.001-0.003 μ m, which does not change the dimensional accuracy of the coil and does not affect subsequent bending and stamping.
3. Surface polishing treatment (a process that optimizes the appearance texture)
Core function: To remove fine scratches and dents on the surface of stainless steel coils through physical grinding, improve surface smoothness and reflectivity, and adapt to decoration, precision equipment and other scenarios that require appearance.
Applicable scenarios: Cold rolled stainless steel coils (hot-rolled coils have rough surfaces, high polishing costs, and are rarely used), such as coils for elevator cars, hotel decorations, and medical equipment casings.
2、 Core Process 2: Dimensional Accuracy Adjustment - Ensure "Specification Compliance" and Adapt to Downstream Processing
Stainless steel coils may have dimensional issues such as "poor plate shape" (such as sickle bending, wave shape) and "thickness deviation" when leaving the factory. These issues need to be corrected through process adjustments to ensure dimensional stability during downstream cutting, stamping, and bending. The main processes include:
1. Leveling treatment (correcting plate shape, improving dimensional accuracy)
Core function: By using a "leveling machine" to lightly roll stainless steel coils (with a small rolling force and a reduction of 0.5% -2%), the "wave shape" (local wrinkling) and "sickle bend" (the edge of the coil is curved) of the coil are corrected, and the surface smoothness is adjusted (such as improving the fineness of the 2B surface through leveling), ensuring that the coil is flat and has no obvious deformation after unfolding.
Applicable scenarios: All cold-rolled stainless steel coils (must be flattened to meet precision machining requirements); If hot-rolled coils are used in scenarios with high requirements for plate shape (such as building curtain walls), they also need to be flat.
2. Process characteristics:
Equipment: mostly four roll leveling machines (with two working rolls on each side to prevent the roll from slipping);
Accuracy control: The "sickle bend deviation" of the flattened coil is ≤ 1mm/m, and the "wave height" is ≤ 2mm/2m, ensuring no waste during downstream cutting.
2. Slitting/slitting processing (adjust width as needed, suitable for small-sized processing)
Core function: Cut large width stainless steel coils (such as 1219mm and 1500mm wide) into small width coils (such as 50mm, 100mm, and 300mm wide) along the length direction using a "longitudinal cutting machine" according to downstream requirements, facilitating subsequent processing into narrow width parts (such as pipes and profiles).
Applicable scenarios: Downstream scenarios that require small width coils (such as narrow coil welding for stainless steel pipe production and narrow coil stamping for hardware parts).
Process key:
Positioning: Ensure that the cutting line is parallel to the edge of the coil through a guiding device to avoid width deviation;
Burr control: Cut with high-precision longitudinal scissors (such as high-speed steel blades), and remove edge burrs (burr height ≤ 0.05mm) through a "deburring machine" after cutting to avoid scratching the mold or operators during subsequent processing;
Roll up: The small width roll material after cutting is rolled up separately, with width and length marked for easy management.
3、 Core Process 3: Performance Optimization Processing - Adjusting "Mechanical Properties" to Adapt to Different Usage Needs
Some stainless steel coils (such as alloy stainless steel coils and quenched stainless steel coils) do not meet downstream requirements in terms of hardness and toughness when they leave the factory, and their mechanical properties need to be adjusted through heat treatment. Common processes include:
1. Annealing treatment (reduces hardness, enhances toughness, and facilitates processing)
Core function: By heating (the heating temperature is adjusted according to the steel type, such as the annealing temperature of 304 stainless steel at 1050-1100 ℃), insulation, and slow cooling, the "internal stress" generated during the rolling process of stainless steel coils is eliminated, the grain size is refined, the hardness is reduced (such as the hardness of cold-rolled 304 coils before annealing is about 200HV, and after annealing it drops to 130-150HV), the plasticity and toughness are improved, and it is convenient for subsequent bending, stamping, and welding (to avoid cracking during processing).
Applicable scenarios: Cold rolled stainless steel coils (metal hardens during the cold rolling process and must be annealed to restore workability); If hot-rolled stainless steel coils are used in scenarios that require high toughness, such as low-temperature environmental components, they also need to be annealed.
2. Common types of annealing:
Bright annealing: Annealing under inert gas (such as nitrogen) protection to avoid surface oxidation, and the surface of the coil remains smooth after annealing (such as bright annealing of BA cold-rolled coil);
Ordinary annealing: Without protective gas, the surface will produce oxide scale after annealing, which needs to be removed by subsequent acid washing (mostly used for hot-rolled coils or cold-rolled coils with low surface requirements).
2. Straightening treatment (correcting deformation to ensure straightness)
Core function: In response to the possible "bending deformation" of stainless steel coils after unfolding (such as slight bending caused by uneven tension during winding), a "straightening machine" (multi roll straightening machine, such as 11 roll, 17 roll) is used to continuously roll and correct the bending of the coil, ensuring the "straightness" of the coil (straightness deviation per meter ≤ 0.5mm), and adapting to subsequent high-precision processing (such as precision part stamping, laser cutting).
Applicable scenarios: Stainless steel coils for precision machining (such as thin gauge cold-rolled coils for electronic components and medical devices), and coils for ordinary structural components. If the bending is not obvious, this step can be omitted.
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