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What is the cold working process for stainless steel strip
source：m.p-t7.com | Release time：2025年11月25日1、 Core process flow of cold processing (from raw materials to finished products)
The cold processing of stainless steel strip is centered on "cold rolling and rolling", combined with pre-treatment, finishing, deep processing and other links, forming a complete process chain.
2、 Key process details at each stage
1. Raw material preparation and pretreatment (to ensure the feasibility of cold rolling)
Raw material requirements: Hot rolled stainless steel coils (thickness 2.0-12.7mm, such as 304, 316L, 430 and other grades) should be selected, ensuring that the surface of the raw material is free of severe oxide scale, cracks, inclusions, and the chemical composition meets the grade standards (such as 304 stainless steel Cr ≥ 18%, Ni ≥ 8%).
Acid washing treatment:
Purpose: To remove the oxide scale (Fe ∝ O ?, Cr ? O ∝) and rust on the surface of hot-rolled coils, avoid scratching the surface of the strip with oxide scale during cold rolling, and activate the metal surface to improve the subsequent annealing effect.
Process: The hot-rolled coil is immersed in a mixed acid bath of hydrochloric acid (15% -20%) and sulfuric acid (5% -10%), with temperature controlled at 50-70 ℃ and acid washing time of 10-30 minutes. After that, it is washed with water, neutralized (sodium carbonate solution), and dried to ensure that there is no acid residue on the surface.
Annealing treatment:
Purpose: To eliminate internal stress generated during hot rolling, soften the material (reduce hardness, such as HB ≤ 201 after annealing of 304 stainless steel), improve plasticity, and facilitate subsequent cold rolling processing.
Process: Continuous annealing furnace or hood type annealing furnace is used, with a heating temperature of 850-1100 ℃ (higher temperature is required for austenitic stainless steel), insulation for 2-4 hours, and cooling method of air cooling or water cooling (adjusted according to the grade to avoid martensitic transformation).
Leveling treatment:
Purpose: To correct the shape of the annealed strip (such as wavy edges and sickle bends), improve surface flatness (flatness ≤ 3mm/m), and slightly strengthen the material to provide uniform slab for cold rolling.
Process: Mild rolling is carried out using a leveling machine (two roll or four roll), with a reduction controlled at 1% -3%, to ensure uniform thickness and smooth surface of the strip.
2. Cold rolling (core forming process)
Process principle: Using the rolling pressure of a cold rolling mill, the annealed strip is rolled multiple times at room temperature, gradually reducing thickness, improving accuracy and strength through plastic deformation of the metal.
Key equipment: Four roll reversible cold rolling mills or twenty roll Sendzimir mills (suitable for ultra-thin and high-precision strips) are commonly used, and the surface of the rolls is polished (roughness Ra ≤ 0.02 μ m) to avoid scratching the strips.
Process parameter control:
Step compression amount: 5% -20% compression amount per step (the compression amount in the previous step is large, and gradually decreases in the later step), to avoid excessive compression amount causing strip cracking or poor plate shape;
Rolling speed: adjusted according to the thickness and material of the strip, the speed of thin strip (≤ 0.1mm) is ≤ 300m/min, and the speed of thick strip (0.1-3.0mm) can reach 500m/min;
Lubrication and cooling: Special cold rolling oil (mineral oil+additives) is used to lubricate, cool, and clean, reduce the friction coefficient between the rolling mill and the strip (μ ≤ 0.1), and avoid surface burns.
Thickness control: Through real-time monitoring using a thickness gauge (laser thickness measurement or X-ray thickness measurement), the thickness tolerance of the finished product can be controlled within ± 0.001- ± 0.01mm (ultra-thin strip) or ± 0.01- ± 0.05mm (conventional strip), far exceeding the accuracy of hot-rolled strip.
3. Finishing process (improving finished product quality)
Straightening treatment:
Purpose: To further correct the flatness of cold-rolled strip (such as residual waves and warping), improve straightness (straightness ≤ 0.5mm/m), and improve the uniformity of mechanical properties of the strip.
Process: Apply 1% -5% tensile deformation through a stretching straightening machine, combined with the bending effect of straightening rollers, to eliminate internal stress in the strip.
Cutting processing:
Purpose: To cut wide cold-rolled stainless steel strips (such as 1219mm, 1000mm) into narrow strips (width ≥ 5mm) or cut to length (length ≥ 1m) according to customer requirements.
Process: The longitudinal cutting machine (slitting machine) is used, equipped with high-precision blades and tension control system, to ensure that the edges of the cut strip are free of burrs (burrs ≤ 0.01mm) and the width tolerance is ± 0.02- ± 0.1mm.
Surface treatment (optional, according to requirements):
Passivation treatment: Immerse in chromate or chromium free passivation solution to form a dense oxide film (thickness 0.5-2 μ m), improving corrosion resistance (especially resistance to chloride ion corrosion);
Film coating treatment: Cover the surface with PE film or PVC film to prevent scratches during transportation and subsequent processing;
Polishing treatment: Through multiple grinding processes, the surface smoothness is improved (such as 2B surface → BA surface → 8K mirror surface) to meet the needs of decoration or precision applications.
4. Deep processing technology (adapted to terminal applications)
According to customer requirements, cold-rolled stainless steel strips can be further cold processed into shapes:
Stamping: Stamping into shaped parts (such as electronic component casings and automotive components) through punching machines and molds, requiring good strip ductility (elongation ≥ 40%);
Bending: Use a bending machine to bend the strip into angles of 90 °, 135 °, etc. (such as pipeline flanges, equipment supports) to avoid cracking at the bending point;
Stretching: Stretching the strip into cylindrical, cup-shaped, and other structures (such as stainless steel containers and sensor housings) using a stretching machine, requiring uniform and high elongation of the strip;
Rolling forming: The strip is rolled into corrugated, tubular and other profiles (such as heat sinks and stainless steel pipes) by a rolling machine to maintain the dimensional accuracy and mechanical strength of the strip.
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