What grade are stainless steel coils？

I. Material Grade Classification (Based on Core Performance)​

(1) 200 Series (Nickel-Saving Austenitic Stainless Steel)​

Typical Grades: 201 (1Cr17Mn6Ni5N), 202 (1Cr18Mn8Ni5N)​

Compositional Characteristics: Manganese substitutes for nickel, with Ni content at 3.5%-5.5% (much lower than 300 series), strengthened by nitrogen​

Performance Features:​

Corrosion Resistance: Weaker than 304, prone to rust in humid environments, limited acid resistance​

Mechanical Properties: High strength (due to nitrogen), but poor ductility, prone to cracking during processing​

Magnetism: Non-magnetic (austenitic structure), may exhibit weak magnetism after cold working​

Application Scenarios: Low-cost decorative fields (building facades, interior decoration), low-end kitchenware (non-food contact grade)​

(2) 300 Series (Standard Austenitic Stainless Steel)​

1. General Corrosion-Resistant Type​

304 (06Cr19Ni10/UNS S30400):​

Composition: 18-20% Cr, 8-10.5% Ni, carbon ≤0.08%​

Performance: Excellent comprehensive corrosion resistance (resistant to atmosphere, water, most acids), easy to process and weld, non-magnetic​

Standards: GB/T 24511 (China), ASTM A240 (USA), JIS G4305 (Japan)​

Applications: Food processing equipment, medical devices, kitchen utensils, chemical storage tanks​

304L (022Cr19Ni10/UNS S30403):​

Ultra-low carbon (C ≤0.03%), prevents intergranular corrosion, suitable for welded parts and high-temperature environments​

2. High Corrosion-Resistant Type​

316 (06Cr17Ni12Mo2/UNS S31600):​

2-3% Mo added, resistant to chloride ion corrosion (e.g., seawater, salt solutions), high-temperature sulfide resistance​

Applications: Marine engineering, paper-making equipment, pharmaceutical and chemical industry, ship components​

316L (022Cr17Ni12Mo2/UNS S31603): Low-carbon version with better welding performance​

3. Special Function Type​

321 (06Cr18Ni11Ti/UNS S32100): Titanium-stabilized treatment, resistant to intergranular corrosion, used in high-temperature (≤600℃) scenarios (boiler pipes, heat treatment equipment)​

310S (06Cr25Ni20/UNS S31008): 25Cr-20Ni composition, resistant to high-temperature oxidation (up to 1200℃), used for furnace components and thermocouple casings​

(3) 400 Series (Ferritic/Martensitic Stainless Steel)​

1. Ferritic Type (Magnetic, Moderate Corrosion Resistance)​

430 (10Cr17/UNS S43000):​

16-18% Cr, nickel-free, low cost​

Better atmospheric corrosion resistance than carbon steel, but not acid-resistant, magnetizable​

Applications: Architectural decoration (facades, railings), home appliance panels (refrigerators, washing machines), automotive exhaust pipes​

439 (019Cr19NbTi): Low-carbon with titanium, resistant to intergranular corrosion, used for water heater liners and sinks​

2. Martensitic Type (High Strength, Heat-Treatable)​

410 (12Cr13/UNS S41000):​

11.5-13.5% Cr, carbon ≤0.15%, high hardness (HRC 40-45) after quenching and tempering​

Moderate corrosion resistance, used for cutting tools, valves, and mechanical parts​

420J1 (20Cr13): Higher carbon content (0.16-0.25%), higher hardness, used for surgical scalpels and pump shafts​

II. Quality Grade Classification (Based on Production Processes)​

(1) Classification by Processing Technology​

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(2) Surface Quality Grades​

2B Grade: Cold-rolled, heat-treated, and pickled, smooth surface with pickling traces, general industrial grade​

BA Grade: Cold-rolled and bright-annealed, mirror surface (roughness Ra≤0.1μm), used for decoration and medical devices​

8K Mirror Grade: Mechanically polished to mirror finish (Ra≤0.05μm), for high-end decoration (hotel lobbies, luxury displays)​

NO.1 Grade: Hot-rolled and pickled, rough surface with residual oxide scale, used as base material for further processing​

(3) Dimensional Accuracy Grades (Taking Thickness Tolerance as an Example)​

Normal Precision (PT.A): ±(thickness ×1% + 0.04mm) (e.g., 1.0mm thickness allows ±0.05mm tolerance)​

Higher Precision (PT.B): ±(thickness ×0.7% + 0.03mm) (suitable for precision processing scenarios)​

III. Execution Standard Grades (International Applicability)​

(1) International Mainstream Standards​

ASTM (USA):​

A240 (for pressure vessels), A666 (cold-rolled stainless steel for decoration)​

EN (EU):​

EN 10088-2 (corrosion-resistant steel for general purposes), EN 10204 3.1B (material certificate grade)​

JIS (Japan):​

G4305 (cold-rolled steel plates), G4303 (hot-rolled steel plates)​

(2) Domestic Standards​

GB/T 24511-2017 (Stainless Steel for Pressure Equipment): Equivalent to ASME BPVC.ASTM A240, requires stricter intergranular corrosion testing​

GB/T 3280-2015 (Cold-Rolled Stainless Steel Plates and Strips): Specifies surface roughness, hardness (HV≤200 for 304), etc.​

IV. Selection Guide​

Corrosion Environment:​

Atmospheric/freshwater environments: 304 (cost-effective choice), 430 (low-cost option)​

Seawater/chloride environments: 316L (mandatory), 2205 duplex steel (higher strength)​

Temperature Requirements:​

Low temperature (-196℃): 304L (no low-temperature brittleness)​

High temperature (>600℃): 321/310S (creep resistance)​

Processing Performance:​

Deep drawing: 304 (high ductility, r value ≥1.2)​

Welded structures: 304L/316L (low-carbon to prevent intergranular corrosion)​

V. Procurement Considerations​

Require suppliers to provide material certificates (including chemical composition, mechanical properties, and intergranular corrosion test results)​

Specify surface grades clearly (e.g., "2B surface, roughness Ra≤0.4μm")​

For critical applications (e.g., pressure vessels), add non-destructive testing (UT/RT) and hydrostatic pressure tests​

Through this multi-dimensional grade classification, users can select appropriate stainless steel coils based on specific application scenarios (corrosion resistance, strength, processability, cost). It is recommended to specify execution standards, grade correspondence tables (e.g., 304 corresponds to US S30400/China 06Cr19Ni10), and special performance requirements (e.g., food grade must pass GB 4806.9 testing) in contracts.​