Stainless steel coil

Major Classification and Grade System 
Stainless steel coils can be classified into five major categories based on their microstructure, which serves as the fundamental basis for material selection. 
1. Austenitic Stainless Steel (Austenitic Series) – Most commonly used (accounting for about 70%) 
Features: Non-magnetic (slightly magnetic after cold working), excellent corrosion resistance, outstanding formability and weldability, and good toughness. 
Common grades: 
304 (06Cr19Ni10 / SUS304): A versatile steel with the widest range of applications. It offers excellent corrosion resistance, formability, and heat resistance. Commonly used in kitchenware, household appliances, food and medical industries, as well as architectural decoration. 
304L (022Cr19Ni10): Ultra-low-carbon 304, offering superior resistance to intergranular corrosion, making it ideal for components that cannot undergo heat treatment after welding. 
316 (06Cr17Ni12Mo2): Marine-grade stainless steel. Thanks to the addition of molybdenum (Mo), it exhibits significantly better resistance to chloride corrosion—such as in seawater and brine—compared to 304. Commonly used in chemical processing, marine applications, medical devices, and more. 
316L (022Cr17Ni12Mo2): An ultra-low-carbon version of 316, also offering excellent resistance to intergranular corrosion. 
Surface finishes: Common 2B (cold-rolled, followed by annealing, pickling, and bright rolling—smooth with slight reflectivity), BA (bright annealed—highly polished and exceptionally shiny), and No.1 (hot-rolled, then hot-annealed and pickled—coarse texture). 
2. Ferritic Stainless Steel (Ferritic Series) 
Features: Magnetic, with moderate corrosion resistance (better than martensitic grades but significantly inferior to austenitic ones), high strength, excellent resistance to oxidation and stress-corrosion cracking, nickel-free (Ni), and lower cost. 
Common grades: 
430 (10Cr17 / SUS430): A representative ferritic steel. It offers excellent resistance to atmospheric and nitric acid corrosion, making it suitable for applications such as household appliances, decorative items, and automotive exhaust pipes. 
443/439: A higher-performance ferritic steel aimed at replacing 304 in certain applications. 
Surface: Mostly 2D/2B. 
3. Martensitic Stainless Steel (Martensitic Series) 
Features: Magnetic, with strength and hardness significantly enhanced through heat treatment (quenching and tempering), though it exhibits poor corrosion resistance—withstanding only atmospheric corrosion and weak-medium corrosion. 
Common grades: 
410 (12Cr13): Used for parts with high mechanical performance requirements and moderate corrosion resistance needs, such as cutting tools, bearings, and valve components. 
420 (20Cr13): Tool-grade martensitic steel, used for cutting tools, nozzles, and more. 
Surface: Mostly in the annealed or polished condition. 
4. Duplex Stainless Steel (Duplex Series) 
Features: Austenitic and ferritic mixed microstructure, combining the advantages of both—extremely high strength (twice that of 304), excellent resistance to chloride-induced stress corrosion cracking, and outstanding toughness and weldability. However, it comes at a higher cost. 
Common grades: 2205 (022Cr23Ni5Mo3N), used in harsh environments such as chemical processing, petroleum, offshore platforms, and seawater treatment. 
5. Precipitation-Hardening Stainless Steel (Precipitation-Hardening Series) 
Feature: High-strength is achieved by precipitating hardening phases within the matrix through heat treatment, while maintaining sufficient toughness and corrosion resistance. 
Common grades: 17-4PH (05Cr17Ni4Cu4Nb), used in aerospace, the nuclear industry, and high-strength structural components. 
Key Performance Indicators and Terms 
Corrosion Resistance: A key indicator determined by alloy composition (such as Cr, Mo, Ni, Cu, etc.). 
Mechanical Properties: 
Yield Strength (YS), Tensile Strength (TS), and Elongation (El): Fundamental indicators for measuring a material's strength and ductility. 
Surface Finish Grade: 
No.1: Hot-rolled, followed by heat treatment and acid pickling. Rough texture, with no luster. 
2D: After cold rolling, it undergoes heat treatment and acid cleaning. The surface has a matte finish. 
2B: After cold rolling, the material undergoes heat treatment and acid pickling, followed by a final light cold-rolling pass. This is the most commonly used surface finish—smooth with a slight reflective sheen. 
BA: Bright annealed—surface is exceptionally shiny with high reflectivity. 
No.3/No.4: Polished surface (short hairline, long hairline), offering a decorative effect. 
HL: Matte surface. 
Thickness Tolerance: Cold-rolled coils offer significantly higher precision compared to hot-rolled coils. 
Production Process Flow 
Hot-rolling process: Slab → Heating → Rough Rolling → Finish Rolling → Coiling → Annealing → Pickling → Finishing → Hot-Rolled Coil. 
Cold Rolling Process: Hot-rolled coil → Annealing → Pickling → Cold Rolling → Intermediate Annealing → Cold Rolling → Solution Treatment (Annealing) → Straightening → Polishing → Cold-rolled coil. 
Main application areas 
Stainless steel coils serve as the "corrosion-resistant backbone" of high-end manufacturing and modern life. 
Architecture and Decoration: Elevator cabs, curtain walls, doors and windows, decorative trims, roofs, and railings (commonly made from 304/316 stainless steel). 
Home Appliances & Kitchenware: Washing machine drums, refrigerator panels, range hoods, sinks, dinnerware, and cookware (commonly made from 430 and 304 stainless steel). 
Transportation: Automotive exhaust pipes (409/439), train carriages, and marine components (316). 
Industry & Chemicals: Chemical equipment, food and pharmaceutical machinery, energy pipelines, and storage tanks (316L, 2205). 
Electronics & New Energy: Electronic product structural components, battery casings, and photovoltaic mounting brackets.