As a core basic material in industries such as industrial manufacturing, architectural decoration, new energy, food and pharmaceutical, the selection of stainless steel coils directly determines the performance, service life and comprehensive cost of end products. Based on international and domestic authoritative standards such as ASTM, EN and GB/T, this guide provides scientific and accurate procurement references from five core dimensions: core characteristics, selection logic, scenario adaptation, quality identification and procurement guarantee, helping you avoid selection misunderstandings and quality risks.
I. Core Cognition: Basic Definition and Classification of Stainless Steel Coils
Stainless steel coils are alloy coils based on iron, with a chromium content of ≥10.5% and a carbon content of ≤2.0% (except for some grades). They are continuously rolled through hot rolling or cold rolling processes, and delivered after annealing, pickling, surface treatment and other processes. According to core attributes, they can be divided into three categories, with the core characteristics of each category as follows:
(I) Classification by Production Process
|
Process Type
|
Core Characteristics
|
Tolerance Accuracy
|
Applicable Scenarios
|
|
Hot-Rolled Coil (HR)
|
Hot-rolled at high temperature, surface is grayish white (No.1/1D), rough and matte, with high strength and moderate plasticity
|
Thickness tolerance: ±0.15-0.30mm, Width tolerance: ±1-2mm
|
Heavy industrial equipment, steel structure base material, further processing blanks
|
|
Cold-Rolled Coil (CR)
|
Cold-rolled at room temperature, smooth surface (2D/2B/BA, etc.), precise size, excellent formability
|
Thickness tolerance: ±0.02-0.05mm, Width tolerance: ±0.5-1mm
|
Home appliances, food equipment, decorative building materials, precision mechanical components
|
(II) Classification by Material Grade (Mainstream Grades)
|
Series
|
Typical Grade
|
Core Composition (Key Elements)
|
Corrosion Resistance
|
Mechanical Properties (Yield Strength/Tensile Strength)
|
Core Advantages
|
|
Austenitic (General Purpose)
|
304 (SUS304/A240 304)
|
Cr: 18-20%, Ni: 8-10.5%
|
Good, resistant to atmospheric, fresh water and weak acid-base corrosion
|
≥205MPa / ≥515MPa
|
High cost-performance ratio, good processability, versatile and general-purpose
|
|
Austenitic (Corrosion Resistant)
|
316L (SUS316L/A240 316L)
|
Cr: 16-18%, Ni: 10-14%, Mo: 2-3%
|
Excellent, resistant to chloride ion, seawater and chemical medium corrosion
|
≥170MPa / ≥485MPa
|
Resistant to pitting corrosion and creep, suitable for harsh environments
|
|
Ferritic (Economical)
|
430 (SUS430/A240 430)
|
Cr: 16-18%, no Ni
|
General, resistant to atmospheric corrosion, not resistant to acid and alkali
|
≥205MPa / ≥450MPa
|
Low cost, strong magnetism, suitable for decoration and weak corrosion scenarios
|
|
Martensitic (Wear Resistant)
|
420J2 (SUS420J2/A240 420)
|
Cr: 12-14%, C: 0.16-0.25%
|
General, passivation required to improve corrosion resistance
|
≥440MPa / ≥620MPa (after heat treatment)
|
High hardness, high wear resistance, can be strengthened by heat treatment
|
|
Duplex (High Strength & Corrosion Resistant)
|
2205 (SUS2205/A240 2205)
|
Cr: 21-23%, Ni: 4.5-6.5%, Mo: 2.5-3.5%
|
Extremely excellent, resistant to general corrosion and stress corrosion
|
≥450MPa / ≥620MPa
|
High strength, suitable for marine engineering and chemical equipment
|
(III) Classification by Surface Treatment (Core Application Scenarios)
The surface treatment of stainless steel coils directly affects appearance, corrosion resistance and cleanliness. It should be accurately selected according to end-user needs. The mainstream surface treatment types and suitable scenarios are as follows:
|
Surface Code
|
Surface Characteristics
|
Processing Technology
|
Core Applications
|
Supporting Treatment
|
|
No.1 (1D)
|
Rough and matte, grayish white
|
Hot rolling + annealing + pickling
|
Industrial equipment, steel structure base material
|
No additional treatment required
|
|
2B
|
Smooth matte, slightly reflective
|
Cold rolling + annealing + pickling + light polishing
|
General industrial components, home appliance casings, further processing base material
|
Passivation treatment optional
|
|
BA
|
Highly reflective bright surface, mirror effect
|
Cold rolling + controlled atmosphere annealing (hydrogen protection)
|
Home appliance liners, elevator cabs, high-end decoration
|
Passivation treatment mandatory
|
|
No.4
|
Matte, discontinuous filiform luster (hairline texture)
|
Polishing with 120-150 mesh abrasive materials
|
Kitchenware, medical equipment, elevator panels
|
Passivation + cleaning treatment
|
|
HL (Hairline)
|
Continuous slender straight lines, strong decorative effect
|
Continuous friction polishing
|
Architectural interior decoration, electrical panels, high-end bathroom
|
Passivation + anti-fingerprint treatment
|
|
No.8 (Mirror)
|
Highly reflective, no visible grinding marks
|
Multi-pass fine grinding + polishing paste polishing
|
High-end decoration, sculpture, semiconductor equipment
|
Electropolishing + passivation
|
|
EP (Electropolishing)
|
Smooth micro-mirror surface, rounded edges and corners
|
Electrolytic selective dissolution of surface protrusions
|
Medical implants, food and pharmaceutical equipment, high-purity pipelines
|
Compliant passivation verification
|
II. Professional Selection: Four Core Dimensions for Precise Demand Matching
The selection of stainless steel coils should follow the principle of "scenario-oriented + performance matching + cost optimization", focusing on the following four core dimensions to avoid blind procurement of high-priced materials or selection of inappropriate products.
(I) Evaluation of Scene Corrosion Environment
The corrosion environment is the core basis for material grade selection. Different environments correspond to stainless steels of different corrosion resistance levels, with specific matches as follows:
-
Mild corrosion environment (atmosphere, fresh water, indoor dry environment): Priority is given to 304 and 430, which have controllable costs and meet basic corrosion resistance requirements;
-
Moderate corrosion environment (weak acid-base, humid environment, general chemical media): Select 304L (low-carbon 304, resistant to intergranular corrosion) and 316;
-
Severe corrosion environment (seawater, chloride ion media, strong acid-base, high-temperature and high-humidity corrosion environment): Select 316L and 2205 duplex steel, and special materials such as Hastelloy if necessary;
-
Hygienic grade scenarios (food, medicine, medical treatment): Select 304/316L, with BA and EP as preferred surface treatments, which must comply with FDA and EHEDG certification standards.
(II) Matching of Size and Tolerance Accuracy
Determine the thickness, width, length and tolerance accuracy of the coil according to the processing technology and end product requirements. The core references are as follows:
-
Thickness range: Cold-rolled coils 0.3-6.0mm (precision cold-rolled can reach 0.05mm), hot-rolled coils 2.0-14.0mm, customized for ultra-thick requirements;
-
Width range: Conventional 1000mm, 1219mm, 1500mm, supporting non-standard width customization (10-2000mm);
-
Tolerance selection: High-precision tolerance (thickness ±0.02-0.05mm) for precision processing (such as home appliance panels, precision machinery), and conventional tolerance (thickness ±0.1-0.3mm) for general industrial scenarios;
-
Coil weight selection: Conventional coil weight 1-20 tons, determined according to transportation, storage and processing needs. Small-batch procurement can choose slitted coils.
(III) Processing Performance Requirements
Different end processing technologies have different requirements for the ductility, hardness and weldability of stainless steel coils, with specific matches as follows:
|
Processing Technology
|
Core Performance Requirements
|
Recommended Grade/Surface
|
|
Deep drawing, stretching (such as sinks, containers)
|
High ductility, low hardness, elongation ≥40%
|
304 (2B surface), 316L (2B surface)
|
|
Bending, stamping (such as architectural accessories, home appliance components)
|
Good toughness, no cracks after bending
|
304, 430 (2B/No.4 surface)
|
|
Welding (such as pipelines, equipment casings)
|
Excellent weldability, no intergranular corrosion
|
304L, 316L (2B/No.1 surface)
|
|
Cutting, grinding (such as cutting tools, mechanical parts)
|
High hardness, high wear resistance
|
420J2, 440C (annealed state)
|
(IV) Cost Optimization Principles
On the premise of meeting performance requirements, reasonably control procurement costs. The core principles are as follows:
-
Avoid "over-selection": 316L is not required for non-corrosive environments, and BA/No.8 surfaces are not required for general decoration scenarios;
-
Bulk procurement bargaining: 5-10% price discount is available for bulk procurement of conventional grades (304, 430);
-
Priority to spot specifications: Non-standard size customization has a long cycle (7-15 days), and the cost is 10-20% higher than spot specifications.
III. Scenario-Oriented Adaptation: Mainstream Industry Selection Schemes
Combined with the core needs of various industries, targeted stainless steel coil selection schemes are provided to directly match actual procurement scenarios:
(I) Architectural Decoration Industry
Core needs: Decorativeness, atmospheric corrosion resistance, easy processing, anti-fingerprint required for some scenarios
Selection scheme: External wall curtain wall (2205 duplex steel/316L, HL/No.4 surface, anti-fingerprint treatment); Indoor decoration (304, 2B/HL surface); Elevator cab (304/316L, BA/HL surface)
(II) Home Appliance Industry
Core needs: Clean appearance, good formability, hygienic safety (food contact type)
Selection scheme: Refrigerator/washing machine casing (304, 2B surface); Microwave oven liner (304, BA surface); Sink (304/316L, 2B/EP surface, compliant with FDA certification)
(III) Food and Pharmaceutical Industry
Core needs: Hygienic grade, corrosion resistance, easy cleaning, no residue, compliant with industry certification
Selection scheme: Food processing equipment (316L, EP/BA surface, EHEDG certification); Pharmaceutical pipeline (316L, EP surface, GMP certification); Medical equipment (316L/420J2, EP/passivation treatment)
(IV) New Energy Industry
Core needs: Weather resistance, corrosion resistance, high strength, suitable for outdoor/harsh environments
Selection scheme: Photovoltaic bracket (316L, 2B surface); Wind power equipment (2205 duplex steel, No.1 surface); Battery case (304, precision cold-rolled 2B surface, thickness 0.5-1.0mm)
(V) Marine and Chemical Industry
Core needs: Chloride ion corrosion resistance, creep resistance, high strength, suitable for high-temperature and high-pressure environments
Selection scheme: Seawater treatment equipment (316L/2205, 2B/No.4 surface); Chemical storage tank (316L, No.1/2B surface); Marine components (2205 duplex steel, annealed state)
IV. Quality Identification: Six Core Inspection Standards (Avoid Procurement Risks)
When purchasing stainless steel coils, it is necessary to identify quality through three means: "document verification + appearance inspection + performance verification". The core inspection standards are as follows:
(I) Document Verification: Complete Qualifications and Reports
-
Supplier qualifications: Possess ISO9001 quality management system certification, and PED 2014/68/EU certification for pressure equipment;
-
Product reports: Provide third-party inspection reports (such as SGS, CTI), including chemical composition analysis, mechanical property testing, surface quality inspection results. The report batch must be consistent with the product batch;
-
Label information: The labels at both ends of the coil must clearly indicate the grade, specification (thickness/width/coil weight), batch number, production date and execution standard (such as ASTM A240, GB/T 4237).
(II) Appearance Inspection: No Surface Defects
Visually inspect the surface with the help of a magnifying glass. High-quality stainless steel coils should meet: uniform surface luster, no obvious scratches, rust spots, pores, scale, inclusions and other defects; no burrs or cracks on the edges, tight winding of the coil, no looseness or deformation.
(III) Composition Verification: Core Elements Meet Standards
Detect the content of core alloy elements through a spectrometer, focusing on verifying whether the Cr, Ni and Mo contents meet the standards (such as 304 Cr≥18%, Ni≥8%; 316L Mo≥2%), to avoid "shoddy products" (such as 201 passing off as 304).
(IV) Mechanical Property Testing
Check the mechanical property indicators in the inspection report to ensure that the yield strength, tensile strength and elongation meet the requirements (such as elongation ≥40% for deep drawing scenarios). If necessary, samples can be sent to a third-party institution for testing.
(V) Surface Roughness and Adhesion Testing
Surface roughness testing is required for decorative or precision scenarios (such as 2B surface Ra≤0.6μm); Coating adhesion testing is required for coated products (such as PVD coating) to ensure no peeling.
(VI) Corrosion Resistance Verification
For products used in harsh environments, suppliers can be required to provide salt spray test reports (such as 316L no rust in 5% NaCl environment for ≥96 hours), or samples can be taken for salt spray testing.
V. Procurement Guarantee: Supplier Selection and After-Sales Notes
(I) Selection Standards for High-Quality Suppliers
-
Have a complete production industrial chain (cold rolling, annealing, surface treatment, slitting, etc.), rather than just a trader, which can control product quality and delivery cycle;
-
Have complete testing equipment (spectrometer, metallographic microscope, salt spray test chamber, etc.), and can provide full-process quality traceability;
-
Have flexible delivery and value-added service capabilities (such as 72-hour spot delivery, non-standard customization, slitting, laser cutting, JIT supply, etc.);
-
Have a good industry reputation and cases, and can provide similar industry cooperation cases (such as home appliance and pharmaceutical industry customer cases).
(II) After-Sales Guarantee Notes
-
Quality objection: Quality objections must be raised within 7 working days after receiving the goods, keeping samples and inspection reports. The supplier shall respond within 48 hours and negotiate a solution (return and exchange, replenishment, technical support, etc.);
-
Storage requirements: The storage environment must be dry and ventilated (humidity ≤60%), avoid contact with carbon steel (prevent iron ion pollution), and the coil shall be placed vertically to avoid extrusion deformation;
-
Processing support: High-quality suppliers should provide processing technical guidance (such as bending parameters, welding process, surface cleaning method) to help solve problems in the processing process.
VI. Common Selection Misunderstandings and Answers
Misunderstanding 1: Stainless steel never rusts? Answer: The "rust resistance" of stainless steel is relative. It may still rust in harsh environments such as chloride ions and strong acid-base. It is necessary to select the appropriate grade according to the corrosion environment (such as 316L is resistant to chloride ion corrosion), and do a good job in surface passivation, anti-fingerprint and other protective treatments.
Misunderstanding 2: 316L is definitely better than 304? Answer: 316L has better corrosion resistance than 304, but its price is 25-30% higher than 304. 304 has higher cost-performance ratio for non-corrosive environments (such as indoor decoration), and there is no need to blindly pursue high-priced grades.
Misunderstanding 3: The brighter the surface, the better the quality? Answer: Surface brightness only reflects the surface treatment process, and has nothing to do with material composition and mechanical properties. The quality should be comprehensively judged by combining core indicators such as composition and performance, not just by brightness.
Misunderstanding 4: All stainless steel is non-magnetic? Answer: Austenitic stainless steel (304, 316L) is usually non-magnetic or weakly magnetic, while ferritic (430) and martensitic (420J2) stainless steel are strongly magnetic. Magnetism cannot be the only standard to judge the authenticity of materials.
This guide is compiled based on current industry standards and market practices. If you have specific application scenarios, size requirements or performance needs, you can contact our technical team to provide you with one-on-one precise selection schemes and product quotes.
