STAINLESS STEEL GRADE SERIES
Among the hundreds of stainless steel grades available to the engineering community, AISI 304 accounts for more than half of all stainless steel produced globally. This dominance is not accidental. The 18% chromium and 8% nickel composition that defines 304 — the origin of its common designation as “18/8 stainless” — delivers a combination of corrosion resistance, formability, weldability, and machinability that no single alternative grade can match across such a broad range of applications. For precision CNC machined components, 304 is the starting point against which all other stainless grades are evaluated.
At ODM PARTS, AISI 304 is the most frequently processed stainless steel across our CNC machining, CNC turning, and sheet metal fabrication lines. Our production experience with this grade spans food processing equipment, semiconductor tooling, medical device components, and structural hardware for the European industrial market.
MECHANICAL PROPERTIES
Core Mechanical Data: AISI 304
| Property | Value | Test Standard |
|---|---|---|
| Tensile Strength | 515–620 MPa | ASTM A370 |
| Yield Strength (0.2% offset) | 205–310 MPa | ASTM A370 |
| Elongation (50mm gauge) | 40–70% | ASTM A370 |
| Hardness (Brinell) | 201 HB max | ASTM E10 |
| Hardness (Rockwell B) | 92 HRB max | ASTM E18 |
| Density | 8.00 g/cm³ | — |
| Modulus of Elasticity | 193 GPa | — |
| Thermal Conductivity | 16.2 W/m·K (100°C) | — |
| Thermal Expansion | 17.2 μm/m·°C (0–100°C) | — |
| Magnetic Permeability | ≤1.02 (annealed) | — |
Chemical Composition (ASTM A276 / EN 1.4301):
| Element | Min % | Max % |
|---|---|---|
| Chromium (Cr) | 18.00 | 20.00 |
| Nickel (Ni) | 8.00 | 10.50 |
| Carbon (C) | — | 0.08 |
| Manganese (Mn) | — | 2.00 |
| Silicon (Si) | — | 1.00 |
| Phosphorus (P) | — | 0.045 |
| Sulfur (S) | — | 0.030 |
| Nitrogen (N) | — | 0.10 |
The chromium content forms a self-repairing passive oxide layer (Cr₂O₃) approximately 1–3 nm thick that provides the fundamental corrosion protection mechanism. This layer reforms within seconds when mechanically damaged in the presence of oxygen, which is why 304 maintains its corrosion resistance through machining, forming, and welding operations — provided the surface is not contaminated with free iron from tooling or fixtures.
Our Precision CNC Machining for Stainless Steel team uses dedicated tooling and fixtures for 304 to prevent cross-contamination with carbon steel or iron particles that would compromise the passive layer.
MATERIAL SERIES AND GRADES
The 304 Family: Selecting the Right Variant
AISI 304 is the base grade of a family of closely related austenitic stainless steels. Understanding the variants is essential for correct specification:
AISI 304 (EN 1.4301)
The standard grade. Carbon content up to 0.08% provides good mechanical properties. Suitable for most applications not involving sustained elevated temperatures or aggressive chloride environments.
AISI 304L (EN 1.4307)
Low-carbon variant with maximum 0.03% carbon. The reduced carbon content prevents chromium carbide precipitation at grain boundaries during welding (sensitization), making 304L the correct specification for welded assemblies that will be exposed to corrosive environments. Mechanical properties are slightly lower than standard 304.
AISI 304H (EN 1.4948)
High-carbon variant with 0.04–0.10% carbon minimum. The higher carbon content improves creep strength at elevated temperatures (above 500°C), making 304H the specification for high-temperature pressure vessels and heat exchangers.
AISI 304N / 304LN
Nitrogen-added variants that improve strength while maintaining or improving corrosion resistance. Used in structural applications where higher strength than standard 304 is required without the cost of duplex grades.
For procurement engineers, the key decision point is whether the component will be welded. If yes, 304L should be specified unless the application requires the elevated-temperature strength of 304H. If no welding is involved, standard 304 provides the best combination of strength and corrosion resistance.
MANUFACTURING CAPABILITIES
Processing AISI 304 at ODM PARTS
AISI 304 is classified as a moderately difficult material to machine due to its tendency to work-harden and its low thermal conductivity, which concentrates heat at the cutting zone. Our production team has developed specific process parameters that consistently achieve the dimensional tolerances and surface finishes required by our customers.
CNC Machining Parameters for 304:
- Cutting Speed: 120–180 m/min (carbide tooling, flood coolant)
- Feed Rate: 0.1–0.3 mm/rev (turning), 0.05–0.15 mm/tooth (milling)
- Depth of Cut: 0.5–3.0 mm (roughing), 0.1–0.5 mm (finishing)
- Coolant: High-pressure flood coolant mandatory (prevents work-hardening)
- Tooling: Sharp, positive-rake carbide inserts; TiAlN coating preferred
Sheet Metal Fabrication of 304:
304 sheet and strip is processed on our press brake, laser cutting, and stamping lines. Key parameters:
- Minimum Bend Radius: 1.0T (annealed sheet)
- Springback Compensation: 2–5° overbend depending on thickness
- Laser Cutting: Nitrogen assist gas for oxide-free cut edges
- Welding: TIG (GTAW) preferred for precision components; MIG (GMAW) for structural work
Available Surface Finishes:
| Finish Designation | Ra Value | Description |
|---|---|---|
| No. 1 (Hot Rolled) | 3.0–6.0 μm | Rough, scale surface; industrial use |
| No. 2B | 0.1–0.5 μm | Standard mill finish; most common |
| No. 4 (Brushed) | 0.5–1.5 μm | Unidirectional brushed; architectural |
| No. 8 (Mirror) | 0.05–0.1 μm | Mirror polished; decorative/optical |
| Electropolished | 0.05–0.2 μm | Passivated, smooth; medical/pharma |
| Bead Blasted | 0.8–3.2 μm | Uniform matte; industrial |
ENGINEERING SELECTION CRITERIA
When to Specify AISI 304
1. General Corrosion Resistance in Non-Chloride Environments
AISI 304 provides excellent resistance to atmospheric corrosion, oxidizing acids (nitric acid up to 65%), and most organic acids. It is the correct specification for food processing equipment, chemical storage vessels, and architectural components in non-coastal environments.
2. Hygienic and Food-Contact Applications
The smooth, passive surface of 304 does not support bacterial adhesion and is compatible with standard food-grade cleaning chemicals (CIP systems). FDA and EU food contact regulations accept 304 for direct food contact without restriction.
3. Cryogenic Applications
Unlike ferritic and martensitic stainless steels, 304’s austenitic structure maintains toughness at cryogenic temperatures down to -196°C (liquid nitrogen temperature). This makes it the standard specification for cryogenic storage vessels, LNG equipment, and laboratory cryogenic systems.
4. Non-Magnetic Requirement
In the annealed condition, 304 has a magnetic permeability of ≤1.02, making it effectively non-magnetic. Applications in MRI equipment, electronic assemblies, and precision instruments where magnetic interference must be avoided specify 304 for this property.
Quantitative Selection Thresholds:
| Requirement | 304 Suitable? | Alternative if Not |
|---|---|---|
| Chloride concentration < 200 ppm | Yes | — |
| Chloride concentration > 200 ppm | No | 316L |
| Service temperature < 425°C | Yes | — |
| Service temperature > 425°C (sustained) | No | 304H or 310S |
| Welded assembly, corrosive environment | Marginal | 304L |
| Tensile strength > 700 MPa required | No | 301 FH or 17-4PH |
MATERIAL COMPARISON
AISI 304 vs. Competing Grades
| Property | AISI 304 | AISI 316L | AISI 301 FH | AISI 430 | Carbon Steel (1045) |
|---|---|---|---|---|---|
| Tensile Strength | 515–620 MPa | 485–620 MPa | 1,275 MPa | 480–520 MPa | 585–760 MPa |
| Corrosion Resistance | Good | Excellent | Good | Moderate | Poor |
| Weldability | Excellent | Excellent | Fair | Good | Good |
| Machinability (relative) | 45% | 40% | 35% | 60% | 100% |
| Magnetic | No (annealed) | No (annealed) | Partially | Yes | Yes |
| Relative Material Cost | 1.0× | 1.4× | 1.0× | 0.7× | 0.15× |
| Food Contact Approved | Yes | Yes | Yes | Yes | No |
The comparison with 316L is the most common decision point for procurement engineers. The 2% molybdenum addition in 316L raises the pitting resistance equivalent number (PREN) from approximately 18 (304) to 25 (316L), providing meaningful improvement in chloride-containing environments. For applications where chloride exposure is confirmed or suspected, the 40% material cost premium for 316L is justified. For dry, atmospheric, or mild chemical environments, 304 provides equivalent performance at lower cost.
INDUSTRY APPLICATIONS
Where AISI 304 Performs
Food Processing and Beverage Equipment
Tanks, vessels, conveyors, pumps, and fittings in food and beverage production are the largest single application sector for 304. The grade’s combination of corrosion resistance, hygienic surface finish, and compatibility with CIP cleaning systems makes it the industry default. Our facility supplies 304 components to food equipment manufacturers across Europe and North America.
Semiconductor and Electronics Manufacturing
Process chambers, gas delivery systems, and tooling fixtures in semiconductor fabrication use 304 for its combination of cleanliness, corrosion resistance to process chemicals, and dimensional stability. The electropolished surface finish achievable on 304 meets the surface roughness requirements of semiconductor process equipment.
Medical Device and Pharmaceutical
Surgical instrument components, pharmaceutical reactor fittings, and sterile processing equipment use 304 for its autoclave compatibility and resistance to cleaning agents. For implantable devices, 316L is specified; for non-implantable instruments and equipment, 304 is the standard.
Architectural and Construction
Curtain wall systems, handrails, elevator interiors, and structural fasteners in commercial construction specify 304 for its combination of aesthetic appearance and corrosion resistance in urban environments. The No. 4 brushed finish is the most common specification for architectural applications.
Chemical Processing
Storage tanks, heat exchangers, and piping for non-chloride chemical processes use 304 extensively. The grade’s resistance to nitric acid, phosphoric acid, and most organic acids covers a wide range of chemical processing applications.
Automotive and Transportation
Exhaust system components, trim parts, and structural fasteners in automotive applications use 304 for its combination of corrosion resistance and formability. For high-temperature exhaust applications, 309S or 310S are specified instead.
ODM PARTS BRAND COMMITMENT
Our Commitment to AISI 304 Quality
Every AISI 304 component manufactured at ODM PARTS is produced from certified mill material with full chemical and mechanical traceability. Our quality system requires mill test reports (MTR) for all incoming material, with verification testing for critical applications.
Quality Certifications:
- ISO 9001:2015 — Quality Management System
- ISO 13485:2016 — Medical Device Quality Management
- AS9100D — Aerospace Quality Management
- IATF 16949 — Automotive Quality Management
Dimensional Capabilities:
- Tolerance: ±0.01mm on precision CNC machined features
- Surface Roughness: Ra 0.4 μm (standard finish), Ra 0.1 μm (electropolished)
- Flatness: ±0.02mm per 100mm on ground surfaces
- Roundness: ±0.005mm on precision turned diameters
Lead Times:
- Prototype (1–10 pieces): 5–7 business days
- Small batch (10–100 pieces): 10–15 business days
- Production (100–1,000 pieces): 20–30 business days
Included with Every Order:
- Material Test Report (MTR) with heat number
- Dimensional Inspection Report (CMM or manual, per specification)
- Surface Roughness Certificate (where specified)
- Complimentary DFM Review
Our Full Precision CNC Machining Services, CNC Turning Services, and ISO 9001 Quality Assurance infrastructure ensure consistent quality across all 304 production runs.
CONCLUSION AND CTA
Specifying AISI 304 for Your Next Project
AISI 304 remains the most versatile and cost-effective stainless steel for the majority of precision machined component applications. Its combination of corrosion resistance, weldability, formability, and surface finish capability covers the requirements of food processing, medical, semiconductor, architectural, and general industrial applications without the material cost premium of higher-alloyed grades. The key to successful 304 specification is understanding its limitations — primarily chloride sensitivity and the need for 304L in welded assemblies — and selecting the appropriate variant for the specific application.
For procurement engineers evaluating 304 for a new project, we recommend a DFM review that addresses material variant selection (304 vs. 304L), surface finish specification, and dimensional tolerances. This review is provided at no charge with every inquiry.
Request a Quote for Your AISI 304 Project — Upload your drawing and receive a detailed quotation with lead time within 24 hours.
Contact Our Engineering Team — For technical questions about 304 variant selection, surface finish options, or process capability for your specific application.
ODM PARTS — Precision CNC Machining | CNC Turning | Sheet Metal Fabrication
ISO 9001 | AS9100D | ISO 13485 | IATF 16949 Certified | Xi’an, China
https://odm-parts.com/
