18-8 Stainless Steel: A Comprehensive Guide to Properties and Uses
What is 18-8 stainless steel?
18-8 stainless steel, also known as 304-grade stainless steel, earns its name from its composition—containing approximately 18% chromium and 8% nickel. The remainder consists of iron and a mix of several other elements. Noteworthy designations for this type of stainless steel include 301, 302, and 304.
18-8 stainless steel is a versatile and widely used material due to its excellent balance of properties. The high chromium content forms a passive layer of chromium oxide on the surface, providing exceptional corrosion resistance. This makes it ideal for a variety of applications, especially in environments exposed to moisture and mild chemicals. Additionally, the nickel content contributes to the steel's ductility and toughness, allowing it to be easily formed and welded.
Another significant characteristic is its non-magnetic nature in the annealed (soft) condition. However, it can become slightly magnetic when cold-worked, such as through bending or forming. This is due to a structural change in the steel at a microscopic level. 18-8 stainless steel is also known for its good strength and aesthetic appeal, making it a popular choice for both industrial and consumer products.
Table of Contents
- 18-8 Stainless Steel Chemical Compositions
- 18-8 stainless steel Equivalent Grade
- Properties of 18.8 Stainless Steel
- 18-8 Stainless Steel Mechanical Properties
- 18-8 Stainless Steel Material Properties or Physical Properties
- Type 304 Physical Properties
- Applications of 18/8 Stainless Steel
- Frequently Asked Questions (FAQs) about 18-8 stainless steel
18-8 Stainless Steel Chemical Compositions
| Chemical Composition, % | |||||||||||
| ASTM | AISI (UNS) | C, ≤ | Si, ≤ | Mn, ≤ | P, ≤ | S, ≤ | Cr | Ni | N, ≤ | Product | |
| ASTM A240/A240M | 304 (UNS S30400) | 0.07 | 0.75 | 2.00 | 0.045 | 0.030 | 17.5-19.5 | 8.0-10.5 | 0.10 | Plate, Sheet, and Strip | |
| ASTM A276A/276M | 0.08 | 1.00 | 2.00 | 0.045 | 0.030 | 18.0-20.0 | 8.0-11.0 | – | Bars and Shapes | ||
18-8 stainless steel Equivalent Grade
| US | European Union | ISO | Japan | China | |||||
| Standard | Type | Standard | Grade (Steel Number) | Standard | Grade (ISO Number) | Standard | Grade | Standard | Grade |
| AISI SAE; ASTM A276/A276M; ASTM A240/A240M; | 304 (UNS S30400) | EN 10088-1; EN 10088-2; EN 10088-3 | X5CrNi18-10 (1.4301) | ISO 15510 | X5CrNi18-10 | JIS G4303; JIS G4304; JIS G4305; | SUS304 | GB/T 20878; GB/T 1220; GB/T 3280 | 0Cr18Ni9; 06Cr19Ni10 (New designation) |
| 304L (UNS S30403) | X2CrNi18-9 (1.4307); X2CrNi19-11 (1.4306) | X2CrNi19-11 (4306-304-03-I) | SUS304L | 00Cr19Ni10; 022Cr19Ni10 (New name) | |||||
Properties of 18.8 Stainless Steel
- Corrosion Resistance: Within the 18-8 types, minimal distinctions in corrosion resistance exist. However, subtle variations in chemical composition can render certain grades more resistant to specific chemicals or atmospheric conditions. Notably, 18.8 stainless steel exhibits superior corrosion resistance, outperforming counterparts in the 400 series stainless steel.
- Magnetic Characteristics: A distinctive feature is its non-magnetic nature, setting it apart from materials in the 400 series. This property expands its utility, particularly in applications where magnetic interference is undesirable.
- Hardenability: 18.8 stainless steel demonstrates hardenability solely through the cold working process. This characteristic contributes to its versatility, allowing for customized applications in various industries.
18-8 Stainless Steel Mechanical Properties
| Mechanical Properties | |||||||||
| ASTM Type | AISI (UNS) | Tensile Strength, (MPa), ≥ | Yield Strength, ≥ (MPa) at 0.2% Offset | Elongation in 50 mm (%, ≥) | Reduction of Area, %, ≥ | Brinell Hardness, (HBW) ≤ | Rockwell Hardness, (HRBW) ≤ | Product | Condition |
| ASTM A240/A240M | 304 (UNS S30400) | 515 | 205 | 40 | – | 201 | 92 | Plate, Sheet, and Strip | – |
| ASTM A276A/276M | 515 | 205 | 40 | 50 | – | – | Bars and Shapes | Hot finished | |
| 620 | 310 | 30 | 40 | – | – | Cold finished, Dia ≤ 12.7mm | |||
| 515 | 205 | 30 | 40 | – | – | Cold finished, Dia. > 12.7mm | |||
18-8 Stainless Steel Material Properties or Physical Properties
- Density: 7.9 g/cm³ (Equivalent to 7900 kg/m³ or 7.9 x 10³ kg/dm³)
- Melting Point: Approximately 1400-1450°C (2552-2642°F)
- Magnetic Properties: Generally non-magnetic, distinguishing it from the magnetic 400 series stainless steels.
- Specific Heat Capacity: 500 J/(kg·K) or 0.12 BTU/(lb·°F)
- Electrical Resistivity: 720 Ω·mm²/m (Equivalent to 720 μΩ·m)
- Modulus of Elasticity (Elastic Modulus): Around 193 GPa (Equivalent to 193 kN/mm² or 193 × 10³ MPa)
- Thermal Diffusivity: Approximately 3.8 x 10⁻⁶ m²/s
- Thermal Conductivity: Typically 16-24 W/(m·K)
- Coefficient of Thermal Expansion: 16-17 x 10⁻⁶/K or 16-17 μm/(m·K)
Type 304 Physical Properties
| Physical Properties | |
| Density, g/cm3 (lb/in3) | 7.93 (0.286) |
| Melting point, °C (°F) | 1400-1450 (2550-2650) |
| Specific heat capacity, J/kg·K (Btu/lb ·°F) | 500 (0.12) at 20 °C (68 °F) |
| Electrical resistivity, μΩ·m | 0.72 at 20 °C (68 °F) |
| Conductivity, %, IACS | 2.5 |
| Magnetic permeability | 1.02 (Approximate) |
| Elastic modulus (Modulus of Elasticity), GPa (106 psi) | 193 (28) |
| Thermal diffusivity, mm2/s (in2/s) | 3.84 (0.006) |
| Thermal conductivity, W/m·K (Btu/ft·h·°F) | 16.2 (9.4) at 100 °C (212 °F) |
| 21.5 (12.4) at 500 °C (932 °F) | |
| Coefficient of thermal expansion (CTE), 10-6/K (μin./in·°F) | 17.2 (9.6) at 0-100 °C (32-212 °F) |
| 17.8 (9.9) at 0-315 °C (32-600 °F) | |
| 18.4 (10.2) at 0-538 °C (32-1000 °F) | |
Applications of 18/8 Stainless Steel
Widely utilized across industries, 18/8 stainless steel is a versatile material with applications in the petroleum and chemical industry, metallurgical machinery, aerospace industry, food processing equipment, instruments, household appliances, and hardware manufacturing. It serves as the foundation for intermediate products, including steel sheets, plates, tubes, pipes, bars, flats, rods, and wires. In its final form, 18/8 stainless steel is transformed into a myriad of products such as kitchenware, tableware, medical devices, machinery parts, wire mesh, filters, and architectural and decorative metal products. The material's unique combination of strength, corrosion resistance, and aesthetic appeal makes it indispensable in various manufacturing processes.
| 18-8 stainless steel equivalent grade | |||||||||||||||||
| US | European Union | ISO | Japan | China | |||||||||||||
| Standard | Type | Standard | Grade (Steel Number) | Standard | Grade (ISO Number) | Standard | Grade | Standard | Grade | ||||||||
| AISI SAE; ASTM A276/A276M; ASTM A240/A240M; |
304 (UNS S30400) |
EN 10088-1; EN 10088-2; EN 10088-3 | X5CrNi18-10 (1.4301) | ISO 15510 | X5CrNi18-10 | JIS G4303; JIS G4304; JIS G4305; | SUS304 | GB/T 20878; GB/T 1220; GB/T 3280 |
0Cr18Ni9; 06Cr19Ni10 (New designation) |
||||||||
| 304L (UNS S30403) |
X2CrNi18-9 (1.4307); X2CrNi19-11 (1.4306) |
X2CrNi19-11 (4306-304-03-I) | SUS304L | 00Cr19Ni10; 022Cr19Ni10 (New name) |
|||||||||||||
Frequently Asked Questions (FAQs) about 18-8 stainless steel
Is 18-8 a good type of stainless steel?
Yes, no doubt! 18-8 is a popular and reliable stainless steel for all sorts of things. Its main benefit is that it does a good job resisting rust and corrosion in everyday circumstances. The one thing to know is that it does NOT do good near salt water ( if you are near the ocean!) because the chloride can create corrosion over time.
Is 18-8 stainless steel good for cookware?
It is a good material for cookware, and practical. You will see a lot of it out there, particularly if you want something affordable with durability. It is rust resistant. If you are looking for completely upscale cookware that has even better resistance to tarnishing and corrosion; then look for some "18/10" stainless steel (the extra nickel gives it a little extra corrosion resistance)! But for 99% of cooking in the kitchen, 18-8 is perfectly fine.
Is 18-8 stainless steel safe for food grade?
Yes! 18-8 type stainless steel, particularly the common Type 304 is considered food grade. That all means that 18-8 or 304 is safe to use with food.
Can 18-8 stainless steel rust?
While highly resistant to rust, 18-8 stainless steel can rust under certain aggressive conditions, such as prolonged exposure to chlorides (salt), harsh chemicals, or if its protective chromium oxide layer is damaged and cannot reform. "Rust" is typically a sign of localized corrosion.
What is the temperature resistance of 18-8 stainless steel?
18-8 stainless steel can be used for continuous service up to about 870°C (1600°F) and for intermittent service up to 925°C (1700°F) without significant scaling. However, its strength decreases at elevated temperatures.
How strong is 18-8 stainless steel?
18-8 stainless steel offers good strength. For example, Type 304 typically has a tensile strength of around 515 MPa (75,000 psi) and a yield strength of about 205 MPa (30,000 psi) in the annealed condition. Cold working can significantly increase its strength.
What is the yield strength of 18-8 stainless steel?
The yield strength of 18-8 stainless steel is approximately 205 MPa (30,000 psi) in its standard, annealed condition. This value can be significantly increased through cold working, a process that strengthens the metal by shaping it at room temperature. This makes 18-8 stainless steel a very versatile material for applications requiring good strength without sacrificing ductility or corrosion resistance.