18/8 stainless steel is a stainless steel containing 18% chromium and 8% nickel, also known as 304 stainless steel. It is known for its excellent corrosion resistance and good heat resistance and is suitable for use in a variety of applications, including kitchenware and medical equipment.18/8 stainless steel has good room-temperature processing properties such as deep drawing and bending, and does not harden after heat treatment. However, it is important to note that while it is resistant to impregnation by most food processing media, corrosion may occur at elevated temperatures, especially in environments containing concentrated acid and chloride components. In addition, 18/8 stainless steel is resistant to organic compounds, dyes, and a wide range of inorganic compounds.
18/8 Stainless Steel Composition
The numbers “18” and “8” in 18/8 refer to the percentages of Chromium and Nickel alloying elements in the stainless steel composition:
18% Chromium (Cr)
Chromium is the primary alloying element in stainless steel that provides corrosion resistance. The high chromium content forms a passive oxide layer on the surface of the steel, which helps protect it from oxidation and corrosion.
8% Nickel (Ni)
Nickel enhances the stainless steel’s resistance to corrosion and adds to its overall strength. The nickel content also contributes to the steel’s ability to maintain its austenitic structure at various temperatures.
Other Elements
In addition to chromium and nickel, 18/8 stainless steel may contain small amounts of other elements, such as carbon, manganese, silicon, and other trace elements. These elements help fine-tune the steel’s properties for specific applications. The specific chemical composition is defined by the product standard. The common industry judgment is that as long as the Ni content is greater than 8 percent and the Cr content is greater than 18 percent.
Chemical Composition Chart
| Standard | Grade | C | Mn | P | S | Si | Cr | Ni | N |
|---|---|---|---|---|---|---|---|---|---|
| ASTM A240 | 304 | ≤0.08 | ≤2.00 | 0.045 | 0.030 | 0.75 | 18-20 | 8.0-11 | ≤0.10 |
| ASTM A240 | 304L | ≤0.03 | ≤2.00 | 0.045 | 0.030 | 0.75 | 18.0-20.0 | 8.0-12 | ≤0.10 |
| ASTM A240 | 304H | 0.04-0.10 | ≤2.00 | 0.045 | 0.030 | 0.75 | 18-20 | 8.0-10.5 | – |
| ASTM A240 | 304N | ≤0.08 | ≤2.00 | 0.045 | 0.030 | 0.75 | 18-20 | 8.0-10.5 | 0.10-0.16 |
| ASTM A240 | 305 | ≤0.12 | ≤2.00 | 0.045 | 0.030 | 0.75 | 17.0-19.0 | 10.5-13.0 | – |
Mechanical Properties Chart
| Standard | Grade | Yield Point | Tensile Strength | Elongation | Hardness | Hardness |
|---|---|---|---|---|---|---|
| MPa | MPa | % | HRB | HB | ||
| ASTM A240 | 304 | ≥ 205 | ≥ 515 | ≥ 40 | ≤ 92HRB | ≤ 201 |
| ASTM A240 | 304L | ≥ 170 | ≥ 485 | ≥ 40 | ≤ 92HRB | ≤ 201 |
| ASTM A240 | 304H | ≥ 205 | ≥ 515 | ≥ 40 | ≤ 92HRB | ≤ 201 |
| ASTM A240 | 304N | ≥ 240 | ≥ 550 | ≥ 30 | ≤ 95HRB | ≤ 217 |
| ASTM A240 | 305 | ≥ 170 | ≥ 485 | ≥ 40 | ≤ 88HRB | ≤ 183 |
18/8 Stainless Steel Characteristics
- Excellent corrosion resistance, 18/8 Stainless Steel is composed of 18% chromium and 8% nickel, which is where it gets its name. It also contains around 50% iron and 0.8% carbon. The chromium in the steel can bond with oxygen, which helps to prevent rust and corrosion.
- Durability, the nickel content is what gives stainless steel its durability. Generally speaking, the more nickel that Stainless Steel contains, the more durable it will be.
- Versatility, it is one of the most widely used stainless steel due to its excellent properties.
- Non-magnetic, structure of 18/8 stainless steel is austenitic at room temperature in the solution annealed condition, which makes it non-magnetic.
- Hardenable by cold working.
- It can resist most types of corrosion, but it can be damaged by salt water.
- Food-grade stainless steel.
18/8 Stainless Steel Applications
18/8 stainless steel is the combination of corrosion resistance, strength, and ease of fabrication making it a popular choice for many applications where exposure to moisture, chemicals, and harsh environments is a concern.
Chromium can improve the strength and corrosion resistance of stainless steel, nickel has high brightness and corrosion resistance—application products such as corrosion-resistant containers, cutlery, household, railings, and medical equipment.