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18-8 and 304 stainless steel are two main types of metal that can significantly resist rust. Both are austenitic stainless steel. So18-8 steel falls in a general group. It is named for its 18% chromium and 8% nickel.
Now, the other one is 304 stainless steel. It is the most common type of 18-8. This is the point we are going to discuss in this article. You will read the basic comparison of 18-8 and 304 in detail. Moreover, we will try to teach you the basic concepts about differences and uses.
What is 18-8 Stainless Steel
18-8 stainless steel is not a single metal. It is an entire group belonging to stainless steel, each with a specific type. So, in simpler words, you can say 18-8 is a family of metals that have the same core properties. However, their individual traits are different.
Now the question is what are those key ingredients? These are 18% chromium and 8% nickel. So these two ingredients make 18-8 stainless steel a lethal combination. According to a research published in The Brighter Side on November 25, 2024, In 18-8 family there is a new edition of SS-H2 stainless steel. It has revolutionized green hydrogen production. This new development was presented by material researchers in the University of Hong Kong.
18-8 Composition in Detail
Chromium
In 18-8 stainless steel, chromium is the main ingredient. It is 18%. What does it mean? It makes an invisible protective layer on the stainless steel surface. Basically, this layer is very thin but is very strong to prevent oxygen and moisture from reaching iron in the steel. So this chromium layer makes a material of stainless steel.
Nickel
In 18-8 stainless steel, Nickel is available in 8% so it improves steel’s defense further such as fighting against acids. Moreover, it is nickel that helps CNC machining companies to form it in any shape without any fear of brittling.
A Family of Grades Under 18-8
Now the next step is to understand the familiar grades of the 18-8 family. These are
- 302
- 303
- 304
- 304L
General Chemical Composition
Earlier, you read the composition of Chromium and Nickel, and there are further compositions also. These are:
- Chromium: 18%
- Nickel: 8%
- Iron: 50-70%
- Carbon: 0.08%
Key Properties of 18-8 Stainless Steel
18-8 stainless steel gives two major benefits: resistance against corrosion and oxidation. So, it is a good choice for applications that are exposed to chemicals and moisture. Moreover, 18-8 surface is very smooth, which is easy to clean, and provides good hygiene as well, especially in the kitchen and medical field.
The other advantage is that it can significantly bear pressure and stress. Moreover, machining centres use this material to make complex designs for parts.
Common Applications of 18-8 Steel
Food and Beverage Industry
As mentioned above, 18-8 has a hygienic nature and can resist food acids easily. This materials is very common in food and kitchen accessories-making plants. The common examples are sinks, cookware, storage tanks, and food serving equipment.
Medical and Pharmaceutical Fields
Sterile components are very important in the medical field. Therefore, CNC machining companies incorporate 18-8 stainless steel to make surgical parts. These are sterilization trays, scissors, trocars and cannulas, and vascular clamps. These parts can significantly resist sterilization process.
Household Appliances
Household appliances remain vulnerable in day to day operations. For example, dishwashers, ovens, and refrigerators often face moisture and oxidation. So these appliances are mostly made up of 18-8 stainless steel.
Architecture and Construction
These days people are more interested in installing fancy girls, facades, and roofings. Change in weather can impact these installations so 18-8 stainless steel is used to make these parts for long-term performance.
Industrial Equipment
In manufacturing companies, larger machine units should be high-quality and wear-resistant. These parts are expensive and can’t be changed frequently. Therefore, 18-8 stainless steel is a good choice to make these parts. Some common examples of these parts are heat exchangers, tanks and vessels, compressors, and conveyor systems.
Advantages of 18-8 Stainless Steel
- Rust-resistance is good
- Can be used in different industries
- Better lifespan and strength
Limitations of 18-8 Stainless Steel
- They are susceptible to Harsh Environments
- Strength Compared to Specialized Steels
- Scratch Potential
What is 304 Stainless Steel
| Element | Weight Percentage |
|---|---|
| Carbon | 0.08 max |
| Manganese | 2.00 max |
| Phosphorus | 0.045 max |
| Sulphur | 0.030 max |
| Silicon | 0.75 max |
| Chromium | 18.00- 20.00 |
| Nickey | 8.00- 12.00 |
| Nitrogen | 0.10 max |
| Iron | 67- 71 |
304 stainless steel falls into the 18-8 family. It has very balanced properties and is a very reliable material used in several domestic and industrial applications. Interestingly, 304 stainless steel is also recognized by the American Iron and Steel Institute. Sometimes, it is also called A2 stainless steel. You can say these are common nicknames for grade 304.
304 Stainless Steel Composition
In the first section, you read the chemical composition of 18-8 in detail. However, for 304, we are going into more precise details. So 304 is made up of 8 ingredients. These are:
Chromium
Chromium contribution in 304 is 18-20%. It is the key and the most abundant ingredient. So this proportion is carefully controlled to maintain its effectiveness.
Nickel
Nickel improves corrosion resistance and its share is 8-10.5% in 304 stainless steel. It is particularly good against acid substances. This improves steel formability and strength. 304 carries a little higher nickel compared to other 18-8 stainless steel grades.
Carbon
Material engineers deliberately keep carbon share low which is 0.08%. The reason is, that if you keep the carbon ratio high, it can make welding very tough.
Manganese
Manganese increases the tensile strength of the steel. Its ratio in 304 steel is 2.0%. Manganese makes the manufacturing process easy especially in hot-forming operations.
Silicon
Silicone works as a deoxidizer during steel production. Its contribution is a maximum of 1.0% and it significantly improves the strength and oxidation resistance in high temperatures.
Silicon acts as a deoxidizer during steel production and also contributes to strength and resistance to oxidation at high temperatures.
Phosphorus and Sulfur
Phosphorus and sulfur are kept very low to improve weldability. Their ratio is 0.045% and 0.03% respectively. They also improve corrosion resistance and prevent brittleness.
Nitrogen
Nitrogen is found in 304 and its ratio is 0.10% maximum. It is good for improving yield strength and preventing corrosion.
Iron
Iron is the base of 304 alloys. It works with all other elements to modify and enhance 304 properties.
Qualities of 304 Stainless Steel
304 is highly resistant to corrosion and rust. For example, it can perform excellent against organic food-related acids and moisture. Moreover, its tensile strength is good which makes it a good choice to bear wear and tear.
Simultaneously, 304 stainless steel is very easy to work with. You can easily fabricate it in different complex shapes. Furthermore, it’s easy to clean which means good for hygienic applications, and can bear pressure up to 870°C.
AISI 304 Stainless Steel Applications
You have previously read that 304 has balanced properties. This makes it a good choice for a range of applications.
Food and Beverage Processing
304 is a very common material to make food processing parts. Some of the common examples are sinks, worktables, transport containers, and cookware items. Similarly, milk and juice processing factories also use parts made up of 304 materials.
Chemical Processing
Since it 304 can act very well against chemical applications, you will find this material in chemical plants. 304 stainless steel is also used to make tanks and vessels to store and transport chemicals.
Medical Industry
Medical facilities tend to keep hygiene to the highest standard. For that purpose, medical staff sterilize instruments. Regular sterilization weakens these instruments. Therefore, machining companies incorporate 304-grade materials to make sterilization trays, containers, plates for bine repair, and hospital furniture.
Automotive Industry
Modern vehicles especially electronic cars, need high-resistance materials to perform in severe conditions. Therefore, car manufacturers prefer installing parts made up of 304 steel. The common examples of these parts are catalytic converters, trim and grills, and exhaust systems.
Marine Applications
In the marine industry, 304 components are used in freshwater environments. You can say on the banking areas like dock hardware where saltwater density is low. In the marine industry, 304 stainless steel is used to make vessels, lakeside railings, and boat fitting hardware.
Benefits of 304 Stainless Steel
- Good Corrosion Resistance
- Widley Applicable in different industries
- Good balance of properties
- Affordabe and easily available
Limitations of 304 stainless steel
- Vulnerable to high density salt water
- Susceptible to crevice corrosion
- Lower strength compared to specialized grades
18-8 vs. 304 Stainless Steel: Head-to-Head Comparison
18-8 and 304 are both austenitic stainless steels. Both have some stronger and weaker sides.
Chemical Composition
18-8 stainless steel chemical composition is flexible. Although chromium and nickel have general ranges but material engineers add other metals according to the required specifications. You can say, it has less strict rules.
On the other hand, in 304, the rules are a bit strict. You need to put the exact amount of ingredients. It has a tightly controlled range. You need to define chromium, nickel, and carbon amounts exactly to get the best results. Therefore, 304 is more consistent and reliable.
Corrosion Resistance
18-8 stainless steel has a generally decent range of resistance. You can say, it is good for everyday situations like water, air, and harsh chemicals. Since it has a flexible chemical composition, its exact rust-level protection also changes.
On the other hand, 304 stainless steel has a fixed chemical composition which makes it an excellent choice against corrosion resistance. It is effective against rust, corrosion, food acids, and industrial chemicals.
Mechanical Properties
18-8 comes with good mechanical properties such as it provides fair strength and toughness. So it can bear normal wear and tear. Like corrosion, its mechanical properties also vary depending on the requirements.
304 Stainless steel has a good balance of mechanical properties. You can use this material for structural applications. Similarly, it extends the product’s life also. Moreover, 304 is very easy to form and process the complex shapes.
Mechanical and Physical Properties Table
Mechanical Properties
| Property | 18-8 Stainless Steel | 304 Stainless Steel |
|---|---|---|
| Tensile Strength | 500-700 MPa | 515-750 MPa |
| Yield Strength | 190-215 MPa | 205-230 MPa |
| Elongation (in 50mm) | 40-45% minimum | 40-45% minimum |
| Hardness (Brinell) | 123-262 HB | 123-215 HB |
Physical Properties
| Property | 18-8 Stainless Steel | 304 Stainless Steel |
|---|---|---|
| Density | ~8.0 g/cm³ | 7.93 – 8.0 g/cm³ |
| Melting Point | 1400-1455 °C | 1400-1450 °C |
| Thermal Conductivity | ~16.2 W/m·K (at 100°C) | 16.2 W/m·K (at 100°C) |
| Electrical Resistivity | ~720 nΩ·m (at 20°C) | 720 nΩ·m (at 20°C) |
| Modulus of Elasticity | ~193 GPa | 193 GPa |
| Thermal Expansion | ~17.3 µm/m-°C (at 20°C) | 17.2 µm/m-°C (at 20°C) |
| Specific Heat Capacity | ~500 J/kg·K (at 20°C) | 500 J/kg·K (at 20°C) |
Conclusion
Summing up, you have read the difference between 18-8 stainless steel and 304 stainless steel. Both have their pros and cons. You just need to check your parts’ requirements before choosing any material. For this purpose, Richconn can help you. Our company provides precision CNC machining for manufacturing stainless steel parts. Our material engineers can effortlessly handle stainless steel like 304 and 18-8 grades.
