Austenitic 304 vs 316 stainless steel are often referred to as surgical or medical-grade stainless steels and are among the most commonly used.
The primary distinction between 304 and 316 stainless steel lies in the addition of molybdenum to 316, which significantly enhances its corrosion resistance, particularly in saline or chloride-rich environments.
So, how do you decide between them? In this article, we’ll break down their properties, similarities, and differences to help you make the right choice.
1. What is 304 Stainless Steel?
304 stainless steel or 304 SS is austenitic grade steel that contains 18% chromium and 8% nickel (hence the name 18/8) and other alloying elements such as carbon, phosphorus, sulfur, silicon, and manganese.
304 stainless steel is one of the most popular and versatile stainless steels available. It is part of the austenitic family, meaning it has a face-centered cubic crystal structure, which contributes to its excellent corrosion resistance and high formability.
Physical and mechanical properties：
- Density: The density of 304 stainless steel is 7.93 g/cm³.
- Tensile strength: Tensile strength (σb) ≥ 520 MPa.
- Conditional yield strength: Conditional yield strength (σ0.2) ≥ 205 MPa.
- Elongation: Elongation (%) ≥ 40.
- Hardness: The hardness value is different under different test methods, for example, the hardness value is 187 HB; 90 HRB; and 200 HV.
- Melting point: The melting point is between 1398-1454℃.
- Specific heat capacity: The specific heat capacity is 0.50 KJ/kg·K.
- Thermal conductivity: The thermal conductivity is 16.3 W/m·K at 20℃ and 21.5 W/m·K at 500℃.
- Linear expansion coefficient: The linear expansion coefficient is 17.2×10^-6/℃ at 0-100℃ and 18.4×10^-6/℃ at 0-500℃.
- Resistivity: The resistivity is 0.73×10^-6 Ω·m.
304 stainless steel has a wide range of applications, as follows:
- Architectural decoration: 304 stainless steel has good corrosion resistance and aesthetics, and is widely used in the manufacture of architectural decoration materials, such as doors, windows, railings, stair handrails, etc.
- Petrochemical industry: 304 stainless steel has good corrosion resistance and high-temperature strength, and is used in chemical equipment, containers, and pipelines in the petrochemical industry.
- Food processing: 304 stainless steel is non-toxic, odorless, and does not produce harmful substances.
It is widely used in food processing, storage, and transportation, such as beverage production equipment, food storage containers, food processing machinery, etc. - Medical equipment: 304 stainless steel has good corrosion resistance, non-toxicity, and glossiness, and is widely used in the manufacture of medical equipment, such as surgical instruments, orthopedic implants, etc.
- Automobile manufacturing: 304 stainless steel has good corrosion resistance and wear resistance, and is used in exhaust pipes, fuel pipes, doors, windows, bodies, and other parts in automobile manufacturing.
- Household items: 304 stainless steel has good corrosion resistance and aesthetics, and is widely used in the manufacture of kitchen utensils, such as pots, bowls, plates, knives, forks, etc.
It is also used in the manufacture of bathroom supplies, such as faucets, bathtubs, toilets, etc.
In addition, 304 stainless steel is also used in furniture manufacturing, such as sofas, beds, chairs, etc.; building materials; chemical industry; agricultural equipment; ship parts and other fields.
Its excellent corrosion resistance, heat resistance, low-temperature strength, and mechanical properties, as well as good processability and weldability, make 304 stainless steel an ideal choice for many industrial and household applications.
2. What is 316 Stainless Steel?
316 stainless steel or 316 SS is the second most popular austenitic grade of stainless steel, and it comprises iron, 10-14% nickel, and 16-18% chromium.
The real distinction in the stainless steel 316 vs 304 SS comparison is the presence of molybdenum (2-3%) alongside the other alloying elements such as carbon, manganese, and silicon.
Physical and mechanical properties：
- Density: The density of 316 stainless steel is 8.0g/cm³.
- Hardness: Typically measured by Brinell hardness, with a maximum hardness of about 215 HB for bar and section forms.
- Melting Point: Approximately 1400 to 1450 °C (2552 to 2642 °F)
- Specific Heat Capacity: Around 484 J/kg·K at room temperature.
- Coefficient of thermal expansion: At 20℃, the coefficient of thermal expansion of 316 stainless steel is 16.5×10⁻⁶/℃, which means that for every 1℃ increase in temperature, the length of the material will increase by a corresponding proportion.
- Thermal conductivity: The thermal conductivity of 316 stainless steel is 16W/(m·K).
- Resistivity: The resistivity of 316 stainless steel is 7.2×10⁻⁷Ω·m.
- Tensile strength: Usually between 500 and 700 megapascals (MPa).
- Conditional Yield Strength (0.2% Proof Stress): Typically around 220 MPa for plate forms.
316 stainless steel has a wide range of applications, as follows:
- Marine Engineering: 316 stainless steel has excellent resistance to seawater corrosion, so it has been widely used in marine engineering fields such as ships, offshore platforms, and submarine pipelines.
- Chemical Production: It can resist the erosion of most harmful chemicals and is often used as a manufacturing material for equipment such as storage tanks and reactors.
- Pharmaceutical Manufacturing: It has little impact on drugs and is easy to clean and disinfect, so it is often used as a manufacturing material for pharmaceutical processing and storage equipment.
- Food Processing: As food-grade stainless steel, it is used to manufacture food processing equipment, tableware, kitchen utensils, and other utensils.
- Medical Equipment: It has good biocompatibility and corrosion resistance, and has been widely used in the manufacturing of medical equipment, such as artificial joints, dental instruments, surgical instruments, etc.
- Architectural Decoration: It has a beautiful appearance, solid texture, and strong anti-fouling performance. It is often used as an interior decoration material in the field of architectural decoration.
- Petrochemical Industry: It is used for industrial pipelines such as petroleum, chemical, medical, food, light industry, and mechanical structural components.
In addition, 316 stainless steel is also used to make kitchen utensils such as knives, cutting boards, etc., as well as household facilities such as kitchen countertops, sinks, range hoods, etc. due to its excellent corrosion resistance and high-temperature strength.
3. Key Differences Between 304 vs 316 Stainless Steel
To effectively choose between 304 and 316 stainless steel (SS), it’s essential to understand their key differences. Below are the distinctions that matter most:
Chemical Composition
304 SS: Composed of Carbon (0.07%), Silicon (1%), Manganese (2%), Phosphorus (0.045%), Sulphur (0.015%), Nitrogen (0.10%), Chromium (18%), and Nickel (8%).
316 SS: Contains Carbon (0.07%), Silicon (1.00%), Manganese (2.00%), Phosphorus (0.045%), Sulphur (0.015%), Nitrogen (0.10%), Chromium (16%), Nickel (10%), and Molybdenum (2.00%).
The primary distinction lies in the presence of molybdenum and the varying percentages of chromium and nickel, affecting their properties.
Mechanical Properties
- Yield Strength: Measures the maximum force a material can withstand before permanent deformation. 304 SS has a yield strength of 215 MPa, whereas 316 SS has a yield strength of 205 MPa. This subtle difference is crucial for high-precision applications.
- Hardness: Reflects a material’s resistance to deformation and indentation. 316 SS is harder, with a Rockwell B hardness of 79, compared to 304 SS at 70 Rockwell B. Thus, 316 SS is better suited for demanding projects that require higher hardness.
- Modulus of Elasticity: Indicates how a material resists deformation under stress. 304 SS has a higher modulus of elasticity (193-200 GPa) compared to 316 SS (164 GPa), making it more resilient to deformation.
Corrosion Resistance
Both grades are corrosion-resistant, but 316 SS, thanks to its molybdenum content, excels in resisting corrosion, particularly in chloride and sulfuric acid environments.
Its enhanced corrosion resistance ensures easier cleaning without concerns over chemical compatibility.
Heat Resistance
- 304 SS: Performs well at high temperatures but may experience corrosion if continuously exposed to temperatures between 797-1580°F.
- 316 SS: Maintains functionality at temperatures exceeding 1550°F and below 850°F, making it more stable across a broader temperature range.
Cost
Due to its higher elemental content and added molybdenum, 316 SS is approximately 40% more expensive than 304 SS.
The increased corrosion resistance justifies the higher cost, making 316 SS a premium choice for specialized applications.
4. 304 vs 316 Stainless Steel: Similarities
Despite their differences, 304 and 316 share several common traits that make them reliable choices for many applications.
Magnetism
Both grades are non-magnetic in the annealed condition but may become slightly magnetic when cold-worked.
Abrasion Resistance
Both grades offer excellent abrasion resistance, making them suitable for environments where wear and tear are significant concerns.
Weldability
Both 304 and 316 stainless steel can be easily welded, although care must be taken to avoid post-weld corrosion in more demanding environments.
Formability
The formability of both grades is excellent, allowing them to be used in complex designs without cracking.
Durability
Both types offer long-term durability and resistance to environmental factors.
Tensile Strength
Both grades have excellent tensile strength, The SS 304 and SS 316 have a tensile strength of 500-700Mpa, making them suitable for working under the same conditions.
5. 304 vs 316 Stainless Steel: How to Select the Right One?
Selecting the correct stainless steel grade depends primarily on the specific usage scenario and requirements. Each grade—304 and 316—has its unique advantages:
304 Stainless Steel
- Advantages: Good general corrosion resistance and affordability.
- Usage: Suitable for resisting most everyday chemicals, including water, beverages, and food products.
- Applications: Commonly used in food processing equipment, kitchen utensils, and general household items.
- Cost: Relatively economical, making it a practical choice for standard applications.
316 Stainless Steel
- Advantages: Enhanced corrosion resistance, particularly against chlorides, and higher durability.
- Usage: Ideal for harsh environments like marine settings or where contact with saltwater is common.
- Applications: Preferred for medical equipment, high-end kitchenware, and scenarios requiring superior material quality.
- Cost: More expensive than 304, reflecting its superior properties and longer lifespan.
In summary, 304 stainless steel offers good corrosion resistance at a moderate price, making it ideal for everyday use.
316 stainless steel, with its added molybdenum, provides exceptional resistance to chloride corrosion and is best for demanding environments and applications where durability is critical.
6. Conclusion
Choosing between 304 and 316 stainless steel largely depends on the specific requirements of your project. While both alloys are durable and corrosion-resistant, 316 stands out in environments where chloride-induced corrosion is a concern.
Evaluate the environmental conditions, maintenance needs, and budget constraints to make the best selection for your application.
FAQ
Q: Is 316 stainless steel stronger than 304?
A: In terms of tensile strength, both are similar, but 316 exhibits better resistance to stress corrosion cracking.
Q: Can 304 stainless steel be used in marine environments?
A: While 304 can be used in some marine applications, it is more susceptible to chloride-induced corrosion compared to 316.
Q: Can both 304 and 316 stainless steel be welded?
A: Yes, both can be easily welded, although care should be taken to avoid corrosion post-weld, particularly with 316 in harsh environments.
