316 vs. 18-8 Stainless Steel: Which Material Is Best for Your Fasteners?
When your products are going to be used in corrosion-prone or harsh environments, the fasteners you choose to build them matter. You need to choose a stainless-steel option that can withstand tough conditions.
Both 316 vs 18-8 are austenitic stainless steels that are commonly used in fasteners. However, they are engineered for different exposure levels. In this guide, we discuss both stainless steel options and their differences, relating to corrosion resistance, composition, strength, and applications, to help you select the right choice for your products.
Understanding 18-8 Stainless Steel Fasteners
The common terminology of 18-8 stainless steel refers to a broad category of stainless alloys containing ~18% chromium and ~8% nickel. It encompassesmultiple grades (including 304 stainless steel), making it versatile and cost-effective. Some of the key properties of 18-8 stainless steel include:
- Good general corrosion resistance
- Durable and non-magnetic in an annealed condition
- Suitable for indoor and moderate outdoor environments
- Common in construction, machinery, general hardware, heating, ventilation, and air conditioning (HVAC)
What Makes 316 Stainless Steel Different
The common terminology of 316 stainless steel is a specific alloy that contains 2-3% of added molybdenum. The addition of molybdenum dramatically improves resistance to chlorides and harsh chemicals by strengthening and stabilizing the passive chromium oxide film on stainless steel. This is why 316 is often referred to as “marine-grade” stainless steel. Other key characteristics of 316 include:
- Superior corrosion resistance in marine applications and salt environments
- Better resistance to pitting and crevice corrosion
- Excellent performance in chemical processing and coastal applications, including high-temperature environments
Key Differences Between 316 and 18-8 Stainless Steel
Although 316 and 18-8 are both stainless steels, they have differences that impact how they perform and what applications each one is best for. They include:
Corrosion Resistance
Both options offer good corrosion resistance, but at different levels. 18-8 is suitable for general environments with moisture exposure, while 316 is designed for excellent corrosion resistance in saltwater, chlorides, and corrosive conditions. The chromium content in 18-8 and the molybdenum content in 316 provide high corrosion resistance.
Chemical Composition
Both 18-8 and 316 are austenitic stainless steels, but their compositions are different. 18-8 is made of around 18% chromium and 8% nickel, while 316 features around 16-18% chromium, 10 to 14% nickel, and 2 to 3% of molybdenum. The addition of the molybdenum, as well as the higher nickel content, provides enhanced protection against corrosion caused by salt and chemicals, making 316 a more durable option for use in harsh marine environments.
Strength and Mechanical Properties
When it comes to strength, 18-8 and 316 stainless steels are generally similar. Both have ductility around 40–70% elongation, but 18-8 tends to have better formability. 18-8 has a typical yield strength of around 205–215 megapascals (MPa) and a tensile strength of 500–750 MPa, while 316 has a yield strength of 205–300 MPa and a tensile strength of 480–620 MPa.
Since their strengths are similar, the primary differentiator between 18-8 and 316 is their corrosion resistance, not their strength.
Cost Considerations
Generally, 316 is more expensive than 18-8. This is because 316 has alloying elements like molybdenum that increase its corrosion resistance and make it better for harsh marine conditions. Since 18-8 doesn’t have molybdenum, it comes at a lower cost while still offering excellent performance for most applications.
Typical Applications for Each Material
To determine which material is better for your product or project, consider where each performs best:
Where 18-8 Stainless Steel Performs Best
18-8 stainless steel is best suited for use in:
- General construction and manufacturing
- Indoor or mildly outdoor environments
- Automotive components
- Equipment and machinery
- Food processing equipment and general hardware
This means it is ideal for creating food-grade kitchenware, general-purpose hardware, HVAC systems, medical devices, and more. It is best in moderate, non-chloride environments like home kitchens.
Where 316 Stainless Steel Is the Better Choice
316 stainless steel is the best choice in:
- Marine environments and coastal installations
- Chemical processing equipment
- Saltwater exposure
- Harsh industrial conditions
- High-humidity or corrosive environments
It is best for use in demanding, high-chloride industrial environments since it resists pitting and crevice corrosion. 316 is a popular choice for producing outdoor architectural features, boat hardware, pharmaceutical equipment, and more.
When 316 Stainless Steel Is Worth the Extra Cost
Although 316 is more costly than 18-8, there are situations where the higher cost is definitely worth it. The upfront price is 20–30% higher compared to 18-8 stainless steel, but it provides a substantially better lifecycle value in harsh, saline, or acidic environments.
If a lower grade of stainless steel is used in these aggressive environments, it can lead to risks like pitting, crevice corrosion, increased maintenance costs, and premature replacement. Therefore, it’s best to choose 316 stainless steel when your products need better corrosion resistance to withstand harsh, marine-grade conditions.
How to Choose the Right Stainless Steel for Your Fasteners
To choose the right type of stainless steel for your fasteners, consider this decision checklist:
- Will your fasteners be exposed to salt, chemicals, or chlorides?
- What are the required lifespan and maintenance expectations of the fasteners?
- What are the load and mechanical requirements of the fasteners?
- Do you have budget constraints?
- Are there certifications or industry requirements you must comply with?
If your fasteners will be used in marine-grade environments, need to withstand corrosion for long periods, and you have a higher budget, 316 is often the better choice. If your fasteners will be used in moderate conditions, need mild corrosion resistance, and you have a lower budget, 18-8 will often be sufficient. However, always consider the industry requirements, certifications, and load requirements, as well.
Fasteners Etc., Inc. Supplies Stainless Fasteners You Can Trust
When you need corrosion-resistant fasteners for demanding environments, Fasteners Etc., Inc. is here to help. Whether 316 fasteners are better for your needs or 18-8 is what you’re looking for, our team can help you identify the ideal fasteners for your products. At Fasteners Etc., Inc., we pride ourselves on being a solution-oriented partner for material selection. Whether you know exactly what you need or require assistance in narrowing down your options, our knowledgeable team is available. To learn how our fasteners can streamline your operations and reinforce your products, contact us or request a quote today.