18-8 (A2) vs 316 (A4) Stainless Steel Fasteners

When choosing the correct fasteners for a project, understanding the features and differences between them is vital for safety reasons. Two of the most commonly used materials for fasteners are 18-8 (A2) and 316 (A4) stainless steel. Both have unique properties that make them ideal for specific applications, but which one is right for your project?

Today, we'll compare and contrast A2 vs A4 stainless steel fasteners, highlighting their properties, uses, and how to identify them so you can make the best choice for your next project.

Properties of 18-8 (A2) Stainless Steel Fasteners

18-8 stainless steel, also known as type 304 or A2 stainless steel, is an austenitic alloy with a mix of characteristics, making it ideal for many applications. It is named 18-8 due to its composition—approximately 18% chromium and 8% nickel, along with iron and other elements.

18-8 stainless steel fasteners are well-known for their high corrosion resistance, especially in normal weather or atmospheric conditions. They're durable, with high tensile and yield strength, making them suitable for general use in many different environments.

18-8 fasteners are most commonly seen in appliances, construction, and general engineering applications. For identification, look for the markings of "A2" or "304"

Properties of 316 (A4) Stainless Steel Fasteners

316 stainless steel, also known as A4 or marine grade stainless steel, is another popular type of fasteners. Like its 18-8 counterpart, 316 is an austenitic alloy with additional elements—most importantly, 2-3% molybdenum.

The addition of molybdenum greatly improves resistance to chloride corrosion, making 316 fasteners the best choice for highly corrosive environments such as marine or chemical processing industries. 316 can withstand exposure to saltwater, certain acids, and high temperatures much better than 18-8 fasteners. For identification, look for the markings of "A4" or "316".

Difference Between 316 (A4) and 18-8 (A2) Stainless Steel

The main difference between 18-8 and 316 stainless steel is corrosion resistance and durability due to their differing compositions. 

corrosion resistance

18-8 stainless steel is corrosion resistant under normal atmospheric conditions, but is vulnerable to chlorides and chemicals. 316 includes molybdenum, a key element that will increases resistance to corrosive substances, such as chlorides, saltwater, and chemicals. This makes 316 a better choice for marine and industrial environments.

Strength and Longevity

Both offer high tensile strength, but 316 fasteners have greater resistance to pitting, stress corrosion, and extreme environments.

Cost Differences

18-8 fasteners are more affordable and suitable for general applications. 316 fasteners have a higher price point but perform better in extreme environments.

How to Identify A4 and A2 Stainless Steel Screws

tainless Steel A4 vs. A2 Strength

• A2 stainless steel has high strength and excellent general corrosion resistance.
  
  
• A4 stainless steel has superior durability, especially in saltwater, chemical, and extreme temperature environments.
  
  
• A4 screws are more resistant to rusting and pitting than A2 screws.

Common Types of A2 and A4 Grade Stainless Steel Fasteners

Both A2 and A4 stainless steel fasteners come in various types, including:

• Hex bolts and screws
• Machine screws
• Wood screws
• Self-tapping screws
• Socket cap screws
• Washers and nuts
• Threaded rods

A2 stainless steel fasteners are widely used in construction, automotive, and general engineering projects. A4 stainless steel fasteners are preferred in marine, chemical, and medical industries.

A2 Stainless Steel Fasteners Chemical Composition

A2 stainless steel consists of:

• Chromium (17-19%)
• Nickel (8-10.5%)
• Carbon (max 0.08%)
• Manganese (max 2%)
• Silicon (max 1%)
• Phosphorus (max 0.045%)
• Sulfur (max 0.03%)

These elements contribute to its high corrosion resistance and mechanical properties, making it suitable for most standard applications.

Typical Chemical Property Range of SS A4 Fasteners

A4 stainless steel contains:

• Chromium (16-18%)
• Nickel (10-14%)
• Molybdenum (2-3%)
• Carbon (max 0.08%)
• Manganese (max 2%)
• Silicon (max 1%)
• Phosphorus (max 0.045%)
• Sulfur (max 0.03%)

The addition of molybdenum in A4 fasteners greatly improves their resistance to pitting, crevice corrosion, and stress corrosion cracking, making them ideal for harsh environments.

Browse Our 316 and 18-8 Stainless Steel Fasteners

At ASMC Industrial, we offer a wide range of 18-8 and 316 stainless steel fasteners suitable for a variety of applications. We understand the need for quality and durability, which is why our products are designed to meet your high standards. 

Whether you're working on a marine application that requires 316's superior corrosion resistance or a general project where 18-8's durability is ideal, we've got you covered. Browse through our selection today or contact us for a quote. Let us help you find the perfect fastener solution for your needs.