Stainless steel is used primarily for long lasting applications, due to its corrosion-resistant nature and durability. Scratching or burring the metal will not create surface rust as the corrosion resistance exists within the metal itself. Stainless is a soft metal due to the low carbon content, therefore most stainless steel bolts are cold-formed and not heat treated or thru-hardened. Cold forming and threading cause stainless bolts to become slightly magnetic, some fasteners will be more magnetic than others depending on size and how quick the cold forming process is. Stainless fasteners are typically a clean silver color, which also makes them common in finishing and decorative applications. Stainless Steel should never be used with aluminum, galvanic corrosion is likely to occur.
Stainless steel will not rust due to scratching due to the thin layer of chromium creating an invisible protective layer. This thin layer will rebuild itself in the presence of oxygen. Note: If you are not in an oxygen rich environment the material will take longer to rebuild or not rebuild at all. This will leave it open to possible corrosion. Stainless steel can be broken down into three different types: Austenitic, Martensitic and Ferritic.
Below are some of the many bolt grades of stainless steel that we carry.
(Between 15%-20% Chromium, Between 5%-19% Nickel) - Austenitic stainless has the highest degree of corrosion resistance of the three types. This type of stainless includes these grades: 302, 303, 304, 304L, 316, 32, 347 and 348. They also have a tensile strength of between 80,000 - 150,000 PSI.
(Between 12%-18% Chromium) - Martensitic stainless steel is considered a magnetic steel. It can be heat treated to increase its hardness and is not recommended for welding. This type of stainless includes: 410, 416, 420 and 431. They have a tensile strength of between 180,000 and 250,000 PSI.
(Between 15%-18% Chromium) - Ferritic stainless steel has a tensile strength of 65,000 - 87,000 PSI. While it is still corrosion resistant, it is not recommended for areas where corrosion is likely to occur. This material cannot be heat treated. Due to the forming process it is magnetic and not suitable for welding. Ferritic grades of stainless include: 430 and 430F.
(18% Chrome, 8% Nickel, .08% Maximum Carbon) - 18-8 Stainless refers to 300 series stainless steel. 303 and 304 Stainless are the most commonly listed grades, the standard grade for stainless fasteners. They are corrosion-resistant and durable. They are often used in marine applications in freshwater environments but will not work as effectively in a salt-water environment as 316 stainless. Stainless alloy resists oxidizing and rusting, however it can tarnish over time. Equivalent to metric A2 Stainless Steel.
(17%-19% Chrome, 8%-10% Nickel, .12% Maximum Carbon) - This grade has been developed specifically to improve the cold heading qualities of 18-8. Corrosion resistance and physical qualities are equal to Type 304. 305 stainless steel is most commonly used to make deck screws, which are used to fasten wood or composite boards to the main beams of a deck.
(16%-18% Chrome, 10%-14% Nickel, .08% Maximum Carbon, 2.00% Maximum Molybdenum) - This grade of steel is used and recommended for applications in severe, harsh or marine environments. Its corrosion resistance is greater than 18-8 stainless, which is why we recommend using 316 stainless steel fasteners for salt-water application. It is important to remember that even the salt in the air near a body of salt-water can do damage to dry applications, so 316 is the material of choice. Common applications of 316 stainless fasteners include use on boats, docks, piers, and pools.
(11.5%-13.5% Chrome, .15% Maximum Carbon) - Since this grade of stainless steel can be hardened up to approximately 40 Rockwell C, it is durable in most environments. Harder than 18-8 stainless but with less corrosion resistance, 410 stainless is commonly used to make roofing screws, siding screws and self-tapping (or self-drilling) screws, because it is a harder material than the metal being fastened in these types of applications.