Stainless steel fasteners are specified for construction applications primarily for their resistance to corrosion, but are often misunderstood with reference to material compatibility, performance and availability.
If you want to learn more, please visit our website Qifeng.
What fastener grade is needed and how will it perform
Many people may recognize a fastener made from stainless steel, but find it difficult to determine what grade is needed and how it may perform in the application.
Typically, stainless steel is defined as a family of iron-based alloys that contain a minimum of approximately 12% chromium. It's primarily this chromium that gives steel its corrosion resistance properties when exposed to weather, much like pure chromium plate used on automobile trim. The chromium reacts with oxygen and forms chromium oxide, which is very thin passive film that is invisible, self-forming and self-healing. Other elements are added in various amounts that will enhance corrosion resistance, workability and increase strength. Generally, stainless grades that have higher chromium content will be more resistant to red rust (iron oxide).
The two most popular types of stainless steel fasteners are 18-8 (300 series) and 400 series. Of these two, the 18-8 series provides the best corrosion resistance and ductility. This stainless family consisting of type 302, 304, 305 and 316, is one of the most misunderstood. Each grade offers almost identical corrosion protection, but varies in performance with reference to installation and resistance to chemical attack. These grades cannot be heat treated and rely on cold-working for additional strength.
One of the more popular grades is type 302, and is typically used in sheet metal and machine screws. Although this grade provides exceptional corrosion resistance, it does not work-harden enough to produce the thread hardness required to minimize thread rollover caused by tapping high-tensile or thick steel.
The same problem occurs when using type 305. To reduce the amount of thread failure, a special modified 304 stainless steel material was developed in the early s primarily for use in the metal building industry. This special grade of 304 stainless is more durable, and characteristically work-hardens during the fastener's fabrication, thereby producing tougher threads. It offers virtually identical corrosion protection and strength as 302 and 305, and it becomes slightly magnetic during the cold-working process.
304 stainless steel fasteners are readily available in self-tapping screws. As with any self-tapping fastener, using the proper hole size is critical to optimize fastener performance and minimize thread rollover. They are typically plated to provide additional lubricity for tapping, and reduce thread failure. An installation speed of 1,000 rpm or less is required to preserve thread integrity and holding power.
Want more information on best stainless steel screw press? Feel free to contact us.
Self-drilling fasteners are also available in 304 and can have a harden carbon steel drill tip welded to the screw shank in order to drill steel. These fasteners are widely used in aluminum framing and a variety of panel applications. They are available in a wide range of sizes and head styles. Once again, slower speed screw-guns are required to minimize thread rollover.
Another grade of 300 series stainless steel is 316, and was originally developed for sulfurous acid applications. This grade has a higher molybdenum content, which provides additional corrosion protection in highly corrosive applications and works well in chloride type environments. This grade is primarily available in self-tapping screws.
For less severe applications, 410 stainless fasteners are often specified. They are available in self-tapping and self-drilling styles and come in a variety of diameters and lengths. 410 stainless fasteners provide good corrosion resistance in mild atmospheres like light industrial environments. In some applications, 410 may show signs of red rust due to its lower chromium content (compared to 18-8 grades), and will continue to rust although at a much slower rate than carbon steel. As previously mentioned, it's the chromium in the form of chromium oxide that protects the surface and provides the corrosion resistance in normal atmospheres.
It is important to remember that all metals and alloys will corrode in some given environment. Be sure to minimize the chance for galvanic reaction by choosing materials that are close to each other on the galvanic chart. We recommend contacting a corrosion specialist to assist in the selection. Stainless steel fasteners offer tremendous additional protection against red rust compared to carbon steel fasteners. The proper use of 304 or 410 grades will provide many years of long-life service.
Josh Krohn is engineering services manager at Triangle Fastener Corp., Pittsburgh. To learn more, visit www.trianglefastener.com or call (800) 486-.
18-8 stainless steel, also sometimes called 304 stainless, is the most common type used for fasteners such as machine screws and nuts. It contains 18% chromium and 8% nickel and features strong corrosion resistance, but is softer, and thus weaker, than some other grades such as 410 stainless. Self-drilling screws are available in 18-8, but are generally recommended only when drilling into wood or soft materials. 18-8 is a non-magnetic type of stainless steel.
303 stainless steel is similar to 18-8 stainless, but has a larger sulfur content, making it one of the more machinable stainless steel grades. This machinability has made it very popular in the fastener industry, particularly in the manufacture of spacers and standoffs. It is non-magnetic in it's standard state, but can become magnetic as a result of cold working (being shaped while not heated).
316 stainless steel is both hardened and extremely corrosion resistant, making it a good choice for larger nuts, bolts and washers used in harsh environments, such as coastlines. We carry hex cap screws, along with machine, self-drilling & u-drive screws in 316 stainless. It is non magnetic.
410 stainless steel is a hardened type common in some fastener lines, especially self-drilling screws. The hardening allows for more strength and stability, especially when being installed into metal materials. We offer many other screw types in 410 stainless, as well as some mil-spec parts and washers. 410 is a style of stainless material that actually is magnetic.
We offer several mil-spec part lines in general 300 series and 400 series grades, and coiled spring pins and roll/spring pins in 420 stainless. Many of our 18-8 and 410 stainless lines also feature parts with a black oxide finish.
If you want to learn more, please visit our website refined oil plant.