The Definition of Stainless Steel
There is little debate that stainless steel lives up to its namesake. The metal is as strong as traditional steel and retains excellent corrosion resistance over long useful lifetimes. Additionally, there is an enormously wide range of stainless-steel alloys available for all manner of mechanical fasteners. Before diving in further, it’s helpful to first understand some basics concepts about stainless steel.
The simplest definition of stainless steel is that it is a steel alloy that is created by taking an ordinary low carbon alloy steel, which means that it has a “low” amount of carbon, on the order of 0.3%-0.5%. This ordinary low alloy steel has at least 10% Chromium added as an alloy ingredient. The Chromium alloying element does all the heavy lifting of providing corrosion resistance and is the key ingredient that sets stainless steel apart.
Advantages of Stainless Steel Fasteners
The primary advantage of stainless steel fasteners is that surface protection comes free without any additional surface coatings or treatments. This means that stainless steel fasteners possess a high degree of durability and resistance to corrosion right out of the box. These fasteners retain the strength of traditional low alloy steel fasteners and can be used wherever traditional steel fasteners are specified. Stainless steel fasteners retain good resistance to corrosion over long useful lifetimes, and as such, they retain a shiny appearance for much longer than a traditional low alloy steel fastener.
The chemistry of exactly how stainless steel fasteners are able to resist corrosion is crucial to understand. The alloyed Chromium element in stainless steel reacts with Oxygen in the air to create a metal-oxide layer on the exposed surface that serves as an additional protective layer against corrosion. Incredibly, this layer can, in some cases, regenerate if it is exposed to enough oxygen in its use environment.
In this way, the oxygen chemically re-bonds with newly exposed, available chromium in the metal to reform the protective surface layer where it has been compromised. This raises another important point- to maximize corrosion resistance of stainless‑steel fasteners, for maximum protection, it’s important to ensure that the use environment possesses at least some level of available oxygen. In an open-air application, this is an easy thing to accomplish, but it becomes much more difficult for more exotic applications such as within oil or hydrocarbon fluid environments.
Two Most Common Stainless Steel Fastener Alloys
Broadly speaking, there are two types of stainless steel fasteners that are most widely used in machine designs. These two alloys are 304 Stainless Steel and 316 Stainless Steel, and are available in a wide range of fastener sizes and specifications. As evidenced by their names, both alloys are from the 300 family of stainless steels, but their mechanical properties differ as a result of their chemical composition.
|304 Stainless Steel||18-20% Chromium|
|316 Stainless Steel||16-18% Chromium|
304 stainless steel is more commonly used than 316 stainless steel. It has a composition Chromium and Nickel as listed in the chart above. These alloying ingredients provide good resistance to oxidation and corrosion. To this end, 304 stainless steel is used widely in piping, kitchen equipment, pressure vessel, and auto parts.
Conversely, 316 stainless steel is comprised of similar compositions of Chromium an Nickel. However, 316 stainless steel has an additional Molybdenum as listed in the chart above which is added specifically to protect against salt corrosion. Because of this, 316 will provide a higher level of corrosion resistance in common environments that are known to be more corrosive than simple open-air environments, such as oceanic applications. To achieve this higher degree of performance, the base material cost is greater when compared to 304 stainless-steel fasteners. You can find 316 stainless-steel fasteners in boat construction as well as other machine designs where fasteners may be exposed to exotic corrosive environments.
Choose Your Stainless Steel Fastener
It is easy to become overwhelmed by the huge number of steel alloys and fastener designations, but this guide should give you enough information to navigate the basics of stainless-steel fasteners. It’s also vital to remember that stainless steel isn’t completely corrosion-proof. The performance of stainless-steel fasteners will depend on a number of other factors, such as the installation and end-use environment. MISUMI has a wide selection of stainless steel fasteners available and ready to meet any need! Explore the selection here.