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- Stainless Steel Fasteners
Choosing the wrong grade
The most important thing to note when using stainless steel fasteners is to check the grading of the steel. 304 and 316 are the two most commonly employed stainless steel grades that offer resistance to corrosion better than any other grade available in the market. For an environment that is highly susceptible to corrosion, 316 stainless steel is a perfect fit, given the resistance it provides against the effect of metal oxidization.
Contamination of the exposed surface
The bare part of the stainless steel exposed to the atmosphere is susceptible to contamination by metallic dust, which can ultimately lead to formation of rust on the surface causing gradual decay of the material, internally. The most common example is the sticking of iron fillings that result from grinding of steel. It’s recommended to cover the part with stainless steel fasteners during the period of operation.
Making conditions favorable for galvanic corrosion
Galvanic corrosion occurs when two different metals and alloys come in electrical contact with each other to apply corrosive effect. Not only can it affect the stainless steel fasteners, but also the metal that comes in physical contact with the particular fastener. You need to minutely investigate if there is a possible situation of a galvanic corrosion taking place and to what extent it can be inhibited. Using tools made of stainless steel is a smart choice, since similar electropotentials do not trigger corrosion. You can also use nylon washers as a barrier to isolate the metals from touching each other.
Opting for the low-nickel stainless steel
It’s a proven fact that stainless steel fasteners of the 200 series are chromium deficient, apart from higher percentage of manganese and lower proportion of nickel. Such a combination is ideally not suitable to resist the action of rusting, as compared to the corrosion-resistant properties offered by 316 stainless steel studs.
Improper cleaning schedules
The longevity of stainless steel fasteners depend on the cleaning schedules employed for the equipment. If you allow the contaminants to settle over a long period of time, it does not only become difficult to carry out cleaning practices, but also to restore the distorted appearance of stainless steel. It’s advisable to expose the surface to rainwater, so that all the dust particles wash off and there is no damage done to the protective layer of the steel.
Uneven finishing of stainless steel fasteners can leave space for entrapment of dusty particles that can destroy the protective layer of chromium oxide, which provides the necessary resisting action against corrosion. A smoother finish eliminates the chance of particle settling and allows for easier cleaning practices.
About the Author
Started my career in the fastener world in 1969 at, Parker Kalon Corp. a NJ based screw manufacturer located in Clifton, NJ working in inventory control, scheduling secondary production and concluding there in purchasing. In 1971 I accepted a sales position at Star Stainless Screw Co., Totowa, NJ working in inside sales and later as an outside salesman, having a successful career at Star I had the desire with a friend to start our own fastener distribution company in 1980 named: Divspec, Kenilworth, NJ. This was a successful adventure but ended in 1985 with me starting Melfast in August 1985 and have stayed competitive and successful to date. Melfast serves the OEM market with approximately 400 accounts nationally.
How do the following screw types fare in an outdoor (wet) long-term application?
Stainless steel screw:
4 Answers 4
The stainless steel screw will absolutely be the best screw to resist rust. Stainless steel screws are rust-resistant throughout the entire screw, not just on the surface.
The other screws are only covered with a rust-resistant coating on their surface, which will break down or wear off over time. Galvanization is a process that coats with zinc. Other screws may be zinc coated as well using another process, or they may be coated with something else.
I have some screws on an outdoor fence which have rusted inside the slots in the screw head, because the screw driver tip wore away some of the coating in the slots at time of installation. Phillips-head screws in particular are notorious for getting ground up when the tip “cams out” and jumps out of the screw head.
Stainless steel is undoubtedly the best material for resisting rust and corrosion in screws. Why, then, would anyone use anything other than stainless steel outdoors? Two reasons:
(1) Stainless steel is slightly softer than the hard steel used in deck screws or other similar screws. You can’t just “go crazy” with the power tools and slam the screws into place. It is easier to chew up the heads on stainless screws, or to snap the heads right off by over-torquing them (though that is more of a problem with bolts than wood screws). You have to slow down and be a little more careful.
(2) Stainless steel screws are more expensive. Galvanized or other coated screws are just plain cheaper.
Despite those drawbacks, the rust prevention is unmatched by other screws. I live in a rainy wet climate, so I use stainless screws on anything outside that I might need to ever take apart again.
There are interesting stories about most fasteners.
The standard galvanised nails should not be used with Cedar because the tannic acid in cedar will react with the galvanisation. Just as Aluminium nails should not be used with pressure treated wood.
Many new coatings exist that work even better, and are often colour matched to our wood, like green and brown screws. All of these things are coatings put over a regular steel screw.
Stainless steel is by definition a steel (actually a ferrous alloy) that has at least 12% Chromium content. Right, Chrome, like the old bumpers that were Chrome coated. Here they are putting this material mixed right into the steel. Too much chrome and it becomes brittle, too little and it can rust. In fact there are many different formulations of “stainless steel”, each designed to work with particular problems, not just water rust.
The standard screw and nail construction stainless steel are called the 300 series, or 18-8 (which means about 18% chromium and 8 % nickel). These are the ones that will not rust. Others which are actually stronger, will be lest resistant to rusting. So part of the “bad rap” on stainless steel is that less expensive but stronger fasteners are being sold for a purpose where they are not appropriate.
For our decking and fencing, we want screws that are labelled 304 or 18-8 (the same screw, just two systems of labelling) or maybe even more corrosion resistance with a 316, but stay away from the 400 series. Some manufacturers do put these identifications on the label as you can see in the photo, while many do not yet. If all the Stainless Steel screws available at your store have no ratings, insist that the store staff check the catalogues to see that what you are buying is in the 300 series or is identified as 18-8. Then they won’t rust and stain the fence.
Stainless steel is a highly used metal and prized for its corrosion resistance. Did you know that stainless steel actually can corrode? It’s not even that hard to make it happen. Before you buy your fasteners here are five stainless steel facts you need to know before buying fasteners.
1. Stainless Steel Is A Soft Metal (Sort Of)
Stainless steel is considered a soft metal meaning it is not great for many high load applications that require intense strength. However, certain grades are hardened to create a stronger version. It may effect the corrosion resistance of the fastener however. A classic example of this is Grade 410 Stainless Steel.
2. Stainless Steel Can Still Corrode
Stainless steel is prized for its corrosion resistance. Beyond that many don’t know anything about it. Stainless steel comes in many different grades, 304, 305 and 316 are just a few examples and each come with their own benefits. If you are within 20 miles of the beach for example, you need to make sure you use 316 stainless steel.
3. Stainless Steel Is Not Non-Magnetic
It is important to know that stainless steel is not fully non-magnetic. In situations where the non-magnetic quality of a material is critical, stainless steel is not a recommended choice.
4. Stainless Steel Has An Invisible Self Repairing Outer Layer
Stainless metals form an invisible oxide coating that protects it from external factors. This is the main reason stainless steel is so resistant to corrosion. As long as the material is in an oxygen rich environment, even if the metal is damaged removing the oxide layer, it will reform and protect the metal again.
5. Stainless Steel Reacts Negatively With Aluminum
Stainless Steel and Aluminum are two separate kinds of metal. One is positively charged (anode) and one is negatively charged (cathode). As these metals are connected and an electrolyte is introduced, such as saltwater, a transfer of electrons occurs which will ruin the integrity of the materials resulting in galvanic corrosion. To avoid these situations either use some sort of in-between like a rubber material or simply do not use them together (recommended).
Working With Stainless Steel
Ultimately stainless steel can be a bit more complicated than you thought. Stainless steel fasteners are still an excellent choice for many situations. Just take these 5 things into consideration when buying your fasteners to help you choose the appropriate material and grade.