Stainless steel is a commonly used material in applications ranging from medical instruments or chemical storage to transport or power generation because of its high corrosion resistance, hygiene, and strength. While there are more than 3,500 grades of steel, not all stainless steel grades are created equally.
With so many options, how can you ensure you’re selecting the appropriate grade for your specific needs?
To determine which grade of steel will uphold best in a given environment, think about the conditions your final product will face. Extremely low pH, high stresses and high temperatures, and crevice corrosion negatively impact stainless steel performance. Steels in the austenitic T3XX series, like the common types 316 and 304 alloys, retain their strength, toughness, and corrosion-resistant properties over the broadest temperature range.
Corrosion resistance is the main reason for choosing austenitic stainless grades. Type 316, with its molybdenum addition, even resists chloride ions found in marine and chemical processing applications. With any steel grade, high-quality structural design is the best defense against corrosion.
Next, consider these three top mechanical qualities:
Stainless steel contains 10–30% chromium as its alloying element, which is what helps it resist corrosion. The nickel addition in austenitic grades provides the highest toughness and ductility among stainless grades. Grades high in chromium, molybedenum, and nickel are the most resistant to corrosion.
Alloy content is not the only aspect to consider when choosing a grade of stainless steel; the material’s processing also affects the mechanical response. The duration of time steel is held at different temperatures as part of its cooling process, as well as the total speed at which it is cooled can affect its overall quality.
While the hardness of carbon steels can be increased by heat treatment, austenitic stainless is hardened by cold working operations like rolling, bending, swaging, or drawing at temperatures below the recrystallization temperature. Be aware that increased hardness by cold working operations decreases other properties like elongation and impact resistance.
Austenitic stainless steel is widely available in bar, wire, tube, pipe, sheet, and plate forms; Most products require additional forming or machining before they can be used for their specific application.
Stainless steel tubing, for instance, may need bending or coiling, re-drawing, machining, welding, or end forming. If your stainless steel will see machining processes like CNC machining, drilling, reaming, bevel cutting, chamfering, knurling, or threading, choose a machining rate that mitigates the risk of work hardening or select a “free-machining” grade containing sulfur.
When welding any stainless steel parts, embrittlement in the weld area is a top concern. Choose a lower carbon grade like 304, 304L, or 316L to reduce carbide formation.
Many designers choose stainless steel for its aesthetic appearance, whether that appearance is a shiny, electropolished “bright” finish, a dull “pickled” finish, a matte surface polished to a specific RMS, or a light-absorbing black oxide coating. Austenitic stainless steel grades can take any of these finishes plus the common addition of passivation.
Customers may also need certification for application-specific specifications. For instance, ASTM A213 and A249 should be used for boiler, superheater, and heat-exchanger tubes, while ASTM A908 should be used for hard-drawn austenitic stainless steel industrial needle tubing. There are more than 12,000 ASTM standards, and each addresses a specification so customers know the technical standards tested for chemical composition, heat treatment or temper, and other physical and mechanical attributes.
Although high-performing austenitic stainless steels are the most expensive stainless steels upfront, they are well worth the investment. Choosing a corrosion-resistant material well-suited to its application reduces maintenance, downtime, and replacement costs. Life-cycle costing methods can quantify current and future costs and create an “apples-to-apples“ comparison of different materials.
At Eagle Stainless we can help you prioritize your material requirements and guide you toward choosing the perfect stainless steel grades for your application. With quality management certifications in place since 1998, our commitment to quality is evident at every step of the process and designed to help you make the best steel selection for your industrial application.
To help you avoid the common mistakes made when specifying and using stainless fasteners, we have put together a short Do's and Dont's guide.
There are many different grades of stainless steel. The two commonly used grades are 304 and 316, with 316 being more corrosion resistant than 304. The rule of thumb is that if the fastener is in a corrosive environment (e.g. within 5km of the coast), 316 is preferable, particularly if the fastener is to be seen, as 316 is less likely to 'tea-stain' or develop a brown discolouration (see photo of bracket showing tea-staining). The Nickel Institute have provided a great design guideline for the selection and use of Stainless Steel to help with this.
10 metres from the beach. Bracket is 304 and showing signs of rust. 316 nuts/bolts are performing well.
In addition to 304 or 316, there are other grades specifically suited to different applications. Please see our guide to selecting the correct grade of stainless steel for your fastener at "Which stainless is right for me?"
Top stainless fastener engineers recommend that all stainless steel threads should be lubricated before being assembled, to reduce the risk of galling (this is when threads lock up). We have found the most risk of galling is with larger threads (M16 upwards), and also when using nyloc nuts. We suggest Lanotec or Nickel Anti-Seize lubricants such as Tef Gel.
The smoother or more polished the finish, the better the corrosion resistance. Some stainless products have a brushed, satin or 'rougher' finish - e.g. sometimes on hinges, fittings, down pipes. This type of finish can trap minute particles (e.g. salt) which damage the protective chromium oxide layer on the stainless steel, causing 'tea-staining', and therefore giving a rusty appearance. This is made worse if the stainless steel is not exposed to rainwater to wash off the particles (see #5 and #6 below).
Electro-polishing or passivating (forms of acid treatment) improves corrosion resistance by thickening the naturally occurring protective chromium oxide layer that forms on stainless steel. All stainless fasteners supplied by Anzor are passivated and can also be electro-polished upon request.
Stainless steel products 'on show' need to be cleaned to remove contaminants (e.g. salt) and therefore maintain the stainless steels appearance. For more information, please see our Cleaning Guidelines.
Stainless steel resists corrosion due to its naturally occurring protective layer ('Chromium Oxide'). When contaminants settle on stainless steel, depending on the grade and the surface finish, these can damage this protective layer, allowing oxygen to react with the iron.
In the stainless steel causing it to rust. If the stainless steel is exposed to rainwater, then this should wash these contaminants away, restoring the stainless steel's protective layer.
Therefore if stainless steel is going to be sheltered from the rain, and it is in a corrosive environment, then consider options to enhance the corrosion resistance: select a more corrosion resistant grade; a smooth/polished/mirror finish; and electro-polishing.
Also consider a cleaning schedule to remove contaminants.
This is where your tools pass on minute contaminants (e.g. iron fillings). This rust on the surface of the stainless steel can kick-start corrosion. This can also occur when iron fillings from grinding steel are blown onto stainless steel.
This is where two dissimilar metals are in contact, react and cause corrosion. For example, lead or copper flashings on a zinc/aluminium roof. Galvanic corrosion may be a risk for the other metals when they are in contact with stainless steel and the join is wet. We recommend investigating situations where you have concerns related to possible Galvanic corrosion. Isolating metals with Tef-Gel or nylon/rubber barriers (e.g. a nylon washer) is a way to keep the metals apart to reduce the risk of this occurring. Note however, it still may occur when one metal might be contaminated by another after water passes from one to the other.
Some proprietary grades with high manganese and low nickel have found their way onto the market and are being sold as 304 or 316. Some are even stamped as such. These alloys also have low chromium and are not suitable for Australia's harsh conditions - especially coastal environments.
Anzor only deals with high quality, reputable suppliers. We also have a material testing program using an X-Ray Spectrometer to provide quality assurance.
For more information on Galvanic or Dissimilar Metal Corrosion you can read this article from ASSDA
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