Stainless Steel: Understanding and Identifying the Ideal Enclosure Material, Part 1

April 28 2016

Stainless steel is a steel alloy, consisting of at least 11% chromium. Chromium provides the shiny appearance stainless steel is known for, but also offers superior corrosion resistance. Unprotected carbon steel rusts quickly when exposed to air and moisture, degrading its mechanical properties and appearance. Stainless steel generally retains its properties in most conditions. However, there are some environments that can cause corrosion for stainless steel, such as low oxygen, high salinity (salt) and some extreme conditions (i.e., mines, strong acids). When stainless steel does experience corrosion, it is commonly by means of pitting, which appear as reddish spots on the surface.

The chromium present in the stainless alloy creates a thin, transparent passive oxide film when it comes in contact with oxygen. This film acts to protect the steel from corroding agents. While the film can be scratched away, the chromium present throughout the alloy allows the film to nearly self-heal instantly. If a zinc-plated, or painted, sample of mild steel is scratched, it will corrode and spread to areas beyond the scratch.

Stainless steel is available in many grades or formulations. The most common are in the 300 series, with 15-20% chromium. These are largely non-magnetic; however, forming and cold working can induce magnetic characteristics. The stainless steel in the 400 is typically magnetic due to higher levels of iron.

Stainless steel has become the standard material choice in many industries. For example, in the food and beverage industry, stainless steel allows for steam cleaning, while in pharmaceutical applications, stainless steel provides a clean, antibacterial surface. Stainless steel is also notable in various consumer products such as sinks and appliances.

Grades of stainless

There are many different grades of stainless steel to accommodate diverse application requirements.

  • Type 304 is the most common grade of stainless steel, also known as 18/8 for its composition of 18% chromium and 8% nickel. The 300 series feature an austenitic crystal structure. Type 304 will resist corrosion in most environments; however, when exposed to salt and other chlorides, it will experience corrosion. In industrial environments, chlorides may be present in dust and flying ash, which if left unwashed on flat surfaces, will result in pitting.
  • Type 316 is similar to type 304, with increased corrosion resistance due to more nickel and the introduction of molybdenum. Type 316 shows stronger resistance to a range of environments, and is recommended in coastal regions where salt is present in the air, especially within one mile of the coast. Salt can also be deposited via rain. Chlorides can also be found in cold weather environments where salt is applied to roadways. Salt road spray can be carried surprisingly long distances both vertically and laterally away from the actual road surface. Type 316 also shows increased resistance to corrosion by strong acids, which may be found in paper mills and mines. An alternative version to type 316 is type 316l, which has lower carbon content. Lower carbon allows for better welding characteristics.
  • Type 321 is a grade typically reserved for weldments subjected to severe corrosive environments and high service temperatures from 800 to 1,600 degrees Fahrenheit. The formulation of type 321 is similar to type 304, with the addition of titanium. When type 304 is heated above 1,292 degrees Fahrenheit for an extended period of time it may suffer weld decay, which will initially display corrosion on the areas around the weld. Weld decay is lessened by the addition of titanium, making type 321 stainless steel ideal for use inside aircraft exhaust manifolds, boiler shells and fire walls.
  • Ferritic alloys feature a different crystal that affords better corrosion resistance than austenitic grades. However, ferritic alloys are less durable than types 304 or 316 stainless steel grades. Ferritic alloys (types 405 or 409) are usually less expensive, and are most often used on automobile exhaust components.
  • Martensitic alloys also feature a distinct crystal structure. They offer superior wear resistance but decreased corrosion resistance in comparison to austenitic alloys. Common martensitic alloy grades are types 410, 420 and 440, of which types 420 and 440 are commonly used in cutlery. Martensitic alloys are also highly machinable.
  • Type 500 series alloys are heat-resisting chromium alloys.
  • Type 600 series alloys are martensitic alloys, and are further strengthened through precipitation hardening, or age hardening.
  • Type 2205 is a grade known as duplex, for its ferritic and austenitic characteristics. Type 2205 offers superior corrosion resistance with high strength.

In Part 2: a cost comparison between stainless and mild steel, available surface finishes, manufacturing processes, and a comparison to plastic and composite enclosures.


This article was first published as a white paper by Pentair. Read the entire document here: www.pentairprotect.com/wcsstore/AuroraStorefrontAssetStore/UserDownloads/WhitePapersCaseStudies/WP-00032_EN.pdf.

 

 

Related Articles


Latest Articles


Changing Scene

  • Intralec Named New Sales Agency Partner for IDEAL Electrical in Central & Southwestern Ontario

    Intralec Named New Sales Agency Partner for IDEAL Electrical in Central & Southwestern Ontario

    July 7, 2025 Intralec Electrical Products is proud to announce our new partnership with IDEAL Electrical as their sales agency for the Central & Southwestern Ontario regions. As a Canadian manufacturer with over 60 years of experience producing quality products—many of which, like the Can-Twist wire connector and Yellow 77 lubricant, are made in Ajax,… Read More…

  • City of Winnipeg Continues to Improve Online Permits System

    City of Winnipeg Continues to Improve Online Permits System

    July 4, 2025 The City of Winnipeg has launched an improved Permits Online web portal. This upgrade aims to make the permit process more convenient for customers. Permits Online is a one-stop shop to manage the permit process. Now, the web portal is easier to use because customers can navigate it using their mobile device. The portal… Read More…

  • Schneider Electric Launches Chapter 3 of Sustainability School

    Schneider Electric Launches Chapter 3 of Sustainability School

    July 4, 2025 Schneider Electric, the leader in the digital transformation of energy management and automation, has launched Chapter 3 of its online Sustainability School, a free training program designed to empower its channel ecosystem partners to become leaders in sustainability. This chapter will focus on teaching businesses how to decarbonize and unlock the competitive… Read More…

  • United Chargers Launches Grizzl-E Club Charger-as-a-Service Subscription Model

    United Chargers Launches Grizzl-E Club Charger-as-a-Service Subscription Model

    July 4, 2025 United Chargers Inc., known for the Grizzl-E line of EV chargers, announces Grizzl-E Club, a first-of-its-kind charger as a service that provides a free EV Charger and pays drivers back for charging. Grizzl-E Club is designed to make EV ownership more rewarding, accessible, and future-ready. Beginning July 1st, Canadians can join the Grizzl-E… Read More…