Stainless Steel Shafting in Corrosive Environments

Every application is unique, and each one dictates what type of steel should be implemented. Within corrosive environments, the choice for shafting remains stainless steel. In this article, we offer some background on the different categories of steel, and then further investigate the different types of stainless steel shafting, including their characteristics and applications within industrial automation.

A quick background on steel.

There are four broad categories of steel. In addition to stainless, they include carbon steels, alloy steels, and tool steels. Carbon steels are the most common and evident by their dull, matte appearance, with each grade containing different percentages of carbon. Alloy steels contain a mixture of alloys such as silicon, copper, and aluminum that offer varying degrees of corrosion resistance and strength. Tool steels are hard and sought after for their heat and scrape resistance.

The darling of the family.

The fourth type, stainless steel, utilizes a mix of low carbon content coupled with no less than 10.5% chromium. This group is the shiny overachiever, offering strength and resistance to high temperatures and corrosion, as well as options for special requirements. The group is divided into five types that include ferritic, austenitic, martenistic, duplex, and precipitation hardened. In this article, we are focusing primarily on austenitic steel, which is the most common, and makes up our 300 series stainless steel shafting. Below is an in-depth look at the most common types of stainless steel used within industrial automation.

303 Stainless Steel – A blend of machinability and corrosion resistance

Type 303 stainless steel is non-magnetic and cannot be hardened by heat treatment, which makes it unsuitable for use with rolling element bearings. Its basic alloy composition is 18% chromium and 8% nickel stainless steel, with the addition of selenium or sulfur making it highly machinable. Type 303 was designed with added sulfur content to allow for improved machinability over other similar materials, but also hold good mechanical and corrosion resistant properties. While the sulfur content aids in making 303 stainless highly machinable, it also slightly decreases corrosion resistance and toughness, comparatively.

• Magnetic: No
• Hardenable: No (Limited bearing choices and reduced life)
• Machinability: High
• Weldability: Poor
• Corrosion resistance: High, but less than other types of 300 series
• Washdown environments: Not preferred
• Cost: Expensive compared to other materials
• Applications: Areas where parts need to be heavily machined

304 Stainless Steel – The popular choice

Type 304 is the most popular 300 series stainless steel type, accounting for over 50% of the worldwide usage. Like type 303, it is non-magnetic and unsuitable for use with rolling element bearings because of its non-hardenable heat treatment properties. The advantage of 304 is that it provides high resistance to oxidization and exceptional corrosion resistance to chemical and atmospheric exposure. 304 is also the most weldable type of 300 series stainless, which can help with ease of fabrication.

• Magnetic: No
• Hardenable: No (Limited bearing choices and reduced life)
• Machinability: Poor compared to 303 stainless steel
• Weldability: Most weldable form of 300 series
• Corrosion resistance: Exceptional
• Washdown environments: Preferred material
• Cost: Expensive compared to other materials
• Applications: Food industry

316 Stainless Steel – The best corrosion resistance

Type 316 stainless steel contains 3% molybdenum, which helps to provide the best corrosion resistance of any grade of 300 series. Much like type 303 and 304, it is non-magnetic and unsuitable for use with rolling element bearings because of its non-hardenable heat treatment properties. 316 is better suited for chloride environments that often times involve structural pitting and crevices. It will perform well at high temperatures and contains excellent tensile strength and weldability. There are many applications that 316 excels in, and many within industrial automation industry consider 316 to be the premium grade.

• Magnetic: No
• Hardenable: No (Limited bearing choices and reduced life)
• Machinability: Lowest of the 300 series
• Weldability: High with excellent tensile strength
• Corrosion resistance: Highest
• Washdown environments: Preferred material
• Cost: Expensive compared to other materials
• Applications: Food preparation equipment and systems, evaporators and tanks, condensers, marine environments, textiles and pharmaceuticals

Ceramic Coated – The lightweight solution

Ceramic coated (aluminum based) shafting has several unique characteristics that can make it a valuable product. This product is extremely light weight compared to all other linear shaft products. The weight differential is more noticable as the shaft diameter increases. As is typical of this material type, as the diameter increases, the comparable cost to other materials goes down. Ceramic coated shafting is non-magnetic and extremely hard due to the finish. However, the hardness depth is nominal, making rolling element bearings a poor choice for this type of shafting.

• Magnetic: No
• Hardenable: No (Limited bearing choices and reduced life)
• Weight: Very lightweight
• Corrosion resistance: High
• Washdown environments: Yes, depending on the conditions
• Cost: Inexpensive, especially at larger sizes
• Applications: Medical, medical devices, aerospace, and some washdown

Carbon Steel – The most common shafting material

The common types of carbon steel are 1060, 52100 & 1566. There are some differences in material types, but generally they are used interchangeably in similar applications. Carbon Steel is the dominant material used in industrial automation accounting for roughly 85% of all shafting sold. It is the least expensive and easily hardenable, which gives it outstanding performance with all bearing types, predominately with ball bearings. The high carbon content allows for this shaft to be easily machinable, but susceptible to corrosion. There are a variety of plating options that are used to help slow the corrosion process, most common of which would be chrome. Carbon steel is used in a wide array of factory automation applications where the environment can be controlled.

• Magnetic: Yes
• Hardenable: Yes (works with all bearing types)
• Machinability: High
• Weight: Heavy
• Corrosion resistance: Poor
• Washdown environments: No
• Cost: Inexpensive, common material
• Applications: Ideal surface for ball bearings

400 Series Stainless – The true compromise

The 400 Series is a very popular material type for industrial automation linear shafting because it combines some corrosion resistance with the ability to harden, which makes it possible to use with rolling element bearings. While 400 Series is a true compromise product because the material does not harden as well as Carbon, and the corrosion resistance isn’t as good as 300 series, many consumers find the blend to be acceptable for their needs.

• Magnetic: Yes
• Hardenable: Yes (works with rolling element bearings)
• Machinability: High
• Weight: Heavy
• Corrosion resistance: Moderate (some applications)
• Washdown environments: No
• Cost: More than carbon steel, less than carbon steel with plating
• Applications: General factory automation where some corrosion concerns are present

We have added common in-stock sizes to our 316 stainless steel shafts inventory!

If you have any questions regarding which shafting material to use on your next project, please contact one of our application engineers at +1-800-221-0811, or online.