Stainless Steel: Properties, Families and Grades

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What is stainless steel?

Let’s recall it: steel is an alloy of iron and carbon with a maximum carbon content of 2.1%. So when it comes to stainless steels, we need to remember they represent a group of steels that are resistant to corrosion thanks to the addition of alloying elements such as chrome; and the reduction of carbon percentage.

Stainless steels are a family of approximately 200 alloys of steel. Their outstanding heat and corrosion resistance properties make them very attractive for a vast range of applications.

Completely recyclable, stainless steel is environmentally neutral and inert, and it meets the needs of sustainable manufacturing thanks to its longevity. Stainless steel is also aesthetically engaging, exceptionally hygienic, easy to maintain and greatly durable, which explains why it plays a prominent role in an array of industries.

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General properties of stainless steel

Aesthetics

Stainless steel has a wide range of surface finishes and it offers significant design scope using finishes which are distinctive; in fact, it can be used on flat or curved surfaces and to form complex shapes.

Corrosion Resistance

This distinguishing property of stainless steel is responsible for its many unique applications in the industry. High oxidation resistance is a result of chromium in stainless steel, which can go up to 26% in some grades.

Corrosion resistance happens as a result of stainless steel constantly being protected by a passive layer of chromium oxide that forms naturally on the surface through the reaction of the chromium with oxygen from air or water. If the surface is scratched, it regenerates itself.

Recyclability

Stainless steel is the “green material” by excellence as it is environmentally neutral and inert when in contact with elements such as water. These qualities make stainless steel ideally suited to applications exposed to adverse weather. Stainless steel’s longevity fulfils the requirements of sustainable manufacturing, and low maintenance guarantees the user unparalleled service life.

Its non-biodegradable nature also prevents it from contaminating resources as it does not break down and seep into soil or water reservoirs.

Versatility

From rail vehicles to silverware, and from surgical implants to turbine blades, stainless steel is an exceptionally versatile material.

However, in order to make the most of this material, when considering its use every aspect of the design should be taken in consideration. Nevertheless, it seems certain that we will see more use of stainless steel in the future, not less.

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Most common stainless steel families

Austenitic stainless steels

This family is the most popular and widely used around the world.  While non-magnetic when annealed with a solution, certain cold worked grades are magnetic. Heat-based hardening will not work with these types of steel.

Popular grades of austenitic stainless steel include SAE 300 series (chromium-nickel) and 200 series (chromium-manganese), with 15% to 30% chromium. They have good formability as well as toughness and weldability.

Ferritic stainless steels

Ferritic grades can be found within the 400 series and contain 10.5% to 20% chromium; due to their lower nickel content, they are one of the most cost-effective families available. While they have better properties than austenitic grades (they are highly resistant to scaling and cracking at elevated temperatures), the corrosion resistance and weldability are worse.

They cannot be hardened by heat treating but they can be cold worked and softened by annealing. Although stainless steels are generally considered to be non-magnetic, ferritic grades are an exception to this rule.

Martensitic & Precipitation Hardening stainless steels

Also within the 400 series, Martensitic steels are straight chromium steels and contain 11.5% to 18% chromium. As opposed to ferritic stainless steels, they were developed to be corrosion resistant and hardenable by heat treating. They are magnetic and are used where hardness, strength and wear resistance are required.

Duplex stainless steels

This family includes many of the most recent alloys created. With Duplex 19% to 28% chromium, this stainless steel group is a combination of austenitic and ferritic materials in equal proportions. It produces a higher strength and superior resistance to stress corrosion cracking. In fact, strength is approximately twice as high as austenitic stainless steels, and duplex grades also benefit from improved resistance to pitting, crevice corrosion and stress-corrosion cracking.

Compared with super-austenitic grades, similar material properties can be achieved but with a lower overall alloy content which makes duplex grades more cost-effective. The most commonly used duplex type is 2205. Applications for duplex stainless steels can be found in the marine, chemical, petrochemical, and pulp and paper industries.

Final thoughts

Stainless steel provides corrosion resistance in addition to the regular properties of steel. Besides from corrosion resistance, other advantages of its own include endurance and long service life.

Notwithstanding some of its drawbacks, stainless steel remains a great material and has a very positive impact on the industry as a whole. Given the many grades and their different properties, applications can be numerous.

And most importantly… our parts are manufactured with this material providing you with the best quality!

Contact us today for any information you may need!