Ask Dr. Steel: What is Stainless Steel?
Stainless steel has been hailed as one of the greatest advances in metal alloy developments in the past 100 years. Because of its resistance to rusting and corrosion it has been used in a variety of applications and projects around the world, and around your house. From the magnificent St. Louis Arch to the Whirlpool refrigerator in your kitchen, stainless steel is all around us. In this article we'll look into exactly what stainless steel is and go over some of its more widely used applications.
In the scientific community stainless steel is known as a ferrous alloy that contains 10.5% chromium content at minimum. Stainless steel has a high resistance to both rust and corrosion thanks to the chromium content that forms a shiny barrier around the steel that is both impervious to water and oxygen, both of which are factors in rust and corrosion. This layer is also self-healing, if stainless steel is scratched the layer will reform to protect the steel, although the scratch is visible the metal is still protected.
Other factors also contribute to the wide use and success of stainless steel. Its low-maintenance factor makes it ideal for use in both home and commercial projects. The relative low-cost of stainless steel as compared to other metals is what makes it popular in many home appliance projects and outdoor uses.
All these factors have combined to make stainless steel the premier choice for architects in some of the world's most famous projects. The Chrysler Building in New York City is adorned with stainless steel cladding. The St. Louis Arch is a 630-foot high stainless steel monument to the Westward Expansion in the USA . Even many dining and fast food establishments feature stainless steel ornamentation and fixtures.
When it comes to environmental concerns many will be happy to know that stainless steel is 100 % recyclable. Over 50% of new stainless steel is made from recycled stainless steel material.
Stainless steel is more than one type of steel. There are actually several types and they are classified by their crystalline structure. The four most common include:
- Austenitic Stainless Steels. This particular steel is the variety that most of us are familiar with and it makes up 70% of total steel production. You will most often find this type of steel is your kitchen your flatware is composed of Austenitic Steel. This type of steel provides protection and structural integrity at a high range of temperatures which makes it well suited for a variety of applications.
- Ferritic Stainless Steels. Highly corrosion resistant, but not as durable as Austenitic Steels.
- Martensitic Stainless Steels. Low corrosion resistance, but extremely durable and highly machineable. This type is often used in stainless steel applications where magnetic is involved.
- Duplex Stainless Steels. These steels are a 50/50 blend of both Austenitic and Ferritic steels. They aim to combine the high corrosion resistance and strength of the two.
Stainless steel is also graded for further classification. The major categories of the grading system include:
- 200 Series Austenitic Iron-Chromium-Nickel-Manganese Alloys
- 300 Series Austenitic Iron-Chromium-Nickel Alloys
- 400 Series Ferritic and Martensitic Alloys
- 600 Series Martensitic Precipitation Hardening Alloys
Finally, in our journey in stainless steels, one of the most common uses of stainless steel is in Stainless Steel Finishes. Through the use of these finishes stainless steel is rolled to produce the desired visual effect of the steel. This method is used mainly for home and decorative purposes, such as your stainless steel stove or refrigerator.
Finishes are graded as follows:
- No 0. Hot Rolled, Annealed, Thicker Plates
- No 1. Hot Rolled, Annealed and Passivated
- No. 2D Cold Rolled, Annealed, Pickled and Passivated
- No 2B Same as 2D but with an additional pass through polished rollers
- No. 2BA Bright Annealed, same as 2B but with highly polished rollers
- No. 3 Coarse Abrasive Finish applied mechanically
- No. 4 Fine Abrasive Finish
- No. 6 Matt Finish
- No. 7- Reflective Finish
- No. 8 Mirror Finish
Now that you know what makes up stainless steel, and the wide variety and finished available, take a look around the next time you are out. You may be surprised how much stainless steel you see being used all around you.