Why is Stainless Steel Non Magnetic?

Image Credit: 
Main Image: 

Stainless Steel  is commonly called as "Inox" or "Rostfrei" and is a type of steel. Stainless Steel is not any single pure magnetic metal. It is an alloy of metal iron, carbon, and chromium. Stainless Steel contains 10.5 wt % of chromium which is oxidized to chromium oxide "CrO". The coating protects the iron against most corrosion, stain, or rust. Hence the term “StainlessSteel emerged. The Chromium layer is too thin to be visible but adds a shine to the metal beneath. Other metals present in the Stainless Steel alloy is nickel which is non magnetic in nature. Nickel is added to the Stainless Steel compound to strengthen the protective qualities of the chromium. Apart from that, nickel alters the physical composition of Stainless Steel and removes any magnetic properties. There are other elements used to make the alloy including molybdenum and nitrogen. Stainless Steel remains non-reactive to adverse atmospheric conditions such as moisture, carbon dioxide, electrical fields, salt, sulfur, ozone, chloride compounds and extremes weather conditions. Stainless Steel is cent percent recyclable and eco-friendly material. In fact, over 50% of new Stainless Steel products are made from remelted scrap metal. Product dusts from processing are found to be corrosion resistant, insoluble, non-biodegradable in nature. The hazardous waste badly affect the fish, plants, animals and the environment if released. However, the degree of pollution depends on the particle size and quantity released.  



What are the uses of Stainless Steel?

Stainless Steel is used extensively to produce cutlery, cookware, hardware, surgical appliances, industrial equipment, automotive parts, aerospace components, construction structures used in large buildings, jewelries, bridges, firearms, watch, storage tanks, tankers, monuments and sculptures.



What is the history behind Stainless Steel?

Stainless Steel was accidentally discovered in the the 20th century. In 1913 , a Sheffield chemist Harry Brearley was trying to find a trying to find a solution to the rapid erosion of the inside of rifle barrels. He experimented with a steel variant containing a high proportion of chromium. It was found that steel with high proportion of chromium did not dissolve in acid (a test  followed at that time). Besides, the steel stayed shiny. Brearley realized the potential of newly discovered steel that would not rust and would remain highly resistant to tarnishing and rusting. This is how Stainless Steel was discovered and got its name for its unique rust-resisting property. 



What are different varieties of Stainless Steel?

There are over 100 different grades of Stainless Steel which are usually sub-classified into separate metallurgical families such as the austenitic, ferritic, martensitic , duplex and precipitation hardening.

  • Austenitic Stainless Steel: This is also referred as the 300 series or 18/8 Stainless Steel. It is most commonly used steel type. It has a composition of 16% chromium, 0.15% carbon, nitrogen, nickel, and manganese. It is non-magnetic, ductile and highly resistant to rust and corrosion. This Stainless Steel type is used for making pumps.
  • Martensitic Stainless Steel: It is known as the 400 series. This type of steel contains a higher proportion of carbon (nearly 1%) and 18% chromium. It also contains traces of nickel and molybdenum. It possesses magnetic properties and can be hardened by heating. This Stainless Steel type is non-corrosive but has less durability than austenitic steel. It is used in making molds, surgical instruments and stainless cutlery.
  • Ferritic Stainless Steel: This particular type is known as the 400 series. It contains 10.5% carbon and up to 27% chromium. It cannot be hardened by heating. It is less ductile, durable and has poor strength. Ferritic steel demonstrates magnetic properties. Ferritic steel is highly resistant to corrosion. It is used in making washing machines and boilers.
  • Duplex Stainless Steel: This Stainless Steel is a mixture of austenitic and ferritic steel in a 50:50 proportion. Duplex steel contains a higher percentage of chromium and a lower quantity of nickel. It is very tough and resistant to corrosive stress. It shows some magnetic properties.
  • Precipitation Hardening Stainless Steel: Initially this type of steel is austenitic. It hardens at a relatively lower temperature. Certain other elements are added to make it tougher. It can be easily transformed into different shapes by heating. It is highly corrosion resistant similar to austenitic steel and is used in making aircraft components, shafts and pumps. It is non magnetic in nature.



Is Stainless Steel Magnetic?

Magnetic property depends on the micro-structure of the steel. A 100% non-magnetic material has a magnetic permeability of 1. Austenitic Stainless Steel (300 series) is normally non-magnetic with magnetic permeability of approximately 1.0. Martensitic, Ferritic, Duplex and Precipitation Hardening Stainless Steel show magnetic properties. The 400 series contain iron and chromium, but without the presence of nickel. Hence, they exhibit magnetic qualities. The degree of magnetic attraction varies. It is possible for items made with the 400 series stainless steel to attract magnets, and in some cases small metal items to its surface.

External References
Related Videos: 
See video
Related Images: