wisepowder: The Magnet Test for Stainless Steel is Not Accurate

The Magnet Test for Stainless Steel is Not Accurate

15 Mar 2021 at 07:52

The magnet test is NOT a correct way to verify stainless steel.
Stainless steel is a common name for metal alloys that consist of 10.5% or more Chromium (Cr) and more than 50% Iron (Fe). Although it is called “Stainless” a better term for it is “highly stain resistant.” It is a darker metal. There are two process methods to make it bright, both are surface treatments.To get more news about 316 stainless steel, you can visit stainless-steel-supplier official website.

There are three major classes of stainless steel.
1. Austenitic: Chromium-nickel-iron alloys with 16%-26% chromium (Cr), 6%-22% nickel (Ni), and low carbon content, with non-magnetic properties. Type 304 ( 18% chromium, 8% nickel ) is the most commonly used grade or composition.
2. Martensitic: Chromium-iron alloys with 10.5%-17% chromium and carefully controlled carbon content. It has magnetic properties! Type 420 is a typical example. It is mostly used in knives and kitchen equipment.
3. Ferritic: Chromium-iron alloys with 17%-27% chromium and low carbon content, with magnetic properties! Type 430 is the most commonly used ferritic.

The chromium content in stainless steel alloys is what generally prevents corrosion. The chromium works by reacting with oxygen to form a tough, adherent, invisible, passive layer of chromium oxide film on the steel surface. If damaged mechanically or chemically this film is self healing as long as it has enough oxygen. Since oxygen is necessary for reaction, liquids and other things stored for a prolong time in stainless can prevent oxygen contact and thus promote corrosion. If you remove rust with a cloth the chromium will chemically react with the oxygen in the air and produce a new protective layer.

An increase of chromium content improves the corrosion resistance of stainless steel. The addition of nickel is used to raise the general corrosion resistance required in more aggressive usage or conditions. The presence of molybdenum (Mo) improves the localized corrosion resistance. Other alloy metals are also used to improve the structure and properties of stainless steel such as Titanium, Vanadium, and Copper. Non metal additions typically include natural elements such as Carbon and Nitrogen as well as Silicon. The S304 we use to make our stainless casters has 8.07% nickel (Ni) and 18.23% chromium (Cr).

The process of stamping and surface polishing can change the non-magnetic property of S304. The pressure used in stamping and forming changes the distribution of chemicals in the alloy. The stamping die used can also chemically leave iron ions on the surface of the stainless steel. Both factors can cause change to the non-magnetic property of the stainless and thus create magnetism! Foreign residue can also be corrosive.


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