More and more people like stainless steel tools or furnishings, due to its beautiful appearance, corrosion resistance, the advantages of not easy to damage. Pots and pans in the kitchen, urban sculptures, architectures, decoration of the living room and other field, stainless steel are widely used nowadays. Some customers often take a magnet in stainless steel utensils sucked around when they in the purchase of stainless steel kitchenware. They think that when the magnet is sucked, the material is not stainless steel, while not sucked is stainless steel; They believe good stainless steel are not magnetic. In fact, this is a misunderstanding of stainless steel.
The fact is that, for stainless steel, regardless of whether the magnet can be absorbed or not, as long as it meets its quality standards, it is stainless steel.
Therefore, from the point of view of metallurgy, there is no stainless steel. The main element of stainless steel corrosion resistance is chromium. Chromium element content of 10.5% or more of the steel will not rust. Smelting to add different alloying elements, there is a magnet to absorb the difference between and can not absorb. Stainless steel is generally divided into several categories, such as austenite, ferrite and martensite, according to the organizational structure. If you add a different proportion of chromium-nickel to the steel, austenitic steel is the magnet can not absorb the stainless steel; If you add chromium and a small amount of nickel to the steel (or no nickel), the steel is the magnet can absorb the stainless steel, also called ferritic stainless steel; Martensitic stainless steel is the main alloying elements are chromium, iron and carbon. There are more than 100 different kinds of stainless steel due to the different alloy content. In addition to austenitic stainless steel magnet can not be absorbed, ferritic, martensitic stainless steel are magnetic.
The element nickel has very few reserves in the world and is more expensive. Therefore, the high nickel content of stainless steel in the market price is also higher, and the magnet can not be absorbed. In fact, there is a stainless steel magnets can not be absorbed. That is high manganese less nickel or nickel-free stainless steel. The market price of this stainless steel is more than 1000 yuan per ton lower than the stainless steel with high nickel content. Some dealers deceive consumers, by using “good stainless steel magnets can not absorb” to misunderstand clients. They quote the same expensive price as high nickel stainless steel .
What is stainless steel?
As an alloy, stainless steel is made up of a combination of metals with the balance being iron but the main alloying element being Chromium. Stainless steel resists tarnishing and rust because of the elements contained within: iron, chromium, silicon, carbon, nitrogen, and manganese. It must be composed of at least 10.5% chromium and at most 1.2% carbon to be recognised as stainless steel.
Chromium (combined with nickel) is the component that gives stainless steel its corrosion resistance. While stainless steel is frequently called stainless, it is not really stainless, because the chromium builds up on its surface making it able to withstand abuse much longer than regular steel without chromium. Passivation is the process of applying chromium to stainless steel to keep the shiny, silver finish.
Types of stainless steel
Stainless steel comes in over 57 types of standard alloy, as well as numerous custom alloys produced by stainless steel manufacturers. The composition of each type varies. Based on their metallurgical properties and microstructures, stainless steels can be divided into five categories:
Austenitic Stainless Steels
Ferritic Stainless Steels
Martensitic Stainless Steels
Duplex Stainless Steels
The Duplex stainless steel combines austenitic and ferritic crystals, so it offers the best of both worlds and is magnetic whilst also having generally greater corrosion resistance than the austenitic 304 and 316 stainless steels.
Ferritic stainless steels – these steels are magnetic primarily due to the presence of ferrite, a compound of iron and other elements. The crystals of ferrite and iron make this type of stainless steel magnetic. It is also important to note that some stainless steels with ferrite have a weak magnetic pull.
Stainless steel grades 409, 430, and 439 are also known as ferritic stainless steels.
Martensitic stainless steels – this category has many types of stainless steel that are magnetic. It is possible for martensitic stainless steel to have a ferromagnetic crystal structure if iron is present. The magnetism of martensitic steel is due to iron being the main component. Martensitic stainless steel has carbon trapped in its crystals are can be hardened to become extremely strong but have reduced chemical resistance compared to austenitic stainless steels.
There are three grades of martensitic stainless steel – 410, 420, and 440.
Austenitic stainless steels – the majority of stainless steels falling into this category are non-magnetic due to high levels of austenite. Despite the fact that some of the alloys, such as grades 304 and 316, contain iron, these materials are non-ferromagnetic. It is the crystal structure that is important for magnetic properties.
By using a thermal process or work hardening (e.g. bending, drilling, etc) austenitic stainless steels can be partially magnetic, forming ferrite in some areas. As a result, austenitic grades exhibit a slight magnetism at mechanically operated edges like sheets.
What makes stainless steel magnetic?
It is necessary that steel contains iron and has either a martensitic or ferritic crystal structure in order to be magnetic.
There must be iron in the alloy
The alloy must possess martensitic or ferritic crystal structures
Which types of stainless steel are magnetic?
Below are a few examples of magnetic and non-magnetic, given as a quick summary.
Ferritic stainless steel grade 430 is magnetic
The austenitic stainless steel grade 304 is not magnetic but it may become a little magnetic in areas that have been cold working (bending, deforming, etc.).
Austenitic stainless steel grade 316 is not magnetic
The table shows the different magnetic response in the different stainless steel