Ordinary consumers have some misunderstandings about stainless steel, they think that the magnetic stainless steel is not qualified 304 stainless steel. As we know, according to the structure under room temperature，stainless steel can be divided into Austenite such as 201, 304, 321, 316, 310, Martensite or Ferric such as 430, 420, 410. Austenites are non-magnetic or weakly magnetic and Martensite or ferrite are magnetic. 304 is a representative grade of the austenitic stainless steel, it has excellent workability, weldability and corrosion resistance, account for 60% of the world consumption of stainless steel, generally, it is no magnetic, but sometimes it is magnetic or weak magnetism caused by smelting chemical composition fluctuations or processing, but we cannot think this is fake or substandard, what reason is this?
304 is metastable stainless steel, is a single austenite structure after annealing state, with no magnetic. Smelting composition segregation or improper heat treatment will produce a small amount of martensite or ferrite structure, so with a weak magnetic. In addition, after the cold processing deformation (such as stamping, stretching, rolling, etc.), part of the austenite structure also underwent phase change (general mutagenesis into martensite) and with magnetic.
For example, in the same batch of steel strips, the outer diameter of 76mm steel pipe has no obvious magnetic while the outer diameter of 9.5mm steel pipe has obvious magnetic. The magnetic properties of the square rectangular tube are more obvious because the cold bending deformation is greater than that of the round tube, especially in the bending part.
Most of the water sink is made of 304 stainless steel. Many consumers judge it is made of 304-grade stainless steel according to whether the water tank is magnetic or not. At present, there are many kinds of processing technology for the sink, such as welding forming, integral tensile forming, etc., if used 304 material welding forming, is generally annealed after the plate processing, will not be magnetic or weakly magnetic (because of the surface treatment of the sink); One of the water tank drawing molding needs to go through several stretching, general annealing and then stretching (annealing increases the cost, and 304 is not necessary to anneal again), it will be magnetic, that is a very normal phenomenon.