Reasons and preventive measures for magnetic properties of austenitic stainless steel in cold processing

It is well known that the vast majority of stainless steel materials are suitable for cold forming. Austenitic stainless steel itself is not magnetic, but cold processed austenitic stainless steel will have strong magnetic properties, especially those made of austenitic stainless steel, such as head, elbow and so…..
Why will the austenitic stainless steel suddenly appear to be magnetic after cold processing?
The main reason is that most of the microstructure of austenitic stainless steel is mostly metastable austenite, so the more accurate term should be the metastable austenitic stainless steel.
When the metastable austenite stainless steel for cold forming, part of austenite in the steel will transform into martensite, and maintain a coherent and original austenite, produce diffuse phase transition in a very short period of time by shear form, which is called the martensitic transformation induced by martensitic transformation or deformation.
In a stainless steel microstructure of martensite is usually a martensite centered cubic structure with dense Hugh six party structure of martensite two forms, including alpha martensite with magnetic characteristics, martensite organization has no magnetic characteristics, but only when the nickel content is relatively high, will form. Martensite. So when some of the common austenitic stainless steels are transformed from austenite to martensitic structure, magnetic properties will be formed.
The stability of austenite is determined by the corresponding chemical composition, and the transformation of martensite caused by processing is also related to the intensity of the process. If materials are used for common uses such as food industry, magnetism does not affect the use of products, so some standards are usually allowed to exist.
But if the magnetic presence is not allowed, the corresponding preventive measures should be done.
According to the causes of martensite formation and the influencing factors, the main preventive measures are the following.
The first is to prepare for the processing of stainless steel plate in the content standards within the allowable range of austenitizing elements to enhance tissue; secondly it can be upgraded materials, such as the use of 316L and 310 nickel content relatively large stainless steel materials; also can optimize the processing technology of stainless steel; solution heat treatment measures can be taken, it can completely eliminate the phenomenon of magnetic and the work hardening. But the cost of this method is relatively high, and it has a great impact on the size and deformation of the products. Finally, it is necessary to strictly avoid the influence of unnecessary mistakes on the quality of products according to the relevant production standards.
Source: China Stainless Steel Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

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