Hot Rolled Stainless Steel Strip various kinds
People often according to the magnetic properties of stainless steel to determine the pros and cons and authenticity, most people think that stainless steel is not magnetic, and with the magnet to identify stainless steel, this method is very scientific. Do not smoke non-magnetic, that is good, genuine; suction who have magnetic, that is counterfeit fake, which is a very one-sided, unrealistic identification of the wrong way.
A variety of stainless steel, according to the organizational structure at room temperature can be divided into several categories 1. Austenitic type such as 304,321,316,310; 2. Martensite or ferrite type such as 430,420,410; The body is non-magnetic or weakly magnetic, martensitic or ferrite is magnetic. Most of the stainless steel, which is usually used as a decorative tube sheet, is mostly austenitic 304 material. Generally speaking, it is non-magnetic or weakly magnetic, but magnetic properties may occur due to chemical composition fluctuation or processing status, but this can not be considered Fake or unqualified, what is the reason for this?
Austenite is non-magnetic or weak magnetic, and martensite or ferrite is magnetic, due to smelting component segregation or improper heat treatment, will result in austenitic 304 stainless steel in a small amount of martensite or ferrite. In this way, 304 stainless steel will be with a weak magnetic. In addition, 304 stainless steel after cold processing, the structure will be transformed into martensite, cold forming deformation of the greater the greater the transformation of martensite, steel, the greater the magnetic. As a batch of steel, production Φ76 tube, no obvious magnetic induction, production Φ9.5 tube. Due to Ling bending deformation of the larger magnetic sense is obvious, the production of rectangular tube deformation due to large diameter, especially the corner part of the deformation is more intense magnetic more obvious. In order to completely eliminate the above-mentioned causes of the 304 steel magnetic, through the high temperature solution to restore the stability of austenite structure, thereby eliminating the magnetic.
Here to be particularly emphasized is due to the above reasons caused by the 304 stainless steel magnetic, and other materials such as stainless steel, such as 430, carbon steel is not the same level of magnetic, that is, 304 steel magnetic always shows the weak magnetic. If the stainless steel is weakly magnetic or completely free of magnetic, it should be judged as 304 or 316 material; if it is the same as the magnetic properties of carbon steel, it shows strong magnetic properties, because it is not 304 material. 304 and 316 are austenitic stainless steel, single phase. With weak magnetic properties.
Stainless steel is generally quenched, such as as a tool steel, must be quenched by the state to improve its hardness. But the steel is also a large number of applications in the structural steel, this time heat treatment must choose quenching and tempering (quenching + tempering) use, for tempering, we must pay attention to some problems.
Will have been quenched steel re-heated to a certain temperature, and then a certain method of cooling called tempering. The aim is to eliminate the internal stress produced by quenching, reduce hardness and brittleness to achieve the desired mechanical properties. Tempering high temperature tempering, tempering tempering and low temperature tempering three categories. Tempering with quenching, normalizing with the use.
1, aging treatment: In order to eliminate precision measuring tools or molds, parts in the long-term use of size, shape changes, often in the low temperature tempering (low temperature tempering temperature 150-250 ℃) before finishing, the workpiece reheated to 100- 150 ℃, to maintain 5-20 hours, this is the stability of precision parts processing, known as aging. It is especially important to treat the steel members under low temperature or dynamic load conditions to eliminate the residual stress and stabilize the steel structure and size.
2, quenching and tempering treatment: quenching after high temperature tempering heat treatment method known as quenching and tempering treatment. High temperature tempering refers to tempering between 500-650 ° C. Quenching and tempering can make the performance of steel, the material has been a great degree of adjustment, its strength, plasticity and toughness are better, with good comprehensive mechanical properties.