We often listen to the business in stainless steel pipe and other stainless steel products in the processing, especially the use of nitrogen in the welding process. Maybe many friends do not know, why to use nitrogen in stainless steel pipe welding?
In stainless steel pipes, nitrogen plays an important role in three aspects: stainless steel matrix structure, mechanical properties and corrosion resistance. Nitrogen is an element that forms and stabilizes the austenite phase and enables it to phase large. It can replace the nickel in stainless steel pipe, reduce the content of ferrite in steel, make austenite more stable. Martensitic transformation can be avoided by preventing interphase precipitation of harmful metals even under cold working conditions.
The effects of nitrogen on the mechanical properties of welded stainless steel tube mainly include: Nitrogen can improve the strength of stainless steel pipe, but can not reduce its plasticity. Nitrogen can improve the creep, fatigue, wear resistance and yield strength of stainless steel pipe. Nitrogen is an element to improve corrosion resistance. It can form NH4+ in the hole, eliminate the generated H+, inhibit PH value, thus inhibiting pitting and metal dissolution rate in the hole, and improve local corrosion performance.
In life we often judge the quality of stainless steel according to whether the tube is magnetic, but in fact this method is very unscientific. Like our common zinc alloy pipe, copper alloy tube can imitate stainless steel exterior color commonly, and it is not magnetic, and easy to be mistaken for stainless steel pipe. Even if we are currently the most commonly used pipe of 304 steel grade, after cold working, there will be different degrees of magnetic tube, so it can not rely on whether there is magnetic tube to judge the quality of stainless steel, so why will 304h stainless steel have magnetic?
And we used to say 304 stainless tubing is non-magnetic stainless steel pipe. Pipe refers to the magnetic index falling below a certain value, that is to say, the general stainless steel are more or less with certain magnetic tube. 304 stainless tubing is after cold working, and the organizational structure will tube to the martensitic transformation, and with the cold deformation of tube processing, the greater the martensitic transformation of tube is, the more the magnetic would be the stronger. So the magnetism of the material is determined by whether the molecular arrangement tube is regular, and the coorientation of the electron spin, which can be considered as the physical performance of the material, and the corrosion resistance of the material is decided by the chemical composition of the material. It is the chemical performance of the pipe, and whether the material has magnetism has nothing to do with it.