The issue of the magnetism of 304 non-standard screw ribbons has become a long-standing and difficult problem. After delivering 304 non-standard screws to customers, some customers sometimes take direct measures to test them, using a magnet to attract them. Even though they are 304 non-standard screws, they have magnetism like iron screws. Non standard screw customization inspection method: The inspection method for standard fasteners is specified in the technical specifications of the product. And professional standards have been established for the testing methods of fasteners (size and geometric accuracy). Customers often call to inquire:; Why do 304 non-standard screws have magnetism? Is there a quality issue? Is there a problem with the original data; Here, we will also give a simple and difficult science popularization on the common problem of screws in the industry.
The original information of non-standard screws can be found in Baidu Baike. Its important components are: 1. Carbon C can increase hardness and strength, and excessive content can reduce its ductility and corrosion resistance. 2. Chromium Cr can increase corrosion resistance and oxidation resistance, refine the grain size, increase strength, hardness and wear resistance. 3. Nickel Ni can increase high temperature strength and corrosion resistance, and improve the rate of cold work hardening. 4. Molybdenum Mo increases strength and has excellent corrosion resistance to oxides and seawater. 5. Copper Cu is conducive to cold work forming, and its magnetic properties are reduced. 6. Mn is only used for the magnetic properties of landing materials. Non standard screw customization inspection method: The inspection method for standard fasteners is specified in the technical specifications of the product. And professional standards have been established for the testing methods of fasteners (size and geometric accuracy). Non standard screws are divided into three main parts: size, mechanical properties, and surface defects. The specific inspection items for each section have different regulations based on different products. 316 has the same carbon content as 304, and the other elements are also similar. However, 316 has 20-30% more molybdenum, resulting in a 20-30% decrease in absolute iron content, making it less magnetic. 304 does not have molybdenum, but has 30% more absolute iron content, making it more magnetic. 304, 316, and 201 are all austenitic stainless steels. Austenite is non-magnetic, so it does not actually carry magnetism. In fact, stainless steel with various materials sometimes exhibits weak magnetism due to the fact that 100% austenite is not obtained after solid solution treatment, and there is often a small amount of ferrite in the metallographic structure. In addition, during cold heading, when the deformation rate of the material is relatively high, local austenite will undergo martensitic transformation. Both ferrite and martensite have magnetic structures, resulting in weak magnetism in these three types of stainless steel.
Using a magnet to test the original data of non-standard screws will reveal that they were originally non-magnetic, but after being cooled by a screw machine and tested with the same magnet, the screws will have weak magnetism. So, non-standard screw ribbon magnets are not really a quality issue, nor are they a failure of the original data, but rather due to the peculiar characteristics of the non-standard screw original data during the cold processing process. After cold processing, the magnetic strength of the material is 316<304HC<201. However, if it needs to be completely non-magnetic, demagnetization treatment may be performed. There are companies that specialize in demagnetizing screws.
