Non-magnetic stainless steel is a special stainless steel material that has the characteristic of very weak magnetization in a magnetic field, that is, the so-called "non-magnetic" phenomenon. The magnetic permeability μ value of this material is slightly greater than 1, so in motor engineering, non-magnetic steel is mainly used as a generator guard ring material.

The room temperature structure of non-magnetic stainless steel is required to be stable austenite, because austenite has a face-centered cubic structure, is paramagnetic, and has a very low magnetic permeability. By appropriately adding alloying elements to expand the austenite region in the Fe-C alloy phase diagram and heat treatment methods, a stable single-phase austenite structure can be obtained at room temperature, thereby keeping the magnetic permeability of the steel material at a low level.

Non-magnetic stainless steel has important applications in some microwave devices. The eddy current loss generated by it under a pulsed magnetic field is smaller than that of copper or other metals. This is because the electrical conductivity of non-magnetic stainless steel is less than that of copper.

According to the composition of steel, non-magnetic steel can be divided into high Ni steel, high Mn steel, high Cr-Ni steel, high Cr-Mn-N steel, etc.; according to the performance, non-magnetic steel can be divided into austenitic non-magnetic stainless steel and non-magnetic structural steel. Austenitic non-magnetic stainless steel must add sufficient amounts of Ni and Mn to ensure austenite stability. At the same time, to ensure stainless performance, the mass fraction of Cr in the steel should be at least greater than 13%.

Non-magnetic steel is widely used in many fields such as electricity, rail transportation, construction, and national defense and military industry. For example, in the power industry, non-magnetic steel can be used in the design of generator guard rings to reduce magnetic leakage at the end of the rotor; in the construction industry, magnetic shelters are made of non-magnetic steel to avoid the influence of magnetic fields; in the field of national defense and military industry, non-magnetic steel is used to manufacture the hull of minesweepers and non-magnetic engines, structural materials for concealed submarines, etc.

In addition, non-magnetic stainless steel is also used in daily life, such as containers used in microwave ovens, which are safe heating options because they do not cause sparks or fires. However, it should be noted that not all stainless steels are non-magnetic. For example, martensitic stainless steel is magnetic and can be attracted by magnets.