Magnetic permeability of electrical steel,free hindi comedy films to watch,first aid kits for pets red cross,electronic pulse arc cigarette lighter 12v - PDF Books

You must have JavaScript enabled in your browser to utilize the functionality of this website. Ferromagnetic Materials Materials that are strongly attracted to a magnet (either permanent or electro) and that can themselves form permanent magnets. Magnetic Permeability The ease by which a magnetic material can be magnetised is expressed by the Magnetic Permeability.
Curie Temperature Some metals have a temperature at which they change from ferromagnetic to non-magnetic.
All common carbon steels (including mild steel), low alloy steels and tool steels are ferromagnetic. Castings in austenitic stainless steels have slightly different compositions compared to their wrought counterparts. In the case of both welds and castings the small amount of ferrite results in a small amount of magnetic response, but it can be readily detected with a good hand-held magnet. Even although wrought austenitic stainless steels are non-magnetic in the annealed condition they may develop magnetic response when cold worked. This has a dramatic effect on tensile strength and even more so on yield strength; a heavily cold drawn grade 304 wire can achieve a tensile strength of up to around 2000MPa. Cold drawn 304 also has high tensile strength, but this is not due to the magnetic response – both the magnetic response and the high strength are due to the cold work. Magnetically soft steels are used in electrical applications involving changing electromagnetic induction. The magnetic response of a piece of steel is a quick and qualitative test that can be useful for sorting grades of stainless steel.

What Can Be Sorted Austenitic (both 300-Series and 200-series) stainless steels from other steels. Tips & Traps Some austenitic stainless steel grades, particularly 304, are to some degree attracted to a magnet when cold worked, eg by bending, forming, drawing or rolling. Austenitic stainless steel castings and welds are also usually slightly magnetic due to a deliberate inclusion of a small percentage of ferrite in the austenitic deposit. The response of a stainless steels to a magnet is an interesting physical property and can be a useful sorting test but it is not as clear-cut as is often thought. Hard magnetic materials retain a large amount of residual magnetism after exposure to a magnetic field.
Austenitic stainless steels, both the common 300-series (Cr-Ni) and the lower nickel 200-series (Cr-Mn-Ni) are non-magnetic. Note that different heats of steels of the same grade may exhibit different magnetic responses because of minor differences in the amounts of each element. Cold drawn 304 (and to a lesser degree 316) is attracted to a magnet, but this has no effect on the corrosion resistance. Applications where absence of magnetic response may be required include MRI equipment and in naval mine-hunter vessels. Solenoids and relays are typical examples, and where these components also need to have corrosion resistance a ferritic stainless steel can be a good choice. All other steels are attracted to a magnet, including all the ferritic, duplex, martensitic and precipitation hardening stainless steels. Stress relieving at cherry-red heat will remove this response due to cold work, but this stress relief may sensitise the steel and should not be performed on an item which is later to be used in a corrosive environment.

The % ferrite can be measured by the amount of magnetic response, and special instruments are available for this. Soft magnetic materials can be magnetised by a relatively small magnetic field and when this is removed they revert to low residual magnetism. It is common for wrought austenitic stainless steels to contain a very small amount of ferrite, but this is not sufficient to significantly affect magnetic performance except in very critical applications. Some of the most highly corrosion resistant stainless steels are strongly magnetic… examples are the duplex and super duplex grades and highly alloyed ferritic grades such as 29-4C. Specialist guaranteed low magnetic response stainless steels can be sourced for such applications.
For critical applications specialist ferritic bar grades are available (subject to mill enquiry) with guaranteed magnetic properties. Even although the duplex grades are mixtures of austenite and ferrite they are still strongly attracted to a magnet.
A weld can be viewed as a small, long casting, and for the same reason as detailed above austenitic welds have about 4 – 8% ferrite.

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