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Valbruna Grade

MG4

Steel type

Ferritic Soft Magnetic Steel

Description of material

MAGIVAL® MG4 is a free machining ferritic stainless steel grade with the machinability and corrosion resistance as MG3, and offering a higher magnetic permeability and lower coercive force than MG1. Its higher Silicon content allows it to reduce the eddy currents losses in components working in AC, and its Molybdenum content allows applications in mild chloride corrosive environments. It is extensively used in the automotive industries and soft magnetic components. A carefully controlled chemical analysis as well as special metallurgical processes provide a ferritic structure that is very sensitive to magnetic fields. MG4 can be supplied (1) as annealing+ cold finished or (2) annealed+ cold finished + magnetic annealed + cold finished. See Soft Magnetic Steels brochure for more information about magnetic, mechanical and physical properties.

Applications

Typical applications of MG4 are solenoid valves, pole pieces, magnetic cores, electromagnetic pumps and devices, fuel injections components, electromagnetic switches and relays, antilock brake systems, sensors in automotive applications, actuators and fuel pumps.

Melting practices

Argon Oxygen Decarburization

Corrosion resistance

Even though the Molybdenum content is able to reduce or avoid pitting corrosion, it is important to know that, as with all free machining grades, Sulphur is added to improve machinability, and the formation of MnS inclusions could prime points of pitting if exposed to some corrosive environments. MG4 has a good resistance to mildly corrosive environments such as fresh water, crude oil, gasoline, alcohol, some beverages, mild chemical and atmospheres. It should be noted that this grade, as for every kind of stainless steel, surfaces should be free of contaminant and scale, heat tint, and passivated for optimum resistance to corrosion.

Machinability

MG4 has a good machinability typical of all Ferritic free machined grades but a little bit lower than MG1/MG2 due to its Molybdenum content. Productivity gain depends on types of machines, the kind of tools used and their geometry, cutting fluids and kind of machine operations on the pieces produced. It is important to point out that MG4 in the magnetic annealing condition, could have large grain size and very low hardness. This kind of structure influences the surface finish (roughness) and the chip morphology. Within certain limits, a little bit harder structure typical of annealing+ cold finishing ( as cold drawing ) offers advantages in some machine operations and better surface roughness but a vacuum or protective atmosphere annealing of machined parts should be done if an improvement of magnetic properties is required. This grade cannot be cold deformed or upset worked.

Weldability

MG4, as with other free machining grades with high Sulphur content, is not recommended for welding because the fused zone tends to form porosity. In any case, low heat inputs and a type 430+Mo filler metal should be used. Austenitic fillers in order to increase ductility of weld, don’t solve the problems in HAZ unless a PWHT is applied. It should be pointed out that the low magnetic permeability of the Austenitic structure of the fused zone dramatically modifies the magnetic flux causing a flux leakage generated by the high difference of magnetic permeability between the two structures. Autogenous high energy welding shouldn’t form any martensitic structure in fused zone thanks to the low content of Carbon, and Nitrogen of MG4.

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