Magnesium

Silvery white light metal with a high degree of oxygen affinity which immediately forms an invisible protective oxide layer in air and is thus very stable.

Symbol                                            Mg
Ordnungszahl                                 12
Atomgewicht                                   24,32
spezifisches Gewicht bei 20° C       1,74 g/cm3
Schmelzpunkt                                  650° C
Siedepunkt                                     1105° C
Schmelzwärme                                268 kJ/kg

 

Magnesium is primarily obtained by means of fused-salt electrolysis of magnesium chloride or water-free carnallite (potassium-magnesium chloride).

Magnesium in the steel
Magnesium is insoluble in solid iron; the solubility of iron in magnesium is 0.026% at 650°C. Although magnesium is a very efficient deoxidizer it is not used diretly as as a metal in steel manufacture as it causes an explosive reaction when added to the steel bath. Magnesium is added to heat-resistantnickel-chrome alloys for complete deoxidation and desulfurization. The deoxidation of these alloys with magnesium improves the mechanical properties and the hot forming; magnesium contents of 0.1% are already sufficient to bind the sulfur.

By injection of a mixture of magnesium and lime powder into the steel bath the sulfur content in the alkaline arc furnace could be reduced to 0.007%. Calcium-silicon-magnesium and ferro-silicon-magnesium have equally proven effective although these alloys should not contain more than 8% Mg in order to make adding to the steel bath easier.
In connection with calcium, silicone, and iron magnesium can be used for deoxidation of steel which improves the macro and micro structure of the steel blocks and thus leads to improved mechanical properties. Additions of magnesium or cerium alloys should refine the grain of non-corroding austenitic steels and improve their hot formability. Addition of magnesium-containing ferrosilicon together with cerium alloys also has a favorable influence.

Magnesium in the cast iron
Magnesium dissolved in the gray cast iron significantly promotes chill. However, this influence can be largely eliminated by means of inoculants. If the cast iron has a magnesium content of approximately 0.04% or more, this leads to the formation of nodular graphite.
Magnesium has a very high affinity to sulfur. The magnesium added first bonds with the sulfur to form magnesium sulfide which is released as slag at the bath surface. Therefore, the magnesium addition must be sufficient and take the quantity bonded by the sulfur into account. Magnesium can be added in form of a nickel-magnesium alloy containing up to 20% Mg. Alternatively, it is also possible to add magnesium-containing ferro-silicon, nickel-silicone-magnesium alloys or pure magnesium metal.

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