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Important Facts on
Stainless Steel
Manganese (Mn) Melting point 1221° C
Mn deoxidizes. It compounds with sulphur to form Mn Sulphide, thus reducing
the undesireable effect of the Iron Sulphide. This is of particular importance
in free-cutting steel; it reduces the risk of red shortness. Mn very pronouncedly
reduces the critical cooling rate, thus increasing hardenibility. Yield
point and strength are increased by addition of Mn and, in addition, Mn
favourably affects forgeability and weldability and significantly increases hardness
penetration depth. Contents > 4% also lead with slow cooling to formation
of brittle martensitic structure, so that the alloying range is hardly used.
Steels with Mn contents > 12% are Austenitic if the C content is also high,
because Mn considerably extends the Gamma phase. Such steels are prone
to very high de-gree of strain hardening where the surface is subjected to
impact stress, whilst the core remains tough. For this reason, they are highly
resistant to wear under the influence of impact. Steels with Mn contents of
18% remain unmagnetizable even after relatively pronounced cold forming
and are used as special steels as well as steels remaining tough at subzero
temperatures which are subjected to low temperature stress. The coefficient
of thermal expansion increases as a result of Mn, whilst thermal and electrical
conductivity are reduced.
Molybdenum (Mo) Melting point 2622° C
Mo is usually alloyed together with other elements. Reducing the critical cooling
rate improves hardenabilty. Mo significantly reduces temper brittleness ,
for example in the case of CrNi and Mn steels, promotes fine grain formation
and also favourably affects weldability. Increase in yield point and strength.
With increased Mo content, forgeability is reduced. Pronounced carbide former;
cutting properties with high speed steel are improved thereby. It
belongs to the elements which increase corrosion resistance and is therefore
used frequently with high alloy Cr steels and with austenitic CrNi steels.
High Mo contents reduce susceptibility to pitting. Very severe restriction of
the Gamma phase. Increased high temperature strength, scaling resistance
is reduced.
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