wasi katalog zum download (14 mb)

Important Facts on
Stainless Steel
Sulphur (S) Melting point 118° C
Sulphur produces the most pronounced segretation of all steel accompanying
elements. Iron Sulphide, leads to red shortness or hot shortness, as the low
melting point Sulphide eutectics surround the grains in reticular fashion, so
that only slight cohesion of the latter occurs and during hot forming the grain
boundaries tend to break down. This is further increased by the action of oxygen.
As sulphur possesses a considerable affinity for manganese, it is combined
in the form of Mn sulphide, as this is the least dangerous of all existing
inclusions, being present distributed in point form in the steel. Toughness in
transverse direction is reduced significantly by S. S is added intentionally to
steels for automatic machining up to 0.4%, as the friction on the tool cutting
edge reduced by the lubricating action permits increased life between work
piece and tool. In addition, short chips occur when free-cutting steels are
machined. S increases susceptibility to welding cracks.
Silicon (Si) Melting point 1414° C
Si is contained in all steel in the same way as Manganese, as iron ores incorporate
a quantity of it according to their composition. In Steel production itself,
Silicon is absorbed into the melt from the refractory furnace linings.
But only those steels are called Silicon Steels which have an Si content of
>0.40%. Si is not a metal, but a metalloid as are also, for example, Phosphorus
and Sulphur. Si deoxidizes. It promotes Graphite precipitation and restricts
the Gamma phase significantly, increases strength and wear resistance (Si-Mn
heat treatable steels); significant increase in the elastic limit, thus useful alloying
element in spring steels. It significantly increases scale resistance, so that
heat resisting steels are alloyed with it. The possible content is limited however
on account of its impairing hot and cold formability. With 12% Si, acid
resistance is achieved to a large extent, but such grades can only be produced
as very hard, brittle steel castings which can be machined only by grinding.
On account of significant reduction of electrical conductivity, coercive
field intensity and low wattage loss, Si is used in steels for electrical quality
sheet.
Nitrogen (N) Melting point –210° C
This element can occur both as a steel parasite and as an alloying element.
Parasitic because of the reduction in toughness through precipitation processes,
causing susceptibility to ageing and blue brittleness (deformation in the
blue heat range of 300° C - 350° C) and on account of the possibility of initiation
of intercrystaline stress cracks in unalloyed and low alloy steels. As an
alloying element, N extends the gamma phase and stabilizes the austenitic
structure. In Austenitic Steels increases strength and above all the yield point
plus mechanical properties in the heat. As a result of Nitride formation during
nitriding, N permits high surface hardness to be achieved (= nitriding).
12
607