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Important Facts on
Stainless Steel
Chromium (Cr) Melting point 1857° C
Cr renders steels oil and air-hardenable. By reduction of the critical rate of
cooling necessary for martensite formation, it increases hardenability,
thus improving ist susceptibility to hardening and tempering. Notch toughness
is reduced however, but ductility suffers only very slightly. Weldability
decreases in pure Chromium Steels with increasing Cr content. The tensile
strength of the steel increases by 80-100 N/mm2 per 1% Cr. Cr is a
carbide former. Its carbides increase the edge-holding quality and wear
resistance. High temperature strength and high-pressure hydrogenation
properties are promoted by Chromium. Whilst increasing Cr contents
improve scaling resistance, a minimum content of about 13% chromium is
necessary for corrosion resistance of steels; this must be dissolved in the
matrix. The Element restricts the gamma phase and thus extends the ferrite
range. It does however stabilize the austenitic Cr-Mn and Cr-Ni steels.
Thermal and electrical conductivity are reduced. Thermal expansion is
reduced (alloys for glass sealing). With simultaneously increased carbon
content, Cr contents up to 3% increase remanence and coercive field
intensity.
Carbon (C) Melting point 3540° C
Carbon is the most important and influential alloying element in steel. In
addition to Carbon however, any unalloyed steel will contain silicon, manganese,
phosphorus and sulphur, which occur unintentionally during manufacture.
The addition of further alloying elements to achieve special effects
and intentional increase in the Manganese and Silicon contents result in
alloy steel. With increasing C content, the strength hardenability of steel
increase, but its ductility, forgeability, weldability and machinability (using
cutting machine tools) are reduced. Corrosion resistance to water, acids
and hot gases are practically unaffected by the carbon.
Copper (Cu) Melting point 1084° C
Copper is added to very few steel alloys, as it concentrates under the layer
of scale and through penetrating into the grain boundery, causes high
surface sensitivity in hot forming processes, for which reason it is regarded
as steel parasite. The yield point and the yield point/strength ratio are
increased. Contents above 0.30% can cause precipitation hardening. Hardenability
is improved. Weldability is not affected by copper. In alloy and
low alloy steels, Cu producers significant improvement in weathering resistance.
In acid resistant high alloy steels, a Cu content above 1% producers
improvement in resistance to hydrochloric acid and sulphuric acid.
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