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© Copyright: Aalco Metals Ltd, The Hersham Centre, Hersham Green, Hersham, Surrey KT12 4HP
Stainless Steel – Alloying Elements
Carbon (C): Iron is alloyed with carbon lo make steel
and has the effect of increasing the hardness and strength
of iron. Pure iron cannot be hardened or strengthened by
heat treatment but the addition of carbon enables a wide
range of hardness and strength. In Austenitic and Ferritic
stainless steels a high carbon content is undesirable,
especially for welding due to the threat of carbide
precipitation.
Manganese (Mn): Manganese is added to steel to
improve hot working properties and increase strength,
toughness and hardenability. Manganese, like nickel, is an
Austenite forming element and has been used as a
substitute for nickel in the AISI200 Series of Austenitic
Stainless Steels, e.g. AISI 202 as a substitute for AISI 304.
Chromium (Cr): Chromium is added to steel to
increase resistance to oxidation. This resistance increases
as more chromium is added. 'Stainless Steels have a
minimum of 10.5% Chromium (traditionally 11 or 12%).
This gives a very marked degree of general corrosion
resistance when compared to steels with a lower
percentage of Chromium. The corrosion resistance is
due to the formation of a self-repairing passive layer of
Chromium Oxide on the surface of the stainless steel.
Nickel (Ni): Nickel is added in large amounts, over
about 8%, to high Chromium stainless steels to form the
most important class of corrosion and heat resisting steels.
These are the Austenitic stainless steels, typified by 18-8
(304/1.4301), where the tendency of Nickel to form
Austenite is responsible for a great toughness (impact
strength) and high strength at both high and low
temperatures. Nickel also greatly improves resistance to
oxidation and corrosion.
Molybdenum (Mo): Molybdenum, when added to
chromium-nickel austenitic steels, improves resistance to
pitting and crevice corrosion especially in chlorides and
sulphur containing environments.
Nitrogen (N): Nitrogen has the effect of increasing the
Austenite stability of stainless steels and is, as in the case
of Nickel, an Austenite forming element. Yield strength is
greatly improved when nitrogen is added to stainless
steels as is resistance to pitting corrrosion.
Copper (Cu): Copper is normally present in stainless
steel as a residual element. However, it is added to a few
alloys to produce precipitation hardening properties or to
enhance corrosion resistance particularly in sea water
environments and sulphuric acid.
Titanium (Ti): Ttitanium is added for carbide
stabilization especially when the material is to be welded.
It combines with carbon to form titanium carbides, which
are quite stable and hard lo dissolve in steel, which tends
to minimise the occurrence of inter-granular corrosion.
Adding approximately 0.25 / 0.60% titanium causes the
carbon to combine with titanium in preference to
chromium, preventing a tie-up of corrosion-resisting
chromium as inter-granular carbides and the
accompanying loss of corrosion resistance at the grain
boundaries. However, the use of titanium has gradually
decreased over recent years due to the ability of
steelmakers to deliver stainless steels with very low carbon
contents that are readily weldable without stabilisation.
Phosphorus (P): Phosphorus is usually added with
sulphur, to improve machinability. The Phosphorus
present in Austenitic stainless steels increases strength.
However, it has a detrimental effect on corrosion
resistance and increases the tendency of the material to
crack during welding.
Sulphur (S): When added in small amounts Sulphur
improves machinability. However, like Phosphorous it has
a detrimental effect on corrosion resistance and
weldability.
Selenium (Se): Selenium was previously used as an
addition to improve machinability.
Niobium / Colombium (Nb): Niobium is added to
steel in order to stabilise carbon, and, as such, performs in
the same way as described for Titanium. Niobium also
has the effect of strengthening steels and alloys for high
temperature service.
SiIicon (Si): Silicon is used as a deoxidising (killing)
agent in the melting of steel and as a result most steels
contain a small percentage of Silicon.
Cobalt (Co): Cobalt becomes highly radioactive when
exposed to the intense radiation of nuclear reactors, and,
as a result, any stainless steel that is in nuclear service will
have a Cobalt restriction, usually approximately 0.2%
maximum. This problem is emphasized because there is
normally a residual Cobalt content in the Nickel used in
producing Austenitic stainless steels.
Calcium (Ca): Small additions are used to improve
machiniability, without the detrimental effects on other
properties caused by Sulphur, Phosphorus & Selenium.
abc® Aalco is a registered trademark of Aalco Metals Ltd
© Copyright: Aalco Metals Ltd, The Hersham Centre, Hersham Green, Hersham, Surrey KT12 4HP
Affect of Alloying Elements on Properties of Stainless Steel
Property C CR Ni S Mn Si P Cu Mo Se Ti
or
Nb
Corrosion Resistance - √ √ X - - √ - √ - -
Mechanical Properties √ √ - - √ √ √ √ √ - √
High Temperature
Resistance
- √ √ X - - - - √ - √
Machinability X X - √ - - √ - - √ -
Weldability X X - X √ - X - √ - √
Cold Workability X X √ X - - - √ - - -
Key
√ = Beneficial
X = Detrimental
This information is based on our present knowledge and is given in good faith. However, no liability
will be accepted by the Company is respect of any action taken by any third party in reliance thereon
As the products detailed may be used for a wide variety of purposes and as the Company has no control
over their use; the Company specifically excludes all conditions or warranties expressed or implied by
statute or otherwise as to dimensions, properties and/or fitness for any particular purpose. Any advice
given by the Company to any third party is given for that party’s assistance only and without liability on
the part of the Company.
Any contract between the Company and a customer will be subject to the Company’s Conditions of
Sale. The extent of the Company’s liabilities to any customer is clearly set out in those Conditions; a
copy of which is available on request.
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