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Carbon steels usually contain less than 1,2% carbon and small quantities of manganese, copper, silicon,
sulfur, and phosphorus Alloy steels are carbon steel with other metals added specifically to improve
the properties of the steel significantly. Stainless steel are considered a separate group.
The principle elements that are used in producing alloy steel include nickel, chromium,
molydenenum, manganese, silicon and vanadium. Cobalt, copper and lead are
also used as alloying elements.
Elements may encourage formation of graphite from the carbide. Only a small
proportion of these elements can be added to the steel before graphite forms destroying
of the steel, unless elements are added to counteract the effect. Elements which encourage the formation
of graphite include silicon, cobalt, aluminium and nickel
Relative effect alloying elements
The combined effect of alloying elements results from many complex interactions resulting
from the processing history, the number and quantities of constituents, the heat treament, the section
shape etc etc.. Some basic rules can be identified.
Notes on alloying elements
Range 0-2%..This increases resistance to oxidation and scaling, aids nitriding and restricts grain
Enhances air hardenability and reduces scaling.
In tool steels allows use at high temperatures without softening.
Range 0,2% to 0,5%... Improves corrosion resistance and yield strength of low alloy steels.
Range 0 to 0,25% improves machinability in non-alloy low carbon steels. Reduces strength and ductility.
Range 0,3% to 1,5% alway present in steels to reduces the negative effects of
impurities carried out forward from the production process e.g sulphur embrittlement.
Range 0,3% to 5%. Stabilises carbides and promotes grain refinement and increases high
temperature strength, creep resistance and hardenability. Useful in cutting
tool materials. In nickel-chromium steels reduces temper embrittlement.
Range 0,2% to 5% Improves strength, toughness, and hardenability without seriously
affecting the ductility. Encourages grain refinement
Can graphitise carbide resulting in softening.
Range 0-0,05% Residual element from production process (Casting). Results in weakness
in the steel. Kept below 0,05%. Can improve machinability and in larger quantities improves
fluidity in cast steels.
Range 0,2% to 3%. Used mainly in production of cast iron causing
graphitisation and is not used in large proportions in high carbon steels.
Up to 0,3% improves fluidity of casting steels without the weakening effect of phosphorus
Up to 1% improves the heat resistance of steels.
At 3% improves strength and hardenability. Acts as a de-oxidiser.
Range up to 0,5% Residual impurity from production process. Weakens steel
and additional process are used to remove sulphur. Neutralised by the presence of manganese.
Sometimes added to low carbon steels to improve machinability with the accepted
penalty of reduced
strength. Reduces ductility and weldability.
Strong carbide forming element. In range 0,2% to 0,75% it is used in maraging steels
to make them age hardening with resulting high strength. Stabilises austenic stainless steel.
Forms hard stable carbides and promotes grain refining with great hardness at high
temperatures. The main alloying element in high speed tool steels.
Constituent in permanent magnet steels.
Carbide forming element and deoxidiser used together with nickel and or chromium to increase
strength Improves hardenability and grain refinement and combines with carbon
forming wear resistant structure. Is used as a deoxidiser in casting steels to
reducing blowholes and increasing hardness and strength. Vanadium is used with
in high speed steel based on pearlitic chromium. "Improves fatigue properties of hardened
Stainless steels are steels with a high degree of corrosion resistance and chemical resistance to most a wide range
of aggressive chemicals. The corrosion resistance is mainly due to their high chromium content.
Stainless steels normally have more than 12% chromium. Chromium makes the surface
passive by forming a surface oxide film which protects the underlying metal from corrosion. In
order to produce this film the stainless steel surface must be in contact with oxidising agents.
Stainless steels are classified as Austenitic, Martensitic or
These are usually alloy containing three main elements Iron Chromium and Nickel (6% to 22%).
These steels cannot be hardened by heat treatment. They retain an austenitic structure
at room temperature and are ductile and have good corrosion resistance compared
to ferritic stainless steel. They are at risk of intergranular corrosion unless heat
treated to modify their chemical composition.
This steel normally contains 11% to 30% chromium with a carbon content below 0,12%. Other alloying elements
are added to improve its corrosion resistance or other characteristics such as machinability.
Because of the low carbon content ferritic stainless steels are not normally considered heat treatable. However there
is some hardness improvement resulting from quenching from high temperatures. The carbon
and nitrogen content of these steels must be maintained at low levels for weldability , ductility and corrosion
These steels contain 12% to 17% chromium with 0,1 to 1% Carbon. They can be hardened by
heat treatment in the same way as plain carbon steels. Very high hardness values can be
obtained for carbon levels approximately 1% using correct heat treatment. Small amounts of other
alloying elements may be included to improve corrosion, resistance, strength and toughness.
Maraging steels are a class of high-strength steel with a low carbon content and the use
of substitutional (as opposed to interstitial) elements to produce hardening from formation
of nickel martensites. The name maraging has resulted from the combination of mar(tensite) + age (hardening)
High Strength Low Alloy Steels (HSLA)
High strength low alloy (HSLA) steels are a group of low carbon steels that utilise
small amounts of alloying elements to attain yield strengths in excess of 550 MPa in
the as-rolled or normalised conditions. These steels have better mechanical
properties than as rolled carbon steels, largely by virtue of grain refining and precipitation
hardening. Because the higher strength of HSLA steels can be obtained at
lower carbon levels, the weldability of many HSLA steels is at least comparable to
that of mild steel. Due to their superior mechanical properties, they allow
more efficient designs with improved performance, reductions in manufacturing costs
and component weight reduction to be produced. Applications include oil and gas
pipelines, automotive sub-frames, offshore structures and shipbuilding.
BS EN ISO 4957:2000...Tool steels
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Last Updated 06/04/2012