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Gold is for the mistress - silver for the maid
Copper for the craftsman cunning in his trade.
"Good!" said the Baron, sitting in his hall
But iron - cold iron is the master of them all.
Rudyard Kipling

Steel Alloys

Steel Additives

C
Carbon
The addition of up to 1.8% carbon turns iron into steel. Over this precentage yields cast or pig iron.
The eutectoid of plain carbon steel is .77% carbon. This means that at this carbon content all the carbon goes into solution and so does all the iron. So there is no free iron or carbon. Above the eutectoid(hypereutectoid) some of the carbon is pushed out of solution while below the eutectoid(hypoeutectoid) some of the iron is pushed out of solution.
Maximum hardness can be achieved at .65% carbon. More than this helps to improve abrasion resistance but does not increase hardness appreciably. Further more any more carbon than is absolutely required for hardness will make the steel more brittle. Below .65% hardening becomes increasingly more difficult without resorting to fast quenches.
The above comments relate to plain carbon steels only as the addition of other constituents can change the arrest points and eutectoid.
Cr
Chromium
Chromium raises the arrest points. It improves wear resistance and hardness. It forms carbides with any available carbon and is used in bearings and races. Above 12% it yields what is generally considered to be stainless steel.
Co
Cobalt
Cobalt makes a steel red hard so is suitable for use in machine tooling and will keep an edge at high cutting temperatures.
Cu
Copper
Copper delivers a higher yield strength in austenitic alloys and improves resistance to corrosion.
Fe
Iron
Its the primary constituent of any steel and combines with carbon to form carbides. Chemically pure iron is a practical impossibility. A plain carbon steel will also have some manganese, phosphorus, silicon and sulphur in it. Pure iron will have a melting point higher than steel or cast iron. Arrest points are 1537C, 1403C, 906C, and 768C.
Mn
Manganese
Manganese is found in all steels. It scavanges sulfer to form manganese sulfide. It lowers the arrest points and the eutectoid. Quenching speed is slower and quench penetration is improved. So it can be used to improve the hardenability of medium to low carbon steels. It combines with carbon to form carbides.
Mo
Molybdenum
Molybdenum raises the arrest points. "Molly be damned" as it was called in the movie, improves impact resistance, tensile strength and the elastic limit. It combines with carbon to form carbides.
Ni
Nickle
Nickle lowers the arrest points and improves the tensile strength, toughness and elastic limit.
Ps
Phosphorus
Phosphorus is found in trace amounts in all steel but should be minimised as it reduces impact resistance considerably at normal temperatures, in other words it is "cold short" and tends to crack. It is considered to be an impurity.
Si
Silicon
Silicon is found in all steels and raises the arrest points.
S
Sulfer
Sulfer is pretty much a no no in knifemaking especially with the forgers. If the alloy also has a high enough manganese content the sulfer combines with it to form manganese sulphide(MnS). Sulfer without sufficient manganese combines with iron to form iron sulfide(FeS). Sulfer improves the machinability of steel and reduces impact resistance at forging temperatures, so therefore it is said to be "hot short" and has a tendancy to crack.
V
Vanadium
Vanadium steels are resistant to alternating mechanical stress. It reduces grain growth and refines the structure of the alloy. Such steels have a high tensile strength and elastic limit while at the same time retaining a measure of ductility. It combines with carbon to form carbides.
W
Tungsten
Tungsten or wolfram raises the arrest points. It produces a dense fine matrix. In tandem with iron it combines with carbon to produce a double carbide. The alloy is red hard so tools made from it will stay sharp even when hot due to cutting friction in machine tooling. It forms carbides in combination with carbon.

Steel Scrap

Steel Type

These charts are subject to change.