Useful information concerning the steel alloy elements

Carbon (C):

Carbon is the foremost alloy element of steel and it has the farthest reaching influence on it. In addition to carbon every unload steel contains silicon, manganese, phosphorous and sulphur which are introduced unintentionally during the manufacture. The addition of further alloy elements to produce specific, desired effects and the intentional increase of the contents of manganese and silicon gives rise to alloy steel. As the carbon content rises, the mechanical strength and the hardening properties of the steel improve, but its elasticity, forging, welding, and cutting properties suffer. The carbon content has substantially no influence at all on the corrosion resistance to water, acids and hot gases.

Cobalt (Co) Melting Point 1492 °C:

Cobalt doesn’t form carbide. It hinders the grain growth at higher temperatures and greatly improves the resistance to tempering and the hot tensile strength; it is therefore, often an alloy element of high speed steel, hot work steels, and heat resisting raw materials. It acts favorably on the graphitic formation, and greatly increases residual magnetism, coercive force, and thermal conductivity, therefore the alloy basis for high grade permanent magnet steels and alloys. If subjected to neutron rays it forms a strong radio-active isotope Cobalt 60 for which reason it is undesirable in steels for atom reactors.

Chromium (Cr) Melting Point 1920 °C:

Chromium increases the hardness and strength and only minimally reduces the elasticity. It improves the resistance to heat and non scaling properties. With higher Chrome content the steels become corrosion resistant and with Carbon form a high wear resisting Carbide. The welding properties deteriorate in pure Chromium steels with increasing Chromium content. Chromium is a strong Carbide former. The tensile strength of the steel rises by 8----10 Kg/mm² per 1% Chromium. The yield point is likewise increased, however not at the same rate, but the notch impact value is lowered.

Manganese (Mn) Melting Point 1244 °C:

Manganese improves the strength properties of steel, while only slightly impairing its elasticity: furthermore, manganese has a favorable influence on the forging and welding properties. Higher contents of manganese in the presence of carbon increase the wear resistance very substantially. With up to 3% Mn the tensile strength of the steels is increased by about 10 Kg/mm²  for every percent of Mn with Mn contents above 3 to 8% the increase rises more slowly and at more than 8% of Mn it drops off again. The yield point behaves in a similar manner. Manganese increases substantially the depth of hardening.

Molybdenum (Mo) Melting Point 2610 °C:

Molybdenum improves the tensile strength and especially the heat resistance and also a favorable influence on the welding properties. Steel with a higher Mo content tends to be difficult to forge. Molybdenum is frequently used in conjunction with chromium. The behavior of Molybdenum resembles that of Tungsten. When used in alloy steels in combination with Chromium and Nickel, Molybdenum may produce high yield point and tensile strength values. Molybdenum has a strong tendency to form Carbide and is the alloy element of choice in high speed and hot working steels; in austenitic corrosion- resistant steels, case hardening and heat-treating steels as well as in heat resistant steels, also in view of the diminution to over-drawing brittleness.

Nickel (Ni) Melting Point 1453 °C:

Nickel raises the strength of steel less than does Silicon or Manganese with elasticity dropping only insignificantly. Ni ensures good through hardening, especially so when the steel contains also Chromium. Chrome nickel steels are stainless and resistant to scaling and also heat resistant. Nickel doesn’t impair the welding properties. Nickel increases the notch impact value of structural steels considerably, especially at low temperatures. In the sphere of steel alloying Nickel is especially suitable for use in austenitic steels, steels resistant to corrosion and scaling and in casehardening and heat treating steels to improve their toughness.

Phosphorus (P) Melting Point 44 °C:

There are various kinds of Phosphorus, viz. white (yellow0, red (purple), Black Phosphorus and others. Quite generally, Phosphorus is considered to be detrimental to steel so that it is endeavored to keep the P content in high grade steels at a maximum level of 0.03 to 0.05%.

Sulphur (S) Melting Point 118 °C:

Sulphur produces “red shortness”, makes steel brittle and is therefore harmful-Contents of 0.025% or 0.030% are permitted. Exceptions are the free-machining steels to which is added up to 0.30% so that the small distributed Sulphide inclusions disturb the metallic cohesion and therefore contribute to the formation of short turnings.   

Silicon (Si) Melting Point 1410 °C:

Like Manganese, Silicon is present in all steels since the iron ores used in their manufacture contain a varying amount of it. Further Silicon stemming from the refractory lining of the furnace is introduced into the melt during the manufacturing of steel. The term “Silicon steels” however, includes only steels having Silicon content above 0.40%. Si is not a metal but rather a so-called metalloid like, for example, Phosphorus and Sulphur. Silicon increases the mechanical strength, the resistance to scaling and the density; especially of cast steel. The elasticity is only insignificantly affected; while the tensile strength is increased by about 10 Kg/mm²  for each percent of Si and the yield point is raised to a similar degree. Steel having a higher content of Silicon turns coarsely granular. A high Silicon content (about 14%) enables steel to resist chemical attacks but it can no longer be forged.