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What is Alloying of Steel and Properties ?


Steel is among the most popular materials used in the construction industry.Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties.Alloy steels are broken down into two groups: low alloy steels and high alloy steels. The difference between the two is disputed. Smith and Hashemi define the difference at 4.0%, while Degarmo, et al., define it at 8.0%. Most commonly, the phrase "alloy steel" refers to low-alloy steels.

The following list identifies the known effects of adding certain elements, in known quantities to steel:
Aluminum (Al):- Aluminum is an active deoxidizer used in producing steel. It is used to control inherent grain size.

Boron (B):- The addition of boron improves hardenability.

Carbon (C):- An increase in the carbon content of steel alloys usually produces higher ultimate strength and hardness; however, this lowers ductility and toughness. Carbon increases air-hardening tendencies and weld hardness.

Chromium (Cr):- Chromium increases steel's response to heat treatment. It also increases depth of hardness penetration. Most chromium-bearing alloys contain 0.50-1.50% chromium. Stainless steels contain chromium in large quantities, 12-25%, frequently in combination with nickel, and possess increased resistance to oxidation and corrosion.

Columbium (Nb):- Columbium in 18-8 stainless steel has an effect similar to titanium in making the steel immune to harmful carbide precipitation and the resultant intergranular corrosion.

Copper (Cu):- Copper normally is added in amounts of 0.15-0.25% to improve resistance to atmospheric corrosion and increase tensile and yield strength with only a slight loss in ductility. Higher-strength properties can be obtained by precipitation hardening copper-bearing steel. Iron (Fe). Iron contains other elements in varying quantities that produce the required mechanical properties. Iron lacks strength, but it is very ductile and soft, although it does not respond very well to heat treatment to an appreciable degree.
Lead (Pb) :- Lead in steel greatly improves its machinability. When the lead is finely divided and uniformly distributed, it has no known effect on the mechanical properties of the steel in the strength levels most commonly specified. It is usually added in amounts of 0.15-0.35%.

Manganese (Mn):- Next in importance to carbon is manganese. It normally is present in all steel and Eunctions both as a deoxidizer and to impart strength and responsiveness to heat treatment. Manganese usually is present in quantities from 0.5 to 2'30, but certain special steels are made in the range of 10-1 5%.

Molybdenum (Mo) :- Molybdenum adds to the penetration of hardness and increases toughness. Molybdenum helps steel to resist softening at high temperatures and is an important means of assuring high creep strength. It generally is used in comparatively small quantities, ranging from 0.10 to 0.40%.

Nickel (Ni) :- Nickel increases strength and toughness but has 4%, although higher quantities are possible. Steels containing little effect on hardenability. It is added in quantities of 1 to nickel usually  have more impact resistance, especially at low temperatures. Certain stainless steels employ nickel up to about 20%.

Phosphorus (Ph) :- Phosphorus is present in all steel. It increases yield strength and reduces ductility at low temperatures. Phosphorus is believed to increase resistance to atmospheric corrosion.
Silicon (Si) :- Silicon is one of the common deoxidizers used in the manufacturing of steel. It also may be present in varying quantities up to 1% in finished steel and has a beneficial effect on certain properties, such as tensile strength. It is used in special steels in the range of 1.5 to 2.5% silicon to improve the hardenability. In higher percentages, silicon is added as an alloy to produce certain electrical characteristics in the socalled silicon electrical steels and finds certain applications in some tool steels, where it seems to have a hardening and toughening effect.

Sulfur (S) :- Sulfur is an important element in steel, because when present in relatively large quantities, it increases machinability. The amount generally used for this purpose is from 0.06 to 0.30%. Sulfur is detrimental to the hot forming properties.

Titanium (Ti) :- Titanium is added to 18-8 stainless steels to make them immune to harmful carbide precipitation. It sometimes is added to low-carbon sheets to make them more suitable for porcelain enameling.

Tungsten (W) :- Tungsten is used as an alloying element in tool steel and tends to produce a fine, dense grain, when used in relatively small quantities. In larger quantities of between 17 and 20% and in combination with other alloys, it produces a high-speed steel that retains its hardness at the high temperatures developed in high-speed cutting. It usually is used in combination with chrome or other alloying elements.

Vanadium (V) :-  Vanadium steels have a much finer grain structure than steels of a similar composition without vanadium, which gives additional strength and toughness.


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