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Effect of chemical elements in steel

Effect of chemical elements in steel
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                                                                   Effect of chemical elements in steel
 
Carbon 

Carbon is the most important element in steel, it is essential in steels which have to be hardened by quenching and the degree of carbon controls the hardness and strength of the material, as well as response to heat treatment (hardenability).
And ductility, forgeability and machinability will decrease if the amount of carbon increases, as well as weldability properties of the steel.

Silicon

Silicon is one of the principal deoxidizers for steel. Silicon helps to remove bubbles of oxygen from the molten steel. It is the element that is most commonly used to produce semi- and fully killed steels, and normally appears in amounts less than 0.40 percent, usually only small amounts (0.20%) are present in rolled steel when it is used as a deoxidizer. However, in steel castings, 0.35 to 1.00% is commonly present.
Silicon is the same as Manganese in the sense that all steel grades contains silicon and even though it is less than manganese, it still increases the strength and hardness. The strengthening factor is due to the silicon which dissolves in the iron.
It plays an important role as a deoxidizer in order to prevent defects and/or damages. In a case where silicon is mainly used as a deoxidizer for rolled steel the content will be kept to a small percentage. Electrical steels contain a high amount of silicon as the electrical conductivity is reduced by its presence.


 


Manganese (Mn)
Manganese is one of the elements found in many commercial steels with the primary purpose of increasing the hardenability and strength of the steel. The effect of manganese on the hardenability as well as on the strength of the steel is to a lesser degree than that of carbon. The increased hardenability is due to the cooling rate which is decreased by manganese during the hardening process. Apart from the effect on hardening and strength it also fulfils the role of a mild deoxidiser.
Combining it with sulphur, Manganese Sulphide  will form to increase the machinability of the steel, including the weldability and forgeability. Brittleness is prevented by this combination, which leads to a better surface finish of the steel.


 

Phosphorus (P)
The maximum amount of phosphorus in higher grade steel is between 0.03 to 0.05% due to the fact that is detrimental. Up to 0.10% of phosphorus in low-alloy high-strength steels will increase the strength as well as improve the steel's resistance against corrosion. The possibility of brittlement increases when the content in hardened steel is too high. Even though the strength and hardness is improved, the ductility and toughness decreases.
The machinability is improved in free-cutting steel, but weld brittle and/or weld cracks can occur during welding if the phosphorus content is more than 0.04%. Phosphorus also affects the thickness of the zinc layer when galvanizing steel.


 

Sulphur (S)
Sulfur is normally regarded as an impurity and has an adverse effect on impact properties when a steel is high in sulphur and low in manganese. Sulphur improves machinability but lowers transverse ductility and notched impact toughness and has little effects on the longitudinal mechanical properties. Its content is limited to 0.05% in steels but is added to free cutting steels in amount up to 0.35% with the manganese content increased to counter any detrimental effects since alloying additions of sulfur in amounts from 0.10% to 0.30% will tend to improve the machinability of a steel. Such types may be referred to as “resulfurized” or “free machining”. Free cutting steels have sulphur added to improve machinability, usually up to a maximum of 0.35%.
Even though the effect of sulphur on steel is negative at certain stages, any sulphur content less than 0.05% has a positive effect on steel grades.


 

Chromium (Cr)

The hardenability of steel is first and foremost increased by Chromium, the most powerful element. Corrosion resistance of steel as well as the yield strength in increased with higher percentage of chromium content. Only 1% is required to improve the newtons per square millimeter of the tensile strength with 8 - 100 N/mm2.

When the Cr content is more than 12% , it makes the steel has good high-temperature oxidation resistance and oxidation resistance of corrosion, also increase its hot strength. 

Cr is the main alloy element in stainless steel, acid-resistant steel and heat-resistant steel. 

When the Chromium content exceeds 15%, the strength and hardness will decrease, and the elongation and shrinkage of cross-section will be increased. 

Nickel ( Ni )

At the lower temperatures Nickel is used to increase the toughness of the steel. The weldability of the steel is not decreased by the presence of this element.  

The beneficial effects of nickel are: high strength, high toughness,  good hardenability, high resistance and high corrosion resistance.

When it is combined with Cr, W or Cr and Mo, the hardenability can be increased, Nickel-molybdenum steel also has a high fatigue limit.

Nickel steel is generally not easy to overheat, so it can prevent the growth of grain in high temperature, can still maintain fine grain structure.


Molybdenum( Mo)

Mo  has effects similar to manganese and vanadium, and is often used in combination with one or the other. 

It increases hardenability and elevated temperature strength and also improves corrosion resistance as well as increased creep strength.

It is added to stainless steels to improve their resistance to corrosion to organic acids, sulfuric acid erc. 

Vanadium (V)


Vanadium is mainly in the form of carbides in steel.

its main function is to refine the structure and grain of steel and reduce the strength and toughness of steel. 

Vanadium increase the tempering stability of hardened steel and produce secondary hardening effect. 

the amount of Vanadium in steel is no more than 0.5% except for high-speed tool steel.