1. Phosphorous. The quantity of phosphorous present in pig iron varies from 0.1 to 2.0%. It combines with iron to form Fe3P which embrittles cast iron. Phosphorous is introduced into iron from phosphate in the ore. Phosphates get reduced in the reducing atmosphere in the blast furnace and phosphorous is formed. This phosphorous combines with iron to form Fe3P. Some of the phosphorous may get oxidized too into P2O5. This oxidation of phosphorous to P2O5 is an exothermic reaction and takes place at lower temperature
, if formed, is removed by the slag which is basic in character. In this way the quantity of phosphorous in iron is reduced. Its amount is kept as low as possible.
Phosphorous when present in pig iron increases the fluidity of molten iron and thus makes the filling of the moulds in a better way. However, wrought iron made from phosphatic iron is brittle when cold.
2. Sulphur. The quantity of sulphur present in ores varies from 0.4% to 1.0%. Presense of manganese in iron lowers the percentage of sulphur by combining with sulphur in iron and forming MnS. MnS formed thus combines with CaO and is removed. In this way the percentage of sulphur in iron is reduced. The reaction of sulphur with manganese is as follows:
FeS + Mn → Fe + MnS
MnS + CaO → MnO + CaS (Slag)
MnO + C → Mn + CO
It may be noted that FeS has a low melting point and it forms between the grains that make up the alloy. Iron sulphide being very brittle, whole alloy becomes brittle.
Presense of sulphur tends to make iron hard and produces unsound castings. Wrought iron and steel produced from iron containing sulpher makes wrought iron and steel to be brittle when heated.
3. Silicon. Percentage of silicon present in pig iron varies from 1.0 to 4.0%. Source of silicon in iron is from its presence in any of the raw materials. At low temperatures some silicon is oxidized into silica and basic slag removes it. In this way there may occur some elimination of silicon from iron.
Silicon affects the hardness and strength of iron. Both these properties worsen by presence of silicon in iron. Presence of silicon in steel increases its electrical resistance. Silicon when present in steel promotes the decomposition of cementite to form graphite.
4. Manganese. The quantity of manganese varies from 0.2 to 1.5%. The source of this impurity in iron is from the ore. Manganese dioxide in ore is reduced at higher temperature as the reduction reaction is endothermic in nature. Manganese thus formed gets mixed up with iron. Some of the manganese is removed by acid slag.
Presence of manganese in iron reduces the sulphur content by forming MnS thereby improving the quality of alloy since MnS is not harmgul as harmful as FeS. Manganese increases the tensile strength of iron. Since Mn promotes combined carbon, it increases hardness of cast iron.
5. Carbon. The quantity of carbon in pig iron varies from 4 to 4.5%. Source of carbon in steel is coal. Carbon is present in pig iron either in free state as graphite or in combined state as iron carbide. Carbon in pig iron increases its hardness. Due to presence of impurities in pig iron, pig iron is too brittle and possesses very little strength and ductility. So most of pig iron is converted into steel.
Pig iron is the direct metallic product from the blast furnace without any change in it while cast iron is prepared from pig iron with or without refining or alloying treatments, or it may be prepared from mixtures of pig iron with steel or scrap or alloying agents.
, if formed, is removed by the slag which is basic in character. In this way the quantity of phosphorous in iron is reduced. Its amount is kept as low as possible.
Phosphorous when present in pig iron increases the fluidity of molten iron and thus makes the filling of the moulds in a better way. However, wrought iron made from phosphatic iron is brittle when cold.
2. Sulphur. The quantity of sulphur present in ores varies from 0.4% to 1.0%. Presense of manganese in iron lowers the percentage of sulphur by combining with sulphur in iron and forming MnS. MnS formed thus combines with CaO and is removed. In this way the percentage of sulphur in iron is reduced. The reaction of sulphur with manganese is as follows:
FeS + Mn → Fe + MnS
MnS + CaO → MnO + CaS (Slag)
MnO + C → Mn + CO
It may be noted that FeS has a low melting point and it forms between the grains that make up the alloy. Iron sulphide being very brittle, whole alloy becomes brittle.
Presense of sulphur tends to make iron hard and produces unsound castings. Wrought iron and steel produced from iron containing sulpher makes wrought iron and steel to be brittle when heated.
3. Silicon. Percentage of silicon present in pig iron varies from 1.0 to 4.0%. Source of silicon in iron is from its presence in any of the raw materials. At low temperatures some silicon is oxidized into silica and basic slag removes it. In this way there may occur some elimination of silicon from iron.
Silicon affects the hardness and strength of iron. Both these properties worsen by presence of silicon in iron. Presence of silicon in steel increases its electrical resistance. Silicon when present in steel promotes the decomposition of cementite to form graphite.
4. Manganese. The quantity of manganese varies from 0.2 to 1.5%. The source of this impurity in iron is from the ore. Manganese dioxide in ore is reduced at higher temperature as the reduction reaction is endothermic in nature. Manganese thus formed gets mixed up with iron. Some of the manganese is removed by acid slag.
Presence of manganese in iron reduces the sulphur content by forming MnS thereby improving the quality of alloy since MnS is not harmgul as harmful as FeS. Manganese increases the tensile strength of iron. Since Mn promotes combined carbon, it increases hardness of cast iron.
5. Carbon. The quantity of carbon in pig iron varies from 4 to 4.5%. Source of carbon in steel is coal. Carbon is present in pig iron either in free state as graphite or in combined state as iron carbide. Carbon in pig iron increases its hardness. Due to presence of impurities in pig iron, pig iron is too brittle and possesses very little strength and ductility. So most of pig iron is converted into steel.
Pig iron is the direct metallic product from the blast furnace without any change in it while cast iron is prepared from pig iron with or without refining or alloying treatments, or it may be prepared from mixtures of pig iron with steel or scrap or alloying agents.
6 comments:
this is good for some information
Nice post, things explained in details. Thank You.
Concept of impurity in pig iron well explained
Really helpful...tq..keep posting
Can we produce pig iron with 5 silicon and nil ir traces carbon
Profiling and controlling impurities level and their side pharmaceutical effects is crucial in both drug development and manufacturing process as they may affect the efficacy and safety of APIs, Impurities
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