Chemical Engineering - Materials and Construction - Discussion
Discussion Forum : Materials and Construction - Section 5 (Q.No. 39)
39.
Which of the following constituents of cast iron is mainly responsible for imparting it an anti-corrosive property ?
Discussion:
1 comments Page 1 of 1.
Bibhas said:
7 years ago
I think B is correct.
Though Chromium and Nickel serve the purpose mainly.
Silicon, 14Si28.0855:
Silicon increases strength and hardness but to a lesser extent than manganese. It is one of the principal deoxidizers used in the making of steels to improve soundness, i.e. to be free from defects, decays or damages. Silicon is present in all steels to a certain extent. Its content can be up to 4% for electric sheets that are widely used in alternating current magnetic circuits.
In welding, silicon is detrimental to surface quality, especially in the low carbon, resulphurized grades. It aggravates cracking tendencies when the carbon content is fairly high. For the best welding condition, silicon content should not exceed 0.10%. However, amounts up to 0.30% are not as serious as high sulphur or phosphorus content.
For galvanizing purposes, steels containing more than 0.04% silicon can greatly affect the thickness and appearance of the galvanized coating. This will result in thick coatings consisting mainly of zinc-iron alloys and the surface has a dark and dull finish. But it provides as much corrosion protection as a shiny galvanized coating where the outer layer is pure zinc.
Phosphorus, 15P30.973761:
Phosphorus increases strength and hardness, but at the expense of ductility and impact to toughness, especially in higher carbon steels that are quenched and tempered. As such its content in most steel is limited to a maximum of 0.05%. Phosphorus prevents the sticking of light-gage sheets when it is used as an alloy in steel. It strengthens low carbon steel to a degree, increases resistance to corrosion and improves machinability in free-cutting steels. In terms of welding, the phosphorus content of over 0.04% makes weld brittle and increases the tendency to crack. The surface tension of the molten weld metal is lowered, making it difficult to control.
Sulphur, 16S32.065:
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 sulphur is beneficial to machining. For welding, weldability decreases with increasing sulphur content. Sulphur is detrimental to surface quality in low carbon and low manganese steels and it promotes hot shortness in welding with the tendency increasing with increased sulphur.
Though Chromium and Nickel serve the purpose mainly.
Silicon, 14Si28.0855:
Silicon increases strength and hardness but to a lesser extent than manganese. It is one of the principal deoxidizers used in the making of steels to improve soundness, i.e. to be free from defects, decays or damages. Silicon is present in all steels to a certain extent. Its content can be up to 4% for electric sheets that are widely used in alternating current magnetic circuits.
In welding, silicon is detrimental to surface quality, especially in the low carbon, resulphurized grades. It aggravates cracking tendencies when the carbon content is fairly high. For the best welding condition, silicon content should not exceed 0.10%. However, amounts up to 0.30% are not as serious as high sulphur or phosphorus content.
For galvanizing purposes, steels containing more than 0.04% silicon can greatly affect the thickness and appearance of the galvanized coating. This will result in thick coatings consisting mainly of zinc-iron alloys and the surface has a dark and dull finish. But it provides as much corrosion protection as a shiny galvanized coating where the outer layer is pure zinc.
Phosphorus, 15P30.973761:
Phosphorus increases strength and hardness, but at the expense of ductility and impact to toughness, especially in higher carbon steels that are quenched and tempered. As such its content in most steel is limited to a maximum of 0.05%. Phosphorus prevents the sticking of light-gage sheets when it is used as an alloy in steel. It strengthens low carbon steel to a degree, increases resistance to corrosion and improves machinability in free-cutting steels. In terms of welding, the phosphorus content of over 0.04% makes weld brittle and increases the tendency to crack. The surface tension of the molten weld metal is lowered, making it difficult to control.
Sulphur, 16S32.065:
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 sulphur is beneficial to machining. For welding, weldability decreases with increasing sulphur content. Sulphur is detrimental to surface quality in low carbon and low manganese steels and it promotes hot shortness in welding with the tendency increasing with increased sulphur.
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