QusAns

GENERAL METALLURGY


Q.1. Define metal ?
Ans. Metal is that material, which possesses lusture, strength, high hardness, high ductility and high thermal and electrical conductivities.
Ex : copper, iron, nickel, aluminum etc.

Q.2. Define non-metal ?
Ans. Non metal is that material, which has low value of lustre, strength, hardness and conductivity.
Ex : carbon, sulphur, phosphorus, glass etc.

Q.3. What is metalloid ?
Ans. Metalloid possesses the characteristics of both metals and non metals, such as antimony and arsenic.

Q.4. Define Ores ?
Ans. Ores are metal bearing minerals from which that metal can be extracted economically.

Q.5. Why sulphide ores are first roasted ?
Ans. In general direct reduction of sulphide ores of metal are not possible. Thus, these are first roasted before smelting to get in its oxide form.

Q.6. What do we mean by term mechanical metallurgy ?
Ans. This is the branch of metallurgy deals with the response of metals to loads. Thus we get knowledge of strength of materials and other mechanical properties of materials from this subject.

Q.7. What are the main uses of metals and alloys ?
Ans. In almost all fields, metals and alloys are used. Our daily useful items like window, lock, utensil, stoves, bus, car, engine, aeroplanes, buildings any structure cannot be imagined, without the use of metals or alloys. Atomic plants utilities U, Th, Zr, electric industry utilities Zr, Si. Mechanical working tools utilities carbides of Mo, W and special steels and many metal and alloys are used for different specific purposes.

Q.8. What are the vacuum treated metals ?
Ans. Vacuum treated metals are clean and pure metals. These are free from any contamination of other metals blowhole, porosity, dirt, inclusion etc. This metal provides sufficient strength and requires specific property of that metal.

Q.9. What do you mean by drying operation ?
Ans. Drying means removal of moisture or water from any material. Generally solid materials are dried by heating so that water present in it, is evaporated.

Q.10. How do we accomplish drying of gases ?
Ans. If we required drying of gases or air, it may be performed by passing it, over suitable drying agents, such as calcium carbide, silicagel, or sulphuric acid. These substances absorbed water.


STEEL MAKING



Q.1. What is steel ?
Ans. Steel consist of iron and carbon with little amount of sulphur, phosphorus, silicon, manganese. Different alloying elements such as molybdenum, vanadium, chromium, cobalt, silicon, tungsten etc may be further added to achieve specific properties in steel.

Q.2. What is the principle of cementation process ?
Ans. It is the method of steel making in which wrought iron is carburized in solid state by heating it, in contact of carbonaceous materials.

Q.3. What do you mean by after blow period in Bessemer process ?
Ans. The first blow continues for about ten minutes as ordinary blow period of acid Bessemer process, to oxidise the impurities C, So and Mn. This also called fore-blow and then flame drops. Then the second stage of blow starts which is called after blow to remove phosphorus and sulphur of pig iron. This blow generally continue for five minutes.

Q.4. What are the refractory materials used for the lining for acid and basic Bessemer process ?
Ans. The pear shaped steel vessel of acid Bessemer converter is lined with highly acid refractory materials such as gainster or silica bricks. But in basic converter the lining is of tarted dolomite and magnesia bricks.

Q.5. What do you mean by fettling of a furnace ?
Ans. It is the operation adopted before charging the furnace. After tapping any heat furnace hearth, walls, banks etc are inspected and it is patched with suitable refractory material, wherever it has been eroded. Generally it is thrown manually with the help of shovel.

Q.6. What is the special features of LD steel making ?
Ans. Steel with low C, S, P gas contents N2 can be made by this process.
Carbon content can be reduced to 0.04%, nitrogen 0.003%, phosphorus 0.012 to 0.017% even few alloy steels including stainless steel can be made by this process.

Q.7. What is the JFN in LD steel making process ?
Ans. The jet force number indicates the depth of penetration of a jet in a bath. Which is

JFN = oxygen pressure × nozzle throat dia / height of nozzle.

Q.8. What are the difference between acid and basic electric furnace ?
Ans. In acid arc furnace sulphur and phosphorus cannot be reduced but it is possible in basic electric arc furnace. The raw material taken for acid furnace should contain very low in sulphur and phosphorus.

Q.9. What is the double slag process ?
Ans. In double slag process, refining is done first under oxidising condition and after that reducing condition. Thus this process has advantage of both. In oxidising condition C, Si, Mn, P are brought to desire level and then this slag is removed. After that reducing slag is made to remove sulphur from molten bath.

Q.10. What is the molecular theory of the slag ?
Ans. This is the slags which are composed entirely of neutral molecules such as various oxides, silicates, phosphate etc. It is also assumed that even complex molecules dissociate in to its simpler molecules. As example : CaO. SiO2 = CaO + SiO2.

Q.11. What is the effect of Mn/S ratio in steel making ?
Ans. Mn improves hot workability by preventing the formation of low melting iron sulfide (FeS). Steels with a Mn/S ratio of at least 8/1 do not exhibit hot shortness. Manganese sulphide (MnS), which forms preferentially to FeS, has a high melting point and appears as discrete and randomly distributed globules. Although solid at hot working temperatures, the MnS inclusions are soft enough to deform into elongated stringers during rolling or forging. Their presence may be harmful or beneficial, depending on the product form and its application. MnS is necessary in any steel that must be machined since it is an effective chip breaker. Also since MnS counters the brittleness from S, it is beneficial to the surface finish of C steel.
The shape and orientation of MnS inclusions after hot working, along with that of other nonmetallic inclusions, gives the steel a characteristic texture (anisotropic microstructure). The elongated MnS inclusions are having different effective area when loaded along different axes. This results in anisotropy of monotonic properties as reflected in directional ductility and impact properties. Where these properties are not critical, MnS is essentially harmless.

Q.12. What is the calcium treatment (Ca) in steel making processes ?
Ans. The addition of Ca is made for Al killed steels in order to decrease the volume fraction of oxide and sulphide inclusions through deoxidation and desulphurization and to control the composition, morphology, and distribution of those remaining inclusions. A major advantage of this practice is that nozzle clogging during the continuous casting of liquid steel is eliminated since solid Al2O3 inclusions are transformed to liquid calcium aluminates which do not clog the nozzle.
Ca has two beneficial effects. The first is that reduces the total number of inclusions remaining in the steel  (S, for example, can be brought down to 0.001 % – 0.003 % with a little extra care and down to 0.007 % in routine practice) and the second is that it modifies the shape of the remaining inclusions into one that is less detrimental to mechanical properties in the final product. Thus, Ca breaks up inter dendritic Al2O3 galaxies into fine Type III inclusions. These minute particles will remain in the steel through solidification but, unlike the original galaxies, have no tendency to clog continuous caster nozzles.

Q.13. What is MU-Metal ?
Ans. Mu-metal is a nickeliron soft ferromagnetic alloy with very high permeability, which is used for shielding sensitive electronic equipment against static or low-frequency magnetic fields. It has several compositions. One such composition is approximately 77% nickel, 16% iron, 5% copper, and 2% chromium or molybdenum.
Mu-metal typically has relative permeability values of 80,000–100,000 compared to several thousand for ordinary steel. It is a "soft" ferromagnetic material. 
It has low magnetic anisotropy and magnetostriction, giving it a low coercivity so that it saturates at low magnetic fields. This gives it low hysteresis losses when used in AC magnetic circuits. Other high-permeability nickel–iron alloys such as permalloy have similar magnetic properties; mu-metal's advantage is that it is more ductile, malleable and workable, allowing it to be easily formed into the thin sheets needed for magnetic shields.

Q.14. What is Hot shortness in steel ?
Ans. Hot shortness is a tendency for some alloys to separate along grain boundaries when stressed or deformed at temperatures near the melting point. In metallurgy, it is brittleness, usually of steel or wrought iron, when the metal is hot, due to high sulfur content. The term is used for the character of steel, which becomes brittle at hot working temperatures above 0.6 Tm (recrystallization temperature, where strain hardening is removed). Hot shortness hinders hot-working operations.

Q.15. What is Cold shortness in steel ?
Ans. Cold shortness occurs when a material is lowered to a temperature where it becomes brittle. A material can be ductile at one temperature and very hard and breakable at another if it is affected by cold shortness. Not all materials are affected by cold shortness. For materials that are affected by cold shortness, the temperature at which brittleness occurs varies from material to material.




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