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Correct choice is (c) Argon

Best explanation: In the METHOD of recirculation degassing, argon GAS is USED which is bubbled through the porous holes located at the bottom side of ladle. The speed of degassing will increases with the INCREASE in rate of circulating the liquid METAL through the vacuum region. And the circulating speed is increased by the increase in flow rate of argon gas.

The correct choice is (a) True

Explanation: During solidification of molten casting in mould cavity, EXCESS of nitrogen is extracted from the melt which can cause blow holes and EMBRITTLEMENT of heat affected zone of casting component. So, it is very necessary to REMOVE nitrogen from the melt to produce castings of desired QUALITY and DEFECTS free.

Correct choice is (a) True

The best I can explain: It is always aimed to have higher steel YIELD in steel industries through attributes of EQUIPMENT and TECHNOLOGIES used in steel making. The steepest DECREASE in the amount of scraps is mainly ACHIEVED by the application of continuous casting method which has highest casting or steel yield.

Right answer is (b) False

Explanation: Solubility of hydrogen in the melt is generally low at ambient temperature. Hydrogen in MOLTEN casting damages or weakens the MECHANICAL PROPERTIES which ALSO results in occurrence of porosity and losing of tensile ductility in the casting parts. Thus, removal of excess hydrogen is very NECESSARY during solidification of the molten casting.

The correct answer is (a) DUPLEX stainless steels

The best I can EXPLAIN: Duplex stainless steels contain APPROXIMATELY 25 % of CHROMIUM while rest of the stainless steels contain less than that of duplex stainless steels. All the stainless steel materials contain chromium and carbon besides other elements. In production of stainless steels, controlling of carbon and chromium content should be proper.

Right answer is (b) False

To elaborate: Obsolete scrap GENERALLY contains iron and steel parts which are rejected due to end of their service life. It is often mixed with other metals like copper, zinc and TIN to FORM other steel alloys. And home scrap is KNOWN as the scrap which is relatively pure and chemical composition is known.

Right option is (a) True

The explanation is: The argon oxygen DECARBURIZATION (AOD) process is mainly CARRIED out in a converter type of vessel which is generally LINED up with magnesite bricks. Then a combination of argon and oxygen is filled by the application of tuyeres located on the SIDE of the converter vessel. Then the MELT of steel is charged into the vessel for further processing.

The CORRECT answer is (B) False

For explanation I would say: In steel making, dust is produced in the electric furnace during melting of steel. The produced dust is carried away in the off-gases which basically contains iron and some non-ferrous materials like ZINC and lead. So not only ENVIRONMENTAL considerations but also for the economic considerations, the dusts are collected and recovery of valuable materials is done.

The correct choice is (a) True

Explanation: The reduction in TEMPERATURE changes the composition of equilibrium STEEL and hence mass TRANSFER coefficient changes dynamically. The effect of temperature change is generally neglected during the vacuum degassing process, but the temperature change is analyzed so that the OPERATION does not finish at the low temperatures.

The correct CHOICE is (C) Carbon ferrochrome

The EXPLANATION: Decarburization technology uses high carbon ferrochrome to decarburize the molten steel at lower temperatures. If carbon oxidizes first with RESPECT to chromium at low temperatures, then the reduction in pressure from atmosphere to a lower VALUE will be required. Reduction in pressure is mostly done by vacuum oxygen decarburization (VOD) method.

Right OPTION is (b) False

Explanation: In the manufacturing of stainless steel, both chromium and carbon can be oxidized due to decarburization of MOLTEN casting. Carbon oxidation in COMPARING with chromium oxidation may occur at TEMPERATURE above 1220 ⁰C in the pure state conditions. But EXPERIMENTALLY, carbon oxidation can occur at temperature above 1800 ⁰C than that of chromium.

Correct CHOICE is (a) True

The best I can EXPLAIN: Temperature of melt DECREASES during the vacuum treatment of molten metal. This is BASICALLY caused by EXPOSING of more surface area to the vacuum chamber. To maintain the heat from the molten metal additional heating of the metal is usually done to compensate for the loss of heat.

Right option is (a) True

For explanation I would say: The energy required for steel making in the electric VESSEL is MAINLY for the MELTING down of scrap material. Preheating of scrap material can reduce the energy requirement which further reduces the time in making of steel that can directly increase the OVERALL productivity. Other advantages include decrease in electrode consumption and the refractory wear.

The correct option is (b) False

To explain: The viscosity influences the efficiency of vacuum degassing; a high viscosity is considered to have negative influence on the reaction rate. The viscosity is generally not considered in the kinetics; instead, a constraint is used that limits the viscosity to be below 0.5 Pas. The melt should have low viscosity which also REDUCES the TIME involved in the PROCEDURE.

The CORRECT CHOICE is (b) False

Explanation: The effectiveness of vacuum treatment is always increased by the increase in surface area of the molten metal exposed to vacuum. The increased surface area of the molten metal exposed to the vacuum; for EXAMPLE, in the form of a thin gas induced stirs which can accelerate the degassing operation. And the degassing time should be kept MINIMUM as MUCH as possible.

Correct CHOICE is (d) R = 7.42*10^3*Q^1/3*d^1/3*{ln(P1/P2)}

Best explanation: The circulation rate (R) in recirculation DEGASSING is given by-

R = 7.42*10^3*Q^1/3*d^1/3*{ln(P1/P2)} , where R is the circulation rate in Kg/sec, Q is the injection rate of argon gas, P1 is the PRESSURE at the base, P2 is the pressure in the vacuum chamber and D is the internal diameter.

The CORRECT answer is (B) False

For explanation: During production of casting products, gases such as oxygen, hydrogen and nitrogen GET dissolved in the casting. The term degassing is EMPLOYED for the removal of these gases from the casting melt. Dissolved oxygen from molten casting cannot be extract as molecular oxygen, REMOVING of oxygen from melt is called as de-oxidation.

The correct choice is (b) False

To explain: In general, magnesium alloy component tends to have coarse grain structure UNLESS some suitable procedures are taken to insure the formation of fine grains. The procedure INVOLVES superheating of molten metal to 2500 or 3000 ⁰C. And then after holding it there for a certain period of time, it cools down to the desired temperature and POURING operation takes place without any DELAY.

The correct option is (a) True

The BEST explanation: It is not possible to remove copper from steel scraps by the METHOD of conventional refining. It can be removed by TREATING steel scraps with sulphide fluxes and also by treating it at reduced pressure of the gas phase which BASICALLY includes vapourization of copper from the steel scraps.

Correct ANSWER is (C) Copper

To explain I would say: Magnesium metal in itself is not one of the STRONGEST metals and is HENCE adulterated with other materials to form strong ALLOYS. Among the following, aluminium, zinc and manganese are highly used in making magnesium alloys.

The correct answer is (b) False

The best I can explain: Most of the refractory oxides like zirconia and alumina react with molten titanium to generate a layer which is ENRICHED in oxygen or inter-metallic compounds of titanium. The oxide mixes in molten titanium which gives rise to a contaminated layer that can be considered as precipitate as a SEPARATE phase on COOLING.

Correct answer is (B) 650°C

Explanation: The temperature at which the PURE form of MAGNESIUM gets ignited by itself is 473°C, and the temperature at which magnesium in its PUREST form is found to melt is 650°C.

Right option is (d) 700°C

The best I can explain: During the mixture getting processed, first the magnesium is melted, and then zinc METAL is added. Aluminum is MIXED in it through STIRRING. While this is happening, it has to be ensured, that the COMPLETE alloying PROCESS takes place at 700°C.

Right answer is (b) WHITE

Easiest explanation: The purest FORM of magnesium is CONSIDERED to be in its weakest form, and HENCE other elements are added in it to enhance its quality. The physical qualities too change on addition of other elements. Originally, the color of pure magnesium metal is SILVERY white.

The correct answer is (b) False

To explain I would say: At ZERO level TEMPERATURE of copper ALLOY castings, no any kind of embrittlement occurs; in FACT, the tensile STRENGTH of copper castings enhances at low temperature. Therefore, the copper castings can be used at very low temperatures without any significant changes to the properties of the castings.

The correct OPTION is (c) Sodium

Explanation: Copper ORIGINALLY does not possess a very high amount of strength. For properties of copper to be USED, but with more strength, this copper needs to be mixed with certain material, which will provide it the required strength. Cadmium, silver and aluminium oxide are few of those MATERIALS which will aid in INCREASING its strength.

Correct OPTION is (a) True

To elaborate: Titanium has good PROPERTIES LIKE strength, low-thermal EXPANSION with low modulus with respect to its low-high cycle of fatigue strength, corrosion resistance, and weld-ability. Titanium is the only material that includes this combination of properties over a temperature RANGE starting from the surrounding temperature to approx 550 ⁰C.

Correct option is (a) True

The best I can explain: Copper MAY resists the oxidation, but it is HIGHLY reactive with sulphur and its chemical compounds, it produces copper SULPHIDE during the reaction which can be unpleasant for the CASTING components. The main copper contaminants significantly are PHOSPHOROUS and iron besides oxygen.

Right option is (B) False

To explain: Titanium has the ability to un-react with any coating or MATERIAL, so thereby it shows a high degree of resistance against the attacks of CHLORIDES and mineral ACIDS. Pure titanium is a nontoxic material, so its ALLOYS and it can be compatible with human tissues and bones biologically without any significant effects to the human body.

Correct choice is (b) False

For explanation: TITANIUM castings generally have beta structure which is combined with EXCELLENT creep RESISTANCE, fatigue crack resistance and tensile properties. But the titanium castings exhibits very low fatigue strength DUE to the presence of porosities in the castings. These porosities can be treated by isostatic pressing to IMPROVE properties of the titanium castings.

Correct option is (a) True

For EXPLANATION: The metal copper has its occurrence in LARGE QUANTITIES. This material can be successfully EXTRACTED from the mines before the iron is extracted, the reason being, copper extraction happens at lower temperatures.

Right answer is (a) True

Easiest explanation: When moulding materials like silica, moisture and BINDERS make contact with magnesium, the reaction takes place which arise problems in the CASTINGS of magnesium alloys. To AVOID reaction, the mould is MODIFIED by using some techniques like drying and by including INHIBITORS in the moulding materials.

Right answer is (a) 490 MPa

Easy EXPLANATION: 759 mega pascals is the TENSILE strength of QUENCHED and tempered copper-aluminium ALLOY. 676 MPa is the tensile strength of cold worked zinc. 324 MPa is the tensile strength of annealed zinc and 490 MPa is the tensile strength of cast manganese bronze.

Correct option is (a) True

For explanation I would SAY: Many problems arise in process of melting and casting of titanium due to its great chemical reactivity with mould material and its great affinity for surrounding gases. To avoid such problems, graphite or INVESTMENT moulding is preferred which are also difficult but possible to PRODUCE equipment in aero engine and biomedical applications.

Correct option is (a) True

The explanation: REFRACTORINESS is a property at which a refractory material deforms under its own load. The refractoriness is generally INDICATED by Pyrometric cone equivalent (PCE). It should ALWAYS be GREATER than the application temperatures. Refractoriness is decreased when the refractory material is continuously under loading conditions.

The correct ANSWER is (a) THERMOCOUPLE

The explanation is: The flux is first melted inside a crucible and then a thermocouple is inserted into the molten flux. After the COOLING process of molten flux, the temperature VARIATIONS are recorded with respect to time. The melting nature, the variation in viscosity and the melting RANGE of the molten flux with temperature is recorded.

Right answer is (a) True

Easy explanation: MAGNESIUM cannot be used extensively for precision casting APPLICATIONS because it is highly reactive with silica containing constituents like plaster or other mould materials. Silica is mostly present in slurry in which it acts like binding MATERIAL. Reaction of magnesium with silica produces magnesium oxide and magnesium silicide which may imparts defects in the casting components.

The correct answer is (d) Cupola FURNACE melting

The EXPLANATION is: Various melting methods are used for melting of titanium metal. For EXAMPLE, INDUCTION, vacuum arc and electron beam melting, in which vacuum arc and electron beam melting methods are widely used, though efforts are made continuously for producing other different methods to gain BETTER control on melting and to have better utilization of scrap materials. And cupola furnace is basically used for melting iron alloys.

Correct answer is (b) False

Explanation: No any SPECIAL protective treatments are REQUIRED for copper alloys against CORROSION, as they have capability to protect themselves from corrosion. For the SEA water applications, copper alloys are used which have high resistance to corrosion and CHLORIDE which is present in sea water in an abundant amount.

The CORRECT CHOICE is (b) False

For explanation I would say: Copper is a non-polymorphous MATERIAL with face centered cubic (FCC) structure. The FCC structure is the only reason for ductility in the copper material. Pure copper is generally reddish in color, and addition of zinc produces the yellow color of the copper and nickel produces the SILVER color of the same.

Right option is (b) 760°C

Explanation: When it COMES to casting of MAGNESIUM alloys, the casting temperatures have to be kept in real control, that is, if the temperatures go too high, the metal might catch FIRE. The TEMPERATURE range for casting magnesium alloys is 720°C to 800°C.

Correct choice is (a) True

The best I can EXPLAIN: Refractories are inorganic nonmetallic materials which can RESIST very high TEMPERATURE without any physical or chemical variations. It is essential to generate a certain range of refractory materials with different FEATURES to be resistant to thermal shock, be chemically inert and to POSSESS good thermal conductivity.