Frequently asked top Mechanical Engineering Interview Questions and answers on Material Science (MS) and Heat Treatment (HT) for Freshers and 2-5 year Experienced Mechanical Engineers. For students, viva questions are also provided.
1) What do you mean by Smelting ?
Process of extraction of iron is called Smelting.
2) What do you understand by Specific Gravity and Tenacity ?
- Specific Gravity . It is the ratio of the mass of 1cubic cm. of a substance to the mass of the same capacity of water.
- Tenacity .It is the property of metal due to which a metal becomes strong enough to resist the pulling force.
3) Define the following metal properties (a) Machinability (b)Malleability
- (a) Machinability is the property of metal due to which a metal can easily be cut by cutting tools to obtain good surface finish. E.g.: Brass, Mild steel
- (b) Malleability is the property of the metal on account of which it can be extended in all directions by hammering or rolling. E.g.: Tin, Lead
4) Define Hardness of the metal ?
It is the property of the metal which makes a metal capable to resist surface penetration by other metals .Hard metals are High carbon steel and High speed steel.
5) What is the Toughness of metal ?
Toughness is the property of metal due to which without fracture a metal is able to withstand bending or torsion. Mild steel and wrought iron are tough metals.
6) Define the following properties of metal : (a) Fusibility (b) Stiffness (c) Ductility
- Fusibility. It is the property of metal due to which a metal becomes fluid when it is heated.
- Stiffness. It is the property of metal due to which a metal is capable of resisting deflection due to an externally applied load.
- Ductility. It is the property of metal due to which a metal can be drawn into the form of wires without rupture.
7) Why are cast iron seasoned before machining ?
For easy machining and saving the cutting edge of the tool.
8) How does carbon affects the properties of steel ?
If carbon content is higher the degree of hardness is more and the melting point is lower, If carbon percentage is lower it is easy to forging and forge welding.
9) Why are machine beds made of cast iron ?
Because it has more compressive strength and negligible shrinkage. It can easily cast into any integral shape, wear resisting and can absorb vibrations.
10) What is the difference between Wrought iron, Cast iron and Pig iron ?
Wrought iron contains less than 0.1% carbon and this is a product of puddling furnace. Cast iron is produced from cupola furnace. It contains 33.5% carbon in combined or free state. Pig iron is an iron carbon alloy contains 35% carbon along with impurities like manganese, sulphur and phosphorous. It is a product of blast furnace.
11) How is steel classified ?
According to carbon percentage
- Low carbon steel : Less than 0.25% carbon
- Medium carbon steel: 0.25%0.7% carbon
- High carbon steel: 0.7%1.5% carbon
According to percentage of alloying elements
- a. Low alloy steel: Alloying element less than 8%
- b. High alloy steel: Alloying element more than 8%
12) Why is the most of cutting tools made out in H.S.S ?
Because it resist the heat on the cutting edge of tool and it smoothly work in high speed.
13) What do you mean by Stainless Steel ?
It is an alloy steel which contains mainly 8% Nickel and 18% Chromium. Stainless steel main applications in measuring and surgical instruments.
14) Why are the delicate parts quenched in oil ?
To avoid cracks on the part.
15) What are the chemical composition of Gun metal, German silver and Duralumin ?
- Gun metal is an alloy of 88% copper, 10% tin and 2% zinc. It is generally used for casting boiler fittings, bearings ,bushes etc.
- German silver is an alloy of copper, nickel, tin and led. It is used for making utensils and resistances in electrical work.
- Duralumin is the aluminium alloy contains 3.54.5% copper,0.40.7% magnesium,0.40.7% manganese and remaining aluminium .Mainly used for making bars, tubes, rivets, sheets ,forgings and stampings.
16) Write the chemical composition and uses of the following: (1) Babbit metal (2) Bright steel (3) High speed steel
- Babbit metal is a tin base white metal which contains 88% tin, 8% antimony and 4% copper .This is mainly used as a bearing metal.
- Bright steel contains 0.05 to 0.45% carbon and up to 0.2%lead.It is used for making set screws, bolts, pins which withstand high loads at longer time.
- High speed steel is an alloy of 18% tungsten, 4% chromium,1% vanadium,4%cobalt and 0.7% carbon. This is generally used for making machine tools like lathe ,planer, shaper, taps , drills and milling cutters.
17) What are the differences between Brass and Bronze ?
- Brass is an alloy of copper and zinc. Generally brass contains 60% copper and 40% zinc. These are used for making bearings, pump fittings, bushes and utensils.
- Bronze contains copper and tin. It is comparatively hard, surface wear is less, can be remolded into any shape like wires, sheets, rods etc.
18) How will you identify cast iron, mild steel and high carbon steel ?
By spark: When a metal is held against grinding wheel it gives sparks. Cast iron gives thick and short sparks. Mild steel gives medium and dense sparks and High carbon steel gives long and dense sparks. By hammering : When a blow of hammer is given with these metals there will be a deep spot on mild steel, less deep spot on high carbon steel and cast iron may break.
19) What is Heat treatment ?
Heat treatment is an operation involving heating and cooling of metals to change its properties.
20) Why heat treatment of steel is necessary ?
- To improve machinability.
- To obtain desired properties.
- To increase resistance of corrosion.
- To change electrical and magnetic properties.
- To relieve the stresses after cold or hot working.
- To refine the grain size.
21) What is meant by lower and higher critical points ?
While heating a steel part, the temperature raises and it changes the structure of steel part .The temperature point at which the change starts is called lower critical point and the temperature at which the change ends is called higher critical point.
22) What are the common heat treatment processes used in industries ?
The following heat treatment processes are generally used in manufacturing :
- Case hardening
23) What do you mean by Carburising ?
Carburising is a case hardening process in which carunaceous materials such as leather scraps, charcoal dust, nut shells, bone powder etc. are packed with low carbon steel parts and heated together, thus dissolved carbon combines with the outer surfaces of the parts. After reheating the parts to above critical temperature it is suddenly cooled for making outer surface harder.
25) What is Case hardening ?
It is a process of making outer surfaces harder of the steel part. Generally it is done for the following purposes,
- To make outer surface harder.
- To bring the cost cheaper
- To utilize low carbon steel.
26) Describe the Annealing process ?
The process for softening the steel part is called Annealing. Generally it is done for the following purposes,
- To soften the steel for machining.
- To refine the grain size in the steel.
- To increase ductility in the steel.
- To relieve internal stresses.
- To change electrical and mechanical properties.
27) Define Normalising ?
Normalising is a process to make the steel part to its normal stage. The main purposes are
- To reduce grain size of steel.
- To achieve desired mechanical properties.
- To remove internal stresses caused by working.
28) What is Nitriding ?
It is the case hardening process in which work piece is heated in a steam of ammonia at 500 to 550 degree C.
29) Why is it not possible to harden unalloyed tool steel part right through its full thickness ?
Because it requires very high cooling rate which is only possible for its outer surface.
30) What are the advantages of flame hardening ?
- The work piece can be hardened on the required spot.
- Heat can be given to required portion of the work piece.
- Time can be saved.
31) Where is induction hardening applied ?
Induction hardening is done by using electricity. It is applied on wearing surface of crank shafts, cam shafts, axles etc.
32) Sometimes a thin brown and red oxide layer is formed on the surface of a copper part .How can it be removed ?
Pour few drops of hydrochloric acid on the copper part having oxide layer and wipe it with a cloth.
33) Differentiate between hardening and tempering ?
The main purpose of hardening is to resist wear and enable it to cut the other metals and reheating is not necessary. The main purpose of tempering is to reduce some of hardness and to increase the toughness. It consists of reheating after hardening to the temperature below the critical range.
34) What are the commonly found iron ores ?
Hematite, Magnetite, Limonite, Siderite and Iron pyrite are the main iron ores.
35) Differentiate between carbon steel and alloy steel ?
Carbon steel is the combination of iron and carbon. It is easily rusted and malleable. It can be easily machined and magnetic. Alloy steel is the combination of iron, carbon and other alloying elements. It is rust proof and harder and tougher. It is hard for machining and non magnetic.
36) Why is the soldering iron bit made of copper and not of steel ?
Because copper is good conductor of heat and quickly transfer its heat to the metal at the joint than the steel.
37) What do you mean by Brazing ?
Brazing is the process through which metal pieces are jointed by means of alloy of copper and zinc called spelter. The metal pieces to be joined should be heated instead of using a soldering iron bit. For this muffle as well as Smith’s furnaces are used. It provide much stronger joint as compared to soft soldering.
38) Why cast iron cannot be forged ?
Because it will break if heated and beaten by hammer.
39) What are the advantages of forging ?
- Metal can be forged to any shape.
- Metal can be forged in short time without wasting.
- The strength of steel as well as granular structure can be improved.
- The manufacturing cost is lesser than machining.
40) Which type of grains formed after hardening the steel ?
Hardened steel have contains fine grains.
41) Why is cast iron drilled dry ?
The cutting fluid is not necessary during cast iron drilling because the graphite in the casting reduces the friction and chips breaks easily .The mixture of cutting fluid and cutting chips may clog the drill in the hole may cause poor work finish.
42) What is immersion brazing ?
It is the process for brazing the articles in mass production.
43) What is the difference between White cast iron and Grey cast iron ?
- White cast iron : It contains 2.5 to 3% carbon in combined form. This is very hard and brittle and difficult to be machined. It is used for lower quality castings where hard coating is required.
- Grey cast iron : It contains 3.25 to 3.75% carbon in free state or graphite. It has better machinability .It is generally used to make machine beds and frames ,brackets, cylinders pipes etc.
44) What is High carbon steel ?
It contains 0.715 % carbon. HCS is harder ,stronger, less ductile and can be hardened and tempered. It is mainly used for making chisels, files, dies, drills ,taps etc.
45) What are the different alloying elements and their effects on the properties of the steel ?
- Cobalt: It gives excellent magnetic property and improves the cutting quality of the steel.
- Chromium: It gives greater hardness and resists corrosion and forging.
- Molybdenum: It gives greater hardness and resistance to drawing and forging.
- Nickel: It lifts the tensile strength, improves wearing property and protects from corrosion.
- Tungsten: It gives fine grain structure, greater hardness and cutting toughness.
- Vanadium: It gives cutting toughness resistance to wear and tear and greater hardness.
46) What is the difference between Metal and Alloy ?
- Metal: Metal is a substance which is manufactured after purifying the iron ores with limited properties. All metals are found in solid form except mercury.
- Alloy: It is the combination of two or more metals and has special properties depending upon the quality of alloying elements. Commonly found in solid form.
47) What is Soldering ?
It is a process of joining two or more metal pieces by using solder.
48) What do you mean by Mild steel ?
It contains 0.05 to 0.25% of carbon. M.S is ductile, malleable and easy for forging, welding. Mainly used to make sheets ,rods ,wires ,flats, round angles channels and other structural works.
49) What is the material of gears ?
The material of gears should be selected according to the capacity and nature of work. Gears are generally made of cast iron, bronze, tool steel, chromium steel , alloy steel etc.
50) Explain briefly the rates of contraction of different metals and alloys ?
Generally following rates of contraction are considered, Steel2%,Cast iron1%,Aluminium 1.8%,Brass 1.4%
51) Why is the head of a chisel not hardened ?
The chisel is not hardened all over. Its head is left soft as hardened head may damaged due to brittleness when resisting the hammer blow.
52) During forging what will happen if the metal is heated to:
(1) too low temperature (2) too high temperature
- When forging it is necessary to heat the metal to correct forging temperature. Heated in low temperature there is a risk for formation of cracks in the metal.
- If the metal is heated at too high temperature, the metal will loss its strength.
53) What is the function of hood in the forge ?
To collect gases through the fire and control the smoke and sparks.
54) Why new files should not be used on castings and forgings ?
Because they have hard outer surface, when new files are used on these over sides the teeth either break or get blunt easily.
55) For machining cast iron which rake angle is given on shaper tool ?
Negative rake angle
56) What is the material of shaper tool ?
Generally used HSS(High Speed Steel),sometimes satellite, carbide tipped tools may also be used.