Mechanical-Engineering
The brown smoke during the operation of a Bessemer converter indicates that the —-? (RRB Kolkata Diesel JE 25.10.2009)
- air is burning out silicon and manganese
- silicon and manganese has burnt and carbon has started oxidising
- the converter must be tilted to remove the contents of the converter run at high speed
- the brown smoke does not occur during the operation of a bessemer converter
Explanation:
- The brown smoke during the operation of a Bessemer converter indicates that the air is burning out silicon and manganese.
In basic Bessemer, the furnace is lined with —-? (DMRC JE 20.04.2018)
- silica bricks
- a mixture of tar and burnt dolomite bricks
- Either (a) or (b)
- None of these
Explanation:
- Acidic Bessemer furnace is lined with silica bricks. Basic Bessemer furnace is lined with a mixture of tar and dolomite bricks. This process is applicable for making steel from pig iron containing more than 1.5% phosphorous.
In blast furnace ____ is used as fuel. (RRB Mumbai C&G JE 25.10.2009) (DMRC JE 2013)
- producer gas
- coal
- coke
- diesel
Explanation:
- In a blast furnace, coke is used as fuel. Fuel (coke), ores, and flux (limestone) are supplied through the top while hot air is blown through tuyeres.
For the product of LD converter is used —-? (RRB Malda SSE 25.10.2009)
- steel
- polythene
- graphite
- cast iron
Explanation:
- LD converter (Linz and Donawitz) is used for the production of steel. It is a refined version of the Bessemer converter where blowing of air is replaced with blowing oxygen.
Drills are usually made of —-? (DMRC JE 20.04.2018)
- Carbon steel
- High carbon steel
- High speed steel
- Carbides
Explanation:
- Drills are usually made of High Speed Steel (HSS) due to its application temperature over 600°C, high cutting speeds, high strength, good regrindability, and relatively low price.
First product of the blast furnace in the process of converting iron ore into useful metal by reduction is called —-? (Konkan Railway SSE 2015) RRB Chennai Section Engineer, 12.02.2012
- Cast iron
- Wrought iron
- Pig iron
- Steel
Explanation:
- Pig iron is the first product of the blast furnace. It is a crude form of iron containing 90-92% iron with carbon (1-5%), silicon (1-2%), manganese (1-2%), sulphur and phosphorous (1-2%).
Raw material for all iron and steel product is —-? (RRB Chandigarh SSE 25.10.2009) (RRB Mumbai C&G JE 25.10.2009)
- Cast iron
- Wrought iron
- Pig iron
- Steel
Explanation:
- Pig iron is the raw material for all iron and steel products. It is made by heating iron ore in a blast furnace.
Grey cast iron has —-? (RRB Allahabad JE 25.10.2009)
- brittleness
- low electrical conductivity
- low compressive strength
- All options are correct
Explanation:
- Grey cast iron has 3 to 3.5% carbon with carbon present as free graphite. It has low tensile strength, high compressive strength, low electrical conductivity, and no ductility.
Which one of the following is the ferrous materials? (RRB Bhubneshwar JE II 29.11.2008)
- Zinc
- Iron
- Silicon Carbide
- Copper
Explanation:
- Ferrous metals contain iron. Examples include steel, cast iron, and alloys of iron with chromium, nickel, manganese, molybdenum, and vanadium.
Alloys with Carbon content higher than 2.1% are known as —-? (DMRC JE 2013)
- high speed steel
- hypoeutectoid steel
- hypereutectoid steel
- cast iron
Explanation:
- Alloys with carbon content higher than 2.1% are cast iron. Hypo-eutectoid steel: 0-0.8% C, Hypereutectoid steel: 0.8-2.1% C, Hypo-eutectic cast iron: 2.1-4.3% C, Hyper-eutectic cast iron: 4.3-6.67% C.
German silver is an alloy of —-? (RRB Allahabad JE 19.12.2010)
- Silver and Tin
- Silver and Gold
- Nickel and Copper
- Nickel, Copper and Zinc
Explanation:
- German silver is an alloy of Copper (50%), Zinc (19%), and Nickel (30%).
In the structure of steel, globular form of Cementite is obtained through —-? (JMRC JE 10.06.2017)
- Normalizing
- Carbonizing
- Spheroidising
- Malleabilising
Explanation:
- Spheroidising of high carbon steel produces globular form of cementite. Spheroidite is the most ductile and machinable form of steel.
Which is the purest form of iron? (DMRC JE 22.09.2017)
- Cast iron
- Wrought iron
- Mild steel
- High Carbon Steel
Explanation:
- Wrought iron is the purest iron containing 99.5% to 99.9% iron with carbon content about 0.02%. It is tough, malleable, ductile, and can be easily forged or welded.
Pure iron is the structure of —-? (RRB Allahabad SSE 19.12.2010) (RRB Mumbai SSE 05.10.2008) (DMRC JE 2013)
- Ferrite
- Pearlite
- Austenite
- Cementite
Explanation:
- Ferrite (α-iron) is the pure form of iron with 0.006% carbon. It is soft, can be cold worked, strongly magnetic at room temperature, and has BCC structure.
Pure iron at room temperature has following micro structure —-? (Konkan Railway STA 2017)
- γ-iron
- δ-iron
- Cementite
- α-iron
Explanation:
- Pure iron at room temperature is α-iron (ferrite). Ferrite: 0.022% C below 725°C, Austenite: 2.14% C at 910-1410°C, Cementite: 6.67% C below 1175°C, Pearlite: 0.8% C at 723°C.
Which will be the product if iron ore goes through reduction and blast furnace treatment? (Konkan Railway SSE 2015)
- Pig iron
- White cast iron
- Wrought iron
- Ductile cast iron
Explanation:
- Pig iron is the crude form of iron obtained from blast furnace and is used as raw material for producing other ferrous materials. Cast iron is obtained by remelting pig iron with coke and limestone.
Steel having combination of 6.67% carbon and 93.33% iron is known as —-? (RRB Chandigarh SSE 25.10.2009)
- Cementite
- Pearlite
- Martensitic
- Austenitic
Explanation:
- Cementite has 6.67% carbon and 93.33% iron. It is the hardest structure on the Fe-C diagram, obtained below 1175°C.
When steel containing less than 0.85% carbon cooled slowly below the lower critical point, it contains —-? (RRB Gorakhpur RDSO SSE 25.10.2009)
- Ferrite mainly
- Pearlite mainly
- Ferrite and pearlite
- Pearlite and cementite
Explanation:
- When hypo-eutectoid steel (less than 0.85% C) is cooled slowly below the lower critical point (727°C), it contains pearlite and eutectoid ferrite.
Blast furnace is used to produce —-? (RRB Allahabad JE 25.10.2009)
- Pig iron
- Cast iron
- Wrought iron
- Steel
Explanation:
- Blast furnace is used to produce pig iron. Cupola furnace is used to produce cast iron.
% of carbon in cast iron is —-? (RRB Bhopal TM SSE 25.10.2009)
- < 0.8%
- < 1.3%
- >2%
- >6.3%
Explanation:
- Cast iron contains 1.7% to 4.5% carbon, i.e., >2% carbon. White cast iron: 1.75-2.3%, Spotted cast iron: 1.75%, Malleable cast iron: 2-2.5%.
Molybdenum high speed contains —-? DMRC JE 17.04.2018, 4:30-6:45pm
- 6% vanadium, 2% chromium and 4% tungsten
- 2% vanadium, 4% chromium and 6% tungsten
- 4% vanadium, 6% chromium and 2% tungsten
- 2% vanadium, 6% chromium and 4% tungsten
Explanation:
- Molybdenum high speed steel contains 6% Tungsten, 6% Molybdenum, 4% Chromium, and 2% Vanadium. It is mainly used for drilling and tapping tools.
Heating elements are generally made of —-? (RRB Kolkata SSE 09.09.2012)
- invar
- peminvar
- white metal
- nichrome
Explanation:
- Heating elements are generally made of Nichrome 80/20 (80% Nickel, 20% Chromium). It has relatively high resistance and forms an adherent layer of chromium oxide when heated.
How much percentage of chromium is present in high speed steel which is specified by designation 18-4-1? (RRB Chandigarh SSE 09.09.2012) (RRB Allahabad JE 09.09.2012)
- 4
- 18
- 1
- None of the above
Explanation:
- 18-4-1 high speed steel contains: Tungsten 18%, Chromium 4%, Vanadium 1%, Carbon 0.7%. It is used for making high speed cutting tools.
Presence of cobalt in steel improves its —-? (DMRC JE 22.09.2017)
- Cutting ability
- Corrosion resistance
- Tensile strength
- None
Explanation:
- Cobalt increases bonding strength in steel matrix and improves cutting ability. Cobalt steels are used where high frictional heats are developed, imparting red hardness.
Vanadium when added to steel —-? (JMRC JE 10.06.2017) (BMRCL JE 24 Feb.2019)
- Increases tensile strength
- Decreases tensile strength
- Raises critical temp
- Lowers critical temp
Explanation:
- Vanadium increases yield and tensile strength of steel. In combination with chromium, it makes steel extremely tough and strong, used for spring steels, high speed tool steel, and crankshafts.
High speed steel should have —-? (RRB Bhubneshwar JE-II 19.12.2010)
- only A (wear resistance)
- only B (hardness)
- only C (toughness)
- Both A and B
Explanation:
- High speed steel should have both wear resistance and hardness. It is used for cutting metals at much higher speeds than ordinary carbon tool steels.
Steel containing 11% to 14% chromium and 0.35% carbon is called —-? (RRB Allahabad SSE 19.12.2010)
- Martensitic stainless steel
- Ferritic stainless steel
- Austenitic stainless steel
- None of these
Explanation:
- Martensitic stainless steel contains 12-14% chromium and 0.12-0.35% carbon. It can be easily welded and machined and is magnetic in nature.
Steel containing 18% chromium and 8% nickel is called —-? (RRB Mumbai JE 05.10.2008)
- Martensitic stainless steel
- Ferritic stainless steel
- Austenitic stainless steel
- None of these
Explanation:
- Austenitic stainless steel (18/8 steel) contains 18% chromium and 8% nickel. It is non-magnetic in nature.
In grey cast iron, carbon is present in the form of —-? (DMRC JE 2013)
- Cementite
- Pearlite
- Flakes
- Spheroids
Explanation:
- In grey cast iron, most carbon is present as graphite flakes, making the material softer, more machinable, and less brittle than white cast iron. It has 3 to 3.5% carbon.
Which of the following when used in ordinary low carbon steels, makes the metal ductile and of good bending qualities? (RRB Mumbai SSE 05.10.2008)
- Sulphur
- Phosphorus
- Manganese
- Silicon
Explanation:
- Manganese serves as a valuable deoxidizing and purifying agent. When used in low carbon steel, it makes the metal ductile and of good bending qualities. Phosphorus raises yield point and improves atmospheric corrosion resistance.
Which of the following is correct for cast iron? (Konkan Railway SSE 2015)
- High compressive strength
- More ductile
- High tensile strength
- All of the above
Explanation:
- Cast iron is an alloy of iron and carbon (2-3.5% C). It is a brittle material with high compressive strength.
Stainless steel contains —-? (DMRC JE 2013)
- Chromium, iron, Nickel
- Chromium and Nickel
- Iron and Carbon
- Chromium, Nickel, Iron and Carbon
Explanation:
- Stainless steel contains Chromium, Nickel, Iron, and Carbon. It has excellent corrosion resistance due to its chromium content (10.5-20%).
Stainless steel resist corrosion due to —-? (DMRC JE 2013)
- Carbon
- Manganese
- Chromium
- Sulphur
Explanation:
- Stainless steel resists corrosion due to chromium content (10.5-20%).
Among the following metals, which metal has the least carbon content? (DMRC JE 2013)
- Pig iron
- Cast iron
- Wrought iron
- Medium carbon steel
Explanation:
- Carbon content: Wrought iron (0.02-0.03%), Carbon steel (0.05-2%), Malleable cast iron (2.2-3.6%), Grey cast iron (2.5-3.75%), Pig iron (4.3-6.67%).
Silicon is added in low carbon steels to increase property —-? (RRB Kolkata Diesel JE 25.10.2009)
- Hardness
- Brittleness
- Porosity
- Softness
Explanation:
- Silicon increases the strength and hardness of steel without lowering ductility. Silicon steels (1-2% Si, 0.1-0.4% C) have good magnetic permeability and high electric resistance.
Grey cast irons are often used at the base of heavy machines because of its high —-? (DMRC JE 2013)
- Stiffness
- Strength
- Toughness
- Damping capacity
Explanation:
- Grey cast iron is used at the base of heavy machines because of its high damping capacity. It has 3-3.5% carbon, low tensile strength, high compressive strength, and no ductility.
Cupola produces the following material —-? (RRB Mumbai JE 19.12.2010)
- Cast iron
- Pig iron
- Wrought iron
- White iron
Explanation:
- Cupola furnace is used to produce cast iron by converting pig iron.
Percentage of carbon in low carbon steel is —-? (RRB Mumbai SSE 19.12.2010)
- 0.05%
- 0.15%
- 0.30%
- 0.50%
Explanation:
- Low carbon or mild steel contains 0.15% to 0.45% carbon. Dead mild steel: upto 0.15%, Medium carbon steel: 0.45% to 0.8%, High carbon steel: 0.8% to 1.5%.
The hot forging of steel specimen is carried out at a temperature of —-? (DMRC JE 20.04.2018)
- 400°C
- 600°C
- 500°C
- 950°C
Explanation:
- Hot forging of steel is carried out at 950°C, above recrystallization temperature. It requires lower loads because flow stress is reduced at higher temperatures.
Manganese in steel increases its —-? (Konkan Railway STA 2017)
- Tensile strength
- Hardness
- Ductility
- Fluidity
Explanation:
- Manganese increases tensile strength by increasing hardenability. Phosphorus increases strength and hardness at the expense of ductility and toughness.
Which form of the iron is having existence between 910°C and 1403°C? (Konkan Railway TA 2017)
- α-iron
- γ-iron
- β-iron
- δ-iron
Explanation:
- α-iron: room temperature to 910°C (BCC, ferromagnetic), γ-iron: 910-1403°C (FCC), δ-iron: 1403-1539°C (BCC).
Which of the following best describes the strength of mild steel compared to alloy steel? RRB JE Stage 2 (22.04.2025 9:00 AM-11:00 AM)
- Alloy steel generally has higher strength than mild steel
- Mild steel is stronger in compression but weaker in tension than alloy steel
- Mild steel generally has higher strength than alloy steel
- Both mild steel and alloy steel have the same strength
Explanation:
- Alloy steel is manufactured by adding specific alloying elements like chromium, nickel, etc., which significantly enhances strength.
Which of the following is NOT a type of nitriding process? RRB JE (Re-Exam) 04.06.2025
- Vacuum nitriding
- Gas nitriding
- Liquid nitriding
- Plasma nitriding
Explanation:
- Vacuum nitriding is not a type of nitriding process. The types are Gas nitriding (uses ammonia), Liquid nitriding (molten salt bath), and Plasma nitriding (uses plasma).
Which cooling method is used in full annealing? RRB JE Stage 2 (22.04.2025 9:00 AM-11:00 AM)
- Air cooling
- Slow cooling inside a furnace
- Quenching in water
- Cooling in an oil bath
Explanation:
- Full annealing involves heating above upper critical point, holding, and then slow cooling inside the furnace to ensure uniform and gradual cooling for a soft and ductile state.
How long should a steel component be heat treated before nitriding? RRB JE 29-08-2019
- 5-20 hours
- 300-500 hours
- 21-100 hours
- 100-200 hours
Explanation:
- Nitriding is a surface hardening process using nitrogen gas. Before nitriding, steel components should be heat treated for 21-100 hours.
Which of the following is/are the objective of Normalising? RRB JE 29-08-2019
- All of the options
- To improve the machinability
- To remove internal stresses
- To enhance the mechanical properties
Explanation:
- Normalising objectives: refine grain structure, improve machinability, remove internal stresses from cold working, enhance mechanical properties, and remove dislocations from hot working.
Which of the following is the hardest constituent of steel? RRB JE 29-08-2019
- Ledeburite
- Austenite
- Martensite
- Bainite
Explanation:
- Martensite is the hardest constituent of steel. It is a metastable phase formed by rapid quenching of austenite.
What is the expansion of PwHT in welding? RRB JE 29-08-2019
- Post Weld Heat Treatment
- Post Weld Heating Torch
- Post Weld Horizontal Treatment
- Pre Weld Heating Torch
Explanation:
- PwHT stands for Post Weld Heat Treatment, used to reduce residual stress and control hardness in welded parts.
Which annealing process is carried out in a heavy casting to make austenitic grains homogeneous? RRB JE 30-08-2019
- Full annealing
- Process annealing
- Diffusion annealing
- Spheroidise annealing
Explanation:
- Diffusion annealing is carried out on heavy castings at 820°C to make austenitic grains homogeneous. Full annealing aims to soften metal, refine grain structure, relieve stresses, and remove trapped gases.
The diffusing hardening element in case of the carburizing process is —-? RRB JE 30-08-2019
- Nickel
- Manganese
- Chromium
- Carbon
Explanation:
- Carbon is the diffusing hardening element in carburizing. It is carried out for low carbon steel that doesn’t respond readily to quenching.
Quenching is not necessary when hardening is done by —-? RRB JE 30-08-2019
- Nitriding
- Induction hardening
- Case hardening
- Flame hardening
Explanation:
- Nitriding does not require quenching. Hardening is caused by fine scale precipitation of alloying element nitrides, not by quenching.
____ is formed when martensite is warmed to about 400°C. RRB JE 30-08-2019
- Pearlite
- Austenite
- Troosite
- Bainite
Explanation:
- Troosite is formed when martensite is warmed to about 250-450°C. Martensite has a BCC structure.
In which of the following process does mild steel absorb carbon and nitrogen to obtain a hard surface? RRB JE 30-08-2019
- Carburizing
- Cyaniding
- Nitriding
- Annealing
Explanation:
- Cyaniding hardens steel surfaces by adding nitrogen and carbon. The workpiece is immersed in molten sodium cyanide and sodium carbonate at 950°C.
Which of the following processes permits transformation of austenite to martensite, throughout the cross-section of a component without cracking or distortion? RRB JE 31-08-2019
- Tempering
- Annealing
- Austempering
- Martempering
Explanation:
- Martempering permits transformation of austenite to martensite throughout the cross-section without cracking or distortion by heating above upper critical point and quenching to upper martensite range.
____ is a process for placing a thin phosphate coating on steel. RRB JE 31-08-2019
- Anodizing
- Galvanization
- Parkeringing
- Sheradizing
Explanation:
- Parkeringing places a thin phosphate coating (0.004-0.008mm) on steel at about 88°C. It acts as a primer or base coat for paints and enamels.
Cyaniding is carried out at a temperature of —-? RRB JE 31-08-2019
- 300°C
- 500°C
- 950°C
- 175°C
Explanation:
- Cyaniding is a surface hardening process where low carbon steel is immersed in cyanide salt bath maintained at 850°C to 950°C.
Which of the following phase is obtained as the end product, after complete heat treatment cycle in austempering process? RRB JE 31-08-2019
- Pearlite
- Bainite
- Martensite
- Austenite
Explanation:
- Austempering produces Bainite as the end product. Steel is heated above upper critical temperature (875°C), then quenched in salt bath at 250-525°C to transform austenite to bainite.
What is meant by HVOF in metal coating? RRB JE 31-08-2019
- High Velocity Oxidised Filler
- High Viscous Oxidised Fluid
- High Viscous Oxygen Fuel
- High Velocity Oxygen Fuel
Explanation:
- HVOF stands for High Velocity Oxygen Fuel, a modern thermal spray coating process using fuels like propylene, propane, kerosene, acetylene, and hydrogen.
Which carburising method has high production rate? RRB JE 31-08-2019
- Solid powder carburising
- Liquid carburising
- Pack carburising
- Gas carburising
Explanation:
- Gas carburising has high production rate. In this method, CH4, C2H6, or C3H8 are used at 810-980°C for 3-12 hours.
The lower critical point for all steels is —-? (DMRC 18.02.2017, 8.30 a.m)
- 600°C
- 723°C
- 800°C
- 913°C
Explanation:
- Lower critical point for all steels is 723°C, where new grain formation starts on heating. Upper critical point is where changes end on heating.
Annealing is a heat treatment carried out to —-? (RRB Patna JE 25.10.2009)
- Harden and toughen the material
- Increase carbon content
- Restore ductility
- Induction harden
Explanation:
- Annealing restores ductility by heating 30-50°C above critical temperature, holding, and slow cooling in furnace. It also softens metal, refines grain structure, relieves stresses, and removes trapped gases.
Hardness of steel depends upon amount of —-? (RRB Jammu JE 25.10.2009)
- Pearlite
- Ferrite
- Cementite
- Martensite
Explanation:
- Hardness of steel depends upon the amount of cementite. More cementite means more hardness.
____ structure is obtained by austempering process of heat treatment. (RRB Chandigarh SSE 09.09.2012)
- Sorbite
- Bainite
- Martensite
- Troosite
Explanation:
- Bainite structure is obtained by austempering. Bainite is a mixture of microscopic crystal ferrite and cementite, produced at initial temperature 625°C.
Hardness of cementite is of the order of BHN —-? (RRB Jammu SSE 09.09.2012)
- 200
- 300
- 400
- None of these
Explanation:
- Hardness of cementite is around 550 BHN. Cementite is an intermetallic compound of iron and carbon, hard and brittle with 6.7% carbon.
The essential constituent of hardened steel is —-? (DMRC JE 20.04.2018)
- Pearlite
- Austenite
- Martensite
- None of these
Explanation:
- Martensite is the essential constituent of hardened steel, obtained by rapid quenching of carbon steels.
Under microscope ferrite appears as —-? RRB Allahabad JE 09.09.2012 RRB Secundrabad Technical (Eng.) 20.05.2007
- White
- Light
- Dark
- None of these
Explanation:
- Ferrite appears as Light under microscope. Austenite and Cementite appear White. Pearlite appears Dark. Fresh Martensite appears Mostly white. Bainite and tempered Martensite appear Dark.
____ structure has maximum hardness. (RRB Bhubneshwar JE II 29.11.2008) (DMRC JE 22.09.2017)
- Troosite
- Pearlite
- Martensite
- Sorbite
Explanation:
- Martensite has maximum hardness. It is a metastable phase consisting of supersaturated interstitial solid solution of carbon in α-iron.
____ iron is the magnetic allotrope of iron. (JMRC JE 10.06.2017) (BMRCL JE 24 Feb. 2019)
- α
- β
- γ
- δ
Explanation:
- Alpha iron is the magnetic allotrope of iron. Alpha iron has BCC structure forming when molten iron cools to 910°C. Gamma iron is non-magnetic.
Austenite is a solid solution of carbon in ____ iron. (RRB Bhubneshwar JE-11 19.12.2010)
- alpha
- beta
- gamma
- delta
Explanation:
- Austenite is the interstitial solid solution of carbon in gamma (γ) iron with FCC structure. It can have maximum 2.14% carbon at 1143°C and is non-magnetic and soft.
Under microscope pearlite appears as —-? (RRB Allahabad JE 19.12.2010)
- White
- Light
- Dark
- Finger print
Explanation:
- Pearlite appears as finger print under microscope. Ferrite appears light, Cementite appears white, and lamellar pearlite cementite appears dark.
Surface hardening process gives maximum hardness to the surface —-? (RRB Mumbai SSE 05.10.2008)
- Pack hardening
- Nitriding
- Cyaniding
- Induction hardening
Explanation:
- Nitriding has the highest penetration value on surface among surface hardening processes.
By which of the following heat treatment processes, a small selected portion of the job can be hardened? (DMRC JE 2013)
- Nitriding
- Cyaniding
- Pack hardening
- None of these
Explanation:
- Induction hardening (not listed) allows localized heating of small selected portions. The part is placed within an inductor coil through which high frequency current is passed.
The pH value of neutral solution is —-? (Konkan Railway STA 2017)
- Equal to 7
- Less than 7
- Greater than 7
- None of these
Explanation:
- pH value of neutral solution is 7. Sea water: 8.4, Blood: 7.4, Milk: 6.4, Urine: 6, Lemon: 2.2.
____ is obtained by isothermal hardening operation. (Konkan Railway TA 2017)
- Cementite
- Sorbite
- Acicular troosite
- Bainite
Explanation:
- Bainite is formed by austempering, which is an isothermal hardening method. Austenite is cooled at critical rate, maintained at a certain temperature, producing bainite microstructure.
Steel can be hardened quickly by ____ process. (RRB Mumbai C&G JE 25.10.2009) (RRB Makda SSE 25.10.2009)
- carburizing
- cyaniding
- induction hardening
- None of these
Explanation:
- Steel can be hardened quickly by induction hardening. Alternating current through an inductor induces eddy currents in surface layers generating heat.
What is the structure obtained when steel is quenched in water? (RRB Patna JE 25.10.2009)
- Pearlite
- Sorbite
- Troosite
- Martensite
Explanation:
- Martensite structure is obtained when steel is quenched in water. Martensite is a very hard form of steel crystalline structure formed by rapid cooling of austenite.
The percentage of carbon that must be present in steel before it can be hardened noticeably is —-? (RRB Allahabad SSE 09.09.2012)
- 0.05
- 0.1
- 0.2
- 0.3
Explanation:
- Low carbon steel (0.2% C) does not contain enough carbon to harden when heated and quenched. Dead mild steel: 0.05-0.15%, Mild steel: 0.15-0.45%, Medium carbon: 0.45-0.8%, High carbon: 0.5-1.5%.
Case hardening is —-? (RRB Gorakhpur Design SSE 09.09.2012)
- Done to get a soft ductile interior with a very hard surface
- Done to get a hard ductile interior with a very hard surface
- Followed by tempering
- None of the above
Explanation:
- Case hardening is done to get a soft ductile interior with a very hard surface by adding alloying elements like carbon and nitrogen to the surface.
Pearlite is a combination of —-? (RRB Chandigarh SSE 09.09.2012)
- ferrite and cementite
- cementite and gamma iron
- ferrite and austenite
- ferrite and iron graphite
Explanation:
- Pearlite is a combination of ferrite (87%) and cementite (13%). Cementite consists of 93.33% iron and 6.67% carbon.
The process in which molten metal is forced through a nozzle into a steam of water or air is called —-? (RRB Allahabad JE 09.09.2012)
- Electrolysis
- Atomization
- Shouting
- Reduction
Explanation:
- Atomization is the process where molten metal is forced through a nozzle into a stream of water or air. It is used for low melting point materials like brass, bronze, Zn, Al, and Pb.
Working of metal above the recrystallisation temperature is known as —-? (RRB Bhubneshwar JE II 29.11.2008)
- pressing
- forging
- cold working
- hot working
Explanation:
- Hot working is working above recrystallisation temperature. Cold working is working below recrystallisation temperature.
After cold forming, steel balls are subjected to —-? (RRB Jammu SSE 09.09.2012)
- normalising
- tempering
- electroplating
- stress relieving
Explanation:
- After cold forming, steel balls are subjected to stress relieving because cold forming increases hardness and strength.
Which of the following mediums is used to achieve the fastest cooling rate during quenching of steel? (RRB Gorakhpur Design SSE 09.09.2012)
- Water
- Brine
- Oil
- Air
Explanation:
- Brine solution gives the fastest cooling rate. Brine is a high-concentration solution of salt (NaCl) in water.
The purpose of normalizing is —-? (RRB Mumbai SSE 19.12.2010)
- Grain structure refinement
- Removal of strains caused by cold working
- Removal of dislocations in internal structure due to hot working
- All of the above
Explanation:
- Normalizing refines grain structure, removes strains from cold working, and removes dislocations from hot working.
What is the structure obtained when steel is quenched in water? (RRB Mumbai SSE 19.12.2010) (DMRC JE 2013)
- Pearlite
- Sorbite
- Troosite
- Martensite
Explanation:
- Martensite is formed when steel is quenched in water, a very hard crystalline structure formed by rapid cooling of austenite.
In which of the following range process annealing is carried out? (RRB Mumbai SSE 19.12.2010)
- Ferritic range
- Austenitic range
- Cementitic range
- Martensitic range
Explanation:
- Annealing is carried out in the austenitic range to reduce hardness, relieve internal stress, and increase machinability.
Purpose of normalizing is to —-? (RRB Chandigarh SSE 25.10.2009)
- improve strength
- increase hardness
- remove internal stresses
- all of these
Explanation:
- Normalizing removes internal stresses, refines grain structure, and improves machinability, tensile strength, and weld structure.
Eutectoid steel contains following percentage of carbon —-? (RRB Jammu JE 25.10.2009)
- 0.02%
- 0.3%
- 0.63%
- 0.8%
Explanation:
- Eutectoid steel contains 0.8% carbon. Hypo-eutectoid: less than 0.8% C. Hyper-eutectoid: more than 0.8% C.
The slowest cooling rate is achieved when steel is quenched in —-? (RRB Allahabad JE 25.10.2009)
- fused salt
- air
- brine
- mixture of water and oil
Explanation:
- Cooling rate order: Brine > Water > Oil > Air. Air gives the slowest cooling rate. Furnace cooling gives coarse pearlite, air gives fine pearlite, oil gives very fine pearlite, water gives martensite.
Solid solution of carbon in gamma iron is called —-? (RRB Kolkata SSE 09.09.2012)
- Austenite
- Sorbite
- Troostite
- Ferrite
Explanation:
- Austenite is solid solution of carbon in gamma iron. Cementite is hardest structure on Fe-C diagram. Martensite is needle-like supersaturated solution. Ferrite is softest interstitial solution.
Normalizing operation is carried out in —-? (RRB Bhopal SSE 09.09.2012)
- Furnace
- Air
- Water
- Oil
Explanation:
- Normalizing is carried out in air, requiring subsequent machining or surface finishing to remove scale or decarburized layers.
The melting point of pure iron is —-? RRB Jammu SSE 09.09.2012 RRB Chandigarh Section Eng. (Mech.) 26.02.2012
- 1355°C
- 1500°C
- 1553°C
- 1535°C
Explanation:
- The melting point of pure iron is 1535°C (1539°C).
Austenite is a combination of —-? (RRB Bhubneswar JE 11 29.11.2008)
- Ferrite and pearlite
- Cementite and gamma iron
- Pearlite and cementite
- Ferrite and cementite
Explanation:
- Austenite is a combination of cementite and gamma iron. At 727°C, austenite decomposes into ferrite and cementite (pearlite). Pearlite is 88% ferrite and 12% cementite.
A zinc diffusion process is called —-? (DMRC JE 20.04.2018)
- Galvanising
- Anodising
- Parkeising
- Sherardizing
Explanation:
- Sherardizing is a zinc diffusion/coating process. Galvanising deposits zinc, Parkeising is phosphate coating, Cloradizing is Al coating, Chromizing is Cr coating.
Identify the heat treatment process which results into a very hard surface even though the core may remain soft and ductile. RRB Mumbai JE 05.10.2008 RRB Chandigarh Section Eng. Mech. 15.03.2009
- normalizing
- tempering
- cyaniding
- annealing
Explanation:
- Cyaniding results in a very hard surface while the core remains soft and ductile.