Metallurgy Interview Questions | Metallurgy Interview

• What is the composition of Grey cast iron Grade 20?

Carbon      : 3.10 – 3.25%         Silicon : 1.75-1.95%    Manganese : 0.50 – 0.7%Sulphur : 0.05 – 0.07%       Phosporous : 0.04 – 0.07%

• What is the composition of Cast iron Grade 35?

Carbon=2.90-3.10%Manganese=0.60-1.00%Silicon=1.50-1.90%Sulphur=0.10%

Phosphorus=0.15%  Chromium=0.30%        Molybdenum=0.30%   Cupper=0.25%

• What are the super alloys?

Super alloys is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, having good surface finish.

• Why the Super alloys used for land-based turbines?

Super alloys are the top most alloys used for their excellent strength and corrosion resistance as well as oxidation resistance. No other alloys can compete with these grade.

• What kinds of NDT methods are available?

1.Visual Inspection

2.Microscopy inspection

3.Radiography Test

4.Dye Penetrate technique

5.Ultrasonic testing

6.Magnetic Particle inspection

7.Eddy Current technology

8.Acoustic Emission

9. Thermograph

10.Replica Metallographic

• What is Stress Corrosion cracking?

Stress corrosion cracking (SCC) is a process involving the initiation of cracks and their propagation, possibly up to complete failure of a component, due to the combined action of tensile mechanical loading and a corrosive medium.

• What is meant by D2 Material used for Die tooling?

D2 – High Carbon Cold Work Tool Steel

D2 is a high Carbon, high Chromium, Molybdenum, Vanadium, Air hardening alloy tool steel which offers good wear resistance, high surface hardness, through hardening properties, dimensional stability and high resistance to tempering effect. D2 tool steel is also suitable for vacuum hardening.

Typical Composition

C.-1.50%

Si.-0.30%

Cr. -12.00%

Mo. -0.80%

V. -0.90%

• What is Vacuum Induction Melting?

As the name suggests, the process involves melting of a metal under vacuum conditions. Electromagnetic induction is used as the energy source for melting the metal.

Induction melting works by inducing electrical eddy currents in the metal. The source is the induction coil which carries an alternating current. The eddy currents heat and eventually melt the charge.

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Aerogel | World’s Lightest Material | Aerogel Lighter Than Air | Aerogel Insulation

Aerogel is a very special type of foam which is 99.8% air. Aerogel is a low-density solid-state material derived from gel in which the liquid component of the gel has been replaced with gas. The result is an extremely low density solid with several remarkable properties, most notably its effectiveness as a thermal insulator. Aerogels are solid, but can be less dense then air. Despite their sparse molecular structure aerogels are strong.

It was first invented in the 1930s by Samuel Stephens Kistler, but was very brittle and could not be shaped. Aerogels are traditionally expensive and difficult to manufacture, and they are difficult to handle. Now a team of scientists have discovered how to make it flexible so that it does not break so easily. This means there are a lot of ways in which it can be used to solve problems.

It is nicknamed frozen smoke, solid smoke or blue smoke due to its translucent nature and the way light scatters in the material; however, it feels like exploded polystyrene (Styrofoam) to the touch.

Aerogels posses the lowest density and highest internal surface area of any known solid material, which makes them extremely high performance material for collision, damping, acoustic and thermal insulation, structural support and surface chemistry.

Properties:

1. Extremely low density
2. Very good thermal insulator
3. High specific surface area
4. Lowest dielectric constant

Metal aerogel Properties:

1. High specific surface area (100-500m2/g)
2. Electrically conductive!
3. Enhanced catalytic activity
4. Surprisingly capable thermal insulator

Interesting Facts:

1. A paperclip has a mass of approximately one gram. A one gram sample of aerogel has an internal surface area of between 250 and 3000m2 per gram (when produced in a weightless environment).
2. Lowest solid density: The lightest man-made material is an Aerogel with a density of only three times the density of air. However industrial aerogels can be made denser, up to 0.6 g/cc or more.

1. Highest porosity: Perhaps the only material that can have over 95% porosity, and a very wide pore size distribution, ranging from Angstroms (10-10 meter) to microns (10-6 meter).
2. Very high surface area: For some Aerogels, one ounce can have a surface area equal to a football field (over 3000 square meters per one gram).
3. Versatile compositions: Aerogels can be made with a wide range of chemical compositions.
4. Functional properties by design: Combinations of the above features can lead to Aerogel materials with useful properties such as:
   • adsorbents,
   • catalysts,
   • insulators,
   • semiconductors,
   • piezoelectric,
   • dielectric,
   • ferroelectric,
   • diffusion controllers,
   • electric conductors,
   • electric insulators,
   • and optical features.
5. Can hold (theoretically) 500 to 4,000 times its weight in applied force.

Types of Aerogels:

1. Silica:

•Silica aerogel is the most common type of aerogel and the most extensively studied and used. It is a silica-based substance, derived from silica gel.

•The world’s lowest-density solid is a silica Nano foam at 1 mg/cm3, which is the evacuated version of the record-aerogel of 1.9 mg/cm3.The density of air is 1.2 mg/cm3.

•Silica aerogel strongly absorbs infrared radiation. It allows the construction of materials that let light into buildings but trap heat for solar heating.

•It has remarkable thermal insulative properties, having an extremely low thermal conductivity: from 0.03 W/m·K down to 0.004 W/m·K, which correspond to R-values of 14 to 105 for 3.5 inch thickness. For comparison, typical wall insulation is 13 for 3.5 inch thickness. Its melting point is 1,473 K (1,200 °C or 2,192 °F).

•Silica aerogel holds 15 entries in Guinness World Records for material properties, including best insulator and lowest-density solid.

2. Carbon:

•Carbon aerogels are composed of particles with sizes in the nanometre range, covalently bonded together. They have very high porosity (over 50%, with pore diameter under 100 nm) and surface areas ranging between 400–1000 m²/g. They are often manufactured as composite paper: non-woven paper made of carbon fibres, impregnated with resorcinol-formaldehyde aerogel, and pyrolyzed.

• Depending on the density, carbon aerogels may be electrically conductive, making composite aerogel paper useful for electrodes in capacitors or deionization electrodes. Due to their extremely high surface area, carbon aerogels are used to create super capacitors, with values ranging up to thousands of farads based on a capacitance of 104 F/g and 77 F/cm³.

•Carbon aerogels are also extremely "black" in the infrared spectrum, reflecting only 0.3% of radiation between 250 nm and 14.3 µm, making them efficient for solar energy collectors.

Manufacturing:

Aerogels a formed by a process known as supercritical drying, in which the liquid from the gel base is removed and replaced by a gas, leaving a solid structure.

It is prepared like gelatine by mixing a liquid silicon compound and a fast-evaporating liquid solvent, forming a gel that is then dried in an instrument similar to a pressure cooker.

The mixture thickens, and then careful heating and depressurizing produce a glassy sponge of silicon.

Recent Development:

NASA’s Glenn Research Centre developed a polymer Aerogel which is strong, flexible, and robust against folding, creasing, crushing, and being stepped upon. These aerogels are among the least dense solids, possess compressive specific strength similar to aerospace grade graphite composite, and provide the smallest thermal conductivity for any solid.

The new aerogels are up to 500 times stronger than their silica counterparts. A thick piece actually can support the weight of a car.

Silica aerogels would crush to powder if placed under a car tire. As seen above, the same is not true of the new polymer aerogels, even if the car is only a Smart car. Overall, the mechanical properties are rather like those of a synthetic rubber, save that the aerogel has the same properties (and far smaller thermal conductivity) with only about 10 per cent of the weight.The new class of polymer aerogels also have superior mechanical properties. For example silica aerogels of a similar density have a resistance to compression and tensile limit more than 100 times smaller than the new polymer aerogels. And they can be produced in a thin form, a film so flexible that a wide variety of commercial and industrial uses are possible.

Applications:

Example 1:

Military aeroplane and helicopter engines produce a lot of heat. This means they can be attacked by heat-seeking missiles. If the engine is surrounded by a layer of Aerogel, then less heat escapes for the missiles to detect.

Example 2:

Aerogel can also be used to stop heat from escaping from hot water pipes. When heat escapes energy is wasted, which means more of the earth’s energy supplies are used up. Lots of other materials can be used to stop heat escaping, so that aerogel was used.

Example 3:

Scientists look at the dust from comets to find out what the Solar system was like when it was first formed. They want to know what the dust is made of and what shape it is. But it is hard to catch the fast moving dust. If the dust rubs against anything, friction makes the dust hot which can change it. If the dust hits anything hard, that can also change its shape. So scientists use Aerogel in a dust collector on the Stardust spacecraft. As the very small dust particles go through the Aerogel they leave little paths. These paths are used to find the dust particles when the probe comes back to Earth.

More Applications:

1. Fire retardant

1. Oven (regular, pizza, etc.)
2. Grill
3. Furnace
4. Blacksmith forge

2. Insulation (hot or cold):

a. Auto

1. Air intake
2. Engine
3. Exhaust
4. Manifolds

b. Clothing – Only for cold, not warm, since it’ll trap body heat!

c. Home

1. Furnace
2. Grill
3. Kitchen
   1. Oven
   2. Pot holders
   3. Pots and pans
   4. Coolers and refrigerator’s
4. Pipes & air ducts
5. Walls & Roof
6. Windows

3. Blacksmith forge

4. Pulling water out of materials

5. Shock absorption

6. Sound insulation

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Next-Generation ‘SKYACTIV’ Technologies

Highlights of the SKYACTIV technologies:

• SKYACTIV-G: a next-generation highly-efficient direct-injection gasoline engine with the world’s highest compression ratio of 14.0:1
• SKYACTIV-D: a next-generation clean diesel engine with the world’s lowest compression ratio of 14.0:1
• SKYACTIV-Drive: a next-generation highly-efficient automatic transmission
• A next-generation manual transmission with a light shift feel, compact size and significantly reduced weight
• A next-generation lightweight, highly-rigid body with outstanding crash safety performance
• A next-generation high-performance lightweight chassis that balances precise handling with a comfortable ride

- First product to be equipped with SKYACTIV technology will be a Mazda Demio featuring an improved, fuel-efficient, next-generation direct-injection engine that achieves fuel economy of 30 km/L.

Overview of the SKYACTIV technologies

1. SKYACTIV-G

A next-generation highly-efficient direct-injection gasoline engine that achieves the world’s highest gasoline engine compression ratio of 14.0:1 with no abnormal combustion (knocking)

• The world’s first gasoline engine for mass production vehicles to achieve a high compression ratio of 14.0:1
• Significantly improved engine efficiency thanks to the high compression combustion, resulting in 15 percent increases in fuel efficiency and torque
• Improved everyday driving thanks to increased torque at low- to mid-engine speeds
• A 4-2-1 exhaust system, cavity pistons, multi hole injectors and other innovations enable the high compression ratio

2. SKYACTIV-D

A next-generation clean diesel engine that will meet global emissions regulations without expensive NOx after treatments — urea selective catalytic reduction (SCR) or a Lean NOx Trap (LNT) — thanks to the world’s lowest diesel engine compression ratio of 14.0:1

• 20 percent better fuel efficiency thanks to the low compression ratio of 14.0:1
• A new two-stage turbocharger realizes smooth and linear response from low to high engine speeds, and greatly increases low- and high-end torque (up to the 5,200 rpm rev limit)
• Complies with global emissions regulations (Euro6 in Europe, Tier2Bin5 in North America, and the Post New Long-Term Regulations in Japan), without expensive NOx after treatment

3. SKYACTIV-Drive

A next-generation highly efficient automatic transmission that achieves excellent torque transfer efficiency through a wider lock-up range and features the best attributes of all transmission types

• Combines all the advantages of conventional automatic transmissions, continuously variable transmissions, and dual clutch transmissions
• A dramatically widened lock-up range improves torque transfer efficiency and realizes a direct driving feel that is equivalent to a manual transmission
• A 4-to-7 percent improvement in fuel economy compared to the current transmission

4. SKYACTIV-MT

A light and compact next-generation manual transmission with crisp and light shift feel like that of a sports car, optimized for a front-engine front-wheel-drive layout

• Short stroke and light shift feel
• Significantly reduced size and weight due to a revised structure
• More efficient vehicle packaging thanks to its compact size
• Improved fuel economy due to reduced internal friction

5. SKYACTIV-Body

A next-generation lightweight, highly-rigid body with outstanding crash safety performance and high rigidity for greater driving pleasure

• High rigidity and lightness (8 percent lighter, 30 percent more rigid)
• Outstanding crash safety performance and lightness
• A "straight structure" in which each part of the frame is configured to be as straight as possible. Additionally, a "continuous framework" approach was adopted in which each section functions in a coordinated manner with the other connecting sections
• Reduced weight through optimized bonding methods and expanded use of high-tensile steel

6. SKYACTIV-Chassis

A next-generation high-performance lightweight chassis that balances precise handling with a comfortable ride feel to realize driving pleasure

• Newly developed front strut and rear multilink suspension ensures high rigidity and lightness (The entire chassis is 14 percent lighter than the previous version.)
• Mid-speed agility and high-speed stability — enhanced ride quality at all speeds achieved through a revision of the functional allocation of all the suspension and steering components

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About Welding Machine | Electro Slag Welding ESW | Narrow Gap Welding

Electro slag welding is a welding process of heavy plates in the vertical position, wherein coalescence is produced by molten slag which melts the filler metal and the surfaces of the work to be welded. It’s an arc less process that utilizes resistance heating of the slag pool covering the molten steel as the weld’s heat source.

Parts to be joined are positioned approximately an inch apart and an electrode (weld wire) guide tube is positioned between the parts. Copper cooling shoes are clamped to the sides, bottom and top of the joint and contain the molten slag and metal during the weld.

After the components are assembled power is applied and the wire is fed through the guide tube. When the wire reaches the start block there is momentary arcing which melts the granulated flux, forms the slag pool and extinguishes the arc. The process is initiated by filling the joint with the flux and starting an arc by short circuiting. The consumable guide tube directs the electrode (welding wire) and conducts the welding current to the molten slag pool. The electrical resistance of the slag pool generates heat which melts the wire, the guide tube and the edges of the two components to be joined. The temperature obtained is approximately 1800 degree Celsius at the surface and 1930 degree Celsius inside under the surface. This much heat is sufficient to fuse the edges of the work pieces and the welding electrode.

As the wire and guide tube are melted by the flux the liquid metal sinks through the slag to the metal pool below and solidifies. Since the slag is less dense than liquid steel, it floats to the top and protects the metal from exposure to air. With continuing addition of weld wire the molten steel fills the gap, solidifies and fuses the two components. The weld is terminated when it reaches the top of the run-out cooling shoes above the rail running surface. Unnecessary weld reinforcement is removed immediately while the weld is hot.

A DC current of 750 – 1000 A is applied from a DC generator with flat volt-ampere. Load voltages generally range from 30 to 55 V, therefore the minimum open circuit voltage of the power source should be 60 V. Speed range of Electro slag welding are 17 to 150 mm/s.

History:

Single pass welding of heavy plates are desired one to avoid multi pass welding techniques. In the early 1950’s Russian scientists announced the single pass vertical welds by the principle of electrically conductive slag. In 1959 Electro slag welding was introduced in United states.

Applications:

• ESW is often used to weld stiffeners’ in structural box columns and wide flanges.
• Manufacture of large Presses and machine tools work with large heavy plates.
• Other machinery applications include kilns, gear blanks, motor frames, press frames, turbine rings, shrink rings, crusher bodies, rebuilding metal mill rolls and rims for road rollers
• Pressure vessels for the chemical, petroleum, marine, and power generating industries

Advantages:

• Electro slag welding can have extremely high deposition rates, but only one single pass is required no matter how thick the workpiece is.
• Unlike SAW or other arc welding processes, there is no angular distortion in ESW because the weld is symmetrical with respect to its axis.
• High Welding Speed and good stress distribution across the weld.

• Joint preparation is often much simpler than other arc welding processes.
• Residual stresses and distortion produced are low
• Flux composition as compared to submerged arc welding (SAW) is very low.

Disadvantages:

• However, the heat input is very high and the weld quality can be rather poor, including low toughness caused by the coarse grains in the fusion zone and the heat-affected zone.
• In Electro slag welding, there is some tendency toward hot cracking and notch sensitivity in the heat affected zone.
• Electro slag welding is restricted to vertical position welding because of the very large pools of the molten metal and slag.
• It is difficult to close cylindrical welds
• Electro slag welding tends to produce large grain sizes.
• Submerged Arc Welding is more economical than electro slag welding for joints below 60 mm.

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Syllabus

Friends
i have attached the 1 & 2nd semester syllabus

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syllabus

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Composite Materials

Composites Materials

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composite materials unit 2

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Heat treatment unit 1

Friends
 i have attached the heat treatment unit 1 lectures ..

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Notes 1
Notes 2
Notes 3
Notes 4

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