1. What are the various alloying elements of steel? Explain any five of them.

Alloying elements are added to steel to improve its mechanical, physical, and chemical
properties. These elements alter the hardness, strength, toughness, corrosion resistance, wear
resistance, and other characteristics.

Common alloying elements in steel:

• Carbon (C)
• Manganese (Mn)
• Chromium (Cr)
• Nickel (Ni)
• Molybdenum (Mo)
• Vanadium (V)
• Silicon (Si)
• Tungsten (W)
• Cobalt (Co)
• Sulfur (S) and Phosphorus (P) (normally considered impurities)

Explanation of five key alloying elements:

1. Carbon (C):
o Most important element in steel.
o Increases hardness and strength by forming carbides.
o Too much carbon reduces ductility and weldability.
o Used in low carbon steel (mild steel), medium, and high-carbon steels
depending on application.
2. Manganese (Mn):
o Acts as a deoxidizer and removes sulfur from steel.
o Improves tensile strength and hardenability.
o Provides wear resistance and impact strength.
o Used in Hadfield steel (about 12% Mn) for rail tracks, rock crushers.
3. Chromium (Cr):
o Increases hardness, toughness, and wear resistance.
o Provides excellent corrosion resistance (key element in stainless steel).
o Forms hard chromium carbides.
o Common in tool steels and high-speed steels.
4. Nickel (Ni):
o Improves toughness and ductility.
o Increases corrosion and impact resistance.
o Often used with chromium in stainless steel for marine and chemical
applications.
5. Molybdenum (Mo):
o Enhances hardenability and high-temperature strength.
 o Helps resist softening at elevated temperatures (creep resistance).
o Used in high-strength low alloy (HSLA) steels and tool steels.

2. Explain TTT diagram with a neat sketch and explain the cooling of steels at
various cooling rates.

TTT Diagram (Time-Temperature-Transformation Diagram):

• TTT diagram shows the transformation of austenite into other phases like pearlite,
bainite, or martensite at constant temperatures.
• It is an isothermal diagram – transformations are plotted against time and
temperature.

Explanation of transformation at various cooling rates:

1. Slow cooling (e.g., furnace cooling):

o Austenite transforms to coarse pearlite.
o Structure is soft and ductile.
2. Moderate cooling (e.g., air cooling):
o Fine pearlite forms.
o Stronger and harder than coarse pearlite.
3. Rapid cooling (quenching and holding above Ms):
o Bainite forms.
o Has a feather-like microstructure, strong and tough.
4. Rapid quenching below Ms temperature:
o Martensite forms.
o Hard and brittle due to supersaturated carbon in BCT structure.

Significance:

• Helps choose appropriate heat treatment for required mechanical properties.

3. What are the various methods of production of powders? Draw neat
sketches.

Powder production methods are grouped into:

A. Mechanical Methods:

1. Atomization:
o Molten metal is disintegrated using high-pressure gas or liquid.
o Forms spherical powders.
o Used for steel, aluminum, copper.
2. Milling (Mechanical Pulverization):
o Metal is crushed into powder using ball mills or hammer mills.
o Irregular-shaped powders.
o Suitable for brittle materials like ceramics.
3. Crushing and Grinding:
o Used for hard and brittle materials.
o Results in coarse particles.

B. Chemical Methods:

1. Reduction:
o Metal oxides are reduced using hydrogen or carbon monoxide.
o Produces sponge-like powders.
o Used for iron, copper.
2. Electrolytic Deposition:
o Metal is deposited on cathode in electrolytic cell.
o Produces high purity powders.
o Used for copper, silver.
3. Precipitation:
o Metal salts are precipitated from solution and dried to form powder.
o Common for ceramics.

4. Explain flame hardening and induction hardening with neat sketches.

Flame Hardening:

• Surface heating method using oxy-acetylene flame.

• The surface is rapidly heated above transformation temperature and quenched.
• Only outer layer hardens into martensite; core remains soft.

Applications: Gear teeth, camshafts, rail tracks.

Sketch:

• Show flame torch heating a rotating steel surface

• Quenching system immediately following

Induction Hardening:

• Uses electromagnetic induction to heat the surface.

• Alternating current induces eddy currents on surface – rapid localized heating.
• Followed by rapid quenching for martensitic layer.

Advantages:

• Precise control, clean and efficient.

Applications: Shafts, axles, crankshafts.

5. What are the applications and advantages of powder metallurgy?

Applications of Powder Metallurgy (PM):

• Automotive parts (gears, bearings, bushings)

• Aerospace components
• Electrical contacts and magnets
• Filters and porous parts
• Cutting tools and tungsten carbide tips

Advantages:

1. Material Savings:
o Near net shape – minimal waste.
2. Complex Shapes:
o Intricate geometries achievable without machining.
3. High Production Rate:
o Suitable for mass production.
4. Controlled Properties:
o Tailored porosity, density, and composition.
5. Difficult-to-machine materials:
o Easily processed (e.g., tungsten, ceramics).
6. What are the various steps in the fabrication of a component through
powder metallurgy?

Steps in Powder Metallurgy:

1. Powder Production:
o Using atomization, reduction, electrolytic or mechanical methods.
2. Blending/Mixing:
o Powders are mixed with lubricants or alloying elements for uniformity.
3. Compacting:
o Powders are compressed in a die under high pressure.
o Produces “green compact” with sufficient shape.
4. Sintering:
o Green compact is heated below melting point in a controlled atmosphere
furnace.
o Particles bond metallurgically, gaining strength.
5. Secondary Operations (Optional):
o Coining (repressing), heat treatment, machining, or impregnation for final
properties.

7. Explain carbo nitriding and cyaniding.

Carbo-Nitriding:

• Surface hardening process where steel is heated in a carbon and nitrogen-rich

atmosphere (e.g., gas with ammonia and hydrocarbons).
• Carburization + nitriding simultaneously.
• Temperature: 700–900°C.
• Quenched after treatment to form hard martensitic layer.

Advantages:

• Hard wear-resistant surface

• Tough core
• Less distortion than carburizing

Applications: Gears, fasteners, bushings

Cyaniding:

• Steel is immersed in molten cyanide salt bath (e.g., NaCN, KCN).

• Both carbon and nitrogen diffuse into surface.
 • Temperature: 800–900°C.
• Shorter cycle time.

Advantages:

• Fast, uniform case depth

• Good wear resistance

Disadvantages:

• Toxic chemicals – environmental hazard

8. What are the differences between annealing and normalizing?

Feature Annealing Normalizing

Soften material, relieve internal Refine grain structure, improve

Purpose
stress toughness

Heated above critical temp, slow Heated 30–50°C above critical, air
Temperature
cooled cooled

Cooling Furnace cooled slowly Air cooled in still air

Grain Structure Coarse grains Fine, uniform grains

Mechanical Harder and stronger than annealed

Soft, ductile
Props steel

Applications Cold working prep, machining Forgings, castings