What is the sequence of the powder metallurgy process?

Blend the powder, compact it in a die, then sinter below the melting point

Which feature is a design limitation of a powder metallurgy part?

Undercuts and cross holes, because the part must eject from the die

Use of hard alloys such as tungsten carbide

How does normalising differ from annealing?

Normalising cools in still air and gives fine uniform grain with moderate strength; annealing cools slowly in the furnace for a soft, ductile steel

Normalising uses a furnace cool; annealing uses air

Normalising never heats above the critical temperature

Why is hardened steel tempered, and what design care does quenching need?

To reduce brittleness and internal stress; avoid sharp corners and sudden thickness changes because quenching causes distortion and cracks

To increase brittleness; no care is needed

To make it harder; use sharp corners

To melt the martensite; use blind holes

Practice · 3+3 marks

Notes on powder metallurgy and heat treatment

Short answer

Powder metallurgy compacts and sinters metal powders into near-net shapes, but dies require ejectability, uniform sections, and porosity reduces strength. Annealing gives softness, normalising refines grain, hardening yields martensite, and tempering adds toughness; design must avoid sharp corners and section changes to prevent quench cracking.

Write short notes on: (a) powder metallurgy and its design limitations; (b) heat treatment processes for steel (annealing, normalising, hardening and tempering) and their effect on design.

(a) Powder metallurgy (P/M)

Metal powder is blended, compacted in a die under high pressure (hundreds of MPa) and sintered below the melting point (about 70 to 90% of the melting temperature in a protective atmosphere). Optional sizing, impregnation with oil (self-lubricating bearings) or infiltration follows.

Advantages: near-net shape, little scrap, good for gears, bushings, filters, cutting tool tips, and alloys that cannot be cast (tungsten carbide).
Design limitations: part must be ejectable from the die (no undercuts or cross holes), uniform section, limited size and length-to-diameter ratio, porosity lowers strength and ductility, sharp corners and thin walls crack, die cost high so it suits large quantity.

(b) Heat treatment of steel

Process	Operation	Result
Annealing	Heat above critical temperature, soak, cool slowly in furnace	Soft, ductile, stress-free; improves machinability
Normalising	Heat above upper critical, cool in still air	Fine uniform grain, moderate strength
Hardening	Heat to austenite, quench in water/oil	Hard, brittle martensite
Tempering	Reheat hardened steel to 150 to 650 °C	Reduces brittleness and internal stress, gives toughness

Effect on design: quenching causes distortion and cracking, so avoid sharp corners, sudden thickness changes and blind holes; keep sections uniform; allow grinding allowance after hardening; choose a steel with enough hardenability for the section size; design stresses must use the strength of the heat-treated condition.

✓ Answer checked by Claude Opus 5.5 (high effort)

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Notes on powder metallurgy and heat treatment

(a) Powder metallurgy (P/M)

(b) Heat treatment of steel

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