Engineering Unit 4

Carbon content of low carbon steel

0.07 - 0.3%

Carbon content of medium carbon steel

0.3 - 0.6%

Carbon content of high carbon steel

0.6 - 2.0%

What steel is used for automobile body parts?

Low carbon

What steel is used for wire products?

Low carbon

What steel is used for structural plates and sections?

Low carbon

What steel is used for seamless tubes?

Low carbon

What steel is used for boiler plates?

Low carbon

What steel is used for automotive components?

Medium carbon

What steel is used for shafts?

Medium carbon

What steel is used for axles?

Medium carbon

What steel is used for gears?

Medium carbon

What steel is used for crankshafts?

Medium carbon

What steel is used for stampings and forgings?

Medium carbon

What steel is used for train rails?

Medium carbon

What steel is used for wheels?

Medium carbon

What steel is used for high strength springs and wires?

High carbon

What steel is used for cutting tools?

High carbon

What steel is used for punches and dies?

High carbon

Which polymers have high thermal, chemical and electrical resistance?

All of them

Which polymers have high impact strength?

ABS and PC

Which polymers have high dimensional stability?

ABS and PC

Which polymers have good low-temperature resistance?

ABS

Which polymers have high abrasion resistance?

PA6

Which polymers have high fatigue resistance?

PA6

Which polymer is used to make automobile parts?

ABS

Which polymer is used to make PPE?

ABS and PC

Which polymer is used to make electrical equipment?

ABS

Which polymer is used to make high strength construction applications?

ABS

Which polymer is used to make lenses?

PC

Which polymer is used to make face shields?

ABS, PC

Which polymer is used to make security windows and windscreens?

PC

Which polymer is used to make electrical housings?

PC

Which polymer is used to make machine guards?

PC

Which polymer is used to make machine parts?

PA6

Which polymer is used to make medical implants?

PA6

Which polymer is used to make electrical connectors?

PA6

Which polymer is used to make fishing line?

PA6

Effect of hot working on grain structure

Refines structure and resolves internal stresses, reduces dislocation density

Effect of hot working on strength, hardness, ductility, predictability

decreases, decreases, increases, increases

Effect of cold working on strength, hardness, ductility, predictability

increases, increases, decreases, decreases

Effect of cold working on grain structure

Distorts grains and increases internal stresses, increases dislocation density

Process annealing

Heated and held below critical temperature before air cooling, resolves internal stresses without changing microstructure, typically for low carbon steels

Full annealing

Heated and held above critical temperature before furnace cooling, new and undistorted grains form with a coarse pearlite structure

Goal of annealing, and advantages of the two methods

Improves workability, full annealing better prepares the metal for machining, process annealing retains microstructure without excessive softening

Normalising

Heated and held above critical temperature before air cooling, makes very fine grains with less internal stresses, improving strength, ductility and predictability

Hardening; mediums and resultant products

Furnace (coarse pearlite), air (fine pearlite), oil (mostly martensite, some pearlite that increases as C content decreases), water (martensite)

Martensitic reaction

When carbon diffusion doesn’t have time to occur due to high cooling rate, it gets trapped in a supersaturated solid solution of heterogenous grains known as martensite

Tempering

Heating to below critical temperature and cooling at a controlled rate, improves toughness (greater ductility without losses in strength)

Tempered martensite

Limited diffusion occurs, rearranging the trapped carbon into a ferrite matrix containing cementite particles, increases ductility without losing much strength or hardness

Eutectic point - temperature, concentration, reaction

183ºC, 61.9% Sn, L → α+β

Pb - pure melting temperature, max solubility in β, room temperature solubility in β

327ºC, 2.2%, <1%

Sn - pure melting temperature, max solubility in α, room temperature solubility in α

232ºC, 18.3%, 2.2%

Hypo/hypereutectic composition range

18.3<Sn<61.9%/61.9<Sn<97.8%

Eutectoid point

723-727ºC @ 0.76% C

Allotropic point of pure iron

912ºC where austenite changes into ferrite

Ferrite, austenite, cementite maximum carbon solubility

0.022% @ 723-727ºC, 21.4% @ 1147ºC, 6.67% (fixed)

Ferrite, austenite, cementite - structure

BCC, FCC, intermetallic compound