Week 6: Strengthening of Metals

Question 1

How do metals plastically deform?

Answer 1

Deformation is due to the dislocation motion.

Question 2

Why does forging change properties?

Answer 2

Forging changes the dislocation movement of the material and thus how it will plastically deform

Question 3

Why does deformation occur at stresses smaller than those for perfect crystals?

Answer 3

Perfect crystals have little to no plastic deformation.

In materials that aren’t perfect crystals, a lower stress is required to deform than compared to perfect crystals

Question 4

GS - grace sold

SS - seventy snakes
PH - per hour
SH - so honest

What are methods to strengthen metals?

Answer 4

1. Grain size reduction
2. Solid-solution alloying
3. Precipitation hardening
4. Strain hardening

Question 5

Annealing

Answer 5

Heating above critical temperature and cooling slowly

Question 6

What does annealing lead to?

Answer 6

A higher ductility

Question 7

Tempering

Answer 7

Heating below the critical temperature, where it’s then held and then quenched (middle ground between quenching and annealing)

Question 8

Quenching

Answer 8

Heating above crtiical temperature and then cool rapidy in a fluid

Question 9

Properties that it changes include

What does quenching lead to?

Answer 9

Higher hardness and strength while making it more brittle

Question 10

What does tempering lead to?

Answer 10

Leads to higher ductility and toughness while maintaining same hardness

Question 11

Recovery

Answer 11

Occurs after cold work where temperature is hot enough for dislocation to move.

Question 12

When does a change in microstructure occur?

Answer 12

During recystallisation

Question 13

Recrystallisation

Answer 13

All grains formed into new grains on top of old ones when metal reaches recrystallization temperature