Annealing & Hot Working

Question 1

A material is considered to be _____________ if its grains are in a distorted condition after plastic deformation is completed.

Answer 1

cold-worked

Question 2

is the process by which the distorted cold-worked lattice structure is changed back to one which is strain-free through the application of heat.

Answer 2

Full Annealing

Question 3

This process is carried out entirely in the solid state and followed by slow cooling in the furnace from the desired temperature.

Answer 3

Annealing

Question 4

Annealing is divided into 3 stages:

Answer 4

Recovery, recrystallization, grain growth

Question 5

Effects on Properties:

• a slight increase in hardness and strength
• increase in electrical conductivity

Answer 5

Recovery

Question 6

• Primarily a low-temperature process and the property changes produced do not cause appreciable change in the microstructure (stress-relief annealing)
• The principal effect of it seems to be the relief of internal stresses due to cold working.

Answer 6

Recovery

Question 7

incubation period

• to allow the strainfree nuclei to reach a visible microscopic size
• corresponds to the irreversible growth of the embryos

Answer 7

recrystallization

Question 8

• As the upper temperature of the recovery range is reached, minute new crystals appear in the microstructure, usually in the grain boundaries and slip planes.
• takes place by a combination of nucleation of strain-free grains and growth of these nuclei to absorb the entire cold-worked material

Answer 8

recrystallization

Question 9

refers to the approximate temperature at which a highly cold-worked material completely recrystallizes in 1hr

Answer 9

Recrystallization temperature

Question 10

a deformation of approximately 7% is required before any change in grainsize occurs

Answer 10

critical deformation

Question 11

The driving force of ________ is the ideal condition that the lowest energy state for a metal would be as a single crystal.

Answer 11

Grain growth

Question 12

As the temperature increases, the rigidity of the lattice decreases and the rate of _______ is more rapid.

Answer 12

Grain growth

Question 13

the factors that govern the final recrystallized grain size are:

Answer 13

degree of prior deformation, time at temperature, annealing temperature, heating time, insoluble impurities

Question 14

the most important factor to favor nucleation and decreases the final grain

Answer 14

degree of prior deformation

Question 15

increasing the time at any temperature above the recrystallization temperature favors grain growth and increases the final grain size

Answer 15

time at temperature

Question 16

the lower the temperature above the recrystallization temperature, the finer the final grain size

Answer 16

annealing temperature

Question 17

the shorter the time heating to the the annealing temperature, the finer the final grain size

Answer 17

heating time

Question 18

the greater the amount and the finer the distribution of _____________, the finer the final grain size. they not only increase nucleation but act as barriers to the growth of grains.

Answer 18

insoluble impurities

Question 19

Effect on Properties

• the material returns very nearly to its original properties:
• decrease in hardness and strength - increase in ductility

Answer 19

grain growth

Question 20

usually described as working a material above its recrystallization temperature without taking into account the rate of working

Answer 20

Hot working

Question 21

hot worked materials react with oxygen as it cools down to room temperature and forms a dark oxide called _________

Answer 21

scale