Ch 7 Flashcards
Define annealing
(Two things)
Heat treatment process that reduces the effects of cold working and can restore the properties and dislocation structure to the pre-cold work state
Annealing can reverse the effects of what
Strain hardening
Three things annealing does
What type of activated process is annealing and what does it involve?
Thermally activated process
Involves atomic rearrangement, especially with atoms, located in dislocations
List the three stages of annealing in order
Recovery
Recrystallization
Grain growth
Describe the extent to which the properties changing each of the three stages of annealing
Recovery: minor changes in properties
Recrystallization: significant changes in properties
Grain growth: minor changes in properties
Describe the order of activation energy for each of the three stages of annealing
Recovery: smallest
Recrystallization: larger
Grain growth: largest
What two processes might not occur in annealing, and what always occurs
Green growth and recrystallization
Recovery always happens
What are the three vertical sections on this diagram?
Describe what happens to the grains during annealing
Define recovery
The relief of some of the internal strain energy of a previously cold worked metal, usually by heat treatment
In a light microscope is recovery visible
No
Define stress relief anneal
Reduces the internal residual stress is caused due to cold work (strain hardening)
Does a stress relief anneal result in significant property changes
No
What phase of annealing does a stress relief anneal occur
Recovery
What happens during recovery?
Thermal energy added from heat, triggers, diffusion, and some dislocation motion can occur to either redo strain, energy, or reduce the number of dislocations
What does equiaxed grain structure mean?
Grains with nearly equal dimensions
Define nucleation
The initial stage in phase transformation
Evident by the formation of small particles (nuclei) of the new phase that are capable of growing
Define recrystallization
Equiaxed grains nucleateand grow in the deformed (elongated) greens until these elongated grains have been totally replaced
What does recrystallization reverse?
The effects of cold, working, or strain hardening
During recrystallization what decreases in what increases
Strength decreases
Ductility increases
When does the recovery stage occur?
(in terms of temp)
Occurs at lowest temp her first at higher temps
(since it has the lowest activation energy
Stress relief anneal: what is retains and what is removed?
Strength is retained
Internal stresses are removed
Is there any recrystallization during a stress relief anneal?
NO
Recrystallization: will not occur unless what
A certain amount of %CW has been done
(About 2-20%, about 5% for iron)
Recrystallization: what happens if you plot % completion versus log t
You get sigmoidal (S shaped curves)
Recrystallization: what does a higher temperature mean?
Faster reaction
Small drop in temperature means large increase in time
Define recrystallization temperature
Attempt at which a heavily cold work (greater than 50% CW) will fully recrystallized in one hour
What represents recrystallization temp?
What is grain growth driven by?
Reduction in green boundary area
(Reduction in energy associated with high energy green boundaries)
What can green growth be visualized as?
Soap, bubbles getting bigger
Define the Hall-Petch relationship
Drain Greengrove there is a drop in strength with increase in grain size proportional to
1/sqrt(d)
At what temperature is hot working done
Above a metal’s recrystallization temperature
Define hot working
Plastic deformation with dynamic recrystallization occurring at the same time as a generation in multiplication of dislocations
Hot working: why can’t the dislocation density increase significantly?
Due to recrystallization
When would a hot working not be used?
If good appearance or accurate dimensions are important
Hot working: can produce a very large what
Reductions in area
Is this hot working or cold working and what is the temp?
Is this hot working or cold working and what is the temp?
Annealing reduces the total ______ of cold worked metal
Energy
Annealing: reduces ________ density significantly
Dislocation
When is kneeling often used?
And why?
Between cold working steps to reverse the effects of cold work
So that the final properties can be tailored for a particular dimension of part
Does annealing alter the dimensions of a part
NO
Lower dislocation density means what two things
Strength is lower
Ductility is higher
