Treatment Of Steels Flashcards
What do the properties of steel depend on
Percentage of carbon
Why do we heat treat
Varying the carbon we can obtain different mechanical properties of steel, due to the change in microstructure
How are phase transformations brought about?
By varying temperature, composition and pressure
What is the most convenient method to induce phase transformation
Temp changes by heat
What happens during phase transformation
Alloy proceeds towards an equilibrium state that is characterised but the phase diagram
How is thick coarse pearlite formed
Through high diffusion rates which allow for larger grain growth
Alternating layers of ferrite and Fe3C
Harder and stronger than spherodite but not as ductile
How is fine pearlite formed
The transformation is controlled by a rapid necleutation but slow atomic diffusion which form fine grains.
Alternating layers of ferrite and Fe3C
Harder and stronger than course pear lite
Not as ductile
How is bainite formed
Formed when austenite is cooled
Has ferrite and cementite phases
Needles and plates
Higher conc of dislocations in ferrite make it harder than normal
Very fine and elongated particles of Fe3C in an ferrite matrix
Stronger than fine Pearlite
How is spherodite formed
Heated to and left at a temp below the eutectoid for a long period of time.
Fe3C phase appears as sphere like particles embedded in a continuous phase ferrite matrix
Soft and ductile
How is Martensite formed
When austenite is rapidly cooled to a low temp
Non equilibrium phase structure that results from a diffusionless transformation of austenite in which carbon atoms that do not have time to diffuse out are trapped
From FCC to BCT
Carbon remains as interstitial impurities
Lower density
Easily destroyer by heat
Very hard and brittle
What happens if you slow cool austenite
Forms pearlite
What happens if you moderately cool austenite
Forms bainite
What’s happens if you rapid quench austenite
Forms martensite
What happens when you reheat martensite
Forms tempered martensite
