1/40
AHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
Name | Mastery | Learn | Test | Matching | Spaced |
---|
No study sessions yet.
Eutectic point
the lowest temperature an alloy melts at, occurs at a specific concentration of each element in the alloy
Microstructural Composition (C < 2 wt% Sn)
At room temperature, polycrystalline with grains of alpha phase having a composition of C.
Microstructural Composition (2 wt% Sn < C < 18.3 wt% Sn)
At temperatures in alpha + beta range, polycrystalline with alpha grains and small beta phase particles.
Microstructural Composition (18.3 wt% Sn < C < 61.9 wt% Sn)
Contains alpha phase particles and a eutectic microconstituent.
Eutectic Microstructure (C = Ceutectic)
Eutectic microstructure characterized by alternating layers (lamellae) of alpha and beta phases.
Cooling Curve (Pure Metal or Eutectic Alloy)
Near equilibrium; may experience supercooling if nucleation is difficult.
Cooling Curve (Binary Alloy)
Solidification occurs over a range of temperatures; Tb is the start and Tc is the completion of solidification.
How to find phase compositions in a two phase region
Use tie lines
Equation for Relative amount of each phase:
Conversion between volume fraction and mass or weight fraction if densities are the same
volume fraction = weight fraction
Conversion between volume fraction and mass or weight fraction if densities are NOT the same
Average Density of Eutectic Mixtures
Weight Fraction Equation
Volume Fraction Equation
Hyper-eutectic
to the left of the eutectic point, eutectic structure with beta regions
Hypo-eutectic
to the right of the eutectic point, eutectic structure with alpha regions
Superheating
heating above a material’s boiling point
Supercooling
heating below a material’s boiling point
Non-equilibrium solidification
when the rate of cooling is limited
Advantages of eutectic alloys
significantly low melting point
Properties of eutectic alloys
significantly low melting point
Effect of diffusion on microstructure development
causes lamellar microstructures
Appearance of Alpha Phase Microconstituent
Appearance of Beta Phase Microconstituent
Appearance of Eutectic Microconstituent
Hardenability
the capacity of a steel to be hardened in depth when quenched from austenitizing temperature, higher hardenability means it needs a slower cooling to form martensite
Bainite
elongated Fe3C particles in alpha ferrite
upper bainite
forms at higher temperatures, lathes of ferrite separated by cementite particles
lower bainite
forms at lower temperatures, fine lathes of ferrite separated by carbides
pearlite
lamillae of ferrite and cementite
martensite
forms when austenite is rapidly cooled (quenched)
Gamma to martensite transformation
forms when austenite is quenched
Grain Size Effect on Hardenability
Increase in grain size results in increased hardenability of steel.
Pearlite Transformation
Transformation process that slows as austenitic grain size increases.
Quench Media (Oil)
Moderate to fast cooling; helps prevent cracking and distortion.
Quench Media (Water)
Rapid cooling with a risk of cracking and distortion.
Proeutectoid
a phase that forms before the eutectoid austenite decomposes when a material is cooledformed when there are more nuclei and the cooling is fast
Fine pearlite
formed when there are more nuclei and the cooling is fast
Coarse pearlite
formed when it is slow cooled and there are fewer nuclei
Quench media
the substance in which a heat treated part is submerged to cool down
Properties of fine vs coarse pearlite:
Fine pearlite is stronger than coarse pearlite, but is more ductile than fine pearlite, both have good toughness