230425 - Advanced Materials Technology Flashcards
Increase strength
Add carbon –> Perlite
Add manganese
Solid Solution (atoms, not visible in the light microscope) mixed crystals
Phases of steel
Classification of steels
Microalloyed steels: grain size, form, precipitations.
Multiphase steels: volumes.
High maganese steels: stabilize austenite at room temperature.
Nomenclature of high strength steel
DIn 10027
H: high strength E (ductile)
C, D, X: cold rolled, hot rolled, no information (hot or cold rolled?)
nnn: minimum yield stress
Tnnn: minimum tensile stress
HCTT690: high strength cold rolled minimum tensile stress 690
Mild steels
ULC ultra low carbon, no perlite, simple ferritic structure
LC low carbon
improved formability, the higher the quality, the better the formability is
Cotrell clouds
Some small C or N atoms get, slightly bigger than the interstitial sites and this distorts the crystal lattice, blocks dislocations.
BH steel
Bake-Hardening steel:
* Forming: Number of dislocations increases (strain hardening, they hinder between themselves).
* Annealing: Increase temperature, bell or continuous annealing, carbon atoms start to move and build cotrell clouds.
Improves the yield point (50 MPa)
Paint baking, increase the strength, car bodies. Material fits perfectly together to the paint baking process.(
How do you describe the bake hardening effect?
Bake hardening without preforming (BH0).
Bake hardening with 2% preforming (BH2).
IF steels
Interstitial Free steels
No C or N interstitially dissolved, (0%: technically, not feasible)
Very good formability with increased strength compared to mild steels.
HSIF: + other alloy elements
Disadvantage
Aging at room temperature:
BH and Mild steels: 3 months
IF steels: no variation
WHY?
-30 deg Celsius will keep the material properties
Microalloyed steels
very small amount of alloy elements
niubium, titanium, vanadium
fine precipitations of carbides, that cause grain refinement
regular percentage of carbon in steels?
