DMS - Steel & Wrought Alloys Flashcards
define alloy. (3)
Two metals that form a common lattice structure
The metals are soluble in one another
They form a solid solution
name the two types of solid solutions formed by alloys and their subtypes (3).
- Substitutional solid solution:
Two subtypes;
Random - Both types of atoms within the structure are arranged in a random fashion
Ordered - You can predict the type of atom based on its location. - Interstitial solid solution - Two atoms marked different in size
what are wrought alloys?
Alloys which can be manipulated by cold working - can be drawn into a wire.
Name the metals within a steel alloy. (4)
Iron
Carbon
Nickel
Chromium
iron is describe as allotropic - define this.
in a solid state it can exist in 2 crystalline forms/phases depending on the temperature.
at what temperatures is iron a body centred cubic crystalline structure?
< 900 degrees
> 1400 degrees
at what temperatures is iron a face centred cubic lattice structure?
between 900 and 1400
list the phases of iron. (3)
Austenite (high temp) - key phase
lattice containing iron in rows and columns with carbon atoms interspersed.
Ferrite:
Very dilute solid solution
Exists when cooled slowly
Cementite
Exists when cooled slowly
3 iron to 1 carbon
what phases of iron are undesired and why is this the case? (2)
Ferrite and cementite
only formed if you cool the alloy extremely slowly = generate large grains with poor mechanical properties = not desired.
what does quenching iron produce?
martensite (type of stainless steel)
how do we prevent quenched iron producing martensite instead of austenite?
This can be suppressed by having the correct proportions of chromium and nickel.
18% chromium & 8% Ni
12% chromium & 12% Ni
what’s the difference between steel and stainless steel?
stainless steel > 12% chromium
what is the key attribute of chromium?
creates an oxide which increases corrosion resistance
what are the advantages of nickel? (3)
Lowers austenite to martensite temperature
Improves strength
Improves corrosion resistance
name the 2 types of stainless steel
austenitic
martensitic