L7 Engineering metals Flashcards
(35 cards)
What is the two differences between crystal structure FCC and HCP.
FCP is easier to deform and has mor slip systems than HCP
What one thing is plastic deformation dependent on?
Dislocation movement
What can effect the amount of dislocation movement? (2 things)
Binding strength and crystal structure
How to decrease dislocation movement?
Hardening mechanisms which change the microstructure
Three types of hardening mechanisms:
- Solution hardening, precipitation hardening, work hardening
How does cold working effect the metal?
Much higher dislocation density which leads to higher yield stress
How does hot working effect the metal?
It is done at temperatures that allow re-crystallisation. It provides plastic deformation without raising the yield strength. Increases ductility of materials.
How does casting effect the microstructure?
It can cause different structure in different parts and defects can occur. (Which causes it to have slightly inferior mechanical properties than rolled or forged materials)
What are the effects after welding? (3)
It gets casting structure
The heat alter the microstructure causing different hardening and grain growth.
Often crack
How is precipitation hardening done?
- Heating: Alloy elements are dissolved
- Quenching: Lowering temperature so no atomic movement occur
- Ageing: Partivles are precipated
How is steel manufacured?
- Iron oxide is reduced to pig iron in blast furnace
- Carbon of pig iron is adjustet to contain the amount wanted. The steel is alloyed and scrap can be added
How to form steel? (3)
- Casting
- Varmvalsning
- Kallbearbetning som tråddragning och kallvalsning
Three heat treatments of steel?
Normalization: Heating and slow cooling which provides a normal microstructure. Is good when stiffness is important
Soft annealing: Heating to temperatures below melting point. Diffusion, grain growth, spheriodized perlite, lower yield strenth. Used for steel to be machined and then hardened
Hardening: Heating and quenching, tempering. The carbon content
determines the proportion of cementite. The temperature and time of
determine the size of the cementite particles. Used when hardness and yield
strength are important
Why is steel alloyed sometimes? (4st)
- Increase hardenability
- Provide carbides other than Fe3C with more
stable high temperature properties - With Cr => chromium oxide layer, corrosion
resistance - Stabilize austenite at room temperature
Two types of structural steel?
Low carbon steels and HSLA
Properties of low carbon steels? (3)
Cheap
Svetsbar
Cannot be hardened
(ex buildings and ships)
Properties of HSLA? (4)
High yield stress
Can be welded
Cannot be hardened
Greater mechanical properties than carbon steel
Ex: Vehicle plate and bridges
Properties of alloy steel? (3)
Medium carbon content
Can be hardened
Harder to weld
Ex: railway rails, hand tools,
machine parts
Properties of tool steel? (2)
High carbon content
Stable carbides at high temperature
Ex: moulds, pressing tools,
cutting tools, ball bearings
Steel + Cr = ?
Stainless steel
Three types of stainless steel and their properties?
Ferritic, it’s cheap
Austenitic, good resistance but low temperature properties
Martensitic, can be hardened
Difference between ductile and gray iron?
Both has high amount of carbon (2-4%)
Gray is relatively brittle and has worse mechanical properties but is good at vibration damping.
Properties of aluminnium? (4)
- Low density (2.7kg/dm3)
- Good malleability (FCC structure)
chineability (bearbetbarhet och smidbarhet) - Good conductor
- Unsensetive to corrosion
Three types of alumnium alloys
Heat-treatable forging alloys
Non-heat-treatable forging alloys
Casting alloys
