6.1 Flashcards
What is slag?
When any impurities float to the surface in a furnace
What happens to steel when carbon levels are increased?
Hardness and tensile strength increases
Low carbon steels contain how much carbon?
0.1-0.3%
Medium carbon steel contains how much carbon?
0.3-0.5%
High carbon steel contains how much carbon?
0.5-1.05%
What does AISI stand for?
American iron and steel institute
What do the first two digits in alloy steel designation stand for?
The primary alloying elements
What do the last two digits in alloy steel designation stand for?
The percentage of carbon contains in the alloy
For example if an alloy steel was designated XX30, what does this indicate?
It has 0.3% carbon
What is the quenching process?
Heat up a metal a and rapidly cool in water, oil, or brine
What determines hardness in steel?
The amount of carbon
What is the fastest way to quench?
By using brine (salt water)
What is the slowest way to quench?
By using oil
What is a eutectoid?
When a metal can exist in more than one form at the same temperature
What is stainless steel also known as?
Corrosion-resistant steel (CRES)
What are 200 and 300 series steels classified as?
Austenitic steels
What are 400 series steels classified as?
Ferritic and martensitic steels
Where are precipitation-hardened stainless steels used?
Airframe
Where are high-strength low-alloy steels used?
Landing gear
What is the purpose of heat treatment?
To improve mechanical properties
What are the four types of heat treatment?
- Annealing
- Normalising
- Hardening
- Tempering
What is annealing?
Heating 50F above critical temperature and allowing to soak
What is the purpose of annealing?
To release internal stresses and to make it soft
What is normalising?
Heating 100F above its critical temperature and allowing to cool slowly in air
What is the purpose of normalising?
To release internal stresses and make it stronger
What is hardening?
Heating above the critical temperature and then quenching
What is the purpose in hardening?
It increases hardness
What is tempering?
Heated below critical temperature and held at Temperature then slowly cooled
What is the purpose in tempering?
To release internal stresses caused by rapid cooling (hardening)
What is hydrogen embrittlement?
When hydrogen enters a grain structure and reacts with carbon to form methane which leads to cracks
How can hydrogen embrittlement be removed ?
By baking at 375F for at least 3 hours
What are the three steel alloy rework precautions?
- stress concentrations
- hydrogen embrittlement
- untempered martensite
How should metal removal be done?
By hand or with slow-speed hand-held power tools
When do stainless steels require protective treatment?
When in contact with light weight alloys
What is galvanic corrosion?
When two dissimilar metals corrode by being next to each other
What is necessary for galvanic corrosion to take place?
An electrolyte (eg. Water)
What does it mean if a metal is less noble?
It is more susceptible to corrosive attack
What does it mean if a metal is more noble?
It is less susceptible to corrosive attack
What does it mean if a metal has a lower number on the galvanic scale?
It is less noble
What does it mean if a metal has a higher number on the galvanic scale?
It is more noble
Why is case hardening completed?
To make low carbon steel components hard and tough
Why is case hardening not completed on high carbon steels?
Because they will become more brittle
What type of metals aren’t suitable for case hardening?
Non-ferrous metals
What is carburising?
When a thin layer of high carbon steel is produced on the surface of a low carbon steel component
What are the three types of carburising?
- pack carburising
- gas carburising
- liquid carburising
What temperature is carburising completed at?
Up to 1700F
What is pack carburising?
Heating whilst packed into a carbon rich material
What is gas carburising?
Heating in a carbon dioxide rich atmosphere
What is liquid carburising?
Heating in a bath of either sodium cyanide or barium cyanide
What is flame hardening?
Heating the surface above the transition temperature with a torch and then quenched immediately with water jets from the same torch
What material can flame hardening be carried out on?
Steels with at least 0.4% carbon and after they have been normalised
What is induction hardening?
When an induction coil surrounds the component and heats with eddy currents in the surface of the steel and then quenched
What is nit riding?
Heating metal to 1000F in ammonia which allows nitrogen into the surface
