6.1- Aircraft Materials- Ferrous Flashcards
Iron in its pure form has what characteristics?
Soft, malleable and ductile.
How is cast iron formed?
Molten iron with more than 2% carbon poured into a mould.
How is iron extracted from iron ore?
Mixed with coke and limestone and heated in a furnace. Iron sinks to the bottom.
How is steel made using pure iron?
Pure iron is remelted in a furnace where carbon is introduced.
Why is the use of steel restricted for aircraft?
High density
Susceptible to corrosion.
What are some of the characteristics considered when picking an alloying element?
Service temp Strength Stiffness Fatigue Properties Fabricability.
What does using carbon as an alloying element do?
Allows heat treatment of steel
Hardness and tensile strength are increased.
Low carbon steel contains what percentage of carbon?
0.1-0.3%
High carbon steel contains what percentage of steel?
05.-1.05%
What does using sulphur as an alloying element do?
Decreases ductility and weld ability.
Normally kept at low levels, or paired with manganese
Improves machineability.
What does using manganese as an alloying element do?
Contributes to strength and hardness
significant effect on hardenability of steel
What does using silicon as an alloying element do?
Deoxidiser
Detrimental to surface quality in low carbon steel.
What does using phosphorus as an alloying element do?
Increases strength, hardness and corrosion resistance
Decreases ductility.
What does using Nickel as an alloying element do?
Increases hardenability and impact strength.
What does using chromium as an alloying element do?
Increase corrosion/oxidation resistance
increase hardenability and high temp strength.
What does using molybdenum as an alloying element do?
Produces secondary hardening of steel during quenching.
What does using vanadium as an alloying element do?
Increases yield strength and tensile strength.
What does using titanium as an alloying element do?
Improve toughness.
What system is used to give designations to low carbon steels?
AISI (American Iron and Steel Institute).
What do the first two digits refer to in AISI (steel designation)?
Specific alloying element.
What do the last two digits refer to in AISI (steel designation)?
Percentage of carbon
It is the last three digits in a 5 digit designation.
What does a 10xx refer to?
Plain carbon steels (carbon and manganese).
What does a 41xx refer to?
Chromium and Molybdenum alloy steels.
What does a 43xx refer to?
Nickel, chromium and molybdenum alloy steels.
What does a 52100 refer to?
Chromium alloy with 1% carbon.
What does a 93xx refer to?
Nickel, chromium and molybdenum alloy steels but in a different ratio to 43xx steels.
If you saw a steel with designation 4340 what is its breakdown?
Nickel-chromium-molybdenum alloy with 0.4 carbon.
What is the specific name of Nickel-Cobalt alloy with 0.3% carbon?
9Ni-4Co.30C
9 refers to percent of Nickel
4 refers to percent of cobalt.
European designations differ slightly where can you find information on them?
Metallic material list in the SRM.
What does SAE stand for?
Society of Automotive Engineers.
What does annealing do?
Softens carbon steel to malleable state.
What does quenching do?
Hardens to a state nearly as rigid and brittle as glass.
What does tempering do?
Decrease hardness which increases ductility and toughness of quenched metal.
Quenching often produces stresses in steel, what process relieves these?
Tempering.
Why is accurate temperature control needed during tempering?
To ensure consistent replication of properties.
What are the most accurate methods of temperature measuring?
Pyrometers and thermocouple controlled ovens.
What is a less accurate way of measuring temperature of the metal during treatment.
Observing the colour, it is possible but not accurate and only possible with high carbon steels.
What colour ranges does high carbon steel have whilst heating?
Yellow- brown- purple- blue.
What can’t be done to pure/wrought or extremely low carbon steels?
They can’t be heat treated due to not having a hardening element.
How is steel hardened?
Heated above critical temp, so that carbon dispenses through iron matrix. Then rapidly cooled by quenching.
What liquids can be used to quench?
Water, oil, brine.
Oil is the slowest quench and brine the fastest.
What happens if the quench is too quick?
The structure becomes martensite, a super saturated solution of carbon in the iron matrix.
What is wrong with having a martensite structure?
Its far to brittle and hard for most uses.
What is the process of annealing?
Heating to 50°F above critical temp and allowing it to soak, then slowly cooling in the furnace or a bath of hot sand.
What is normalising?
Relieving stresses from machining or welding.
How is normalising carried out?
Heating steel to 100°F above critical temp and soaking. It is then cooled at room temp.
What does normalising do to the structure in terms of the carbon particles?
Allows the carbon to precipitate out of the austenitic structure.
What do the two axis of the carbon phase diagram display?
% of carbon content and temperature.
What is a metal called that can exist in two forms at the same temp?
Eutectoid.
What is ferrite?
Pure iron, BCC that will absorb 0.02% carbon.
What is austenite?
FCC iron, can absorb up to 2% carbon.
What is cementite?
Chemical compound of carbon and iron, the more carbon the more cementite. But will be harder and more brittle. >2% carbon.
What is pearlite?
Two phase lamellar structure, which alternating layers of alpha-ferrite (88%) and cementite (12%).
What are the important factors in heat treatment of carbon steel?
Carbon content, temperature and time taken to cool.
Since the 1940’s stainless steel has also been known as what?
CRES- corrosion resistant steel.
What are the key characteristics of CRES?
Corrosion resistance, strength, toughness and resistance to high temps.
CRES doesn’t use the SAE system but instead uses what?
A 3 digit system.
What are the 200 and 300 series of CRES known as?
Austenitic.
