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M6 Mac > 6.1 Ferrous > Flashcards

6.1 Ferrous Flashcards

1
Q

How is iron extracted from iron ore

A

By mixing coke and limestone and heating in a furnace

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2
Q

What are the main restrictions of using steel on aircraft

A

High density (approx 3 times than aluminium) and susceptibility to corrosion

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3
Q

What are the advantages of high strength steels

A

High strength and high modulus of elasticity

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4
Q

How much carbon does low, medium and high steels contain

A

Low - 0.1 - 0.3%
Medium - 0.3 - 0.5%
High - 0.5 - 1.05%

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5
Q

When would carbon steels with 0.3 - 0.5% be used

A

For surface finish purposes

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6
Q

When would steels with 0.5 - 1.05% be used

A

Extreme hardness required, typical applications are springs, files and cutting tools

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7
Q

What is the purpose of using sulphur as an alloying agent

A

Decreases ductility and weld ability with increasing content.

Increases machinability

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8
Q

What is the benefit of using manganese as an alloying agent

A

Contributes to strength and hardness but less than carbon

Increasing amounts of manganese will result in a decrease of ductility and weld ability

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9
Q

What is the purpose of silicon as an alloying agent

A

One of the principle de-oxidisers in steel making

Bad for surface quality

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10
Q

What is the purpose of phosphorus as an alloying agent

A

Increase of strength and hardness and corrosion resistance but decreases ductility

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11
Q

What is the purpose of Nickel as an alloying agent

A

Increases harden-ability and impact strength of steels

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12
Q

What is the purpose of chromium as an alloying agent

A

Increase corrosion resistance, hardenability and high temperature strength

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13
Q

What is the benefit from using molybdenum as an alloying agent

A

Increases hardenability, increases creep strength at high temps

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14
Q

What are the benefits of using Vanadium as an alloying agent

A

Increases yield strength and tensile strength of carbon steels

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15
Q

What is the purpose of using titanium as an alloying agent

A

Increases toughness

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16
Q

What is the AISI

A

The American Institute of Steel and Iron

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17
Q

What is SAE

A

Society of Automotive Engineers

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18
Q

What is the purpose of tempering

A

Decrease hardness and increase ductility and toughness in steel after that have been quenched. Also relieves internal stresses caused during quenching

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19
Q

Why would steels need to be treated after they have been quenched

A

In their quenched state they are far to hard and brittle for any use on aircraft

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20
Q

What are the main ways of temperature control during the tempering process

A

Pyrometers and thermocouple controlled ovens. A less accurate way is by observing the colour

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21
Q

Why cannot pure iron, wrought iron or extremely low carbon steels be hardened by heat treatment

A

As they have no hardening agent (Carbon)

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22
Q

What provides the slowest and quickest quench

A

Oil for slowest quench and brine for the fastest

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23
Q

What happens to an alloy if it is quenched too quickly

A

The structure will be known as martensite, a super hard material which would be too hard and brittle for most uses

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24
Q

What is the purpose of annealing

A

Softens steels and relieves internal stresses

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25
Q

How is the annealing process carried out

A

Heating a steel to 50°F above its upper critical limit and soaking it at this temperature. When the required soak time has been met it is cooled very slowly in a furnace or bath of hot sand

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26
Q

What will the main characteristics of steel be when it has been annealed

A

Very soft and ductile

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27
Q

What is the purpose of normalising

A

When a steel is forged, welded or machined, it will have residual stresses contained within the material. These stresses can lead to structural failure. The process of relieving these stresses is known as normalising

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28
Q

What is the normalising process

A

Heating steel to 100°F above upper critical limit and soaking it for a prescribed amount of time. After soaking the steel is allowed to cool at room temperature. This allows the particles of carbon to precipitate out of the Austenitic structure and relives internal stresses

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29
Q

What is a Eutectoid

A

A metal can exist in more than one form at the same temperature

I.e - Ferrite

  • Austenite
  • Cementite
  • Pearlite
30
Q

What is a Ferrite structure

A

The name given to pure iron. A BCC lattice that will absorb up to 0.2% carbon

31
Q

What is Austenite

A

An FCC form of iron which can absorb a lot of carbon into solid solution (up to approx 2%) than Ferrite

32
Q

What is cementite

A

A chemical compound made up from iron and carbon

33
Q

What is cementite also known as

A

Iron carbide

34
Q

What is pearlite

A

A two phased layered structure composed of alternating layers of alpha-Ferrite(88%) and cementite (12%)

It forms by a eutectoid reaction

35
Q

What are the most important characteristics of CRES

A

Corrosion resistance, strength, toughness and resistance to high temperatures

36
Q

How are stainless steels identified

A

By a 3 digit system (I.e 200 and 300 series)

37
Q

What are 200 and 300 stainless steels known as

A

Austenitic

38
Q

What is 400 series stainless steel known as

A

Martensitic

39
Q

What series of stainless steels are most commonly used

A

300 series called the 18-8 as they contain 18% chromium and 8% Nickel

40
Q

How are stainless steels divided into 3 general groups

A

Based on their structures. Austenitic, Ferritic, Martensitic

41
Q

What are Austenitic stainless steels (200 & 300 series)

A

Chromium Nikel and chromium Nikel manganese alloys

Hardened only by heat treatment

Heat treatment only anneals them

Non magnetic in annealed condition but may be slightly magnetic after cold working

42
Q

What uses to stainless steels have in the aircraft industry

A

Limited uses however can be used for sea water applications as they are resistant to most corrosives

43
Q

What are ferritic stainless steels (400 series)

A

Contains very low carbon

Cannot be hardened by heat treatment and quenching

Can be work hardened/strain hardened

Always magnetic

15-30% chromium

44
Q

What use on aircraft would ferritic stainless steels have

A

Limited to piping and tubing

Excellent corrosion resistance at high temperatures and under sulphide corrosion

45
Q

What are martensitic steels (400 series)

A

Straight chromium alloys that harden intensely if they are allowed to cool rapidly from high temperatures

12-18% chromium, no Nikel

Heat treatable by quench and temper

Used in turbine blades

46
Q

What kind of conditions/uses would martensitic 400 series stainless steels be used for

A

Mild conditions. They will rust in moderate to severe corrosion conditions due to having low chromium content and no Nikel

47
Q

What are the disadvantages of stainless steels

A
  • More difficult to cut
  • Welding more difficult
  • Loose corrosion resistance under high temperatures
  • As it is hard to weld and cut, the technician must be well trained to work with it successfully
48
Q

What are precipitation hardened stainless steels

A
  • Very little carbon
  • 15-17% chromium, 4-7% Nikel
  • Solution heat treated and can be hardened to very high strengths
  • Good corrosion resistance in marine environment
49
Q

What typical uses would precipitation hardened stainless steels have in the aircraft industry

A
  • Airframe applications where high strength and excellent corrosion resistance is required
  • Also used in elevated temperature conditions
  • Very good corrosion resistance in marine environment
50
Q

What are high strength low alloy steels

A

Iron based alloys that can be hardened to very high strengths

180-200ksi usually 4130

51
Q

What is 300m stainless steel used for

A

Landing gear

52
Q

What are the most widely used high strength steels in the aircraft industry

A

4330m heat treated to 220-240ksi

4340m heat treated to 275-300ksi

53
Q

What are 4330m and 4340m steels also known as and why

A

Vacuum remelt steels due to the manufacturing process to obtain superior properties

This process results in increased ductility, fatigue and fracture toughness properties

54
Q

What is hydrogen embrittlement

A

Occurs in particularly ferrous and titanium alloys under sustained loads at stresses far below the actual ultimate tensile stress

55
Q

What percentage of the ultimate tensile strength could steel fail if it has suffered from hydrogen embrittlement

A

As low as 30% it’s ultimate tensile strength

56
Q

Other than sustained loads how would metals suffer from hydrogen embrittlement

A

Can be introduced during processes such as welding and pickling

57
Q

What stainless steels are not affected by hydrogen embrittlement

A

300m and precipitation hardened steels

58
Q

What precautions must be observed when doing reword operations on steel parts

A
  • Stress concentrations
  • Hydrogen embrittlement
  • Untempered martensite
59
Q

When would a stainless steel need a protective surface treatment

A

Only when in contact with light weight alloys

They are coated with

  • Cadmium plating
  • Zinc spraying or chromate passivating

This is to avoid galvanic corrosion of the light weight alloys

60
Q

What types of surface treatment would non stainless steels have

A
  • Cadmium plating with a paint finish
  • Phosphating with a paint finish
  • Aluminium spraying
  • Hard chromium plating
  • Chemical Nikel plating
  • Silver plating (as long as not in contact with aluminium)
61
Q

What is galvanic corrosion

A

A measure of how dissimilar metals will corrode when placed against each other in an assembly.

62
Q

What is case hardening of steel

A

Some steels require a hard durable surface that is suitable for load baring, whilst retaining a tough core

Best suited to low carbon steels

63
Q

What types of metals is case hardening not suitable for

A

Non ferrous metals

64
Q

What is the purpose of carburising

A

Produces a thin layer of high carbon steel on the surface of a low carbon component

65
Q

What are the 3 methods of carburising

A
  • Pack carburising
  • Gas carburising
  • Liquid carburising
66
Q

What is pack carburising

A

Heating the component to temperatures of 1700°f whilst it is packed in to a carbon rich material such as charcoal. The carbon penetrates the surface of the metal causing it to harden

67
Q

What is gas carburising

A

Similar to pack carburising, but utilises the carbon dioxide rich atmosphere within the oven instead of a carbon rich solid

68
Q

What is liquid carburising

A

Works by heating up the metal in a bath of either sodium cyanide or barium cyanide. Either liquid will provide the necessary carbon to surface harden the metal

69
Q

What is flame hardening

A

Heated above upper critical temperature with oxy acetylene torch and immediately quenched with a jet of water supplied by a lance attached to the assembly

70
Q

When can steels only be flame hardened

A

Only on steels with a carbon content of at least 0.4% and only after the steel has been normalised

71
Q

What is induction hardening

A

Similar process to flame hardening except that the whole circumference of the steel is heated simultaneously by an induction coil

The coil heats the steels temperature, after it has reached its required temperature it is quenched

72
Q

What is nitriding

A

Produces an improved surface finish compared to carburising as the component is hardened, tempered and ground to its final dimensions prior to surface hardening

Heating material to 1000°f in an amonia rich environment. The amonia brakes down allowing the nitrogen to penetrate the surface

M6 Mac (11 decks)

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