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CVA106 > Metals > Flashcards

Metals Flashcards

1
Q

2 main categories of metal

A
  1. Ferrous, these are mainly iron

2. Non- Ferrous, contain no or only very small traces of iron

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2
Q

What are the main structural metals

A

Steel and aluminium alloys

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3
Q

What does iron ore contain

A
  • Iron Oxides
  • Earthy Impurities
  • Manganese, silicon, phosphorus and sulphur
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4
Q

How is iron ore reduced

A

Reduction is removing the oxygen by heating

iron oxide + carbon = Iron + oxide of carbon

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5
Q

Properties of wrought iron

A
  • Resists corrosion better than steel
  • Ductile and resists shock loads
  • Can’t be strengthened by heat treatment due to lack of carbon and therefore it is mainly used for ornamental ironwork and sometimes chains
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6
Q

What is wrought iron

A

Iron alloy with low carbon content and contains fibrous slag

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7
Q

What is pig iron

A

Crude iron made by smelting iron ores, high carbon content

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8
Q

2 main ways steel is produced

A
  1. Basic Oxygen Process

2. Electric Arc Furnace

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9
Q

Describe the basic oxygen process

A
  1. Molten pig iron is converted into steel with the action of oxygen being blown into the melt
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10
Q

Describe the electric arc furnace process

A
  1. Only uses scrap metal
  2. graphite electrodes provide an electric current creates an arc between the electrodes
  3. Heat melts the charge
  4. Mainly used for alloys, stainless, special carbon and low-alloy grades
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11
Q

2 types of casting steel

A
  1. Ingot Casting

2. Continuous Casting

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12
Q

describe ingot casting

A
  1. Steel from furnaces is poured into moulds to form ingots

2. Ingots are placed in soaking pits to bring them to uniform temperature before being rolled into blooms

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13
Q

Describe continuous casting

A
  1. Molten steel is poured into the reservoir of a casting machine
  2. It leaves the reservoir through water cooled copper moulds
  3. The outer surface solidifies and the steel is drawn downwards through a system of rollers and water sprays to emerge as solid steel
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14
Q

What is steel

A

An alloy of iron and carbon

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15
Q

What is ferrite and what are its properties

A

Almost pure iron, is soft, tough and ductile. Slip of atomic layers occurs easily

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16
Q

What is cementite and its properties

A

Intensely hard and brittle
Carbon content is 6.67%
Undesirable in steel in any significant amount

17
Q

What is pearlite and its properties

A
  • Layers of ferrite and cementite
  • stronger and less ductile than pure ferrite because of the mechanical interference between the layers
  • Carbon content is 0.85%
18
Q

What is toughness

A

-The ability to absorb energy under load

Resistance to brittle failure

19
Q

What is notch toughness

A

The ability to cope with a notch or crack

20
Q

What is impact resistance

A

Toughness under high strain rate loading

21
Q

Properties of low-alloy constructional steels

A
  • Usually contain less carbon and more manganese
  • Total alloy content is 3-4%
  • Better than mild steel in impact strength, static strength and corrosion resistance
22
Q

Properties of weather resistant steels

A
  • Contain more phosphorous, plus chromium and copper
  • The layer is non porous and the corrosion rate slows to make the steel self-protecting
  • The layer doesn’t form in continuously wet or high chlorine or sulphur dioxide conditions
23
Q

Properties of stainless steel

A
  • A protective chromium oxide film forms in the presence of oxygen
  • Corrosion resistance enhanced by the addition of nickel
24
Q

What is welding

A

Joining 2 pieces of metal by melting, adding filler metal and cooling to solid

25
Q

What effect does increasing carbon content in steel have

A
  • Increase of strength
  • Loss of ductility
  • Greater susceptibility to heat treatment
26
Q

Properties of aluminium

A
  • Good electrical and thermal conductivity

- In its pure form its not strong enough for structural use

27
Q

Comparison of aluminium and steel

A
  • Aluminium doesn’t have a yield platform like steel
  • The strength weight ratio of aluminium is about 3 times that of steel
  • Cost of aluminium is much higher
28
Q

Properties of lead

A
  • Good durability and ease of working
  • Densest common metal
  • Low melting point
  • High thermal movement
  • Prone to creep
29
Q

Properties of copper

A
  • Noblest metal commonly used
  • High corrosion resistance
  • When alloyed with zinc, forms brasses
  • When alloyed with tin forms bronze
30
Q

What is corrosion

A

A reaction between a metal and its environment which results in the metal being converted to an oxide or metal atoms being removed as ions

31
Q

How to protect metals from corrosion

A
  1. Detailing, prevent traps for dirt into which water can run
  2. Impervious coating, paints keep out water
  3. Cathodic Protection, make to member to be protected the cathode
  4. Impresses Current Protection, make the metal part of an electric circuit. This provides electrons to prevent corrosion
  5. Passivation, steel in an alkaline environment doesn’t corrode. so reinforcement in concrete is protected
32
Q

2 ways of creating cathodic protection

A
  1. Sacrificial Anode: this must be wired to the cathode to allow electrons to flow externally. Anodes must be sufficiently close together to overcome voltage drops along the cathode as current flows. Zinc, aluminium and magnesium are often used
  2. Metal Coating: If the coating is scratched a cell is set up by water at the scratch, but only the metal coating corrodes. Zinc or aluminium are used
33
Q

When oxidation occurs at the surface of the metal during corrosion what factors effect the behaviour of the metal and oxide

A
  1. Relative Stability: If large amounts of energy are given out when the oxide is formed it is stable
  2. Physical Properties of the oxide layer: if the metal ion is smaller than the metal atom the metal shrinks on oxidation and the oxide film is in tension, therefore oxygen can pass through and corrosion continues. If the ion is larger the oxide film is in compression and the passage of oxygen slows eventually stopping
  3. Temperature: As temperature increases so does ion mobility and the rate of corrosion
  4. Alloying elements: Alloys can produce a protective film at the surface of the metal which will inhibit corrosion
34
Q

Which electrode does corrosion occur on

A

Anode

35
Q

Which way is electron flow in corrosion

A

Always from anode to cathode

36
Q

What is the carbon content of structural mild steel

A

0.05-0.25%

CVA106 (9 decks)

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