Metals

Question 1

2 main categories of metal

Answer 1

1. Ferrous, these are mainly iron

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

Question 2

What are the main structural metals

Answer 2

Steel and aluminium alloys

Question 3

What does iron ore contain

Answer 3

• Iron Oxides
• Earthy Impurities
• Manganese, silicon, phosphorus and sulphur

Question 4

How is iron ore reduced

Answer 4

Reduction is removing the oxygen by heating

iron oxide + carbon = Iron + oxide of carbon

Question 5

Properties of wrought iron

Answer 5

• 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

Question 6

What is wrought iron

Answer 6

Iron alloy with low carbon content and contains fibrous slag

Question 7

What is pig iron

Answer 7

Crude iron made by smelting iron ores, high carbon content

Question 8

2 main ways steel is produced

Answer 8

1. Basic Oxygen Process

2. Electric Arc Furnace

Question 9

Describe the basic oxygen process

Answer 9

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

Question 10

Describe the electric arc furnace process

Answer 10

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

Question 11

2 types of casting steel

Answer 11

1. Ingot Casting

2. Continuous Casting

Question 12

describe ingot casting

Answer 12

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

Question 13

Describe continuous casting

Answer 13

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

Question 14

What is steel

Answer 14

An alloy of iron and carbon

Question 15

What is ferrite and what are its properties

Answer 15

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

Question 16

What is cementite and its properties

Answer 16

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

Question 17

What is pearlite and its properties

Answer 17

• 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%

Question 18

What is toughness

Answer 18

-The ability to absorb energy under load

Resistance to brittle failure

Question 19

What is notch toughness

Answer 19

The ability to cope with a notch or crack

Question 20

What is impact resistance

Answer 20

Toughness under high strain rate loading

Question 21

Properties of low-alloy constructional steels

Answer 21

• 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

Question 22

Properties of weather resistant steels

Answer 22

• 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

Question 23

Properties of stainless steel

Answer 23

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

Question 24

What is welding

Answer 24

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

Question 25

What effect does increasing carbon content in steel have

Answer 25

- Increase of strength - Loss of ductility - Greater susceptibility to heat treatment

Question 26

Properties of aluminium

Answer 26

- Good electrical and thermal conductivity | - In its pure form its not strong enough for structural use

Question 27

Comparison of aluminium and steel

Answer 27

- 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

Question 28

Properties of lead

Answer 28

- Good durability and ease of working - Densest common metal - Low melting point - High thermal movement - Prone to creep

Question 29

Properties of copper

Answer 29

- Noblest metal commonly used - High corrosion resistance - When alloyed with zinc, forms brasses - When alloyed with tin forms bronze

Question 30

What is corrosion

Answer 30

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

Question 31

How to protect metals from corrosion

Answer 31

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

Question 32

2 ways of creating cathodic protection

Answer 32

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

Question 33

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

Answer 33

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

Question 34

Which electrode does corrosion occur on

Answer 34

Anode

Question 35

Which way is electron flow in corrosion

Answer 35

Always from anode to cathode

Question 36

What is the carbon content of structural mild steel

Answer 36

0.05-0.25%