Steel

Question 1

What are the two main types of steel used in construction?

Answer 1

1) Structural steel

2) Rebar Steel for reinforcement

Question 2

What does S275 mean?

Answer 2

Structural steel with fy = 275MPa.

Question 3

How many possible levels of ductility are there?

Answer 3

A, B and C in ascending order where class B is rebar steel.

Question 4

What is steel in construction composed of?

Answer 4

plain-carbon steel with low carbon contents of <0.3%.

Question 5

What does structural steel favour?

Answer 5

Ductility over strength therefore has lower carbon content.

Question 6

What does steel reinforcement favour?

Answer 6

Strength over ductility therefore has higher carbon content.

Question 7

How do we get the iron that is required to make steel?

Answer 7

iron is not found as a pure metal, we find minerals rich in iron oxide and then split this from the rest of the minerals and separate the iron from the oxygen.

Question 8

What is the primary processing of steel?

Answer 8

From iron to steel

Question 9

What is the secondary processing of steel?

Answer 9

Smelting which is separating the metal from the ore.

Question 10

What does smelting require? (2)

Answer 10

1) Separation of the oxide from the rest

2) High temperature and carbon, to steal oxygens away (reduction reaction).

Question 11

Why are smelting and melting iron not easy?

Answer 11

Due to the very high temperature required.

Question 12

What is equipment is able to achieve steel at high temperatures?

Answer 12

Blast Furnace

Question 13

Describe the blast furnace process.

Answer 13

Lots of coke and blasted in air. Temperature is sufficient to melt iron ore. Coke provides the carbon to remove the oxygen from the oxide. Liquid slag floats over heavier liquid iron, therefore, easier to separate. Limestone provides additional carbon and Ca to bind with the slag, resulting in pig iron which has 5% carbon there cannot be called steel. Convert pig iron to steel, removing the carbon.

Question 14

What was the Bessemer process?

Answer 14

Blowing pure oxygen instead of ai this was called basic oxygen steelmaking BOS process.

Question 15

What is hot rolling?

Answer 15

Used to produce universal beams and columns. Steel is heated to 1200 degrees C but cools during rolling to around 750 degrees C.

Question 16

What is cold rolling?

Answer 16

Higher-strength- lower ductility, lightweight sections. Large deformation to the grains therefore causes strain hardening. Often used for purlins and facade elements.

Question 17

What is the percentage of recycled structural steel and reinforcement steel for concrete?

Answer 17

60% for structural and 100% for reinforcement.

Question 18

How do we achieve a yield strength of 500N/mm^2?

Answer 18

1) Micros-alloying
2) Quenching and self-tempering
3) Cold rolling
4) Ribs are required to help bond concrete.

Question 19

How can we join different profiles together?

Answer 19

bolt knots, rivets or pins.

Question 20

What type of connections are rivets?

Answer 20

Permanent mechanical connections

Question 21

What are the pins?

Answer 21

Smooth bar allowing for rotation.

Question 22

What is welding?

Answer 22

Joining two metal parts together by supplying heat to them.

Question 23

How can heat for welding be supplied?

Answer 23

1) Oxygen acetylene flame e.g. gas welding
2) Electric arc e.g. arc welding and stud welding
3) resistance to the passage of current.

Question 24

What is the most common type of welding?

Answer 24

Arc welding

Question 25

Name 3 different types of arc welding?

Answer 25

1) Shielded metal arc
2) Metal active gas
3) SAW

Question 26

What does having gas over the welded area avoid?

Answer 26

Oxidation

Question 27

What is stud welding?

Answer 27

Used to attach shear studs to metal decking/steel beams. An arc is struck between the stud and the metal plate, the stud and plate are brought together under pressure and weld forms.

Question 28

What happens to a metal’s strength as temperature increases?

Answer 28

Decreases

Question 29

What temperature is considered to be failure temperature for mild steel?

Answer 29

550 degrees C.

Question 30

How can we prevent failure in fires?

Answer 30

Metals used in construction have to be insulated from high temperatures.

Question 31

What metals fail and don’t at low temperatures due to brittle fracture?

Answer 31

Steel but not aluminium.

Question 32

What does the Charpy impact test do?

Answer 32

Identify at what temperatures this transition to brittle failure occurs.

Question 33

What makes steel corrode, two main ingredients?

Answer 33

Water and oxygen

Question 34

What also impacts corrosion?

Answer 34

Atmospheric pollution and micro-climate.

Question 35

How can steel surface be prepared to make sure no rust or contaminants are on it?

Answer 35

1) Abrasive blasting- 100% effective
2) Ultra high-pressure water jetting.
3) Acid pickling- 100% effective

Question 36

What is hot-dip galvanising steel?

Answer 36

Where steel is dipped into molten zinc at approx 450 degrees C.

Question 37

Is coating steel expensive?

Answer 37

Very expensive

Question 38

What is an alternative to coating?

Answer 38

Change the composition of the steel:
1) COR-TEN forms a hard protective oxide film (patina). 2) Stainless steel (inox) has at least 10.5% Chromium forming passive oil in the air which is anodic.

Question 39

What has a lower electrode potential?

Answer 39

The anode therefore that will corrode first.