1. Engineering Materials and Processes Lecture 11 – Iron and steel
Prescribed Text:
Ref 1: Higgins RA & Bolton, Materials for Engineers and Technicians, 5th edition, Butterworth Heinemann. ISBN:
Readings:
Callister: Callister, W. Jr. and Rethwisch, D., 2010, Materials Science and Engineering: An Introduction, 8th Edition, Wiley, New York. ISBN
Ashby 1: Ashby, M. & Jones, D., 2011, Engineering Materials 1: An Introduction to Properties, Applications and Design, 4th edition, Butterworth-Heinemann, Oxford UK. IBSN:
Ashby 2: Ashby, M. & Jones, D., 2011, Engineering Materials 2: An Introduction to Microstructures and Processing, 4th edition, Butterworth-Heinemann, Oxford UK. IBSN:
Lecture (2 hrs):
Ref 1, Ch 1: Engineering materials;
Ref 1 Ch 2: Properties of materials.
Laboratory 1 (2 hrs): Hardness test
Callister: Ch 1, 2, 18-21
Ashby 1: Ch 1, 2
Ashby 2: Ch 1
wikipedia 1

2. Iron and steel Reference Text Section
Higgins RA & Bolton, Materials for Engineers and Technicians, 5th ed, Butterworth Heinemann
Ch 11
Additional Readings
Section
Engineering Materials and Processes

3. Note: This lecture closely follows text (Higgins Ch11)
Iron and steel
Note: This lecture closely follows text (Higgins Ch11)
Engineering Materials and Processes

4. Iron and steel: Intro (Higgins 11.1)
Since the onset of the Industrial Revolution, the material wealth and power of a nation has depended largely upon its ability to make steel.
Every new country ramping up into industrialisation begins by focussing on steel production – Britain and Europe, then US then USSR then Japan and Korea, and the lastest example China…
The last few decades of Asian development have been good for Australia’s mining industry.
Engineering Materials and Processes

5. Iron and steel: Intro (Higgins 11.1)
China now dominates steel production – almost half the world’s production!
Engineering Materials and Processes

6. Smelting (Higgins 11.2)
Blast Furnace turns iron ore to pig iron, which has too much carbon. This is removed in later process such as oxygen process, to make steel.
Steel from Start to Finish (Promo. US)
Steelmaking (UK)
Continuous Casting (More modern system that suits electric arc and recycled steel, but not really suited to blast furnace which is a batch process)
Engineering Materials and Processes

7. Smelting (Higgins 11.2)
Despite research on 'direct reduction' of iron ore, the blast furnace still dominates iron production. The thermal efficiency of the blast-furnace is very high, also helped by injection of oil or pulverised low-cost coal to reduce the amount of expensive metallurgical coke consumed.
A blast furnace runs non-stop for several years (life of the lining) since it is quite a procedure to stop and start it.
However, a typical blast-furnace releases about 6600 tonnes of carbon dioxide every day.
Hebei province accounts for a quarter of the China's total steel production capacity
Engineering Materials and Processes

8. Steel-making (Higgins 11.3)
Converting pig iron to steel is done by oxidation of impurities, so that they form a slag which floats on the surface of the molten steel or are lost as fume.
The Bessemer process 1856 brought steel to the masses. That process is now obsolete. The open-hearth process followed but modern processes are basic oxygen processes (1952) or in the electric-arc furnace.
Corus Steel (UK)
Description of steel making processes
Engineering Materials and Processes

9. Steel-making (Higgins 11.3)
Basic Oxygen Process.
Higgins
Engineering Materials and Processes

10. Steel-making (Higgins 11.3)
Plain-carbon steels: less than 1.7 % C.
Ordinary steels: up to 1.0 % Mn (left over from a deoxidisation process that slightly increases strength and hardness, and reduces sulphur content of the steel.
Both sulphur and phosphorus are extremely harmful impurities which give rise to brittleness in steels. Usually specify max 0.05% S and Ph, and high quality steels no more than 0.04%. (or as low as 0.002% in modern steel for pipelines).
The majority of steel is mild steel and low-carbon steel for
structural work, none of which is heat-treated except for stress relief.
Engineering Materials and Processes

11. Cementite (Higgins )
Ordinarily carbon in steel exists as iron carbide (cementite). Cementite is very hard. So increasing carbon content increases the hardness of the steel.
Cementite is actually an intermetallic compound in steel alloys with the chemical formula Fe3C. This phase has a specific chemical formula, unlike most phases which have ranges of chemical composition. Cementite is hard and brittle.
IMAGE: Journal of Molecular Catalysis A: Chemical Volume 269, Issues 1–2, 18 May 2007, Pages 169–178
Engineering Materials and Processes

12. Carbon in Steel
Engineering Materials and Processes

13. This diagram will meet you again soon (not today).
The Iron-Carbon equilibrium diagram over a very small range of Carbon (0 to 2% by weight, or 0 to 7% by atoms)
This is as much carbon as steel can handle before it turns into cast iron, and then into useless rock.
This diagram will meet you again soon (not today).
Larger version
Engineering Materials and Processes

14. Figure 11.4 The iron-carbon equilibrium diagram.
The small dots in the diagrams depicting structures
containing austenite do not represent visible particles of cementite — they are meant to indicate the
concentration of carbon atoms dissolved in the austenite and in the real microstructures would of course be
invisible. The inset shows the 'peritectic part' of the diagram in greater detail.
Engineering Materials and Processes

15. Steel grain structures
Equilibrium grain structures
Identify:
Ferrite
Cementite
Pearlite
Austenite is not visible in any of these – why not?
watlas.mt.umist.ac.uk/internetmicroscope/micrographs/microstructures.html
Engineering Materials and Processes

16. Eutectoid
Engineering Materials and Processes

17. Iron Carbon Equilibrium Diagram Follow Higgins notes 11.5.1
Teach yourself phase diagrams
Handout
Engineering Materials and Processes

18. 0.4 % C
These then are the main stages in the foregoing process of solidification and cooling of the 0.4 per cent carbon steel:
1 Solidification is complete at Si and the structure consists of uniform austenite.
2 This austenite begins to transform to ferrite at Ui, the upper critical temperature of this steel (about 825°C).
3 At 723°C (the lower critical temperature of all steels), formation of primary ferrite ceases, and, as the austenite is now saturated with carbon, the eutectoid pearlite is produced as alternate layers of ferrite and cementite.
4 Below 723°C, there is no further significant change in the structure.
Engineering Materials and Processes

19. Hyper Eutectic
Engineering Materials and Processes

20. Carbon vs Properties
Figure 11.8 A diagram showing the relationship between carbon
content, mechanical properties, and uses of plain-carbon steels which
have been slowly cooled from above their upper critical temperatures.
Engineering Materials and Processes

21. Normalising (Higgins 11.6.1)
The main purpose in normalising is to obtain a structure which is
uniform throughout the work-piece, and which is free of any 'locked-up'
stresses.
Read Higgins
Engineering Materials and Processes

22. Normalising (Higgins 11.6.1) Larger version
Engineering Materials and Processes

23. Annealing (Higgins 11.6.2) Three types of annealing:
Type 1: Annealing of castings
Same as normalising but slower cooling (controlled in furnace) to prevent cracking.
Engineering Materials and Processes

24. Annealing (Higgins 11.6.2) Type 2: Spheroidisation annealing
An annealing process which is applied to high carbon steels in order to improve their machinability and, in some cases, to help with cold-drawing.
Engineering Materials and Processes

25. Annealing (Higgins 11.6.2) Type 3: Annealing of cold-worked steel
Recrystallisation of distorted ferrite grains to restore ductility (e.g. to allow further cold working processes).
Engineering Materials and Processes

26. Annealing (Higgins 11.6.2) Summary of ranges on the Fe-C diagram.
Engineering Materials and Processes

27. Brittle Fracture in Steels (Higgins 11.7)
Ferrite is very susceptible to brittle fracture at low temperatures, especially below the transition temperature.
This transition temperature can be depressed to a safe limit by increasing the manganese content to about 1.3%.
For use at even lower temperatures, it is better to use a low-nickel steel.
Engineering Materials and Processes

28. Online Resources. Teach yourself phase diagrams Handout
Scale of material structure
Wikipedia: Steel Production
h ttp://
S how this website on screen. Will be using this later.
Engineering Materials and Processes 28

29. Spheroidisation annealing Work-hardened annealing
GLOSSARY
Smelting
Pig Iron
Basic Oxygen Process
Blast Furnace
Electric arc furnace
Ferrite
Cementite
Austenite
Pearlite
Eutectic
Eutectoid
UCT
LCT
Hypo eutectoid
Hyper eutectoid
Normalising
Annealing
Spheroidisation annealing
Work-hardened annealing
Brittle fracture transition temperature
Engineering Materials and Processes 29

30. Define all the glossary terms.
QUESTIONS
Moodle XML: Some questions in Steel
Define all the glossary terms.
Give at least 4 reasons why iron is by far the most important metal to man.
Explain how carbon atoms join the iron structure in equilibrium conditions of solidification. Give the chemical name and the metallurgical name for this structure. Is this structure substitutional, interstitial or intermetallic? Which is the solute and solvent element? Is this non, complete or partial solubility?
Describe the cooling of a hypo-eutectoid iron-carbon mixture under equilibrium conditions. What differences are there with a hyper-eutectoid steel?
In the Fe-C thermal equilibrium diagram, identify the a b g and d phases. Which phases exist at room temperature. At what temperatures do the others exist? Explain why the d phase gets very little mention.
What is the main difference in the process of normalising of a forging vs annealing of a casting?
What is the main difference in the process of annealing rolled sheet vs annealing of a casting?
Identify Ferrite, Cementite and Pearlite in photomicrographs.
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