1. STEEL
PAT 204

2. IRON VS STEEL
A few definitions and general descriptions are in order „
Iron: Iron is an element and can be pure. „
Cast iron: Iron that contains about as much carbon as it can hold which is about 4%. „
Wrought iron: Iron that contains glassy inclusions. „
Steel: Iron with a bit of carbon in it— generally less than 1%.
Pig iron: Raw iron, the immediate product of smelting iron ore with coke and limestone in a blast furnace. Pig iron has a very high carbon content, typically 4-5%, which makes it very brittle and not very useful directly as a material.

3. Product example Cast Iron product Wrought iron product
Pig iron – raw iron

4. Product example
Steel products

5. Introduction to Steel
Alloy steel: A generic term for steels which are alloyed with elements other than carbon.
Why alloys? The mechanical behavior iron is changed hugely by the addition of carbon and other additives (or alloys).

6. Steel manufacturing process

7. Steel manufacturing process
All constructional steel are hot rolled. These steel are heated to temperature of oC to make them soft enough to deform and shape
Primary process
Secondary process
Mechanical forming process
used to convert ingot or continuously cast materials into the shapes and sizes required
adjust the carbon and manganese contents to give the grade of steel required, because with carbon it will improves strength and manganese gives low temperature toughness.
by hot rolling or
cold rolling.
Deoxidization of the metal
adding manganese and silicon, which react with dissolved oxygen to form insoluble particles of oxide
It is mainly for light weight sections
refers to the refining processes used to produce liquid steel
The aim is to produce a melt of the required composition
refining process used for example, the Bessemer / Thomas process, the open-hearth (Siemens) process, the basic oxygen process and electric arc steelmaking.

8. Steel product- grade of steel

9. Steel product- grade of steel

10. Steel product- grade of steel

11. Rolled and Formed Sections
very efficient compression members in lattice girders, in building frames, for purlins, sheeting rails, etc.
very efficient compression members in lattice girders, in building frames, for purlins, sheeting rails, etc.
very efficient compression members in lattice girders, in building frames, for purlins, sheeting rails, etc.
Common types of structural steel hot-rolled section as stipulated in British Standard BS 4848 which are used in construction
Rolled and Formed Sections
Compound Sections
Built-up sections
Cold-rolled Sections

12. very efficient compression members in lattice girders, in building frames, for purlins, sheeting rails, etc.
very efficient compression members in lattice girders, in building frames, for purlins, sheeting rails, etc.
very efficient compression members in lattice girders, in building frames, for purlins, sheeting rails, etc.
Common types of structural steel hot-rolled section as stipulated in British Standard BS 4848 which are used in construction
These are very efficient sections for resisting bending moment about the major axis.
Rolled and Formed Sections
Universal beam, UB
Universal columns, UC
Channels, C
Equal and unequal angles, L
Structure tees, T
Circular, square and rectangular hollow sections, CHS, SHS, RHS
very efficient compression members in lattice girders, in building frames, for purlins, sheeting rails, etc.
These are sections produced primarily to resist axial in high radius of gyration about the minor axis to prevent buckling that plane.
produced by cutting a universal beam or column into two parts. Tees are used for truss members, ties and light beams.
used for beams, bracing members, truss members and in compound members.
used for bracing members, truss members and for purlins and sheeting rails

14. Compound Sections Compound sections are formed by the following means
Strengthening a rolled section such as a universal beam by welding on cover plates
Combining two separate rolled sections, as in the case of the crane girder. The two members carry loads from separate directions.
Connecting two members together to from a strong combined member. Examples are the laced and battened members.

15. Built-up sections
Built-up sections are made by welding plates together to form I, H or box members which are formed plate girders, built -up columns box- girders or columns, respectively. These members are used where heavy loads have to be carried and in the case of plate and box girders where long spans may be required.

16. Cold-rolled Sections
Thin steel plates can be formed into a wide range of sections by cold rolling. The most important uses for cold-rolled sections in steel structures are for purlins and sheeting rails.

17. Reinforcement in Concrete
Concrete has low tensile and bending strengths and higher compressive strength. Therefore steel reinforcement is used to overcome the deficiencies in tensile and bending strength. Steel must have adequate tensile properties and form strong bondage to transmit loads to steel.

18. Reinforcement in Concrete

19. Prestressing Steel
Prestressing steels (tendons) are produced in the form of wire and strand to BS 5896:1980 or of bar to BS 4486: Steel for prestressing material may be made by any process except the air and mixed air/oxygen blown processes. The cast analysis must not show more than 0.040% sulphur or 0.040% phosphorus.
Prestressing steel (stand) has range of tensile properties of characteristic strength between 1570 and 1860 N/mm2 and maximum relaxation of % for initial stress equal to 70% of characteristic strength.
Prestressing steels are used in construction of bridges, buildings, stadium and others

20. Wires Strand Bars Prestressing Steel
Wire made to BS 5896:1980 is made by cold drawn with high carbon content steel rod through a series of reducing dies. The wire may be crimped mechanically or have the surface indented to improve bond when used in short units.
Wires
Seven-wire strand made to BS 5896: 1980 is made by spinning six cold drawn wires in helical form round a slightly larger straight central wire. The strand is then stress-relieved or 'hot stretched’. Die-drawn strand is made by drawing a seven-wire strand through a die under controlled tension and temperature for low relaxation quality control than single wire of same nominal diameter.
Strand
Prestressing bars to BS 448 6: 1988 are made by hot rolling microalloyed steel s under controlled conditions and then stretching them in a controlled manner at about 90% of their characteristic strength. Bars may be plain or deformed with a maximum length of 18m. The prepared ends are threaded by cold rolling and bars can be joined end to end by couplers.
Bars

22. A Selection of Mechanical Properties (from Gordon (1979))

23. Thermal Expansion of Various Materials (from CISPI (1994))

24. Structural steel vs reinforcement steel
Types of steel used in construction
†Structural steel—plates, bars, pipes, structural shapes. †
Reinforcing steel—concrete reinforcement. †
Miscellaneous shapes for applications such as forms.

26. Example of a local manufacturer

27. STEEL PRODUCT - High Tensile Steels Bolt.
Bolt should have adequate tensile strength and toughness and should not slacken owing to relaxation at elevated temperature. Fatigue strength is also required especially for structures subjected to varying stress example by tidal water.
2 types of bolt
Ordinary bolts in clearance holes
High Strength Friction Grip Bolts
consist of ' black' hexagon head bolt, nuts and washers
Grade 4.6:
Mild Steel: Yield Stress = 235 N/mm2
Grade 8.8:
High-Strength Steel: Yield stress = 627 N/mm2
High strength friction grip bolts are used extensively for field connections. There is no slip or movement between the connected parts; hence this type of joints is useful where rigid connections are required.

28. Properties of steel –advantages & disadvantages
great importance for long-span bridges, tall buildings, and for structures having poor foundation conditions
advantages
High Strength
Uniformity
Elasticity
Permanence
Ductility
Ability to be fastened "together by several simple connection device including welds, bolts and rivets.
Adaptation to prefabrication.
Toughness and fatigue strength.
Ability to be rolled into a wide variety of sizes and shapes.
Possible reuse after a structure is disassembled
Weldability
The properties of steel do not change appreciably with time as do these of a reinforced concrete structure
Steel behaves closer to design assumptions than most materials because it follows Hooke’s Law up to fairly high stresses.
Steel frames that are properly maintained will last indefinitely
The property of a material by which can withstand extensive deformation without failure under high tensile stresses

29. Properties of steel –advantages & disadvantages
Most steels are susceptible to corrosion when freely exposed to air and water and must therefore be periodically painted
Disadvantages
Maintenance costs
Fire proofing costs
Susceptibility to Buckling
Fatigue
Corrosion
Deterioration of metals which results by inherent surface instability.
Causes:
Oxidation
Acidic & electrolyticcorrosion
Steel is an excellent heat conductor such that non- fire proofed steel members
Prevention of corrosion - coatings
The longer and slender compression members will result the greater the danger of buckling. Steel has a high strength per unit weight and when used as steel columns, it is sometimes not very economical because considerable material has to be used merely to stiffen the columns against buckling.
its strength may be reduced if it is subjected to a large number of stress reversal or even to a large number of variations of stress of the same character (i.e. tension or compression)

30. Stainless steel
is a steel alloy with a minimum of 10.5% chromium content by mass.
not readily corrode, rust or stain with water as ordinary steel does. However, it is not fully stain-proof in low-oxygen, high-salinity, or poor air-circulation environments
Stainless steel is used where both the properties of steel and corrosion resistance are required.

31. Type of stainless steel
The main alloying element is chromium, with contents typically between 11 and 17%
yield strengths in the range of 275 to 350 MPa.
The main disadvantages of the ferritics are:
Limited toughness - Not acceptable for sub zero temperatures
lower ductility
Weldability - Rapid grain growth in thick sections (greater than about 3mm) leads to poor weld toughness . 
Type of stainless steel
Feritic
Austenitic
Martensitic
Duplex 
Precipitation hardening (PH)
addition of Nickel, Manganese and Nitrogen
18% chromium , 11% nickel
weldability and formability
1. Formability is the ability of a given metal workpiece to undergo plastic deformation without being damaged
similar to ferritic steels in being based on Chromium but have higher Carbon levels up as high as 1%. This allows them to be hardened and tempered much like carbon and low-alloy steels. They are used where high strength and moderate corrosion resistance is required. They are more common in long products than in sheet and plate form. They have generally low weldability and formability. They are magnetic.

32. Type of stainless steel Feritic
These steels can develop very high strength by adding elements such as Copper, Niobium and Aluminium to the steel.
With a suitable “aging” heat treatment, very fine particles form in the matrix of the steel which imparts strength.
These steels can be machined to quite intricate shapes requiring good tolerances before the final aging treatment as there is minimal distortion from the final treatment. This is in contrast to conventional hardening and tempering in martensitic steels where distortion is more of a problem.
Type of stainless steel
Feritic
Austenitic
Martensitic
Duplex 
Precipitation hardening (PH)
These steels have approximately 50% ferritic and 50% austenitic.
This gives them a higher strength than either ferritic or austenitic steels.
They are resistant to stress corrosion cracking.
They are weldable but need care in selection of welding consumables and heat input.
They have moderate formability.
They are magnetic but not so much as the ferritic, martensitic and PH grades due to the 50% austenitic phase.
1. Formability is the ability of a given metal workpiece to undergo plastic deformation without being damaged

33. STEEL TENSILE TEST
Mechanical test for steel include tension, bending, hardness and impact. For structural steel and reinforcement steel the tension or tensile test is the most important
The typical tensile test specimen is a 12 mm diameter cylinder machined to a smooth or reinforcement bar that has accurate circular cross section. The specimen is clamped at each end or threaded into a testing machine that applies an axial pull at a uniformly increasing rate until the specimen breaks. As the pulling proceeds, the force is constantly indicated in digits or by a dial on the machine. Tensile stress is calculated by dividing the force by the original cross sectional area.
Stress and strain are determined at regular intervals from readings of force and the measured increase in distance between the marks. A curve of stress versus strain is plotted to determine whatever information is desired. The yield stress and rupture stress are often specified as lower limits for acceptance of steel

34. Tensile test machine

35. Typical stress- strain curve
Stress is a measure of the internal force an object is experiencing per unit cross sectional area. Hence, the formula for calculating stress is the same as the formula for calculating pressure:
The (ultimate) tensile strength is the level of stress at which a material will fracture. Tensile strength is also known as fracture stress. If a material fractures by 'crack propagation' (i.e., it shatters), the material is brittle.
yield stress is the level of stress at which a material will deform permanently. This is also known as yield strength.
Strain is a measure of how much an object is being stretched
Young's Modulus is a measure of the stiffness of a material. It states how much a material will stretch (i.e., how much strain it will undergo) as a result of a given amount of stress. 

36. Typical stress- strain curve
Point A: At origin, there is no initial stress or strain in the test piece. Up to point A Hooke's Law is obeyed according to which stress is directly proportional to strain. That's why the point A is also known as proportional limit. This straight line region is known as elastic region and the material can regain its original shape after removal of load.  Point B: The portion of the curve between AB is not a straight line and strain increases faster than stress at all points on the curve beyond point A. Point B is the point after which any continuous stress results in permanent, or inelastic deformation. Thus, point B is known as the elastic limit or yield point.  Point C & D: Beyond the point B, the material goes to the plastic stage till the point C is reached. At this point the cross- sectional area of the material starts decreasing and the stress decreases to point D. At point D the workpiece changes its length with a little or without any increase in stress up to point E.  Point E: Point E indicates the location of the value of the ultimate stress. The portion DE is called the yielding of the material at constant stress. From point E onwards, the strength of the material increases and requires more stress for deformation, until point F is reached.  Point F: A material is considered to have completely failed once it reaches the ultimate stress. The point of fracture, or the actual tearing of the material, does not occur until point F. The point F is also called ultimate point or fracture point.

38. TUTORIAL
Based on the previous graph, discuss the stress- strain for the 3 stated material. Why they have different curve.
Submit your tutorial on 24th November 2016