Story of steel …..!!

Presented by

H.M.A.Mahzuz

WHERE IS IRON ORE MINED?

• Iron ore can be found all over the world, in the form of rocks and other minerals. To be economically viable for mining, iron ore must contain at least 20% iron.

• Magnetite ore has the highest proportion of iron, at 65%.

• Haematite ore also has a high content of iron at 60%.

• All iron ore contains ferric oxide and it is from this that iron is extracted. Approximately two billion tonnes of iron ore are mined each year.

The pictogram/ graph below, shows the world distribution of iron ore mining. China, Australia and Brazil dominate this world trade.

https://en.wikipedia.org/wiki/List_of_countries_by_iron_ore_production

Common forms of steel

1) Rebar (short for reinforcing bar), also known as reinforcing steel, reinforcement steel, is a steel bar or mesh of steel wires used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and hold the concrete in tension. Rebar's surface is often patterned to form a better bond with the concrete.

The Rebar Sizes

http://www.harrissupplysolutions.com/steel-rebar-sizes-stock.html

Physical view of different rebars

• http://www.constructionknowledge.net/metal/metal_structural_steel.php

2) Rolled section

3) Screw/ nut/bolt

Why steel is extensively with concrete?

Fig 1:

Concrete

and Steel

stress-

strain

curves

1) Steel can offer tremendous stress at almost similar strain of concrete up to 60% of fc’.

2) Steel has a thermal expansion coefficient nearly equal to that of concrete.

Rebar Grades

• Rebar is available in grades and specifications that vary in yield strength, ultimate tensile strength, chemical composition, and percentage of elongation.

• The grade designation is equal to the minimum yield strength of the bar in ksi (1000 psi) for example grade 60 rebar has a minimum yield strength of 60 ksi. Rebar is typically manufactured in grades 40, 60, and 75.

• In countries that use the metric system, the grade designation is typically the yield strength in megapascals (MPa), for example grade 400 (similar to Grade 60).

Steelmaking Process: • The process of making a semi-product, a Square Billet,

includes melting steel scrap to remove impurities and casting the Square Billets through adjustment of chemical composition.

STEP 1 Charging Steel Scrap into the Electric Furnace

STEP 2 Electric Furnace (Smelting)

STEP 3 Refining

STEP 4 Continuous Casting

STEP 5 Transfer

STEP 1 Charging Steel Scrap into the Electric Furnace

• Steel scrap is considered one of the most important resources which accounts for more than about 70 percent of the manufacturing costs of steel products in steelmaking process.

• Manufacturing complains are striving for the stable supply and management of steel scrap, and carrying out strict inspections throughout the entire process from sourcing to charging into the furnace in order to generate high-quality steel products.

STEP 2 Electric Furnace (Smelting)

• The electric furnace stage is called a smelting process of melting steel scrap into molten metal. An electric furnace uses electricity (or fuel) to heat steel scrap. Depending on heating methods, it is divided into arc-type furnaces and DC (direct current)-based furnaces.

STEP 3 Refining• The ladle serves to increase the temperature of

the molten metal transported from the electric furnace and adjust the composition of five chemical properties of steel including C, Mn, Si, P and S in accordance with the related regulations. The properties and temperature of steel are significant factors to decide the quality and shapes of steel. Molten steel temperature reaches at between 1,550 and 1,600 °C.

STEP 4 Continuous Casting

• This is a process of making the ladle-refined steel into billets. Throughout the continuous casting, the steel that has so far remained liquid is solidified into a shape. The semi-finished billet is utilized to produce a wide range of products after various processes.

STEP 5 Transfer

• Billets made in the continuous casting process are fed into the mill through an automatic transfer system.

What is Billet??

• Billet is simply a "bar of metal”. In general, semi-finished solid metal form, generally having a cross-section of 105 to 230 cm2 (4-6 square in2), and rolled into finished 'long products' such as bars, channels, and rods.

• Billet is piece of raw steel, before it is shaped into a finished product. Billets are malleable and ductile, which allows to give them the specific shapes and properties desired.

• Steel billets are not practical for use in products until they have been processed into more functional shapes. A billet is the first shape that steel takes after it has been forged or rolled for the first time, usually a bar or rectangle.

• Billets, compared with more processed steel, have distinct characteristics. They require a specific grain structure that is easy to manipulate, and are malleable and ductile. Before they are sold, billets undergo a number of heating and cooling tests. If cracks or fractures develop, they are rejected, because they will be useless for further processing.

• Billets became popular in the early 1800s, when British and American entrepreneurs produced bronze and brass billets. The production of bronze and brass billets would become a major industry. These billets were almost always shipped to Britain for further processing.

• Bangladesh imports Billet to produce rebar.

Rolling ProcessIn the rolling process, the Square Billets are reheated and processed to the desired standards and shapes that suit best for customers.

STEP 2 RollingSTEP 1 Reheat Furnace STEP 3 ACooling Bed (Ordinary Rebar)

STEP 4 Sawing (Ordinary Rebar)

STEP 5 Inspection and Packaging

STEP 1 Reheat Furnace

• In the reheat furnace, the Square Billets at room temperature of 20 to 30 °C transferred from the steelmaking process are reheated to up to 1,050 to 1,150 °C so that they become soft enough to be lengthened to the desired thickness and length.

STEP 2Rolling

• The Square Billets extracted from the reheat furnace is passed through about 22 stands comprising of roughing stands, intermediate stands and finishing stands to form shapes of steel bars. With a 6-meter Square Billet, an up to 1.4-kilometer long, 10-milimeter wide rebar is manufactured.

STEP 3-ACooling Bed (Ordinary Rebar)

• On the cooling bed, the Square Billets passed through the rolling mill are cooled down. The walking beam cooling bed system allows them to cool down by air flow created on all sides and move to the sawing machine.

STEP 4Sawing (Ordinary Rebar)

• After the stringent quality test, the products transported from the cooling bed are cut to the lengths desired by customers and packed by bundle through an automated machine. The packed products go through the identification process in which rebars are color coded according to their specific grade and are sent to end users.

STEP 5 Inspection and Packaging

• The coiled rebars are bent after going through a rigorous quality test and a variety of inspections and are sent to customers with a product tag attached.

Types of scrap

Types of scrap

What is furnace

• A furnace is a device used for high-temperature heating. Iron ore or scrap areburnt here to have pure iron.

Types of furnace

• 1) Blast furnace (oil/ gas/ coke base)

• 2) Electric arc furnace

Blast furnace

- Use iron ore and coke as main fuel and sources of energy.

- Melt iron ore and coke to produce pig iron high in carbon content which is fed into a converter to remove. impurities, manufacturing the desired products after the adjustment of metal properties.

- Need a high investment in facility development and take up a large area.

- Produce a large amount of pig iron for a longer period of time.- Make it easy to produce clean steel containing less impurities.- Emit a large amount of carbon dioxide, creating

environmental issues.

Pig iron

• Pig iron is the intermediate product of smelting iron ore. It is the molten iron from the blast furnace, which is a large and cylinder-shaped furnace charged with iron ore, coke, and limestone. Charcoal and anthracitehave also been used as fuel. Pig iron has a very high carbon content, typically 3.5–4.5%, along with silica and other constituents of dross, which makes it very brittle and not useful directly as a material except for limited applications.

The blast furnace

The raw materials (haematite, coke and limestone) are fed into the top of the furnace.

Hot air is blasted into the furnace from the bottom. Oxygen from the air reacts with coke to carbon dioxide.

carbon + oxygen —> carbon dioxideC(s) + O2(g) —> CO2(g)

The carbon dioxide reacts with more hot coke to make carbon monoxide gas.

carbon dioxide + carbon —> carbon monoxideCO2(g) + C(s) —> 2CO(g)

Carbon monoxide is a reducing agent which reduces iron oxides into iron.

Iron (III) oxide + Carbon monoxide —> Iron + Carbon dioxide Fe2O3(s) + 3CO(g) —> 2Fe(l) + 3CO2(g)

The iron formed is molten and sinks to the bottom of the furnace. It is then run off into moulds.

The impurities in the iron ore are removed by the limestone to form a molten slag. This slag floats on top of the molten iron and is tapped off, cooled and used for making roads.

Electric arc furnace

- Use electricity as main sources of energy to melt scrap and adjust the properties in a ladle furnace, consequently manufacturing the desired products

- Need relatively lower investment costs and take up less space

- Take less time to manufacture products, enabling a prompt response to demand

• Strengths of electric arc furnace steelmaking- Easily adjust the furnace temperature and excellent in heat efficiency- Easily control oxidization and reduction, making it easier to remove phosphorous and sulfur- Less limit for fuel types and enable refining of all types of steel, making it more advantageous to produce special steel- Less expensive in facility installation and less limit for location, compared to other steelmaking methods

Weaknesses of electric arc furnace steelmaking- Consume a huge amount of electricity- High manufacturing costs due to the use of expensive scrap

• The electric arc furnace is used to reduce iron from iron ore. Heat is generated from an electric arc between electrodes. Oxygen is blown into the furnace, and lime and other materials are added to combine with the impurities and form slag. Molten iron is extracted and poured out via a tapping spout. It is then processed again in an electric arc furnace to make steel –particularly special quality steel.

Tests of rebars

Sl. No. Frog mark

Nominal

Dia

Actual

Dia

Actual Unit

Weight

Average of

Acctual

Unit Weight

Yield or

Proof Load

Yield or Proof

Strength*

Average Yield or

Proof Strength*

Ultimate

Load

Ultimate

strength*

Average

Ultimate

Strength*

Gauge

Length

Length

after

Elongation

ElongationAverage

ElongationBend Test

Rebend

Test

mm mm kg/m kg/m kN Mpa Mpa kN Mpa Mpa mm mm Percentage Percentage

1KSRM- 60 G

40010

10.00 -

-

37.0 471.10473.22

53.0 674.82679.06

150 179 19.33

19.56 satisfactory -10.00 - 37.5 477.46

(68626 psi)54.0 687.55

(98477 psi)150 180 20.00

10.00 37.0 471.10(4825 kg/sq.cm)

53.0 674.82(6924 kg/sq.cm)

150 179 19.33

2KSRM- 60 G

40012

12.00 -

-

55.0 486.31483.36

80.0 707.35707.35

150 179 19.33

19.11 satisfactory -11.90 - 55.0 486.31

(70097 psi)81.0 716.20

(102580 psi)150 178 18.67

11.90 54.0 477.46(4929 kg/sq.cm)

79.0 698.51(7213 kg/sq.cm)

150 179 19.33

3KSRM- 60 G

40016

16.00 -

-

96.0 477.46479.95

140.0 696.30699.62

150 178 18.67

18.67 satisfactory -15.90 - 97.0 482.44

(69602 psi)142.0 706.25

(101458 psi)150 178 18.67

15.90 96.5 479.95(4894 kg/sq.cm)

140.0 696.30(7134 kg/sq.cm)

150 178 18.67

4KSRM- 60 G

40020

19.90 -

-

145.0 461.55463.67

210.0 668.45672.69

150 177 18.00

18.22 satisfactory -19.80 - 146.0 464.73 (67241 psi) 212.0 674.82 (97554 psi) 150 178 18.67

20.00 146.0 464.73(4728 kg/sq.cm)

212.0 674.82(6859 kg/sq.cm)

150 177 18.00

Note: Samples were received in sealed/unsealed condition. * Strength is based on nominal/actual cross section area. Conversion factor: 1.0 kg/cm2=14.219 psi (Ib/in2)=0.09807 MPa (N/mm2)

• Thanks for now