Why is Steel a preferred engineering material?

  Man has the ability to utilize natural resources for his benefit. This ability gave him an upper hand over other animals and he gradually took over the charge. As science and technology made progress and new and innovative ideas started making dreams a reality, search for suitable engineering materials gained pace. Metals took the charge from wood and stones. The modern era has seen the development of synthetic and composite materials.

  In spite of all this, when we look around, we find that steel is actually present in all the spheres of our life. Why is it so? To gain an insight of this phenomenon, we will have an overview of the factors that affect the selection process of any engineering material.

The above figure shows that the selection of any engineering material primarily depends on:

1. Intended use i.e. the material should be fit for the work environment where it is going to be employed. For example, if we need something to write on and we have paper, soil, wood and steel; you know the preferred answer!


2. Availability plays an important role as it is a prime contributor in cost. The budget of the client is also important. The material (if it is not a special purpose material like radioactive compound or aero-space materials where goal is preferred over cost) should be available in abundance and that too at an affordable price.  


3. Depending on the conditions of the work environment and intended use, the mechanical, electrical and thermal properties of the material play an important role in selection of the material. For example, when we want to transfer heat, metal is good but for insulating from heat, insulation material is needed.


4. When we select a material, it is very important that different manufacturing processes can be performed on it easily so that required article/product can be made. 
5. Whenever any component or equipment is designed, it is designed to give a certain life so that the use becomes profitable for the end user or the equipment can save life without failing.

  Based on the above facts, steel is a material that is easily available at reasonable price. It also has good mechanical properties over a wide range of use and good electrical and thermal conductivity. A large number of manufacturing processes from casting to cutting to welding to machining can be performed on it to make something useful. The life of steel products is also pretty high.

  This makes steel a preferred choice as an engineering material.

Industrial Fuel

While in industry, we use a lot of energy obtained from various sources to help in varied activities. Fuels play an important role here. We have a lot of choices also: traditional fuels such as Fossil Fuels, Bio-Fuels (animal excrete and agricultural waste) and modern atomic fuels. It seems quite obvious that we don't use atomic fuels in industries.

So, the most important question arises: What fuel must I use?

 

The following points will help identify a good fuel:

1. Low Cost

2. High calorific value

3. Moderate temperature of combustion

4. Moderate rate of combustion

5. Controllable combustion

6. Harmless combustion products

7. Low smoke

8. Uniform size with low moisture and non-combustible parts

9. Easy, safe and cost-effective transportation and storage

 

Proximate and Ultimate analysis of fuel tells more about its efficiency as a fuel. To measure the calorific value, a bomb caloriemeter is used.

Everything that shines......

This post comes after almost a year! It was really a long time....

 

Today I'll talk of the dull steel and the shiny steel. After operating for almost 90 years and producing different types of steel for various segments, Tata Steel decided to go for cold rolling mill. When I joined this team in 1999, our general conception of steel was dark-dull metal which was being produced. When we started interacting with cold-rolling experts, our generic ideas got shattered!

It was like a cultural shock for us. We were used to the dull dark steel made from red-orange molten metal or rolled out of straight moving orange metal slabs or billets. The concept of shiny cold steel strip going up and down the rolls seemed like the story of "Alice in wonderland"!

When the Mill was setup, it created history in many ways! We worked day in and day out to roll out the first coil. The eagerness to see a shiny metal strip come out of rolls in ambient temperature was the catalytic force behind our motivation! The joy of seeing the first coil was overwhelming. The feeling can't be bounded in words.

When the 10th anniversay of 1st coil was celebrated, many new and old people gathered. The shine of pride was seen in the eyes of everyone who was a witness of the historic moment 10 years ago!

So, every thing that shines is not gold! It may also be cold-rolled steel and the pride in the eyes of people who make it.

Production processes

Steel is a metal on which, various operations can be performed to make something useful out of it. In this post, I'll touch some of them.

1. Cutting: Solid metal is cut into different shapes either by a mechanical cutter or energy source. The basic operations of cutting a metal piece by hand (saw) or by machining (cutting saw, lathe, milling machine, planer machine etc) or by energy source such as gas-cutting or laser (CNC machines) can be combined into this category.

2. Joining: Joining two or more parts by using mechanical means (nuts-bolts, rivets, pins etc) or welding can be counted here. Welding can be gas, arc or MIG-TIG. Other welding processes like heating the parts and pressing them against each other so that metal diffuses, also come under this category.

3. Forging: Heating the metal and hitting it hard with a heavy tool to make something useful comes under this category. It is the age old blacksmith's process. Most of the older swords, arrows etc were made by this method. In the mordern world, the most important part being manufactured by this process is the axles of vehicles.

4. Casting: Pouring liquid metal into predesigned casts to make a certain shape comes under this category. This method is widely used to manufacture automobile engines, valves and other complex design equipments.

5. Rolling: Rolling the metal under heavy pressure either at ambient temperature (cold rolling) or at elevated temperature (hot rolling) comes under this category. Rolling improves the mechanical properties of the metal, making it available for more processes.

6. Drawing: This operation is mainly performed on bars to make thin wires by pulling the ends under heavy pressure. The drawn wires are either sold as it is, or further converted into bolts, screws, nails, nuts, rivets etc.

7. Forming: The thin sheets of metal are pressed in a die of particular shape. This process is mainly used in auto industry and other white-goods manufacturing companies. The complex looking shape of sports car are due to this process.

8. Finishing Process: Grinding, buffing and polishing are some of the finishing processes that are done to imporove on the asthetic values of the product. Coating (of other metals or paint) is also done to improve the looks of the finished good.

Coke: black revealed!

What comes to your mind when I say "coke"? Well, Its not your usual drink! Its is a form of coal that is used in the blast furnaces as a reducing agent.
Coal is a fossil fuel that is found in abundance in the nature. Most of them are found underground and require sophisticated mining skills to take them out.
There are three basic qualities that characterises the coal:
1. Heat generated
2. Ash content
3. Moisture content
If the ash and moisture contents are high, coal will generate low heat per unit weight burned. Based on its purity and calorific value, coal can be classified in four categories:

Lignite: It is a soft, brownish-black coal that forms the lowest level of the coal family. The largest portion of the world's coal reserves is made up of lignite. The ash and moisture contents are high and calorific value is lowest.
Subbituminous: Coming up next is subbituminous coal, a dull black coal. It gives off a little more energy (heat) than lignite when it burns.
Bituminous: More purity in terms of less ash and moisture results in still more energy in bituminous coal, sometimes called "soft coal."
Anthracite: Anthracite is the hardest coal and gives off a great amount of heat when it burns. The composition is very near to pure carbon with very-very low ash and moisture.

So what would be a metallurgists desire? Of course, Anthracite!
WHY?
Simply because high calorific value and high carbon content mean
1. More heat in less fuel
2. More Carbon available for reduction
resulting in a lower blast furnace cycle and lower cost of production.
But, the coal reserves does not provide us with enough of anthracite. What to do now? Coal experts blend different types of coal to make it useful for the iron-steel industry. This coal is termed as "MET" coal or coke.
Coal is crushed and heated in the COKE-OVEN Batteries in the absence of air. The impurities are removed and the resulting thing is called COKE! Coke is fed in the blast furnace along with the ore and sinter to enhance reduction process and also act as a fuel.

The Blast Furnace (Basics)

For the purpose of extracting iron from its ore, blast furnace is the most important setup. In todays post, I'll talk about the basics of a blast furnace.

Blast furnace is a big structure where iron ore is melted to extract the iron.

Now, we have certain points in this statement.
1. The furnace is a big structure.
2. Iron ore goes in.
3. Ore is heated.
4. Molten iron is collected.
Now, we can figure out that when ore is heated, there must be some heating arrangement. There must also be some arrangement for the insulation of heat so as to prevent heat loss and for the safety of the people working there. Similarly, when the ore melts, it will have pure iron and some impurities. These needs to be tackled with. Continuous supply of ore, tapping of molted metal and slag and taking care of the gases are some of the issues which make iron-steel industry, a hazardous place to work in.
In the blast furnace, iron ore (basically Hematite or Magnetite) is injected into the furnace along with lime and coke. A pre mixed injection mixture is called sinter. Making lime, coke and sinter is an important aspect in an integrated steel plant. But this is not my topic today.

A blast of hot air is provided to burn up the coke from the bottom of the furnace.
C + O2 = CO2 + Heat
Due to lot of coke, CO2 converts to 2CO. This carbon mono-oxide is responsible for the reduction of iron ore. Lime stone is added to remove the sulfur and other impurities.
CaCO3 = CaO + CO2
FeS + CaO + C = CaS + FeO + CO
The impurities like CaS, Silica (SiO2), Alumina (Al2O3), Magnesia (MgO) or Calcia (CaO) becomes part of the slag.
The "hot metal" and the slag goes down to the bottom of the furnace. The slag being less dense, floats on the molten metal. Two tapping points, upper one for slag and lower one for metal is used to collect the material from the blast furnace. This operation is done periodically.
Molten metal is collected in large lined steel buckets (laddles) and poured in moulds to make ingots.
Slag is collected and can be thrown away or reused in cement manufacturing.
The poisionous gases that evolve in the reaction are NOT let away in the atmosphere. They are stored in secured installations and further used as a fuel.

Getting It out

Earth's crust has lots of magical elements in it. The key lies in its finding and extraction. When we talk of Iron Ore, let us us talk of two more words: abundance and commercial mining.

What is abundance?
Well, as the word suggests, it is the amount of ore that is present in a particular area.

What is commercial mining? How does it relate to abundance?
Again, commercial mining is the deployment of heavy machines and skilled work force to get huge amount of ores so that the cost incurred in the process can be profitably recovered. If lots of money goes into a mine which gets exhausted in only 5 - 6 years, can it be termed as profitable? NO. The key lies in large amount of ore for a long period of time, say 70, 80, 90 or 100 years.
The site of mining may contain good quality ore (% Fe is more) at the upper crust or very deep below the earth. So, it can either be an open or underground mine.
The ore obtained from the mines is washed, cleaned and sorted into various categories. These are then send to the Blast furnaces for melting and getting the Iron out from the ore.

Will talk of blast furnaces some other day.