Heat Treatment of steel

Heat treatment of metal is a term used to describe an operation or a series of operations which involves heating and cooling of a metal or an alloy when it is in the solid state for obtaining some desirable properties (without changing the chemical composition ).

The main objective of Heat Treatment of Steel

1. Enhancing the hardness of the steel. 

2. Stress reliving from the metal after hot rolling or cold working. 

3. To improve the machinability. 

4. To make the metal soft. 

5. The structure of the metal can be modified to improve the electrical and magnetic propeeties. 

6. To change the grain size of the metal. 

7. After heat treatment metals are more resistant to heat, corrosion and wear. 

Various Heat Treatment processes 

a. Normalizing: 

• In Normalizing the soaking temperature is 30-50 degree centigrade within the range of  austenite field. 
• After soaking the alloy is cooled. The cooling rate and temperature helps to get smaller grains. 
• Normalizing improves toughness and strength. 

b. Annealing:

• Process involes heating the steel above the critical temperature, maintaining the temperature and and then cooling
• Increases ductility, softens the metal, and improve cold working properties. 

c. Spheroidising: 

• It is done at about 727 degree centigrade temperature. This process is limited to the steels having a carbon percentage of 0.5%. 
• High temperature recrystallizes the ferrite. The Iron Carbide present in the pearlite takes the shape of ball or sphere. This is called 'ball up'
• Because of these changes hardness and strength reduces.    

d. Hardening and Tempering:

• Hardening and tempering is done using very high temperatures. The temperature depends on the amount of carbon present in the steel . 
• Tempering means heating the steel again but this time the temperature is not that high. 

e. Surface Hardening or Case Hardening :

• The main reason for hardening steel is to retard wear on bearing and rubbing surfaces. But harder steel is brittle and that's why its not fatigue and shock resistant. So the hardening process is done on the surface only. It is very much cost effective. 

image courtesy: www.wikihow.com

Please read : 

Mechanical Properties of Material 

Mechanical Properties of Mild Steel 

What is Stress and Strain relationship ? 

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Bernoulli's Equation and Euler's Equation - Different terms

Bernoulli's Equation states that - 

For an incompressible liquid (density constant) which is flowing in a continuous stream; the total energy remains the same for all the particles, when the particle is moving from one point to another point.

Mathematical expression of Bernoulli's equation:

P₁/w + (v² )₁/2g + z₁ = P₂/w +( v²)₂ /2g + z_{1 = constant} 

_Here 

P₁ , P₂ = Pressure at points 1 and 2

V₁,V₁ = velocity at points 1 and 2

Z₁ , Z₂  = datum head at points 1 and 2

w= weight density of the liquid (also denoted by Greek letter gamma)

Please read : A Complete Guide to Fluid Mechanics 

Different types of energies or head in Bernoulli's equation 

1. Potential energy or potential head: 

Potential energy is the energy stored in a body because of changing its position above the fixed datum head. It's denoted by Z. 

2. Kinetic energy or head: 

It is due to the velocity of the fluid. It is denoted by v² /2g.  Here, v is the velocity and g is the gravitational acceleration. 

3. Pressure energy or pressure head:

 This energy is due to the pressure of the liquid. It is denoted by P/w . 

P has the unit Newton/square meter ,N/m² 

W has the unit Newton / cubmic meter , N/m³

So, 

Total Energy = Pressure energy + Kinetic energy + Potential energy 

Total Head = Pressure Head + Kinetic Head + Potential Head  

Applications of Bernoulli's Equation: 

1. A modified equation for the measurement of velocity in a pitot tube and pitot static can be got from Bernoulli's equation. 

2. The flow through venturi meter and orifice meter can be measured by this equation. 

3. Flow over notches and weirs can be calculated. 

Euler Equation or Bernoulli Differential Equation 

Euler's equation is expressed as 

dp/ρ + g.dx + v.dv = 0 

Euler's Equation is based on some assumptions: 

1. Non-viscous flow. 

2. Incompressible  and homogeneous flow. 

3. Steady flow. 

4. Continuous flow. 

5. Uniform velocity of the flow. 

Please Read:

• How to read Moody Diagram
• How to solve fluid mechanics problems by moody chart 
• Newton's law of viscosity 
• Methods of Dimensional analysis in fluid mechanics 
• Importance of fluid Mechanics for engineers and physicists 
• Fluid and some of its properties 

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What is stress and strain- Stress Strain Graph

Stress-strain are very important terms of solid mechanics. Strength of materials is a branch of engineering which deals with the material's properties to resist its failure. This topic also discusses about the behavior of materials under different level of forces.

What is stress and strain

In this topic we will discuss the definition of stress and strain, their formula as well as relationship and units.

What is stress ? 

When a body is subjected to external forces, equal and opposite internal forces are developed at the various sections of that body. This resisting force is known as unit stress or stress. 

Formula of stress :  

Stress = Force / Cross sectional are = P/A 

Stress is generally denoted by the Greek letter sigma . 

IN system international (S.I) the unit of stress is Pascal (Pa) . 

1 Pa = 1 Newton /1 square meter. 

In practical calculation, bigger units like megapascal (Mpa) or gigapascal (Gpa) is used.  I hope that meaning of stress is very much clear now.  

What is Strain ? 

When a body experiences a system of force, some deformation (elastic or plastic) takes place. This deformation per unit length of the body is know as the unit strain or simply strain.

Formula of Strain: 

Strain = Change in the length of the body / Original length 

Strain is generally expressed by the Greek letter epsilon . 

Stress Strain Relationship 

For understanding the stress strain relationship we can explain the stress-strain diagram for mild steel which is under tensile load. 

From the stress strain graph we can find the yield stress, ultimate stress and breaking stress. After passing the yield point plastic deformation occurs. 

Please Read:

• Mechanical Properties of Mild Steel 
• Mechanical Properties of Materials 

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Different Mechanical Properties of Materials

A design engineer must have a good concept about the mechanical properties of materials. Different manufacturing processes and heat treatment can change the properties of materials. A good design engineer should have a good knowledge about these properties.


Engineering materials are divided in the following divisions -

1. Metal and Metal Alloys . Example : Iron, Copper, Nickel etc.
2. Non- Metals . Example : Ceramics. rubber, glass etc.

Please read :

• What is Stress and Strain ?
• Mechanical Properties of Mild Steel 

Important Mechanical Properties of Materials  are Described Below :

a. Strength: This term describes the ability of the material to resist external forces. Without Yielding (Yield point is the point at which plastic deformation starts)breaking.

b. Stiffness: This is measured by the modulus of elasticity.  It is the ability of the material to resist deformation when stress is applied. 

c. Elasticity: Elasticity is the ability of the material to regain its original form when the external force is removed. Steel's elasticity is greater than rubber. 

d. Plasticity: This property is the ability of the material to deform permanently. It helps to shape the material to make into thin plates or molds. 

e. Ductility: Ductility is the property of the material which makes it enable to become thin wire with the application of tensile force (equally intense pull). The mechanical properties of mild steel show that it is very ductile. 

f. Brittleness:  Brittleness refers to the property of the material due to which a material breaks with association of very little distortion. Brittle materials are glass, ceramic, cast iron. 

g. Malleability: It helps the material to be converted to thin sheets or plates. It is actually a special case of ductility. Malleable materials are prone to plastic deformation. They need not be strong. Lead, soft steel, copper etc are very much malleable which are used in the engineering process. 

h. Toughness: It is the ability of the material to prevent fracture when high impact load and shocks are applied. Toughness is reduced when the material is heated. 

i. Resilience: This property is also needed for resisting shocks and impacts. Resilience refers to the energy absorbed within the elastic limit per unit volume. 

j. Creep: This property of the material states the phenomenon of permanent and slow deformation of the material when subjected to constant stress at high temperatures. IC engines, boilers etc. are designed keeping this term in head. 

k. Fatigue: when material is subjected to repeated loads, it fails before reaching the yield point. This type of failure is called fatigue. At first cracks developed in the machine parts in microscopic level and with time the probability of failure increases. 

l. Hardness: Hardness has different meanings. Resistance to wear, deformation and scratches are expressed by hardness.

Mechanical properties of materials differ in metals and non metals. Metallurgical and Mechanical Engineers should have good knowledge about material properties.

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Mild steel - Properties of Mild Steel (Mechanical Properties)

Mild steel is the most commonly used steel. It is used in the industries as well in the different everyday objects we use. Even the pans and spoons of the kitchen are sometimes made of mild steel. The main target of this article is to discuss about different mild steel properties. The mild steel is very important in the manufacturing of metal items. Almost 90% steel products of the world is made up of mild steel because it is the cheapest form of steel.  

Read: Mechanical Properties of Materials 

What is mild steel? 

Mild steel is the most widely used steel which is not brittle and cheap in price. Mild steel is not readily tempered or hardened but possesses enough strength. 

Mild steel Composition  

Mild steel contains - 
carbon 0.16 to 0.18 % (maximum 0.25% is allowable)
Manganese  0.70 to 0.90 %
Silicon maximum 0.40% 
Sulfur maximum 0.04% 
Phosphorous maximum 0.04% 

Mildest grade of carbon steel or mild steel contains a very low amount of carbon - 0.05 to 0.26% 

Importance of knowledge of mild steel properties 

The use of mild steel is huge and a person who is into manufacturing or production business need to know a lot about the important characteristics of mild steel. 
The study of mild steel becomes more significant for a student of mechanical engineering or metallurgical engineering. Mild steel is an alloy. And alloy is a product made by mixing metals and non metals. Sometimes a pure metal cannot fulfill all the properties needed for manufacturing product. So additives are included in the pure metal to obtain some specific properties necessary for the production. Mild steel is made by adding carbon and other elements in the iron. These elements improve the hardness, ductility and tensile strength of the metal.   

Most Important Mild Steel Properties

• A small amount of carbon makes mild steel to change it properties. Different amount of carbon produces different types of steels. There are small spaces between the iron lattice. Carbon atoms get attached to this spaces and makes it stronger and harder. The harder the steel the lesser the ductility. 
• The modulus of elasticity calculated for the industry grade mild steel is 210,000 Mpa. It has a average density of about 7860 kg/m3. 
•  Mild steel is a great conductor of electricity. So it can be used easily in the welding process. 
• Because of its malleability, mild steel can be used for constructing pipelines and other construction materials. Even domestic cookwares are made of mild steel. It is ductile and not brittle but hard. 
• Mild steel can be easily magnetized because of its ferromagnetic properties. So electrical devices can be made of mild steel. 
• Mild steel is very much suitable as structural steel. Different automobile manufacturers also use mild steel for making the body and parts of the vehicle. 
• Mild steel can be easily machined in the lathe, shaper, drillling or milling machine. Its hardness can be increased by the application of carbon. 
• Mild steel is very much prone to rust because it has high amount of carbon. When rust free products are needed people prefer stainless steel over mild steel. 

Image courtesy : http://waqarsteel.com/

I hope this compilation of mild steel properties will help the people involved in the manufacturing process as well as the engineering students. 

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Pros and Cons of Solar Energy

The energy from the sun reaching the earth per day ranges from about 600 Btu (British Thermal Unit) / square feet for Northern Europe to about 2000 Btu/square feet for arid regions near the equator. More energy from sun strikes the earth in one hour than all energy consumed on the planet in a year! A summer day’s sun at noon provides a square, meter of land with a power input almost a kilowatt. One might wonder why solar energy has not replaced the conventional energy sources, not even a significant fraction. So there are definitely some pros and cons of solar energy. In this article I will discuss about the pros as well as cons of this vast energy source.

Pros of Solar energy

No pollution

There is no pollution while producing energy from the solar panels. Only pollution we can talk about is the pollution that can happen while making the solar panels.

Great for household use 

Theoretically the sunlight falling on a typical single house can easily provide from one third to one half of the heating needs of that house anywhere in hot countries even in the cooler climates and even when there is persistent cloudiness.

Zero dependence on the fossil fuels 

The dependence on the fossil fuels can be reduced a great deal. In one day the solar energy falling on India alone is greater than the energy in their present annual coal consumption. 

Reasonable Cost 

One installed the cost of electricity production is very low though the cost of producing solar cells are high. And in the remote areas the installation cost will be comparatively very low.

Solar panels can be set up in the house roof tops. So there is no requirement of finding spaces for installing the solar panels.

Availability 

Most of the areas of the world are exposed to the sun’s rays and capable of using this energy very easily.

No transportation cost of fuels 

No need of transportation of fuels from one place to another. The fuel is everywhere!

The harnessing of electricity is very much easy in the remote areas when these areas are not connected to the national grid. 

Cons of Solar energy

Cost

The solar energy has not been the prevailing one because of its cost. The primary reason is clearly the cost of solar energy based technology, especially in comparison to the lower priced commercial fuels.

Some adverse environmental effects of solar energy

Large scale utilization of solar energy is associated with adverse environmental effect. To produce an electrical equivalent of 10 terra watt of solar electricity a land area as big as 220000 square kilometer will be required. An area of this size cannot be covered with solar energy collecting devices without making any adverse environmental effect.

Storage of captured energy

The devices for storing solar energy are of low efficiency and high costs. This can cost thousands of dollars for a buyer to set up a solar panel in houses as well as in factories. 

Though there are some cons of solar energy in the near future we must find a way to properly utilize solar energy because the fossil fuel storage are at the verge of getting finished. And the harm occurred due to the use of these solar energy is irreparable. So Solar energy pros and cons should be properly studied.

Please Read:

• Renewable Energy: the great green hope for clean environment
• What are the cheapest sources of non-conventional energy - Biomass  
• Solar Air Heater Classification and Advantages
• Solar pond pump-features of solar fountain pump
• Hydroelectric Power Facts - Advantages and Disadvantages 
• Alternative energy sources graphical representation  
• Biomass - pros and cons 

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