Categories
Building Materials

Steel – Composition, Properties & Types

Steel is the alloy of iron and carbon. Nowadays, steel has become the backbone of civil engineering construction. Steel may be plain carbon steel or alloy steel. Plain carbon steel is the steel at which carbon only forms an alloy with iron.

About 92% of steel is produced as plain carbon steel. Alloy steel is that at which iron is alloyed with other metals and carbon. About 85% of steel is found as alloy steel.
An increase in the carbon content increases the tensile and compressive strength of the steel. But the brittleness of the steel increases and thus the malleability and ductility decreases.

(A) Composition of steel

Steel is composed of iron, carbon and other alloying metals. Steel containing only iron and carbon is known as plain carbon steel.

Depending upon the carbon content, steel is classified as low carbon steel, medium carbon steel, and high carbon steel.

  • Steel containing less than 0.25% of carbon is known as low carbon steel.
  • If the carbon content lies between 0.25% to 0.7% then the steel is known as medium carbon steel.
  • In this, the carbon content is greater than 0.7% it is referred to as high carbon steel.

If the steel contains other metal also in the form of alloy with iron, steel is known as alloy steel. Stainless steel, nickel steel, vanadium steel, tungsten steel, etc. are examples of alloy steel.

(B) Properties of steel

Mechanical properties of the steel is determined by the carbon content in the steel. In general following are the properties of steel:

  1. Steel possesses high strength than other forms of iron such as cast iron or wrought iron.
  2. It can absorb shock and is elastic.
  3. It is malleable and ductile.
  4. Heat treatment can be done in the steel to improve the grain distribution and the quality of steel.
  5. Some alloy steel has corrosion resistance, but plain carbon steel is affected by corrosion.
  6. It can be welded to plain carbon steel easily.

(C) Types of steels

Depending upon various modes classification of steels can be of various types. However, the classification on the basis of their Chemical Composition is very commonly adopted.

Two major groups of steels recognized on this basis are-
A) Plain carbon steels and
B) Alloy steels

(I) Carbon steel or Plain Carbon Steel

This is the first major group of steels. In them, carbon is the only controlling component besides iron.

They are further sub-divided into three sub-types.

Low carbon steels(C= 0.05 to 0.35%) – These are also termed as soft steels or very commonly as mild steel (MS). The mild steels are tough and ductile. These can be easily welded. These steels are used for making nuts, bolts, rivets, sheets and other parts of common utility.

Medium carbon steels (C=0.35 to 0.55%) – These are also termed as medium steels. These are hard and strong comparatively. Are resistant to wear. They are used commonly for construction purposes as structural members and reinforcement.

High carbon steels(C=0.55 to 1.5%) – These are also termed as hard steels. It posses very great hardness and high compressive strength values. They are resistant to wear. They are used commonly for the manufacturing of ball bearing roller, saw, crushers, and locomotive tyres.

Functions of carbon in steels

Carbon in steel plays a very vital role in controlling their properties, Thus, the tensile strength of steel increases with an increase in the carbon content until its proportion reaches 0.83%. Any increase in carbon content beyond this limit will affect the tensile strength of steel adversely.
The ductility of steels decreases with an increase in carbon content. Also, the hardness of steels increases with the increase in carbon content. The compressive strength is also found to increase with the increase in carbon content.

Usual impurities in steel and their effects

  1. Manganese (0.2 to 1%- has positive influence like increases tensile strength and hardness of steel. But beyond this limit, it increases the brittleness of steel)
  2. Silicon (Kept below 0.4%, since this acts as a deoxidizer. Beyond this limit this increases the brittleness.)
  3. Phosphorus (Kept below 0.05%. This shows a cold-short effect if exceeds this limit.)\
  4. Sulphur (Kept below 0.05%. This shows a red short effect if exceeds this
    limit.)

(II) Alloys Steel (Steel Alloys)

Besides carbon other elements that impart distinctive characteristics to steel are add in iron to produce steel alloy. Formation of steel alloy is made to increase strength, hardness, toughness, resistance against corrosion, etc.

Important steel alloys and function of alloying elements are discussed below.

1. Stainless steel

Stainless Steel is the alloy steel containing more than 12 of the chromium alloyed with the iron Chromium forms a dense and tough layer of oxide around the metal surface and is highly resistive to corrosion.

It is basically sub-categorized into three groups

  1. The first group of stainless steel consists of less than 14% of Chromium and is known as Plan Chromium stainless steel. It contains sass than 0.4 % of carbon with traces of copper, tungsten, Nickel, etc, This Group of stainless steel can be hardened, Welded, machined and are satisfactory corrosion resistant, They are used to prepare steam valves turbine besides surgical instrument scissors knifes gears shafts ball bearing spring, etc.
  2. The second group of stainless steel consists of 14-20% of chromium and o.45 of carbon. They are more brittle and difficult to heat treatment. Also can be forget welded machined and rolled. They are used to prepare wire pipes. They are also used in chemical and food plants.
  3. When the steel contains at least 24 of combined Chromium and Nickel, then it goes under the third category of steel Generally 188 stainless steel –18chromium and nickel alloyed with Iron_ is very common in use. This steel has excellent resistance against corrosion and improved tensile strength. This steel is very tough. It can be welded, forged and rolled. Machining of this steel is difficult. These steels are used in chemical plants, tanks, cooking utensils, preparing pump shaft, screw, nut bolt, etc.

2. Nickel steel

Nickel steel contains about 3.5% of nickel alloyed with iron. It contains 0.5% to 1% of carbon. The presence of nickel imparts hardness, toughness, improves strength and corrosion resistance. This type of alloy steel is used in automatic parts, airplanes, cables, and shafts. Inver, widely used to prepare to measure tape is the alloy of nickel and steel. It consists of 30-40 % of nickel and has a very coefficient of thermal expansion.

3. Tungsten steel

Tungsten steel is known as high-speed steel as it is used in the high-speed cutting tools and drilling machines. It contains 14-20% of tungsten and 3-8% of chromium. It also contains carbon, vanadium, and molybdenum.

4. Vanadium steel

Vanadium steel possesses a high value of elasticity and is capable of resisting shocks. It is very strong and more ductile. Also, it improves fatigue resistance. It is used for making tools. It contains 0.1 to 2% of vanadium.

5. Manganese steel

Manganese steel contains different amounts of manganese ranging from 1-14% depending upon the purpose of the resulting product. Very hard, tough and strong in nature. It improves the plasticity of metal. It is used in preparing machine parts, rails, etc. manganese steel is non-magnetic.

Join our Facebook group: Engineering Knowledge

Sharing is caring. ??

Categories
Question Paper

Download Trivuwan University IOE Old Question Paper Collection

Download Complete IOE Old Question Paper Collection Of Trivuwan University of All engineering faculty since 2057.

We have a collection of old question semester wise in pdf format enjoy it. Share with Friends!!!

Trivuwan University IOE First Year Part I Complete Question

Trivuwan University IOE First Year Part II Complete Question

Trivuwan University IOE Second Year Part I Complete Question

Trivuwan University IOE Second Year Part II Complete Question

Trivuwan University IOE Third Year Part I Complete Question

Trivuwan University IOE Third Year Part II Complete Question

Trivuwan University IOE Fourth Year Part I Complete Question

Trivuwan University IOE Fourth Year Part II Complete Question

Download

For more detail about IOE Visit official website Click Here.

Join our Facebook group: Engineering Knowledge

Share this article with friends because

Sharing is caring. ??

Categories
Electricity

DC Circuit Analysis

Circuit and its elements

A Circuit is that encloses conducting path through which an electric current flows. The circuit consists of active and passive elements.

Active elements are those which have their own energy and they transfer energy to passive elements. Examples are voltage and current.

Passive elements are those which do not have their own energy. They receive energy from the active elements. Examples are resistors, capacitors, inductors.

Active and Passive Networks

Active Networks are those which contain one or more passive elements.

Passive Networks are those which does not contain any active elements and it is the combination of only passive elements.

Resistor And Resistance

A resistor is a device that resists the flow of current and Resistance is the property of a substance due to which it opposes the flow of current. It is a dissipative element i.e. it converts electrical energy into heat energy as current flows from through it.

They provide a way to control voltage and currents that’s why they are very common in circuits. Resistors are uses to divide voltage and limit the amount of current. The resistor is denoted by R. The unit of resistance is ohm “Ω”.

A resistance has color stripes on them that represent their value of resistance. Resistor those uses in the circuit have special color coding from which resistivity of the resistor can be determine.

Diode

The diode conducts in only in one direction conduction is form anode to cathode.

The diode is said to be forward biased if anode is connected to the positive terminal and cathode to negative and reverse biased if connected vice-versa.

Zener Diode

Zener diode behaves like an ordinary diode if forward biased or reverses biased with small voltage. If Zener diode is reverse biased with a voltage greater than a certain amount called Zener diode, it conducts easily. The voltage of the Zener diode is fixed when a Zener diode is manufactured. Zener diodes are used to regulate the output power supply circuits.

Capacitor

Capacitor consists of two metals plates with a layer of insulator called dielectric. The capacitance of capacitor is measured in farad. Generally there is a mark to show cathode terminal of the capacitor otherwise larger terminal indicates positive and shorter the negative.

Transistor

Transistors are three-terminal semiconductor devices. Based on composition, they are of PNP type and NPN type. They are used for switching and amplification.

Transistors enclosed in plastic case has flat surface and that metal case has tag on its rim to identify the terminals wires.

IC (Integrated Circuits)

Devices made by the integration of electric components like transistors, diodes, and resistors into a single chip are called Integrated circuits. They may vary in combination and size according to their types and usage. For example, comparators consist of 23 transistors, 2 diodes, and 19 resistors in its one type. Other examples are Audio Amplifier ICs, Timer ICs, Logic ICs, Memory chips, etc. They are used for amplification, multi-switching, and storing data as RAM and ROM, etc.

LED

LED stands for light-emitting diodes. They are used as indicators. Some LEDs are even multicolor use to indicate the different status of voltage and current in circuits. Usually, not always, the cathode wire is shorter than the anode wire. Another way is to look at the rim. The rim is flat on the side nearer to the cathode terminal.

Inductor

Generally, Inductor is a coil of wire. It often has a core. There are two main types of inductors: Chokes and Tuning Coils. Two or more coils are wrapped on one former to make a transformer. It is also a storage device, but store energy in terms of magnetic field or electric field. Its unit is (H) Henry.