C.K.PITHAWALA COLLEGE OF ENGG. & TECHNOLGY Presented By :- Group No :- 6 1 DereViral M Rajwadwala Faizal Mavdiya Yash Patel Akshaykumar Semester: 5 th Subject :- Design Of Machine Element Department :- Mechanical Topic:- Effect of alloying element and HT on steel Guided By : - Mahesh N. Patel

What is Alloy & Alloy element ? An alloy can be defined as a defined as a substance possessing metallic properties, having metallic bond and composed of two or more than two elements out of which at least one is metal. Metal present in larger proportion is called base metal, while the other metallic or non metallic elements are known as alloying elements.

Effects of alloying elements on properties of steel Alloying elements when added to steel, perform different functions depending upon their characteristics, amounts and the subsequent heat treatment. Effects of alloying elements are as follow: 1)Aluminium ( Al ): It acts as a deoxidizer, restricts great growth and forms hard nitrides when heated in contact with nitrogen.

2) Boron ( B ): It increases hardenability. It is used as an inoculator to obtain fine grain size. 3) Chromium ( Cr ): It improves corrosion resistance, increases hardenability, provides strength, wear and oxidation resistance at elevated temperatures. 4) Cobalt ( Co ): It produces red hardness by retaining hard carbides at a high temperatures. It increases hardness and strength, but too much of it decreases impact resistance of the steel.

5) Copper ( Cu ): It increases resistance to atmospheric corrosion and also act as a strengthening agent. 6) Manganese ( Mn ): It deoxidizes, contributes to strength and hardness, counter-effects sulphur, increases hardenability, decreases the critical cooling rate. 7) Molybdenum ( Mo ): It promotes hardenability, increases strength and impact resistance of high temperatures, retards grain growth at high temperatures.

8) Nickel ( Ni ): It provides toughness, corrosion resistance, deep hardening and increases impact resistance at very low temperatures. 9) Silicon ( Si ): It act as a deoxidizer, promotes resistance to high temperatures oxidation, increases strength and hardness, increases magnetic permeability and decreases hysteresis loss. 10) Titanium (Ti ): It is the strongest carbide former. It is added to fixed carbon in stainless steels to prevent precipitation of chromium carbide.

11 ) Tungsten ( W ): It forms hard abrasion resistance particles, imparts red hardness, increases hardenability to a great extent. It is an important alloying element in H.S.S. 12) Vanadium ( v ): It is a strong deoxidizer. It increases hardenability. It refines the grain and reduces grain growth. It improves fatigue resistance.

Heat Treatment Of Steel It is defined as the operations or combination of operations, involving the heating and cooling of a metal or an alloy in the solid state for the purpose of obtaining certain desirable conditions without changes in chemical composition.

Objectives Of Heat Treatment To increase the hardness of metals. To relive the stresses set up in the material after hot or cold working. To improve machinability. To soften the material. To modify the structure of the material to improve its electrical and magnetic properties. To change grain size. To increase the qualities of a metal to provide better resistance to heat, corrosion and wear.

Various Heat Treatment Process Normalising Annealing Spheroidsing Hardening Tempering Surface hardening or case hardening

Normalising Objectives :- To refine the grain structure To Remove strains caused by cold working To remove dislocations caused by hot working To improve mechanical & electrical properties

This process consists of heating the steel from 30 to 50 C above its upper critical temperature or Acm line. It is held at this temperature for about fifteen minutes and then allowed to cool down in still air. The alloy steel also be normalized but they should held for two hours at a specified temperature and then cooling down in the furnace.

Annealing Objectives To soften the steel. To refine the grain size and structure. To relieve internal stress which caused by hot or cold working. To alter electrical, magnetic or mechanical properties. To remove gas trapped in the metal during critical casting.

A)Full annealing:- The process consist heating the steel from 30 to 50 C above the upper critical temperature for hypoeutectiod steel and by the same temperature above the lower critical temperature holding it at this air temperature for sometimes to enable the internal changes takes place. This time allowed is approximately 3 to 4 minutes for each millimeter of thickness of the largest section and cooling slowly in the furnace. The rate of cooling varies from 30 to 200 C per hour depending upon the composition of steel.

B ) Process Annealing :- This process is used for releving the internal stresses previously set up in the metal and for increasing the machinability of the steel. In this process of steel is heated to a temperature below the lower critical temperature, held at this temperature for sometimes and then colled slowly. This process is used in the sheet and wire industries.

Spheroid sing It is another from of annealing in which cementite in the granular from is produced in the structure of steel. This is usually applied to high carbon tool steels which are difficult to machine. The opertaion consists of heating the steel to a temperature slightly above the lower critical temperature 730 to 770 C. It is held at this temperature for some times and then cooled slowly to a temperature of 600 C. The rate of cooling is from 25 to 30 C.

Hardening Objectives :- To increase the hardness To enable it to cut other metals.

This process consists heating the metal to a temperature from 30 to 50 C above the upper critical point for hypoutectoid steels and by the same temperature above the lower critical point for hypereutectoid steels. Keeping the metal at this temperature for considerable time, depending upon this thickness. Quenching in a suitable cooling medium.

Tempering Objectives:- To reduce brittleness of hardened steel To remove internal stresses To make steel through to resist shock and fatigue.

The steel hardened by rapid quenching is very hard and brittle. It is also contain internal stress which are serve and unequally distributed to causes cracks or even rupture of hardened steel. This process consist of reheating the hardened steel to some temperature below the lower critical temperature, followed by any desired rate of cooling. The exact tempering temperature depends upon the purpose for which the article or tool is to be used.

Surface hardening In many engineering application, it is desirable that a steel being used should have a hardened surface to resist wear and tear. At the same time, it should have soft anfd tough interior or cone so that it is able to absorb shocks, etc. This is achieved by hardening the surface layers of the article while the rest of it is left as such. This type of treatment is applied to gear, ball bearings and railway wheel etc.

Various Surface Hardening Processes Carburising Cyaniding Nitriding Induction hardening Flame hardening