PRESENTED BY - 1. ANIL 2. BALJINDER 3. AMAR 4. DEEPAK

HEAT

TREATMENTS

INTRODUCTION• THE VARIOUS MICROSTUCTURES

DEVELOPED DURING METAL PROCESSING CAN BE MODIFIED BY HEAT TREATMENT TECHNIQUES,INVOLVING CONTROLLED HEATING AND COOLING OF THE ALLOYS AT VARIOUS RATES (ALSO KNOWN AS THERMAL TREATMENT) .

PROPERTIES OF MATERIAL

• The internal reactions of a metal to external forces are known as mechanical properties. The mechanical properties are directly related to each other. A change in one property usually causes a change in one or more additional properties.

For example, if the hardness of a metal is increased, the brittleness usually increases and the toughness usually decreases. Following is a brief explanation of the mechanical properties and how they relate to each other.

TYPES OF PROPERTIESTENSILE STRENGTHSHEAR STRENGTHCOMPRESSIVE STRENGTHELASTICITYDUCTILITY

MALLEABILITYTOUGHNESS HARDNESSMACHINABILITY AND WELDABILITYHEAT AND ELECTRICAL

CONDUCTIVITYBRITTLENESS

TENSILE STRENGTH• Tensile strength is the ability of a metal to

resist being pulled apart by opposing forces acting in a straight line (Figure 2-1).It is expressed as the number of pounds of force required to pull apart a bar of the material 1 inch wide and 1 inch thick.

SHEAR STRENGTH• Shear strength is the ability of a metal to resist

being fractured by opposing forces not acting in straight line (Figure 2-2). Shear strength can be controlled by varying the hardness of the metal.

COMPRESSIVE STRENGTH• Compressive strength is the ability of a metal

to withstand pressures acting on a given plane (Figure 2-3).

ELASTICITY• Elasticity is the ability of metal to return to its

original size and shape after being stretched or pulled out of shape (Figure2-4).

DUCTILITY• Ductility is the ability of a metal to be drawn or

stretched permanently without rupture or fracture (Figure 2-5). Metals that lack ductility will crack or break before bending.

MALLEABILITY• Malleability is the ability of a metal to be hammered,rolled,

or pressed into various shapes without rupture or fracture (Figure 2-6).

TOUGHNESS• Toughness is the ability of a metal

to resist fracture plus the ability to resist failure after the damage has begun. A tough metal can withstand considerable stress, slowly or suddenly applied, and will deform before failure.

HARDNESS• Hardness is the ability of a metal to resist

penetration and wear by another metal or material. It takes a combination of hardness and toughness to withstand heavy pounding. The hardness of a metal limits the ease with which it can be machined, since toughness decreases as hardness increases.The hardness of a metal can usually be controlled by heat treatment.

CORROSION RESISTANCE

•Corrosion resistance is the resistance to eating or wearing away by air, moisture, or other agents.

MACHINABILITY AND WELDABILITY•Machinability and

weldability are the ease or difficulty with which a material can be machined or welded.

HEAT AND ELECTRICAL

CONDUCTIVITY•Heat and electrical

conductivity is the ease with which a metal conducts or transfers heat or electricity.

BRITTLENESS• Brittleness is the tendency of a

material to fracture or break with little or no deformation, bending, or twisting.Brittleness is usually not a desirable mechanical property. Normally, the harder the metal, the more brittle it is.

TREATMENT PROCESSESANEALINGNORMALIZINGTEMPERINGQUENCHINGCASE HARDENING.CARBURIZING

ANEALING

NORMALIZING

TEMPERING• Tempering is a process of heat treating, which is used to

increase the toughness of iron-based alloys. Tempering is usually performed after hardening, to reduce some of the excess hardness, and is done by heating the metal to some temperature below the critical point for a certain period of time, then allowing it to cool in still air. The exact temperature determines the amount of hardness removed, and depends on both the specific composition of the alloy and on the desired properties in the finished product. For instance, very hard tools are often tempered at low temperatures, while springs are tempered to much higher temperatures.

QUIENCHING• Quench hardening is a mechanical process in which steel

and cast iron alloys are strengthened and hardened. These metals consist of ferrous metals and alloys. This is done by heating the material to a certain temperature, depending on the material. This produces a harder material by either surface hardening or through-hardening varying on the rate at which the material is cooled. The material is then often tempered to reduce the brittleness that may increase from the quench hardening process. Items that may be quenched include gears, shafts, and wear blocks.

HARDENING

NITRIDING

CAUSES AND REMEDIES

THE END