This document provides an overview of heat treatment processes for metals and alloys. It discusses how heat treatment involves heating and cooling metals in the solid state to achieve desired properties by inducing microstructural changes. The main parts of any heat treatment process are heating the metal to a predetermined temperature, soaking it at that temperature to achieve a uniform structure, and then cooling it at a controlled rate to form the intended microstructure. Common heat treatment processes are described including annealing, normalizing, hardening, tempering, and various case hardening techniques.

1. HEAT-TREATMENT
By
SUBHRAJIT GHOSH

2. CONTENTS
• INTRODUCTION
• HEAT TREATMENT PROCESSES
• IRON-CARBON EQUILIBRIUM DIAGRAM
• TTT / IT DIAGRAMS
• CCT DIAGRAM
• CRITICAL TEMPERATURES
• COMMON PHASES
• ANNEALING
• NORMALIZING
• HARDENING
• TEMPERING
• HARDENABILITY
• PRECIPITATION AND AGE HARDENING
• SECONDARY HARDENING
• AUSTEMPERING
• MARTEMPERING
• PATENTING

3. INTRODUCTION
Heat treatment refers to a combination of
operations involving heating and cooling of
metals and alloys in the solid state for the
purpose of obtaining certain desired
properties. Changes in properties result from
microstructural changes in the material
produced by heat treatment operations.
All heat treatment processes may be
considered to consist of three main parts:
1. Heating of the metal to predetermined temperature.
2. Soaking of the metal at that temp until the structure
becomes uniform throughout the mass.
3. Cooling of the metal at some predetermined rate to cause
formation of desirable structures within the metal for the
desired purposes.

4. PURPOSES
• Improve machinability.
• Relieve internal stresses.
• Improve mechanical properties (ductility,
strength, hardness, toughness).
• Change the grain size.
• Increase resistance to corrosion, wear etc.
• Modify electrical/magnetic properties.
• Change the chemical composition.
• Remove entrapped gases (H,N,O).
• Change the surface condition (to produce
hard surface on a ductile interior).
• Soften the metals for further working.
• Make the structure of metal more
homogeneous.

5. HEAT TREATMENT PROCESSES
• Annealing
• Normalizing
• Hardening
• Tempering
• Case hardening (carburising,
nitriding, carbonitriding, cyaniding).
• Surface hardening (induction, flame,
laser, plasma).
• Precipitation and Age hardening.
• Patenting.