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Heat treatment

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Subhrajit Ghosh

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.

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HEAT-TREATMENT By SUBHRAJIT GHOSH
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
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.
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.
HEAT TREATMENT PROCESSES • Annealing • Normalizing • Hardening • Tempering • Case hardening (carburising, nitriding, carbonitriding, cyaniding). • Surface hardening (induction, flame, laser, plasma). • Precipitation and Age hardening. • Patenting.
Heat treatment
Heat treatment

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Heat treatment

  • 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.