This document provides an overview of heat treatment processes and their effects on material microstructure and properties. It discusses how annealing is used to relieve stresses and modify microstructure by exposing materials to elevated temperatures over time. Process annealing and stress relief annealing are described. Phase diagrams, TTT diagrams, and CCT diagrams are introduced as essential tools for understanding heat treatment of ferrous alloys like steel. Key terms related to heat treatment processes and phase transformations are defined.

1. HEAT TREATMENT LAB Prepared by: S.Balachandran, K.T.Hartwig

2. Objective To understand the effects of heat treatment on the microstructure and property of a material

3. Background What is annealing? Material is exposed to an elevated temperature for an extended time period and slowly cooled. Why is this done? a) Relieve stresses b) Increase ductility c) Obtain specific microstructure.

4. Terminology Process Annealing: Heat Treatment to negate the effect of cold work, usually done to increase ductility. Remember: Recovery-> Recrystallization->Grain growth. Usually fine grained structures are preffered hence grain growth control is desired.

5. (Add images) Worked sample (high dis den) Recovered (lower disloc density) Recrystallization and grain growth.

6. Terminology Stress relief annealing: To relieve internal stresses, the material is heated and held at relatively low temperatures. Where is this used? After machining operations. Where non-uniform cooling of w/p is involved (eg: welding and casting). Phase transformations leading to different phases that induce high stresses.

7. Heat Treatment of Ferrous Alloys To heat treat steel, an understanding of: Phase Diagrams TTT and CCT Diagrams is essential. If you do not understand these, make sure you do. Ask your TA or Dr.Hartwig.

8. Phase Diagram (Fe-Fe3C)

9. A-austenite, B-bainite, M-martensite, P-pearlite F-proeutectoid ferrite TTT Diagram CCT Diagram for Eutectoid Steels

10. Terminology Spheroidizing Full annealing Ac 1 , Ac 3 ,Ac m are the phase boundaries