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Unformatted text preview: etain original neighbors. Carbon atoms are trapped in the
Martensite lattice is distorted. HARDNESS AND STRENGTH OF MARTENSITE
Hardness Increases with carbon content which decreases ductility and toughness
• dislocation density
• packet size
• lath size ISOTHERMAL DECOMPOSITION
Rapid cooling to below the eutectoid temperature
Transformation occurs with time at a constant temperature. STEPS IN ISOTHERMAL TRANSFORMATIONS
1. Austenitize 2. Rapidly cool to isothermal temperature 3. Allow time to transform the specimen ISOTHERMAL TRANSFORMATIONS ISOTHERMAL DIAGRAMS
By repeating the steps and using different transformation
temperatures a C-curve relationship occurs. PEARLITE TRANSFORMATION
Occurs between 723ºC and ~550ºC.
Time and temperature dependent.
Finer pearlite spacing occurs as
temperature decreases. Maximum growth rate
(fastest formation) occurs
at the shortest time in the
C-curve. BAINITE TRANSFORMATION
Occurs between approximately 550ºC and 250ºC.
Non-lamellar structure of ferrite and cementite.
Intermediate between martensite and pearlite.
Carbon transforms by diffusion.
Austenite to ferrite by shear. NON - EUTECTOID ISOTHERMAL DIAGRAMS
Hypoeutectoid Produces a proeutectoid ferrite
C-curve ahead of the pearlite curve.
Decreasing carbon decreases the
time for transformation. Hypereutectoid Produces a proeutectoid cementite
C-curve ahead of the pearlite curve. CONTINUOUS COOLING TRANSFORMATION DIAGRAMS In the real world, steel is generally continuously cooled from the austenitizing temperature to room
The transformation of austenite occurs over a
range of temperatures rather than a single
isothermal temperature. Connection between Isothermal Diagram,
Continuous Cooling Diagram, and Cooling Rate Curves C-T DIAGRAM
The final microstructure, as a result of transformation
over a range of temperatures, is very complex.
The continuous cooling diagram transformation start
and finish lines are shifted to longer times and lower
temperatures in relation to the isothermal diagr...
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This document was uploaded on 02/27/2014 for the course NANO 108 at UCSD.
- Fall '13