Companion to the TTT diagram, built by cooling samples at many fixed rates and recording where each phase starts and finishes. Overlaid cooling curves show whether a given quench or air cool ends up as ferrite and pearlite, bainite or martensite, often with predicted hardness at the end of each curve. Engineers read it to choose between oil, polymer and gas quenching for a specific steel and section size.
CCT diagram says 8620 at that cooling rate goes half bainite, so don't expect full core hardness off a gas quench.
Also heard as
- continuous cooling transformation diagram
- CCT curve
Related terms
TTT diagram
Time-temperature-transformation chart showing how long austenite takes to transform when held at a fixed temperature.
Hardenability
A steel's ability to form martensite to a given depth, set by its chemistry and grain size, not its hardness.
Quench severity
How fast a quenchant pulls heat out of steel, usually rated by the Grossmann H value.
Martensite
The hard, needle-like phase that forms when austenite is quenched fast enough to trap its carbon.