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Isothermal transformation diagrams (also known as time-temperature-transformation (TTT) diagrams) are plots of temperature versus time (usually on a logarithmic scale). They are generated from percentage transformation-vs time measurements, and are useful for understanding the transformations of an alloy steel at elevated temperatures.
[1] [3] Commercial use of bainitic steel thus came about as a result of the development of new heat-treating methods, with those that involve a step in which the workpiece is held at a fixed temperature for a period of time sufficient to allow transformation becoming collectively known as austempering.
Time-temperature transformation (TTT) diagram for steel. The red curves represent different cooling rates (velocity) when cooled from the upper critical (A3) temperature. V1 (quenching) produces martensite. V2 (normalizing) produces both pearlite and martensite, V3 (annealing) produces bainite mixed with pearlite.
English: TTT diagram of the isothermal transformations of a hypoeutectoid carbon steel, together with its relationship with the Fe-C phase diagram of carbon steels. Without exact values, only for educational purposes.
Steel with a high carbon content will reach a much harder state than steel with a low carbon content. Likewise, tempering high-carbon steel to a certain temperature will produce steel that is considerably harder than low-carbon steel that is tempered at the same temperature. The amount of time held at the tempering temperature also has an effect.
Type 2: This is the plot beginning with the transformation start point, cooling with specific transformation fraction and ending with a transformation finish temperature for all products against cooling rate or bar diameter of the specimen for each type of cooling medium.. TTT diagram for constant cooling rate transformations of steel.
These first Heisler–Gröber charts were based upon the first term of the exact Fourier series solution for an infinite plane wall: (,) = = [ + ], [1]where T i is the initial uniform temperature of the slab, T ∞ is the constant environmental temperature imposed at the boundary, x is the location in the plane wall, λ is the root of λ * tan λ = Bi, and α is thermal diffusivity.
2009-04-01 07:40 Slinky Puppet 607×404 (23247 bytes) Illustration of a continuous cooling transformation diagram for steel. Created by Slinky Puppet. Created by Slinky Puppet. Captions