How do you explain TTT diagram?

Isothermal transformation diagrams (also known as time-temperature-transformation (TTT) diagrams) are plots of temperature versus time (usually on a logarithmic scale).

What does the TTT curve show?

The TTT diagram is really a simplified diagram of the kinetics of pearlite and bainite formation, and the diffusion-less transformation of martensite. It is a diagram of overlapping curves (Figure 6). The shape and position of the curves depend on the alloy composition, grain size, and carbon content.

Which types of curves are used to construct TTT diagrams?

Explanation: S curve, C curve isothermal diagram and Bain’s curve are all names given to time temperature transformation diagrams.

What are TTT diagrams list any 3 information that a TTT diagram can provide?

TTT diagram gives 3- Stability of phases under isothermal transformation conditions. 4- Temperature or time required to start or finish the transformation. 5- Qualitative information about the size scale of the product. 6- Hardness of transformed products.

Which is hardest structure in TTT diagram?

Cementite or iron carbide • Cementite or iron carbide, is very hard, brittle intermetallic compound of iron & carbon, as Fe3C, contains 6.67 % C. It is the hardest structure that appears on the diagram, exact melting point unknown. Its crystal structure is orthorhombic.

Why is TTT curve C shaped?

The C curve for TTT is usually represented by superimposing both Pearlite and Bainite region. Now in the CCT curve which is a Continuous Cooling Transformation curve. The lower curve is not formed because of the insufficient time for upper range of transformation and hence it Directly forms Martensite.

What is the difference between TTT and CCT diagram?

The primary difference between TTT diagrams and CCT diagrams is that TTT diagrams examine the progress of transformation as a function of time, at a fixed temperature. CCT diagrams examine the progress of transformation as a function of changing temperature.

What is bainite structure?

Bainite is a plate-like microstructure that forms in steels at temperatures of 125–550 °C (depending on alloy content). A fine non-lamellar structure, bainite commonly consists of cementite and dislocation-rich ferrite.

How bainite is formed?

Bainite forms by the decomposition of austenite at a temperature which is above MS but below that at which fine pearlite forms. All bainite forms below the T0 temperature. All time–temperature–transformation (TTT) diagrams consist essentially of two C–curves (Fig.

What are the temperature limits for Austenitizing steel 0.5 C?

The austenitizing temperature is usually in the range 850 to 950 °C. Decreasing the austenitizing temperature increases the initial rate and decreases the time for the stage I transformation.

How is the TTT diagram used in metallurgy?

Time-Temperature-Transformation (TTT) Diagram T (Time) T (Temperature) T (Transformation) diagram is a plot of temperature versus the logarithm of time for a steel alloy of definite composition. It is used to determine when transformations begin and end for an isothermal (constant temperature) heat treatment of a previously austenitized alloy.

What do the curves on the TTT diagram mean?

TTT Diagram In Figure 1a the area on the left of the transformation curve represents the austenite region. Austenite is stable at temperatures above LCT but unstable below LCT. Left curve indicates the start of a transformation and right curve represents the finish of a transformation.

What does the TTT diagram of austenite mean?

TTT diagram indicates when a specific transformation starts and ends and it also shows what percentage of transformation of austenite at a particular temperature is achieved. Look at figure 1b and 1c. Figure 2. Upper half of TTT Diagram (Austenite-Pearlite Transformation Area)

How to describe a time temperature transformation curve?

For a given steel, the information given by a series of such curves, each curve determined at a different temperature, can be summarized by a single diagram called a Time-Temperature-Transformation (TTT) curve. This is shown in Figure 5.