Ductile region

Similarly it seems that retained austenite may be beneficial in certain circumstances , probably because the austenite acts as a barrier to the diffusion of hydrogen, although in high concentrations (such as those obtained in duplex stainless steels) the austenite can also act as a crack stopper (i.e. a ductile region in the microstructure which blunts and stops the brittle crack). 

Beyond point E, the material begins to plasticly deform, and at point Y the yield point is achieved. The stress at the yield point corresponds to the yield strength, Oy [see Eq. (5.20)]. Technically, point Y is called the upper yield point, and it corresponds to the stress necessary to free dislocations. The point at which the dislocations actually begin to move is point L, which is called the lower yield point. After point L, the material enters the ductile region, and in polycrystalline materials such as that of Eigure 5.26, strain hardening occurs. There is a corresponding increase in the stress... 

Table 1 Main differences between the brittle zone and the ductile region of large hydrothermal systems. Pressure and temperature ranges are only indicative values.

In crystalline rocks, this transition may occur over a broad temperature range, but typically occurs between 300-450°C (Manning and Ingebritsen 1999 Simpson 1999). For typical crustal gradients of 30°C/km, transition from the brittle to the ductile region occurs between 10- to 15-km depth. 

Figure 11-14. Schematic representation of the tensile stress aw as a function of strain e at constant temperature for an elastomer E, a partially crystalline thermoplast T, and a hard-elastic thermoplast HT. The ductile region is la-II-III. The necking effect shown below the diagram is typical of normal thermoplasts, but does not occur with elastomers or hard-elastic thermpolasts. The diagram is not drawn to scale for example, elastomers show a much larger elongation at break than do thermoplasts.

Point II is the maximum of the force/deformation curve and is called the yield stress The drawing stress is at point III. Finally, the tenacity at break or the tensile strength and the elongation at break occur at the point IV. The region between the points la, II, and III is what is known as the ductile region. The decrease in tensile stress with increasing strain between... 

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