Transformations bainite

P segregation or if there are martensitic or bainitic transformation structures. The Mn level around linear cracks may be twice that in the matrix, whereas the P level may be elevated by a factor of 10.129... 

Sri] Magnetically checking for carbide separation during quenching, TEM, electron diffraction austenized at 1250°C and water quenched specimens were isothermally held at 285°C and frnally quenched into cold water, 7.9 mass% Cr and 1.11 mass% C 3.3 mass% Cr and 0.6 mass% C Bainite transformation... 

Eno] Enomoto, M., Tsubakino, H., Morphology and Thermodynamics of Bainitic Transformation in Ferrous and Non-Ferrous Alloys , Mater. Trans., JIM, 32(8), 642-657 (1991) (Phase Relations, Thermodyn., Kinetic, Abstract, 114)... 

Mor] Morozov, O.P, Relation Between Exeess Ferrite Preeipitation and the Upper Bainite Transformation of Austenite in Steels (in Russian), Fiz. Met. Metalloved., (8), 154-162 (1991) (Morphology, Phase Relations, Experimental, Kineties, 24)... 

Gri] Grigorkin, V.I., Korotushenko, G.V., hifluence of Carbon on die Rate of Bainite Transformation in Iron-Manganese Alloys , Steel USSR, 3,1034-1035 (1973) (Kinetics, Experimental, 12)... 

In the review [2004Tak], two models of the overall kinetics of the bainite transformation, one of which is the diffusion controlled growth model of the bainitic laths and the other is the nucleation of bainite ferrite plates controlled model, have been discussed. It was shown that formation and competition of bainitic ferrite and cementite can be predicted quantitatively. 

Tak] Takahashi, M., Reeent Progress Kinetics of die Bainite Transformation in Steels , Curr. 

Rey] Optical metallography, transmission electron microscopy Austenite-Bainite transformation, 3 mass% Ni, < 0.6 mass% C... 

Qui] [2002Qui] Dilatometry, microscopic observations Austenite-Bainite transformation, 4.9 mass% Ni, 0.49 mass% C... 

Met] observed the formation of the martensite from the residual austenite supersaturated in carbon which normally leads to the bainite transformation at 420°C. The common crystallographic plane between ferrite and austenite is a (3,15,10)cfc type witii a Greninger-Troiano orientation [1970Met]. The temperature Ms of the martensitic transformation is estimated to be -130°C. The martensitic phase could not be developed if the spheroid graphite is present in the sample [1973Sch2]. 

Sch2] Schissler, J.-M., Metauer, G., Influence of the Isothermal Bainitic Transformation at 420°C on Graphitization by Ulterior Recovery in Hypereutectoid Fe-C-Si Alloys with 3.9% Siheon (in French), Compt Rend. Hebd. Acad. Set, Ser. C, 277(20), 997-999 (1973) (Experimental, Crys. Stmcture, 4)... 

Bainite, a plate- or spearhead-shaped product consisting of a ferrite matrix in which carbide particles are dispersed. The bainitic transformation mechanism depends sensitively on alloy composition and the temperature of transformation, yielding essentially two microstructural variants. A somewhat coarser transformation product formed at about 450 is called upper bainite and a finer transformation product formed at about 350 °C is termed lower bainite. 

K. Tsuzaki and T. Maki, "Some aspects of bainite transformation in Fe-based alloys". Journal De Physique Iv, 5(C8), 1995 pp. 61-70. 

Bainite forms isothermally as an intermediate transformation product above but below the temperature of eutectoid decomposition in ferrous alloys. This product is a mixture of ferrite and carbide, which is distinctly different from pearlite (a eutectoid product), and is termed bainite in honor of E. C. Bain who first observed such microstructures in collaboration with Davenport (Davenport and Bain, 1930). Bainite also forms during continuous cooling. Bainite transformations occur not only in ferrous alloys but also in non-ferrous... 

The high-temperature jS-b.c.c. (A2, cI2) phase of binary and ternary Cu-Zn alloys and binary Ag-Cd and Ag-Zn alloys transforms when cooled or quenched into a metastable ordered b.c.c. phase that has either a B2 (cP2), DO3 (cF16) or L2i (cF16) structure. This metastable phase undergoes a bainite transformation during isothermal aging into a f.c.c.-based a phase (also called a, phase) having either a 9R or 18R... 

Figure 13. Macroscopic shape change during bainite transformation in a Cu-40Zn alloy subjected to a tensile stress of 98 MPa at 473 K. The curve is theoretical (After Takezawa and Sato, 1986)...

It has been accepted that a compositional change occurs in association with bainite transformation, but when diffusion actually occurs has been in debate. Recent studies with analytical electron microscopy, which has improved resolution, have revealed that the compositions of an ot, bainite plate and the surrounding matrix are distinctly different even at a very early stage of growth in Cu-Zn (Cliff et al., 1990), Cu-Zn-Al... 

This model appears most plausible in describing certain observations associated with bainite transformation. However, there are some unexplained phenomena, e.g. the observation that the initial composition of bainite plates in Cu-Zn-Al and Cu-Zn-Au alloys is almost equal to that of the equilibrium f.c.c. a phase. 

Bainite transformations occur in many ordered b.c.c. phases upon isothermal aging above and below eutectoid temperatures. Bainite plates form martensitically either immediately after, or simultaneously with, some compositional change at a local region of the matrix that has lattice defects, whose localized stress fields assist solute atoms to diffuse. Upon prolonged aging, the... 

Detailed structural and chemical analyses of bainite forming in ordered intermetallics have upgraded experimental understanding of bainite transformation. However, a lack of imderstanding of theoretical aspects remains. 

The time-temperature dependence of the bainite transformation may also be represented on the isothermal transformation diagram. It occurs at temperatures below those at which pearlite forms begin-, end-, and half-reaction curves are just extensions of those for the pearlitic transformation, as shown in Figure 10.18, the isothermal transformation diagram for an iron-carbon alloy of eutectoid composition that has been extended to lower temperatures. All three curves are C-shaped and have a nose at point N, where the rate of transformation is a maximum. As may be noted, whereas pearlite forms above the nose [i.e., over the temperature range of about 540°C to 727°C (1000°F to 1341 °F)], at temperatures between about 215°C and 540°C (420°F and 1000°F), bainite is the transformation product. 

Note that the pearlitic and bainitic transformations are competitive with each other, and once some portion of an alloy has transformed into either pearlite or bainite, transformation to the other microconstituent is not possible without reheating to form austenite. 

Briefly explain why there is no bainite transformation region on the continuous-cooling transformation diagram for an iron-carbon alloy of entectoid composition. 

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