Continuous temperature-transformation

Temperature-Transformation Diagram (TTT Diagram), Continuous-temperature-Transformation Diagram (CTT Diagram) and Critical Cooling Rate... 

Heating mantles. These consist of a flexible knitted fibre glass sheath which fits snugly around a flask and contains an electrical heating element which operates at black heat. The mantle may be supported in an aluminium case which stands on the bench, but for use with suspended vessels the mantle is supplied without a case. Electric power is supplied to the heating element through a control unit which may be either a continuously variable transformer or a thyristor controller, and so the operating temperature of the mantle can be smoothly adjusted... 

For a number of applications, particularly those associated with conditions of continuous cooling or heating, equilibrium is clearly never approached and calculations must be modified to take kinetic factors into account. For example, solidification rarely occurs via equilibrium, amorphous phases are formed by a variety of non-equilibrium processing routes and in solid-state transformations in low-alloy steels much work is done to understand time-temperature-transformation diagrams which are non-equilibrium in nature. The next chapter shows how CALPHAD methods can be extended to such cases. 

Fig. 4.15 Characteristic free-energy temperature diagram (a) and DSC traces (b) for the enantiotropic relationship between polymorphs. The Gi and Gu curves cross at the transition temperature 7[ n below their melting points mpi, and mpn all indicated on the temperature axis. DSC trace A at the transition temperature modification I undergoes an endothermic transition to modification II, and the heat absorbed is A/fi n for that transition. Modification II then melts at mpn, with the accompanying AHfu. DSC trace B Modification I melts at mpi with A//n followed by crystaUization of II with A//ni at the intermediate temperature. Modification II then melts with details as above. DSC trace C modification II, metastable at room temperature, transforms exothermically to modification I with A/fn i at that transition temperature. Continued heating leads to the events in trace A. DSC trace D modification II exists at room temperature and no transition takes place prior to melting at mpn, with the appropriate A//ni- (After Giron 1995, with permission.)...

Fig. 18. Continuous-cooling transformation diagram for a Type 4340 alloy steel, with superimposed cooling curves illustrating the manner in which transformation behavior during continuous cooling governs final microstmcture (1). Ae is critical temperature at equiHbrium. Ae is lower critical...

Okoyuma et al. have reported that the strained Dewar paracyclophanes (98) can be converted into the benzenoid parent compounds (99) by irradiation of the compounds in a diethylether-isopentane glass at 77 K using 365 nm light. Interestingly when (99, R = CN, = H) is allowed to thaw to room temperature there is a thermal reaction that converts it back into the Dewar form which provides the first observation of such a thermal cyclization. Irradiation at 254 nm of the tetraene (100), a hk-Dewar benzene, at 77 K in a matrix results in its conversion into the paracyclophane (101). Continued irradiation transforms (101) into the (4+4)-adduct (102). The products from this low temperature... 

In situ HT investigation of the Lao,64Cao,o4Ti03 and Lao.eCao.iTiOs structures revealed the continuous phase transformations from orthorhombic to tetragonal structure (space group P4/mmm) above the temperatures 704... 

D. Time-Temperature-Transformation and Continuous-Heating-Transformation Curing Diagrams of PF Resins in situ in the Joint... 

VI. TEMPERATURE-TIME-TRANSFORMATION AND CONTINUOUS-HEATING-TRANSFORMATION CURING DIAGRAMS OF MUF RESINS WHEN ALONE AND HARDENING IN A WOOD JOINT (OR OTHER INTERACTIVE SUBSTRATE)... 

The thermodynamic differences between spinodal decomposition (a continuous phase transformation) and nucleation and growth (a discontinuous phase transformation) are illustrated in Figure 6.6. At a given temperature, the volume free... 

Fig. 3.1-113 Continuous-cooling-transformation (CCT) diagram for a 4130 grade low-alloy steel. Acs and Ac signify the temperatures of the y/ y+a) and eutectoid reation, respectively. A - austenite, F - ferrite, B - bainite, P - pearlite, M - martensite. The cooling rate is measured at 705 °C. The calculated critical cooling rate is 143 K/s [1.80]...

This critical cooling rate ( q ) has been estimated by use of isothermal time-temperature transformation ( IT T) diagrams (Uhhnann 1972) or continuous cooling transformation (CT) curves Onorato and Uhlmann 1976). 

Chapter 1 (Phase Equilibria in Binary and Ternary Hydro-thermal Systems, V. M. Valyashko, Russia) contains a description of the general trends of sub- and supercritical phase behavioin in binary and ternary systems taking into accoimt both stable and metastable equilibria. A presentation of the various types of phase diagrams aims to show the possible versions of phase transitions under hydrothermal conditions and to help the reader with the determination of where the phase equilibrium occurs in p-T-X space, and what happens to this equilibrium if the parameters of state are changed. Special attention is paid to continuous phase transformations taking place with variations of temperature. 

For hardening and subsequent tempering operations, the heat treatment contractor should be guided by the recommendations of the steel maker given in the data sheets for the material concerned. These heat treatment recommendations are derived from the chemical composition of the steel used. Material-specific, continuous and isothermal Time-Temperature-Transformation (TTT) diagrams, as shown in Figure 4.80, describe the transformation behaviour of the steel s microstructure [3]. 

FiGURE 4.80 Continuous and isothermal time-temperature-transformation diagram of the steel 1.2343 (X37CrMoV5-1) [4]... 

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