Isothermal time-temperature

Fig. 20.48 Isothermal time temperature transformation curves for (a) a eutectoid steel and...

The effects of quench rate on IGC for Al-Gu, Al-Gu-Mg, and Al-Cu-Mg-Mn alloys as well as for austenitic stainless steels is considered to be well-understood [43, 74, 75, 106]. Integration of the effects of precipitation and solute depletion at each temperature during a quench (i.e., quench factor analysis) can be compared to isothermal time-temperature-sensitization diagrams in order to predict the quench rate required to avoid IGC [43, 74]. Alloys... 

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). 

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]... 

Isothermal Time-Temperature-Transformations 14.2.1 Austenitic to Ferritic Transformation... 

The phase diagram tells us only what phases can exist in equilibrimn. The final micro-structure is controlled by the rate of transformation. A sketch of a typical isothermal time-temperature-transformation (often called a T-T-T diagram) map for the austenitic to ferritic transformation is shown in Figure 14.3. 

Time-temperature-transformation (T-T-T) diagrams are used to present the structure of steels after isothermal transformation at different temperatures for varying times. The T-T-T diagram for a commercial eutectoid steel is shown in Fig. 20.48a. Also shown on the curves are the points at which the microstructures illustrated in Figs. 20.46 and 20.47 are observed, and the thermal treatments producing these structures. When a steel partially transformed to, say, pearlite, is quenched from point a in Fig. 20.48a to below nif, the untransformed austenite transforms to martensite. 

Fig. 1 shows the thermal decomposition curves of HDPE mixed with Al-MCM-41, with respect to time, at isothermal operating temperatures. Lag periods were formed at the initial stage of decomposition, possibly due to the heat transfer effect, which could delay the decomposition of a sample until the latter reaches the operating temperatures. As the reaction ten erature increased, the reaction time became noticeably shorter. The shortening of the reaction time was clearly observed when the reaction occurred at the reaction teirperatures between 420 and 460 °C. The HDPE on Al-MCM-41-P decomposed faster than that on blank and that on A1-MCM-41-D, as shown in Fig. 1(b). 

As a result of fliese temperature - programmed runs, additiond experiments were conducted isothermally at temperatures between 723 - 873 K. Based on tbe second phase peak (peak 2), the conversion - time profiles at different temperatures exhibited a characteristic Sigmoid shape and may therefore be used to interpret the solid carburization kinetics. As detailed in Brown [5], the transient convrasion data may be d cribed by... 

We will consider gases under two possible conditions isothermal and isentropic (or adiabatic). The isothermal (constant temperature) condition may be approximated, for example, in a long pipeline in which the residence time of the gas is long enough that there is plenty of time to reach thermal equilibrium with the surroundings. Under these conditions, for an ideal gas,... 

Figure 3 shows a plot of the volume normalized nucleation time constant as a function of isothermal crystallization temperature for PEO droplets, taken from the work of Massa and Kalnoki-Veress [84]. As expected, droplets of different volumes have the same value of r V. The inset in Fig. 3 is a plot consistent with classical nucleation theory (see Eqs. 1, 4) only the last four data points correspond to the work of Massa and Kalnoki-Veress. The first... 

Fig. 9 Inverse of the crystallization half-time as a function of isothermal crystallization temperature for PCL11 homopolymer and for the PCL block of the indicated copolymers. All experiments were performed after the PPDX block had been previously crystallized until saturation. Solid lines are fits to the Lauritzen and Hoffman theory. (From [103]. Reproduced with permission of the Royal Society of Chemistry)...

The non-isothermal crystallization dynamics were performed using DSC, employing cooling rates of 2.5, 5, 10, 20, 25, 30, 35 and 40°C/min. The isothermal crystallization dynamics were studied for each sample heated to 290 °C, with a 5 min hold time, and cooled to the isothermal crystallization temperature using a cooling rate of 200°C/min, and then holding for 40 min to obtain the crystallization exotherm. 

Detector Flame ionization D elector oven 300°C Oven Temperature 130° C isothermal Time per run 30 minutes... 

In situ frequency dependent electromagnetic-impedence measurements provide a sensitive, convenient, automated technique to monitor the changes in macroscopic cure processing properties and the advancement of the reaction in situ in the fabrication tool. This chapter discusses the instrumentation, theory, and several applications of the techniques, including isothermal cure, complex time—temperature cure, resin film infusion, thick laminates, and smart, automated control of the cure process. 

Figure 24-10 Comparison of (a) isothermal (constant temperature) and ( >) programmed temperature chromatography. Each sample contains linear alkanes run on a 1.6-mm-diameter x 6-m-long packed column containing 3% Apiezon L (liquid phase) on 100/120 mesh WarAport 30 solid support with He flow rate of 10 mL/min. Detector sensitivity is 16 times greater in panel a than in panel b. [From H. M McNair and E. J. Bonelli, Basic Gas Chromatography (Palo Alto. CA Varian Instrument Division. 1968).]...

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