Question

3. For some transformation having kinetics that obey the Avrami equation, the parameter n is known to have a value of 1.7. If, after 100 s, the reaction is 50% complete, how long (total time) will it take the transformation to go to 99% completion? 4. Compute the rate of some reaction that obeys Avrami kinetics, assuming that the constants n and k have values of 3.0 and 7 x 10%, respectively, for time expressed in seconds. 5. Suppose that a steel of eutectoid composition is cooled to 550°C (1020°F) from 760°C (1400°F) in less than 0.5 s and held at this temperature. How long will it take for the austenite-to-pearlite reaction to go to 50% completion? To 100% completion. Eutectoid temperature 700 Temperature (°C) Temperature (°F) M (start) M + A M (50%) M 90% 100 200 10- 1 1 10 102 Times 103 104 106 Figure 1. The isothermal transformation diagram for an-iron-carbon alloy pf eutectoid composition.

Answer 1

sustine Avarami's kinetics n=1-7 time (t), sec I transformation 50%. 100 999% [f(t)= a -e kth/ avaram's kinetic equation. - (2.759 xrő^)(-) 0.5=1-ek (100)! en(0-5) = -K [1oogle? en (0-5) -Trooglof ek 0.99=1-€62.75axian) ** tn (1-0.99) = i 17 en (0.01) (2.759 x174) t - (16691-45) time t = 304 sec [ k=2.759x10

given data m=3 - 3 K = 7 xio hookt 27 faction transformed med allt) - le ... -K(+)" of ste en (1-4)= -kt" Here iam assuming t=4500 sec (trice) 6450239 f = le

Answer 2

It is known that the kinetics of recrystallization for some alloy obey the Avrami equation and that the value of n in the exponential is 2,5. If, at some temperature, the fraction recrystallized is 0,40 after 200 min, determine the rate of recrystallization at this temperature