Question

6.5 18. (8 pts) The Diffusivity of nitrogen in y-iron is 4 times higher at 1200°C than at 950 C. (a) Find the activation energy for nitrogen diffusion in iron. R 1.987 cal/mol-K Do exp (1.987- wal vevisit lo ala exo 29 26, 451 l 2430. 10 alalS 29 24.851 2430 29 2a 24 30. 19. (10 pts) To improve the wear resistance of a steel gear, a carburization process is employed to harden the surface of the machine element by exposing it to a carbon rich atmosphere at high temperatures. Determine the surface C concentration required to reach 0.60wt % at a depth of 0.75mm within 35 min if the initial C concentration in the steel part is 0.2wt%. The diffusivity at the processing temperature is 1.5944 x 10"cm2/s ** 70 mafe t1o t.86min0s2z100 sec Imin is-G.2 math erro r. ts-o. 76-9.60.05 ((-0.2) -0.6 0.65 (6-0,13 C-0.65 G.4 a(1-0.65) 0.9 Cs 1.34X elese

Answer 1

- 18 soli 8) soli Diff nitrogen (D.) = 4 Diffurinity of veiran (₂) Pia 4 P2 un () ( + Ti=1200 +278=1478k. 12 = 9 so t278 - 1228 k ole R = 1.987 cal/molk. 68 1228 1478 1.987 Cal molik .377 4K 10 - 1.3862 = - -13 1 1987 code Ea 1.987 cal mol E a = 19998.307 cal Ea= 19.998 kcal mol