8.33 (a) Estimate the activation energy for creep (i.e., Qc in Equation 8.20) for the S-590 alloy having the steady-state creep behavior shown in Figure 8.31. Use data taken at a stress level of 300 MPa (43,500 psi) and temperatures of 650°C and 730°C. Assume that the stress exponent n is independent of temperature. (b) Estimate &, at 600°C (873 K) and 300 MPa. 1000 800 600 650°C 400 730°C 200 815°C 925°C 100 80 60 40 20 10-6 10-5 104 10-3 1p2 102 10 103 Steady-state creep rate (h-l) o = 300Mpa T=650C=923K,ɛ =8x10-5 T, =730C=1003K,ɛ,=8x10-(1/h) E =ko" exp(- RT R=8.314.J.mol-K-l=8.62×10-SeV atomK-1 Stress (MPa)

8.33 (a) Estimate the activation energy for creep (i.e., Qc in Equation 8.20) for the S-590 alloy having the steady-state creep behavior shown in Figure 8.31. Use data taken at a stress level of 300 MPa (43,500 psi) and temperatures of 650°C and 730°C. Assume that the stress exponent n is independent of temperature. (b) Estimate &, at 600°C (873 K) and 300 MPa. 1000 800 600 650°C 400 730°C 200 815°C 925°C 100 80 60 40 20 10-6 10-5 104 10-3 1p2 102 10 103 Steady-state creep rate (h-l) o = 300Mpa T=650C=923K,ɛ =8x10-5 T, =730C=1003K,ɛ,=8x10-(1/h) E =ko" exp(- RT R=8.314.J.mol-K-l=8.62×10-SeV atomK-1 Stress (MPa)