THE CREEP-BEHAVIOR OF 310-TYPE STAINLESS-STEEL

The primary and steady-state creep behaviour of 310-type stainless ste el has been investigated over the temperature range 500-700-degrees-C (0.46-0.58T(m)). The steady-state stress exponent, n, increased slight ly with increasing grain size, d, from n = 5.9 at d = 40 mum to n = 6. 4 at d = 100 mum at a test temperature T = 600-degrees-C. The activati on energy for steady-state creep, Q(c), determined at sigma = 300 MPa was 250 +/- 6.4 kJ mol-1 for d = 40 mum. This value of Q(c) is approxi mately equal to that for the volume self-diffusion of iron (280 kJ mol -1). The activation energy determined for primary creep is almost the same as that for secondary creep. The grain diameter parameter, m, in the equation epsilon(c) = Asigma(n)d(m) exp (-Q(c)/RT) was determined to be -1.67 for sigma = 300 MPa and T = 600-degrees-C. This value is s lightly different from a previously published value of m = -2, which w as obtained at a lower applied stress. Using the strain-time data obta ined in these tests, constitutive equations have been developed to des cribe both the primary and secondary creep behaviour. The creep strain , epsilon(c), is given by the polynomial expression: epsilon(c) = a0 a1t1/3 + a2t2/3 + a3t, where a0 is related to the initial strain on l oading, a1, a2 and a3 are all polynomial coefficients and t is the tim e. This equation fits the measured creep curves to an accuracy of 95-1 00%.