Issue 42

A. Strafella et alii, Frattura ed Integrità Strutturale, 42 (2017) 352-365; DOI: 10.3221/IGF-ESIS.42.36 357 a) 0 200 400 600 800 1000 1200 1400 -0,005 0,000 0,005 0,010 0,015 0,020 0,025 sscr-Derivative creep strain [%/h] time[h] Derivative Creep Strain - [560 MPa] Derivative-Creep Strain % - [400MPa] Derivative Y1-Creep Strain % - [300 MPa] Derivative-Creep Strain % - [500 MPa] b) 0 200 400 600 800 1000 1200 1400 1600 0,0 0,5 1,0 1,5 2,0 2,5 T= 550°C Air Creep Strain [%] Time [h] Creep Strain Medio % - [560MPa] Creep Strain % - [300 MPa] Creep Strain % - [400MPa] Creep Strain % - [500 MPa] Linear Fit Figure 6 : sscr calculus: minimum of first derivative (a) and fit linear of secondary creep stage (b) . The steady strain creep rates were plotted in a log–log graph. Fig. 7 shows the variation of sscr with the applied stress. The variation of sscr with applied stress obeys a power law relationship in the form of Norton-type: n sscr A   (1) where σ is the applied stress, n is the stress exponent, and A is an empirical constant. For 15-15Ti(Si) steel, the found A and n values are shown in Tab. 3.