In Situ Growth-Stress Measurement of Cr2O3 Scale Formed on Stainless Steels by Raman Spectroscopy
Raman spectroscopy was conducted to evaluate mechanical stress in growing α-Cr2O3 scale upon oxidation of austenitic 25mass%Cr-20mass%Ni and ferritic 17mass%Cr stainless steels at 1173 K in air for up to 24 h. Sintered α-Cr2O3 pellet was heated to 373-1173 K and examined in order to obtain the temperature dependence of the wave length of the major Raman peak. For 1.2 mm thick 25mass%Cr-20mass%Ni steel specimen, compressive growth stress was indicated for α-Cr2O3 scale right upon oxidation and the stress increased until oxidation for 3 h, but it saturated and remained constant thereafter. The growth stress of α-Cr2O3 scale was 0.7 ± 0.1 GPa at 1173 K. For 1.2 mm thick ferritic 17mass%Cr steel specimen, mechanical stress was compressive, but the saturated growth stress was around 0.2 GPa, considerably smaller than the “strong” 25mass%Cr-20mass%Ni steel specimen. For 0.1mm thick austenitic 25mass%Cr-20mass%Ni steel specimen, the test results were similar. These were attributed to the different high-temperature strength of the metal substrate. Hence, for high-temperature oxidation of thin foils and/or ferritic steels of which high-temperature strength of the metal substrate is relatively poor, stress relaxation of protective α-Cr2O3 scale can result and the growth stress of α-Cr2O3 scale may be lowered by the “weak” metal substrate. Raman spectroscopy can offer useful information on the mechanical stress of protective oxide scale even at high temperatures.
Shigeji Taniguchi, Toshio Maruyama, Masayuki Yoshiba, Nobuo Otsuka and Yuuzou Kawahara
K. Kitamura et al., "In Situ Growth-Stress Measurement of Cr2O3 Scale Formed on Stainless Steels by Raman Spectroscopy", Materials Science Forum, Vols. 522-523, pp. 489-496, 2006