Calculation of the oxide growth rate of 2-1/4 Cr - 1 Mo steel in air and the subsequent measurement of the strain required to crack the oxide

Abstract

This study examined the growth rate of 2-1/4 Cr - 1 Mo steel in air under isothermal growth conditions. Two oxidizing temperatures were used, 403 degrees and 499 degrees, for five specimens each with oxidizing times varying from six hours to 700 hours, Average oxide growth rate as a function of time and temperature was found to be rate = 2.10 X 10(-3) exp -12950/RT whereas maximum oxide growth rate corresponds to rate = 4.50 x 10(-3) exp -13520/RT . These values were found to be in general agreement with the limited data available in the literature. The second part of the experiment related to the measurement of the strain required to crack the oxide. Discrete surface strains were imparted to oxidized specimens via a four-point-bend straining apparatus. The strained specimens were optically scanned for cracks with a stereoscope microscope capable of 70X magnification. A process of crack decoration was employed to enhance crack visibility. Because of certain equipment limitations, however, only an upper limit of strain tolerance could be determined, Methods of improving strain tolerance measurements are discussed.