Effect of a Small Amount of Carbon and Carbon + Lanthanum on the Creep Characteristics of a Fe-20Cr-5Al Alloy

Abstract

The present paper reports the effect of a small amount of carbon (50-300 ppm) and carbon plus lanthanum (0.04-0.15mass%) on the high temperature creep characteristics of a Fe-20Cr-5-Al ferritic stainless steel. Testing was conducted over the stress range from 3.9 to 6.9 MPa at 1173 K. It was found that creep life increases with increase in caron concentration. The beneficial effect of carbon, however, decreases with increase in applied stress and carbon concentration especially when the carbon concentration exceeds 150 ppm. For steels with 0.1 mass % lanthanum, creep life increases with increase in carbon up to 300 ppm. The average creep rate of the steels with 150 ppm carbon is inversely proportional to the lanthanum concentration. This suggests that dislocations drag their solute atmosphere of lanthanum. For the steels with 0.1 mass % lanthanum and various amounts of carbon, the average creep rate is inversely proportional to the carbon concentration whereas that for the steels without lanthanum is not proportional to the reciprocal of carbon concentration. The effect of this type of carbon was interpreted by the I-S interaction with which the carbon increases the apparent size misfit of lanthanum atom.