High Temperature, High Cycle Fatigue Demeanor of 10wt% cr Steel and Unlike Metal Weld

Abstract

The present study primarily focuses on understanding the high cycle fatigue behavior (HCF) of alloy 10wt%Cr Ferritic Steel and Dissimilar metal weld (DMW) joint between 617M and 10wt%Cr Ferritic Steel. For assessing the HCF behavior, tests were conducted under stress controlled cycling, by employing dissimilar stress ratios (R) and wide range of temperatures (300 K – 853 K). The S-N curves plotted at R= -1 and temperatures (300 K,673 K,853 K) for 10wt%Cr Ferritic Steel shows that fatigue life decreased with increase in stress amplitude. It is also observed that fatigue life of 10wt%Cr Ferritic Steel falls with increase in the temperature regardless of the stress amplitude, clearly showing the strong dependence of fatigue life on the temperature. An effort has been made to find out the fatigue parameters at 300 K and 853 K using Basquin equation. These fatigue parameters were used for life prediction, showed that predicted life is in good agreement with experimental life with in a scatter band of 2. At 853 K, Goodman diagram shows that limiting alternating stress decreases with increase in the mean stress. The results were linked with the detailed scanning electron microscope investigation where it is analyzed that at 300 K, the fatigue failure was by trans-granular mode, characterized by striations while at 673 K and 853 K, intergranular mode and strong oxidation is seen, thus lowering the life at said temperatures. The standard S-N behavior for DMW at R= -1 and at temperature of 853 K showed that the welding reduces the number of cycles to failure. Vicker’s hardness measurements show that there is softening in the 10wt%Cr side & hardening in the butter layer resulting in failure of all non-defective samples on the 10wt%Cr side. HCF test was also showed on damaged samples at 230 MPa and 200 MPa, found, that crack initiates & propagates near the damage at 230 MPa while at 200MPa crack initiates and propagates in the 10wt%Cr side irrespective of the damage.