Influence of Pre-Aging on Creep Rupture Strength of Tungsten Alloyed 9%Cr Ferritic Steel and Creep Damage Evaluation by Electrochemical Method

Abstract

The influence of pre-aging on creep rupture strength has been investigated to understand the creep damage mechanism of tungsten alloyed 9%Cr ferritic steel KA-STBA29/KA-STPA29. Additionally, we have also examined changes in strengthening factors during creep and thermal aging by a nano-indentation test. Experimental results revealed that the creep rupture strength of thermally aged materials decreased with prolonged pre-aging and that the decrease in solid-solution strengthening due to Laves phase precipitation was mainly responsible for this reduction of creep rupture strength. Based on the results, an electrochemical nondestructive procedure, which quantitatively detected the amount of Laves phase, has been proposed to evaluate creep damage accumulation in the steel. By using this electrochemical method and a newly proposed parameter based on kinetics of Laves phase precipitation, a testing temperature or applied stress of creep-damaged materials can be nondestructively estimated with relatively high accuracy.