Evaluation method for creep damage of tempered martensitic steel

摘要

PROBLEM TO BE SOLVED: To evaluate creep damage-level, by sweeping and reversely sweeping an object at constant sweeping speed in the noble or base direction, and comparing peak current density at reverse sweep with known relation between creep damage level and peak current. SOLUTION: By specularly grinding surface on an examined area of a hot component consisting of steel containing about 8-12wt.% Cr, and masking the surface with insulating coating leaving 0.5-1cm2 of area to be measured, a test piece 1 is formed. Electrolyte solution is filled into circumferencial part of the test piece 1 to immerse the specularly-ground surface in it, and a reference electrode 5, a salt bridge 4, and a counter electrode 2 are installed. Natural electric potential of the test piece 1 which is in the zero voltage state is measured, then the piece 1 is polarized in the noble direction at a constant potential sweep speed, and after this condition is maintained for a given time the piece 1 is swept at same speed in the base direction. Current peak which appears during sweeping in the base direction is measured and the peak current density is determined. By comparing the peak current density with relational graph between peak current density and creep damage level which are predetermined from the known test piece, creep damage level on an examined area can be evaluated.