PURPOSE: To easily and surely measure the deterioration of time aging for heat- resisting steel, by measuring the size of subgrain near the initial austenite bondary of ferrite heat-resisting steel used at high temperature, and comparing it with the criterion.
CONSTITUTION: The ferrite heat-resisting steel used at high temperatures such as steam turbine members forms the subgrain with the rearrangement of transformation introduced at heat treatment near ex-austenite. The subgrain size is measured, and the degree of deterioration formed from the fatigue deterioration test is compared with the deterioration criterion chart showing the relation between the subgrain size and the deterioration to estimate the deterioration of heat-resisting steel. For example, if the subgrain size is 2.5μ at point A, and the ratio of the creep deterioration of steel to fatigue deterioration is analyzed as 6:4 from the operation pattern, the life expectancy can be estimated from the figure as about 40%. This value is well in agreement with the simulated deterioration test.
NAKAMURA SHINICHI
NAKABASHI MASAKO
TAKEDA HIROMITSU
