Transient Creep and Strain Recovery of 2 1/4% Cr-1% Mo Steel under Bending

Abstract

The cantilever-bending creep tests of 21/4% Cr-1% Mo steel were carried out under steady or interrupted loads at 500°C to 580°C. The tests have revealed the following facts: In the transient creep stage the log-log plots of stress versus creep rate at the outermost fibre of the specimen lie on a straight line or two at any duration of time, and their slopes decrease with the time, indicating the time-dependency of the non-linear stress-distribution over the cross-section of the specimen. The creep rate ε during the transient stage is related to the time t according to ε=at^m or ε=at^m+k, where a, m and k are constants sensitive to temperature and load, similar to those in the conventional tensile creep test. The creep strain is partly recovered during the subsequent period of stress removal, and the strain recovery is characterized by the straight-line relationship between log (rate of strain recovery) and log (time), and by the recovery percentage decreasing with the increasing creep strain.