Creep Behavior Analysis of a 2.25 Cr-1Mo Steel under Accelerated Test Conditions

Creep behavior has been studied of a 2.25 Cr-1Mo steel under accelerated test conditions. The experimental results show that the minimum creep rate, εm, is well expressed by an equation from wihch an Arrhenius term is absent. This fact implies that the state equation for minimum creep rate fails to reflect the unique rate controlling process relevant to the creep mechanism. In a strain region where ε>εm (εm:strain corresponding to εm), the value of ln εincreases linearly with increasing strain, and the slope of the straight lines decreases with increasing initial stress. This fact shows implicitly that microstructure becomes hard at high stresses and soft at low stresses although creep rate increases with increasing time. The relation between creep life (tr) and εm is expressed by an equation, εmY·tr= KM-G orεmY'·(tr/εr)=KD-M, where Y, Y', KM-G and KD-M are constants. The time to minimum creep rate (tmin) was connected with creep life irrespectively of stress and temperature by an equation of tmin=0.111×tr1.07. When the extent of structural degradation is expressed by a minimum creep rate ratio of used to unused specimens, the remaining creep life of degraded materials is readily converted into the minimum creep rate ratio.