Cyclic Creep Behavior and Modified Life Prediction of Bainite 2.25Cr-1Mo Steel at 455 °C

Hao Jiang,Bingbing Li,Zizhen Zhao,Xu Chen,Oluwadamilola Ogunmola

doi:10.3390/met10111486

Abstract

Uniaxial static and cyclic creep tests were carried out on bainite 2.25Cr-1Mo steel at 455 °C. Effects of the unloading rate from 0.6 to 39 MPa/s and valley stress duration from 0 to 30 min on the cyclic creep deformation behavior were discussed. The results indicated that the fracture behavior under static and cyclic creep conditions showed a consistent ductile mode. The strain accumulation rate under cyclic creep was significantly retarded as compared with static creep due to the presence of anelastic recovery which was apparently influenced by the unloading conditions. For cyclic creep tests, the unrecoverable strain component determined by a systematic classification of the stress–strain curve was the true damage. A modified life prediction method proposed based on the unrecoverable strain component presented a good life prediction for cyclic creep.

Highlights

Many engineering structures and components are frequently subjected to cyclic loadings during normal operation, which generally leads to a complicated failure mechanism caused by a combined damage mode of creep, fatigue, and their interactions [1,2,3,4,5]
The study of 9–12% Cr steel showed that the strain rate in cyclic creep was between that under ratcheting fatigue and static creep, i.e., the creep damage was more pronounced than the fatigue damage and the static creep rate determined the upper rate of the cyclic creep [11]
Research on the cyclic creep response of a nickel-based super alloy, DZ125, under different gradients of stress amplitudes and temperatures showed that cyclic creep accelerated the strain accumulation rate compared to static creep

Summary

Introduction

Many engineering structures and components are frequently subjected to cyclic loadings during normal operation, which generally leads to a complicated failure mechanism caused by a combined damage mode of creep, fatigue, and their interactions [1,2,3,4,5]. With the increase in duration under peak stress, a transition in dominant damage type from fatigue to creep can be found, and the fracture mode transformed from a brittle to ductile failure [10]. Research on the cyclic creep response of a nickel-based super alloy, DZ125, under different gradients of stress amplitudes and temperatures showed that cyclic creep accelerated the strain accumulation rate compared to static creep. The fatigue rate without a peak stress hold was reported to be the upper rate of the cyclic creep [14]. Other cases where fatigue damage dominated could be found on pure metal copper [15]

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