Cyclic Creep Behavior and Modified Life Prediction of Bainite 2.25Cr-1Mo Steel at 455 °C
Round 1
Reviewer 1 Report
Page 8, line 209-211
Please check and correct these sentences, because the meaning is not clear.
"According to the correlation between anelastic recovery and dislocations motion. The value of applied stress is constant under all tests in this work, increase in the unlading rate means a decrease in the unloading time."
Author Response
Thanks for your valuable comment. The two sentences are modified as follows:
Moreover, the correlation between anelastic recovery and dislocations motion could be reflected by a micromechanical modeling [40]. In this work, the applied stress amplitude is constant in all tests ( σmax=455MPa and R=0.0375), thus the higher unloading rate leads to shorter unloading time.
Reviewer 2 Report
1. The quality of the drawings should be improved. Probably .jpg or other bitmap files were pasted. I suggest pasting drawings in vector graphics or other.
2. I propose - but this is for the future - that in the case of creep, ideal body models, e.g. the Kelvin-Voigt model, preferably multi-parameter model, should be used for mathematical description.
Author Response
- The quality of the drawings should be improved. Probably .jpg or other bitmap files were pasted. I suggest pasting drawings in vector graphics or other.
Answer: Thanks for your valuable suggestions deeply. After careful checking, we found the low quality of the drawings in the manuscript of PDF version you reviewed is caused by the transversion process from Word to PDF, which reduces the quality of drawings. All the drawings we provide in the manuscript is in accordance with the requirements of the journal.
- I propose - but this is for the future - that in the case of creep, ideal body models, e.g. the Kelvin-Voigt model, preferably multi-parameter model, should be used for mathematical description.
Answer: Thanks very much for your suggestion. We will try to study and apply the above-mentioned models in the future studying.
Reviewer 3 Report
General comments
This research study the creep deformation and fracture behavior of bainite 2.25Cr-1Mo steel under uniaxial static and cyclic creep in stress-controlled tests at temperature of 455°C, and examines the effect of unloading rate and valley stress duration on the cyclic creep deformation. Longer endurance life was received under cyclic creep than under static creep according to anelastic recovery phenomenon, which is related to dislocation motion. A ductile fracture mode was observed under both static and cyclic creep loading cases. Yet, the ductility of samples fractured after cyclic creep was somewhat lower than that achieved after static creep.
The current study is innovative and the manuscript is well organized and easy to read. The work presented here is interesting and the subject is relevant for the readers of Metals. Therefore, I recommend to publish this contribution in Metal after minor revision as explained below.
- Introduction
(1) The introduction is well written, focused and easy to follow. Yet, at the end of the introduction part, the goal of the current study should be explained.
- Materials and Methods
(2) The quality of Figure 1 should be improved.
(3) What was the standard that used in order to produce the specimens and what was the standard that used during the creep testing?
(4) What was the total number of specimens that were tested during the experiments of the current research, and how many specimens were tested for each condition?
(5) Line 88: “Uniaxial static creep and cyclic creep tests were carried out on an electronic creep testing machine”. Additional information about the electronic creep testing machine is needed. What is the error associated with this type of testing machine and experiments?
(6) Information should be added concerning the SEM instrument that was used for the fractographic observation. What were the working conditions under the SEM microscope during the observation of the fracture surface?
- Results and Discussion
(7) The part of the results and discussion is clearly written and well organized. The caption of Figure 5 should be corrected. Line 150, Figure 5 caption: “SEM observations of fractured surfaces: (a) static creep and (b) enlarged inner fibrous zone; (c) cyclic creep at 12 MPa/s and (d) 39 MPa/s unloading rate without valley stress duration; (f) cyclic creep with 10 min and (g) 30 min duration under valley stress with an unloading rate of 12 MPa/s.” Section (e) is missing in the caption and section (g) does not appear in Figure 5 and should be removed from the caption.
- Conclusions
The conclusions are significant, clearly stated, focused and easy to follow.
- References
The references are written according to the journal guidelines.
Author Response
- The introduction is well written, focused and easy to follow. Yet, at the end of the introduction part, the goal of the current study should be explained.
Answer: Thank you for your valuable suggestion. The modified introduction is rewritten as follows and is added to the revised manuscript to replace the original one:
" In this study, a series of uniaxial cyclic creep tests under stress-controlled mode on bainite 2.25Cr-1Mo steel at 455°C in air were conducted. The strain accumulation processes under different unloading conditions were analyzed through the strain classification. Specific attention was paid to the effect of unloading rate and valley stress duration on the anelastic recovery behaviour. Moreover, scanning electron microscopy (SEM) observations of fracture surfaces were performed. The goal of the current study is to identify the failure mechanism of static creep and cyclic creep on 2.25Cr-1Mo steel at high temperature, and propose a modified life prediction method for cyclic creep considering anelastic recovery.".
- The quality of Figure 1 should be improved.
Answer: Thank you for your very valuable suggestion. The high-quality Figure 1 is replaced in the revised manuscript.
- What was the standard that used in order to produce the specimens and what was the standard that used during the creep testing?
Answer: Thank you for your very valuable suggestion.
The standard of the specimen machining and creep tests is added to the revised manuscript in Section 2. Materials and Methods of line 88-89: “The standard used in this work for the specimen machining and creep tests preformation is ISO 204;2009.”.
- What was the total number of specimens that were tested during the experiments of the current research, and how many specimens were tested for each condition?
Answer: Thank you for your very valuable suggestion. Eight specimens were tested during the experiments of the current research, where the cyclic creep at 12 MPa/s unloading rate without valley stress duration was tested twice to verify repeatability.
- Line 88: “Uniaxial static creep and cyclic creep tests were carried out on an electronic creep testing machine”. Additional information about the electronic creep testing machine is needed. What is the error associated with this type of testing machine and experiments?
Answer: Thank you for your very valuable suggestion. The additional information about the electronic creep testing machine was added to the revised manuscript in Section 2. Materials and Methods of line 97-100: “The module of electronic creep testing machine mainly includes high-temperature heating furnace, three K-type thermocouples and heat resistant rail-type extensometers. The temperature is held within a fluctuation of ±1°C. The deformations recorded on the gauge section of specimen are measured with an accuracy of 1 μm.”.
- Information should be added concerning the SEM instrument that was used for the fractographic observation. What were the working conditions under the SEM microscope during the observation of the fracture surface?
Answer: Thank you for your very valuable suggestion. The detailed information about the SEM instrument and operation parameters employed during the observation process are added in Section 2. Materials and Methods of line 112-114: “Moreover, all the fractographic observations were carried out on the Hitachi s-4800 High resolution SEM. The SEM investigations during the observation of the fracture surface were all conducted using 15 kV acceleration voltage and 10 mm working distance.”.
- The part of the results and discussion is clearly written and well organized. The caption of Figure 5 should be corrected. Line 150, Figure 5 caption: “SEM observations of fractured surfaces: (a) static creep and (b) enlarged inner fibrous zone; (c) cyclic creep at 12 MPa/s and (d) 39 MPa/s unloading rate without valley stress duration; (f) cyclic creep with 10 min and (g) 30 min duration under valley stress with an unloading rate of 12 MPa/s.” Section (e) is missing in the caption and section (g) does not appear in Figure 5 and should be removed from the caption.
Answer: Thank you for your very valuable suggestion. The caption of Figure 5 is corrected.
