The Influence of Temperature on the Fracture Toughness and Fracture Mechanism of Ferritic Nodular Cast Iron
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors are advised to revise the manuscript and address the following comments to enhance its quality:
- Page 1, Line 17: Consider stating the temperature range for different conditional fracture toughness in the abstract.
- Line 30-32: specify grade of sherardized graphite, such as ASTM A536 or ISO 1083 for better clarity on the grades of NCI.
- At the end of the introduction section, add a clearer statement of the specific knowledge gap this research aims to fill.
- Line 102: A method for the quantitative measurement of spheroidization should be cited.
- Line 122-124: Please specify the loading rate and the specific procedure within the standard ISO 12135:2021 used.
- Lines 146-148: The manuscript correctly provides the thickness requirement (Eq. 4) for a valid plane strain fracture toughness (K IC ) test. As no test results are provided, the plane thickness requirement is a critical finding of the manuscript, and it should be a key point in the Results or Discussion section, justifying why the parameter is referred to as KQ​ rather than K
- Line 240-241: The text claims a clear trend for KQ increasing above -80°C and decreasing below -100°C. However, Figure 8a shows considerable scatter in the data points. Need a better interpretation of the transition behavior.
- Figure 11(c): at -100°C, the "dimple morphology completely disappeared". Please clarify if this is a representative observation across all specimens at this temperature. A small fraction of the dimple is still visible in the image.
- Lines 343-347: Please provide more quantitative justification for the stress field at the crack tip and compare it with the theoretical critical cleavage stress for this material.
- Lines 355-370: What is the effect of the matrix/nodule interface, particularly at low temperatures?
Author Response
Comment 1: Page 1, Line 17: Consider stating the temperature range for different conditional fracture toughness in the abstract.
Response: Thank you for pointing out this problem. Due to the large volume of the sample, we did not conduct repeated experiments at higher temperatures. Considering the dispersion of fracture toughness, we conservatively did not provide a temperature range but only depicted the trend of change.
Comment 2: Line 30-32: specify grade of sherardized graphite, such as ASTM A536 or ISO 1083 for better clarity on the grades of NCI.
Response: Thank you for pointing out this problem. Subsequently, we referred to ISO 1083:2018 and determined the grade of NCI based on its mechanical properties.
Figure 4 presents the engineering stress-strain curves of NCI with the temperature ranged from 20 °C to -120 °C. According to the test results, the NCI used in the experiment is EN-GJS-350-22 grade according to the ISO 1083: 2018.
Comment 3: At the end of the introduction section, add a clearer statement of the specific knowledge gap this research aims to fill.
Response: Thank you for pointing out this problem. We have made corresponding modifications in the article.
By comparing the test values and microstructures under different testing conditions, the influence of temperature on the fracture properties and mechanisms of NCI was investigated. Provided data support for the practical application of NCI.
Comment 4: Line 102: A method for the quantitative measurement of spheroidization should be cited.
Response: Thank you for pointing out this problem. In fact, the measurement of microscopic parameters is completed by software accompanying the microscope. When measuring, only the corresponding standard (GB/ISO/STM) needs to be selected, so there is no further citation or explanation.
Comment 5: Line 122-124: Please specify the loading rate and the specific procedure within the standard ISO 12135:2021 used.
Response: Thank you for pointing out this problem. The loading rate is given in the following text’ Displacement-controlled loading with 0.025mm/s was maintained as a quasi-static condition.’ Considering that the experiment itself is relatively simple and the data processing method is provided later, no specific procedure has been added.
Comment 6: Lines 146-148: The manuscript correctly provides the thickness requirement (Eq. 4) for a valid plane strain fracture toughness (K IC ) test. As no test results are provided, the plane thickness requirement is a critical finding of the manuscript, and it should be a key point in the Results or Discussion section, justifying why the parameter is referred to as KQ​ rather than K
Response: Thank you for pointing out this problem. It is mentioned in lines 236-237 that ' No test result satisfied the plane thickness requirement.' And for materials with good toughness such as NCI, we can only expect to obtain plane strain fracture toughness Kâ… C by reducing the temperature or increasing the sample thickness. In fact, we successfully obtained Kâ… C by reducing the temperature to -140℃. However, on the one hand, it is difficult to maintain stability under low temperature conditions, and on the other hand, there are few repeated experiments. Considering that Kâ… C is not the focus of this study, we ultimately did not include this part in the paper
Comment 7: Line 240-241: The text claims a clear trend for KQ increasing above -80°C and decreasing below -100°C. However, Figure 8a shows considerable scatter in the data points. Need a better interpretation of the transition behavior.
Response: Thank you for pointing out this problem. As mentioned above, due to the large sample size, it is not possible to conduct many repeated experiments. In fact, some experimental data were not originally intended to be included in the article, but considering the overall lack of experimental data, we ultimately added them. The issue of data dispersion will be further studied in the future.
Comment 8: Figure 11(c): at -100°C, the "dimple morphology completely disappeared". Please clarify if this is a representative observation across all specimens at this temperature. A small fraction of the dimple is still visible in the image.
Response: Thank you for pointing out this problem. We did not notice this issue during the subsequent modification process. This section discusses the situation below -100 °C but cites images from -80°C. In addition, even at low temperatures, the collective around the graphite sphere will still undergo limited deformation, so we have modified it to a more rigorous expression
When approaching the lower shelf temperature (-100 °C), specimens exhibit complete cleavage fracture surface. From Figure 11(e), it can be seen that the dimple morphology almost completely disappeared in fracture zone.
Comment 9: Lines 343-347: Please provide more quantitative justification for the stress field at the crack tip and compare it with the theoretical critical cleavage stress for this material.
Response: Thank you for pointing out this problem. Previously, we conducted some relevant simulation calculations, but as they were not systematic and the temperature range varied greatly, we did not provide quantitative analysis here
Comment 10: Lines 355-370: What is the effect of the matrix/nodule interface, particularly at low temperatures?
Response: Thank you for pointing out this problem. From the observation results, graphite spheres often serve as the core for void nucleation. The bonding force between the matrix and graphite interface is low, which promotes the occurrence of fracture
Reviewer 2 Report
Comments and Suggestions for AuthorsIn the paper entitled „The Influence of Temperature on the Fracture Toughness and Fracture Mechanism of Nodular Cast Iron”, the Authors present the results of studies concerning the mechanical properties of nodular cast iron grade oriented for exploitation in low temperatures. Generally, the section Introduction, Results, Discussion and Conclusions are clear and elaborated on an acceptable scientific level. Moreover, the discussion of research results is proper for the considered problem and is additionally well-connected with results obtained by other researchers. However, the paper needs major revision in the range of the title and the section Materials and Methods. The detailed comments are given below:
#1: The studies concern the ferritic nodular cast iron with mechanical properties, i.e. UTS and EL proper for EN-GJS-350-22-LT grade according to EN 1563 Standard. However, in any part of the manuscript, the Authors do not give this information. Therefore, I suggest changing the title to:
“The Influence of Temperature on the Fracture Toughness and Fracture Mechanism of Ferritic Nodular Cast Iron”
or
“The Influence of Temperature on the Fracture Toughness and Fracture Mechanism of Nodular Cast Iron EN-GJS-350-22”
#2: In connection with comment #1, the grade EN-GJS-350-22-LT should be mentioned in the section Materials and Methods, as studied nodular cast iron.
#3: In Table 1, the chemical composition of the studied nodular cast iron is presented. In my opinion, the chemical composition is incomplete because it lacks Mg concentration. Mg is the key element in the technological process of nodular cast iron, because it is responsible for spheroidization of graphite. Moreover, please add the data of the emission spectrometer used in the chemical composition determination.
#4: In connection with comment #3, in section Materials and Methods, it lacks basic information concerning the technological process of the studied nodular cast iron, i.e.:
- What kind of furnace was used to melt the charge?
- What kind of spheroidization method and what grade of spheroidizer were used?
- What kind of inoculation method and what grade of inoculant were used?
- What was the pouring temperature, and what kind of mould was used?
- What was the geometry of test casting, in particular, the thickness of the casting wall, which is important for readers from the point of view of the strong impact of the wall thickness on phase composition of the matrix in the microstructure of cast iron?
#5: In lines 98-99 is mentioned that to achieve full ferritization of the matrix, the heat treatment was used. However, in this section, it lacks a detailed description of this heat treatment. I suggest adding the scheme Temperature – Time for applied ferritizing annealing.
Author Response
Comment 1: #1: The studies concern the ferritic nodular cast iron with mechanical properties, i.e. UTS and EL proper for EN-GJS-350-22-LT grade according to EN 1563 Standard. However, in any part of the manuscript, the Authors do not give this information. Therefore, I suggest changing the title to:
“The Influence of Temperature on the Fracture Toughness and Fracture Mechanism of Ferritic Nodular Cast Iron”
or
“The Influence of Temperature on the Fracture Toughness and Fracture Mechanism of Nodular Cast Iron EN-GJS-350-22”
Response: Thank you for pointing out this problem. We have made modifications to the corresponding content of the article
Figure 4 presents the engineering stress-strain curves of NCI with the temperature ranged from 20 °C to -120 °C. According to the test results, the NCI used in the experiment is EN-GJS-350-22 grade according to the ISO 1083: 2018.
Comment 2: In connection with comment #1, the grade EN-GJS-350-22-LT should be mentioned in the section Materials and Methods, as studied nodular cast iron.
Response: Thank you for pointing out this problem. Same as Response 1
Figure 4 presents the engineering stress-strain curves of NCI with the temperature ranged from 20 °C to -120 °C. According to the test results, the NCI used in the experiment is EN-GJS-350-22 grade according to the ISO 1083: 2018.
Comment 3: In Table 1, the chemical composition of the studied nodular cast iron is presented. In my opinion, the chemical composition is incomplete because it lacks Mg concentration. Mg is the key element in the technological process of nodular cast iron, because it is responsible for spheroidization of graphite. Moreover, please add the data of the emission spectrometer used in the chemical composition determination.
Response: Thank you for pointing out this problem. We have added corresponding content. Due to receiving the experimental materials directly, we are not clear about the specific smelting process and composition. At least no Mg component has been found in the current test results.
An inductively coupled plasma atomic emission spectrometer (ICP-AES, Shimadzu ICPE-9810, Shimadzu, Colombia, MD, USA) was used to determine the precise chemical compositions and the results are shown in Table 1.
Comment 4: In connection with comment #3, in section Materials and Methods, it lacks basic information concerning the technological process of the studied nodular cast iron, i.e.:
- What kind of furnace was used to melt the charge?
- What kind of spheroidization method and what grade of spheroidizer were used?
- What kind of inoculation method and what grade of inoculant were used?
- What was the pouring temperature, and what kind of mould was used?
- What was the geometry of test casting, in particular, the thickness of the casting wall, which is important for readers from the point of view of the strong impact of the wall thickness on phase composition of the matrix in the microstructure of cast iron?
Response: Thank you for pointing out this problem. As mentioned above, we directly obtained the sample material, so there is no further information about the composition and smelting process.
Comment 5: In lines 98-99 is mentioned that to achieve full ferritization of the matrix, the heat treatment was used. However, in this section, it lacks a detailed description of this heat treatment. I suggest adding the scheme Temperature – Time for applied ferritizing annealing.
Response: Thank you for pointing out this problem. Same as Response 4
Reviewer 3 Report
Comments and Suggestions for AuthorsThis manuscript presents a comprehensive experimental investigation of temperature-dependent fracture behavior in nodular cast iron (NCI), employing both tensile testing and fracture toughness evaluation across a temperature range from 20°C to -120°C. The work addresses a practically significant engineering problem with direct applications to nuclear containment systems and provides valuable insights into ductile-brittle transition mechanisms.
Recommendation:
Accept with Minor Revisions.
Required Revisions:
- Enhance statistical analysis with confidence intervals and uncertainty quantification. So, supplement existing graph in Figure 5 with error bars representing for example Standard deviation; Would require additional information about the reliability of the measurement, for example, using measurement uncertainty.
- Address minor language and formatting issues. For example: Figure 5 is not mentioned in the text; Line 42: "countries such as China and Japan also conducted research" → "countries including China and Japan have conducted research"; Reference Formatting, inconsistent journal name abbreviations, for example: Referece 5: "ISIJ International" (abbr.), Reference 8: "Engineering Fracture Mechanics" (full title)).
The manuscript provides valuable engineering data and mechanistic insights that will benefit the materials science community, particularly for nuclear containment applications.
Author Response
Comment 1: Enhance statistical analysis with confidence intervals and uncertainty quantification. So, supplement existing graph in Figure 5 with error bars representing for example Standard deviation; Would require additional information about the reliability of the measurement, for example, using measurement uncertainty.
Response: Thank you for pointing out this problem. Due to the small difference in the results of repeated experiments on tensile strength and yield strength, the standard deviation of test results at different temperatures ranges from 2 to 6. Compared to the test values, which are not obvious in the graph, the actual effect presented is relatively poor. Therefore, we removed the standard deviation from the graph.
Comment 2: Address minor language and formatting issues. For example: Figure 5 is not mentioned in the text; Line 42: "countries such as China and Japan also conducted research" → "countries including China and Japan have conducted research"; Reference Formatting, inconsistent journal name abbreviations, for example: Referece 5: "ISIJ International" (abbr.), Reference 8: "Engineering Fracture Mechanics" (full title))
Response: Thank you for pointing out this problem. We will further optimize the language issue in our future work. As for the format of the references, we have rechecked and revised it. The full name of the journal for reference 5 is "ISIJ International", formerly known as "Transactions of the Iron and Steel Institute of Japan"
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
I regret to say that the changes introduced in the manuscript according to my comments are unsatisfactory. Therefore, I kindly ask You to revise the paper again. Below are the details.
Second review of paper entitled „The Influence of Temperature on the Fracture Toughness and Fracture Mechanism of Nodular Cast Iron” from the point of view of the first review:
Response to comment #1 is not accepted, because suggested changes in the title of the paper have not been made.
Response to comment #2 is accepted.
Response to comment #3 is not accepted, because it is not possible to manufacture the nodular cast iron without Mg, unless rare earth metals (mischmetal) spheroidization has been used, but this should also be described. In the current version, the chemical composition shown in Table 1 corresponds to grey cast iron with flake graphite and not to nodular cast iron.
Please check again the chemical composition of the studied casting and correct Table 1.
Response to comment #4 is accepted.
Response to comment #5 is not accepted, because this is a significant gap in the methodology. The authors should give at least the annealing temperature and the cooling method.
Author Response
Comment 1：Response to comment #1 is not accepted, because suggested changes in the title of the paper have not been made.
Response: Thank you for pointing out this problem. After discussion, we have changed the title of the article to “The Influence of Temperature on the Fracture Toughness and Fracture Mechanism of Ferritic Nodular Cast Iron”
Comment 3：Response to comment #3 is not accepted, because it is not possible to manufacture the nodular cast iron without Mg, unless rare earth metals (mischmetal) spheroidization has been used, but this should also be described. In the current version, the chemical composition shown in Table 1 corresponds to grey cast iron with flake graphite and not to nodular cast iron.
Response: Thank you for pointing out this problem. We have provided additional explanations on the relevant content. The experimental ductile iron was spheroidized using mixed rare earth elements, but we were not informed of the composition of the mixed rare earth elements due to confidentiality.
An inductively coupled plasma atomic emission spectrometer (ICP-AES, Shimadzu ICPE-9810, Shimadzu, Colombia, MD, USA) was used to determine the precise chemical compositions and the results are shown in Table 1. The experimental NCI was spheroidized with mixed rare earth elements, and the rare earth composition was not listed for some reasons.
Comment #5 is not accepted, because this is a significant gap in the methodology. The authors should give at least the annealing temperature and the cooling method.
Response: Thank you for pointing out this problem. After communication, we were informed of some relevant information and supplemented the corresponding content
To achieve full ferritization, the as-cast material underwent controlled annealing. The specific process is as follows: heating to 920 °C for 2 hours, followed by furnace cooling to 720 °C for 4 hours, and then air cooling to room temperature after furnace cooling to 600 °C.
Reviewer 3 Report
Comments and Suggestions for AuthorsDespite minor revisions required the research provides significant engineering data for temperature-dependent fracture behavior prediction, warranting publication.
Author Response
Comment 1: Despite minor revisions required the research provides significant engineering data for temperature-dependent fracture behavior prediction, warranting publication.
Response：Thank you for your recognition of our work. Based on the suggestions received, we have made modifications and additions to some details.
An inductively coupled plasma atomic emission spectrometer (ICP-AES, Shimadzu ICPE-9810, Shimadzu, Colombia, MD, USA) was used to determine the precise chemical compositions and the results are shown in Table 1. The experimental NCI was spheroidized with mixed rare earth elements, and the rare earth composition was not listed for some reasons.
To achieve full ferritization, the as-cast material underwent controlled annealing. The specific process is as follows: heating to 920 °C for 2 hours, followed by furnace cooling to 720 °C for 4 hours, and then air cooling to room temperature after furnace cooling to 600 °C.
Round 3
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
I accept all your responses to my comments.
Author Response
Dear reviewer
Thank you for your recognition of our work
