Evolution Behavior and Closure Mechanism of Porosity in Large Billet during the Reduction Pretreatment
Round 1
Reviewer 1 Report
In this manuscript authors investigated the evolution behavior and closure mechanism of porosity in large billet during the reduction pretreatment. The porosities were characterized by ultrasonic scanning and 3D reconstruction. The results showed that the porosities near the surface of the billet were firstly closed during the reduction pretreatment. Firstly, the experiments were designed to simulate the reduction pretreatment process, and the morphology and distribution characteristics of shrinkage porosity in billet were detected by an ultrasonic scanning microscope and 3D reconstruction. Then, a three-dimension model was built to analyze the strain distribution during the reduction pretreatment. Finally, the evolution behaviors of porosity were modeled to study the closure mechanism of porosity during the reduction pretreatment process. This work can provide a theoretical guidance for future research on the reduction pretreatment process.
The paper is suitable to be published in METALS.
The type of the used steel should be mentioned (or give it suitable name).
How did the authors measure the chemical composition the steel?
Put “BAL” in table 1.
Merge figures 1-3 to be figure 1 a,b,c.
Why was the friction coefficient between the billet and the roller set to 0.3? (put ref)
What the effect of roll gap on the steel behavior?
The images were binarized by Matlab, which version?
The error between simulated and experimental results should be plotted.
Equation 2 needs ref.
Why does the density of the internal porosities decreases when the reduction is small?
Why the maximum strain still appears near the surface of the billet when the reduction is small (Figure 15(a)).
Author Response
Reviewer reports: Reviewer 1
Comments and Suggestions: In this manuscript authors investigated the evolution behavior and closure mechanism of porosity in large billet during the reduction pretreatment. The porosities were characterized by ultrasonic scanning and 3D reconstruction. The results showed that the porosities near the surface of the billet were firstly closed during the reduction pretreatment. Firstly, the experiments were designed to simulate the reduction pretreatment process, and the morphology and distribution characteristics of shrinkage porosity in billet were detected by an ultrasonic scanning microscope and 3D reconstruction. Then, a three-dimension model was built to analyze the strain distribution during the reduction pretreatment. Finally, the evolution behaviors of porosity were modeled to study the closure mechanism of porosity during the reduction pretreatment process. This work can provide a theoretical guidance for future research on the reduction pretreatment process.
The paper is suitable to be published in METALS.
(Please check the attachment)
- The type of the used steel should be mentioned (or give it suitable name).
R: Thank you for your advice. The steel used for experiments can be named as 40MnSi according to its chemical composition. The “experimental steel” has been replaced by 40MnSi in the manuscript.
- How did the authors measure the chemical composition the steel?
R: Thank you for your question. We use chemical analysis to determine the chemical composition of the steel. We apologize for missing this information. It has been modified to “The actual chemical compositions were examined using chemical analysis”.
- Put “BAL” in table 1.
R: Thank you for your advice. We have put “BAL” in table 1.
- Merge figures 1-3 to be figure 1 a,b,c.
R: Thank you for your advice. We have merged figures 1-3 to be figure 1 a,b,c.
- Why was the friction coefficient between the billet and the roller set to 0.3? (put ref)
R: Thank you for your question. Coulomb friction was used in the calculation, and the friction coefficient was set to 0.3 according to reference [14]. Reference [14] has been put in the appropriate place.
- What the effect of roll gap on the steel behavior?
R: Thank you for your question. The roll gap affects the reduction of the billet. Each cross section of the bullet-shape billet had a different reduction amount after deformation. The reduction amount studied in this paper was from 0% to 26%. Before the experiment the calculation showed that a roll gap should be set to 92 mm.
- The images were binarized by Matlab, which version?
R: Thank you for your suggestion. The images were binarized by Matlab R2012b. It has been put in the appropriate place.
- The error between simulated and experimental results should be plotted.
R: Thank you for your advice. We agree with your suggestion that the error between simulated and experimental results should be plotted. The correlation coefficient and the average absolute relative error (AARE) are used to evaluate the error between simulated and experimental results.
where and are the experimental temperature and the mean values of , and are the simulated temperature and the mean values of , and is the number of data points. The simulated and experimental results have been plotted as shown in Fig. 7(b). The simulated and experimental temperatures are basically consistent, the correlation coefficient R and the average absolute relative error (AARE) are 0.997 and 1.3%, respectively. It has been modified in the manuscript.
Fig. 7(b). Correlation between simulated and experimental temperature.
- Equation 2 needs ref.
R: Thank you for your advice. Equation 2 used in the manuscript is from reference [23]. Reference [23] has been put in the appropriate place.
- Why does the density of the internal porosities decreases when the reduction is small?
R: Thank you for your question. Our description about the density of the internal porosities was ambiguous and has been modified to “The number of the internal porosities decreases when the reduction increases from 6% to 12%”.
- Why the maximum strain still appears near the surface of the billet when the reduction is small (Figure 15(a)).
R: Thank you for your question. Our description about the maximum strain was inappropriate and has been modified to “It can be seen that the maximum strain appears near the surface of the billet when the reduction is 6%”.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The abbreviation PCCS should be explained in the text.
How was the temperature field (on the surface of the casting) measured by an infrared thermometer? This seems impossible at one particular moment. It would be more appropriate to use a thermal camera/imager.
Uniaxial compression tests: what was the range of experimental conditions (temperature, strain rate)? If the temperature was 900 - 1350 °C, it is unnecessary to deal with the ZDT value.
In [23] I did not find the reported data on zero ductility temperature. The ZDT value can be routinely determined experimentally by a set of uniaxial tensile tests (up to fracture).
Hensel-Spittel law (not Hansel...) is not described in [22] - the original source should be cited.
Porosity degree at the reduction positions of 6% - 21% (see Figure 14): the change in trend using the largest reduction should be discussed in more detail. During real forming processes, the effect of a small change in strain is usually less pronounced.
When defining the deformation in a scientific article, it is not very appropriate to use the height reduction - I recommend to calculate the local effective strain value.
A crucial remark: the results and conclusions obtained are presented as much more general / universal than they actually are. See e.g. statement "The temperature difference can reach 400℃ between the surface and the center of 462 the billet." (row 462) which apply more or less only to a specific experiment. Moreover, a different geometry of the rolling process (e.g. the ratio between the diameter of the rolls and the height of the billet) could fundamentally change the penetration of plastic deformation into the individual areas of the billets (central parts). This should be reflected in the discussion of results and conclusions.
Author Response
Reviewer reports: Reviewer 2
Comments and Suggestions:
(Please check the attachment)
- The abbreviation PCCS should be explained in the text.
R: Thank you for your advice. “PCCS” is the abbreviation of “Porosity Control of Casting Slab”. Porosity Control of Casting Slab (PCCS) has been explained in the manuscript now.
- How was the temperature field (on the surface of the casting) measured by an infrared thermometer? This seems impossible at one particular moment. It would be more appropriate to use a thermal camera/imager.
R: Thank you for your question. After many tests, it showed that the surface temperatures at different positions we were interested in were very close, therefore, the temperature at the center point of the surface could characterize the temperature conditions during deformation. So we measured the temperature at the center point of the surface by an infrared thermometer. We have revised it in the manuscript now.
3.Uniaxial compression tests: what was the range of experimental conditions (temperature, strain rate)? If the temperature was 900 - 1350 °C, it is unnecessary to deal with the ZDT value.
R: Thank you for your question. A series of hot compression tests were conducted at deformation temperatures of 900-1350℃ and strain rates of 0.001-10s-1. The deformation temperatures are lower than ZDT, so it is unnecessary to deal with the ZDT value. We just deal with the data used for the linear fitting at 1350 °C and a strain rate of 0.001s-1 , because the compression specimen began to melt under this condition. The flow stress at 1350 °C and a strain rate of 0.001s-1 was set to a very small value close to 0 during calculation. It has been modified in the manuscript.
- In [23] I did not find the reported data on zero ductility temperature. The ZDT value can be routinely determined experimentally by a set of uniaxial tensile tests (up to fracture).
R: Thank you for your question. The deformation temperatures are lower than ZDT, so it is unnecessary to deal with the ZDT value. The reference[23] has been deleted.
- Hensel-Spittel law (not Hansel...) is not described in [22] - the original source should be cited.
R: Thank you for your advice. Hensel-Spittel law used in the manuscript is from reference [22]. The new references [22] have been put in the appropriate place.
- Porosity degree at the reduction positions of 6% - 21% (see Figure 14): the change in trend using the largest reduction should be discussed in more detail. During real forming processes, the effect of a small change in strain is usually less pronounced.
R: Thank you for your question. The center of billet where the temperature is above 1300°C is very sensitive to tensile stress, so plastic damage may occur here in spite of a small change in strain. At the position where the reduction is 21%, the porosity degree is significantly larger than those of other reduction positions. Due to a high center temperature, the grain boundary strength is lower than the intragranular strength. Grain boundary slip controlled by diffusion gradually replaces the dislocation movement. At the grain boundary perpendicular to the direction of tensile stress, the stress exceeds a critical value with the increase of reduction amount, and thus porosities are formed by vacancy aggregation. It indicates that an excessive reduction is not beneficial to improve the internal quality of the billet. It has been modified in the manuscript.
- When defining the deformation in a scientific article, it is not very appropriate to use the height reduction - I recommend to calculate the local effective strain value.
R: Thank you for your advice. I agree with you that the local effective strain is appropriate. The local effective strains are calculated by the method in reference [24]. The local effective strains corresponding to the reduction of 6%, 9%, 12%, 15%, 18%, and 21% are 0.07, 0.10, 0.13, 0.17, 0.21 and 0.24, respectively. It has been modified in the manuscript.
[24] Lee, Y.; Kim, Y.H. Approximate analysis of roll force in a round-oval-round pass rolling sequence. J. Mater. Process. Technol. 2001, 113, 124–130.
Doi: https://0-doi-org.brum.beds.ac.uk/10.1016/S0924-0136(01)00712-9.
- A crucial remark: the results and conclusions obtained are presented as much more general / universal than they actually are. See e.g. statement "The temperature difference can reach 400℃ between the surface and the center of 462 the billet." (row 462) which apply more or less only to a specific experiment. Moreover, a different geometry of the rolling process (e.g. the ratio between the diameter of the rolls and the height of the billet) could fundamentally change the penetration of plastic deformation into the individual areas of the billets (central parts). This should be reflected in the discussion of results and conclusions.
R: Thank you for your suggestion. The results and conclusions have been modified in the manuscript.
After completely solidification, an obvious temperature difference exists between the surface and the center of the billet.
A different geometry during rolling could fundamentally change the deformation penetration, therefore, the shape ratio has a great influence on the deformation penetration of heavy plate. The shape ratio is the ratio of the projection length of contact arc between roll and billet to the average thickness of the billet, which is calculated with the following formula:
Where is the roll radius, is the billet thickness before rolling and is the billet thickness after rolling. The larger the shape ratio, the better the deformation penetration during rolling. Each cross section of the bullet-shape billet in the experiment has a different thickness. When the reduction is 6% at all different thickness positions, the shape ratio changes from 0.3 to 0.32. When the reduction is 21% at all different thickness positions, the shape ratio changes from 0.6 to 0.65. The shape ratio of each cross section of the bullet-shape billet has small difference when the reduction is the same. Therefore, the effects of reduction and temperature on deformation penetration are mainly discussed. Discussion has been added to the manuscript.
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear authors,
my pleasure to read this work. I work with center porosities and know how important that for factories, Modeling posibilities are helpful for factories and their keyses. Need to believe, that I'll read your next work about center porosities and reducing the rolling ratio.
Best regards
Author Response
Reviewer reports: Reviewer 3
Comments and Suggestions: My pleasure to read this work. I work with center porosities and know how important that for factories, Modeling posibilities are helpful for factories and their keyses. Need to believe, that I'll read your next work about center porosities and reducing the rolling ratio.
R: Thank you for your Comment.
Round 2
Reviewer 1 Report
The manuscript is well written and could be published after minor revision.
More discussion on “The number of porosities at the reduction positions of 6%, 9%, 12%, 15%, 18%, and 21% were counted respectively in the specimen with reduction. In the specimen without reduction, the number of porosities at the corresponding positions were also counted. The number of porosities in a unit volume of 1 cm3 at the corresponding positions of the two samples are shown in Figure 11.”
Strengthen the introduction using modeling of cooling and heat conduction in permanent mold casting process; Industrial reheating furnaces: a review of energy efficiency assessments, waste heat recovery potentials, heating process characteristics and perspectives for steel industry and others.
Author Response
Reviewer reports: Reviewer 1
Comments and Suggestions: The manuscript is well written and could be published after minor revision.
- More discussion on “The number of porosities at the reduction positions of 6%, 9%, 12%, 15%, 18%, and 21% were counted respectively in the specimen with reduction. In the specimen without reduction, the number of porosities at the corresponding positions were also counted. The number of porosities in a unit volume of 1cm3 at the corresponding positions of the two samples are shown in Figure 11.”
R: Thank you for your advice. We have added more discussion on the distribution characteristics of the number of porosities. We have revised it in the manuscript now.
As shown in Figure 11, for the specimen without reduction, the average number of porosities less than 0.3 mm in diameter is 245 per unit volume, and that more than 0.5 mm in diameter is 14 per unit volume. The number of small porosities is several times as many as that of large porosities. There is a small difference in the number of porosity with the same diameter among different positions.
For the specimen with reduction, at the position where the effective strain is 0.07, the number of porosities less than 0.3 mm in diameter obviously decreases, which shows that the reduction effect on the small porosities is better than that on the large porosities. When the deformation increases from 0.07 to 0.13, the number of small porosities continues to decrease. As the number of large porosities decreases to a certain value, it is difficult for large porosities to continue to decrease due to insufficient deformation. At the position where the effective strain is 0.2, the reduction can effectively act on the center of the billet. The number of porosities less than 0.4 mm in diameter is significantly reduced. The number of porosities between 0.4 mm and 0.5 mm in diameter at the deformation of 0.2 is more than those at the deformation of 0.1. The reason might be that the large porosities are compressed into small porosities when the reduction amount is larger. At the position where the effective strain is 0.25, the number of porosities is less than that in the specimen without reduction but more than that at other reduction positions. It shows that excessive reduction will cause high temperature plastic damage and the increase in the number and sizes of porosities, which is not beneficial to improve the internal quality of the billet.
- Strengthen the introduction using modeling of cooling and heat conduction in permanent mold casting process; Industrial reheating furnaces: a review of energy efficiency assessments, waste heat recovery potentials, heating process characteristics and perspectives for steel industry and others.
R: Thank you for your advice. We have strengthened the introduction using modeling of heat conduction. We have revised it in the manuscript now.
According to the temperature measurement results, the inverse calculation module of the software Procast2013 was used to calculate the value of the heat transfer coefficient h with varying time. The solidification with phase change and the temperature distribution inside the billet can be described by an unsteady-state heat conduction equation [22,23]:
|
|
(1) |
Where is the temperature (K), is time (s), is the thermal conductivity (W/m K), is specific heat (J/kg K), is the density (kg/m3), is the latent heat (J/kg). The steel material parameters calculated with the commercial software Jmatpro are shown in Table 2. The liquidus and solidus temperatures of the steel are 1490℃ and 1425℃, respectively. The latent heat of solidification is 245000 J/kg. In the calculation, the casting process was ignored, and the mold was assumed to be instantaneously filled with molten steel at an initial temperature of 1500℃. The heat transfer coefficient at the interface between the molten steel and the mold is determined, as shown in Table 3. After the heat transfer coefficient was obtained, a three-dimensional model of the heat transfer was established by the software Thercast2011, as shown in Figure 1(c). The temperature field of the billet during the solidification process could be calculated by this model.
- Zhao, J.; Ma, L.; Zayed, M.E.; Elsheikh, A.H.; Li, W.; Yan, Q.; Wang, J. Industrial reheating furnaces: A review of energy efficiency assessments, waste heat recovery potentials, heating process characteristics and perspectives for steel industry. Process Saf. Environ. Prot. 2021, 147, 1209–1228.
Doi: https://0-doi-org.brum.beds.ac.uk/10.1016/j.psep.2021.01.045.
- Janik, M.; Dyja, H. Modelling of three-dimensional temperature field inside the mould during continuous casting of steel. J. Mater. Process. Technol. 2004, 157, 177–182.
Doi: https://0-doi-org.brum.beds.ac.uk/10.1016/j.jmatprotec.2004.09.026.
Author Response File: Author Response.pdf
Reviewer 2 Report
Authors accepted almost all my remarks and improved the text markedly.
However, I would assume that they will use effective deformation values throughout the article. They simplified their work with a sentence
The local effective strains corresponding to the reduction of 6%, 9%, 12%, 15%, 18%, and 21% are 0.07, 0.10, 0.13, 0.17, 0.21 and 0.24, respectively [24].
and kept all other data on relative deformation / reduction.
Author Response
Reviewer reports: Reviewer 2
Comments and Suggestions: Authors accepted almost all my remarks and improved the text markedly.
- However, I would assume that they will use effective deformation values throughout the article. They simplified their work with a sentence
The local effective strains corresponding to the reduction of 6%, 9%, 12%, 15%, 18%, and 21% are 0.07, 0.10, 0.13, 0.17, 0.21 and 0.24, respectively [26].
and kept all other data on relative deformation / reduction.
R: Thank you for your recognition of most of our improvements. According to your suggestion, we have used the local effective strain to describe the deformation throughout the article (including all figures). Once again thank you for your suggestion. We have revised it in the manuscript now.
“After reduction, the effective strain of the section marked with the tracking point is calculated to characterize the local deformation [26].”
Author Response File: Author Response.pdf
