Application Status and Development Trend of Continuous Casting Reduction Technology: A Review

Round 1

Reviewer 1 Report

The manuscript presents a review for the application and development of reduction technology in continuous casting process. The manuscript is interesting, and would be helpful for the readers. Hence, I recommend minor revision. The comments are as follows.

1. In the section of research methodologies, recent numerical investigations should be added.

2. References about the technical methods should be showed in of Table 1.

3. It is suggested to improve and rewrite the section of prospects of reduction technology.

4. Abbreviations for keywords should be consistent with the context.

5. There are some grammatical and format errors, please checked and revised carefully.

Author Response

1. In the section of research methodologies, recent numerical investigations should be added.

Thank you very much for your suggestion I have added simulation result according to your suggestion.

The steel plants are constantly trying to manufacture the higher quality products with low cost. The continuous casting process is an indispensable process of the steelmaking. The segregation of alloying elements, central porosity, internal crack defects and non-metallic inclusions are common casting defects, which can easily generate [73, 74] during solidification process and have an adverse effect on the final product. The association of software engineers and steel industries is an effective campaign to optimize the parameters of continuous casting mainly the reduction section. Therefore, numerical simulation can easily detect the physical phenomenon behind formation of internal defects during the implementation of reduction technology. Liu et al., [75] developed a thermal-mechanical coupled FEM model to predict proper soft reduction amount for continuous casting slab. Kajatani et al., [76] used a finite-volume scheme to simulate the deformation-induced macrosegregation in continuous casting steel. It is shown that the positive centerline segregation of carbon in the slab is well reproduced with this model. Guan et al., [77] developed a multiphase solidification model combining turbulent fluid flow, heat transfer, solute transport with back diffusion and shell deformation; The simulation results showed that a large reduction applied just before the solidification end could significantly reverse the flow of solute-enriched melt.

 

2. References about the technical methods should be showed in of Table 1.

Yes I have inserted the references of technical methods in Table 1, which is now Table 2 after revision.

3. It is suggested to improve and rewrite the section of prospects of reduction technology.

Thank you for your useful suggestion. I revised the prospects section according to your suggestion and highlighted as:

Future perspective:

Currently, the main problems during implementation of reduction technology are as follows.

(1) How to measure the temperature distribution of the billet during solidification? and how to calculate the volume shrinkage at solidification end to provide a basic for the theoretical calculation of the reduction parameters. New research methods and ideas should be adopted for the reduction technology, such as the effect of alloy composition on the mechanical properties of cast products, the relationship between cooling water intensity and billet solidification, etc., and breakthrough in quantification of reduction parameters.

(2) The research on the secondary cooling process is not enough to implement it in the practical application of the reduction technology, especially the relationship between the water intensity in the secondary cooling zone and solidification.

(3) It is difficult to accurately jdge the position of the solidification end of the cast products, especially when the casting speed and cooling water intensity was changed. The selection of appropriate reduction interval and amount also need to be further investigation. The exact control of solidification end point is needed to improve the internal quality of cast products. Further research should be conducted on the transition states of different steel grades and the fluidity of molten steel in the two-phase zone along with the optimization in the design of reduction rollers.

(4) How to use the reduction technology for industrial production as the investigations on reduction technology is mainly discontinuous, and a complete research system of reduction technology has not been designed. According to the actual working conditions and the current investigations, a systematic research system of reduction technology should be designed to automatically adjust the reduction parameters such as reduction interval, reduction amount and reduction equipment.

(5) With the progress of HR technology, the mechanical equipment also needs to be upgraded to improve the fault-tolerance of HR technology during its use in the industry. The safety measures should be highly considered according to the results of destructive experiments in order to avoid the serious tragedy during the industrial production process.

 

 

4. Abbreviations for keywords should be consistent with the context.

Yes the abbreviations of keywords are thoroughly consistent in whole paper.

5. There are some grammatical and format errors, please checked and revised carefully.

Yes I have corrected the grammatical according to your suggestion and highlighted in manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments for author File: Comments.pdf

Author Response

Line 10: segregation and further puts forward the common solutions to overcome these problems.

Line 12: The history of the development of the reduction technology is summarized and classified according to the

Line 15: the similarities and differences between soft reduction and heavy reduction technologies with particular focus

Thank you very much for your suggestions I have corrected the abovementioned mistakes according to your suggestion and highlighted the changes by yellow color in the abstract of revised manuscript as:

Continuous casting is a dominant steelmaking process due to its steady-state nature, enhanced yield of steel production, low consumption of energy and manpower. However, the production of defect free cast products is still a big challenge as the internal defects including, macrosegregation of alloying elements, cracks and pores can be easily formed during the solidification process, which seriously deteriorate the microstructure and mechanical properties of the cast products. Therefore, this paper puts forward the common solutions to overcome these problematic. The reduction technology can effectively improve the center segregation of the billet, bloom and slab. The history of the development of the reduction technology is summarized and classified according to the variations in research trend. Furthermore, the basic principle and parameters of reduction technology are described to implement them in the actual production process. This paper compares the similarities and differences between soft reduction (SR) and heavy reduction (HR) technologies with particular focus on the theoretical research of HR technology and further elaborates the key parameter and equipment problems during implementation of HR. Moreover, this paper also considers the HR technology adopted by Baosteel as a case study, which helped to put forward some viewpoints for the future development of reduction technology.

 

 

 

 

Comments and suggestions on the order and content of the review:

1. Start with the basic principle of the continuous casting reduction technology. How is it done?

Thank you for your suggestion I have revised your mentioned section and highlighted as:

Li et al., [30] developed a two dimensional thermal-mechanical coupled model to investigate the deformation behavior of round bloom during soft reduction (SR) in the reduction force mode. They found that the shrinkage porosity in the center of the round bloom was almost vanished with the implementation of reduction process. The changes in the solidification structure of  billet was investigated with the reduction amounts of 1, 2, 3 and 4 mm respectively at cooling time of 120 s and 150 s, which showed that the shrinkage porosity was significantly decreased at reduction amount of  2 mm and cooling time of 120s  [31]. For the billet or bloom soft reduction pretreatment, the continuous caster uses pulling and withdrawal units with fixed cylinders to adjust the roll gap between the one set of rolls. For slab reduction pretreatment, the clamping cylinders are fixed at the entrance and exit to control the reduction rate at the solidification crater end. The main purpose of soft reduction technology is to control the formation of macrosegregation by suppressing of volume shrinkage at final solidification stage and also interrupt the suction flow of residual and segregated molten metal, as shown in Figure 1. The basic principle of reduction technology [32-34] is to apply an external force in an appropriate area of cast product during the solidification process, which compensates the volume shrinkage at the solidification end. The implementation of small reduction amount on the surface of billet or slab is an effective method to reduce the center segregation of alloying elements and internal defects in cast products during solidification process, which is known as soft reduction. The applied reduction amount breaks the dendrites, promotes the dendrites nucleation, refines the grains, increases the number of equiaxed dendrites, reduces the center segregation, and improve the internal quality of the cast products.

2. What are the different methods of continuous casting? Define each and then compare andcontrast the different methods. What are the applications?

This paper is based on the reduction technology and to discuss thoroughly your raised question No. 2, 3 and 4 is irrelevant to reduction technology which can be written as another review article. However, according to your suggestion we have added elaborated the manuscript with basic of continuous casting technology and clearly shows the different methods, their shortcoming, advantages, application and challenges in Table 1 as.

1.1. The continuous casting technology

Continuous casting process of steelmaking is a dominant cast method in which the molten steel is solidified into partly finished billet, bloom or slab. The different steel grades are cast into a wide variety of dimensions and a large amount approximately 95% of the world’s steel is manufacturing by the continuous casting process. Continuous casting is more significant and distinguishable process than the other casting methods due to its steady-state nature, high quality along with the enhanced yield of steel production, and low consumption of energy and manpower. However, the production of defect free cast products is still a big challenge and it needs further research and development to control the internal defects during casting of difficult steel grades The different continuous casting methods are shown in Table 1. Solidification is the last step of the continuous casting process, which is started in the copper mould and is of great importance to obtain the desire microstructure before the further operation and delivery of cast products. Several physiochemical processes occur in mushy zone during casting and ingot solidification process, which include interdendritic flow of molten metal, solute redistribution and crystallization. During solidification, the outer surface of strand solidified earlier and the molten metal remained in center region, which causes a temperature gradient from outer shell towards the center region. The solid/liquid interface evolution is the primary reason for the macro-structural changes. Moreover, the alloy segregation, porosities, surface and internal cracks and non-metallic inclusions are common casting defects, which can easily form during solidification process and need to compensate during continuous casting process. The reduction technologies are of great importance to control these internal defects formation. The main objective of reduction technology is to apply a small reduction amount on the surface of cast products at the solidification end to suppress the solidification shrinkage volume. The implementation of small reduction amount on the surface of ingot is an effective method to reduce the center segregation of alloying elements and internal defects in cast products during solidification process, which will be further summarized in the following sections.

 

Table 1. The different continuous casting methods.

Type	Advantage	Shortcoming	Application	Challenge
Vertical type [1]	Inclusions can easily float and dissipate heat.	Large height, High investment cost, difficult maintenance	Zhong Yuan Special Steel Company, et.	How to reduce  equipment height and investment cost.
Vertical type with bending [2,3]	The height of the whole machine is less than others.	Transverse corner cracks can form	Dillinger Steel Plant in Germany et.	How to eliminate the cracks in straightening process.
Circular arc type with straight mould [4]	Float of inclusions, low investment cost	Crack defects can easily produced	NKK,  Nippon Steel et.	How to eliminate the cracks in straightening process.
Circular-arc type [5]	Low investment cost, beneficial to improve the quality	Inclusions can easily segregate at the inner arc.	NSC Muroran Works, et.	How to control the inclusion formation.
Horizontal        type [6]	Low investment cost, high surface quality	Low production capacity.	Fukuyama works of nippon kokan et.	How to increase production capacity.

 

 

 

 

 

 

 

 

 

 

 

3. Include the advantages and disadvantages of each method.

Yes, this question is answered in along with question number 2. 

4. What are the challenges of the different methods and how they are being addressed if they are?

Yes, this question is answered in along with question number 2. 

Note: Most of the answers to the questions above are in the draft already. It’s just a matter of rearranging them to improve the flow of the narrative and to make it clearer to the readers.

 

Author Response File: Author Response.docx

Reviewer 3 Report

This review article is based on previous research during the last three decades showing that the soft reduction technology can significantly reduce the internal defects and improve the internal quality of continuously cast products. Center segregation, porosity, chemical homogeneity of constituent elements and equiaxed crystal zone were shown to be improved.

The work compiles and reviews the previous studies. Up to this point the review article is worth publishing.

The main drawback in the work is that it is not well organized and the presentation needs some improvements. Some suggestions for improvement of the parts that need further revision and improvements are:

1) English language needs improvement as the text contains many grammatical and style errors. Examples are highlighted in red in the attached reviewed copy of the manuscript.

2) The text contains repetitions and redundancy in some parts, such as: lines 96-114, and the work generally is not well organized to be smoothly read and moving from one point to another. Some examples are shown in the following points.

3) The section titled “1.4. Classification of reduction technology” should include another paragraph referring to different types of steels investigated (low, medium, high carbon, alloyed steels, etc.) This may be fit in any where else if the authors think that this is not the right place.

(4) Title 2. Reduction technology suggest being Research on reduction technology.

Also, sub-sections

(1) Experimental research

(2) Numerical simulation research

(3) Industrial research

Each should start with an opening line reviewing the investigated parameters through each methodology, followed by the detailed exploration of the research work.

It is recommended to change the title (3) Industrial research to Industrial field research to avoid conflict with section (3) appearing later titled “3. Industrial application of reduction technology”. It is also recommended to change the latter to (3) 3. “Industrial implementation of reduction technology”.  Also, the industrial research misses the article “Industrial Application of Mechanical Reduction on Continuous Casting of Bearing Steel Bloom” Processes 2021, 9(12), 280; 

https://doi.org/10.3390/pr9122280

5) The message of section 2.2 Key links of reduction technology is not clear. The authors need to start this section with a definition of what they mean by key links. Why have the authors not added this section to 2.1.2. Technical parameters of reduction technology since it discusses the same point of equipment and process parameters?

6) lines from 549- 555 should be at the beginning of the paper and the main findings discussed at the end.

 

 

Author Response

This review article is based on previous research during the last three decades showing that the soft reduction technology can significantly reduce the internal defects and improve the internal quality of continuously cast products. Center segregation, porosity, chemical homogeneity of constituent elements and equiaxed crystal zone were shown to be improved.

The work compiles and reviews the previous studies. Up to this point the review article is worth publishing.

The main drawback in the work is that it is not well organized and the presentation needs some improvements. Some suggestions for improvement of the parts that need further revision and improvements are:

• English language needs improvement as the text contains many grammatical and style errors. Examples are highlighted in red in the attached reviewed copy of the manuscript.

Thank you very much for your suggestion. The English grammar and style mistakes are corrected in the manuscript, and also the final revised manuscript is well organized. Moreover, we cannot find your attached reviewed copy in which you red highlighted the grammar mistakes, but we have thoroughly checked the English language.

 

 

• The text contains repetitions and redundancy in some parts, such as: lines 96-114, and the work generally is not well organized to be smoothly read and moving from one point to another. Some examples are shown in the following points.

Thank you very much for your suggestion. We have revised the repetitions in manuscript and highlighted by yellow as:  

. The main functions of reduction technology are as follows [32-33, 37]:

(1) It compensates the solidification shrinkage at the center of  billet, reduces or eliminates the internal shrinkage cavity and porosity formed by the volume shrinkage at the solidification end.

(2) Under the extrusion effect of applied reduction amount, the molten steel enriched with solute elements is forced to flow in the opposite of the casting direction, which controls the transverse flow of molten steel, and reduces the center segregation.

(3) The applied reduction amount can significantly breaks the “crystal bridge”, and homogenizes the residual melt between the dendrites and controls the carbon macrosegregation, which further  promotes the reverse flow of melt, and homogenizes the composition of constituents elements at the solidification end. The homogenization of melt further promotes the dendrites nucleation, refines the grains, increase the number of equiaxed dendrites and improves the internal quality of billet and slab.

 

3) The section titled “1.4. Classification of reduction technology” should include another paragraph referring to different types of steels investigated (low, medium, high carbon, alloyed steels, etc.) This may be fit in any where else if the authors think that this is not the right place.

ØThank you very much for your suggestion. I have added your mentioned changes and highlighted as:

There are two types of reduction technology including, SR and HR. The difference between HR and SR technology are as follows.

The HR technology at the solidification end of continuous casting billet is developed on the basis of the SR technology. The basic principle and technical research methods are basically same for the both technologies. The main differences between HR and SR are as follows:

(1) The reduction interval is different, as the SR is implemented at solid fraction range of 0.3-0.8, while the HR is implemented at the solidification end.

(2) SR can only be achieved by adjusting the roll gap, while HR has to concern with pressure control besides the roll gap.

(3) SR has a major role to overcome internal defects formation in ordinary steel grades, medium and low carbon steels, while the HR has outstanding results for high-quality steels, medium and high carbon steels. The similarities and differences between HR and SR technology are shown in Table 5.

 

 

Table 5. Differences between HR and SR technology.

-	Reduction parameter	Section	Casting speed	Steel grade	Effect
SR	Small reduction amount, forward reduction interval, implemented at small solid fraction.	Small section billet	High casting speed	Medium and low carbon steel,   alloyed steel	Improve the center segregation and center porosity.
HR	Large reduction amount, backward reduction interval, implemented at high solid fraction.	Large section billet	Low casting speed	Medium and high carbon steel,  alloyed steel	Improve center segregation and eliminates porosity.

 

 

4) Title 2. Reduction technology suggest being Research on reduction technology.

Also, sub-sections

(1) Experimental research

(2) Numerical simulation research

(3) Industrial research

Yes, I have revised them according to your suggestion.

Each should start with an opening line reviewing the investigated parameters through each methodology, followed by the detailed exploration of the research work.

Thank you for your suggestion I have revised your mentioned section and highlighted as:

2.1. Experimental research

There are many type defects in the billet, such as segregation of alloying elements, central porosity, internal crack defects, and reduction technology is beneficial to solve these defects. In the experimental conditions, the influence of reduction parameters such as reduction amount, cooling time and reduction interval et., on the internal quality of the casting billet were discussed by researchers . The data obtained from experimental research is more accurate as compare to the numerical simulation data, and it is also beneficial to find and the possible problems which could be faced during the experimental process.

 

2.2 Numerical simulation research

The steel plants are constantly trying to manufacture the higher quality products with low cost. The continuous casting process is an indispensable process of the steelmaking. The segregation of alloying elements, central porosity, internal crack defects and non-metallic inclusions are common casting defects, which can easily generate [73, 74] during solidification process and have an adverse effect on the final product. The association of software engineers and steel industries is an effective campaign to optimize the parameters of continuous casting mainly the reduction section. Therefore, numerical simulation can easily detect the physical phenomenon behind formation of internal defects during the implementation of reduction technology.

 

2.3 Industrial field research

Due to the complex production conditions in the field, reduction technology may still be problematic in industrial applications. For example, the combined effect of different factors such as casting speed, steel grade, and cooling water intensity might be problematic during the production process of cast steel. Optimizing the reduction parameters according to production process or production results is very helpful to improve the quality of the casting billet.

 

It is recommended to change the title (3) Industrial research to Industrial field research to avoid conflict with section (3) appearing later titled “3. Industrial application of reduction technology”. It is also recommended to change the latter to (3) 3. “Industrial implementation of reduction technology”.  Also, the industrial research misses the article “Industrial Application of Mechanical Reduction on Continuous Casting of Bearing Steel Bloom” Processes 2021, 9(12), 280; 

https://doi.org/10.3390/pr9122280

Yes, I have revised all the titles according to your suggestions and added the findings mentioned in article, Industrial Application of Mechanical Reduction on Continuous Casting of Bearing Steel Bloom. All the changes are mentioned by yellow highlights as:

2. Research on reduction technology

Prior research reports [22, 63, 64, 65] have investigated the dynamic reduction technology from the perspective of numerical simulation, and analyzed it by using the solidification heat transfer theory and finite element difference method to establish mathematical model. Moreover, the nail shooting experiment were conducted to explore the solid fraction with regard to the different reduction amount, reduction interval, reduction rate and other parameters [32-35]. The detailed research progress and development status of reduction technology have been elaborated in following sections.

2.1. Experimental research

The cast billet is prone to serious defects such as segregation of alloying elements, central porosity, internal crack defects. The influence of reduction parameters such as reduction amount, cooling time and reduction interval etc., on the internal quality of the casting billet were investigated by differnt researchers through laboratory experiments. The data obtained from the experimental research is more accurate as compare to the numerical simulation data, and it is also beneficial to find the possible problems which could be faced during the actual production process.

Some researchers carried out experimental research from the perspective of theoretical analysis to study the reduction parameters. Ali et al. [66] investigated the optimized reduction amounts by analyzing the final microstructure of medium carbon steel via EBSD and X-ray computer tomography. They found that the reduction amount of 2mm and 4mm is enough to compensate the solidification shrinkage porosity, while the size of the shrinkage cavity was significantly increased ~2 times with the increase of the reduction amount to 6 mm. Yao et al. [67] studied the solid-liquid temperatures and mechanical properties of GCr15 bearing steel. According to the experimental results and heat transfer model, the reduction interval and optimized reduction amount was proposed for dynamic SR technology. The optimized process parameters, reduced total carbon content in the middle and later stage of solidification, setting of reasonable reduction interval and reduction amount can improve the central segregation of cast products and also resulted in the homogeneous microstructure. Bleck et al., [68] performed the soft reduction experiments by using laboratory casting machine, while the solid fraction in the core area of billets was varied. They found that the center segregation, porosity, chemical homogeneity of constituent elements and equiaxed crystal zone were significantly improved with implementation of soft reduction, especially when the solid fraction was about 0.9. Wang et al., [69] explored the factors which affected the reduction efficiency of bloom during SR. The results showed that the center solid fraction affected the reduction efficiency of bloom, while the reduction amount, the dimensions of casting strand and the diameter of roller have little effect on reduction efficiency. Zong, et al., [70] investigated the internal cracking surrounding primary carbides in high carbon steel as-cast blooms induced by SR. It was found that the carbides precipitation in the vicinity of existing internal cracks was located at the middle of the surface and centreline of the bloom, which further increased the existence of the segregated bands in the hot-rolled wire rods. Ali et al., [71] investigated the effect of SR amount increasing from 1-4mm with a cooling time of 120s and 180s to reduce the internal crack defects. The results showed that the minimum reduction amount was enough to compensate the solidification shrinkage defects and center segregation of medium carbon steel ingots. Jin et al., [72] improved the internal quality of 42CrMo steel bloom, and found that the SR has a little effect on the solidification structure, but the central compactness and alloying segregation was improved significantly. The size of the largest porosity point at the bloom center was reduced from 1106 μm x 608 μm to 600 μm x 334 μm, while the carbon segregation index was reduced from 0.889 ~ 1.095 to 0.962 ~ 1.064. It can be inferred that the soft reduction technology can significantly reduce the internal defects and improve the internal quality of cast products. The difference is just existed in the experimental schemes and equipment, but these all are explored on the basis of the actual production process. The experimental research parameters include but not limited to experimental steel grades, reduction parameters, and detection methods, etc.

2.2 Numerical simulation research

The steel plants are constantly trying to manufacture the higher quality products with low cost. However, the segregation of alloying elements, central porosity, internal crack defects and non-metallic inclusions are common casting defects, which can easily generate [73, 74] during solidification process and have an adverse effect on the final product. The association of software engineers and steel industries is an effective campaign to optimize the parameters of continuous casting mainly the reduction section. Therefore, numerical simulation can easily detect the physical phenomenon behind formation of internal defects during the implementation of reduction technology.

 Liu et al., [75] developed a thermal-mechanical coupled FEM model to predict proper soft reduction amount for continuous casting slab. Kajatani et al., [76] used a finite-volume scheme to simulate the deformation-induced macrosegregation in continuous casting steel. It is shown that the positive centerline segregation of carbon in the slab is well reproduced with this model. Guan et al., [77] developed a multiphase solidification model combining turbulent fluid flow, heat transfer, solute transport with back diffusion and shell deformation; The simulation results showed that a large reduction applied just before the solidification end could significantly reverse the flow of solute-enriched melt.

The temperature field, stress field, liquid core flow field and other complex fields during solidification process were analyzed by means of numerical simulation, and different mathematical models were established to explore the relevant parameters of reduction technology. Numerical simulation has lower cost, higher efficiency and visual detection as compare to the experimental research, which gives insight of reduction technology. Jiang et al., [78] used numerical simulation to study the flow of molten steel and solute distribution in the continuous casting slab by using reduction technology. The simulation results showed that the velocity of molten steel enriched with solute elements was restrained after the implementation of reduction technology, which significantly reduced the center segregation.

SR has a major impact to control the internal quality of cast products, but it can also leads to the cracks formation. The shape of roller can significantly reduce the crack formation during continuous casting process, as the convex-shaped roller improves the reduction efficiency, reduces the cracks formation and microsegregation, which does not require upgrading the equipment, and can also reduce equipment wear. Zhou et al., [63] performed the FEM simulation, and investigated that the convex roll can increase the deformation at the slab center, which further increases the reduction efficiency up to 15.10 pct. Ma et al., [64] investigated the effect of SR on the center macrosegregation during the continuous casting process, and developed mathematical model including fluid flow and solute transfer. Moreover, this model was further incorporated with soft reduction model. The simulation results revealed that the carbon enrichment was occurred at the solidification front while the center segregation ratio at the center region was 0. 1.11 and 1.09, respectively with soft reduction .

2.3 Industrial field research

Due to the complex production conditions of steel industry, reduction technology might have some limitations. For example, the combined effect of different factors such as casting speed, steel grade, and cooling water intensity might be problematic during the production process of cast steel. The optimization of reduction parameters according to the actual production process is very helpful to improve the quality of the casting billet.

Han et al., [79] established a dynamic control model for the SR of slab., according to the reduction parameters were inversely optimized with consideration of roll gap, reduction interval, feedback information of the model and metallurgical process standards, which significantly maintained the production of high-quality slabs during slab continuous casting process. The solidification of high-alloyed steel (0.4C–1.5Mn–2Cr–0.35Mo–1.5Ni) was resulted in a high temperature gradient of solidified shell with the formation of columnar crystal, which contributed to the center segregation and cracking due to the high carbon content, and was significantly improved by optimized SR parameters [33]. Chen et al., [80] conducted the industrial experiments on machine soft reduction (MSR) and improved the internal quality of the bearing billet. They found that the suitable casting condition for bearing steel (GCr15) should have a casting speed of 0.88 m/min and MSR rate of 2.4 mm/m or 2.1 mm/min for the 9# caster in NISCO.

 

• The message of section 2.2 Key links of reduction technology is not clear. The authors need to start this section with a definition of what they mean by key links. Why have the authors not added this section to 2.1.2. Technical parameters of reduction technology since it discusses the same point of equipment and process parameters?

Yes, your mentioned suggestions are solved, now the title of 2.2 is revised and also start with paragraph for clear understanding as highlighted below.

2.4.3.Factors affecting the reduction technology

There are different factors which have important role to control  the internal quality of cast products and are briefly discussed in above sections. Herein, the optimized and much influential factors can be concluded to solve the internal segregation and porosity defects of wide and thick continuous casting billet and slab. 

 

• lines from 549- 555 should be at the beginning of the paper and the main findings discussed at the end.

Thank you for your suggestion. The prospects of reduction technology is thoroughly revised and now can be easily concluded. These changes are highlighted by yellow as:

4. Prospects of reduction technology

This paper elucidates the development history of reduction technology, describes the basic principles along with the classification of different types of reduction technology. Moreover, this paper focuses on the theoretical research of HR technology and elaborates the key parameter and equipment problems during the implementation of HR. Taking the No.3 slab continuous caster of Baosteel as an example, the actual industrial test and application effect of the HR technology are explained, and put forward some viewpoints on the future development of reduction technology.

The basic principle of reduction technology is to apply an external force in an appropriate area of billet during the solidification process, which compensates the volume shrinkage at the solidification end, and improve the internal quality. The research on the reduction technology includes the reduction amount, reduction interval, reduction ratio parameters and numerical simulation. However, the effect of secondary cooling water intensity, alloy composition, mechanical equipment, etc. on the center segregation and cracks of the billet are rarely been discussed.

Future perspective:

Currently, the main problems during implementation of reduction technology are as follows.

(1) How to measure the temperature distribution of the billet during solidification? and how to calculate the volume shrinkage at solidification end to provide a basic for the theoretical calculation of the reduction parameters. New research methods and ideas should be adopted for the reduction technology, such as the effect of alloy composition on the mechanical properties of cast products, the relationship between cooling water intensity and billet solidification, etc., and breakthrough in quantification of reduction parameters.

(2) The research on the secondary cooling process is not enough to implement it in the practical application of the reduction technology, especially the relationship between the water intensity in the secondary cooling zone and solidification.

(3) It is difficult to accurately judge the position of the solidification end of the cast products, especially when the casting speed and cooling water intensity was changed. The selection of appropriate reduction interval and amount also need to be further investigation. The exact control of solidification end point is needed to improve the internal quality of cast products. Further research should be conducted on the transition states of different steel grades and the fluidity of molten steel in the two-phase zone along with the optimization in the design of reduction rollers.

(4) How to use the reduction tchnology for industrial production as the investigations on reduction technology is mainly discontinuous, and a complete research system of reduction technology has not been designed. According to the actual working conditions and the current investigations, a systematic research system of reduction technology should be designed to automatically adjust the reduction parameters such as reduction interval, reduction amount and reduction equipment.

(5) With the progress of HR technology, the mechanical equipment also needs to be upgraded to improve the fault-tolerance of HR technology during its use in the industry. The safety measures should be highly considered according to the results of destructive experiments in order to avoid the serious tragedy during the industrial production process.

 

 

 

Author Response File: Author Response.docx

Reviewer 4 Report

Comments for author File: Comments.docx

Author Response

The Article Application status and development trend of continuous casting reduction technology: a review by Authors Yi Nian, Liqiang Zhang, Chaojie Zhang, Naqash Ali, Jianhua Chu, Jiale Li, Xiang Liu shows an interesting review the types of billet core defects, the formation mechanism of center segregation and further put forwards the common solutions to overcome these problematic. However, few corrections should be made:

1. Abstract should be rewritten. It doesn’t state the motive behind the review.

• Thank you very much for your suggestion. I have revised the abstract according to your suggestion and highlighted by yellow as:

Continuous casting is a dominant steelmaking process due to its steady-state nature, enhanced yield of steel production, low consumption of energy and manpower. However, the production of defect free cast products is still a big challenge as the internal defects including, macrosegregation of alloying elements, cracks and pores can be easily formed during the solidification process, which seriously deteriorate the microstructure and mechanical properties of the cast products. Therefore, this paper puts forward the common solutions to overcome these problematic. The reduction technology can effectively improve the center segregation of the billet, bloom and slab. The history of the development of the reduction technology is summarized and classified according to the variations in research trend. Furthermore, the basic principle and parameters of reduction technology are described to implement them in the actual production process. This paper compares the similarities and differences between soft reduction (SR) and heavy reduction (HR) technologies with particular focus on the theoretical research of HR technology and further elaborates the key parameter and equipment problems during implementation of HR. Moreover, this paper also considers the HR technology adopted by Baosteel as a case study, which helped to put forward some viewpoints for the future development of reduction technology.

2. Generally, English language should be improved. English language should be checked by professionals.

• Thank you very much for your suggestion. The English grammarand other major mistakes are corrected by expert and yellow highlighted in manuscript.

 

3. Table 2 should have references within the table.

• Yes, now Table 2 hasreferences according to your suggestion.

 

4. It is not necessary, but it would be beneficial to readers if the Figure 2 is redrawn and put in color.

Yes, I redraw the Figure. 2 according to your suggestion as below and add that in revised manuscript.

 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Please find my comment in red font in the attached file

Comments for author File: Comments.docx

Author Response

Thank you for your suggestion, I made up some shortcomings based on your suggestion  and highlighted the changes by yellow color.

Author Response File: Author Response.docx