Influence of Austenitisation Time and Temperature on Grain Size and Martensite Start of 51CrV4 Spring Steel

Round 1

Reviewer 1 Report

Good research work and all the results has been well analysed and validated.

Author Response

The authors wish to thank the reviewer for his time, and are very  appreciative of his kind remarks.

Reviewer 2 Report

1. The resolution of the metallographic structure given in Figures 5 and 7 is too low. Please give a picture with higher resolution to show the difference of the prior austenite grain size.

2. The change rule of Ms temperature given in Figure 8 seems to be very confused. At 800 ℃, Ms temperature decreases with the extension of holding time, while other conditions seem to increase with the extension of time. Please give a clearer explanation, including the trend that changes with the increase of temperature.

3. The language of the manuscript needs to be further improved. For example, on page 7, lines 192-194, "I should be noted that august temperatures above 960 ° C and shorter holding times (5 minutes), the MS temperature are less scanned and increases mainly at the expense of the growth of prior august grains."

4. The classification of data given in Figure 9 is not clear, please identify the austenite grain size under different processes in detail.

Author Response

Many thanks to the reviewer for his time and effort reviewing the paper. We have followed his comments as closely as possible.

1. The resolution of the metallographic structure given in Figures 5 and 7 is too low. Please give a picture with higher resolution to show the difference of the prior austenite grain size.

We apologise for the quality, the resolution of the microstructure figures has been improved.

2. The change rule of Ms temperature given in Figure 8 seems to be very confused. At 800 ℃, Ms temperature decreases with the extension of holding time, while other conditions seem to increase with the extension of time. Please give a clearer explanation, including the trend that changes with the increase of temperature.

Additional text was added: However, at 800 °C, the grain size is not the dominant factor for the M_S, but rather the low dissolution of carbides (even cementite) and subsequently low carbon content. This will be presented in the SEM analysis section later on. ...

... This explains the unusual drop in M_S temperature, supporting the explanation, given before, where the grain size is not the leading factor, but the austenite chemical composition. 

3. The language of the manuscript needs to be further improved. For example, on page 7, lines 192-194, "I should be noted that august temperatures above 960 ° C and shorter holding times (5 minutes), the MS temperature are less scanned and increases mainly at the expense of the growth of prior august grains."

The remark is confusing, as the text presented by the reviewer is not the original. The given sentence originally it read as follows:

“I should be noted that austenitisation temperatures above 960 °C and shorter holding times (5 minutes), the MS temperature are less scattered and increases mainly at the expense of the growth of prior austenite grains.”

Nonetheless, the manuscript was reread and the mistakes were corrected to improve the language.

4. The classification of data given in Figure 9 is not clear, please identify the austenite grain size under different processes in detail.

The diagram in Figure 9 was included in the manuscript with a purpose to present the relationship between the size of the prior austenite crystal grains and the Ms temperature in general for the spring steel studied. The size of the prior austenite crystal grains was in the foreground, and the course of the austenitisation was negligible. The modified diagram with detailed descriptions of the samples was added, as requested by the reviewer.

Reviewer 3 Report

The manuscript "Influence of austenitisation time and temperature on grain size and martensite start of 51CrV4 spring steel" has deal with the study of austenization time and temperature on grain size and martensite start of 52CrV4 spring steel. In the results of the manuscript, one can be note the finding that in the case of complete austenite transformation, the Ms temperature increases with the growth of crystal grains.

I think that the manuscript can be accepted after minor corrections. They are:

- the number of Figure in page 4 should be 2, not 1;

 - the word "boundaries" is missed in lines 44, 45;

- the data on hardness and discussion about carbides should be moved from the paragraph "Optical microscopy" to another place in the manuscript;

- in Figures 8d-f only one extremum is visible, not two;

-the statement in "Conclusions" about inadequate production of material it should be discussed in the manuscript.

 

 

 

are visible in Figure 8d-f;

Author Response

First of all, we would like to express our gratitude to the reviewer for helping us improve our paper.

- the number of Figure in page 4 should be 2, not 1;

Thank you for the comment, there was a minor mistake, we corrected the number of the Figure in page 4 and checked once again all the other Figures.

- the word "boundaries" is missed in lines 44, 45;

The missed words have been added in the manuscript:
“In low-carbon low-alloyed steels, the kinetics of crystal grain growth increases with temperature, and crystal grain boundaries migration decreases with the addition of alloying elements. The movement of crystal grain boundaries can be slowed down due to the segregation of alloying elements at the crystal boundaries (the solute drag effect), and due to undissolved precipitates (carbides, nitrides), so called pinning effect is cancelled at the moment when the particles dissolve in the matrix and the kinetics of grain growth is accelerated [10,14,16,18–23].”

- the data on hardness and discussion about carbides should be moved from the paragraph "Optical microscopy" to another place in the manuscript;

The additional paragraph “Hardness” was created in which the figure with the results of the hardness measurements and an additional explanation of the figure were introduced.

• in Figures 8d-f only one extremum is visible, not two;

Thank you for the remark, the extreme values are  visible at 10 and 30 min, but interestingly the most prominent differences are visible at 10 min. These results are attributed to the changes in segregations. 

-the statement in "Conclusions" about inadequate production of material it should be discussed in the manuscript.

Our description was too hars, and the ”inadiquate” part was removed, but we added an explanation in the results and discussion section as suggested: ”Such chemical segregations are common for the continous casting and hot rolling production route. Furthermore, special metallurgical processes like electroslag remelting can almost completely eliminate segregations, but are, due to the high cost, used in the production of expensive materials like tool steels.”

Reviewer 4 Report

The manuscript investigated the effect of austenitization time and temperature on grain size and martensite start temperature (Ms) of a spring steel. It is commonly accepted that austenite grains grow and Ms decreases with increasing austenitization temperature and time. The present work reported a deviation of Ms above a certain temperature due to dissolution of carbides and segregation of alloying elements. But some modifications should be made.

1.     Fig.6a shows that austenite grains are smaller at 800°C than at 860°C. Why is the hardness of the former is smaller than the former at 5 min and 10 min (Fig.6b)? Please note that carbides don’t dissolve at 800°C and 860°C.

2.     The segregation band in Fig.10a is not clear, please mark segregation band with line and arrow.

3.     The last sentence in conclusion: “a higher concentration of carbides was characterized in the segregated areas”

Which result support this conclusion?

Author Response

The authors would like to thank the reviewer for the useful comments and tips that we have used to improve our paper. We hope that you find our reviewed version worthy of publication

1. 6a shows that austenite grains are smaller at 800°C than at 860°C. Why is the hardness of the former is smaller than the former at 5 min and 10 min (Fig.6b)? Please note that carbides don’t dissolve at 800°C and 860°C.

Correctly, the prior austenite grains after austenitisation at 800 °C are smaller than the prior austenite grains quenched at 860 °C. The hardness of the samples quenched at 800 °C (5 and 10 minutes) has lower values than that the samples quenched at 860 °C (5 and 10 minutes). The lower hardness of the specimens quenched at 800 °C can be explained by incomplete austenitic transformation (pearlite to austenite) and fewer dissolved carbides. Due to the incomplete austenitic transformation, some pearlite grains are present in the microstructure, which affect the hardness of the specimens. In addition, the incomplete transformation leads to a lower carbon concentration in the matrix, so that the quenched martensite is softer. The additional explanation has been added to the manuscript.

2. The segregation band in Fig.10a is not clear, please mark segregation band with line and arrow.

The segregation band was shown in Fig. 11a (now 13a) the arrow and the line marks have been added accordingly to the reviewer instruction.

3. The last sentence in conclusion: “a higher concentration of carbides was characterized in the segregated areas”

Which result support this conclusion?

SEM Figure (Fig. 11a) shows the segregation band and non-segregated area, significant difference between the concentration of carbides in segregation band is visible. Additionally, the EDS microchemical analysis was done to characterize the concentration of the elements in segregation bands comparing to the bulk area. Small but evident difference was analysed.
If the reviewer wants to, the EDS analysis results and additional explanation can be added to the manuscript, but we feel that it does not improve the paper.

Reviewer 5 Report

1.  The paper is very interesting, it contains important results for understanding the heat treatment of steels. It shows an interesting angle on the influence of segregations and homogenisation of steel on the heat treatment process. There are minor remarks that will improve the paper even more and add additional value to the readers.

2. In the abstract- "The stability of carbides during austenitisation were 21 evaluated with scanning electron microscopy (SEM) and thermodynamic calculations of equilib- 22 rium phases using the Thermo-Calc program. MC-type vanadium carbides are stable up to 956 °C 23 under equilibrium conditions, but SEM result show that they were present in the microstructure 24 even after annealing at 1040 °C"- this statement has been written at the end but please explain what might be the postive or negetive effects on mechanical properties after these microsctructural characteristics. 

3. I could not find Figure 2 anywhere, please look at page 3 and 4. Name the figures correctly. 

4. Show pearlite and pro-eutectoid ferrite in Figure 1.

5. Expand the introduction by including more information on both high strength alloys (like Ti alloys) and fatigue life.

6. Explain how heat treatment affects different alloys, and why it is important.

7. Figure 1, mark ferrite and pearlite on the micrograph. Also what was the Nital concentration?

8. Cooling and heating speeds are in K/s change them into °C/s.

9. ThermoCalc has an option to export the chemical composition of a phase at a certain temperature, give the composition of MC type carbide FCC_A1#2 in range from Ae3 to 956 °C.

10. I found some typo-errors, authors must go through the manuscript once again. 

11. A discussion section can be added prior to conclusion with a comparative analysis of the current findings with the past research works. 

12. As the authors are dealing with steel, I can recommend an article which might be considered in the work- DOI: 10.36547/ams.28.3.1556 

 

Overall, I found the article publishable with some minor corrections. Authors must indicate the corrections by using colored fonts. 

Author Response

The authors would like to thank the reviewer for the time and helpful remarks. We have corrected the paper according to your comments and hope you find our correction sufficient.

1. In the abstract- "The stability of carbides during austenitisation were evaluated with scanning electron microscopy (SEM) and thermodynamic calculations of equilibrium phases using the Thermo-Calc program. MC-type vanadium carbides are stable up to 956 °C under equilibrium conditions, but SEM result show that they were present in the microstructure even after annealing at 1040 °C" this statement has been written at the end but please explain what might be the postive or negetive effects on mechanical properties after these microsctructural characteristics. 

Comment added to the abstract and in the results and discussion section.

 

2. I could not find Figure 2 anywhere, please look at page 3 and 4. Name the figures correctly.

The numbering of the Figures has been corrected.

 

3. Show pearlite and pro-eutectoid ferrite in Figure 1.

Pearlite and ferrite phases have been marked in the Figure 1.

 

4. Expand the introduction by including more information on both high strength alloys (like Ti alloys) and fatigue life.

Text was added to expand the introduction.

5. Explain how heat treatment affects different alloys, and why it is important.

Text was added to expand the introduction.

 

6. Figure 1, mark ferrite and pearlite on the micrograph. Also what was the Nital concentration?

The Figure 1 has been corrected. Additional explanation added, nital concentration added 5%.

7. Cooling and heating speeds are in K/s change them into °C/s.

The cooling and heating speeds were corrected and changed into °C/s.

8. ThermoCalc has an option to export the chemical composition of a phase at a certain temperature, give the composition of MC type carbide FCC_A1#2 in range from Ae3 to 956 °C.

The proposed equilibrium chemical composition of FCC_A1#2 carbides were presented in the new Figure in the manuscript. Additional explanation was introduced in the text

“Figure 3 shows the chemical equilibrium composition and the amount of vanadium car-bides between 600 and 956 °C. Besides vanadium and carbon, the particles also contain small amounts of Fe, Cr, Mo and Mn”.

 

10. I found some typo-errors, authors must go through the manuscript once again. 

The manuscript was read again, the found errors was corrected.

 

11. A discussion section can be added prior to conclusion with a comparative analysis of the current findings with the past research works. 

We have already incorporated the discussion in the “results and discussion” section.

12. As the authors are dealing with steel, I can recommend an article which might be considered in the work- DOI: 10.36547/ams.28.3.1556 

 Thank you kindly for your suggestion, we have included the paper in our references.

Overall, I found the article publishable with some minor corrections. Authors must indicate the corrections by using colored fonts.