The Erosion–Corrosion Behavior of Eutectic High Chromium Cast Irons Reinforced by TiC Particles

Round 1

Reviewer 1 Report

This is a good and well-written paper.

Two points of interest could be addressed if the authors agree.

1. How does the high amount of primary TiC particles existing in the melt affect the melt viscosity and castability?
2. TiC has a much lower density than liquid iron. There should be gravity segregation of the TiC particles floating upwards and leading to inhomogeneous particle distribution. NbC has a very similar density to liquid iron and could therefore be a better choice.

Author Response

Reviewer 1

This is a good and well-written paper.

Two points of interest could be addressed if the authors agree.

1. How does the high amount of primary TiC particles existing in the melt affect the melt viscosity and castability?

Reply: Thank you very much for your comments. One of the emphases of this paper is the effect of TiC on high chromium cast iron. The effect of primary TiC on casting has not been studied.

 

2. TiC has a much lower density than liquid iron. There should be gravity segregation of the TiC particles floating upwards and leading to inhomogeneous particle distribution. NbC has a very similar density to liquid iron and could therefore be a better choice.

Reply: Thank you for your comments. We choose TiC mainly because of its high hardness, high melting point, high elastic modulus, good wettability and good thermodynamic stability in molten iron. Adding NbC to the steel will be put into the future study.

 

 

 

Reviewer 2 Report

Manuscript Number: Manuscript ID -metals-1630136 entitled:

The Erosion-Corrosion Behaviour of TiC-Strengthened Eutectic High Chromium Cast Irons

General comment

The paper presents the research regarding the improvement upon the erosion-corrosion and wear resistance of materials for the pumping and handling applications. High chromium cast irons (HCCIs) strengthened with TiC particles, are designed and fabricated by the in-situ solidification method.

Some recommendations and observations are listed below:

1. This paper needs a uniform formatting style. (ie R98-R102) and a description of the units of measurement for all parameters in the inserted equations.
2. At R 79 is written “the as-cast and heat-treated samples are denoted hereinafter as C0-C3 and H0-H3, respectively” is C0-C3 or A0-A3?
3. Verify the Chemical compositions of the samples in Table 1 (it seems to be the same 1:4!). Insert a column with weight amount of Ti: C added in each sample. This is beneficial also for Figure 8 where authors explain the data linked to TiC amount and not to notations probelor.
4. At R 104, it is mentioned by the authors that the impedance and polarization curves were measured when the OPC was stable. However, no impedance data are presented further in the paper.
5. The microstructure of samples should be more detailed. (The morphology of TiC particles their average diameter). Are TiC particles uniformly dispersed throughout the matrix?)
6. Polarization curves give also valued electrochemical parameters as βc and βa, polarization resistance, corrosion rate and inhibition efficiency that can be discussed comparatively for each tested specimen and give a clear images about corrosion inhibition.

Ussually, with  Icorr- total anodic current (μA) and icorr -corrosion current density, μA/cm2 are noted. (icorr = Icorr/A)

Wco = Icorr K E / d A=icorr K E /d

K- a constant that defines the units for the corrosion rate, E- the equivalent weight in grams/equivalent, d- density in grams/cm³, A- area of the sample in cm².

Verify the eq1 and values calculated for corrosion rate in table 3 (specify the n value).

7. Precise the number of replicates for corrosion test and insert in table 3, add the incertitude for each parameter. Replot Figure 7 and include E (V vs SCE) on Y-axis and also in table.
8. In figure 4 insert the unit for Hardness
9. In text for figure 4 and 5 is mentioned the addition of 9.8 vol.% TiC, but in these figures the X scale is from 0.0 to 1.0 TiC volume fraction in (%). The paragraph R164-170 must be rewrite to avoid any confusion.
10. In order to clarify the mechanism of erosion-corrosion wear, the total erosion-corrosion rate, the erosion rate in the absence of corrosion, the corrosion rate in the absence of erosion and the effect of corrosion on the erosion rate and the effect of erosion on the corrosion rate must be quantified and introduced a table with their value.

 Also, the erosion-corrosion mechanism maps will show transition regimes between erosion-corrosion, corrosion-erosion, and corrosion mechanism as a function of total erosion-corrosion rate to effect of erosion on the corrosion rate ratio.

Author Response

Reviewer 2

General comment

The paper presents the research regarding the improvement upon the erosion-corrosion and wear resistance of materials for the pumping and handling applications. High chromium cast irons (HCCIs) strengthened with TiC particles, are designed and fabricated by the in-situ solidification method.

Some recommendations and observations are listed below:

1. This paper needs a uniform formatting style. (ie R98-R102) and a description of the units of measurement for all parameters in the inserted equations.

Reply: Thank you for reminding us to take note of this issue! The modifications are as follows: The electrochemical workstation (Gamry Interface 1000, America) was used to evaluate the polarization behaviour of HCCIs. A sample size of 10 mm ×10 mm × 4 mm was cold-mounted in an epoxy resin. The exposed area (10 mm × 10 mm) was carefully polished. 

 

2. At R 79 is written “the as-cast and heat-treated samples are denoted hereinafter as C0-C3 and H0-H3, respectively” is C0-C3 or A0-A3?

Reply: Thank you for reminding us to take note of this issue! It should be A0 - H0. The modifications are as follows: The as-cast and heat-treated samples are denoted hereinafter as A0-H3 and H0-H3, respectively.

 

3. Verify the Chemical compositions of the samples in Table 1 (it seems to be the same 1:4!). Insert a column with weight amount of Ti: C added in each sample. This is beneficial also for Figure 8 where authors explain the data linked to TiC amount and not to notations probelor.

Reply: Thank you for your comments. One of the objectives of this paper is to study the effect of TiC content on the properties of HCCIs. It has been clearly shown in Table 1 that TiC content increases gradually. So for the convenience of the full text. The different samples were numbered. Each sample corresponds to a different number.

 

4. At R 104, it is mentioned by the authors that the impedance and polarization curves were measured when the OPC was stable. However, no impedance data are presented further in the paper.

Reply: Thank you very much for your comments. The impedance and polarization curves were measured after the OPC stabilized. This is because the test procedure is a complete set of procedures. The purpose is to obtain a more stable polarization curve. Our ultimate goal is just to get the polarization curve.

 

5. The microstructure of samples should be more detailed. (The morphology of TiC particles their average diameter). Are TiC particles uniformly dispersed throughout the matrix?)

Reply: Thank you for your opinion. The size of TiC particle generated in HCCI ranges from nanoscale to microscale. Therefore, the quality of SEM images is not good enough for statistical investigation. With the increase of TiC content, it gradually aggregates and the TiC becomes irregular.

 

6. Polarization curves give also valued electrochemical parameters as βc and βa, polarization resistance, corrosion rate and inhibition efficiency that can be discussed comparatively for each tested specimen and give a clear images about corrosion inhibition.

Reply: Thank you very much for your comments. The corrosion resistance of several materials is simply compared by polarization curves. The purpose is to pave the way for the study of erosion wear performance and mechanism. Therefore, much analysis of the measured polarization curves is not made.

 

7. Ussually, with  Icorr- total anodic current (μA) and icorr -corrosion current density, μA/cm2 are noted. (icorr = Icorr/A)

Wco = Icorr K E / d A=icorr K E /d

K- a constant that defines the units for the corrosion rate, E- the equivalent weight in grams/equivalent, d- density in grams/cm³, A- area of the sample in cm².

Verify the eq1 and values calculated for corrosion rate in table 3 (specify the n value).

Reply: Thank you for your comments. After many times of our calculation and inspection. We found a problem with our calculation formula. The verification results are as follows:

sample	icorr	k	A	n	D	Wco
A0	8.28	3.27	56	2	7.71	98.33
A1	5.75	3.27	56	2	7.59	69.36
A2	10.6	3.27	56	2	7.65	126.87
A3	47.3	3.27	56	2	7.39	586.03
H0	2.13	3.27	56	2	7.47	26.11
H1	2.55	3.27	56	2	7.5	31.13
H2	1.61	3.27	56	2	7.4	19.92
H3	1.85	3.27	56	2	7.22	23.46

Modified as follows:

Where k is a constant, A is atomic weight, n is the number of electrons gained and lost, D is density, and S is sample area.

It is noted that for the as-cast HCCIs, the corrosion rate increased from 98.33 to 586.03 μm/a when the volume fraction of TiC is 9.8%, the increment being as high as five times.

Specifically, the corrosion rates of heat-treated HCCIs were lower than 19.92 μm/a as shown in Table 3.

Sample	A0	A1	A2	A3	H0	H1	H2	H3
Icorr (μA/cm2)	8.28	5.75	10.60	47.30	2.13	2.55	1.61	1.85
wC0 (μm/a)	98.33	69.36	126.87	586.03	26.11	31.13	19.92	23.46
Ecorr (V)	-0.598	-0.625	-0.665	-0.690	-0.456	-0.502	-0.533	-0.556

 

8. Precise the number of replicates for corrosion test and insert in table 3, add the incertitude for each parameter. Replot Figure 7 and include E (V vs SCE) on Y-axis and also in table.

Reply: Thank you for your advice to us. Electrochemical experiments were done three times. So it's not accurate for incertitude, and we didn't add the incertitude. The E value of HCCI has been given in Table 3. incertitude due to inaccuracy. So we didn't draw the value of E.

 

9. In figure 4 insert the unit for Hardness

Reply: Thank you for your comments. In the diagram, the Units of Rockwell hardness (HRC) are already in place.Modified as follows:

 

 

10. In text for figure 4 and 5 is mentioned the addition of 9.8 vol.% TiC, but in these figures the X scale is from 0.0 to 1.0 TiC volume fraction in (%). The paragraph R164-170 must be rewrite to avoid any confusion.

Reply: Thank you for your comments. Figure 4 and 5 has been modified.Modified as follows:

 

11. In order to clarify the mechanism of erosion-corrosion wear, the total erosion-corrosion rate, the erosion rate in the absence of corrosion, the corrosion rate in the absence of erosion and the effect of corrosion on the erosion rate and the effect of erosion on the corrosion rate must be quantified and introduced a table with their value.

Also, the erosion-corrosion mechanism maps will show transition regimes between erosion-corrosion, corrosion-erosion, and corrosion mechanism as a function of total erosion-corrosion rate to effect of erosion on the corrosion rate ratio.

Reply: Thank you very much for your comments. Our aim was only to study the effects of TiC content and heat treatment on the wear and corrosion properties of prepared HCCIs. The possible causes of mass loss during erosion by separate wear and corrosion will be investigated in the future.

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

In the manuscript titled “The Erosion-Corrosion Behaviour of TiC-Strengthened Eutectic High Chromium Cast Irons”, Tu T. Q. et al. investigated the effect of the strengthening of the High Chromium Cast Irons with TiC particles. The authors need to address the following comments prior to publishing their article.

• Comment 1: Typos need to be corrected.
• Comment 2: Line 152- 153: The author stated that the volume fraction of M7C3 decreases after heat treatment due to the formation of secondary carbide M23C6. What is the proof for the formation of secondary carbide M23C6? TEM technique can be used to detect. Please comment.
• Comment 3: Table 3: The values of the Icorr in Table 3 for A0, A1, A2 and A3 are not correct and need to be checked, as it is different from the values extracted from Figure 7.

Author Response

Reviewer 3

In the manuscript titled “The Erosion-Corrosion Behaviour of TiC-Strengthened Eutectic High Chromium Cast Irons”, Tu T. Q. et al. investigated the effect of the strengthening of the High Chromium Cast Irons with TiC particles. The authors need to address the following comments prior to publishing their article.

 

Comment 1: Typos need to be corrected.

Reply: The typos through the manuscript have been revised.

 

Comment 2: Line 152- 153: The author stated that the volume fraction of M7C3 decreases after heat treatment due to the formation of secondary carbide M23C6. What is the proof for the formation of secondary carbide M23C6? TEM technique can be used to detect. Please comment.

Reply: Thank you very much for your advice. It has been reported that M23C6 carbide is formed after heat treatment of HCCI. Therefore, the formation of M23C6 carbide may also cause the decrease of the volume fraction of M7C3 carbide. However, the generation of secondary carbides is not the focus of this paper. Therefore, we do not have much characterization of secondary carbides.Modified as follows:It has been reported that M₂₃C₆ carbide is formed after heat treatment of HCCI[43]. Therefore, the volume fraction of M₇C₃ decreases after heat treatment may due to the formation of secondary carbide M₂₃C₆.

 

Comment 3: Table 3: The values of the Icorr in Table 3 for A0, A1, A2 and A3 are not correct and need to be checked, as it is different from the values extracted from Figure 7.

Reply: Thank you for your comments. The values in Table 3 are proposed after fitting by electrochemical analysis software. The unit of extracted value is changed from A/cm² to μm/cm².

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors made the corrections and respond to the comments. 

Author Response

Thank you for reviewing the manuscript.