Microstructure, Mechanical Properties, and Corrosion Behavior of 06Cr15Ni4CuMo Processed by Using Selective Laser Melting

Round 1

Reviewer 1 Report

 The authors have investigated the microstructure and mechanical properties of 06Cr15Ni4CuMo processed by selective laser, however, this research does not provide the any scientific data and deep discussion on this topic. This manuscript does not suitable for publishing as an article.

 

Introduction

The motivations, novelties and objectives of the study need to be very clearly outlined. It is in the present form rather vague.

The Literature review for this paper is not enough, I suggest authors to study more about the mechanical and microstructure of 06Cr15Ni4CuMo and also SLM technique.

Methodology

This section does not provide any information about the fabrication process of 06Cr15Ni4CuMo

Many parameters are effective in the SLM technique, authors should mention all these parameters in methodology part.

Why authors did not heat treat the sample?

Without heat treatment they fabricated the brittle 06Cr15Ni4CuMo, as clear in their mechanical result part.

Discussion

in discussion part, authors just repeat of other researchers statement and they did not add any new knowledge base on their own results

Author Response

Reviewer-1

The authors have investigated the microstructure and mechanical properties of 06Cr15Ni4CuMo processed by selective laser, however, this research does not provide the any scientific data and deep discussion on this topic. This manuscript does not suitable for publishing as an article.

We thank for reviewer for these comments and his criticism. However, we have modified the manuscript and hope the present version may be suitable for publication.

Introduction

The motivations, novelties and objectives of the study need to be very clearly outlined. It is in the present form rather vague.

The motivation of the study is made clear in the revised form. Now it states: Since there are not many reports that deal with the novel material like 06Cr15Ni4CuMo steel processed by LPBF/SLM process and limited literature is available on their microstructure and properties, the present work aims to explore the microstructure of the 06Cr15Ni4CuMo steel fabricated by SLM and to study their properties in the as-prepared conditions for marine applications.

The Literature review for this paper is not enough, I suggest authors to study more about the mechanical and microstructure of 06Cr15Ni4CuMo and also SLM technique.

Thanks for the comment. The literature review part is modified. However, only one paper is available for this material, which is already included and discussed. Additional details about the SLM process have been introduced and is suitably highlighted.

Methodology

This section does not provide any information about the fabrication process of 06Cr15Ni4CuMo

As suggested by the review, necessary details have been included in the methodology section.

Many parameters are effective in the SLM technique, authors should mention all these parameters in the methodology part.

All the parameters used for the fabrication is introduced in the revised version of the manuscript.

Why authors did not heat treat the sample?

Heat treatment itself is a different metallurgical process and the aim of the present manuscript is the successful fabrication of the marine steel and to initial microstructural examination and test their properties. We are now heat treating these samples and a detailed study on their microstructure and properties will be submitted as a new manuscript.

Without heat treatment they fabricated the brittle 06Cr15Ni4CuMo, as clear in their mechanical result part.

As mentioned above, the present manuscript is about the fabrication, microstructure, and properties of 06Cr15Ni5CuMo parts. Just because the sample is brittle, we did not change from the initial focus of the study.

Discussion

in discussion part, authors just repeat of other researchers statement and they did not add any new knowledge base on their own results.

As per the comments from the reviewer, we have modified the discussion part in the revised version of the manuscript.

Reviewer 2 Report

This manuscript is devoted to selective laser melting of nickel-chromium alloys. This class of alloys is of high importance for industrial applications, therefore the presented results may be of interest to a wide range of readers. The manuscript is well compiled and reflects all the necessary stages of scientific research. However, there are a few comments that need to be corrected before publication.
1. The modes of selective laser melting should be presented in Section 2: power, scanning speed, layer thickness, etc. The rationale for the selected modes should also be presented.
2. How was the carbon content determined in Table 1?
3. Mechanical properties: (i) indicate the measurement error; (ii) it is desirable to provide a stress-strain curve.
4. Unfortunately, without a detailed description of the method of obtaining the studied alloys, the study has no practical significance. I suggest that the authors strengthen Section 2 and describe the SLM process, provide the properties of the initial powder and the equipment used.

Author Response

Reviewer-2

This manuscript is devoted to selective laser melting of nickel-chromium alloys. This class of alloys is of high importance for industrial applications, therefore the presented results may be of interest to a wide range of readers. The manuscript is well compiled and reflects all the necessary stages of scientific research. However, there are a few comments that need to be corrected before publication.
1. The modes of selective laser melting should be presented in Section 2: power, scanning speed, layer thickness, etc. The rationale for the selected modes should also be presented.

As per the comments, the following sentence is introduced: SLM samples (size:  diameter – Φ10 mm and length – 25 mm length) have been fabricated with the layer thickness of 25 µm on Selective Laser Melter (Realizer SLM 50 Germany), using gas atomized powder of 33 µm particle size at 96 W laser Power, hatch distance of 60 µm, hatch distance of 120 µm, exposure time of 25 µs and point distance of 25 µm. The hatch direction between the layers is maintained the same. The entire process was carried out under a nitrogen atmosphere to avoid possible oxidation during the SLM process.

2. How was the carbon content determined in Table 1?

Optical emission spectrometry was used to determine the carbon content mentioned in Table 1.

3. Mechanical properties: (i) indicate the measurement error; (ii) it is desirable to provide a stress-strain curve.

As suggested by the reviewer, we have introduced an error bar for the mechanical data.

4. Unfortunately, without a detailed description of the method of obtaining the studied alloys, the study has no practical significance. I suggest that the authors strengthen Section 2 and describe the SLM process, provide the properties of the initial powder and the equipment used.

SLM process parameters, initial powder, and the equipment used were introduced in the experimental part.

Reviewer 3 Report

1. The SLM process parameters and deposited parts dimensions are missing.

2. In Table 1 title, % of elements in what unit? Wt.% or at.% should be given in detail.

3. Figure 2 shows the microstructures of the SLM processed and wrought alloy with a region of approximately 50 microns. But is the same microstructure evenly distributed throughout the deposited part or not. It is recommended to provide images of the deposited part at different locations.

4. This study is dealing with single-phase alloy and claims that the SLM processed parts consisted of martensite laths only. So, it is important to show the EBSD results as evidence.

5. Section 3.4 deals with the mechanical properties of the SLM processed parts, but there is no information on which direction was tested for mechanical properties and why?

6. Table 3, it is recommended to explain in detail, why the strength is increased and elongation decreased.

7. For Fig. 5, the selected region is too small, it is better to show the low magnification to understand the corrosion behavior of two different alloys in detail.

8. Is the ductility of the SLM processed parts 28% meet the requirements of the marine applications? Please provide the relative standards.

 

 

Author Response

Reviewer-3

1. The SLM process parameters and deposited parts dimensions are missing.

As suggested by the reviewer, we have introduced the SLM parameters and the dimensions.

2. In Table 1 title, % of elements in what unit? Wt.% or at.% should be given in detail.

Sorry for the confusion. The table represents the data in wt.% and is introduced in the revised version of the manuscript.

3. Figure 2 shows the microstructures of the SLM processed and wrought alloy with a region of approximately 50 microns. But is the same microstructure evenly distributed throughout the deposited part or not. It is recommended to provide images of the deposited part at different locations.

We have introduced one image each for both the samples, which are representative of these samples.

4. This study is dealing with single-phase alloy and claims that the SLM processed parts consisted of martensite laths only. So, it is important to show the EBSD results as evidence.

Thanks for the comments. But the same has been already proved using XRD patterns.

5. Section 3.4 deals with the mechanical properties of the SLM processed parts, but there is no information on which direction was tested for mechanical properties and why?

The mechanical properties of the samples were tested along the building direction. This is because the dimensions of the built samples are 10 mm in diameter and 25 mm in length.

6. Table 3, it is recommended to explain in detail, why the strength is increased and elongation decreased.

The increase in strength and the decrease in the elongation in the SLM process material have been described in detail as follows: In the case of the SLM processed material, the strength of the alloy increases because of the following factors: (1) refined microstructure (crystallite size – 16.55 nm), (2) presence of single martensitic phase, (3) increased volume of dislocation density (5 ⅹ 1014 m/m3) – which is one or two orders of magnitude higher than the values observed for the wrought specimens, and (4) solid solution strengthening [4,14,30,32,81–83]. It is also for the very same reason that the increase in the volume of dislocations (dislocation density) will offer little room for additional generation of dislocation and for the dislocation movement during mechanical loading. Since the dislocation movement is obstructed severely and the generation of the new dislocations is restricted, the material offers little ductility. It may also be argued in a way that the activation volume for such SLM processed material is >100b3 and hence leading to bulk forest hardening and offering little plasticity [84]. In addition, these additively manufacturing materials tend to fail prematurely due to the presence of both internal and external defects, which also hampers their deformability [36]. Hence, the SLM processed material shows improved strength at the expense of its plasticity.

7. For Fig. 5, the selected region is too small, it is better to show the low magnification to understand the corrosion behavior of two different alloys in detail.

We would agree with the reviewer on his views. However, the most representative images have been furnished in the present manuscript to show the corrosion effect.

8. Is the ductility of the SLM processed parts 28% meet the requirements of the marine applications? Please provide the relative standards. Most of the wrought alloys are having % Elongation less than 25%( Eg 410, 409 430 3tc) Present alloys elongation is 28% which is inline with them

Normally ductility is the term that is related to the processability of the materials and in real-life applications, toughness is more important than ductility. There are instances, where the SLM process materials have shown better toughness at even lower ductility and have been used in real-life applications. So we are not bothered about ductility in the present case, since the fracture toughness of the sample is yet to be evaluated.

Round 2

Reviewer 1 Report

1.Please add a reference for Russian standards GOST 977-88 standard

2. It would be great if authors provide the XRD, SEM and EDS of the 06Cr15Ni4CuMo powder, this data could help reader to understand the shape, phase and size of powder that used.

3. please add scanning speed for SLM parameter

4. Two hatch distance was mentioned in text, which one is correct60 or 120µm

5. How did authors optimize the printing parameters?

6. It would be great if authors provide the EDS analysis of printed 06Cr15Ni4CuMo

7. Engineering stress-strain curve of SLM  06Cr15Ni4CuMo should be added to the mechanical properties section

8. Please compare results of this research with result of the reference [71] and explain difference

9. Author strongly is suggested to add SEM image of the fracture surface tensile sample

Author Response

Reviewer-1

We thank for reviewer for these comments and his criticism. However, we have modified the manuscript and hope the present version may be suitable for publication.

1.Please add a reference for Russian standards GOST 977-88 standard

As suggested by the reviewer, reference to the Russian standards GOST 977-88 has been added.

2. It would be great if authors provide the XRD, SEM and EDS of the 06Cr15Ni4CuMo powder, this data could help reader to understand the shape, phase and size of powder that used.

As suggested by the reviewer, XRD, SEM and EDS of the 06Cr15Ni4CuMo powder has been introduced in the revised version.

3. please add scanning speed for SLM parameter

As suggested by the reviewer, scanning speed has been introduced.

4. Two hatch distance was mentioned in text, which one is correct 60 or 120µm

Sorry for the error. The correct hatch distance is retained in the revised version of the manuscript.

5. How did authors optimize the printing parameters?

The authors have optimized the printing parameters based on the 316L parameters. Since the manuscript is focused on properties, the optimization of the printing parameters is not discussed.

6. It would be great if authors provide the EDS analysis of printed 06Cr15Ni4CuMo

As suggested by the reviewer, EDS analysis of the printed 06Cr15Ni4CuMo has been introduced.

7. Engineering stress-strain curve of SLM 06Cr15Ni4CuMo should be added to the mechanical properties section

As suggested, stress-strain curve has been introduced.

8. Please compare results of this research with result of the reference [71] and explain difference

The results of the present manuscript are compared with the reference [71] and suitable analysis is introduced in the revised version.

9. Author strongly is suggested to add SEM image of the fracture surface tensile sample

As suggested, fracture surface images of the SLM fabricated tensile sample has been introduced.

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

 Accept