Process Condition Diagram Predicting Onset of Microdefects and Fracture in Cold Bar Drawing

Round 1

Reviewer 1 Report

The central fracture problem is a fundamental problem in the drawing of pure matrix (single-phase) materials. The presence of inclusions is a significant disturbance of the process. Brittle cracking of the sediments and their fragmentation may occur. Depending on the degree of hardening of the matrix and the drawing speed, the sediment particles will be completely surrounded by the metal matrix or will form voids in front of and behind the particles due to the excessively high radial stress values necessary for the plastic flow of the material at these points. It was shown, inter alia, in fig. 7b (i), 7b (iv).
Please explain how the presence of particles was accounted for in equation (3) which was the numerical model of the wire drawing process?

Author Response

Ans) It's a good question. Let me explain Eq. (3) proposed by Ko et al. [19] first. It is one of the numerical models for predicting ductile fracture taking into account deformation parameters (stress triaxiality, equivalent plastic stress and principal stress) when a hub-hole in a wheel disc of a vehicle is expanded. Note that a microcracks tend to occur in the edge of the hole during the expansion process. Eq. (3) assumed that if the mean stress at a point in the material is positive (stress triaxiality > 0), the (micro)void develops at a point, and coalescences, resulting in microcracks at the point. The microcracks then merge and finally lead to (macro)fracture. On the other hand, if the mean stress is negative (stress triaxiality < 0), the void shrinks and a very large plastic deformation is required until fracture.

In conclusion, Eq. (3) did not explicitly consider the presence of inclusions and sediment particles surrounded by a metal matrix. Ko et al. [19] inferred their assumptions were reasonable after compared the predicted ductile fracture with the measurements.

The center element on the cross-section of the material being drawn has a positive stress triaxiality. Hence this paper has applied Eq. (3) and shown the inference was reasonable; This paper showed that there was some reasonable correlation among drawing conditions (α and r), the generation of void around the inclusion, microcraks and fracture on the material being drawn through FE analysis coupled with Eq. (3), a draw bench test, and SEM images.

I put some of what you mentioned and the sentences we added in lines 173~185 in the revised manuscript.

 

Reviewer 2 Report

There are a few points that probably should be explained better. For example in figure 5b there is a fracture that occurs in the safe area which appears to be about 13% lower than the safety line (black dashed line in the figure) which is not taken into account in the description of the figure.

Author Response

Ans) That's a good point. The fracture of the material in the test (α=2° and r=36%) in Figure 5b is due to excessive pulling force. As α decreases, the die/material area increases and the force required for drawing increases. This is because FE analysis used the same coefficient of friction for all values ​​of α. Also the fracture of the material (α=16° and r=10%; α=16° and r=20%) was caused by the dead zone. Equation (3), i.e., ductile fracture criterion is a numerical model that does not take into account the fracture due to the dead zone effect. These explanations have been added in the revised manuscript. Please see lines 235-240, 244-248 and 291-295.

Reviewer 3 Report

Review for metals-1125534

Process Condition Diagram Predicting Onset of Microdefects and Fracture in Cold Bar Drawing

The authors address an interesting research topic for the journal Metals. Overall, I think this is a really innovative and useful study. In addition, it is a rigorous and well-organized paper. The contribution of this paper is relevant, specially the results shown in Figures 5 and 6, so that, in my opinion, the paper deserves to be published. Anyway, some changes should be considered:

Comments and Suggestions for Authors

• Line 31-33. “Multi-pass drawing commences with a 5.5–9.0 mm diameter coil material and, after dozens of passes, produces a long product with a 1.0–0.01 mm diameter, depending on the type of material and its intended end use.” According to previous research works (doi:10.1016/j.proeng.2011.04.583; 10.1016/j.matdes.2011.02.026; doi:10.3390/met6050114), this sentence should be modified as this data depends on the type of material. Please include several of these references and others to discuss this aspect and update the data written in the manuscript.
• Introduction Section: Previous research works (https://doi.org/10.1007/s11003-013-9603-5) dealt with the role of the die inlet angle in multi-pass drawing processes. Thus, This and similar previous work should be included in the manuscript so that the article presents a better selection of the state-of-the-art.
• Line 102. Since the considered material for this study is a high-alloy steel (SUJ2Z), including more information about this material in the manuscript is advisable, e.g. applications. Furthermore, more references related to this material should be included in the manuscript in order to enhance the interest of scientific community for this material.
• Figs 6b and 7a look the same. In that case, Figure 7a could be delated.
• In my opinion, including a better state-of-the-art is advisable.

Author Response

Comments and Suggestions for Authors

• Line 31-33. “Multi-pass drawing commences with a 5.5–9.0 mm diameter coil material and, after dozens of passes, produces a long product with a 1.0–0.01 mm diameter, depending on the type of material and its intended end use.” According to previous research works (doi:10.1016/j.proeng.2011.04.583; doi:10.1016/j.matdes.2011.02.026; doi:10.3390/met6050114), this sentence should be modified as this data depends on the type of material. Please include several of these references and others to discuss this aspect and update the data written in the manuscript.

Ans) A more detailed explanation and introduction of multi-pass drawing has been added, and related papers (doi:10.1016/j.matdes.2011.02.026) were also cited in the revised manuscript. In addition, I included a paper in the reference to discuss this aspect in the revised manuscript. (doi.org/10.1016/j.corsci.2011.06.012) Please see the first page of the revised manuscript.

 

• Introduction Section: Previous research works (https://doi.org/10.1007/s11003-013-9603-5) dealt with the role of the die inlet angle in multi-pass drawing processes. Thus, This and similar previous work should be included in the manuscript so that the article presents a better selection of the state-of-the-art.

Ans) Regarding the role of the die inlet angle in multi-pass drawing processes, an explanation of the change in macroscopic behavior due to microstructure change after drawing has been added in the revised manuscript.

(doi.org/10.3390/met6050114;

doi.org/10.1016/j.actamat.2011.02.017;

doi.org/10.1016/j.msea.2015.02.040;

doi.org/10.1016/j.engfracmech.2014.02.004;

doi.org/10.1016/j.conbuildmat.2011.04.025)

Please see the first page of the revised manuscript.

 

• Line 102. Since the considered material for this study is a high-alloy steel (SUJ2Z), including more information about this material in the manuscript is advisable, e.g. applications. Furthermore, more references related to this material should be included in the manuscript in order to enhance the interest of scientific community for this material.

Ans) The alloy composition information and mechanical property values ​​for SUJ2Z are given in Table 1 and Table 2, respectively. I have searched for more articles related to this material, but have not found it yet.

 

• Figs 6b and 7a look the same. In that case, Figure 7a could be delated.

Ans) Figs 6b and 7a might look the same, those are slightly different. The purpose of Figure 7 is for the readers to easily understand the applicability of a process condition diagram (PCD) proposed in this study; with Figure 7a, process designers may predict roughly the size of microvoids around inclusions and microcracks in the SUJ2Z being drawn for any given α and r combinations without taking SEM photos.

 

• In my opinion, including a better state-of-the-art is advisable.

Ans) This study has focused on applicability. It is unfortunate that this work does not include the latest technologies that are a better state-of-the-art.

Round 2

Reviewer 3 Report

Although the authors could not find any research work related to the material considered for this study (SUJ2Z), they could use studies performed with similar materials (e.g. "Influence of repeated quenching-tempering on spheroidized carbide area in JIS SUJ2 bearing steel; K Egawa et al 2018 IOP Conf. Ser: Mater. Sci. Eng. 307 012045) in order to justify the industrial application of such a material (thereby increasing the interest of the scientific community in this research work).

Author Response

It’s a good idea. The alloy compositions of SUJ2Z and JSUJ2 are actually the same. (please see the table below) Both are used in rolling contact applications where high fatigue strength and wear resistance are required. The letter 'Z' corresponds to the orderer (customer)'s specifications. Please see lines 107~110. I have also added the proceeding paper that you recommended in the Reference in the second revised manuscript.

Grade	Standard	C	Si	Mn	P	S	Cr	Mo	Cu	Al	Ti
SUJ2	JIS G 4805	0.95-1.05	0.15-0.30	0.25-0.45	≤0.025	≤0.008	1.35-1.6	≤0.008	≤0.025	≤0.05	≤0.003
SUJ2Z	USER	0.95-1.05	0.15-0.30	0.25-0.45	≤0.025	≤0.008	1.35-1.6	≤0.008	≤0.025	≤0.05	≤0.003

Author Response File: Author Response.pdf