EP4691658A1

EP4691658A1 - Oxygen-free copper or oxygen-free copper alloy rod with excellent flexibility

Info

Publication number: EP4691658A1
Application number: EP23932190.4A
Authority: EP
Inventors: Seung Hyun Shin; Sangyum Kim; Yong Hee Won; Ji Sung Kim; Chul Hyun Kim
Original assignee: LS Cable and Systems Ltd
Current assignee: LS Cable and Systems Ltd
Priority date: 2023-04-06
Filing date: 2023-05-16
Publication date: 2026-02-11
Also published as: WO2024210256A1; CN121038909A; KR102572477B1

Abstract

The present invention relates to an oxygen-free copper or oxygen-free copper alloy rod with excellent flexibility. Specifically, the present invention relates to an oxygen-free copper or oxygen-free copper alloy rod capable of maintaining flexibility, processability, and the like, which were retained before drawing, as much as possible by recovering the crystal structure of the rod after drawing and heat treatment.

Description

[Technical Field]

[Background Art]

When oxygen exists in copper (Cu), since hydrogen embrittlement occurs by generating H₂O through reaction with Cu₂O and hydrogen, and corrosion resistance also deteriorates, copper (Cu) from which oxygen has been removed by a deoxidizer so that oxygen becomes about 10 ppm or less is referred to as oxygen-free copper (OFC).
Recently, for performance and reliability improvement in magnet wires for motors for electric vehicles, wires for solar cell modules, magnet wires for transformers, and submarine cables, oxygen-free copper (OFC) wire rods are being used, and especially, due to the growth of the electric vehicle and solar power markets, increase in demand for oxygen-free copper (OFC) is expected, and as miniaturization of electronic devices progresses, thinning of oxygen-free copper (OFC) wire rods is required, thereby, improvement in flexibility and processability of oxygen-free copper (OFC) is attracting attention.
As a method of manufacturing oxygen-free copper (OFC) wire rods, there are: a dip forming method of continuously rolling by solidifying oxygen-free copper on an outer circumference of a core rod; an up-cast method of continuously pulling up a solidified ingot which is cooled and solidified inside a mold by vertically placing an oxygen-free copper mold; a horizontal continuous casting method of continuously drawing a solidified ingot which is cooled and solidified inside a mold by horizontally installing a mold on a sidewall of a casting furnace; a belt and wheel type continuous casting and rolling method, also called the Southwire Continuous Rod (SCR) method, of manufacturing an ingot by injecting molten copper tapped from a shaft furnace into a rotating mold formed between a wheel and a belt, solidifying it by cooling, continuously drawing the ingot, and directly rolling it into a wire rod, and the like.
However, in conventional oxygen-free copper (OFC) wire rods, during drawing for thinning, flexibility, processability, and the like were significantly deteriorated due to work hardening, and even after performing heat treatment after drawing, the crystal structure was not recovered, so flexibility, processability, and the like were greatly insufficient.
Therefore, there is an urgent need for an oxygen-free copper or an oxygen-free copper alloy rod that is capable of maintaining to the maximum extent flexibility, processability, and the like before drawing, through recovery of the crystal structure after drawing and heat treatment of a rod.

[Disclosure]

[Technical Problem]

The present invention is directed to providing an oxygen-free copper or an oxygen-free copper alloy rod that is capable of maintaining to the maximum extent flexibility, processability, and the like before drawing, through recovery of the crystal structure after drawing and heat treatment of a rod.

[Technical Solution]

To achieve the objects, the present invention is directed to providing
an oxygen-free copper or oxygen-free copper alloy rod, having a fraction of low angle crystal grain boundaries of 0.76 or more, as defined by Equation 1 below. Fraction of low angle crystal grain boundaries = number of low angle crystal grain boundaries / total number of crystal grain boundaries
In Equation 1 above,
The low angle crystal grain boundary is a crystal grain boundary between two adjacent crystal grains, in which an angle between orientations, which are arrangement directions of majority atoms of each of the two crystal grains, is 15° or less in a crystal structure of the rod.
Here, an average crystal grain size may be 1.5 to 45 µm.
Meanwhile, in accordance with standards KSC 3006 and IEC 60851-3, a spring-shaped rod specimen is manufactured by winding the rod on a mandrel having a diameter 10 times that of the rod, and one end of the rod specimen is fixed, and a prescribed weight is hung on the other end, maintained for 1 minute, and an elongated length of the spring specimen may be 200 mm or more.
In addition, in accordance with standard IEC 60851, after the rod is bent at an angle of 30° for 2 to 5 seconds, and upon removal of a force applied for bending, a return angle to an original state may be 5° or less.
Further, in accordance with standard DIN 46453, as a result of performing a 3-point bending test on the rod, a maximum load applied at a point in time at which the rod is no longer bent may be 7 kgf or less.
Meanwhile, the oxygen-free copper or oxygen-free copper alloy rod may be manufactured by a Southwire Continuous Rod (SCR) method.
Here, the Southwire Continuous Rod (SCR) method may be a method in which molten copper tapped from a shaft furnace is injected into a rotating mold formed between a wheel and a belt, and is solidified through cooling to manufacture an ingot, and the ingot is continuously drawn and directly subjected to continuous rolling to manufacture a rod.
In addition, a temperature of the molten copper may be adjusted to be 1100 to 1140°C, a temperature of the ingot may be adjusted to be 800 to 900°C, and a temperature of the rolled rod may be adjusted to be 45 to 60°C.
Further, a rolling ratio, which is a cross-sectional area ratio of the rolled rod based on a cross-sectional area of the ingot, may be 0.1 to 15%, and a rolling line speed may be 7.5 to 10 mpm (meters per minute).

[Advantageous Effects]

An oxygen-free copper or an oxygen-free copper alloy rod according to the present invention exhibits an excellent effect that can maintain to the maximum extent flexibility, processability, and the like before drawing, by recovering a crystal structure deformed due to work hardening during drawing, through adjusting the crystal structure before drawing, by heat treatment.

[Description of Drawings]

FIG. 1 schematically illustrates a crystal structure of an oxygen-free copper or an oxygen-free copper alloy rod.

[Mode for Disclosure]

Hereinafter, exemplary embodiments of the present invention will be described in detail. However, the present invention is not limited to the exemplary embodiments to be described below and may be specified as other aspects. On the contrary, the embodiments introduced herein are provided to make the disclosed content thorough and complete, and sufficiently transfer the technical teachings of the present invention to those skilled in the art.
The present invention relates to an oxygen-free copper or oxygen-free copper alloy rod with excellent flexibility that is capable of maintaining to the maximum extent flexibility, processability, and the like before drawing, by recovering a crystal structure deformed due to work hardening during drawing, through adjusting the crystal structure before drawing, by heat treatment.
In a crystal structure of a metal, atoms of a crystal grain have an arranged direction, and an arrangement direction of majority atoms of a crystal grain is called orientation.
In a crystal structure before drawing of a cast-rolled rod, when an angle between orientations, which are the arrangement directions of majority atoms of each of two adjacent crystal grains is 15° or less, a crystal grain boundary between the two crystal grains may be defined as a low angle crystal grain boundary, whereas, when the angle is more than 15°, a crystal grain boundary between the two crystal grains may be defined as a high angle crystal grain boundary.
FIG. 1 schematically illustrates a crystal structure of an oxygen-free copper or an oxygen-free copper alloy rod.
As illustrated in FIG. 1, when there exist first crystal grains, second crystal grains, and third crystal grains, which have different orientations, which are the arrangement directions of majority atoms, since an angle (θ₁₂) between an orientation of the first crystal grains and an orientation of the second crystal grains, and an angle (θ₂₃) between an orientation of the second crystal grains and an orientation of the third crystal grains are respectively more than 15°, a crystal grain boundary between the first crystal grains and the second crystal grains, and a crystal grain boundary between the second crystal grains and the third crystal grains, are all high angle crystal grain boundaries, whereas, since an angle (θ₁₃) between an orientation of the first crystal grains and an orientation of the third crystal grains is 15° or less, a crystal grain boundary between the first crystal grains and the third crystal grains is a low angle crystal grain boundary.
In this regard, the inventors of the present invention completed the present invention by experimentally confirming that, when a fraction of the low angle crystal grain boundaries among total crystal grain boundaries of a cast-rolled rod is adjusted to be a predetermined value or less, a crystal structure deformed due to work hardening during drawing of the cast-rolled rod can be recovered to the maximum extent by heat treatment, and thereby, flexibility, processability, and the like before drawing can be maintained to the maximum extent.
Although a causal relationship between a fraction of the low angle crystal grain boundaries and a recovery degree of the crystal structure during heat treatment cannot be clearly identified, it is presumed that the reason is because the low angle crystal grain boundary induces dislocation during drawing processing and such dislocation promotes recrystallization during heat treatment.
Specifically, a fraction of low angle crystal grain boundaries defined by Equation 1 below, in an oxygen-free copper or oxygen-free copper alloy rod according to the present invention, may be 0.76 or more. Fraction of low angle crystal grain boundaries = number of low angle crystal grain boundaries / total number of crystal grain boundaries
In Equation 1 above, the number of the low angle crystal grain boundaries and the number of the total crystal grain boundaries are all measured before drawing after rolling of the rod, and from electron microscope images captured by using an electron microscope equipped with an electron backscattered diffraction (EBSD) detector, the number of the total crystal grain boundaries and the number of the low angle crystal grain boundaries in each of three specimens selected with a predetermined unit area, for example, an area of 4 mm², may be measured respectively, and an average value of ten measured values may be derived. Here, the fraction of the low angle crystal grain boundaries, the number of the low angle crystal grain boundaries, and the number of the total crystal grain boundaries may be derived by automatic analysis in the EBSD detector.
Here, when the fraction of the low angle crystal grain boundaries is less than 0.76, a wire rod drawn from a cast-rolled rod has a problem in that, even when heat treatment is performed, a crystal structure deformed due to work hardening during drawing is recovered only to an insignificant degree, so flexibility, processability, and the like before drawing cannot be maintained.
In addition, the oxygen-free copper or oxygen-free copper alloy rod according to the present invention may have an average crystal grain size of 1.5 to 45 µm. When the average crystal grain size is less than 1.5 µm, being too small, or more than 45 µm, being too large, there may be difficulty in adjusting the number of the low angle crystal grain boundaries. Here, the average crystal grain size may be measured in accordance with ASTM E 1382 standard.
The oxygen-free copper or oxygen-free copper alloy rod according to the present invention, when it possesses the number of the low angle crystal grain boundaries described above, is not particularly limited in a manufacturing method, but preferably, may be manufactured by a belt and wheel type continuous casting and rolling method, also called a Southwire Continuous Rod (SCR) method.
The SCR method is a method of manufacturing an ingot by injecting molten copper tapped from a shaft furnace into a rotating mold formed between a wheel and a belt, and solidifying it through cooling, then continuously drawing the ingot and directly subjecting it to continuous rolling to manufacture a wire rod.
Here, a temperature of the molten copper may be adjusted to be about 1100 to 1140°C, a temperature of the ingot may be adjusted to be about 800 to 900°C, and a temperature of the rolled rod may be adjusted to be about 45 to 60°C. In addition, a rolling ratio, which is a cross-sectional area ratio of the rolled rod based on a cross-sectional area of the ingot, may be 0.1 to 15%, and a rolling line speed may be 7.5 to 10 mpm (meters per minute). In addition, a drawing ratio, which is a cross-sectional area ratio of a drawn wire rod based on a cross-sectional area of the rolled rod, may be 5 to 12%.

[Examples]

1. Manufacturing Example

An oxygen-free copper rod was manufactured by the SCR method, while adjusting process conditions so as to have a fraction of low angle crystal grain boundaries and a fraction of high angle crystal grain boundaries as described in Table 1 below. [Table 1]

Example Comparative Example 1 Comparative Example 2

Fraction of low angle crystal grain boundaries 0.788 0.750 0.707

Fraction of high angle crystal grain boundaries 0.212 0.250 0.293

2. Flexibility evaluation

1) Spring Elongation Number (SEN) evaluation

In accordance with standards KSC 3006 and IEC 60851-3, a spring-shaped rod specimen was manufactured by winding each of an oxygen-free copper rod of the examples and the comparative examples on a mandrel having a diameter 10 times that of the rod, and by fixing one end of the rod specimen, hanging a prescribed weight on the other end, and maintaining it for 1 minute, an elongated length of the spring specimen was measured. The longer the elongated length is, the better the flexibility is.

2) Spring back evaluation

In accordance with standard IEC 60851, each of the oxygen-free copper rods of the examples and the comparative examples was bent at an angle of 30° for 2 to 5 seconds, and after removing a force applied for bending, a return angle to the original state was measured. The smaller the return angle is, the better the flexibility is.

3) Bending load evaluation

In accordance with standard DIN 46453, a 3-point bending test was performed for each of the oxygen-free copper rods of the examples and the comparative examples, and a maximum load applied at a point in time at which the oxygen-free copper rod was no longer bent was measured. The lower the maximum load is, the better the flexibility is.
The flexibility evaluation results are as described in Table 2 below. [Table 2]

Example Comparative Example 1 Comparative Example 2

SEN evaluation (mm) 340 160 100

Spring back evaluation (°) 4.5 5.2 5.5

Bending load evaluation (kgf) 6.2 7.1 7.5
As described in Table 2, the oxygen-free copper rod of the example according to the present invention was confirmed to have excellent flexibility by possessing a fraction of low angle crystal grain boundaries adjusted to 0.76 or more. On the other hand, oxygen-free copper rods of Comparative Example 1 and Comparative Example 2, having a fraction of low angle crystal grain boundaries of less than 0.76, were confirmed to have significantly reduced flexibility.
While the present invention has been described above with reference to the exemplary embodiments, it may be understood by those skilled in the art that the present invention may be variously modified and changed without departing from the technical teachings and scope of the present invention disclosed in the claims. Therefore, it should be understood that any modified embodiment that essentially includes the constituent elements of the claims of the present invention is included in the technical scope of the present invention.

Claims

An oxygen-free copper or oxygen-free copper alloy rod, having a fraction of low angle crystal grain boundaries of 0.76 or more, as defined by Equation 1 below. Fraction of low angle crystal grain boundaries = number of low angle crystal grain boundaries / total number of crystal grain boundaries In Equation 1 above, the low angle crystal grain boundary is a crystal grain boundary between two adjacent crystal grains, in which an angle between orientations, which are arrangement directions of majority atoms of each of the two crystal grains, is 15° or less in a crystal structure of the rod.
The oxygen-free copper or oxygen-free copper alloy rod of claim 1, wherein an average crystal grain size is 1.5 to 45 µm.
The oxygen-free copper or oxygen-free copper alloy rod of claim 1 or 2, wherein, in accordance with standards KSC 3006 and IEC 60851-3, a spring-shaped rod specimen is manufactured by winding the rod on a mandrel having a diameter 10 times that of the rod, and one end of the rod specimen is fixed, and a prescribed weight is hung on the other end, maintained for 1 minute, and an elongated length of the spring specimen is 200 mm or more.
The oxygen-free copper or oxygen-free copper alloy rod of claim 1 or 2, wherein, in accordance with standard IEC 60851, after the rod is bent at an angle of 30° for 2 to 5 seconds, and upon removal of a force applied for bending, a return angle to an original state is 5° or less.
The oxygen-free copper or oxygen-free copper alloy rod of claim 1 or 2, wherein, in accordance with standard DIN 46453, as a result of performing a 3-point bending test on the rod, a maximum load applied at a point in time at which the rod is no longer bent is 7 kgf or less.
The oxygen-free copper or oxygen-free copper alloy rod of claim 1 or 2, wherein the oxygen-free copper or oxygen-free copper alloy rod is manufactured by a Southwire Continuous Rod (SCR) method.
The oxygen-free copper or oxygen-free copper alloy rod of claim 6, wherein the Southwire Continuous Rod (SCR) method is a method in which molten copper tapped from a shaft furnace is injected into a rotating mold formed between a wheel and a belt, and is solidified through cooling to manufacture an ingot, and the ingot is continuously drawn and directly subjected to continuous rolling to manufacture a rod.
The oxygen-free copper or oxygen-free copper alloy rod of claim 7, wherein a temperature of the molten copper is adjusted to be 1100 to 1140°C, a temperature of the ingot is adjusted to be 800 to 900°C, and a temperature of the rolled rod is adjusted to be 45 to 60°C.
The oxygen-free copper or oxygen-free copper alloy rod of claim 8, wherein a rolling ratio, which is a cross-sectional area ratio of the rolled rod based on a cross-sectional area of the ingot, is 0.1 to 15%, and a rolling line speed is 7.5 to 10 mpm (meters per minute).