JP3358438B2 - Hot work crack prevention method for tough pitch copper ingot - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for preventing hot working cracks in a tough pitch copper ingot based on lead (Pb).

[0002]

2. Description of the Related Art When it is desired to obtain a desired product by hot or cold working a tough pitch copper ingot, if there is a large amount of impurities in copper (Cu), cracks may occur during ingot processing. . The cracks at the time of this processing cannot always be completely removed even after the processing of the subsequent steps (rolling, forging, drawing, etc.) is completed. If it cannot be removed, it remains as a history in the final product, and may affect the quality and characteristics of the product. In addition, the effect of impurities in copper on workability is more remarkable in hot working than in cold working. In order to improve the quality and characteristics of products obtained by working ingots, in particular, hot working is required. It is necessary to prevent the ingot from cracking during hot working.

FIGS. 1 (a) and 1 (b) are cross-sectional views schematically showing cross-sectional structures before and after hot rolling of a tough pitch copper ingot containing Pb and containing unavoidable impurities other than Pb. FIG. 3 is a structural diagram showing the effect of Pb on hot working. As shown in FIG. 1A, before rolling, the tough pitch copper ingot 1 has a sound structure. In contrast,
After the rolling, hot working cracks 4 occur along the crystal grain boundaries 3 as shown in FIG. Furthermore, hot working crack 4
In addition, internal cracks 5 also occur along crystal grain boundaries 3.

[0004] The tough pitch copper ingot 1 having such a structure structure 1
When we performed electron probe X-ray microanalysis on
Pb was detected from the crystal grain boundary 3. From the above results, the reason why the hot working cracks 4 and the internal cracks 5 occur during the hot working based on Pb of the tough pitch copper ingot 1 is that the low melting point Pb present in the crystal grain boundaries 3 is generated during the hot working. It is considered that the crystal grains 2 exist at a high temperature in a liquid phase (Pb-rich Cu phase), and as a result, the strength of the crystal grain boundaries 3 is reduced.

[0005] Therefore, in order to prevent hot working cracks 4 in the tough pitch copper ingot 1 caused by impurity elements such as Pb, refining of molten copper is performed before the casting process to remove harmful impurity elements. Need to be removed. As a simple method of refining molten copper with melting equipment in the production line,
Conventionally, dry refining by molten copper oxidation has been used.

[0006]

However, according to the above-mentioned dry refining using molten copper oxidation, in view of the thermodynamic characteristics of Cu ₂ O-based slag and the distribution equilibrium value of impurity elements between the molten copper, Is difficult to remove, and it is not easy to remove hot working cracks and internal cracks. Therefore, the present invention
It is an object of the present invention to provide a method for preventing hot working cracks generated during hot working even when the content of Pb in copper increases.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides a product manufactured by hot working a tough pitch copper ingot containing Pb and containing unavoidable impurities other than Pb. In doing so, the apparent Pb amount per unit grain boundary area [apparent grain boundary Pb concentration (g / mm ² )] is controlled by controlling the crystal grain size of the tough pitch copper ingot .
Tough pitch copper ingot reduced to 5 × 10 ^-8 (g / mm ² ) or less
Has been subjected to hot working.

According to this method, Pb is dispersed in the tough pitch copper ingot by controlling the crystal grains to refine the crystal grain size, and the apparent amount of Pb per unit grain boundary area is reduced. In addition, hot working crack susceptibility during hot working can be reduced .

Thus, the apparent Pb amount per unit grain boundary area (apparent grain boundary Pb concentration C _pb ) is controlled to 3.5 × 10 ⁻⁸ (g / mm ² ) or less by controlling the crystal grains. Thereby, the occurrence of hot working cracks can be eliminated.
According to this method, hot work cracking of the tough pitch copper ingot based on Pb can be prevented, and the quality and characteristics of the final product can be improved.

[0010]

Embodiments of the present invention will be described below. As described above, Pb-containing Pb
Hot working cracks 4 during hot working of tough pitch copper ingot 1 containing unavoidable impurities other than the above occur along crystal grain boundaries 3. Further, Pb can be detected from the crystal grain boundary 3. It is considered that the hot working crack 4 is caused by a decrease in the strength of the crystal grain boundary 3 due to the Pb-rich liquid phase.

Therefore, if the area of the crystal grain boundary 3 is increased, that is, if the crystal grain 2 is made finer, harmful Pb can be dispersed and the hot working crack 4 can be reduced. In the present invention, in the step of hot-working the tough pitch copper ingot 1 containing Pb and containing unavoidable impurities other than Pb to produce a desired product, the unit crystal grain boundary in the tough pitch copper ingot 1 The apparent Pb amount per area (“apparent grain boundary Pb concentration C _pb ”) was defined as follows.

C _pb ≡ [Pb content of ingot (g) / [grain boundary area (mm ² )] The actual “grain boundary area” in the ingot cannot be measured. Here, the “total grain boundary lengthΣl (mm)” of an arbitrary surface of the ingot was actually measured, and the unit thickness 1 of the ingot was measured.
(Mm) is referred to as “grain boundary area [Σl (mm) ×
1 (mm)]. Then, the hot working is performed by controlling the size of the crystal grains 2 so that the value of the grain boundary Pb concentration C _pb becomes 3.5 × 10 ⁻⁸ (g / mm ² ) or less. By controlling the crystal grain size in this way, it is possible to prevent the occurrence of hot working cracks 4 during hot working.

Next, an embodiment of the present invention will be described.

[0014]

EXAMPLES First, a tough pitch copper ingot 1 was prepared using a heating furnace in an Ar (argon) atmosphere with the Pb concentration as a parameter. Next, short length samples having different crystal grain sizes were cut out from the tough pitch copper ingot 1. The sample was heated and held at 800 ° C. for 30 minutes in an Ar atmosphere, and subsequently subjected to hot rolling at a working ratio of 30%. On the basis of these results, hot working cracks 4 generated during working were evaluated using an actual microscope with a magnification of about 10 times.

Tables 1, 2 and 3 show the Pb content (g) and the crystal grain size in the ingot (1 mm ³ ) with respect to the Pb concentration (mass ppm) of the tough pitch copper ingot manufactured as described above. (Calculated by the intercept method), the grain boundary area (mm ² ) in the ingot 1 mm ³ , the apparent grain boundary Pb concentration C _pb (g / m
m ² ) and the evaluation of hot work cracking.
In each of the tables, the symbol “○” means “no cracks occurred”, and ×
The mark means "there is a crack".

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

As is clear from Tables 1, 2 and 3,
When the Pb concentration in the ingot was 2 (mass ppm), no hot working crack occurred even if the crystal grain size was 3.0 (mm). When the Pb concentration was 6 (mass ppm), cracks occurred when the crystal grain size was 2.3 (mm) or more. When the Pb concentration is 10 (mass ppm), the crystal grain size is 1.3 (mm).
As described above, cracks occurred, and when the Pb concentration was 24 (mass ppm) or more, cracks occurred even at a crystal grain size of 0.5 mm to 3.0 mm.

As described above, by making the crystal grain size in the tough pitch copper ingot 1 fine, hot work cracking can be prevented even if a certain amount of Pb is contained.
In Tables 1 to 3, the apparent grain boundary Pb concentration C _pb
When hot work cracking is evaluated from the viewpoint of _Cpb , C _pb is about 3.
It can be seen that hot working cracks 4 do not occur below 5 × 10 ⁻⁸ (g / mm ² ).

As is apparent from the above, even if Pb is contained in the tough pitch copper ingot, the crystal grains thereof are refined,
By reducing the “Pb concentration at the grain boundary”, Pb in the tough pitch copper ingot 1 is dispersed, so that hot working cracks can be reduced. As a result, the quality and characteristics of the product can be improved. In addition, productivity can be improved and cost can be reduced.

The present invention relates to a method for preventing hot working cracks based on Pb in a tough pitch copper ingot. Since about 200 to 500 mass ppm of oxygen is present in tough pitch copper in advance, when an impurity element that is easily oxidized is mixed, it may combine with oxygen in the copper to form an oxide. On the other hand, since oxygen-free copper (O ₂ concentration: about 10 mass ppm) hardly contains oxygen, it is considered that the impurity element mixed into the molten copper naturally behaves differently from the case of tough pitch copper. However, tough pitch copper, oxygen-free copper, and copper containing oxygen more than tough pitch copper, in any case, to refine the grain size of the ingot and disperse the harmful elements present at the grain boundaries is due to its heat. This is effective as a measure to prevent interwork cracking.

The present invention is characterized in that in order to prevent hot working cracks based on the impurity element Pb in the tough pitch copper ingot, the crystal grain size of the ingot is reduced.
As described in the examples, it has been found that the refinement of the crystal grains of the ingot is effective as a measure for preventing cracking. In order to apply this invention to an actual production line, low-temperature casting of molten copper,
The crystal grains are refined by a method such as application of ultrasonic waves to molten copper, electromagnetic stirring during casting, and the like, and the “apparent grain boundary Pb concentration” is set to 3.5 × 10 ⁻⁸ (g / mm ^2). ) It is necessary to reduce the following.

[0024]

As described above, the present invention relates to a method for hot working a tough pitch copper ingot, wherein the amount of Pb per unit grain boundary area of the tough pitch copper ingot is not more than a predetermined value. Since the crystal grain size is controlled to be 3.5 × 10 ⁻⁸ (g / mm ² ) or less, hot working cracks can be reduced, and the quality and characteristics of products can be improved. Also,
Productivity can be improved and cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional structure diagram schematically showing the cross-sectional structures of a tough pitch copper ingot containing Pb and containing inevitable impurities other than Pb before and after hot rolling, and FIG. The cross-sectional structure before rolling is shown, and (b) shows the cross-sectional structure after rolling.

[Explanation of symbols]

 Reference Signs List 1 tough pitch copper ingot 2 crystal grain 3 crystal grain boundary 4 hot working crack 5 internal crack

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takaro Ichikawa 5-1-1 Hidakacho, Hitachi City, Ibaraki Prefecture Inside the Power System Research Laboratories Nippon Cable Co., Ltd. 5-1-1, Nippon Steel Corporation Power System Laboratory (56) References JP-A-2-232326 (JP, A) Masayoshi Aoyama et al., Reduction of hot microcrack in tough pitch copper by grain refinement , Journal of Copper and Copper Technology, Vol. 40, p. 183-188 Hiroshi Yamanobe et al., Simulation of solidification of copper continuously cast by twin belt method, Journal of Copper Brazing Technology, Vol. 40, p. 189-193 (58) Fields investigated (Int.Cl. ⁷ , DB name) C22F 1/08 C22C 9/00-9/10 B22D 11/00-11/06 B22D 21/00

Claims (1)

(57) [Claims] 1. A method for producing a product by subjecting a tough pitch copper ingot containing Pb and containing inevitable impurities other than Pb to hot working to produce a product, controlling a crystal grain size of the tough pitch copper ingot. Apparent Pb amount per crystal grain boundary area [apparent grain boundary Pb
Concentration (g / mm ² )] is ^{less than} 3.5 × 10 ⁻⁸ (g / mm ² )
A method for preventing hot work cracking of a tough pitch copper ingot, which comprises performing hot working on the lowered tough pitch copper ingot.