JPH0348155B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a plastic working tool used for hot rolling rolls and guide rolls of copper and alloy wires mainly composed of copper. Conventionally, cemented carbide, soybean steel, high-speed steel, and the like have been used as plastic working tools for copper and copper alloys. However, the manufacturing conditions for mass-produced products such as wire-drawing rolls are becoming stricter year by year due to higher precision and economic demands, and along with this, plastic working tools are also required to have improved heat resistance, wear resistance, impact resistance, etc. is required. In order to meet these demands, new materials are being developed day and night in the fields of cemented carbide, soybean steel, and high-speed steel (high speed steel), but no material that fully satisfies the above-mentioned performance has yet been found. Not yet. As mentioned above, steel such as tool steel or cemented carbide is generally used as a metal plastic working tool material, and even when looking at the movement towards new plastic working tool materials, only slight changes have been made. On the other hand, ceramic has recently attracted attention as a material for plastic working tools, but its properties such as thermal shock resistance, impact resistance, and brittleness are inferior to the materials mentioned above, so it is one of the most popular materials for plastic working tools. It is only beginning to be used gradually in fields such as guide rolls with low stress, and at present there is almost no idea of using it for hot rolling rolls. The present inventors have arrived at this invention after many years of studying the possibility of using ceramic materials as plastic working tool materials. That is, the present invention relates to a new plastic working tool which is a silicon nitride ceramic, in particular, whose porosity is 5% or less, and which is obtained by pressureless sintering.
In particular, hot rolling rolls or guide rollers. These tools bring about a revolutionary change that overturns the conventional concept of various plastic working tools. The lifespan of conventional plastic working tools varies depending on the metal being plastic worked. For example, in the case of copper or copper alloys, a reaction occurs with the workpiece, causing a welding phenomenon, and the surface layer is welded and separated. Due to this repeated phenomenon, the surface layer becomes rough or worn out, and eventually reaches the end of its life. In addition, particularly during hot working, cracks occur in cemented carbide and soybean steel due to peeling phenomena called spalling and fatigue phenomena due to repeated welding and separation, which can be fatal. Spalling due to repeated welding is a problem specific to hot rolling rolls for copper and copper alloy wires, and is a particularly important and special problem among the damages, so it will be explained in detail. In particular, even for copper and copper alloy wires, in the case of wire drawing dies, wear, material biting, or jamming are more important problems, whereas spalling due to repeated welding is not such a serious problem. The difference between hot rolling rolls and wire drawing dies for wire rods such as copper and copper alloys is that although cemented carbide is suitably used as wire drawing dies for copper wire rods in the prior art, This can be understood from the fact that soybean steel is used as inter-rolling rolls because it suffers from severe wear and tear and cannot withstand use, sacrificing its lifespan. Spalling (surface peeling) of hot rolling rolls for copper and copper alloy wire rods is caused by thermal, mechanical, and chemical interactions between the roll and the rolled material that are specific to hot rolling. First, thermal action is characterized by periodic contact between the roll surface and the rolled material. In this respect, it differs from the steady thermal action that a die receives. The rolls are thus subject to heat cycling and become fatigued, making them susceptible to spalling due to interaction with copper and copper alloy welds. Mechanical action means that the roll surface is subjected to high rolling forces and is placed in high speed contact with the material to be rolled. Wear is not a particularly serious problem here, as is the case with dies. Chemical action refers to the reactivity between the roll surface material and the material to be rolled, and the behavior is particularly complex in the case of hot rolling of copper and copper alloys. For example, it is known that Si ₃ N ₄ sintered bodies have low reactivity with molten copper or copper alloys. However,
When copper or copper alloy wire is hot rolled using a roll made of Si ₃ N ₄ sintered body, spalling occurs due to severe welding or adhesion of copper or copper alloy to the roll surface.
This means that the reactivity with copper during hot rolling of the Si ₃ N ₄ sintered body is completely different from the reactivity with copper in the molten state, and no analogy can be made from this. That is, spalling due to welding of hot rolls of copper and copper alloys is the result of complex reactions caused by the thermal, mechanical, and chemical interactions described above. According to the research of the present inventors,
The reaction between Si ₃ N ₄ and copper wire is that the copper wire forms an oxide film in the atmosphere, cooling water, etc. during the rolling process.
It was concluded that one of the major factors was that it was CuO. The reactivity of Si ₃ N ₄ and CuO in air is 1050
When tested up to ℃, a rapid reaction was confirmed. As a result of these experiments, the present inventors considered the spalling phenomenon caused by welding during hot rolling of copper and copper alloy wires as follows. The Si ₃ N ₄ roll surface is oxidized by CuO under the thermal and mechanical effects described above to produce a SiO ₂ layer. As this SiO ₂ layer diffuses into CuO, the reaction between Si ₃ N ₄ and CuO progresses. especially
The eutectic structure of SiO ₂ −CuO exhibits high reactivity at relatively low temperatures. For this reason, copper welding or adhesion progresses and spalling occurs. As described above, spalling due to welding of copper or copper alloy hot rolling rolls is a very special phenomenon, and it has been extremely difficult to prevent this and provide rolls with a long life. The present invention has succeeded in dramatically extending the service life of conventional rolling rolls and guide rolls made of cemented carbide, dance steel, or high speed steel by preventing spalling due to adhesion as described above. As a result, the conventional concept of jigs and tools has been changed, and the tools of the present invention can be considered as part of the equipment, and for example, it is no longer necessary to manage periodic maintenance of the equipment itself, eliminating any unproductive situations. It was. The tool material of the present invention, which exhibits long life for rolling rolls and guide rolls for such copper and copper alloy wires,
As raw material composition, more than 60% by weight of Si ₃ N ₄ and Al ₂ O ₃
and/or 1 to 40% by weight of AlN, 1 _% of SiO2
The sintered body is characterized by containing 40% by weight of MgO and having a porosity of 5% or less, and may further contain 1 to 5% by weight of MgO. In the above Si ₃ N ₄ −Al ₂ O ₃ −AlN−SiO ₂ system,
Favorable results can be obtained if the SiAlON composition, which is well known in sintered bodies, has a composition of Si ₆ (1-X/8)Al2/3×N(8-X)Ox. A mixture containing this as a main component and a second phase may be formed. Regarding Si ₃ N ₄ used as the main material in this invention, a reaction sintering method in which a molded body of Si metal powder is nitrided and
Two methods are known in which Si ₃ N ₄ and additives are mixed and produced using a powder metallurgy method. However, the former method inevitably leaves more than 10% of pores, making it unsuitable for this invention. It is also known that the properties of the latter method are greatly influenced by the use of additives; however, Si ₃ N ₄ requires 60 % by weight or more was required.
If Al ₂ O ₃ , AlN and SiO ₂ are less than 1%, the strength will be insufficient, and if it is more than 40%, the strength will be low and it will become brittle.
This is not preferable because it reduces wear resistance. When MgO is in the range of 1 to 5%, a dense sintered body can be obtained, and the porosity can be easily controlled to 5% or less. As a result of various experiments, 25% by weight of Al ₂ O ₃ , 5% by weight of AlN, and SiO ₂ were used as roll materials for rolling at high temperatures.
It has been found that a tool made of a sintered body containing 8% by weight of carbon dioxide has the longest life. If the porosity exceeds 5%, the above-mentioned damage due to spalling becomes severe especially at high temperatures, which is not preferable. however,
In areas where the usage conditions are not too harsh, there is no significant effect up to about 10%. The crystal system of Si ₃ N ₄ can be used in either the α type or β type without any difference in effectiveness. Next, an example will be explained. Example 1 Based on Si ₃ N ₄ , 20% by weight of Al ₂ O ₃ , 10% by weight of AlN and 5% by weight of SiO ₂ were weighed and thoroughly ground and mixed in a ball mill. The obtained powder was molded and then sintered at 1650 to 1850°C for 4 hours in an _N2 gas atmosphere to produce a rolling roll with an outer diameter of 200 mmφ.
(The porosity of the sintered body was 3%) and this rolling roll was used as the 10th stage of a finishing rolling roll for copper wire. As a result, the rolling amount until the end of life was 2560 tons. The temperature of the material to be rolled was 500°C, and the temperature of the conventionally used superalloy roll was 350t. Examples 2 to ₄ 15% by weight of Al ₂ O ₃ and 5% of AlN based on Si ₃ N 4
Weighed 10% by weight of SiO ₂ and 3% by weight of MgO, and sintered it in the same manner as in Example 1 to obtain an outer diameter of 220% by weight.
A rolling roll of mmφ was manufactured. The composition of the sintered body is 90% Sialon, and the porosity is 2.0%, which is a mixture of this and a second phase containing MgO.
It was hot. Using this roll, the rolling temperature is 900℃, 700℃,
Rolling was carried out at 500°C, and when the rolling amount until the end of the roll life and the causes of the roll life were investigated, the results shown in Table 1 were obtained, and the rolling amount reached the end of life at approximately the same amount at 900°C and 700°C. Moreover, it was found that the rolling amount actually decreased at 500℃. The comparative roll is made of the same cemented carbide as in Example 1.

[Table] Examples 5 to 7 Example 1 using a pulverized mixture of 65% by weight of Si ₃ N ₄ , 25% by weight of Al ₂ O ₃ , 5% by weight of AlN, and 5% by weight of SiO ₂
In the same way as (but the sintering temperature is 1780℃), the outer diameter
A rolling roll of 250 mmφ was prepared and used in Example 2.
A lifespan test was conducted in the same manner as in method 4. The results are shown in Table 2, and unlike Examples 2 to 4, the rolling amount was greatest when rolling at 900℃, and the rolling amount was the highest when rolling at 900℃.
was the least frequent.

[Table] Example 8 Commercially available Si ₃ N ₄ 80% by weight, Al ₂ O ₃ 10% by weight, SiO ₂ 10
A guide roller for drawing a copper wire was produced by mixing the materials in a weight% manner in the same manner as in Example 1 (however, the sintering temperature was 1700° C.). The dimensions are outer diameter 200mmφ x 40mm,
The porosity of the sintered body was 4%. When we conducted a comparison test on the service life of commercially available guide rollers made of cemented carbide and alumina ceramic, we obtained the results shown in Table 3, indicating that the guide roller of this example was extremely superior. It has been proven that In addition, the speed of the wire is 15
m/sec, and the wire temperature is 500°C.

【table】

Claims (1)

[Claims] 1 60% by weight or more of Si ₃ N ₄ , 1 to 40% by weight of Al ₂ O ₃ and/or AlN, and 1 to 40% by weight of SiO ₂
The main composition of the entire sintered body is Si ₆ (1-X/8)Al2/3×N(8-X)Ox (where X is greater than 0 and less than 6 or equal to 6). ) A hot rolling tool for copper and copper alloy wire, characterized in that it is made of a sintered body having a porosity of 5% or less. 2. A hot rolling tool for copper and copper alloy wire, characterized in that the sintered body according to claim 1 further contains 1 to 5% by weight of MgO.