Patent Application
20150376755
The present invention relates to a copper alloy material for continuous casting mold and a process for producing the same. In more detail, the present invention relates to a copper alloy material for continuous casting mold consisting of 0.05 wt % to 0.6 wt % of Cr, 0.01 wt % to 0.5 wt % of Ag, 0.005 wt % to 0.10 wt % of P, and a balance of Cu and a trace of unavoidable impurities; and a process for producing the same.
Since a mold used for continuous casting (or also referred to as a continuous casting mold) has an inside surface with molten steel of about 1600° C. flowing therethrough and an outside surface being quenched by cooling water at the same time, it is very important to select a material which can withstand thermal shock and thermal strain applied thereto as a material of the mold during the continuous casting process. Accordingly, the continuous casting mold material should show soundness of ingot, high strength and high thermal conductivity (electric conductivity), and further should have softening resistance, in which the mold can be used for a long time period when the temperature of the mold is elevated up to about 300° C. Therefore, a copper alloy material for continuous casting mold used in steel and non-steel industries is needed to have excellent heat resistance, high electric conductivity, high creep properties, excellent abrasion resistance, excellent high-temperature fatigue strength, high tensile strength, high ductility, and excellent processability.
Moreover, a copper alloy material for continuous casting mold should be produced under an air atmosphere to improve work convenience and reduce the production cost. In other words, when a copper alloy material contains a large amount (>0.6%) of Cr or Zr and the copper alloy material is casted under an air atmosphere; the probability of inclusion of oxides thereto becomes very high. Accordingly, in case that the copper alloy material contains a large amount (>0.6%) of Cr or Zr, the casting process is not easy since the copper alloy material should be cast under a vacuum atmosphere or a completely controlled atmosphere.
In general, recently, a copper with silver (silver bearing copper) or chrome based copper alloy material has been widely used as the copper alloy material for continuous casting mold. Although a well-known chrome-zirconium-copper (CuCrZr, or chrome based copper alloy material) has excellent mechanical properties, it has also a drawback of poor thermal properties including its poor thermal conductivity (electric conductivity) and has poor castability due to a large amount (>0.6%) of Cr and Zr included therein. Whereas, a copper with silver (a silver bearing copper) has good thermal properties owing to its excellent heat dissipation capability and such properties make melting and casting of the copper with silver very easy, but the copper with silver has poor mechanical properties due to the same reason.
As an example of the most related patent publications of copper alloy materials developed for use in the continuous casting mold field, Japanese laid open patent application No. 1992-198460 has described a copper alloy material consisting of 0.8 wt % of Cr, 0.2 wt % of Zr, and a balance of Cu, and it has also disclosed that the copper alloy material must include Cr and Zr to meet the requirements of primary mechanical properties, such as tensile strength and hardness.
In addition, Japanese laid open patent application No. 2003-089832 has disclosed a copper alloy material consisting of 0.01 wt % to 0.3 wt % of Zn, 0.01 wt % to 0.25 wt % of Zr or 0.02 wt % to 0.4 wt % of Cr, 0.005 wt % to 1.0 wt % of at least one of Ti, Ni, Fe, Sn, Si, Mn, P, Mg, Co, Al, B, In and Ag, and a balance of Cu. The above patent publication has disclosed that a copper alloy material has inadequate tensile strength while having high conductivity and that there is no description on an elongation ratio and hardness which are required for sufficient processability.
In the meantime, PCT publication WO 04/074526 has disclosed a copper alloy material consisting of less than 0.2 wt % of Ag, 0.1 wt % to 0.4 wt % of Cr, and 0.03 wt % to 0.1 wt % of Zr. However, the above copper alloy material can not be cast under an air atmosphere but should be only used in a vacuum furnace due to the total content of highly oxidative Cr and Zr. In addition, it also requires Zr as a necessary component.
Japanese laid open patent application No. 1995-054079 has disclosed a copper alloy material for mold consisting of 0.5 wt % to 1.0 wt % of Ti, 0.05 wt % to 2.0 wt % of Cr, and 0.05 wt % to 0.7 wt % of Zr. The above patent application has also disclosed that the copper alloy material for mold should include Ti, Cr and Zr, which are highly oxidative, as principal elements.
Meanwhile, Japanese laid open patent application No. 2009-191337 has disclosed a copper alloy material consisting of 0.01 wt % to 2 wt % of Cr, and 0.005 wt % to 1 wt % of Zr as principal elements. The copper alloy material disclosed in the above patent application can include either or both of Cr and Zr, and requires a high frequency induction furnace for forming a vacuum atmosphere or a controlled reaction atmosphere for producing it.
Accordingly, since no copper alloy material for continuous casting mold, which is able to be cast under an air atmosphere and has excellent heat resistance properties including tensile strength, hardness and electric conductivity, has been provided, any copper alloy material for continuous casting mold, which has mechanical properties and heat resistance properties better than a copper with silver generally used currently, has excellent heat dissipation capability better than a chrome zirconium based copper alloy material, and enables easy casting under an air atmosphere, should be required.
To solve the problems, an object of the present invention is to provide a copper alloy material for continuous casting mold which enables easy casting under an air atmosphere and has excellent mechanical properties and excellent heat resistance properties, and a process for producing the same.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a copper alloy material for continuous casting mold consists of 0.05 wt % to 0.6 wt % of Cr, 0.01 wt % to 0.5 wt % of Ag, 0.005 wt % to 0.10 wt % of P, and a balance of Cu and a trace of unavoidable impurities, and has Brinell hardness of higher than 120 HB, and electric conductivity of higher than 85% IACS. The copper alloy material can further include less than 0.1 wt % of at least one of elements selected from a group consisting of Sn, Ti, Mg, Mn, Fe, Co, Al, Si, Mo, Zr and W.
In another aspect of the present invention, a process for producing a copper alloy material for continuous casting mold, includes the steps of casting an ingot consisting of 0.05 wt % to 0.6 wt % of Cr, 0.01 wt % to 0.5 wt % of Ag, 0.005 wt % to 0.10 wt % of P, and a balance of Cu under an air atmosphere, homogenizing the obtained ingot at 700° C. to 950° C. for 30 minutes to 6 hours, hot working the homogenized product at 10% to 90%, cold working the hot worked product at 10% to 80%, precipitating the obtained cold worked product at 400° C. to 600° C. for 1 hour to 8 hours, and cold working the precipitated product at 10% to 80% after cooling the product down to a room temperature. In above production process, the ingot can further include less than 0.1 wt % of at least one of elements selected from a group consisting of Sn, Ti, Mg, Mn, Fe, Co, Al, Si, Mo, Zr and W.
In the meantime, in another aspect of the present invention, a process for producing a copper alloy material for continuous casting mold, includes the steps of casting an ingot consisting of 0.05 wt % to 0.6 wt % of Cr, 0.01 wt % to 0.5 wt % of Ag, 0.005 wt % to 0.10 wt % of P, and a balance of Cu under an air atmosphere, homogenizing the obtained ingot at 700° C. to 950° C. for 30 minutes to 6 hours, cold working the homogenized product at 10% to 80%, precipitating the cold worked product at 400° C. to 600° C. for 1 hour to 8 hours, and cold working the precipitated product at 10% to 80% after cooling the product down to a room temperature. In addition, in above production process, the ingot can further include less than 0.1 wt % of at least one of elements selected from a group consisting of Sn, Ti, Mg, Mn, Fe, Co, Al, Si, Mo, Zr and W.
In another aspect of the present invention, a process for producing a copper alloy material for continuous casting mold, includes the steps of casting an ingot consisting of 0.05 wt % to 0.6 wt % of Cr, 0.01 wt % to 0.5 wt % of Ag, 0.005 wt % to 0.10 wt % of P, and a balance of Cu under an air atmosphere, cold working the obtained ingot at 10% to 80%, precipitating the cold worked product at 400° C. to 600° C. for 1 hour to 8 hours, and cold working the precipitated product at 10% to 80% after cooling the product down to a room temperature. In above production process, the ingot can further include less than 0.1 wt % of at least one of elements selected from a group consisting of Sn, Ti, Mg, Mn, Fe, Co, Al, Si, Mo, Zr and W.
The present invention has following advantageous effects.
A copper alloy material for continuous casting mold and the process for producing the same of the present invention can provide a copper alloy material for continuous casting mold which has high tensile strength and hardness, and excellent electric conductivity, and can be cast in the atmosphere.
The accompanying drawings, which are included to provide further understanding of the disclosure and are incorporated in and constitute a part of this application, illustrate embodiments of the disclosure and together with the description serve to explain the principle of the disclosure.
In the drawings:
Reference will now be made in detail to the specific embodiments of the present invention, and examples of which are illustrated in the accompanying drawings.
In general, since a continuous casting mold used in steel and non-steel industries is subjected to thermal shock and thermal strain as the mold is in contact with high temperature molten metal for a long time, the copper alloy material for continuous casting mold is required to have minimum thermal deformation and excellent resistance to stress, as well as a good heat dissipation performance through the mold.
The copper alloy material for continuous casting mold consists of 0.05 wt % to 0.6 wt % of Cr, 0.01 wt % to 0.5 wt % of Ag, 0.005 wt % to 0.10 wt % of P, and a balance of Cu.
The copper alloy material for continuous casting mold of the present invention includes 0.05 wt % to 0.6 wt % of Cr with reference to the total weight of the copper alloy material. The copper alloy material of the present invention has Cr phases finely scattered in a copper matrix, and thus, improves mechanical properties of the copper alloy material owing to the said Cr precipitates in the copper matrix, and heat resistance properties owing to the Cr precipitates in the matrix by suppressing the grain boundary migration of the copper alloy material upon heat treatment.
When the content of Cr in the copper alloy material is less than 0.05 wt %, the amount of the finely scattered Cr precipitates is too small, and thus it is difficult to secure adequate strength for use in the art. In addition, when the content of Cr in the copper alloy material is more than 0.6 wt %, Cr allows excessive introduction of oxygen into the molten metal and increasing viscosity of the molten metal, and consequently, it is difficult to obtain good quality ingot. Furthermore, serious problems such as surface cracks can be caused by thermal shock at a boundary with the molten metal during production due to the existence of Cr stripes on a surface of a large amount of Cr phases formed on the matrix.
The copper alloy material for continuous casting mold of the present invention includes 0.01 wt % to 0.5 wt % of Ag with reference to the total weight of the copper alloy material. Since Ag is melted during the casting and becomes solid solution throughout the Cu matrix uniformly so as to be distributed on the copper alloy material matrix uniformly, Ag has a solid solution enhancing effect without a falling-off in electric conductivity, to serve improving the mechanical properties, accordingly. When the content of Ag is less than 0.01 wt %, the improvement of strength and electric conductivity due to the addition of Ag is not satisfactory, and when the content of Ag is more than 0.5 wt %, economic efficiency of the addition of Ag becomes falling off significantly due to excessive cost caused by high cost of raw materials.
The copper alloy material for continuous casting mold of the present invention includes 0.005 wt % to 0.10 wt % of P with reference to the total weight of the copper alloy material. P is a principal element which improves de-acidification in the production of the copper alloy material, and improves strength and heat resistance, additionally. Especially, the element P influences electric conductivity which is required for the copper alloy material for continuous casting mold, significantly. If the content of P is less than 0.005 wt %, a residual oxygen quantity in the molten metal becomes excessive to affect castability and makes to fail to obtain a sound ingot. However, if the content of P is more than 0.1 wt %, problems take place, in which the electric conductivity, which is a principal property required for a mold material, drops sharply and accordingly the brittleness of the obtained copper alloy material increases.
In the copper alloy material of the present invention, Copper (Cu) is a principal component, of course. Copper is included as a balance amount in the aforementioned copper alloy material composition in order to make up 100 wt % in total.
Moreover, the copper alloy material for continuous casting mold can further include less than 0.1 wt % of at least one of elements selected from a group consisting of Sn, Ti, Mg, Mn, Fe, Co, Al, Si, Mo, Zr and W. In this case, a content of copper included to the copper alloy material for continuous casting mold as a balance is reduced as much as the element included thereto thus. If the element is added, the obtained copper alloy material provides an equivalent or similar effect with the copper alloy material without such element, and the element does not affect the strength (Hardness and/or tensile strength) and electric conductivity of the copper alloy material significantly.
The copper alloy material of the present invention can include a trace of impurities within a range which does not affect necessary properties of the copper alloy material. The impurities can be, for an example, As, S, Nb, and Sb, or a combination thereof. The impurities can be included as a trace less than 0.01 wt % of the total weight of the copper alloy material. The impurities can be one that can be added unintentionally during general production of the copper alloy material, and since the impurities are added in trace, the impurities do not affect the properties of the copper alloy material of the present invention, significantly.
The thermal properties and the conductivity of the copper alloy material of the present invention can be measured by hardness and electric conductivity after high temperature heat treatment. The hardness of the copper alloy material is dependent on an extent of processing after the heat treatment in the production. It is required that the copper alloy material of the present invention has over 120 HB, and, preferably in the range of 130 HB to 150 HB in Brinell hardness (2.5/62.5 kg), right after a precipitation regardless of an additional cold processing. Moreover, the electric conductivity of the copper alloy material is greater than 85% IACS, and, preferably in the range of 85% IACS to 95% IACS. That is, the copper alloy material of the present invention meets the conditions of hardness of higher than 90 HB and electric conductivity of higher than 80% IACS, which are reference values for a copper alloy material for continuous casting mold, adequately, and is excellent over the references.
The tensile strength of the copper alloy material for continuous casting mold of the present invention can be guessed from measurement of the hardness because the tensile strength is proportional to the hardness, or can also be measured directly according to KS B0802. The tensile strength of Cu—Ag—P based copper alloy material used in the related art was around at a level of 380 MPa, while that of the copper alloy material for continuous casting mold of the present invention is higher than 400 MPa, more specifically, in a range of 450 MPa to 550 MPa. This is because the copper alloy material of the present invention has transgranular and intergranular Cr precipitation phases formed by addition of Cr to serve as a factor for improving the hardness and the tensile strength of the matrix.
A Process for Producing a Copper Alloy Material for Continuous Casting Mold of the Present Invention
The copper alloy material for continuous casting mold of the present invention is produced by a process including the following steps of:
casting an ingot consisting of 0.05 wt % to 0.6 wt % of Cr, 0.01 wt % to 0.5 wt % of Ag, 0.005 wt % to 0.10 wt % of P, and a balance of Cu; homogenizing the obtained ingot at 700° C. to 950° C. for 30 minutes to 6 hours; hot working the obtained homogenized product at 10% to 90%; cold working the obtained hot worked product at 10% to 80%; precipitating the obtained product at 400° C. to 600° C. for 1 hour to 8 hours; and cold working the obtained product at 10% to 80% after cooling the product down to a room temperature.
In the meantime, the copper alloy material for continuous casting mold of the present invention can be produced by a process without the step of hot working the homogenized product, including the following steps of:
casting an ingot consisting of 0.05 wt % to 0.6 wt % of Cr, 0.01 wt % to 0.5 wt % of Ag, 0.005 wt % to 0.10 wt % of P, and a balance of Cu; cold working the obtained ingot at 10% to 80%; precipitating the obtained product at 400° C. to 600° C. for 1 hour to 8 hours; and cold working the obtained product at 10% to 80% after cooling the product down to a room temperature.
In order to produce the copper alloy material of the present invention, at first, all of materials are provided to satisfy the composition of the copper alloy material described above, are melted and cast the ingot. A trace of unavoidable impurities can be included in this step. Furthermore, in the process for producing the copper alloy material of the present invention, the ingot can further include less than 0.1 wt % of at least one of elements selected from a group consisting of Sn, Ti, Mg, Mn, Fe, Co, Al, Si, Mo, Zr and W. If the aforementioned elements are further included, the content of copper is reduced as much.
The obtained ingot is homogenized at 700° C. to 950° C. for 30 minutes to 6 hours. When the ingot is homogenized at a lower temperature than 700° C., the solution heat treatment of Cr in the matrix is not made properly due to failure of adequate heating, and accordingly, the obtained product fails to obtain an adequate precipitation during the precipitating, whereas when the ingot is homogenized at a higher temperature than 950° C., intensive surface oxidation takes place on the obtained product due to a high temperature. In addition, if the ingot is homogenized shorter than 30 minutes, hot workability becomes poor due to heavy working load caused by shortage of a homogenization time period. Further, if the ingot is homogenized longer than 6 hours, excessive surface oxidation is liable to take place. The temperature and the time period of the precipitation can be selected appropriately and combined within the above ranges. The step of homogenization the obtained ingot can be omitted, as necessary. If omitted, the following step of hot working the obtained homogenized product is also omitted.
Then, the obtained product is hot worked at the working rate of 10% to 90%. The step of hot working the obtained product can be omitted, as necessary.
The obtained product is cooled down to a room temperature (about 20° C. to 30° C.), and cold worked at the working rate of 10% to 80%. If the working rate is lower than 10%, the cold working effect is not adequately provided, and, if the working rate exceeds 80%, excessive cold working causes work hardening, and thus, makes further processing difficult.
Then, the obtained cold worked product is precipitated at 400° C. to 600° C. for 1 hour to 8 hours in an annealing furnace. If the precipitation is performed at a temperature lower than 400° C., the effect of the heat treatment can not be obtained adequately, and if the precipitation is performed at a temperature higher than 600° C., the electric conductivity increases but the strength becomes poor due to the over-aging phenomenon.
If the precipitation is performed for a time period shorter than 1 hour, the product can be anisotropic since precipitation of Cr granules as well as re-crystallization of a metallic microstructure from a prior processing is not adequate. Meanwhile, if the precipitation is performed for a time period longer than 8 hour, through increase of the electric conductivity can be expected by over aging, the microstructure becomes coarse to make a quality of the copper alloy material (the final product) poor, and the heat treatment for a long time period makes productivity poor.
Moreover, as described before, the copper alloy material for continuous casting mold of the present invention can be produced, omitting the step of homogenization the obtained ingot together with the step of hot working the obtained product, or the step of hot working the obtained product alone. In this case, the obtained product from the prior step can be cold worked at a working rate of 10% to 80%, and the steps thereafter including the step of first cold working, i.e., the first cold working step, the precipitation step and the second cold working step, can be progressed in the same way.
Depending on a purpose of a final product intended to produce, the step of homogenization the ingot and the successive cold working step can be performed, repeatedly.
Eventually, the process for producing a copper alloy material of the present invention permits not only to cast even under an air atmosphere, but also obtain a final product of a copper alloy material for continuous casting mold, having excellent tensile strength and electric conductivity.
In order to produce the copper alloy material for continuous casting mold of the present invention, after casting ingots each to have the following composition shown in table 1, each of the ingots are cold worked at 60%, and precipitated at 480° C. for 3 hours. Each obtained product is cold worked at 50% after cooling the product down to the room temperature, to obtain a final sample.
Test pieces having the composition shown in table 1 are cut from each of the products by the aforementioned production process. Then, their surface defects, tensile strength (TS), elongation (El), Vickers hardness (Hv), Brinell hardness (BH) and electric conductivity are tested, and the result of the above tests are shown in table 2. The tensile strength and the elongation are measured according to KS B0802, and the electric conductivity, which is related to both of thermal and electric conductivity, is measured according to KS D0240. The Vickers hardness is measured according to KS B0811 and the Brinell hardness is measured according to KS B0805.
In general, the specifications required for a copper alloy material for continuous casting mold used in steel industries are over 80% IACS electric conductivity and over 90 HB. The copper alloy material of the present invention has the Brinell hardness (2.5/62.5 kg) of over 120 HB, and more particularly in the range of 130 HB to 150 HB, measured after processing the copper alloy material at 10% to 80% right after final heat treatment, and the electric conductivity of over 85% IACS, and more specifically, in the range of 85% IACS to 95% IACS. As results of the above experiments, the test pieces of Examples 1 to 8 show similar electric conductivity to that of CuAgP material in comparative example 6, which is commercially available, while the test pieces show the tensile strength and the hardness better than the comparative example 6, and thus, these test pieces of Examples 1 to 8 meet all of specifications required for the copper alloy material for continuous casting mold.
In the meantime, if the photographs of Cr phases finely scattered in the microstructure of the copper alloy material of the present invention are taken with an optical microscope (OP) and a scanning electron microscope (SEM), the finely scattered Cr phases precipitated in a surface of the copper alloy material of the present invention can be noticed. Since Cr phases are scattered transgranularly and intergranularly in the copper matrix, the mechanical properties of the product are increased. Further, since Cr phrases serve to suppress intergranular migration during heat treatment, heat resistance of the copper alloy material of the present invention is increased as well.
The present invention provides a copper alloy material for continuous casting mold which permits casting even in the atmosphere, and has high electric conductivity and excellent hardness; and a process for producing the same.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2011-0080180 | Aug 2011 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR11/07254 | 9/30/2011 | WO | 00 | 2/10/2014 |
