JPH0314900B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a continuous casting mold suitable for manufacturing a tube mold for continuous casting of steel. [Prior Art] Conventionally, phosphorus-deoxidized copper has been used as a mold material for continuous casting of steel, which has the characteristics of good thermal conductivity, easy production, and low cost. By the way, in recent years, due to the demand for improved casting functions, technological improvements such as faster casting speeds and shorter casting cycles have been implemented in operations, but as a result, molds are exposed to even more severe conditions. It became. [Problems to be solved by the invention] However, since conventional phosphorus-deoxidized copper has a low high temperature yield strength and a low softening temperature, during continuous casting of steel,
When the temperature of the inner wall of the mold rises to a high temperature of about 250° C., the mold becomes soft or becomes unable to withstand the thermal stress generated between the inner and outer walls, resulting in deformation and wear. This shortens the life of the mold. Therefore, there is a need for the development of a continuous casting mold made of steel that has excellent wear resistance and heat deformation resistance. The present invention has been made in view of such problems, and an object of the present invention is to provide a method for manufacturing a continuous casting mold that can manufacture a mold with excellent wear resistance and heat resistance. [Means for solving the problems] The method for manufacturing a continuous casting mold according to the present invention includes:
0.05-0.15 wt% Fe and 0.02-0.05 wt%
A step of piercing a copper alloy ingot containing P with the remainder being Cu and unavoidable impurities to a temperature of 700°C or higher, and the process of piercing the resulting raw pipe at 35°C.
A process of cold drawing with an area reduction rate of 45%,
A first heat treatment step of annealing at a temperature of 650 to 700°C for 30 minutes to 1 hour, a second heat treatment step of annealing at a temperature of 500 to 600°C for 2 to 4 hours, and 30 to 45%
The method is characterized by comprising a step of performing cold drawing and drawing processing into a mold shape with a total area reduction rate of , and a third heat treatment step of annealing at a temperature of 250 to 400° C. for 30 minutes to 4 hours. [Function] In the present invention, a copper alloy ingot containing Fe and P in a predetermined composition is first heated to a temperature of 700° C. or higher and hot-pierced. Next, the obtained raw tube is subjected to cold drawing processing at an area reduction rate of 35 to 45%, and then successively subjected to two-stage heat treatment, first and second. In the first heat treatment step, the
The piercing structure is recrystallized by annealing at a temperature of 700° C. for 30 minutes to 1 hour. on the other hand,
In the second heat treatment step, iron phosphide (Fe ₂ P) is precipitated by annealing at a temperature of 500 to 600° C. for 2 to 4 hours to improve conductivity and strength. Then, after performing cold drawing and drawing into a mold shape with a total area reduction rate of 30 to 45%, a third heat treatment is performed. In this third heat treatment step, local stress caused by cold drawing is removed by annealing at a temperature of 250 to 400° C. for 30 minutes to 4 hours. The heat-resistant copper alloy mold produced in this way has significantly superior mechanical properties at room temperature and at high temperatures of about 300° C. than conventional phosphorus-deoxidized copper molds. [Examples] Examples of the present invention will be specifically described below. The continuous casting mold to be produced by the method of the present invention is composed of a heat-resistant copper alloy containing 0.05 to 0.15% by weight of Fe and 0.02 to 0.05% by weight of P, with the balance being Cu and inevitable impurities. ing. First, the reason for the inclusion of components and the reason for limiting the composition of this heat-resistant copper alloy will be explained. The contained components Fe and P have little effect on improving wear resistance and heat resistance and improving strength at room temperature and high temperature when used alone, but when Fe and P coexist,
By forming iron phosphide of Fe ₂ P, the effects of improving wear resistance, heat resistance, and strength can be obtained. When the Fe content is less than 0.05% by weight, the above effects are small. Furthermore, if Fe is contained in an amount exceeding 0.15% by weight, even if P is contained in a range of 0.02 to 0.05% by weight, Fe is dissolved in the copper alloy base material, resulting in a decrease in electrical conductivity and the following effects. Cracks occur during extrusion in the hot piercing process. Therefore, Fe
The content is 0.05 to 0.15% by weight. If the P content is less than 0.02% by weight, 0.05 to
Since the amount of Fe ₂ P formed by combining with 0.15% by weight of Fe is small, the above-mentioned effect of improving mechanical strength is small. On the other hand, if P is contained in excess of 0.05% by weight, a eutectic of Cu + Cu ₃ P (melting point 714°C) will occur at the grain boundaries of the ingot itself, and during hot piercing at temperatures of 700 to 900°C, the grains will At temperatures lower than 700°C, cracks occur at the interface, and deformation resistance increases, making processing impossible. Therefore, the P content is set to 0.02 to 0.05% by weight. Next, processing conditions and heat treatment conditions for the copper alloy material having the above-mentioned composition will be described in detail. Copper alloys with this composition are precipitation-strengthened Cu-Fe-P systems, and basically undergo cold drawing at a low working rate after hot working, and annealing to remove aging and local stress. It is manufactured through the process of In other words, if it can be manufactured using the same hot working method as phosphorus-deoxidized copper, it is possible to manufacture molds with excellent heat resistance and wear resistance at low cost by using conventional equipment as is. However, as a result of repeated manufacturing experiments by the inventors of the present application, it was found that if the intermediate heat treatment was annealed at a temperature of 500°C for 2 hours like general copper alloy materials, the subsequent cold working rate of the piercing material would be low. It was found that due to the low crystallinity, the copper alloy with the above-mentioned composition does not recrystallize and an abnormal structure occurs, weakening the grain boundaries. If the grain boundaries are weak in this way, cracks will occur in the circumferential direction during the subsequent cold drawing process, making it difficult to commercialize the product. Therefore, in order to prevent the occurrence of cracks in the cold drawing process after hot piercing, which is a problem in the production of Cu-Fe-P alloys, the inventors of the present application have conducted various experimental studies on the production conditions. As a result,
The optimal processing and heat treatment conditions were found as shown below. By manufacturing a mold using a copper alloy with the above-mentioned composition under these conditions, we can create a continuous mold with excellent heat resistance and wear resistance by applying the hot piercing method similar to the manufacturing of phosphorus-deoxidized copper molds. A tube mold for casting can be easily manufactured. The processing steps and heat treatment steps for this copper alloy material will be explained below. First, 700 ingots of copper alloy having the above composition were heated.
It is heated to a temperature of ℃ or higher and hot-processed using a piercing method to obtain a raw pipe. After cold drawing this raw tube at a low processing rate with an area reduction rate of 35 to 45%, two successive stages of heat treatment are performed. In the first heat treatment process, this raw tube is
Anneal at a temperature of 700°C for 30 minutes to 1 hour. This is to uniformly recrystallize the low working rate cold structure of the piercing material and to prevent cracks from occurring in the next cold drawing process. If the annealing temperature is less than 650°C, the copper alloy will not recrystallize, resulting in low elongation and no improvement in workability. As a result, cracks occur during the next cold drawing process. When the annealing temperature exceeds 700°C, secondary recrystallization occurs and crystal grains become larger, weakening grain boundaries and lowering hardness and strength. Therefore, the annealing temperature in the first heat treatment step is
The temperature should be 650 to 700℃. The annealing time is determined in order to obtain the above heat treatment effect.
30 minutes or more is required. On the other hand, from the point of view of energy saving, long-term heat treatment is wasteful, so
The annealing time should be within 1 hour. In the second heat treatment process, the raw tube is
Anneal at a temperature of 600°C for 2 to 4 hours. this is,
This is to precipitate iron phosphide (Fe ₂ P), and the precipitation of iron phosphide improves electrical conductivity and improves strength, albeit slightly. However, if the annealing time is less than 500°C, a sufficient precipitation effect cannot be obtained even if annealing is performed for 2 to 4 hours. Furthermore, when the heat treatment temperature exceeds 600°C, although precipitation occurs, the amount of precipitation is small, so that the effect of improving conductivity is small. Therefore, the annealing temperature in the second heat treatment step is 500 to 600°C. If the annealing time is less than 2 hours, the
Even if annealed at a temperature of 600℃, precipitation is insufficient.
On the other hand, if the annealing time exceeds 4 hours, it is uneconomical from the viewpoint of energy saving. Therefore, the annealing time in the second heat treatment step is 2 to 4 hours. Next, after this heat-treated raw pipe is cold drawn, it is further drawn into a square mold shape.
The total processing rate (total area reduction rate) in this process is 30 to
It is 45%. Thereafter, it is annealed at a temperature of 250 to 400°C for 30 minutes to 4 hours. This is to remove local stress caused by cold drawing. If the annealing temperature in this third heat treatment step is less than 250°C, the effect of local stress relief will be small, and if annealed at a temperature exceeding 400°C, the hardness of the copper alloy will decrease. Therefore, the annealing temperature is 250 to 400°C. On the other hand, if the annealing time is less than 30 minutes, the above-mentioned effects will be small.
Further, annealing for more than 4 hours is wasteful from the viewpoint of energy saving. Therefore, the annealing time is 30 minutes to 4
Time. Next, the results of actually manufacturing a pipe mold for continuous casting of steel using the method of the present invention will be explained. Alloys No. 1 to 3 having the compositions shown in Table 1 below were charged into a coreless furnace with a capacity of 6 tons, coated with charcoal and melted in the atmosphere to form an ingot with an outer diameter of 205 mm and a length of 1000 mm. Agglomerated. Alloy No. 3 is phosphorus-deoxidized copper and falls outside the composition range defined in the present invention.

[Table] This ingot was cut to a length of 740mm,
After heating to 850°C, hot working was performed using the piercing method to obtain a raw tube with an outer diameter of 204 mm and an inner diameter of 165 mm.
Next, after rapidly cooling this raw pipe in water from a temperature of 650 to 680°C, the raw pipe is made into a material with a thickness of 19 mm and a width of 19 mm.
A test piece with a length of 150 mm and a length of 200 mm was cut out. The manufacturing method was carried out according to the manufacturing process of a tubular mold as described below. After cold-rolling the raw pipe after piercing at a processing rate of 40%, as shown in Table 2 below,
The first heat treatment (1
The second intermediate heat treatment) was carried out. Next, a second heat treatment (second intermediate heat treatment) was performed by annealing at a temperature of 500 to 575° C. for 4 hours. Further, oxidized scale was removed using sulfuric acid, cold rolling was performed at a processing rate of 35%, and local stress was removed by annealing at a temperature of 350° C. for 2 hours. However, for the phosphorus-deoxidized copper of Comparative Example 3, the intermediate annealing conditions were 400°C for 30 minutes, and the final annealing conditions for local stress relief were 200°C.
℃ temperature for 2 hours. In addition, as in Comparative Example 1, cracks occurred after piercing in the case where the sample was annealed at 500° C. in the first heat treatment. Therefore, the subsequent steps were not performed. Using these samples, the characteristics at room temperature and 300
The results of testing the mechanical properties at high temperatures of 0.degree. C. are also shown in Table 2 above.

[Table] The test method is as follows. (1) Tensile strength and yield strength were tested using 5 mm thick JIS No. 13 B test pieces cut parallel to the rolling direction.
The specimens were heated to a temperature of 300°C using an infrared oven and held for 15 minutes before being subjected to a tensile test. (2) Hardness was measured using a Bitkers hardness tester under a load of 5 kg. (3) Electrical conductivity was measured using a commercially available electrical conductivity meter. The measured value by this conductivity measuring device and
Correction of the measured values using the JISH0505 double bridge method was performed using a separately prepared strip of the same type with a thickness of 2 mm. As is clear from Table 2, in the example molds manufactured by the method of the present invention, cold drawing cracks after piercing were prevented, and compared to the molds of Comparative Examples 2 and 3, Excellent room temperature and high temperature properties. [Effects of the Invention] As explained above, according to the present invention, a copper alloy mold having a predetermined composition is manufactured by a process including piercing similar to the manufacturing process of a conventional phosphorus-deoxidized copper mold. The mold can be manufactured using the same equipment used in the conventional method. The obtained mold has an electrical conductivity that is almost the same as that of a phosphorus-deoxidized copper mold, but its mechanical properties at room temperature and at a high temperature of about 300° C. are significantly superior to that of phosphorus-deoxidized copper. In particular, the mold obtained by the present invention has a yield strength 2.5 times higher than that of phosphorus-deoxidized copper, so it is difficult to deform even when subjected to large thermal stress during high-speed continuous casting of steel.
Therefore, according to the present invention, the life of the mold can be extended, and the time required for mold replacement and maintenance inspection during continuous casting can be shortened.

Claims (1)

[Claims] 1 A step of piercing a copper alloy ingot containing 0.05 to 0.15% by weight of Fe and 0.02 to 0.05% by weight, the balance being Cu and unavoidable impurities, by heating it to a temperature of 700°C or higher. , a step of cold drawing the obtained raw tube with an area reduction rate of 35 to 45%, a first heat treatment step of annealing at a temperature of 650 to 700°C for 30 minutes to 1 hour, and a first heat treatment step of annealing at a temperature of 650 to 700°C for 30 minutes to 1 hour. 2 at temperature
a second heat treatment step of annealing for 30 to 4 hours;
A process of cold drawing and drawing into mold shape with a total area reduction of 45%, and a process of cold drawing and drawing into a mold shape at a temperature of 250 to 400°C.
A method for manufacturing a continuous casting mold, comprising: a third heat treatment step of annealing for 4 hours to 4 hours.