JPH01108351A - Manufacture of mold for continuous casting - Google Patents

Abstract

PURPOSE:To manufacture a mold excellent in wear resistance and heat resistance by subjecting a Cu-alloy ingot having a specific composition containing Fe and P to piercing working, cold drawing, and annealing under respectively specified conditions and then applying cold drawing, and annealing to the above. CONSTITUTION:An ingot of Cu alloy consisting of, by weight, 0.05-0.15% Fe, 0.02-0.05% P, and the balance Cu with inevitable impurities is heated to >=700 deg.C to undergo hot piercing working. The resulting tube stock is subjected to cold drawing at 35-45% reduction in area, and the resulting worked part is passed through a primary heat-treatment stage consisting of annealing at 650-700 deg.C for 30min-1hr to undergo uniform recrystallization of cold structure. Successively, the tube stock is passed through a secondary heat-treatment stage consisting of annealing at 500-600 deg.C for 2-4hr, by which iron phosphide is precipitated. Subsequently, the tube stock is subjected to cold drawing and drawing working into a mold shape at 30-45% total reduction in area. Then, annealing is applied to the above at 250-400 deg.C for 30min-4hr to remove the local stress of the product. By this method, the long-life mold for continuous casting excellent in wear resistance and thermal deformation resistance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a continuous casting mold suitable for manufacturing a 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. 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, the temperature of the inner wall of the mold rose to a high temperature of about 250°C during continuous steel casting. In some cases, the mold becomes soft or cannot 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 includes:
- The purpose 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 contains 06o5 to 0.15% by weight of Fe and 0.02 to 0.05% by weight of P, and the remainder A step of heating a copper alloy ingot, which contains Cu and inevitable impurities, to a temperature of 700°C or higher and performing piercing processing, and cold drawing the obtained raw pipe with an area reduction rate of 35 to 45%. process and 650 to 700℃
A first heat treatment step of annealing at a temperature of 30 minutes to 1 hour, a second heat treatment step of annealing at a temperature of 500 to 600 degrees Celsius for 2 to 4 hours, and cold drawing with a total area reduction of 30 to 45%. and a step of performing drawing processing into the mold shape, and 250
[Function] In the present invention, a copper alloy ingot containing Fe and P in a predetermined composition, First, hot piercing is performed by heating to a temperature of 700° C. or higher. Next, the obtained raw pipe is subjected to cold drawing processing at an area reduction rate of 35 to 45%, and then the first pipe is continuously drawn.
and a second two-stage heat treatment. In the first heat treatment step, the piercing texture is recrystallized by annealing at a temperature of 650 to 700° C. for 30 minutes to 1 hour. On the other hand, in the second heat treatment step, iron phosphide (Fe2P) 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 surface reduction rate of 30 to 45%, a third heat treatment is performed. In this third heat treatment step, 250
By annealing at a temperature of 30 minutes to 4 hours at a temperature of 400° C. to 400° C., local stress caused by cold drawing is removed.

The heat-resistant copper alloy mold thus manufactured has mechanical properties that are significantly superior to conventional phosphorus-deoxidized copper molds at room temperature and at high temperatures of about 300°C.

[Example] Examples of the present invention will be specifically described below.

The continuous casting mold to be manufactured by the method of the present invention has a 0.0.
0.05 to 0.15 wt% Fe and 0.02 to 0.605
It contains 1% P by weight, and the remainder is Cu and inevitable impurities, which are heat-resistant copper alloys.

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 strength at room temperature and high temperature when each is used alone, but when Fe and P coexist and iron phosphide of Fe2P is formed, , the effect 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. Along with this decrease, cracks occur during extrusion in the hot piercing process described below. Therefore, the Fe content is set to 0.05 to 0.15% by weight.

If the P content is less than 2% by weight, it is 0.05 to 0.
．． Since the amount of Fe2P formed by combining with Fe of 15 weight and 1% is small, the above-mentioned effect on mechanical strength is small. On the other hand, when P is contained in an amount exceeding 0.05% by weight, a eutectic of Cu+Cu3P (melting point 714°C) occurs at the grain boundaries of the ingot itself, and during hot piercing at temperatures of 700 to 900°C, Along with cracks occurring at grain boundaries, 70
At temperatures lower than 0° C., deformation resistance increases and processing becomes impossible. Therefore, the P content is between 0.02 and 0.
105% by weight.

Next, processing conditions and heat treatment conditions for the copper alloy material having the above-mentioned composition will be described in detail.

The copper alloy with this composition is a precipitation-strengthened Cu-Fe-P type, and basically consists of cold drawing at a low working rate after hot working, and annealing for aging and local stress relief. 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, a mold with excellent heat resistance and wear resistance can be manufactured at low cost using conventional equipment as is. However, when the inventors repeated manufacturing experiments, -ff
i If annealing was performed at a temperature of 500°C for 2 hours as with the copper alloy material, the subsequent cold working rate of the piercing material would be low, so the copper alloy with the above composition would not recrystallize and an abnormal structure would occur. It was found that the grain boundaries became weaker. If the grain boundaries are weak like this, 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, we found the optimal processing and heat treatment conditions as shown below. By manufacturing a mold using a copper alloy with the above-mentioned composition under these conditions, we can apply the hot piercing method, similar to the manufacturing of phosphorus-deoxidized copper molds, to achieve continuous casting with excellent heat resistance and wear resistance. The processing steps and heat treatment steps for this copper alloy material will be described below, allowing easy manufacture of the tube wall mold.

First, an ingot of a copper alloy having the above-mentioned composition is heated to a temperature of 700° C. or higher, and hot worked by 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 step, this raw tube is annealed at a temperature of 650 to 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 will occur in 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 650 to 700°C.

The annealing time is required to be 30 minutes or more in order to obtain the effect of the heat treatment. On the other hand, from the viewpoint of energy saving, it is wasteful to carry out heat treatment for a long time, so the annealing time is set to within one hour.

In the second heat treatment process, the raw tube is heated to 500 to 600
Anneal at a temperature of 2 to 4 hours. This is iron phosphide (F
This is to precipitate e2P), and the precipitation of iron phosphide improves the electrical conductivity and improves the 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.
When the heat treatment temperature exceeds 600° C., although precipitation occurs, the amount of precipitation is small and the effect of improving electrical conductivity is small. Therefore, the annealing temperature in the second heat treatment step is 500 to 600.
℃.

When annealing time is less than 2 hours, 500 to 600
Even if annealing is performed at a temperature of .degree. C., precipitation is insufficient, and conversely, if the annealing time exceeds 4 hours, it is uneconomical from the viewpoint of energy saving. Therefore, the annealing time of 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 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 set at 250 to 400°C. on the other hand,
When the annealing time is less than 30 minutes, the above-mentioned effect is small, and annealing for more than 4 hours is wasteful from the viewpoint of energy saving. Therefore, the annealing time is 30 minutes to 4 hours.

Next, the results of actually manufacturing a pipe wall mold for continuous casting of steel using the method of the present invention will be explained.

Alloys N081 to 3 with the composition shown in Table 1 below have a capacity of 6
The ingot was charged into a 1-ton coreless furnace, 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. Note that alloy N113 is phosphorus-deoxidized copper and falls outside the composition range defined in the present invention.

Table 1 This ingot was cut to a length of 740 mm, and
After heating to 0°C, hot working is carried out by the piercing method to obtain a raw tube with an outer diameter of 204 mm and an inner diameter of 165 mm.9 Next, after rapidly cooling this raw tube in water from a temperature of 650 to 680 °C, From this raw pipe, the thickness is 19 mm and the width is 150 m.
A test piece with a length of 200+*m was cut out. The manufacturing method was carried out in accordance with the manufacturing process for tube wall molds as described below.

The raw pipe after piercing is cold rolled at a processing rate of 40%, and then annealed at a temperature of 650 to 750°C for 30 minutes to perform the first heat treatment (first intermediate heat treatment), as shown in Table 2 below. ) was carried out. Next, the second heat treatment (second intermediate heat treatment) is performed by annealing at a temperature of 500 to 575°C for 4 hours.
was carried out. Furthermore, oxidized scale is removed with sulfuric acid,
After cold rolling at a processing rate of 35%, 2
Local stress was removed by time annealing. However, for the phosphorus-deoxidized copper of Comparative Example 3, the intermediate annealing conditions were 3 at a temperature of 400°C.
0 minutes, and the annealing conditions for final local stress relief are 20 minutes.
2 hours at 0°C.

Note that, as in Comparative Example 1, in the first heat treatment, 500
For those annealed at ℃, cracks occurred after piercing. Therefore, the subsequent steps were not carried out.

Using these samples, the properties at room temperature and mechanical properties at a high temperature of 300°C were tested, and the results are also shown in Table 2 above.

The test method is as follows.

(1) Tensile strength and yield strength are measured by cutting 5 parallel to the rolling direction.
The test was performed using a JIS No. 13 B test piece of Sekiatsu.

Heating the specimen to a temperature of 300°C using an infrared oven;
After holding for 15 minutes, a tensile test was performed.

(2. Hardness was measured using a Vickers hardness meter at a load of 5 kg.

(3) Electrical conductivity was measured using a commercially available electric conductivity meter.

Measured values by this conductivity measuring device and J I 5HO505
Correction with the measured value by the 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 approximately between that of a phosphorus-deoxidized copper mold, but its mechanical properties at room temperature and a high temperature of about 300° C. are significantly superior to that of phosphorus-deoxidized copper. In particular, the mold obtained according to the present invention has a yield strength as high as 2.5 times 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 for mold replacement and maintenance inspection during continuous casting can be shortened.

Claims (1)

[Claims] 0.05 to 0.15 wt% Fe and 0.02 to 0
．． A process of heating a copper alloy ingot containing 0.5% by weight of P and the remainder being Cu and unavoidable impurities to a temperature of 700°C or higher and performing piercing processing, and piercing the resulting raw pipe by 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 second heat treatment step of annealing at a temperature of 500 to 600°C for 2 to 4 hours. A heat treatment step, a step of performing cold drawing and drawing processing into a mold shape with a total area reduction rate of 30 to 45%, and a third heat treatment step of annealing at a temperature of 250 to 400 ° C. for 30 minutes to 4 hours. A method for manufacturing a continuous casting mold, comprising: