JPS5997714A - High temperature hot hydrostatic extruding method of brass pipe - Google Patents

Abstract

PURPOSE:To produce a brass pipe from which a final product having a good surface characteristic is obtainable with less drawing stage after extruding by extruding a billet heated no an adequate temp. through a die by high temp. hydrostatic extrusion then cooling quickly the extruded billet down to a specific temp. or below. CONSTITUTION:A billet 3 heated to 500-800 deg.C is charged in a container 1 and is successively extruded through a die 2 by hydrostatic pressure via a pressure medium 5 from a stem 4. The resulting extrudate 8 is cooled in a water cooling area 7 provided behind a guide tube 6, at a cooling rate of >=350 deg.C/sec and under the condition under which the temp. after passage through the area 7 attains <=500 deg.C. The extrudate 8 of a blank brass pipe having about <=0.05mm. crystal grain size is thus obtd. Such extruded pipe 8 is made into a final product having a good surface characteristic by less stretch reducing stages of about one or two.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-temperature isostatic extrusion method for brass tubes, and more particularly to a method that allows a final product with good surface quality to be obtained with a small number of drawing steps after extrusion.

In recent years, a method of hot extruding a billet and then pulling out the extruded material has been established as a means of producing brass tubes. In this case, the mechanical properties and surface properties of the final product are
It is adjusted by cold working and annealing after hot extrusion,
In particular, the surface texture depends on the crystal grain size at each processing step.

For example, when aluminum brass is hot extruded using the conventional method at a billet heating temperature of 900°C and an extrusion ratio of 2o, the crystal grain size of the extruded material is 0.08 to 0.15, which is calculated as the area reduction rate. When drawing is carried out once at 40 to 50%, many irregularities are generated on the surface. Further, if the material is annealed at 800° C. after drawing twice, the crystal grain size will be 0.085 to 0.05 try.

Then, if we further extract this with a wavefront ratio of about 40%, we get
A good product with a bright surface can be obtained. As described above, it is known that the crystal grain size of the hot extruded material and the subsequent processing history have a very large effect on the surface quality of the final product.

When extruding copper alloy tubes using high-temperature isostatic extrusion, one feature is that it can be extruded efficiently at a higher extrusion ratio than conventional methods. It is required to finish the final product with a small number of drawing baths of 1 to 2 elongations after biting or extrusion.

[In general, as mentioned above, if the extruded material has coarse crystal grains, the number of drawing passes of 1 or 2 will significantly increase the unevenness of the surface, making it virtually impossible to finish the final product. I can't.

In view of the above-mentioned technical problems, the present invention was made with the purpose of establishing extrusion conditions that ensure that a final product with good surface properties can be obtained in a drawing process with a small number of 1 or 2 elongations after high-temperature isostatic pressure extrusion of a brass tube. The feature is that after extruding a billet heated to 500°C to 800°C through a die by high-temperature isostatic extrusion, the extruded material is cooled in a cooling zone provided at the outlet of the die. The cooling rate is 850℃/kil or higher and the temperature after passing through the cooling zone is 50℃.
The point is to cool it down to below 0°C.

As a result of conducting high-temperature isostatic extrusion on brass tubes under various conditions, the inventor found that the crystal grain size of the extruded material was 0.05 as the necessary extrusion conditions to achieve the above objective.
mm or less, and in order to satisfy this requirement in the case of Aluminum Plus, the extruded material must be cooled at the exit of the die and the temperature should be below 500°C after passing through the cooling zone, as shown in Figure 6. Furthermore, in order to prevent defects from occurring on the surface of the extruded material, a heating temperature of 880°C or less is required, and the preferred method is 80°C.
It was found that the temperature was below 0°C.

These extrusion conditions will be explained in detail below.

Therefore, a sixth example of a device for carrying out the present invention will now be described.
Let me briefly explain the diagram. Figure 86 shows an outline of the equipment near the extrusion side of a high-temperature isostatic extrusion press. is the stem (4
), through the pressure medium (5), and then extruded from the die (2). On the other hand, on the back side of the die, a guide tube (6) is extended, and a water-cooled cooling area (7) of an appropriate length is provided connected to the outlet of the guide tube, and the extruded material from the die (2) is connected to the outlet of the guide tube (6). (8) is sequentially shown in this cooling area (7)
It is configured to pass through.

First, we will examine and discuss the crystal grain size required for extruded tubes (extruded materials) from the relationship between cold working rate and surface roughness. FIG. 1 shows the results of drawing 1 to 4 passes of extruded aluminum plastic pipes having various crystal grain sizes in a diameter range of 25 to 72 mm, and determining the surface conditions in each case. This result shows that the crystal grain size is 0.07~0.10a.
! When using an extruded raw tube in the range of I understand that.

Figure 2 shows the surface and internal structure after drawing of extruded tubes with eight different crystal grain sizes. For those with a diameter of 0.04 yyt, the surface texture after drawing is good, and as is clear from the surface photograph, there are slight depressions. On the other hand, 0.07~
When an extruded raw tube having a crystal grain size of 0.09 m+ is pulled out, the surface texture has large irregularities and the gloss is not good.

In order to finish a product with a good surface condition from an extruded raw tube in one or two passes, it is necessary that the crystal grain size in the state after extrusion is 0.05 to 0.06 gm or less. It can be seen that when the number of drawing passes is large and the processing rate is high, the grain size may become coarser depending on the size of the processing rate.

Next, the cooling conditions for obtaining the crystal grain size in the specific range as described above will be discussed. FIG. 8 shows the results of measuring the surface temperature of the extruded material during hydrostatic extrusion after passing through the cooling zone.

In the same section, condition (2) is when extrusion is performed without circulating cooling water in the cooling zone, and the surface temperature of the extruded material is 9.
Although the temperature reaches about 50°C, the temperature decreases with time. In this case, the crystal grain size of the extruded material is 70 to 100.
μ. On the other hand, condition (2) has a cooling zone length of 0.8 ffJ and a surface temperature of 610℃ after passing through the cooling zone.Condition (2) has a cooling zone length of 1.4m and a surface temperature of 470℃ after passing through the cooling zone. (2) is the case where the cooling zone length is 2.0 m and the surface temperature after passing through the cooling zone is 880°C, and in these cases, the crystal grain size obtained in the extruded material is (55-60μ, ■40μ).
~50μ, ■40~50μ. From this result, if the crystal grain size required for the extruded material to improve the surface quality after drawing is 50μ or less as mentioned above, then
It can be seen that the cooling conditions (2) and (2) are compatible with this.

Table 1 shows the results of investigating the presence or absence of grain growth when aluminum brass with a crystal grain size of 80μ is heated at various temperature and time combinations.
It is clear that there is no effect even at 800(8) at 500° C. within 0.011 ec. That is, when air-cooling an extruded material in a tabletop, it is necessary to cool the extruded material so that the temperature of the extruded material passing through the cooling zone is 500° C. or less.

Table 1 Effect of temperature and time on grain growth ○ No effect ×
As mentioned above, in order to obtain an affected extruded material with a grain size of 50μ or less, the temperature after passing through the cooling zone must be 500℃ or less, but another cooling condition is cooling. It is known that the magnitude of the cooling rate in the region poses a problem. In this case, it goes without saying that the faster the cooling rate, the better. Therefore, as shown in Table 2,
The extrusion ratio was set to 45.70, and the relationship between the average cooling rate and crystal grain size was investigated.

Table 2 Relationship between cooling rate and crystal grain size *l From the extrusion pressure, the temperature of the extruded material was estimated to be 905°C in the same manner as the billet temperature *2.

From this result, if the cooling rate is 860℃/min or higher,
It can be seen that in either case, the crystal grain size is controlled within the range of 40 to 50 microns. In other words, as cooling conditions to obtain the desired crystal grain size of 50μ or less,
It is necessary that the cooling rate in the cooling zone is 850° C./11 ec or higher. Even if the cooling rate is fast, if the product hot water temperature (temperature through which the extruded material passes through the cooling zone) exceeds 500°C (615°C), the crystal grain size will be 55-6.
It can be seen that the grain size becomes 0 μ and the grain becomes coarse on the run-out table.

As mentioned above, in order to obtain an extruded material with the desired crystal grain size of 50μ or less, it is important to appropriately control the cooling conditions after extrusion.
Another important factor is the need to control the heating temperature of the extruded billet. This is because the heating temperature of the billet primarily controls the crystal grain size after extrusion.

FIG. 4 shows an investigation of the relationship between the billet heating temperature and the crystal grain size of the extruded phase when the billet is passed through a cooling zone of 1.4 m. From the same figure, when the billet temperature is 800℃ or less, particles with a particle size of 50μ or less can be obtained, but when the heating temperature exceeds 800℃, particles with a size larger than 50μ may be mixed. I understand. In other words, in order to obtain the extruded material having the desired crystal grain size of 50μ or less, the billet heating temperature should be 800°C.
It is necessary to do the following: Furthermore, even in the case of a heating temperature of 800°C or higher, it is thought that if cooling is performed using a large amount of cooling water under the conditions shown in Figure 4, crystal grains with a grain size of 50 μ or less can be obtained. .

By the way, another condition that must be considered when determining the billet heating temperature is the appearance of surface defects in the extruded material. FIG. 5 shows the results of investigating the relationship between billet heating temperature and the presence or absence of surface defects, and it is observed that the number of cracking defects rapidly increases around 830° C., and the surface quality of the extruded material deteriorates. Such a material may cause surface defects in the drawn material.

Therefore, from the viewpoint of preventing surface defects, it is necessary to keep the billet heating temperature below 880°C, which is naturally satisfied when the heating humidity conditions for controlling the crystal grain size are satisfied. Become.

As described above, the crystal grain size of the extruded material varies depending on the extrusion processing conditions such as extrusion ratio, billet temperature, and cooling conditions. It is practical to control the crystal grain size to an optimum value by adjusting the amount of water, etc.

Note that the lower limit of the billet heating temperature is limited to 500° C. for the following reasons. This is because if the billet heating temperature is too low, the extrusion ratio will not be large and there will be no industrial value. In the case of brass, its deformation resistance rapidly decreases around 500° C., making it possible to extrude at a high extrusion ratio. For example, in the case of brass containing A/2%, the extrusion ratio is about 12-18 (
The pressure is 10000kg/c++, but the temperature is 500℃
The extrusion ratio is approximately 20 (pressure 10,000 kg/d) at a heating temperature of
), the extrusion ratio can be increased to about 40 at a heating temperature of 600°C, and further to about 100 at a heating temperature of 700°C. On the other hand, when carrying out this type of extrusion method, it goes without saying that a larger extrusion ratio is desirable, but the extrusion ratio commonly used in the past is 15
~20. Therefore, in order to satisfy this value, the billet heating temperature must be at least 500°C or higher.

Note that the billet heating temperature is low and the temperature of the extruded material is 50%.
Although it is conceivable to control the temperature to 0° C. or lower, it is not appropriate in view of the above extrusion ratio and the phenomenon of temperature increase during extrusion processing. That is, this is because the heat generated during processing is added to the billet temperature for the extruded material. The calorific value depends on the pressure, but if you keep it, the pressure will increase to 10,000.
kg/m, the exothermic content reaches 180 to 200°C, and even if the billet temperature is 500°C, the product temperature after extrusion will be raised to 680 to 700°C.

The present invention is as explained above, and in high-temperature isostatic extrusion of brass tubes, the billet heating temperature is set at 500°C.
to 800'C, and at a cooling rate of 850°C/850'C in the cooling zone provided on the exit side of the die after extrusion.
Since the extruded material is cooled under conditions such that the temperature is above 500° C. and the temperature after passing through the cooling zone is 500° C. or less, the extruded material has a crystal grain size of 50 μm or less. Therefore, if this extruded raw tube is used for the next drawing process, a final product with good surface quality can be obtained with a small number of drawing passes, about 1 to 2 draws, which has the effect of contributing to improving production efficiency. It will become extremely large.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the effect of processing rate on the crystal grain size of an extruded raw pipe and the surface texture. FIG. 2 is a diagram showing a comparison of the surface and internal structures of extruded raw tubes with eight different crystal grain sizes before and after drawing. FIG. 8 is a diagram showing how the surface temperature of the extruded material decreases after passing through the cooling zone. FIG. 4 is a diagram showing the relationship between billet heating temperature and crystal grain size after extrusion. FIG. 5 is a diagram showing the relationship between billet heating temperature and the presence or absence of surface defects. FIG. 6 is a cross-sectional view showing the outline of the double punching near the extrusion side of the high temperature isostatic extrusion press. (1)...Container, (2)...Dice, (3)...
... Billet, (4) ... Stem, (5) ... Pressure medium, (6) ... Guide tube, (7) ... Cooling region, (8) ... Extruded material. Patent Applicant Kobe Steel, Ltd. Procedural Amendment (Method) 1. Indication of the case 1981 Patent Application No. 208181 No. 2, Issued
Name: High-temperature isostatic pressure extrusion method for brass tubes 3, Relationship with amended personnel fI+ (119) Hayashi Shiki Company Kobe Works 4, Agent 0577 5, -'” (Date of amendment order) March 1982
July 9, 6, Subject of amendment/t3A Description of the detailed description of the invention (1) "Figure 2 is..." on page 5, lines 9 to 17 of the specification
...The gloss is not good either. ” is corrected as follows. ``Figure 2 is a micrograph showing the structure of the tube material before and after drawing.
An extruded raw tube extruded at an extrusion ratio of 33 and a stem speed of 5011 IV/8 is used. Figure 2 (a1) is a micrograph showing the structure of the line cross section of the extruded raw tube when the billet was extruded and cooled to 500°C or less at a high cooling rate.
02-0.025 m. FIG. 2(al) shows the i-weave of the linear cross-section of the drawn pipe when the extruded raw pipe having the structure shown in FIG. The entire photomicrograph @Figure 2 (a3) is a photomicrograph showing the surface of the drawn tube having the structure shown in Figure 2 (al), and the surface texture was good. bl) is a micrograph showing the structure of the line cross section of the extruded raw tube when the cooling rate is low and the cooling rate is 500°C or less after extrusion into the billet, and in this case, the crystal grain size is about 0.
．． It was 04mm. Figure 2 (b2) shows the oil stamping/fj base pipe whose total area reduction is 3 g and 8%, and the first drawing line is 1 line, and the area reduction is 27.6 fD. If @2 drawing is carried out, the total number of drawing tubes will be 1 and navy blue.
The second item (bJ) is 14i power 4.
2 □ Figure [b2] shows the ftmFj of the surface of the front 8 drawing tube.
This is a micrograph shown at t, -2, and there are slight depressions on the surface. Figure 2 (cl) shows the billet i extruded and then cooled. When the speed is small and cooled to below 500"C, at
A micrograph showing the entire structure of the wire cut Iw of the raw pipe, in this case,
The crystal grain size is 0.07 to 0.09. Ta. The vJz diagram (c2) is obtained by performing the first drawing on the curved extrusion element 'Ff whose structure is as shown in Figure 2 (c1') at an area reduction rate of 39.8%, and then drawing the curved extrusion element 'Ff' whose structure is as shown in Figure 2 (c1') at an area reduction rate of 27.6%. A set of cross-sections of the drawn tube after 14 drawings, showing the truth, microscopic photograph,
FIG. 2 (c3) is a micrograph showing the surface Al weave of the drawn tube whose Haya weave is No. 2151 (c2),
On its surface, there are 75 large uneven surfaces and light. The stream is not good either. ” (2) Ming 1! 'III 'i:I)'Is I 3
Page 13 line~! 6th line Or 2nd I'd f';j: This is a comparison of the songs. ” wo, 组 are corrected. "Figure 2 ('al)" (a3), (bJ) ~ (bJ)
, (CJ) to (c3) are the characteristics of the structure of the pipe material before and after drawing.
1 year old, mute photograph (X 100.) All shown. ” (3) The drawing “Figure 2” is attached to Appendix V, 111 ty.

Claims (1)

[Claims] 1. After extruding the billet heated to 500°C to 800°C through a die by high-temperature isostatic extrusion, the extruded material is cooled at a cooling rate of 850°C/l1ee or higher in a cooling zone provided at the exit of the die. A method for high-temperature isostatic extrusion of brass tubes, characterized by cooling under conditions such that the temperature after passing through the zone is 500° C. or less.