JPH02258903A - Manufacture of clad metal tube - Google Patents

Abstract

PURPOSE:To manufacture a clad metal tube reducing the development of defect in the clad layer, such as variation in thickness, bamboo joint-like crack, by executing extrusion-work to two kinds of raw tubes constituting combined billet under applying temp. difference between the tubes. CONSTITUTION:Powder packing layer 4, etc., of Ni base alloy, etc., to be formed as the clad layer is arranged between a base material raw tube 1 of carbon steel, etc., and a thin metal tube (capsule) 5 to form the combined billet. The hot extrusion-work is executed to the clad layer of the Ni base alloy, which has higher deforming resistance in this billet under applying the heating temp. higher than that of the other base material. The temp. difference is made to >=50 deg.C and preferably adjusted so that the ratio of the deforming resistances of both raw materials in the deformation part becomes <=about 2.5.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) This invention is a method of manufacturing a clad metal tube by hot extrusion, in which there is a large difference in deformation resistance between two metals (alloys) to be combined, and The present invention relates to a method for manufacturing a sound rad tube without surface flaws or other defects even when machining is difficult.

(Prior art) Clad materials, which combine two or more metals with different properties (here, pure metals and alloys are collectively referred to as metals) to take advantage of the advantages of both, have already been put into practical use in many fields. ing. The types of metals used and their combinations are diverse, but the one with the highest production volume is -JiJ (mother N
) is made of carbon steel or low-alloy steel, and is laminated with highly corrosion-resistant stainless steel, titanium, etc.

Various clad products are manufactured not only as plates but also as pipes. The method for manufacturing seamless clad pipes is as follows:
Hot extrusion methods (eg, the Eugene-Sejournet method) are the most common. The manufacturing process is schematically shown in FIG.

That is, first, a billet 3 is prepared by combining raw tubes 1 and 2 made of different metals, and this is heated to an appropriate temperature and extruded. The issues here are manufacturing costs and the quality of the clad pipe product.

For example, for applications such as oil pipes that require high strength and excellent corrosion resistance, we use cladding with a base material layer of inexpensive, high-strength carbon steel or low-alloy steel and a craft layer of a nickel-based alloy with excellent corrosion resistance. A tube is promising, but if we try to manufacture it using the conventional hot extrusion method, a composite tube in which the raw tube 1 in Figure 1 is made of carbon @ (or low-alloy steel) and the raw tube 2 is made of a nickel-based alloy will be used. 0 Normally, a hollow cylindrical raw pipe is manufactured through the following steps: melting, casting, forging, and machining (drilling), and these are then fitted together to form a composite billet. shall be. This composite and lettuce are heated to a predetermined temperature in a heating furnace and/or an induction heating device and then hot extruded, but the major problems at that time are as follows.

1) Problems with product surface quality This is particularly due to the difficult-to-process gold N layer that forms the cladding layer of the two metals (in the case of a combination of carbon steel and nickel-based alloy, the nickel-base gold layer). These are variations in thickness and the occurrence of scratches and cracks on the surface.

2) Problems with bonding strength If the bonding between the base material layer and the cladding layer is not perfect, and separation occurs between the 0 layers, which have weak bonding strength, hydrogen will enter there, and the internal pressure will cause the separated area to expand and cause damage to the pipe. This causes swelling and a decrease in strength.

3) Problems with manufacturing costs Because it takes a lot of man-hours to create a composite billet and the material yield is low, the manufacturing costs up to the end of the product increase.
For relatively inexpensive materials such as carbon steel and low-alloy steel, the yield at the time of manufacturing the raw material has little effect on the cost of the final product, but for materials with high raw material costs such as nickel-based alloys,
The material yield during the production of raw tubes has a significant impact on product costs. Moreover, nickel-based alloys are difficult to forge and machine, and the forging and machining required to make the raw tubes is time-consuming.

One solution to the above problems 2) and 3) is to use powder as the material for the raw pipe. For example, use molten material as the base material of carbon steel or low alloy steel,
It has been considered to use powder as a material for the alloy forming the cladding layer, and several proposals have been made in the following specifications and the like.

■U.S. Patent No. 3.753.704 Specification ■U.S. Patent No. 4.01.6,008 (Japanese Patent Publication No. 60-3716
2) ■ JP-A-61-190006 ■ JP-A-61-190007 In each of these, a composite billet as shown in Fig. 2 is first prepared, then heated and hot extruded. This is a method of pipe manufacturing.

The composite billet shown in FIG. 2 consists of a hollow cylindrical body (base material tube) 1 made of carbon steel or the like, a thin-walled metal tube (also called a capsule) 5, and a space between the hollow cylindrical body 1 and the thin-walled metal tube 5. The packed powder layer 4 is made of a gasket, and its upper and lower ends are sealed with end plates 6-1 and 6-2, respectively.

The assembled composite billet is heated to a predetermined temperature and hot extruded to form a clad pipe, after increasing the packing density of the powder packed bed 4 by cold isostatic pressing or the like as required.

That is, the powder packed layer 4 is solidified by the heating, compression, and shear deformation associated with hot extrusion, and the inner circumferential surface of the base material layer into which the hollow cylinder 1 has been formed is clad as an alloy layer. The end plates 6-1 and 6-2 and the thin metal tube 5 are removed by a method such as pickling after hot extrusion.

As mentioned above, the hollow cylindrical body (raw pipe) l that makes up the composite billet is one constituent material (base material layer) of the clad pipe of the final product, and is usually made of carbon steel or low alloy steel. It is a relatively inexpensive material with good hot workability. This is manufactured into a predetermined shape through ordinary processes such as melting, forging, and machining. On the other hand, the powder-filled layer 4, in the example shown in FIG. 2, serves as a cladding layer on the inner surface of the base material layer, and is made of an alloy powder having particularly excellent functions such as excellent corrosion resistance. A typical example of such an alloy is a nickel-based alloy, but if powder of such an alloy is used, almost 100% of the raw material (powder) used will become a product, making it extremely economical. It's advantageous.

Figure 2 shows a billet in which the cladding layer is on the inner surface of the tube, but depending on the purpose of the tube, the cladding layer may be provided on the outer surface of the tube, in which case the capsule 5 is placed on the base material tube 1. Composite billets are used which are arranged on the outside and have a powder filled layer 4 placed in their voids. In addition, in this specification, the hollow cylindrical powder filling layer filled in the thin-walled metal tube (capsule) is also referred to as the "Main Pipe J" that constitutes the composite billet, similar to the material pipe made by machining from melted material. I will call you.

As mentioned above, if powder is used as the material for one of the raw pipes, the bonding strength at the interface will be higher than when a composite billet of melted materials is used. During extrusion, the powder bites into the surface of the other material (molten material) and breaks through the thin oxide film formed on the surface of the material. This is because new surfaces are formed, allowing for a strong and highly reliable bond that cannot be obtained with melt-sawn lumber.

The hot extrusion pipe manufacturing method, in which one of the raw pipes uses a composite billet made of a powder-filled bed, has been put into practical use in some cases, such as in the production of clad pipes made of carbon steel and stainless steel. However, the above-mentioned problem 1) has not yet been resolved. For example, a tube with a base material layer of carbon steel and a cladding layer of a nickel-based alloy such as A11oy 825 or Al1oy 625 can be produced by hot extrusion. When manufactured, large thickness variations occur, especially on the clad layer side, and in severe cases, bamboo knot-like cracks occur.

FIG. 15 is a schematic cross-sectional view showing an example of a clad pipe in which the bamboo knot-like cracks described above have occurred. The base material layer 17 is made of carbon steel with low deformation resistance, and the cladding layer (in this case, the inner surface of the tube) 1
8 is a nickel-based alloy with high deformation resistance.0 As shown in the figure, there are variations in the thickness of the base material layer, but the thickness variation of the cladding layer with high deformation resistance is significant, and in some parts the cladding layer is completely There are some parts that are missing. These portions 19 appear at a constant pitch in the longitudinal direction of the tube, like the knots of bamboo, and are called bamboo knot cracks. Such defects cannot be repaired by product maintenance (repair). , which greatly reduces product yield.

The bamboo knot cracks mentioned above are caused in part by the high deformation resistance of the nickel-based alloy and poor hot workability. Therefore, by increasing the processing temperature, the deformation resistance becomes smaller and bamboo knot cracks can be reduced. it is conceivable that. However, if the heating temperature of the billet exceeds the solidus temperature of the nickel-based alloy, intermetallic compounds will aggregate at grain boundaries or a liquid phase will form in some parts, leading to poor tube manufacturing and deterioration of product quality. Therefore, it is not only impossible to increase the heating temperature unnecessarily, but also simply increasing the billet heating temperature cannot completely prevent bamboo knot-like cracking, and will only lead to wasted heating energy.

It takes a lot of man-hours to clean up the scratches and scrapes that occur on the pipe surface. In particular, internal scratches and cracks are difficult to clean.
Even if pipes with cracks are taken care of, they are often not commercially available.

(Problem to be solved by the invention) The i! ! ! One of the issues is to use composite billets to
When manufacturing clad pipes made of different types of metals, even if the composite billet is a combination of raw pipes made from molten material, or at least one of the raw pipes is made of powder, In any case, it is an object of the present invention to provide a method for manufacturing a clad pipe with excellent surface quality, which has less variation in wall thickness and no bamboo knot-like cracks.

Another object of the present invention is to use a composite billet in which at least one of the blank tubes constituting the composite billet is made of powdered optical MAN made of an alloy with high deformation resistance such as a Ni-based alloy, and to prevent defects such as those shown in M. It is an object of the present invention to provide a method for manufacturing a cladding tube free of cladding.

(Means for Solving the Problems) Based on the experience of numerous tests and actual production, the present inventors have determined that the cause of wall thickness variation and bamboo knot cracks that occur in the cladding layer is simply due to one layer of the cladding pipe. I learned that the major cause is not just the magnitude of the deformation resistance of the metal that forms the cladding layer, but also the difference in deformation resistance at the time of processing of the two metals that form the cladding layer.

Conventionally, composite billets (indicated by 3 in FIG. 1) for manufacturing clad pipes are heated to a uniform temperature throughout, similar to billets made of a single material.

As shown in Figure 8, which will be explained in detail later, even at the same processing temperature, the deformation resistance is gold! 4 (alloy) fil rN
For example, carbon steel and A11oy6
Comparing the deformation resistance of No. 25 at 1000°C, the latter is approximately four times that of the former. If such a composite billet made of a combination of two types of alloys is extruded by uniformly heating the billet to -1 degree, the occurrence of bamboo knot-like cracks is unavoidable.

Therefore, the present inventor focused on processing the raw tubes that make up the composite billet by changing the temperature, and as a result of conducting tests using a large number of metal combinations, the inventors found that one of the raw tubes with greater deformation resistance was selected than the other. It was confirmed that by performing extrusion processing at a high temperature, it was possible to reduce variations in the thickness of the cladding layer and reduce defects in the cladding layer, including bamboo knot cracks.

Furthermore, when processing with a temperature difference like this, the occurrence of fatal bamboo joint cracks can be virtually eliminated by setting the deformation resistance ratio of the image material at the processing deformation part to 2.5 or less. I learned that it is possible.

The gist of the present invention based on such knowledge is the following method for manufacturing a clad metal pipe.

r A method for manufacturing a clad metal tube made of two types of metals with different deformation resistances, in which a composite billet is produced in which raw tubes of these two types of metals, that is, hollow cylinders, are arranged concentrically, and the composite billet is A manufacturing method for a clamped metal pipe, characterized in that the material pipe having a larger deformation resistance is subjected to hot extrusion processing at a higher temperature than the other material." In the present invention, the term "metal" refers to pure metals and alloys, as well as intermetallic compounds or metal carbides,
Also includes materials mainly composed of metal nitrides.

The composite billet used in the above method of the present invention is:
The billets are a combination of the following three types.

■ All raw pipes are manufactured by machining from melted lumber.

■ One part of the raw pipe is made of molten lumber and the other part is made of a layer of metal powder filling.

■ All of the base tubes are made of a powder-filled bed.

The billet ① is shown as 3 in Figure 1, and the base tubes 1 and 2 are made by forging and machining melted materials of the respective metals to form hollow cylinders, and then fitting them together. do.

As shown in Figure 2, the billet (2) has one side (in this case, the outer base material tube 1) made from melted material, and the other side (inner side 4, in this case) made of a powder-filled layer. Normally, the ingot material is carbon steel or low alloy steel, and the powder filling layer is an expensive and difficult-to-process material such as a nickel-based alloy. Depending on the use of the TALLAD tube, the outer and inner layers may be reversed.

As shown in FIG. 3, the billet (2) has metal powder-filled layers on both the inner and outer layers, and the boundary between them is partitioned by a partition wall 8. Such a powder-filled layer uses a thin-walled metal capsule 5-1.5-2 that covers the inner and outer peripheries, and arranges a thin-walled metal tube that becomes the partition wall 8 inside the capsule and fills it with each powder. Created by (In addition, in the example in Figure 3,
For the purpose described later, a heat insulating cladding tube 9 is provided inside the capsule on the inner peripheral side. ) Among the composite billets from ■ to ■ above, billet ■ has the highest practical value. In other words, for example, in seamless pipes for oil transmission pipes, it is desirable to have a base material layer made of carbon steel or low-alloy steel that provides strength, and an inner cladding layer made of a nickel-based alloy that provides corrosion resistance. case,
It is most rational to manufacture the inexpensive base material tube by machining it from a molten material, and to use the expensive base material tube as the rad layer as the powder-filled layer. Note that in UL heat recovery boiler tubes and the like, the outside of the tube is exposed to a strong corrosive environment, so a clad tube with a cladding layer of nickel-based alloy or the like on the outside is required. In this case, the structure of the composite billet is different from that shown in FIG. 2, with a powder filling layer placed on the outside.

Hereinafter, the present invention will be mainly described using, as an example, a case where a composite billet as shown in FIG. 2 is used, which has a packed layer of powder such as nickel-based gold on the inside.

The feature of the method of the present invention is that the extrusion process is performed by applying a temperature difference to the two types of raw tubes that make up the composite billet. Specifically, the raw tube with greater deformation resistance is processed at a higher temperature than the other to minimize the difference in deformation resistance during processing deformation. In particular, when using two types of metals with large differences in deformation resistance, the temperature should be adjusted so that the ratio of deformation resistance of the image material at the deformed part during extrusion is 2.5 or less, preferably 2.3 or less. It's good to make a difference.

FIG. 4 is a schematic cross-sectional view showing the state of processing deformation of the die portion of the hot extrusion device when producing pipes using a composite billet. As shown in the figure, the billet 3 charged into the container 10 is processed between a mandrel 11 and a die 12 and exits as a tube 13 with a predetermined wall thickness. It can be divided into three areas as shown in the figure. Region 1 is a region in which the upturned billet moves toward the die entrance without deformation, and region 2 is a region in which the billet that has approached the die population is plastically deformed by the die, mainly due to shear, and moves toward the die exit. The plastic flow region reaches , and the region (2) is the region where the deformation is completed and the product (clad seamless pipe) separates from the die.

The area where the deformation resistance of the billet becomes most problematic is region (3). When manufacturing clad pipes, the two components that make up the billet
If the difference in deformation resistance in this region H of the seed metal tube is large, the layer thickness (wall thickness) of the metal with greater deformation resistance will fluctuate periodically, and the aforementioned bamboo knot-shaped cracks will occur frequently on the surface. 8 In the present invention, the term "deformed part of extrusion process" refers to this region H. Note that even if part or all of the raw pipe that makes up the billet is powder, it will be sufficiently densified by the upsetting process in region I to reach region H, so deformation in region ■ will not occur. The behavior can be considered to be the same as that of ingot lumber. Therefore, the following explanation regarding deformation resistance applies to both a composite billet consisting only of raw pipes made of molten material and a composite billet in which at least one raw pipe is a powder-filled layer.

Next, deformation resistance will be explained.

Factors involved in deformation resistance are the amount of plastic strain, strain rate, and processing temperature.

FIG. 5 is a diagram illustrating the amount of plastic strain.

−i is the strain amount of the test piece 14 before deformation, as shown in FIG.
If the length of is 111 and the length of the test piece 14' after deformation is l, then it is expressed as the following equation.

ε ε=Iln When a tube is manufactured from a billet, the amount of strain is similarly expressed by the following equation, where the length of the billet is 20, the length of the product tube is P, and the extrusion ratio is T.

ε= i n = l n yro In the production of metal tubes by normal hot extrusion, the extrusion ratio T is 4
〜30 is often in the range, so the amount of strain ε during pipe manufacturing is 1.4〜
There are many cases in the range of 3.4.

The next important thing is the strain rate, which is the amount of deformation strain per unit time, and the extrusion speed V (mm/5ee)
, billet length no (+am) is expressed by the following formula.

1＠/v l・In the production of metal tubes by normal hot extrusion, io is 500
~1200 mm, and ■ is often in the range of 100 to 400 mm/sec, so it is usually about knee o, i ~3 sec-'.

Generally, the higher the processing temperature, that is, the temperature at which the material is deformed, the lower the deformation resistance. The processing temperature is the temperature in region (2) in FIG. Although it is difficult to measure the temperature of area H in actual pipe-making operations, it is easy to estimate the temperature of area H from the temperature of the billet in the container population. The billet is preheated to a certain degree before use, but considering that the billet comes into contact with these and removes heat, it can be assumed that there is a temperature drop of approximately 50°C before it reaches the processed deformation part. The measurement is performed as follows.

Using a test device as shown in Figure 6, a pressure of 11% was measured at a constant temperature.
Perform the test and measure the displacement and load at that time. In Fig. 6, 14 is a test piece, 15 is an induction heating coil, 1
6 is a press. FIG. 7 is a stress-strain curve obtained by such a test.

In the measurement, a compression test is performed at each temperature at a predetermined strain rate up to a strain amount of 1.0, and the average deformation resistance obtained by dividing the total area of stress x strain by the strain is defined as the deformation resistance. Note that the strain rate is determined from the time required to reach the strain amount of 1.0.

Figure 8 shows the carbon steel (JISST) with the chemical composition shown in Table 1.
KM 19 equivalent material), stainless steel (JIS, 5IJS
-304), nickel-based alloy (^1loy 825, A
FIG. 3 is a diagram showing the relationship between deformation resistance and processing temperature determined by the above method for 11oy 625, C276) and a cobalt-based alloy (Stellite #1).

As shown in Figure 8, the deformation resistance of nickel-based alloys and cobalt alloys is much higher than that of carbon steel and stainless steel, and they inherently have poor hot workability6. When the processing temperature (material temperature in region n shown in Fig. 4) is 1100''C, the deformation resistance of carbon steel is 9.
4kg4/+u+", and the deformation resistance of 5IJS 304 is 14.0 kgf/am", so the ratio is approximately 1.
It is 5. On the other hand, the deformation resistance of Al1oy625, a nickel-based alloy, at 1100°C is 27.5 kgf/mm.
Therefore, the ratio of deformation resistance between carbon steel and A11oy 625 is approximately 2.9. The reason why cracks in the rad layer occur in the manufacturing of carbon steel and stainless steel Crasito tubes without any problems is due to the deformation resistance ratio as described above. The main reason is the difference in That is, if the ratio of deformation resistance of the cladding material (nickel-based alloy) to carbon w4 (base material) is large, the fluidity of the material during extrusion processing will be significantly different. As a result, a preferential flow phenomenon of materials with low deformation resistance and a forced flow phenomenon of materials with high deformation resistance occur alternately, and the cladding layer is pushed out with periodic fluctuations in thickness. . This, combined with the large deformation resistance inherent to the nickel-based alloy, eventually causes bamboo-knot-like cracks in the nickel-based alloy layer on the ground N.

The present inventors ascertained the causes of the wall thickness variation and the occurrence of bamboo knot-like cracks as described above, and also conducted tests to determine the limit conditions under which cracks do not occur.

FIG. 9 is a longitudinal cross-sectional view of the composite billet used in the test. That is, a raw pipe 1 made of ingot carbon steel (JrS, STKM 19 equivalent material with the composition shown in Table 1) serving as the base material layer.
A mild steel thin metal tube (capsule) 5 is arranged concentrically inside the tube, and the lower ends of the raw tube 1 and the capsule 5 are fixed with an end plate 6-2. The annular gap between the raw tube 1 and the capsule 5 is filled with powder 4 of nickel-based alloy (^l1oy 625 with the composition shown in Table 1), and the upper ends of the raw tube 1 and the capsule 5 are connected with the end plate 6-1. It is sealed to produce a multi-layered composite billet. Note that 9 is a heat insulating cladding tube, which is used for the purpose of keeping the nickel-based alloy powder layer 4 at a high temperature.

The composite billet as described above was heated and hot extruded under the following conditions.

■ Uniform heating of the entire billet. That is, the machining temperatures of the base material pipe and the powder-filled bed are the same. (1) The powder-filled bed 4 is heated to a higher temperature than the base material pipe l, so that the processing temperature of the former is 50° C. higher than that of the latter.

■ Same as in ■, the powder packed layer 4 is heated to a higher temperature than the base material pipe 1, and the processing temperature is 1 higher than the processing temperature of the base material pipe 1.
Increase the temperature by 00°C.

Note that when there is a temperature difference between the powder-filled bed and the base material tube, a temperature gradient will occur from the high-temperature inside of the billet to the low-temperature outside, but the temperature difference here is at the center of the thickness of the powder-filled bed. It is the difference between the temperature and the temperature at the center of the thickness of the base material pipe. Further, the processing temperature is the temperature immediately before the die shown in FIG. 4, that is, the temperature at the processing deformation part (region 2). This involves heating a billet with a thermometer embedded in it, measuring the temperature of each part immediately before charging it into a container, and then calculating the temperature drop due to heat removal from the container and mandrel (both preheated to 300°C). It was calculated by subtracting this. As mentioned above, this temperature drop is about 50°C.

Table 2 shows the deformation resistance ratio of each combination (the deformation resistance value of the powder-filled layer when the deformation resistance of the base material pipe is 1) based on the processing temperatures of the base material pipe and the powder-filled layer in the above test. ).

(Hereinafter, blank space) Table 2 (Deformation resistance ratio) In Table 2, those marked with an asterisk (*) indicate extrusion pipes that were made without the occurrence of bamboo knot-like cracks.

Figure 1O shows the presence or absence of bamboo knot-shaped cracks in the above test tubes, the temperature of the powder-filled layer, the difference in processing temperature between the base material tube and the powder-filled layer, and the deformation resistance of the base material tube against the powder-filled layer. It is shown in relation to the ratio of deformation resistance of ○ in the figure.
：There is almost no variation in wall thickness and no cracking, Δ：There is slight variation in wall thickness and cracking, but it can be repaired with care.・
represents the occurrence of cracks that cannot be repaired.

When there is no difference in the processing temperature between the base material tube and the powder-filled bed, that is, when they are heated uniformly (■ line in Figure 10), the processing temperature is about 1100"C1 and about 1200"C. Bamboo knot cracks also occurred in the nickel-based alloy layer (cladding layer).The processing temperature was approximately 1200°C, which means that the billet heating temperature reached 1250°C, which means that the billet was heated to the solidus temperature of the nickel-based alloy. Therefore, it is thought that the cracks occurred in the nickel-based alloy layer due to the decrease in ductility due to the formation of a partial liquid phase rather than the influence of the deformation resistance ratio.In addition, the deformation resistance of the unfilled layer at this time As shown in Table 2, the temperature is 2.3 times that of the base material pipe.On the other hand, when the processing temperature of the powder-filled bed is 50°C higher than that of the base material pipe (10th
(■ line in the figure) indicates that the processing temperature of the powder packed bed is approximately i, oso
°C (the processing temperature of the base material pipe is approximately 1000°C), bamboo knot cracks occurred, but the processing temperature of the base material pipe was approximately 1150°C.
In the case of C, a stable bamboo tube without cracking was produced.

The bamboo knot-like cracks occurred when the temperature of the powder-filled bed was approximately 1050°C because the deformation resistance of the powder-filled bed was approximately three times that of the base pipe. If the processing temperature of the nickel-based alloy layer is approximately 1150'C, its deformation resistance is approximately 21.7 kgf/mm'' tear/) from Figure 8, whereas the deformation resistance of carbon steel at 1100°C, which is 50°C lower than this, is is approximately 9.4 kgf/mm'' from FIG. 8, so the deformation resistance ratio during extrusion processing has decreased to approximately 2.3. This is the reason why bamboo joint cracks do not occur.

When the temperature of the powder-filled bed is set 100°C higher than the temperature of the base material tube (the ■ line in Figure 6), the processing temperature of the powder-filled bed is approximately 1100°C and 1150°C. Bamboo knot-like shavings were prevented. At this time, the deformation resistance ratios of the powder-filled layer to the base material tube were approximately 2.3 and 2.1, respectively.

In FIG. 10, Δ indicates that the cladding layer had thickness variations and some defects (microcracks), but these were such that they could be made into products by repair. The deformation resistance ratio in this case was 2.3 to 2.5.

As a result of repeating the above tests by changing the types of metals used (base material tube and powder-filled bed material), we found that regardless of the type of metal, whether the metal is molten material or powder-filled bed material, It has been confirmed that, regardless of whether the material has a large deformation resistance or not, if the extrusion processing is carried out at a temperature higher than that of the other material, the variation in wall thickness of the cladding layer and the occurrence of bamboo joint cracks can be reduced.

It is desirable that the temperature difference at this time is such that the one with greater deformation resistance of the composite billet pixel tube has a temperature that is at least 50 degrees Celsius higher than the other. By providing a temperature difference of ℃ or more, clad pipes without bamboo knot cracks can be produced in most cases.

Another criterion for determining the temperature difference is to set the deformation resistance ratio at the processed deformed part of the image material to 2.5 or less, preferably 2.3.
The following should be achieved.

As shown in Table 2 and Figure 10, if the deformation resistance ratio of both is 2.5 or less, the occurrence of bamboo joint cracks can be almost prevented, and even if defects occur, they are minor; If you have it, you can completely eliminate the cracking of bamboo Jiff 4ffi.

By setting the deformation resistance ratio to 2.3 or less, not only can the occurrence of bamboo knot cracks be completely prevented, but also variations in the thickness of the base material layer and cladding layer as shown in Figure 15 can be extremely minimized. .

As shown in FIG. 8, the difference in deformation resistance tends to become smaller as the tube manufacturing temperature increases to -a. Therefore, if the heating temperature of the entire composite billet is increased, the deformation resistance of nickel-based alloys and cobalt-based alloys will decrease rapidly, and the deformation resistance ratio with respect to carbon steel will decrease. However, if the heating temperature of the billet is raised too high, the solidus line of the metal with a low melting point is exceeded and a liquid phase appears, causing the above-mentioned problems.

In addition, increasing the heating temperature has disadvantages such as an increase in energy costs, an increase in billet scale loss, a deterioration in the quality of the product clad pipe material, and an unbalanced increase in the number of extrusion dies.

Therefore, it is industrially desirable to keep the mother tube with lower deformation resistance as low as possible within the range that allows for pipe production, and to raise the temperature of the mother tube with greater deformation resistance to a higher temperature. Returning to Figure 8 again, suppose that carbon steel is heated to 1100°C5.
^ If 11oy625 is heated to 1150°C, the respective deformation resistances will be 21.7 kgf/mm" and 9.4 kgf/
mm", and the deformation resistance ratio is 2.3. It is sufficient to realize these conditions in the assembled billet. In this way, in the case of a combination of carbon steel or low alloy steel and nickel alloy, nickel-based The deformation resistance ratio is reduced to 2.3 or less by increasing the temperature at the center of the alloy material layer in the thickness direction by approximately 50°C or more higher than the temperature at the center of the thickness direction of the carbon steel or low alloy steel material (base pipe). It can be suppressed.

Even when the materials are made of two metals whose deformation resistance ratio at the hot extrusion processing temperature is originally 2.5 or less, or 2.3 or less, it is meaningful to provide the above-mentioned temperature difference. That is, the properties of the product clad pipe become better as the pipe forming temperature becomes lower (metallurgical & [l-weave becomes more preferable). Therefore,
Even if a combination of materials has a deformation resistance ratio of 2.3 or less even if processed at the same temperature, if the tubes are made at different temperatures, it will be possible to make tubes at a lower temperature than before, which will improve product quality. improvements and practical benefits such as the aforementioned savings in heating energy are obtained.

Furthermore, if the difference in deformation resistance is made as small as possible by creating a temperature difference in the image material, the variation in wall thickness of the product tube can be reduced. Since it is 2.3 or less, bamboo knot cracks will not occur even if processed at the same temperature.However, even in this case, if A11oy825 is heated to a higher temperature to bring its deformation resistance closer to that of carbon steel,
It is possible to manufacture clad pipes of excellent quality with almost no variation in wall thickness.

The method of the present invention can also be applied to a pipe manufacturing method in which a composite billet is produced by combining raw pipes made of two types of metals, and the billet is heated and hot extruded. For example, carbon steel and nickel-based alloys, cobalt-based alloys, titanium or titanium alloys,
The base tubes 1 and 2 shown in Fig. 1 are made from metals that have higher deformation resistance than carbon steel, such as composite materials whose main components are intermetallic compounds, metal carbides, and nitrides. A composite billet 3 is prepared by combining the above, and during hot extrusion, the raw pipe with greater deformation resistance is heated to a high temperature to form a pipe. Thereby, it is possible to suppress wall thickness fluctuations and bamboo knot-like cracks that occur in the side with greater deformation resistance (usually the cladding layer).

A specific method of applying a temperature difference to the composite billet picture material (raw tube) is as follows, for example.

(a) Adjust the frequency and heating rate during high-frequency induction heating to heat the metal layer with higher deformation resistance to a higher temperature than the other layer.

(b) In a gas heating furnace, the metal layer with higher deformation resistance is heated to a higher temperature than the other layer by adjusting the direction of the gas burner.

(After uniformly heating the composite billet in a C1 high-frequency induction heating furnace, gas combustion heating furnace, electric furnace, etc., the material tube with lower deformation resistance is kept at a lower temperature than the other one before extrusion processing. Cooling 0 For example, a metal layer with low deformation resistance is cooled with a cooling medium such as water, inert gas, or air.

In order to supplement the effects of (a) to (C) above, a heat insulating cladding tube 9 as shown in FIGS. 3 and 9 may be used.
When heating and extruding these composite billets,
When the inner surface of the billet contacts the cold mandrel, it is cooled. Therefore, even if the powder-filled layer 4 side is heated to a higher temperature than the base material tube 1 side, the temperature difference may disappear at the processed deformed part. The heat insulating cladding tube is effective in preventing this, and is also effective in preventing the occurrence of defects by lowering the surface temperature of the powder-filled layer itself. When the powder filling layer is placed outside the composite billet, it goes without saying that the heat insulating cladding tube is also placed outside the composite billet.

The heat insulating cladding tube is based on the patent application proposed by the applicant in 1983.
It is preferable to use a material made of two or more thin metal plates (for example, low carbon steel) as described in the specification of No. 331600, with a substance having a small heat transfer coefficient interposed at the interface thereof.

As mentioned above, in order to give a temperature difference to each layer of the composite billet, a hole is made in the center of each layer in the thickness direction, a thermocouple is inserted into the hole, and trial heating is repeated. If the correlation with processing temperature is known in advance for each billet size, processing temperature can be adjusted by simply controlling the heating temperature during actual pipe manufacturing work.

As mentioned above, it is desirable to have a temperature difference of 50°C or more between the composite billet image materials. The temperature difference can be controlled either by the temperature difference immediately before charging or the temperature difference at the processing deformation part.The ideal is to control the temperature difference at the processing deformation part, but it is difficult to do so in actual operation. For example, if the temperature difference of the pixel tube in the container population is set to 50° C. or more, this temperature difference will generally be maintained even in the processed deformed part. It goes without saying that the absolute heating temperature should be determined in consideration of the type of metal and the cooling required to reach the processed deformed part.For example, in the case of a nickel-based alloy, it is in the range of 1000 to 1250 °C. For example, the heating temperature of carbon steel combined with this should be set to 5
Reduce the temperature to 0°C.

The method of the present invention is even more beneficial when applied to pipe manufacturing methods that use metal powder as the material for at least one of the metals forming the cladding layer, and in this case, cold isostatic pressure is applied to the composite billet before heating. It is desirable to densify the packed powder bed by applying pressure (CIP).

Normally, when the gap between the base material tube and the capsule is filled with metal powder, the apparent density of the filled layer is at most about 70% of the true density, even if the filling method is performed while applying vibration. . If this is hot-extruded as is, the compression of the powder layer is large until it becomes a product, so uneven thickness of the cladding layer is likely to occur. In particular, if there is even a slight unevenness in temperature in the powder layer, uneven thickness will be promoted. Furthermore, if the compression allowance of the powder layer is large, the thin metal tube of the capsule will buckle during processing, leading to the formation of m-flaws and becoming the starting point for bamboo lIr5-shaped cracks.

By applying cold isostatic pressure processing, the apparent density of the powder packed bed can be increased to about 80% of the true density.

Thereby, the above-mentioned defects that occur when the density of the powder bed is low can be avoided, product yield is improved, and product design and billet design are facilitated.

Another advantage of cold isostatic processing is that the densification of the powder bed increases the efficiency of induction heating. A powder layer with many pores has high electrical resistance and poor thermal conductivity, resulting in a small amount of heat generated with respect to input power during induction heating. However, by increasing the density, these disadvantages are eliminated, and productivity can be improved by improving energy efficiency and shortening heating time, especially when induction heating is used to heat the final layer (which requires high-temperature heating).

The composite billet may be one in which dissimilar metals as shown in FIG. 3 are both powders. As described above, it is desirable that the metal powder used as one or both of the materials be produced by the gas atomization method.Gas atomized powder is essentially spherical and can have a high packing density.

If the quality of the material of the product is particularly important, it is best to choose a powder with a low content of gas components such as oxygen.

As mentioned above, seamless pipes consisting of a base material layer of carbon steel or low alloy steel and a cladding layer of nickel-based alloy are highly corrosion-resistant oil pipes and boiler pipes. It is expected to have a wide range of applications, including pipes for chemical plants. Hereinafter, the method of the present invention will be explained in more detail using the case of manufacturing such a rad tube as an example.

[Example I]

(A) As shown in Figure 11, 0.08%C-0.35%5i-1.5% with outer diameter 208+am and inner diameter 150am
The inner diameter of the hollow cylindrical tube (base material tube) 1 made of Mn-Fe carbon steel is 77.31 mm! I11, wall thickness 311
A thin metal tube (capsule) 5 made of 0.004% C low carbon steel of Il was arranged concentrically, and the lower ends of the base material tube 1 and capsule 5 were fixed with an end plate 6-2 made of a material equivalent to JIS-5541. . The capsule 5 was shaped to slightly protrude inward in consideration of shrinkage due to cold isostatic pressurization, which will be described later.

In the annular gap between the base material tube 1 and the capsule 5, particles with a diameter of 25
0 /7 II or less 21%Cr-8%Mo-3,4%
Nb-62%Ni-4%Fe A11oy 625 argon gas atomized powder is filled, an end plate 6-1 is attached to the upper end of the base material tube l and the capsule 5, and a 10-' Tor
After evacuation to r, it was sealed by welding. After that, the outer surface was thinly oxidized to form a heat insulating layer with a thickness of 11ml and 5S.
A thin-walled heat insulating cladding tube 9 made of No. 41 was attached to the inside of the capsule 5 to form a composite billet. At this time, the powder packing density (percentage of true density, same hereinafter) was 73%, but in order to achieve higher density, a cold isostatic pressurization treatment was performed at 5000 atm and held for 2 minutes. The density of the powder packed layer determined from the weight and volume of the billet after this pressurization was 82%.

The above composite billet was heated in a gas-fired heating furnace at 1000°C for about 1.5 hours, and then the frequency was set to It by an induction coil to bring the temperature at the center of the wall thickness of the base material tube outside the billet to 1170". CXA11oy 625 powder packed bed temperature was heated to 1230°C, extrusion ratio 11,
Extrusion processing was performed at an extrusion speed of 110+w+w/see, outer diameter 100III11, inner diameter 79mm, cladding thickness 3.4
It was made into a clad tube of mm.

The estimated temperature of the processed deformed part during pipe manufacturing is that the center of the wall thickness of the base material tube is 1120°C5.The center of the wall thickness of the powder packed bed is 1180°C, and the deformation resistance ratio is approximately 2.2 from FIG. ! ! ! The remaining cladding tube was pickled to remove the capsule, the inner and outer surfaces were observed macroscopically and microscopically, and changes in the thickness of the cladding layer were investigated using ultrasonic testing. As a result, no surface defects such as cracks were observed, and the variation in wall thickness was within 10% (within ±5%) of the average wall thickness.

(B) Using the same composite billet as above, the temperature at the center of the thickness of the base material tube is 1125°C, and the temperature at the center of the thickness of the powder-filled layer is 1125°C.
Hot extrusion was performed by heating to 75°C.

In this case, the temperature at the processed deformed part is 107
5°C and 1125°C, and the deformation resistance ratio of the powder-filled layer to the base material tube is about 2.4 as seen in FIG. In this case, the cladding layer had thickness variations and some microcracks, but these defects could be repaired by cutting and grinding.

(C) As a comparative example, a composite billet prepared under exactly the same conditions as in (A) up to cold isostatic pressurization was held at 1000°C for 1.5 hours, and then heated by induction heating to form a base material tube and a powder-filled layer. was heated to a uniform temperature of 1200° C. and pipe-made under the same extrusion conditions. In this case, the temperature of the billet in the processing deformation portion is estimated to be approximately 1150° C. as a whole, and the deformation resistance ratio of the pixel tube is approximately 2.8 as seen from FIG. During the extrusion process of this billet, there were large fluctuations in the extrusion force, and as a result of product inspection, there was a significant fluctuation in the wall thickness of the cladding layer.
At the 01 pitch, cracks in bamboo joints that could not be repaired were observed.

[Example 2] (A) As shown in Fig. 12, the outer diameter is 143 mm and the inner diameter is 62 mm.
On the outside of the base material pipe 1 made of 0.45% C of m+w carbon steel, an outer diameter of 177 mm and a wall thickness of 411111 mm is 0.004 mm.
%C low carbon steel capsules 5 were arranged concentrically, and the lower ends of the base material pipe 1 and the capsules 5 were fixed with an end plate 6-2 made of a material equivalent to 5S41. In this case, the capsule 5 was shaped to protrude slightly outward for the same reason as before.

31%Cr-4%W-1.1%C-1%Si-5 with a grain size of 1259m or less is placed in the gap between the base material pipe 1 and the capsule 5.
Filled with nitrogen gas atomized powder of Stellite #6 containing 6% Co, an end plate 6-1 was attached to the upper ends of the base material tube 1 and the capsule 5, and the tube was evacuated and degassed as in Example 1, and sealed by welding. . Thereafter, a thin-walled heat-insulating cladding tube 9 made of 5S41 with a thickness of 1 ma+ whose inner surface was coated with boron nitride powder was attached to the outside of the capsule 5 to form a composite billet. The powder packing density at this time was 68%, but in order to increase the density, a cold isostatic pressure treatment was performed at 5000 atm for 2 minutes to achieve a density of 79%.

Next, this billet was held in a gas-fired heating furnace at 1170°C for about 2 hours, and then high-pressure water was sprayed on the inside of the billet for 12 seconds just before pipe making to create a temperature difference between the base material tube and the powder layer. Ta. This composite billet was extruded at an extrusion ratio of 9.1 and an extrusion speed of 125 taTa/sec, and the outer diameter was 81.
A kraft tube having a size of 1I11, an inner diameter of 59 ann, and a cladding thickness of 2.1 mm was used.

The estimated temperature of the deformed part during pipe manufacturing was determined from the results of a separate billet measurement experiment, and it was found that carbon steel (base material pipe)
The center of the wall thickness is 1030℃ 1 The center of the wall thickness of the powder-filled layer is 112℃
The deformation resistance ratio was approximately 2.2 at 0°C, and a good seamless pipe with no defects could be manufactured.

(B) As a comparative example, a composite billet was produced under the same conditions as in (^) up to cold isostatic pressing, heated in a gas combustion heating furnace at 1150°C, and extruded as it was, that is, at a uniform temperature. . In that product, bamboo tube-shaped cracks occurred at a constant pitch on the outer cladding layer. Note that the deformation resistance ratio at this time was approximately 2.9.

[Example 3] As shown in Fig. 13, the outer diameter is 250 mm and the inner diameter is 1251 mm.
111 0.1%C-2,2%Cr-0.9%Mo low alloy'
mm, inner diameter 105+*11 15%C"-5%Fe-1
A hollow cylindrical material (clad raw pipe) ■-2 made of C276 melted lumber of 6% Mo-4% W-58% Ni is arranged, and end plates 6-1 and 6-2 of JIS-SO5304 are attached at both ends. Fix the base material pipe 1-1 and clad material pipe 1-2 with a gap of 10
-'Torr, degassed and welded the outer surface of the thin-walled 5IIS 304 heat-insulating cladding tube 9 with a thickness of 4mm, which was thinly oxidized and made into a heat-insulating layer, to the cladding material tube 1-2. It was attached to the inside to form a composite billet.

This billet is heated in a gas-fired heating furnace at 1100°C for about 1.5 hours, and the frequency is adjusted using an induction coil to bring the temperature at the center of the wall thickness of the base material tube outside the billet to 1180°C. , the temperature at the center of the thickness of the clad tube is 1230°.
C, the outer surface was forcedly cooled with water for about 15 seconds, and then the extrusion ratio was 7.3 and the extrusion speed was 110+wm/
Extruded in sec, outer diameter 128mm, inner diameter 941I11,
A clad pipe with a cladding thickness of 3.4 mm was used.

The estimated temperature of the processed deformed part during pipe manufacturing is 1050"C at the center of the wall thickness of the base material pipe, and the center of the wall thickness of the clad pipe is approximately 1
The temperature was 190°C. The deformation resistance ratio in this case is approximately 2.3
The inner and outer surfaces of the obtained clad pipe are shown in Example 1.
When observed under the same conditions as above, it was found that there were no cracks or other defects.

[Example 4] (A) As shown in FIG. 14, an outer capsule 5-1 made of 5S41 with an outer diameter of 218 nua and a wall thickness of 1.61 mm;
0.004%C low carbon steel cylindrical partition wall 8 with 43Il1m, wall thickness lll1+1 and inner diameter 68a+m, wall thickness 3+i1
．． 004%C low carbon steel inner capsules 5-2 were arranged concentrically, and each was fixed with an end plate 6-2 made of 5S41. The inner and outer capsules were shaped to slightly protrude inward and outward, respectively.

The annular gap between the outer capsule 5-1 and the partition wall 8 contains 0.08% C-0.3% 5i- with a particle size of 100 paa or less.
A carbon steel water atomized powder 4-1 of 1,5% Mn-Fe is filled, and the annular gap between the inner capsule 5-2 and the partition wall 8 is filled with 21% Cr-8% Mo- with a particle size of 250 u va or less.
A11ay of 3,4%Nb-62%Ni-4%Fe
Filled with 625 argon gas atomized powder 4-2,
The other end of each cylinder 5-1.5-2.8 was fixed with an end plate 6-1 made of 5S41, and after being evacuated and degassed at 10-' Torr, the cylinder was sealed by welding. At this time, the density of each powder layer is 65% on the carbon steel powder side and 74% on the A11oy 625 rot) side.
Met. This was subjected to cold isostatic pressurization at 5,000 atmospheres for 2 minutes to increase the density to 78% and 82%, respectively.

The composite billet thus obtained was heated by holding it in a gas combustion furnace at 1000°C for about 2 hours, and the frequency was further adjusted by an induction coil to bring the temperature at the center of thickness of the carbon steel powder layer on the outside of the billet to 1170°C. A11o white 25 powder layer was heated to a thickness center temperature of 1230°C, extruded at an extrusion ratio of 11 and an extrusion speed of 115 mm/sec, and the outer diameter was 97.
A clad pipe with a diameter of 75mm, an inner diameter of 75mm, and a cladding thickness of 9+uw was used.

The estimated temperature of the deformed part during pipe manufacturing was that the center of the thickness of the carbon steel powder layer was 1120°C, the center of the thickness of the 625 powder layer was 1180°C, and the deformation resistance ratio was approximately 2.2. . As a result of observing the inner and outer surfaces of the manufactured clad pipe in the same manner as in Example 1, no defects were observed.

(B) Only the outer diameter of the outer capsule is set to 208+ m, other conditions are the same as in (^), and a composite billet produced without cold isostatic pressing is processed at the same heating temperature and the same extrusion conditions, Clad tubes of the same dimensions were obtained.

When we measured the thickness of the cladding layer and observed the inner and outer surfaces, we found that the variation in the thickness of the cladding layer was generally within 5% (within ±2.5%) of the average thickness. There were large wrinkles and these parts were cut off, resulting in a pipe production yield of 95%. However, there were no bamboo tube cracks.

Furthermore, when heating a billet without this cold isostatic pressing, not only does it take time to raise the overall temperature due to poor thermal conductivity, but the temperature on the outside of the billet tends to be higher than the inside. The heating time was reduced and the heating time was about 1.5 times that of the one subjected to the cold isostatic pressure treatment described above.

(Effects of the Invention) When manufacturing a clad pipe made of a combination of two types of metals with different deformation resistances, the present invention reduces fluctuations in the thickness of a layer of a difficult-to-process metal with high deformation resistance, and To provide a method for manufacturing a clad pipe with good surface quality by preventing bamboo knot-like cracks from occurring.

The method of the present invention is effective when using expensive and poorly workable alloys such as nickel-based or cobalt-based alloys as the cladding layer, and is particularly effective when using powder as the material for these alloys. It has great advantages such as reduced manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the process for manufacturing a clad pipe using a hot extrusion method. Figures 2 and 3 show one or both materials (raw pipe)
FIG. 3 is a vertical cross-sectional view of a composite billet in which metal powder is used as a material. FIG. 4 is a schematic cross-sectional view schematically showing the deformation state of the billet during extrusion processing. FIG. 5 is a diagram illustrating the amount of plastic deformation. FIG. 6 is a schematic diagram illustrating a method for measuring hot deformation resistance. FIG. 7 is a diagram showing an example of a stress strain curve for calculating deformation resistance. FIG. 8 is a diagram showing the relationship between processing temperature and deformation resistance of various alloys. FIG. 9 is a longitudinal cross-sectional view of the composite billet used in the test. FIG. 1θ is a diagram showing the test results of examining the effects of the deformation resistance ratio of the base material layer and the cladding material layer (powder-filled layer) and the processing temperature of the cladding material layer on the occurrence of bamboo tubular cracks. FIG. 11, FIG. 12, FIG. 13, and FIG. 14 are longitudinal cross-sectional views showing various composite billets used in Examples. FIG. 15 is a partial cross-sectional view in the longitudinal direction of the clad metal tube, illustrating wall thickness variation and bamboo knot-like cracks.

Claims (10)

[Claims] (1) A method for manufacturing a clad metal tube made of two types of metals with different deformation resistances, in which a composite billet is produced in which raw tubes of these two types of metals are arranged concentrically, and the deformation resistance of the composite billet is A method for producing a clad metal pipe, which comprises hot extruding the larger raw pipe at a higher temperature than the other. (2) The method for manufacturing a clad metal tube according to claim (1), characterized in that when heating the composite billet, the raw tube having a higher deformation resistance is heated to a temperature 50° C. or more higher than the other. (3) After uniformly heating the composite billet, the material tube having the smaller deformation resistance is cooled to a temperature 50° C. or more lower than the other material until extrusion processing. ) manufacturing method for clad metal pipes. (4) Claims (1) to (3) characterized in that the temperature difference of the pixel tubes is adjusted so that the ratio of deformation resistance of the pixel tubes at the deformation part of the extrusion process of the composite billet is 2.5 or less.
Any method of manufacturing clad metal pipes up to. (5) Claim (1) wherein the raw pipes constituting the composite billet are all produced by machining from melted material.
) to (4). (6) The method for manufacturing a clad metal tube according to any one of claims (1) to (4), wherein each of the pixel tubes constituting the composite billet is made of a powder-filled layer. (7) The raw pipe with lower deformation resistance is produced by machining from melted material, and the raw pipe with higher deformation resistance is attached to the inner or outer periphery of the raw pipe with lower deformation resistance. Claims (1) to (1) consisting of a powder-filled bed arranged in
4) The method for manufacturing a clad metal pipe according to any one of the above. (8) Claim (6) wherein the composite billet is cold isostatically pressed in advance to increase the density of the powder packed bed, and then heated and hot extruded.
or (7) the method for manufacturing a clad metal tube. (9) Claims (1) to (8) above, wherein the material of the raw pipe with lower deformation resistance is carbon steel or low alloy steel, and the material of the raw pipe with higher deformation resistance is a nickel-based alloy. A method of manufacturing any clad metal tube. (10) A clad metal tube with few surface defects produced by the method according to any one of claims (1) to (9).