JPS61190052A - Manufacturing method of titanium fin tube - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a titanium fin tube using a welded tube as a raw material.

Conventional technology Chita/ has excellent corrosion resistance and is used as heat exchanger tubes in various chemical plants and power generation condensers.
Expanding the heat transfer area and improving the performance as a heat exchanger,
In order to make devices more compact, irregularly shaped tubes with outer surfaces processed into various shapes have come to be used.

A finned tube is used as one of these irregularly shaped tubes, and the manufacturing method for the finned tube is to use a titanium tube as the material, perform rolling processing to form fins on the outer surface, and leave it as it is. A common method is to use the product in this state.

Problems to be Solved by the Invention However, when using a welded titanium tube made of the above material, there is no problem under normal usage conditions, but the strength in the axial direction of the tube is lower than that of the base material.

In the circumferential direction of the pipe, there are welds with poor ductility.
It is considered unsuitable in cases where an excessive load is applied due to internal pressure, and seamless pipes, which are more expensive than welded pipes, had to be used as the material.

Means for Solving the Problems The present invention aims to solve the above-mentioned conventional drawbacks.The present invention is aimed at solving the above-mentioned drawbacks of the conventional technology. This is a method for manufacturing a titanium fin tube, the gist of which is annealing at 700 to 850°C in an active gas atmosphere.

The present invention will be explained in detail below.

In a welded pipe, the welded part is inferior in strength and ductility to the base metal part, but the same can be said even after the outer surface of such a welded pipe is rolled to form fins. In other words, when the above-mentioned welded pipe is subjected to rolling processing, the fin part is subjected to strong cold working in both the base metal part and the welded part, and the part from the base of the fin to the inner surface of the pipe (hereinafter referred to as the pipe wall thickness) is subjected to strong cold working. The effect of processing also affects the welded part, and both the base metal part and the welded part become work hardened, resulting in a decrease in ductility.

Among these, the ductility of the welded part is significantly inferior to that of the base metal.

The method of the present invention eliminates these drawbacks,
This method uses a welded pipe as the raw material, performs rolling processing to form fins on the outside of the pipe, and then anneals it at a hot water temperature of 700 to 850°C in a vacuum or inert gas atmosphere. , sufficient ductility is ensured in both the base metal part and the welded part, as well as in the fin part, which is subjected to strong cold working, and in the thick part of the pipe, which is subjected to cold working to a lesser extent than the fin part. , it is possible to manufacture a finned tube with properties equivalent to those obtained when a seamless tube is used as the material.

It is generally known that in metal materials, recrystallization begins when annealing is performed after cold working, producing fine crystals and restoring ductility. The method of the present invention applies this phenomenon. It is.

In other words, in a welded pipe, the base metal has a highly ductile equiaxed α structure, while the welded part has a cast structure and the weld heat-affected zone has a needle-shaped transformed β structure, both of which are highly ductile. Although the structure is poor, the method of the present invention involves cold working by rolling to form fins on the outer surface of the welded pipe, and then annealing at a temperature of 700 to 850°C. This is a method of causing recrystallization to create a highly ductile alpha structure in all parts of the tube.

Example A more detailed explanation will be given below based on examples.

As the material for the fin tube, we used a JIS H4631, TTH35W type 2 welded titanium tube with an outer diameter of 19 mm and a tube wall thickness of 1.3 fins, and through rolling processing, the outer diameter was 1911 mm, the fin height was α8, and the base of the fin was Part thickness 0, 8 @-,
A fin tube with 30 fins/1 nch was fabricated, and changes in the microstructure were investigated by changing the annealing conditions.

The hardness and elongation rate in the circumferential direction were measured. The elongation rate is
The calculation was made by filling a groove with water in the tube and sealing it, then applying internal pressure to cause the tube to burst, and measuring the outer circumference at the time of bursting.

Figures 1 to 4 show changes in the microstructure of the base metal and weld due to differences in annealing conditions. When annealed at 650℃ after rolling, Figure 3 shows the same temperature at 700℃.
FIG. 4 shows the same (
This is a case of annealing at 850°C. In addition, annealing is 1
The test was carried out for 0 minutes in an argon atmosphere.

From the above results, when annealing is not performed, both the base metal part and the welded part have the same structure as the material has been processed (see Figure 1), but when annealing at 650°C, the base metal Recrystallization is progressing in some parts (see Figure 2), and the temperature is 700℃.
When annealed at 850°C, almost all recrystallization occurred except for a part of the welded area (see Figure 3)) It can be seen that both the base metal and the welded area were completely recrystallized at 850°C (see Figure 4). .

Table 1 shows the changes in the fracture position, circumferential elongation, and hardness of the tube when the annealing conditions after rolling were changed. -1 indicates that the annealing was performed after rolling. If not, Earth 2 is 600℃, Na3 is 650℃, Na8 is 90℃.
Comparative example, Taka 4 was annealed at 0°C at 700°
C1Na3 is 750℃, 翫6 is 800℃, Na7 is 8
Examples of the present invention, images and images annealed at 50°C, respectively.
9 is a comparison material, which is the test result when a seamless pipe was used as the material and rolled. In addition, all annealing is 1
o minutes in an argon atmosphere.

In Table 1, the fracture position of the pipe when water pressure is applied to the pipe to cause it to rupture is determined when the pipe is not annealed after rolling (in the case of picture 1 in the same table), or when the annealing temperature is the same as in Table 1. 5.8.7 is an example of the present invention. When the annealing temperature is low (Na2. In case 7), the fracture position is not concentrated only in the welded part. Note that the fractures are all parallel to the tube axis direction.

The elongation rate in the circumferential direction of the tube is a5% when not annealed (for Nat in the same table), but increases by annealing, and when the annealing temperature is 700 to 850°C (for NA4 in the same table) - Cases 7) show a value of about 13%. This shows the same elongation rate as when a seamless pipe is used as the pipe material (positive 9 in the same table), and it is thought that this is because the structure of the welded part recrystallized and became an equiaxed α structure. .

In addition, the hardness of the cross section of the pipe is also improved by annealing.
When not annealed (in the case of mt in the same table), the Vickers hardness (100g> is about 182, whereas when the annealing temperature is 700 to 850°C (in the case of 4 to 7 in the same table), it is 1
It shows a low value of about 27 to 138, which is equivalent to or better than the case where a seamless pipe is used as the material (case &9 in the same table).

Note that in the case where the tube was annealed at 900° C. after rolling (case 8 in the same figure), measurement was impossible because the tube was deformed due to thermal stress. That is, it is not preferable to anneal the fin tube at 900° C. or higher after manufacturing it.

From the above results, the annealing temperature conditions after forming are 700
It is desirable to set it as -850 degreeC.

As described in detail, according to the present invention, even if a welded pipe is used as a raw material, it can be annealed at 700 to 850°C in a vacuum or inert gas atmosphere after being subjected to rolling processing to form fins. By doing so, the ductility of the weld can be significantly improved. As a result, even when a load due to internal pressure is applied in the circumferential direction of the tube, there is no need to use a finned tube made of an expensive seamless tube, and the effects of the present invention are extremely large.

[Brief explanation of the drawing]

Figures m1 to 4 are micrographs showing the microstructure of titanium fin tubes under various annealing conditions. The fJ4 diagram corresponds to the case of annealing at 850°C. Figure 311 Hata <"Part 111) Part 2 Figure Welding L Teru Chi 3 wJ Mi 5゛3... Mi,, Hi, i +. Figure 4 (Mire and Gan,・',, Haku Riu S・)

Claims (1)

[Claims] After rolling the outer surface of the titanium welded tube to form fins, it is heated for 70 minutes in a vacuum or inert gas atmosphere.
A method for manufacturing a titanium fin tube, characterized by annealing at 0 to 850°C.