JP2008063598A - Titanium weld part - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a titanium weld part free from the coarsening of crystal grains in the weld zone. <P>SOLUTION: As the base material and weld metal to be welded, a titanium alloy containing 0.05 to 1.0 mass% B, and the balance Ti with impurities is used. The titanium weld part according to this invention has excellent mechanical properties since the weld zone also has a fine crystal structure, and is suitable as various apparatuses and structures, particularly, as a drum for electrodeposited metal foil. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a titanium welded assembly in which the crystal grains of the weld are fine.

  Titanium materials are excellent in the corrosion resistance and acid resistance of seawater, so they are used as heat exchanger tubes for power plants and chemical industries, marine structures, and drum materials for manufacturing electrolytic foils. In these products, it is necessary to weld not a little during the manufacturing process. At that time, the coarsening of the crystal grains of the welded portion (in this specification, the welded portion means a portion obtained by combining the weld metal and the weld heat affected zone in the vicinity thereof) occurs. Since the strength is reduced due to the coarsening of the crystal grains, the structure or the like needs reinforcement. In particular, in an electrolytic foil manufacturing drum, an electrolytic metal foil is deposited on the surface of the drum, so that the irregularities of crystal grains on the surface of the roughened titanium drum are transferred to the electrolytic foil, causing deterioration in quality.

  In order to solve the above problems, the welding method is limited (for example, Patent Document 1 and Patent Document 2), or the vicinity of the welded portion is cold-worked and then subjected to heat treatment to achieve finer graining (for example, Patent Document 1). 3 and Patent Document 4) have been proposed. However, these measures increase the manufacturing cost.

  On the other hand, a method (for example, Patent Document 5, Patent Document 6, and Patent Document 7) in which the solidification structure is refined by containing B and the crystal grains of the titanium material are refined has been proposed. However, the normal melt-solid heat pattern is very different from that in welding. That is, at the time of welding, since the welded portion is remelted and then rapidly cooled, the thermal history of the welded portion is different from that of normal melting-solidification. Naturally, the thermal history of the weld heat affected zone also differs from that of melting-solidification. Therefore, the methods proposed in Patent Documents 5 to 7 do not give any suggestion regarding the refinement of the structure of the weld.

Japanese Patent Laid-Open No. 11-114684 JP2003-311322 Japanese Patent No. 2,967,239 Japanese Patent No. 3,005,755 JP-A-5-255780 JP-A-5-279773 JP 2004-277873 A

  An object of the present invention is to provide a titanium welded joint free from crystal grain coarsening of a weld metal part remelted by welding and a heat-affected part around the weld metal part (as described above, these are collectively referred to as a “weld part”). In particular, the present invention is to provide a titanium welded joint suitable for use as a titanium drum for producing electrodeposited metal foil, in which the crystal grain size of the titanium material is directly linked to the quality of the product.

  The gist of the present invention resides in "a titanium welded joint characterized in that the base metal and the weld metal to be welded contain 0.05 to 1.0% by mass of B, with the balance being Ti and impurities."

  Here, the titanium welded joint is a titanium product having at least one welded joint, and the shape thereof is not limited. Examples of product types include plates, pipes, and various structures combining them. A typical example is a drum for producing an electrodeposited metal foil.

  Since the titanium welded joint of the present invention has a fine crystal grain size at the welded portion, the mechanical properties thereof are excellent, and even when used as a drum for producing an electrodeposited metal foil, the above-described adverse effects do not occur. In addition, the titanium welded joint of the present invention can be manufactured simply by containing a predetermined amount of B in the base titanium material and the welding material, so there is no disadvantage that the manufacturing cost is remarkably increased.

  Hereinafter, the titanium welded joint of the present invention will be described in detail. In the following, “%” regarding the component content means “mass%”.

  When B is added to titanium, it is crystallized as TiB after arc melting, and has the effect of refining the solidified structure by its pinning effect. Thereafter, the titanium material is further refined through forging, hot rolling, and if necessary, cold rolling and annealing.

  When the present inventors weld a titanium alloy containing B as a welding material, in the weld metal part where the titanium alloy is once melted and re-solidified, a finer grain structure is obtained than the above-mentioned solidified structure, forging, etc. It has been found that a structure with a fine particle size close to that of a product subjected to the above processing can be obtained.

  The mechanism of the above phenomenon is not clear yet. However, since the weld metal part is melted within a short time, TiB crystallized during solidification in the manufacturing process of the base material does not completely dissolve, and the pinning effect during re-solidification is exhibited, and welding After that, since it is rapidly cooled, the supersaturation degree of the solid solution B becomes high, and fine TiB crystallizes, and this shows a strong pinning effect. Is presumed to be obtained.

  On the other hand, if the base material is a titanium alloy containing B, in the heat-affected zone around the weld metal, the heating at the time of welding is short, so the TiB crystallized during solidification in the base material manufacturing process disappears. It is presumed that the grain growth is suppressed by the pinning effect.

  The welded joint of the present invention is obtained by welding a titanium material containing 0.05 to 1.0% B as a base material. The welding method may be any of TIG welding, electron beam welding, and the like. When using a welding material (wire or the like), a material whose composition is adjusted so that the weld metal has the above composition (a composition containing 0.05 to 1.0% of B) is used.

A titanium material containing 0.05 to 1.0% of B can be manufactured by adding, for example, B ₄ C powder at the time of melting. B ₄ C decomposes upon dissolution and crystallizes as TiB. As described above, this TiB exhibits a pinning effect and contributes to the refinement of crystal grains.

  Next, the content of B will be described.

  In order to obtain the effect of preventing the above-mentioned coarsening, in other words, the effect of promoting finer graining, 0.05% or more of B must be contained in the heat-affected zone of the weld metal and the base metal. It is. On the other hand, if the content exceeds 1.0%, the effect is saturated and the workability of the titanium material is lowered. For these reasons, the B content of the base metal and the weld metal is set to 0.05 to 1.0%. In addition, the range of more preferable content is 0.05 to 0.5%.

[Example 1]
A raw material obtained by adding various proportions of B ₄ C to titanium sponge was melted in a high-purity argon atmosphere using a non-consumable tungsten arc melting furnace to obtain an ingot. The obtained ingot was hot-worked to obtain a plate material having a thickness of 5 mm. The chemical composition of the plate is shown in Table 1.

  The sample collected from the plate material was subjected to heat history heat treatment corresponding to the heat history of the heat affected zone during welding, and the influence on the crystal grain size was investigated. The heat pattern of heat processing is shown in FIG.

  FIG. 2 is a graph showing the relationship between the B content of the sample and the average crystal grain size of β-Ti. As shown in the figure, the average crystal grain size decreases as the B content increases. From this result, it is clear that the inclusion of 0.05% or more of B can prevent the crystal grains in the heat-affected zone during welding from being coarsened.

[Example 2]
A titanium alloy containing 0.8% B was melted in the same manner as in Example 1, and after forging, hot-rolled to a thickness of 5 mm, surface-cut to remove the black skin, then TIG welded, and welded Micro-observation of the metal part, the heat-affected part and the normal part (the part not affected by the welding heat of the base metal) was performed. The welding conditions were an argon seal, a voltage of 25 V, a current of 180 A, and a welding speed of 750 mm / min.

  Microscopic observation is performed on the surface layer and the center of the plate thickness for each of the normal part of the resulting welded joint (part of the base metal that does not affect the weld heat), the weld heat affected part, and the weld metal part. Observed. The results are shown in FIGS.

  3 shows a normal part, FIG. 4 shows a weld heat affected part, and FIG. 5 shows a weld metal part. The weld heat affected zone in FIG. 4 is a fine crystal grain that has almost no difference from the normal zone in FIG. The weld metal portion of FIG. 5 has slightly coarse crystal grains, but is fine enough to prevent substantial adverse effects on mechanical properties and the like.

  According to the present invention, by including a predetermined amount of B in the titanium material and the welding material, it is possible to suppress the coarsening of the weld metal and the crystal grains of the heat-affected zone during welding, and it is not necessary to restrict the welding conditions in detail. Also, the heat treatment after welding can be simplified. Since the titanium weld joint material of the present invention has a fine crystal structure, it has excellent mechanical properties and can be used as various devices and structures.

It is a figure which shows the heat pattern of the heat processing of the test material in an Example. It is a figure which shows the relationship between B content of a test material, and an average crystal grain size. It is a figure of the microscope organization of the usual part of the titanium welded joint object of the present invention. Similarly, it is a figure of the microstructure of a welding heat affected zone. Similarly, it is a figure of the microstructure of a weld metal part.

Claims (1)

  A welded titanium body characterized in that the base metal and the weld metal to be welded contain 0.05 to 1.0% by mass of B, and the balance is a titanium alloy composed of Ti and impurities.

Images