JP2016140883A - Bonding method of ferrous material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bonding method of a ferrous material capable of bonding at a comparatively low temperature, and suppressing deformation upon bonding.SOLUTION: A ferrous material is bonded by a bonding method of the ferrous material including an organic acid treatment step for boiling a surface including a bonding part of each ferrous material of a plurality of ferrous materials in an organic acid solution, or exposing it to steam containing an organic acid, and a bonding step for butting, heating, pressurizing and bonding each surface of the bonding parts of the boiled or exposed ferrous material .SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for joining steel materials.

Conventionally, stainless steel has been joined by brazing.
In brazing of stainless steel, a brazing material mainly composed of Ag, Cu, Ni and Au is generally used. These melting points are as high as about 800 ° C. or more, and since the brazing material is melted and joined, there is a problem in positioning accuracy and the application range is limited. In addition, flux is used for brazing, but the problem of corrosion of the brazing portion due to flux residue has been pointed out, and elimination is desired. Furthermore, an intermetallic compound (having brittle properties) is formed between the brazing material and the stainless steel material, and the joint becomes brittle.

As other joining methods for stainless steel, laser welding, friction stir welding, and solid phase diffusion joining have also been proposed.
However, these joining methods have the following problems.
Laser welding: deformation may occur in thin plates, porosity and cracks may occur in thick plates, and various welding defects may occur.
Friction stir welding: Since the temperature range in which stainless steel generates plastic flow exceeds 1000 ° C, it is necessary to develop a stirring tool material that can withstand such high temperatures, and the manufacturing cost increases. It is becoming difficult to apply the law. Moreover, although it is common with other joining methods, it is not suitable for precise joining of minute portions.
Solid phase diffusion bonding: When stainless steel is exposed to the atmosphere, a passive film, which is a bonding inhibiting factor, is formed. In order to obtain a joint with high strength, the passive film must be mechanically broken by raising the joining pressure and joining temperature, which naturally increases the energy during joining and increases the deformation of the joined body. There is a problem.

  In addition, it is proposed to remove the oxide film on the surface of the bonding surface by treating the bonding surface of the metal material with a removing solution made of an organic acid before performing solid phase diffusion bonding of the metal material (for example, (See Patent Document 1).

JP 2006-334652 A

  However, in steel materials such as stainless steel, when solid phase diffusion bonding is performed only by treating the surface with an organic acid as in Patent Document 1, sufficient bonding strength cannot be obtained.

  In order to solve the above-described problems, the present invention provides a method for joining steel materials that can suppress deformation during joining and can maintain high positional accuracy.

  The method for joining steel materials of the present invention is a method for joining a plurality of steel materials, wherein the surface including the joint portions of each steel material is boiled in an organic acid solution or exposed to vapor containing organic acids. An organic acid treatment step to be performed, and a bonding step in which the surfaces of the bonded portions of the steel material that have been boiled or exposed are brought into contact with each other, and heated and pressed to join.

  In the joining method of the steel material of the said invention, it can be set as the structure which further includes the process of wash | cleaning the surface of the junction part of a steel material after an organic acid treatment process and before a joining process.

According to the present invention described above, a high bonding strength can be obtained at a bonding temperature lower than that of the prior art.
This makes it possible to lower the bonding temperature, reduce the energy required for heating, and reduce the amount of deformation during bonding.

It is a flowchart of the procedure of the joining method of the steel material of one embodiment of this invention. It is a perspective view of the board | plate material which consists of stainless steel used in experiment. It is a perspective view which shows the joining state in experiment. It is a figure which shows the relationship between the processing time in formic acid, and peel strength. It is a figure which shows the relationship between the processing time in a citric acid, and peel strength. It is a figure which shows the relationship between the joining temperature and peel strength in a formic acid process and a citric acid process. It is the photograph which observed the fracture surface after a peel test with the scanning electron microscope. It is the figure which compared the spectrum of the light absorbency obtained from the measurement by infrared spectroscopy.

Hereinafter, modes for carrying out the invention (hereinafter referred to as “embodiments”) will be described.
The description will be given in the following order.
1. 1. Outline of the present invention Embodiment 3 FIG. Example

<1. Summary of the present invention>
First, an outline of the present invention will be described.
The method for joining steel materials of the present invention is a method for joining a plurality of steel materials.
And in this invention, the surface containing the junction part of each steel material is boiled in an organic acid solution, or the organic acid treatment process which exposes to the vapor | steam containing an organic acid, and joining of the boiled or exposed steel material It includes a joining step in which the surfaces of the parts are butted and joined by heating and pressing.

  In this invention, it can be set as the structure which further includes the process of wash | cleaning the surface of the junction part of a steel material after an organic acid treatment process and before a joining process.

In the present invention, various steel materials such as ordinary steel and stainless steel can be used as the steel material. For example, various stainless steels such as stainless steel having an alloy composition of 13Cr, 18Cr, 18Cr-8Ni can be used.
The plurality of steel materials to be joined may be the same material or different materials as long as they are within the range of the steel material. Among these, examples of combinations of different materials include steel materials having different constituent elements, steel materials having different compositions, and the like.

In the present invention, various organic acids can be used as the organic acid.
For example, one or more selected from formic acid, acetic acid, and citric acid can be used.

A steel material to be joined is boiled in an organic acid or exposed to a vapor containing an organic acid, thereby generating an organic acid salt on the joining surface. Then, the bonding surfaces are brought into contact with each other, and pressure is applied in the vertical direction to the bonding portion and heating in the vicinity of the bonding portion is performed. Thereby, the joined body of steel materials can be formed.
The joined body formed according to the present invention can form a joined body having a joining strength about three times that in the case where the organic acid salt is not generated. Furthermore, as an organic acid, it can select from what produces | generates the organic acid salt decomposed | disassembled at low temperature.

  The organic acid salt film formed on the surface of the joint portion of the steel material causes a thermal decomposition reaction in the joining step of joining the steel material by heating and pressurizing, and the atomic surface of a metal such as iron of the steel material Since it exposes, the adhesiveness of atomic surfaces improves, the metallic contact area | region of steel materials can be increased, and high joint strength can be obtained.

As described above, according to the present invention, a sufficiently high bonding strength can be obtained at a bonding temperature lower than that of the prior art, so that bonding at a low temperature and in a solid state can be performed.
From the same viewpoint as the bonding temperature, it is possible to obtain a sufficiently high bonding strength even if the pressure during bonding is lowered.
As a result, bonding in a solid phase can be performed at a low pressure, and the amount of deformation at the time of bonding can be reduced as compared with various bonding methods conventionally used. In addition, since the direct joining is performed without an insert such as a brazing material, high positional accuracy can be maintained, and it is possible to join a complicated shape or a minute portion that has been difficult to weld.
Further, since bonding can be performed at a low temperature and a low pressure, the structure of the bonding apparatus can be simplified, energy required for heating can be reduced, and energy efficiency can be improved. For example, it becomes possible to reduce power consumption, fuel for heating, time required for joining, and the like.

<2. Embodiment>
The flowchart of the procedure of the joining method of the steel material of one embodiment of this invention is shown in FIG.
As shown in FIG. 1, first, in step S <b> 11, the surface including the joint portion of each steel material is boiled in an organic acid solution or exposed to vapor containing an organic acid.
Thereby, the organic acid salt film is formed on the surface of the joint portion of the steel material.

As the steel material, various steel materials such as ordinary steel and stainless steel can be used.
As the organic acid, formic acid, citric acid, and other organic acids can be used. As the solvent for the organic acid solution, water or various polar solvents can be used.

Next, in step S12, the two steel materials having the organic acid salt film formed on the surface of the joint are joined by heating and pressing.
As a result, since the surface contamination layer is removed or replaced with the organic acid salt, heating and pressurization are performed, so that the organic acid salt is decomposed by a thermal decomposition reaction, so that the metal of the first metal member Since the atomic plane of the atoms is exposed and the passive film is eliminated, the diffusion of the atoms is promoted, and the recrystallization of the steel material in the joint proceeds, so that the bonding strength can be increased. Since a high bonding strength can be obtained, it is possible to obtain a high bonding strength at a lower temperature and lower deformation than in the past.
That is, it is possible to lower the heating temperature and the applied pressure during joining, as compared with a conventional joining method in which steel materials having no organic acid salt film formed on their surfaces are joined together.

According to the above-described embodiment, since a high bonding strength is obtained, a high bonding strength can be obtained at a low temperature, and compared with a conventional case in which a processing step using an organic acid is not performed, The heating temperature can be lowered. That is, bonding in a solid state can be performed at a low temperature.
And even if the pressure at the time of joining is lowered, sufficiently high joining strength can be obtained, and joining in a solid phase can be performed at a low pressure, so that the deformation amount at the time of joining can be reduced. Therefore, it is possible to improve the bonding position accuracy. Further, by improving the bonding position accuracy, it is possible to maintain a high position accuracy, and it is possible to bond complicated shapes and minute parts that have been difficult to weld.
Furthermore, since it becomes possible to join at low temperature and low pressure, energy efficiency can be improved. For example, it becomes possible to reduce power consumption, fuel for heating, time required for joining, and the like.

  In addition, you may provide the step which wash | cleans the surface of the junction part of the steel material which performed the organic acid process by step S11 between step S11 and step S12.

<3. Example>
Next, the steel materials were actually joined according to the present invention, and the characteristics were examined.

(Experiment 1) Formic acid treatment As a joining material, a block plate (10 mm × 15 mm × 5 mm) and a ribbon roll plate (5 mm × 100 mm × 0) each made of SUS304 stainless steel as shown in a perspective view in FIG. .17 mm).
Then, the joining surface of the block-like plate material was finished by mechanical polishing with emery paper, and the joining surface of the ribbon-like roll plate material was finished by buffing.
The composition of the block-shaped plate material is as shown in Table 1 below, and the composition of the ribbon-shaped roll plate material is as shown in Table 2 below.

A joint sample was prepared by the following manufacturing method.
First, each plate material was degreased by ultrasonic cleaning in acetone.
Next, each plate was boiled in a 50% formic acid aqueous solution for a predetermined time within a range of 7 to 15 minutes.
Thereafter, it was washed with distilled water for 10 seconds.
Thus, the test piece for joining was prepared.

Next, as shown in the perspective view of FIG. 3, the ribbon-shaped roll plate material was brought into contact with the block-shaped plate material, and joined by heating and pressurizing.
Then, during the replacement with nitrogen gas (5 L / min), the joint load was 147 N and the joint time was 1.8 ks, and a joint was manufactured.

(Measurement of peel strength)
For the joint obtained by joining, the peel strength was measured by a peel test (crosshead speed: 0.17 mm / second).

(Examination of optimum processing time)
The optimum treatment time for formic acid treatment was examined.
The formic acid treatment time was changed to 0.42 ks (7 minutes), 0.66 ks (11 minutes), and 0.9 ks (15 minutes) to prepare test pieces for bonding, respectively.
Moreover, the test piece which has not performed formic acid treatment was also prepared as a comparison control.
Then, the joint temperature was set to 1073 K (750 ° C.), and the test piece was changed with the formic acid treatment time to produce a joint.
The peel strength was measured for the joint obtained by joining.
FIG. 4 shows the relationship between the treatment time t _m and the peel strength F in the formic acid aqueous solution. In addition, in FIG. 4, the intensity | strength of the sample (as polished) of the comparison control which is not formic acid treatment is also shown.

As can be seen from FIG. 4, the peel strength of the sample treated with 0.66 ks (11 minutes) is the largest, and the peel strength is lowered when the treatment time is increased to 0.9 ks (15 minutes).
The tensile strength decreases when the treatment time is increased because the organic acid salt is excessively generated due to the long treatment time, and the organic acid salt is decomposed to generate gas, resulting in many pores on the joint surface. Presumed to occur.
It can be seen that by optimizing the processing time to 0.66 ks (11 minutes), a peel strength approximately three times that in the case of no processing can be obtained.

(Experiment 2) Citric acid treatment As in the case of Experiment 1, a block-shaped plate material and a ribbon-shaped roll plate material were prepared as bonding materials, and each plate material was finished by polishing.
And the sample of the joint was produced with the following production methods.
First, each plate material was degreased by ultrasonic cleaning in acetone.
Next, each plate was boiled with a citric acid solution for a predetermined time within a range of 5 to 14 minutes.
Thereafter, it was washed with distilled water for 10 seconds.
Thus, the test piece for joining was prepared.

Next, as in Experiment 1, the ribbon-shaped roll plate material was brought into contact with the block-shaped plate material, and was joined by heating and pressing.
Then, during the replacement with nitrogen gas (5 L / min), the joint load was 147 N and the joint time was 1.8 ks, and a joint was manufactured.
For the joint obtained by joining, the peel strength was measured by a peel test (crosshead speed: 0.17 mm / second).

(Examination of optimum processing time)
The optimum treatment time for citric acid treatment was examined.
Test pieces for joining were prepared by changing the citric acid treatment time to 0.30 ks (5 minutes), 0.48 ks (8 minutes), 0.66 ks (11 minutes), and 0.84 ks (14 minutes). .
Then, the joint temperature was 1073 K (750 ° C.), and joining was performed using a test piece in which the citric acid treatment time was changed to produce a joint.
The peel strength was measured for the joint obtained by joining.
FIG. 5 shows the relationship between the treatment time t _m and the peel strength F in the citric acid solution. FIG. 5 also shows the strength of the same comparative sample (as polished) as in FIG.

From FIG. 5, it can be seen that the peel strength of the sample treated for 0.66 ks (11 minutes) is the highest, and the peel strength is lowered when the treatment time is increased to 0.84 ks (14 minutes).
It can be seen that by optimizing the processing time to 0.66 ks (11 minutes), a peel strength of about three times that of the case of no processing can be obtained.

(Experiment 3) Relationship between Bonding Temperature and Peel Strength Next, the relationship between bonding temperature and peel strength was examined.

  Formic acid-treated block plate and ribbon roll plate, citric acid-treated block plate and ribbon, which were processed at the optimum processing time (11 minutes), respectively, in the same manner as in Experiment 1 and Experiment 2. Many plate materials were prepared.

Then, in the same manner as in Experiment 1 and Experiment 2, for the formic acid-treated and citric acid-treated plate materials, the joining temperature was changed, and joint samples joined at each joining temperature were produced.
Further, as a comparative control, even when the organic acid treatment was not performed and the bonding was performed as it was after the polishing finish, a bonding sample bonded at each bonding temperature was prepared by changing the bonding temperature.
There were three bonding temperatures: 1023 K (750 ° C.), 1073 K (800 ° C.), and 1123 K (850 ° C.).

The peel strength of the produced joint sample was measured with a peel tester.
The relationship between the bonding temperature T and the peel strength F in each case when the formic acid treatment is performed (FA), when the citric acid treatment is performed (CA), and when bonded as it is after polishing finish (as polished) It is shown in FIG.

  From FIG. 6, it was found that by applying the organic acid treatment by applying the organic acid film, it is possible to form a connection portion having a peel strength about three times that in the case where the organic acid coating is not applied.

  Further, FIG. 7 shows photographs of the fracture surface after the peel test observed with a scanning electron microscope in the case of performing citric acid treatment and in the case of bonding as it is after polishing finish. The upper part of FIG. 7 is a photograph of the sample when it is joined as it is, and the lower part of FIG. 7 is a photograph of the sample when the citric acid treatment is performed.

From FIG. 7, when the organic acid salt film was not applied, although a region considered to be a non-adhered portion tended to decrease as the bonding temperature T increased, brittle fracture occurred in most regions. .
On the other hand, when an organic acid salt film is applied by performing an organic acid treatment before joining, the non-adhered portion decreases from a lower joining temperature, and the fractured form has irregularities that are considered to have been joined by the joining partner material. The indicated area is now observed. In particular, at a bonding temperature of 1123 K (750 ° C.), a ductile fracture mode including dimples on the fracture surface has been recognized. Such a change in the rupture form was also observed when applying an organic acid salt film using formic acid.

(Experiment 4) Analysis of product after organic acid treatment Among members made of SUS304 stainless steel, a member that has been subjected to formic acid treatment and a member that has been polished without being subjected to formic acid treatment are prepared. Spectroscopic measurement was performed to determine the absorbance spectrum.
The obtained absorbance spectrum is shown in FIG.

From FIG. 8, the member performing the formic acid treatment, the peak of 1350 cm ^-1 and 1650 cm ^-1 were observed.
From these peaks, it can be seen that nickel in SUS304 stainless steel reacts with formic acid to produce nickel formate, that is, nickel (II) Ni (HCOO) ₂ formate.
This nickel (II) formate is thermally decomposed in the vicinity of 403K to generate hydrogen and carbon dioxide to be metallic nickel.
Therefore, when SUS stainless steel subjected to formic acid treatment is joined by heating and pressurizing, the gas generated by thermal decomposition is vaporized during joining, and the nickel metal surface is exposed, and adhesion between the nickel metals is achieved. It is thought that self-diffusion proceeds.

As a result of measurement by infrared spectroscopy, the effect of the organic acid salt coating by the organic acid treatment was confirmed not only on nickel but also on iron and chromium.
Therefore, the present invention is applied not only to stainless steels such as SUS304 stainless steel that have nickel as a main component of the alloy, but also to stainless steels and nickel that do not use nickel as the main component of the alloy. It is thought that the effect by generation of can be obtained.

  The present invention is not limited to the above-described embodiments and experimental examples, and various other configurations can be employed without departing from the gist of the present invention.

Claims (3)

A method of joining a plurality of steel materials,
An organic acid treatment step in which a surface including a joint portion of each steel material is boiled in an organic acid solution, or exposed to a vapor containing an organic acid;
A method for joining steel materials, comprising a joining step in which the surfaces of the joint portions of the steel material that have been boiled or exposed are brought into contact with each other and joined by heating and pressing.   The method for joining steel materials according to claim 1, further comprising a step of cleaning a surface of the joint portion of the steel material after the organic acid treatment step and before the joining step.   The method for joining steel materials according to claim 1 or 2, wherein any one of formic acid, acetic acid, and citric acid is used as the organic acid.