JPH07268476A - Cooling method after joining heat treatment for metal honeycomb structure - Google Patents

Abstract

PURPOSE:To secure both the material and productivity of a honeycomb by joining heat treatment for a honeycomb product. CONSTITUTION:In a cooling stage after heat treatment for joining a honeycomb structure constituted of the thin steel or foil of a ferritic stainless steel in which a gamma phase is formed at a high temp., cooling is executed for >=7min from 850 to 700 deg.C, or soaking is executed for >=2min from 800 to 700 deg.C. Thus, joining heat treatment with high productivity can be executed to a honeycomb while its good material is maintained without forming a martensitic phase thereon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a metal honeycomb structure used for heat exchangers and automobile catalysts.

[0002]

2. Description of the Related Art In recent years, there have been various heat exchangers and catalyst devices for purifying exhaust gas from automobiles, in which flat plates made of heat-resistant metal and corrugated plates are alternately laminated or wound, and a honeycomb body is housed in an outer cylinder. It has been developed and has already been partially put into practical use. Further, as a joining means between the flat plate and the corrugated plate and between the outer peripheral surface of the honeycomb body and the inner surface of the outer cylinder, there is disclosed in JP-A-61-19057.
Brazing described in Japanese Patent Laid-Open No. 4-4018
Resistance welding described in Japanese Patent Laid-Open No. 0-134346.
Laser beam welding and electron beam welding described in Japanese Patent No. 2300952, U.S. Pat.
The diffusion bonding shown in the description of Japanese Patent No. 270947 is common.

As a heat-resistant metal material, Japanese Patent Publication No. 58-2
Fe-Cr-Al alloy foils having excellent oxidation resistance, which are disclosed in Japanese Patent No. 3138, Japanese Patent Publication No. 54-15035, Japanese Patent Laid-Open No. 56-96726, etc., have been used.
Since these Fe-Cr-Al alloy steels are difficult to manufacture and generally expensive, for those used in environments other than those requiring high heat resistance,
The cheaper Cr-based or Cr-Si-based stainless steels are beginning to be used. The present inventors have previously proposed a technique for obtaining a honeycomb body by diffusion bonding using Cr—Si type stainless steel in Japanese Patent Application No. 05-24517.

The stainless steel used for these honeycomb bodies is heated to a temperature of 1000 ° C. or higher by a heat treatment for brazing or diffusion bonding, but it is a low-cost material such as Cr-C.
In the temperature range of r-Si heat-resistant stainless steel, α-
Some have a two-phase structure of γ. These joinings are usually performed using a vacuum furnace, which requires a high process cost, but after the joining is completed, He, Ar, and N are placed in the vacuum furnace to increase manufacturing efficiency.
It is cooled rapidly by introducing cooling gas such as ₂ .

When a honeycomb structure made of the above-mentioned material having a two-phase structure at a high temperature is rapidly cooled in a vacuum furnace, its metal structure contains a martensite phase, and the honeycomb structure becomes hard and brittle. Even if a slight mechanical deformation is applied in the subsequent process, defects such as cracks will occur. In order to avoid this, if cooling is gradually performed from the bonding temperature, it takes time to cool and the productivity is impaired.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides an efficient cooling method which does not generate a martensite phase harmful to the material in the cooling process after the above-mentioned joining heat treatment and does not prolong the cooling time so much. To do.

[0007]

DISCLOSURE OF THE INVENTION The present invention made to solve the above-mentioned problems is to provide a structure after a heat treatment for joining a honeycomb structure made of a ferritic stainless steel thin plate or foil that produces a γ phase at high temperature. 850 ℃ in the cooling process
The method for cooling a honeycomb structure is characterized in that the cooling from the temperature of 1 to the temperature of 700 ° C. is performed over 7 minutes or more. Then, as a method for more reliably performing this treatment on a large amount of honeycomb structures in an actual heat treatment furnace, it is effective to carry out soaking for 2 minutes or more during the cooling process at 800 to 700 ° C. Then, at a temperature other than this temperature, quenching with the introduced gas may be performed.

By cooling in this way, the γ phase generated at a high temperature of 1000 ° C. or higher for brazing and diffusion bonding is completely decomposed into α phase and Cr carbide between 850 ° C. and 700 ° C. Even if the steel is cooled to a temperature below the Ms point at a high speed, a martensite phase does not occur, and brittleness of the metal honeycomb can be avoided. 850 here
The reason why we chose to cool slowly between ℃ and 700 ℃ is that if the temperature exceeds 850 ℃, the driving force to transform the γ phase into α phase and Cr carbide is weak and it takes a long time to transform. Then, atomic vibration becomes inactive, and it takes time to transfer to α + carbide which is in the equilibrium state.

Further, the reason why the temperature lowering time in the above temperature range is set to 7 minutes or more is to surely decompose the γ phase into the α phase and the Cr carbide, and the upper limit is not particularly specified, but it may be within 1 hour. It is preferable for efficiency. Further, the same effect as described above can be obtained by performing soaking for holding at a predetermined temperature within the above temperature range for 2 minutes or more, but the upper limit time is 1 for efficiency.
It is preferably within the time.

Next, specific examples of the present invention will be described with reference to examples.

[0011]

【Example】

Example 1 A stainless steel foil having a chemical composition shown in Table 1 and having a thickness of 50 μm was prepared, and a flat foil and a corrugated flat foil were superposed and wound to form a 100φ × 90 l honeycomb. This was press-fitted into an outer cylinder of 19% Cr steel having a thickness of 1.5 tons, heated to 1200 ° C. in vacuum for diffusion bonding between the honeycombs and between the honeycomb and the outer cylinder, soaked for 40 minutes, and then cooled. did. Cooling was performed by flowing Ar gas into a vacuum furnace, introducing a gas whose temperature had risen to a gas cooling device provided outside the furnace, and returning the gas to the vacuum furnace again to circulate the gas. Here, 1200 ° C. to 850 ° C. is cooled over 11 minutes, and in the temperature range from 850 ° C. to 700 ° C., the flow rate of the cooling gas is reduced and cooling is performed at each time shown in Table 2.
From ℃, increase the cooling gas flow rate again to 150 ℃ 23
It was cooled in minutes and taken out into the atmosphere. The honeycomb taken out is cut, embedded in resin and polished to observe the metal structure,
The presence or absence of a martensite phase was examined, and the results are shown in Table 2.
As shown in Table 2, there was no martensite phase in the one cooled from 850 ° C to 700 ° C over 7 minutes, and the martensite phase was recognized in the one cooled in less than 7 minutes. When the honeycomb of sample No. A in which the martensite phase was generated and the honeycomb of sample No. E in which the martensite phase was not generated were forced out of the outer cylinder by forcibly pushing the center of the honeycomb by a mechanical extrusion test, the honeycomb of sample No. A was found. Indicates brittle fracture, and sample No. E exhibits ductile fracture.

[0012]

[Table 1]

[0013]

[Table 2]

Example 2 Similar to Example 1, a flat foil and a corrugated foil were superposed and wound, and a large number of them were inserted into an outer cylinder of 19Cr steel, and a large amount of carriers were subjected to a heat treatment test. Using a large-sized vacuum heat treatment furnace, 60 carriers are arranged in a tray and these are stacked in 4 layers to make a total of 240 carriers in a vacuum.
It heated at 00 degreeC and soaked for 60 minutes. After that, it was rapidly cooled to each temperature shown in Table 3 by Ar gas, and at each temperature for 1 minute,
After soaking for 2 minutes and 5 minutes, it was rapidly cooled again. Five pieces of the carrier heat-treated under each condition were taken out from each tray and the above mechanical extrusion test was performed to examine the presence or absence of brittle fracture. The results are shown in Table 3 at 800 ° C. and 750
Those that were soaked at ℃ and 700 ℃ for 2 minutes or more showed ductile fracture, and others showed brittle fracture.

[0015]

[Table 3]

[0016]

As shown in the above examples, in the method of the present invention, in the cooling after the heat treatment of the joining of the metal honeycombs that produce the γ phase at a high temperature, the cooling is performed only between 850 and 700 ° C or at 800 to 700 ° C. By performing soaking for a short time, it is possible to shorten the cooling time without producing a martensite phase even in rapid cooling in other temperature ranges, and to provide a highly productive method for manufacturing metal honeycombs. can do.

Front Page Continuation (72) Inventor Hitoshi Ota 5-3 Tokai-cho, Tokai-shi, Aichi Nippon Steel Co., Ltd. Nagoya Steel Works

Claims (2)

[Claims] 1. A heat treatment for joining a honeycomb structure made of a ferritic stainless steel thin plate or foil which produces a γ phase at a high temperature, and then cooling from the heat treatment temperature, at a temperature of 850 ° C. to 700 ° C. A method for cooling a honeycomb structure, comprising cooling to a temperature of ° C over 7 minutes or more. 2. The cooling method according to claim 1, wherein a soaking treatment is performed for 2 minutes or more between a temperature of 800 ° C. and a temperature of 700 ° C.