JPH01284488A - Diffusion joining method for high alloy - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the corrosion resistance of a joint part by subjecting joint surfaces to a high nitriding treatment, then to contact heating at the time of joining the high alloys selected from an austenitic system and a two-phase high alloy contg. a specific ratio of Cr to each other. CONSTITUTION:The alloys to be applied are the austenitic system and two-phase system high alloy which contain >=15wt.% and <30wt.% Cr and are the corrosion resistant high alloys. One or both of the surfaces to be joined are subjected to the high nitriding treatment and thereafter, the surfaces to be joined are joined by contact heating. The deterioration in the corrosion resistance of the joined part is thereby prevented.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a method for bonding high alloys selected from austenitic and dual-phase high alloys after applying high nitriding treatment to the surfaces to be joined. This invention relates to a heating diffusion bonding method.

(Prior Art) Diffusion bonding is well known as one of the methods for bonding metal materials. The mechanism is: ■ Destruction of the oxide film at the bonding interface,
It is said to consist of three steps: ■ Approach of metal elements at the bonding interface, and ■ Achievement of metallic bonding and mutual diffusion. However, in reality, the oxide film at the bonding interface is often quite strong, and the formation of a new film during bonding also becomes an obstacle. Therefore, it becomes necessary to pre-treat the bonding surfaces and control the bonding atmosphere, that is, to create a high vacuum.

As a method to improve these points, a joining method has been proposed in which a low-melting point eutectic alloy is used as an insert material and is turned into a liquid phase during joining to promote removal of the oxide film at the joining interface.

It is also said that a similar effect can be obtained by coating the bonding interface with an element that forms a low melting point eutectic alloy (Japanese Unexamined Patent Publication No. 113170/1983). In this bonding method, as the heating temperature increases, the coating The layer, for example a boron (B) enriched layer, destroys the oxide film on the interface with the molten ξ base material, and over time the element in the coating layer (B in this case) diffuses to the base material side. Then, after a certain period of time has elapsed, almost no B in the coating layer disappears, and the melting point increases, so that it becomes a solid phase and the bonding is completed. Since this method uses a liquid phase, it takes a shorter time than conventional diffusion bonding, and the atmosphere can be controlled relatively easily, that is, bonding can be performed even under low vacuum.

In the conventional diffusion bonding as described above, a method using B as an element for forming a eutectic compound has been put into practical use. but,
In particular, in the joining of high alloys whose main purpose is corrosion resistance, B remaining in the joint becomes a nucleus for the formation of chromium carbide and promotes sensitization, which adversely affects the corrosion resistance of the joint and limits its application.

(Problems to be Solved by the Invention) As described above, the problem with the conventional diffusion bonding method is that the corrosion resistance of the bonded portion deteriorates due to the element added for the purpose of forming a low melting point eutectic when bonding high alloys.

An object of the present invention is to provide a high-alloy diffusion bonding method that does not deteriorate corrosion resistance and has other properties such as strength equivalent to conventional diffusion bonding.

(Means for solving the problem) Conventional diffusion bonding methods are limited to methods that utilize elements that form low melting point eutectic compounds with the main components of the alloy to be bonded, specifically P, B, etc. was.

Therefore, the present inventors conducted various studies focusing on the use of other elements in the diffusion bonding method, and found that nitrogen could be practically used as a diffusion element.

That is, high nitrogen content increases the high-temperature strength of the surface layer of the surfaces to be joined, and during contact heating, local plastic flow is accelerated on the untreated surface side, easily causing destruction of the oxide layer that is harmful to joining. In addition, the diffusion of nitrogen promotes the movement of other metal elements at the bonding interface, resulting in a bond with higher strength. As is well known, nitrogen is allowed to be added to existing austenitic and dual-phase high alloys to improve strength and corrosion resistance, and will not have a negative effect on joint performance.

Therefore, the gist of the present invention is that Cr: 15% by weight
In a method for joining high alloys selected from austenitic and duplex high alloys containing less than 30% by weight, one or both of the surfaces to be joined are subjected to high nitrogen treatment, and then the surfaces to be joined are heated in close contact. This is a high alloy diffusion bonding method characterized by bonding.

(Function) Deterioration of corrosion resistance of the joint, which is a drawback of the conventional diffusion bonding method,
Since this phenomenon is limited to high-alloy steel as a corrosion-resistant material, the applicable alloys of the present invention are austenitic and dual-phase high alloys containing 15% by weight or more and less than 30% by weight of Cr, which is a high corrosion-resistant alloy. Examples include 5IJS 304.5uS316 for austenitic systems, and SOS 329 for two-phase systems. Ferritic and 3
As is well known, in high alloys containing 0% by weight or more of Cr, the toughness deteriorates significantly due to high nitrogen content, and therefore the diffusion bonding according to the present invention cannot be applied.

Gas nitriding,
This high nitrogen concentration can be achieved by either a method such as ion implantation, in which only nitrogen is concentrated on the joint surface, or a method, such as CVD or PVD, in which a compound of nitrogen and base material main constituent elements such as Fe, Cr, or Ni is generated on the joint surface. It is sufficient to perform this on only one surface to be joined, but there is no substantial difference even if it is performed on both surfaces. Note that these means are already well known, and further explanation of their specific conditions will be omitted.

The degree of nitrogen concentration is not particularly limited, but is generally 1 to 1.
The purpose is to provide a separate nitrogen addition step to enrich nitrogen, which is preferably about 15-t%, even in the case of materials with a high nitrogen content.

The heating temperature during bonding is 1100℃ to shorten the bonding time.
or above is desirable, and if it is above 1100°C, 30
minutes is enough. In addition, the pressing force is 0.5 to 5 kgf/
■About 2 is sufficient.

Examples From high alloys having compositions A to G shown in Table 1,
A diffusion bonded test piece having the shape and dimensions shown in Fig. 1 was manufactured by machining, and the test described in 1 was conducted.

(Test 1) High nitrogen treatment shown in Table 2 was applied to one and both sides of the surfaces to be bonded at 1 mA under the following conditions, and then under the conditions shown in Table 3.
Diffusion bonding was performed by contact heating in an atmosphere.

Ion nitriding: Nitrogen ions in a plasma state are implanted into the surface to be bonded under an electric field of 300 V. The N content of the surface is g,
It was 5 wt%.

Gas nitriding: The surfaces to be joined were heated to 550° C. for 1 hour in ammonia gas, and the N content of the surface portion was 7 wt%.

Nitrogen ion implantation: The N content of the surface portion into which nitrogen ions were implanted by irradiating the surfaces to be bonded with a nitrogen ion beam generated by discharge was 15 wt%.

CVD: Cr(OCtlIs)s and N113 gas heated to 400° C. were guided to the surface to be joined, and a Cr nitride layer was formed on the surface.The N concentration of the three surface portions was 10 wt%.

PVD: Nitride was sputter-deposited using stainless steel as a target in Nt13 gas.The Nfi degree of the 6 surface layer was 8.
It was @t%.

Thereafter, a bending test piece containing the joint thus obtained (
4msoT x 10+*mW x 80mmL),
Tensile test piece (parallel part 4u+eφX 50m5+L)
, and corrosion test pieces (2 theory mT x 15 - ■φ) were taken and subjected to each test. In the bending test, close contact bending was performed to evaluate whether or not it would break. Corrosion test at 80℃
The test piece was positively scratched in a 3.5% aqueous sodium chloride solution at a sweep rate of 20 mV/sin and evaluated based on the occurrence of local corrosion.

For comparison, diffusion bonding using a normal B-containing insert material was also performed and subjected to the same test.

The results are also summarized in Table 2.

As shown in Table 2, in the conventional B-containing insert material, corrosion occurred at the joint, but in the material corresponding to the example of the present invention, the base material corroded and no deterioration in the corrosion resistance of the joint was observed. Ta.

(Test 2) One side of the surface to be welded of steel G from w4B in Table 1 was enriched with nitrogen by the same condition 1 ion implantation method as described above, and then closely heated and diffusion bonded. The bonding conditions were the same as shown in Table 3, and the bending test, tensile test, and corrosion test were conducted in the same manner as Test 1.

For comparison, a diffusion bonded portion using a conventional B-containing insert material was also tested.

The results are summarized in Table 4.

As shown in Table 4, B
Corrosion occurred at the joint in the insert material containing the insert material, but in the case of the insert material corresponding to the example of the present invention, the base metal part corroded and no deterioration in the corrosion resistance of the joint was observed.

(Leaving space below) Table 3 (Effects of the Invention) As is clear from the above, the present invention has a significant effect on preventing deterioration of corrosion resistance of joints in diffusion bonding of high alloys selected from austenitic and dual-phase high alloys. have an effect,
Therefore, it can be widely applied to equipment and structural materials used in corrosive environments such as seawater, to which conventional diffusion bonding methods could not be applied, and its utility value is great.

[Brief explanation of the drawing]

FIGS. 1A and 1B are a side view and an end view, respectively, showing the shape and dimensions (an) of a test piece used for diffusion bonding in an example.

Claims (1)

[Claims] In a method for joining high alloys selected from austenitic and dual-phase high alloys containing Cr: 15% by weight or more and less than 30% by weight, one or both of the surfaces to be joined are subjected to high nitrogen treatment, and then the surfaces to be joined are A diffusion bonding method for high alloys, which is characterized by closely heating and bonding.