JPS62227597A - Thin two-phase stainless steel strip for solid phase joining - Google Patents

Abstract

PURPOSE:To reduce the cost of joining by incorporating Fe, Cr and Ni as essential components into a thin strip and specifying Cr equiv. and Ni equiv. so as to satisfy the specific formulas and providing respectively prescribed % of solid soln. N content and alpha phase fraction to said strip. CONSTITUTION:The melt of the two-phase stainless steel contg. Fe, Cr and Ni as the essential components is so prepd. that the Cr equiv. and Ni equiv. expressed by formula I satisfies the condition formula expressed by formula II. The thin strip of the finely crystalline stainless steel is formed from such melt by quick cooling by a cooling roll method, etc. The solid soln. N content is specified to >=0.01% and the alpha phase fraction to >=80% in this stage. Such thin strip is held in place between joining stocks as cast or after cold rolling and the materials are pressurized and joined under heating in a gaseous N2 atmosphere. The superplasticity of the thin strip is easily obtd. by such method and therefore, the joint strength is improved and the cost of joining is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a ribbon for solid phase bonding using duplex stainless steel.

(Prior art) Solid phase bonding using superplastic materials is already well known [for example, ([Superplasticity and metal processing technology], edited by Superplastic Research Group (1980), Nikkan Kogyo Shimbun, Inc., p. 15
See 1)].

However, in -a, many superplastic materials are difficult to process in normal processing, so even though there is an idea for solid-phase bonding in which thin strips are sandwiched in a sandwich-like manner (Japanese Patent Application Laid-Open No. 1983-1999-1), No. 45567) Its practical application was difficult.

In the case of solid phase bonding, the material must be formed into a thin strip several millimeters thick, and conventionally known superplastic materials could not be processed in this manner at industrial cost.

(Problems to be Solved by the Invention) An object of the present invention is to provide a stainless steel ribbon for solid phase welding that does not exhibit superplasticity and eliminates the drawbacks of the prior art as described above.

(Means for Solving the Problems) Thus, after conducting various studies on materials for solid phase bonding, the present inventor found that duplex stainless steel exhibiting superplasticity was particularly excellent. Through further research, the alloy composition was specified, and if there were problems with workability, it was formed into a thin strip by direct forming from the molten metal, resulting in effective superplasticity and forming. Knowing this, he completed the present invention.

Here, the gist of the present invention is that Fe5CrsN
Contains i as a main component, Cr eq = Cr + Mo +
1.5Si, Ni eq = Nt+o, s Mn+3
Cr eq and Ni eq represented by 00+25N satisfy the following formula, and 0.32 Cr eq-5≦N1eq≦
0.79 Cr eq 8.616≦Cr eq≦3
5. The present invention is a two-phase stainless steel ribbon for solid phase bonding, in which the amount of solid solute N is 0.01% or more and the α phase fraction is 80% or more.

According to one aspect of the invention, the ribbon is formed directly from the molten metal, preferably by rapid solidification. The upper limit of the thickness of the thin ribbon is preferably 2 mm, since the thinner the thinner the thinner the cooling rate, the more efficient the bonding will be. There is no particular lower limit, but for reasons of manufacturing the quenched ribbon, it is 20.
It becomes μm.

According to rapid solidification, ribbons with a thickness of 21 mm or less can be produced without any problem. Moreover, superplasticity is more advantageously expressed by making the material microcrystalline due to rapid solidification. When using the rapid solidification method, it is necessary to adjust the cooling rate so that the α phase fraction of the resulting duplex stainless steel is 80% by volume or more. In addition, in the equilibrium state, the α phase fraction is 2
It is 0-80%.

As described above, the present invention preferably provides a ribbon with excellent superplasticity produced directly from a molten metal by rapid solidification,
By using this, it is possible to further improve adhesion due to the excellent lump formation based on its effective superplasticity, and to enable a diffusion bonding method in which the diffusion distance required for bonding is extremely short. .

(Function) Next, the reason why the alloy composition is limited as described above in the present invention will be described.

First, Ni eq and Cre limited as described above
q defines the range in which the ratio of α/(α+γ) is 0.2 to 0.8 in an equilibrium state under solid phase bonding conditions of 750 to 1200°C, and as long as such conditions are satisfied, , α/(α+γ) = 0.
2 to 0.8 is satisfied, and superplasticity is achieved. Preferably, 0.4 Cr eq −4≦N1eq ≦0.6
Cr eq-7, and Cr eq -20 to 30.

The reason why Cr eq and Ni eq are first defined as described above is to obtain the Cr-equivalent equivalent of the ferrite-forming element and the Ni-equivalent equivalent of the austenite-forming element, respectively, as is clear from what has already been said.

In the case of the present invention, each of Cr and Ni is defined as described above in order to adjust the two-phase structure.

In addition, the reason why they are limited to the above-mentioned range is that within this range, the structure becomes a two-phase structure of α phase and T phase, and the ratio of α phase is 0.2 to 0.8 in the equilibrium state during solid phase bonding. This is because excellent superplasticity can be obtained. Preferably, this alpha phase fraction is 5
0-75% body weight.

The main component of the duplex stainless steel used in the present invention is F
es Cr and Ni were selected because although it is possible to obtain a two-phase mixed structure of α phase and T phase by combining other elements, considering the properties and cost of the resulting material. This is because it is more advantageous to have three elements as main components: , Fe, Cr, and Ni, and preferably,
The duplex stainless steel targeted by the present invention contains N by weight%.
i: 3 to 18%, Cr: 15 to 35%, and in addition to these components, if necessary, MoS 2.0%, Cu≦
1.0%, Ti≦0.5%, ZrS2.5%, Nb50
．． 5%, V 60.5%, w≦t, o%, Co≦0.
5%, and at least one of C50.1%,
Or furthermore, SiS2.0% and MnS2.0%
Those containing one or more of the following, or a small amount of Re,
Those containing Ce, La, or Ca are also included. The remainder is Fe and unavoidable impurities.

In addition, in order to express superplasticity, it is preferable that the solid solution N content is high, and when Ti, Zr, etc. are added,
Practically solid? It is preferable to limit 8N≧0.01% because it is an austenite-forming element in order to develop superplasticity during solid phase bonding, and unless the amount of diffused N is increased, the γ phase will This is because uniform spherical dispersion is difficult to occur and the lower limit is 0.01%.

C is not particularly limited, but it is best to reduce it as much as possible since it generates carbides and impairs the properties of the product. Preferably it is C50.05%.

More preferably, the duplex stainless steel used in the present invention has Ni: 3.5 to 9.0%, Cr
:17~27%, Mo:1.0~4.0%, N:0.0
5-0.25% and 0.5-1.5% as deoxidizer
a small amount of St and/or Mn, and the balance F
Although the composition consists of E and unavoidable impurities, more St or Mn may be actively added depending on the required corrosion resistance and other properties.

However, as described above, in the present invention, the α+γ type 2 exhibits an α phase fraction of 20 to 80% in an equilibrium state during bonding.
As long as it exhibits a phase-m weave, its excellent superplasticity phenomenon can be utilized, and it has been confirmed that the addition of the various additive elements described above does not substantially change the α+γ type two-phase structure.

According to a preferred embodiment of the invention, the steel thus prepared is rapidly cooled from a molten metal into a ribbon.

The method of manufacturing the ribbon according to the present invention is not particularly limited, but considering that two-phase materials are generally difficult to process, rapid solidification is preferred, and ordinary single roll, double roll or other methods are preferred. Applicable. Although the cooling rate is not particularly limited! If the I-weave becomes fine, the subsequent superplastic deformability will be improved, so it is preferable that the amount of α phase after quenching be 80% by volume or more, and therefore the cooling rate is preferably 100°C/sec or more. More preferably, it is 103° C./sec or higher.

Since the amount of α phase increases as the cooling rate increases, it can be used as a guideline for the cooling rate. In this way, after quenching, the amount of α phase in volume% was reduced to 8
The reason why it is set to 0% or more is to make it easier to develop superplasticity by precipitating a large number of fine γ grains when heated to the bonding temperature.If the γ phase is present in excess of 20%, they will become coarse and become superplastic. This is because it is harmful.

The thin strip obtained in this way can be used as is for solid phase bonding, but it may also be subjected to cold working etc. in order to improve the plate surface properties and further refine the structure in the subsequent process. . These treatments significantly refine the structure through recrystallization during solid phase welding and improve superplasticity, but it is preferable to apply cold working at a reduction rate of 20% or more.

When performing in-phase welding using the solid-phase welding ribbon obtained according to the present invention, first make the joining surface a clean surface, and then
Bonding may be performed while heating to 00° C. and applying a pressure of, for example, 0.5 kgf/m+m” or more.

The reason why the temperature is limited to 750 to 1200°C is that it is easy to obtain the superplasticity of duplex stainless steel in this range, and the structure of the solid phase joining material will not become coarse and its original properties will not be impaired. It is from. More preferably 900-11
It is preferable to set the temperature to 00°C.

The heating may be performed by such a method, but in order to prevent scaling, it is preferable to perform heating in an Nt gas atmosphere containing a large amount of nitrogen, which is contained in a large amount in two-phase stainless steel.

The compressive force for bonding is, for example, 0.5 kgf/nm"
As mentioned above, if it is too large, buckling and deformation will increase, so it is desirable to keep it below 10 kgf/mm''.

Duplex stainless steel that has been joined by heating and pressurization is cooled as is, but if intermetallic compounds such as sigma phase are formed during cooling, the subsequent toughness will be significantly impaired.
Cool at a cooling rate of ℃/min or higher, preferably 1000℃
It is preferable to rapidly cool the material after processing at around 1200 DEG C., since this is substantially the same as solution treatment.

The material used for bonding is not particularly limited, but iron-based alloys that have good diffusion bonding properties and are less likely to produce Kirkendall voids caused by significant differences in diffusion rates between different elements are preferred, such as low-alloy steel, austenitic stainless steel, and ferritic stainless steel. Steel can be applied, and Ni-based alloys can also be applied.

Next, the present invention will be explained in further detail with reference to Examples, but these are merely shown as examples of the present invention, and the present invention is not unduly limited thereby.

EXAMPLE A molten metal having the chemical composition shown in Table 1 was deposited on the surface of two cemented carbide rolls with a diameter of 3001III11 or a single roll made of Cu with a diameter of 400 mm rotating at 20 to 200 rpm.
Sprayed from a nozzle with a diameter of 5 x 15 mm, 50 to 30
A quenched ribbon with a thickness of 0 μm and a width of 15 mm was produced. Either as cast or after cold rolling for some of them, the above thin strips are sandwiched between various bonding materials with 15 mm diameter end faces finished with l600 emery paper and locally interfrequency applied in an N2 gas atmosphere. After heating and raising the temperature to a predetermined temperature, it was pressurized at a predetermined pressure for a predetermined time and allowed to cool. Thereafter, those bonded under pressure at a temperature of less than 1000°C were subjected to a prescribed heat treatment.

From these, a tensile test piece with a parallel part diameter of 10 m5 and a length of 40 mo+ was cut out and subjected to a tensile test at room temperature.

The respective conditions and test results are summarized in Table 2, and it can be seen that solid phase bonding is easily performed according to the present invention.

Claims (3)

[Claims] (1) Contains Fe, Cr, and Ni as main components, and contains Cre
q=Cr+Mo+1.5Si, Nieq=Ni+0.5
Creq and Nie denoted by Mn+30C+25N
q satisfies the following formula, 0.32Creq-5≦Nieq≦
0.79Creq-8.616≦Creq≦35 A two-phase stainless steel ribbon for solid phase bonding, which has a solid solution N content of 0.01% or more and an α phase fraction of 80% or more. (2) A two-phase stainless steel ribbon for solid-phase bonding according to claim 1, which is formed into a ribbon directly from a molten metal. (3) The two-phase stainless steel ribbon for solid phase bonding according to claim 1 or 2, which has a thickness of 2 mm or less.