JPS62199277A - Diffusion joining method for stainless steel - Google Patents

Abstract

PURPOSE:To avert the deformation of materials and to obtain good joint strength by using stainless steels contg. S at a specific ratio and subjecting the same to diffusion joining at a specific temp. region in a specific atmosphere. CONSTITUTION:The stainless steels satisfying the conditions of <=0.01wt% total content of S in the steel and <=0.003wt% content of S forming unstable sulfide are used in the case of diffusion joining of the stainless steels to each other. The diffusion joining is executed at a 700-1,000 deg.C region in the nonoxidizing atmosphere of <=0.2mmHG O2 concn. The deformation of the materials is thereby averted and the good joint strength is stably obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a diffusion bonding method for bonding stainless steels of the same or different types, and particularly to a diffusion bonding method for obtaining good bondability.

<Conventional technology> Diffusion bonding is used when joining different types of stainless steel or even when joining similar materials, when significant changes in the metal structure as seen in fusion welding are not desired, and when there are internal voids or irregularly shaped passages. This technology is indispensable for manufacturing mechanical parts that are difficult to machine.

As is well known, diffusion bonding involves heating and holding two members to be joined (materials to be joined) at a required temperature while pressing them against each other with an appropriate static pressure in a vacuum or an inert gas atmosphere. Bonding is performed by diffusion of elements between members.

<Problems to be Solved by the Invention> However, such diffusion bonding requires heating to 1100° C. or higher, especially when stainless steel is used. That is, at temperatures below 1100° C., poor bonding occurs. Conventionally, the cause of this poor bonding has been that when the bonding pot is heated, chromium oxides (Or, zo, i) are generated at the stainless steel bonding interface due to an oxidation reaction caused by oxygen remaining in the atmosphere, and this is due to the high It was thought that this was due to its stability, which inhibits the mutual diffusion of elements between the two wave bonding materials.

Setting the heating temperature to such a high level not only causes equipment problems, but also causes significant deformation of the material during bonding, resulting in a significant loss of stability in the bonding operation.

SUMMARY OF THE INVENTION The object of the present invention is to provide a diffusion bonding method for stainless steel, which can suppress the heating temperature to a low level, eliminate the above disadvantages, and obtain a good external bonding state.

<Means/effects to solve the problem> Non-inventors,
As a result of detailed experiments and research using Auger electron spectroscopy, etc., we found that the cause of bonding defects in diffusion bonding of stainless steel 11Y1 was not actually chromium oxide as previously thought, but in the stainless steel as the material to be bonded. It has been found that the occurrence of bonding defects is due to the unstable sulfides present, and the following mechanism is responsible for the occurrence of bonding defects.

That is, during diffusion rubbing, stainless steel is heated in an inert gas or in a vacuum of 10-' Torr or more (normally industrially possible level /I/).
In this case, MnS, N3-8.
Unstable sulfides such as FeS (hereinafter referred to as tvins for brevity) react with oxygen remaining in the atmosphere (F) as shown in the following formula, MnS + O → Mn○1S. 3. This reaction occurs on and near the stainless steel surface (at a depth on the order of -crystal grains), but when this reaction occurs, the generated free S segregates at the stainless steel joint interface, This causes the above reaction with iron and chromium, and with oxygen (Fe, Cr)O+S-+(Fe, Cr')O-8, resulting in the production of a eutectic of Fe-0r-s-o. becomes.

This eutectic has a melting point of about 900 to 940°C,
If heated above this temperature, the material becomes molten and wets the bonding interface, deteriorating bonding properties and causing bonding failure.

Based on this fact, as a countermeasure for bonding failure in diffusion bonding of stainless steel, it is necessary to reduce the amount of unstable sulfides such as MnS in the stainless steel as the material to be joined.
In other words, it is possible to reduce the amount of S that forms unstable sulfides.

The inventors of the present invention have diligently studied specific measures against poor bonding from the perspective of reducing S, and have found that unstable sulfide formation S1 (hereinafter referred to as free S amount) in stainless steel has been reduced to 0.00 awt, %.
If it is reduced to below, it is possible to stably obtain a good joint state while avoiding problems such as deformation of the materials to be joined by low-humidity heating at 1000°C or less, and such a reduction in free S fi = Adjustment of absolute S amount or rare earth elements (Ca, Mg.

It has been found that this can be achieved by fixing the amount of S by adding Ce, La, Y).

In other words, the non-invention is based on such knowledge, and the 9th point is that in diffusion welding of stainless steel, the total S amount in the wire <: 0.01W as the material to be joined.
Using stainless steel that satisfies the conditions of free S content < 0.008W↑・% and an Ox concentration of 02 I-(g
700-1000℃ in the following non-oxidizing atmosphere
The present invention provides a diffusion bonding method for stainless steel, characterized in that diffusion bonding is performed in a 7M ut range.

Here, [free S-1-J] refers to S reeds that form unstable sulfides as mentioned above, and these unstable sulfides include MnS, NiS, etc. , F(βS, etc.) Qualitatively, when oxygen is supplied under a temperature condition of 700 to 1000°C, a metal element combines with the oxygen to liberate S.

Further, "satisfying the condition of free S amount <0.00 a wt, %" specifically refers to either of the following (■) or (■).

■ Reducing the absolute amount of S in steel, that is, the total S amount itself, to less than o, oosw↑・% without using special S-fixing elements; ■ Adding rare earth elements to convert S in steel into stable sulfides, In other words, by fixing it as a sulfide that is stable even in the temperature range of 700 to 1000°C, the self-r11s-t can be reduced to 0.008 wt% or less. In the case of ■, all Si becomes free Si, and in the case of ■ In this case, the amount obtained by subtracting the non-fixed amount due to rare earth elements from the total amount of S in the steel is the free amount.

Hereinafter, the method of the present invention will be explained specifically and in detail.

・In the method of the present invention, the total S amount in the steel (0.01 Wt, %, free S amount < o, o o s w
Use stainless steel that satisfies the t% condition.

There is no particular question regarding the basic M fi+i of stainless steel. Either ferritic or austenitic material may be used, specifically 5US48o, 5US444.5
US405.5UH809,5UH810゜5US30
4,5US816,5US817,5US821.5U
S847 etc. are used.

It goes without saying that the combination of the materials (steel types) of the materials to be joined may be of the same type or of different types.

Regarding the above conditions regarding S in steel, free S amount: As explained earlier, this refers to the amount of S that forms unstable sulfides such as MnS. The amount increases, leading to poor bonding. Therefore, it is necessary to limit the amount to 0.008 wt% or less. It is particularly effective to limit the free Si to 0.001 Wt.% or less.

Specific means for achieving the condition of free S % <0.008 W↑1% include: (1) The absolute amount of S in the steel (total S amount) is set to 0.008 wt.% or less. Total S amount <0. Oo a wt, % is at a level that is sufficiently possible by applying the currently known A, OD Seijui, etc.

■ Total S@ in the reserve is allowed at 0.01Wt, %, Ca,
Mg.

By adding Ce, La, and Y singly or in combination to stably fix S as sulfide, free S3 can be converted to o, o.
o s wt,% or less. Examples of S-fixed elements include Ca0O1~002W↑・%, MgO,
008~0.015Wt, %, Ce o, o 8~0
．． 04W1-,%, La003~0.04Wt,%,
Y0.02~o, oawt% is excessive. The lower limit of each element is the minimum necessary amount determined from the chemical equivalent of each sulfide, and the total S weight is 0.01 wt%.
This is the limit amount that can achieve the amount of free S <0008 wt,% under the conditions. Furthermore, additions exceeding the respective upper limits are not only unnecessary for effectiveness, but also may cause welding defects during welding work.

If the total S amount exceeds 0.01 wt%, the amount of sulfide inclusions will increase, resulting in deterioration of pitting corrosion resistance.

- In the method of the present invention, the materials to be joined are set as described above, and the materials are heated to a temperature range of 700 to 1000°C in a non-oxidizing atmosphere with an 02 concentration of 0.2 fi Hg or less to perform diffusion bonding. It is something to do.

The 0.2 concentration as the bonding atmosphere condition is 02aH.
If it exceeds g, oxidation occurs at the bonding interface due to heating, and the analysis of the free #S at the same interface tends to be promoted, so that sufficient bonding performance cannot be expected. The present invention's condition of 0.2 MHg or less is much looser than the conventionally required condition of 0.01 MHg or less. Relaxation of this condition is brought about by implementing the above-mentioned measures for stainless steel as the material to be joined.

Regarding the heating temperature, when using stainless steel that satisfies the conditions of the present invention regarding S in steel, 100
Sufficient bonding can be obtained by heating at a low temperature of 0° C. or lower. If the heating temperature is 1000° C. or less, the problem of deformation of the materials to be joined that accompanies conventional joining can be avoided.

However, in order to effectively promote the interdiffusion of elements between the materials to be joined and to achieve sufficient joining within the time required for practical punching, a heating temperature of at least 700° C. is required.

The heating retention time varies depending on the temperature, but is approximately 1000
C. and 700.degree. C. for about 10 minutes or more, and if this is exceeded significantly, workability deteriorates and the amount of deformation of the materials to be joined becomes large, which poses a problem.

However, the pressure applied between the two front welding materials during joining is 0.2 of the yield strength of the two front welding materials at the welding temperature.
A value of about 0.8 to 0.8 is good; applying too much pressure will cause significant deformation of the material, which is not good.

<Example> Based on the various stainless steels shown in Table 1, the S amount and additive components (Ca, Mg, Ce, La, Y) t
The diameter of the parallel part is 81 mm and the diameter of the parallel part is 14 mm only on one side by machining from steel with various v conditions as shown in Table 2.
Bar sample with M thread (corresponding to half of the tensile test piece)
was collected.

Using these various rod-shaped samples, the side end surfaces of the parallel parts were brought into pressure contact with each other by applying 8 static pressures using the same type of material or a combination of different types of materials, and diffusion was performed under various conditions of atmosphere Or concentration and heating temperature shown in Table 2. Welded. The heating holding time was 80 minutes in all cases.

The obtained bonded product (in the form of a tensile test piece) was subjected to a tensile test, and the quality of bondability was determined based on the form of fracture.

The results were as shown in the right column of Table 2.

As is clear from the same table, based on the invention, stainless steel as a material to be joined (sample) is
ku0003WtX, ■Total S weight 0.01wt,%+r
CaO, 01-0.02Wt, %, Mgo, oos
~0.015 Wt,%, CeO,08~o,o
4 wt, %, T, a 0.08-0.04 wt%
, Yll, 02~o, oawt% added alone or in combination to reduce free S amount < o, o, o a Wt,%, ■, ■
In the present invention example (X/), in which either of the conditions was satisfied and the bonding conditions were set at 0 concentration O2 llmHg or less and the heating temperature 700 to 1000°C, all bonding properties were maintained regardless of the combination of materials. A good result was shown. Furthermore, in these cases, the deformation of the material due to bonding was extremely small.

On the other hand, in Comparative Examples (X, 2), the bonding strength was 1t except for the case where the heating temperature was set to a temperature exceeding the non-invention range (conditions excluding the heating temperature were within the invention range). .

If the heating temperature exceeds the non-invention range, the material deforms significantly during bonding, and a good bonding pattern cannot be obtained.

<Effects of the Invention> As is clear from the above description, the present invention lowers the heating temperature to avoid material deformation as much as possible in diffusion bonding of stainless steel, and stably obtains good bonding strength. Therefore, the present invention greatly contributes to expanding the scope of application of the industrially very useful diffusion bonding method.

Claims (1)

[Claims] (1) In the case of diffusion bonding stainless steels of the same or different types, the total S content in the steel must be ≤0.
01wt% and the amount of S forming unstable sulfides ≦0
．． Using stainless steel that satisfies the condition of 0.003wt%,
A method for diffusion bonding stainless steel, characterized in that diffusion bonding is performed in a temperature range of 700 to 1000° C. in a non-oxidizing atmosphere with an O_2 concentration of 0.2 mmHg or less.