JP2006297474A - JOINED BODY OF Ti-Al ALLOY AND STEEL, AND JOINING METHOD - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joining method where, when a member made of a Ti-Al alloy and a member made of steel are joined, so as to produce a joined body in which the strength of the joint is higher than the strength of the base metal, the joined body can be stably produced at a high excellent article yield even without making the control of temperature upon the joining severe. <P>SOLUTION: An intermediate material (3) produced by ferritic stainless steel having a C content of ≤0.10% is inserted between a Ti-Al alloy member (1) and a steel member (2), and Ni solder (4) is interposed between the Ti-Al alloy member and the intermediate material, so as to perform diffusion joining. The diffusion joining is carried out by performing heating to a temperature in the range from above the melting point to ≤1,150°C in a vacuum or in an inert gas atmosphere, applying the pressure of 1.5 to 7.0 MPa, and holding the conditions for 10 to 180 s. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a joined body obtained by joining a Ti-Al alloy member and a steel member, and a joining method.

For example, a turbine wheel (hot wheel) used for a turbo device of an automobile engine uses a wheel member made of a Ti-Al alloy (TiAl, Ti ₃ Al, etc.) to withstand high temperatures, and this is used for a steel shaft. After joining to the member, it is manufactured by machining. The joining of the wheel member and the shaft member requires reliability as well as the joining strength, but the conventional technique has not provided a sufficiently satisfactory result.

The Ti-Al alloy member (hereinafter referred to as “titanium member”) and the steel member (hereinafter referred to as “steel member”) were previously joined by first joining the intermediate member to the titanium member and then the intermediate member. It was based on the method of joining a steel member (patent document 1, patent document 2). However, in this case, the joining process becomes two processes, and the efficiency is not good.

Therefore, it is required to perform the joining in one step, and a method of directly joining a titanium member and a steel member using a brazing material has been developed (Patent Document 3). However, when this method is used, it is natural that diffusion bonding is performed, but it is inevitable that the components of both members sandwiching the brazing material diffuse and react with each other during brazing. When the C component in the steel member diffuses and reacts with Ti in the titanium member, brittle carbide is formed. For this reason, a joined part is weak and the product in which joining strength falls below base material strength will be made.

The applicant developed and disclosed a method of placing an “intermediate material” between a titanium member and a steel member and joining them together by friction welding (Patent Document 4). As the intermediate material, austenitic stainless steel or heat resistant steel, or a Ni-based or Co-based superalloy is used. When this bonding method is used, the problem of the formation of the above carbide does not occur.

The hot wheel manufactured in this way is subjected to thermal stress due to the thermal cycle of temperature rise and fall during use, so that especially for small ones, fatigue is caused at the joint between the titanium member and the intermediate material. The danger of destruction was pointed out. What has been proposed as a solution to the problem is friction welding using an intermediate material having a thermal expansion coefficient equivalent to that of a titanium member, specifically, an Fe-based superalloy such as Inconel 909. (Patent Document 5). In the range from room temperature to 600 ° C., the thermal expansion coefficient (8 to 10 × 10 ⁻⁶ / ° C.) of Inconel 909 is that of the titanium member (in the case of TiAl alloy) (9 to 11 × 10 ⁻⁶ / ° C.) It is almost equivalent.

However, in recent years, the use conditions of hot wheels have become more severe, and it has become difficult to be exposed to high temperatures reaching 700 ° C. The thermal expansion coefficient of Inconel 909 is at a substantially constant low value from room temperature to about 400 ° C., but when it exceeds that, it begins to increase rapidly, so the fatigue failure caused by the above-mentioned thermal cycle becomes a problem again.

As a bonding method based on the principle of diffusion bonding, the applicant inserts a “barrier material” between a titanium member and a steel member, and interposes first and second brazing materials on both sides to heat and heat the whole. A joining method for pressurization was developed (Patent Document 6). A specific example of the barrier material is a metal mainly composed of one or more of Fe, Ni, and Co, for example, a Ni-based low thermal expansion alloy having a thickness of 0.01 mm or more. As the brazing material, a Ni-based material (JIS standard BNi-3, that is, 4.5Si-3.2B-Ni) is suitable.
JP-A-2-133183 JP-A-2-157403 JP 10-118764 A JP 18-18151 JP-A-11-320132 JP 2001-205443 A

By the joining method using this barrier material, the formation of carbides in the joined portion was prevented, and a joined body in which the strength of the joined portion exceeded the strength of the base material was realized. However, when implemented, sometimes the yield of good products was low. In pursuit of the reason, one is a decrease in strength due to the formation of boride in the joint, and the other is that the preferred range of the joining conditions, particularly the heating temperature, is narrow and difficult to control to the appropriate conditions. I understood.

The first cause is the decrease in the strength of the joint due to the formation of boride. When the barrier material contains a large amount of Nb or Mo as its alloy component, they react with the B component in the Ni-based brazing material. As a result, NbB and MoB are generated. Since the barrier material requires heat resistance, superalloys are preferably used. These alloys contain a large amount of Nb and Mo as described below. (weight%)
Fe Ni Cr Mo Co Nb Ti Al
Inconel 909 balance (42) 38 13 − 4.7 1.5 0.03 −
Ni-based low thermal expansion alloy-balance 12 18--1.0 1.0

The second cause is that the above-described boride formation is likely to occur at an inadvertently raised temperature. For the heating of the joint part, induction heating by a high frequency induction coil is conveniently used, and the temperature control can be performed relatively precisely by adjusting the input power by combining with a radiation thermometer, but still The temperature range suitable for bonding is narrow, and the generation of defective products is due to the fact that this temperature control must be severe, but it is difficult. In addition, since Ni-based or Co-based superalloys are generally expensive, there is a demand for using an inexpensive alloy as a barrier material.

The purpose of the present invention is to improve the technology for joining titanium members and steel members, and to improve the yield of bonded products, in other words, the strength of the joint can be increased even if the temperature control during joining is not severe. An object of the present invention is to enable a stable supply of a joined body having a performance exceeding the strength of the base material.

The joined body of a Ti-Al alloy member (titanium member) and a steel member (steel member) according to the present invention has a titanium member (1) and a steel member ( 2) with an intermediate material (3) made of ferritic stainless steel sandwiched between the titanium member and the intermediate material and between the intermediate material and the steel member with Ni brazing (4) interposed therebetween. This is a joined body.

In the joined body of the present invention, an intermediate material of ferritic stainless steel sandwiched between a titanium member and a steel member serves as a barrier, and during the joining, the C component in the steel material diffuses to meet Ti and react to carbide. The formation of TiC is prevented and the brazing material B does not react with the barrier material Nb or Mo to form the boride NbB or MoB. As a result, it is possible to obtain a high yield of bonded products without the need for severe temperature control during bonding.

The ferritic stainless steel used as an intermediate material in the present invention has a coefficient of thermal expansion that is approximately between those of the titanium member and the steel member up to a high temperature (about 700 ° C.) region that the hot wheel can reach, It takes a value that increases as it rises. Therefore, the difference in thermal expansion coefficient between the two members and the intermediate material and the problem of thermal stress due to the rapid change in the thermal expansion coefficient of the intermediate material are alleviated, and the risk of fatigue failure is reduced. Ferritic stainless steel is also less expensive than Ni-based or Co-based superalloys.

The joining method of the present invention for providing the above-mentioned joined body is a steel member constituting a shaft and a Ti-Al alloy member which is a hot wheel, as shown in FIG. (7), wherein a sheet of intermediate material (3) made of ferritic stainless steel is sandwiched between a titanium member and a steel member, and the titanium member (6) and the intermediate material (3) And between the intermediate material (3) and the steel member (7), a foil of Ni brazing (4) is sandwiched between the intermediate member (3) and the steel member (7). It is heated to a temperature exceeding the melting point and not higher than 1150 ° C., a pressure of 1.5 to 7.0 MPa is applied, and the condition is maintained for 10 to 180 seconds.

Suitable alloy compositions of ferritic stainless steel forming the intermediate material are, by weight, C: 0.10% or less, Si: 1.5% or less, Mn: 1.5% or less, and Cr: 10.5 to 32 0.0%, P: 0.045% or less, S: 0.045% or less, Ni: 0.6% or less, with the balance being Fe and impurities. In addition to these alloy components, one or two of Ti: 0.01 to 0.5%, Nb: 0.02 to 1.0% and Mo: 0.05 to 2.0% should be contained. Can do. The reason for determining the alloy composition in this way is as follows.

C: 0.10% or less If the C content is 0.10% or less, the amount of the C component diffusing from the intermediate material itself is small, and the formation of carbide TiC due to the reaction with Ti in the titanium member is prevented. However, in order to ensure this effect, it is recommended to use C: 0.05% or less, preferably about 0.02 to 0.03%.

Si: 1.5% or less, Mn: 1.5% or less These are added as deoxidizers during the melting of steel, but if present in large amounts, the toughness is lowered, To do.

Cr: 10.5-32.0%
Cr is an important component for ferritic stainless steel, and improves oxidation resistance and high-temperature strength. This effect can be obtained by addition of 10.5% or more, but even if the addition amount is increased, it is not accompanied by this, and when it exceeds 32%, it is saturated.

P: 0.045% or less, S: 0.045% or less, Ni: 0.6% or less P and S are unavoidable impurities, and deteriorate various properties, so the content should be reduced as much as possible. The above values are acceptable limits. Since Ni is mixed with the raw material, it is stopped within the above standard value.

1 or 2 types of Ti: 0.01 to 0.5%, Nb: 0.02 to 1.0%, Mo: 0.05 to 2.0% Ti is oxidation resistance, Nb is oxidation resistance And, the high temperature strength and Mo improve the high temperature strength, respectively. As described above, these components are dangerous because the formation of carbide TiC, boride NbB, or MoB significantly reduces the strength of the joint or reduces the yield of non-defective products. However, from the viewpoint of improving the properties of the ferritic stainless steel itself at the joint, the presence of a small amount is rather preferable. Therefore, it is advisable to add an appropriate amount within the above-mentioned range selected from the viewpoint that the effect of addition is recognized and the harmful effect does not become dangerous.

If the thickness of the intermediate material is at least 0.05 mm, it serves as a barrier. If it is thinner than this, the C component of the steel material diffuses and reaches the joint surface with the titanium member to form carbide. When manufacturing intermediate materials by slicing ferritic stainless steel rods, it is desirable that the material be easy to cut, so add machinability improving elements such as Pb, Te, Se, etc. It is preferable to use a rod of free cutting steel.

It is natural from the operation of brazing that the bonding temperature must exceed at least the melting point of Ni brazing. If the upper limit of 1150 ° C. is exceeded, Ni, which is the main component in the Ni solder, reacts with TiAl of the titanium member to form a brittle intermetallic compound, so that the bonding interface becomes weak. If the pressure for pressurizing the joint surface is low, voids may occur in the joint part. On the other hand, if the pressure is high, deformation occurs during joining and blisters occur, resulting in a decrease in dimensional accuracy and an increase in the required amount of post processing. cause. There is no such problem as long as it is within the above range. If the time for holding at a constant temperature and pressure is too short, diffusion for bonding will be insufficient, and if it is too long, energy will be wasted, and the reaction between the Ni brazing component and the titanium component will occur. Therefore, the above range is set.

A turbo charger hot wheel was cast by levitation melting-precision casting using a Ti-Al alloy having the following alloy composition. As a steel member for the shaft to be joined to this, a round bar having a diameter of 17 mm and a length of 100 mm made of SCM435H steel having the following alloy composition was selected.
Ti-Al alloy: Ti-33.5Al-4.8Nb-1.0Cr-0.2Si
SCM435H: Fe-0.35C-1.0Cr-1.0Nb-0.2Mo
For the convenience of joining, it was turned into the shape shown in FIG.
Convex material: Hot wheel side, outer diameter 5.9mm x height 5mm
Concave material: Stem side, inner diameter 6.0mm x depth 7mm

Ferritic stainless steels A to D, L, and M having the alloy compositions shown in Table 1 below were prepared as intermediate materials. A to D are alloy compositions according to a preferred embodiment of the present invention, and L and M are alloy compositions outside the preferred range used for comparison. The intermediate materials of Examples and Comparative Examples were processed into a ring shape having an outer diameter of 17 mm × an inner diameter of 6 mm and a thickness of 0.5 mm. As the brazing material, JIS standard BNi-3 (Ni-4.5Si-3.2B) was used, and a ring-shaped body having an outer diameter of 17 mm × an inner diameter of 6 mm and a thickness of 0.04 mm was used.

Table 1 Weight%

Bonding was performed under the conditions listed in Table 2. No. 7 (comparative example) is a case where no intermediate material is used. The joining portion was heated by high frequency induction heating (100 kW, frequency 10 kHz). The atmosphere is Ar gas. After joining, distortion was removed by holding the joined body at 500 ° C. for 30 minutes. The joined portion of the obtained joined body was cut to a diameter of 16 mm and subjected to a tensile test at normal temperature and a torsion test at 450 ° C. (both N = 10 average value). The results are listed in Table 2 together with the standard deviation.

Table 2

The results of Table 2 show that the joined body obtained according to the present invention shows that the joint has high strength against tension and torsion, and that there is little variation in their strength characteristics, and that the joined body can be expected to have a high yield. Is shown. All fractures occurred in the base material (titanium member) and did not occur at the joint.

In addition to Alloys E and F according to the present invention, X (Inconel 909, Fe-based superalloy) and Y (Ni-based low thermal expansion alloy) used in known technologies are used as reference materials as intermediate materials. did. Their alloy compositions are as shown in Table 3. About the intermediate material F, the thing of thickness 0.5mm and the thing of 1.0mm were prepared.

Table 4 below shows a comparison of the thermal expansion coefficients (average values from room temperature to 700 ° C.) of these materials together with those of the titanium member (TiAl) and the steel member (SCM435). The thermal expansion coefficient of the ferritic stainless steel used in the present invention is approximately that of the intermediate materials E and F.

Table 3 Weight%

Table 4
Intermediate material Linear expansion coefficient α (× 10 ⁻⁶ / ° C.)
Titanium member (TiAl) 11.6
Steel member (SCM435) 14.1
Intermediate material E (ferritic stainless steel) 12.5
Intermediate material F (ferritic stainless steel) 12.3
Intermediate material X (Inconel 909) 11.6
Intermediate material Y (low thermal expansion alloy) 13.4

Other than that, the Ti-Al alloy member and the steel member were joined under the same conditions as in Example 1, and the same test was performed. The results are shown in Table 5.

Table 5

As described above, the production of a hot wheel for a turbocharger of an automobile engine has been described. However, the present invention can be applied to the production of a turbine rotor (cold wheel), as well as the joining of an engine valve head and a stem, and titanium. The present invention has a wide range of applications regarding diffusion bonding of members and steel members.

The side view which shows notionally the structure about the joined body of the member made from Ti-Al alloy of this invention, and the member made from steel. Sectional drawing which showed arrangement | positioning of each member just before joining for the case where the turbine wheel of a turbo engine is manufactured as an example in order to demonstrate the joining method of this invention.

Explanation of symbols

1 Ti-Al alloy member (titanium member)
2 Steel members (steel members)
3 Intermediate material 4 Ni brazing material 6 Turbine wheel (hot wheel)
7 Shaft members

Claims (5)

A joined body of a Ti-Al alloy member and a steel member, with an intermediate material made of ferritic stainless steel sandwiched between the Ti-Al alloy member and the steel member, and a Ti-Al alloy member A joined body formed by interposing Ni brazing between the intermediate material and between the intermediate material and the steel member. Ferritic stainless steel forming intermediate material contains, by weight, C: 0.10% or less, Si: 1.5% or less, Mn: 1.5% or less, and Cr: 10.5-32.0% P: 0.045% or less, S: 0.045% or less, Ni: 0.6% or less, and the joined body according to claim 1 having an alloy composition comprising the balance of Fe and impurities. The ferritic stainless steel forming the intermediate material includes Ti: 0.01 to 0.5%, Nb: 0.02 to 1.0%, and Mo: 0.05 in addition to the alloy components defined in claim 2. The joined body according to claim 1 or 2, containing ˜2.0% of one kind or two or more kinds. The joined body according to any one of claims 1 to 3, which is a turbine wheel or a turbine rotor of an automobile engine or an engine valve. A method of joining a Ti-Al alloy member and a steel member, wherein a sheet of intermediate material made of ferritic stainless steel is sandwiched between the Ti-Al alloy member and the steel member, and the Ti-Al alloy Ni brazing foil is sandwiched between the intermediate member and the intermediate member, and between the intermediate member and the steel member, and the temperature exceeds the melting point of Ni brazing in the vacuum or in an inert gas atmosphere. A bonding method comprising heating to a temperature of 1150 ° C. or less, applying a pressure of 1.5 to 7.0 MPa, and maintaining the condition for 10 to 180 seconds.

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