JPH038555A - Method for butt-joining steel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for butt joining steel suitable for butt joining steel pipes.

[Conventional technology]

Conventionally, manual welding has been used for circumferential welding of carbon steel pipes for piping. However, in manual welding, the welder's skill greatly influences joint performance. Therefore, the time required to repair and perform welding defects varies greatly depending on the welder. Furthermore, when manually welding the circumference of a large-diameter pipe, the wall thickness increases as the pipe diameter increases, and the number of welding passes increases accordingly, resulting in a significantly longer construction time. For this reason, liquid phase diffusion bonding has recently been developed, in which a foil-like insert material is interposed between the end faces of steel pipes, the end faces are abutted against each other, and the abutted portion is heated to melt the insert material and join the end faces together. is also used.

[Problems to be Solved by the Invention] However, when butt-joining steel pipes using the liquid phase diffusion welding method, it is necessary to cut out the foil-shaped insert material to match the end face shape. It is also necessary to fix it to the end face by spot welding etc. Therefore, the number of work hours increases, and the expected improvement in workability has not been achieved in on-site construction, and on the contrary, it has caused problems in the management of insert materials. In addition, in the liquid phase diffusion bonding method, the roughness of the surfaces to be bonded also affects the bonding strength, but it is difficult to ensure a satisfactory roughness in on-site construction.

Furthermore, there is a maximum width limit of 100 mm for both commercially available and prototype foil insert materials, and when joining steel pipes with an outer diameter exceeding 100 mm, the insert material becomes a cut and joint, making it difficult to cut and set. This makes bonding more difficult and it becomes difficult to obtain uniform bonding strength over the entire surface.

An object of the present invention is to provide a high-efficiency method for butt-joining ropes by liquid-phase diffusion welding that solves these construction problems.

[Means to solve the problem]

The butt joining method of the present invention is a steel butt joining method that includes:
Cr: 10 to 2 in weight% on at least one of the surfaces to be joined
0%, Si: 4 to 10%, B: 1 to 5%, and the remainder substantially consists of Ni) to a layer thickness of 75 to 200 μm.
m of inserts a are formed, then the surfaces to be joined are abutted against each other, and the abutted portions are heated in an inert atmosphere to a temperature exceeding the melting point of the insert layer for 60 seconds or more,
It is characterized by applying a pressing force of 0.5 kgf/mm" or more to the abutting portion.

The first factor that deteriorates workability in conventional joining methods of this type is the foil-like insert material, but in the joining method of the present invention, the insert layer is directly formed on the surfaces to be joined using powder. Therefore, all problems caused by canting, setting, cutting, etc. when using foil insert materials are solved.

Regarding the end surface roughness, which is the second factor that deteriorates workability, N
i-based powder is used. Si and B are elements that lower the melting point,
Not only does it contribute to lowering the heating temperature of the joint, but since it is an element that easily diffuses into the base material, it prevents the joint layer from becoming brittle.

In particular, since B in the Ni group causes a eutectic reaction with the base material while diffusing into the base material, the tolerance range for the surface roughness of the surfaces to be joined is expanded, and workability is further improved.

[Function] The reasons for limiting the conditions in the joining method of the present invention will be explained below. Note that % indicates weight % unless otherwise specified.

The reason why Ni-based powder is used as the powder used to form the insert layer is mainly to ease the conditions for the roughness of the surfaces to be joined, as will be described later.

The reason for adding Si and B to the Ni-based powder is that these elements contribute to lowering the melting point of the insert layer and are likely to diffuse into the base material during bonding. If Si < 4% and B < 1%, the melting point lowering effect will be insufficient, and if Si > 10% and B > 5%, it will remain in the bonding layer and cause embrittlement, so Si should be 4 to 10%.
, B was 1 to 5%. The melting points of 3124% and 821% powders are 1150'C or less.

B further contributes to increasing the viscosity of the insert layer (liquid phase), and 1
If it is less than %, the viscosity of the liquid phase increases, causing voids on the bonding interface.
Oxides are difficult to discharge and tend to remain as defects.

On the other hand, at 5% viscosity, the liquid phase is excessively discharged due to a decrease in viscosity, resulting in dripping.

Cr contributes to maintaining the viscosity of the liquid phase and improving the ductility of the bonding layer, but if it is less than 10%, these effects are weak, and if it exceeds 20%, it promotes embrittlement of the bonding layer.

Therefore, Cr was set at 10 to 20%.

The above powder is formed into an insert layer by thermal spraying, using a binder, etc., for example.

If the thickness of the insert layer is less than 75 μm, the porosity in the layer will be approximately 5% to 10% at the stage of forming the insert layer.
Moreover, due to the lack of insert material, a sufficient liquid layer cannot be formed on the interface during bonding, and conversely, if the thickness exceeds 200 μm, there will be too much overnight layer on the interface, resulting in insufficient diffusion of Si and B in the powder. 75 to 200μ, as embrittlement occurs.
It was set as m.

The insert layer may be formed on one of the surfaces to be joined, but when it is formed on both surfaces, it is desirable that the total layer thickness be 75 to 200 μm. In addition, in order to keep the porosity low, the particle size of the powder is preferably as small as possible, but it is usually 30 μm or more.
An average particle size of 40 μm is sufficient to achieve the objective.

The heating temperature of the abutting part after abutting the surfaces to be joined is set to a temperature exceeding the melting point of the powder in order to melt the insert layer, preferably about +50"C of the melting point of the powder, the melting point of the powder is 5ilO%, 84% The temperature reached 1000°C, and Si
: 4% and 81% result in 1150'C, so the desirable heating temperature range is 1050-1200°C.

Although a short heating temperature holding time is economical, it is necessary to hold the heating temperature for 6260 seconds or more in order to sufficiently diffuse Si and B, which are elements that lower the melting point, into the base material.

The reason why the pressurizing force was set to 0.5 kg f/mm" or more was to extract the pores in the insert layer (liquid layer) by IP.

From this point of view, it is desirable that the pressing force be large, but an increase in the pressing force causes plastic deformation of the materials to be joined, which impairs the appearance after joining, so in practice it is 1.5 kg f/ml11
It is desirable to limit the number to 2 or less.

The bonding atmosphere is preferably an inert atmosphere to prevent oxidation of the bonding interface, and the amount of O2 is preferably 200 pp- or less. The shielding gas used to secure the atmosphere is Nz
, Ar, etc., but from the economic point of view, N2
is desirable.

The closer the roughness of the surfaces to be joined to the mirror surface, the better the joining strength can be obtained. However, since the powder for forming the insert layer used in the joining method of the present invention is Ni-based and also contains B, it 88 While diffusing into the base material, a eutectic reaction with the base material proceeds. Therefore, if the base material is carbon steel, Fe with the same composition
The eutectic reaction is promoted more than in the case of powder-based powders, and as a result, the allowable range of surface roughness is expanded to approximately 100 μmRmax.

〔Example〕

The composition is shown in Table 1.Outer diameter: 406.4 mm, wall thickness: 7
．． 9 mark, length 600In11 carbon 8w4 tube (SGP,
100A) was cut at right angles to the tube axis, and after blasting on one end surface, the powder shown in Table 2 was sprayed to a layer thickness of 75mm.
An insert layer of ˜200 μm was formed.

The other end face is 50 μmRmax, 100 μmRm
Finished in aχ.

Thereafter, as shown in the first step, the two cut carbon steel pipes 1a+1b were fixed to clamps 2a and 2b, respectively, with their cut surfaces butted against each other.

The clamps 2a, 2b are connected to a transformer 4 via hydraulic cylinders 3a, 3b. Next, carbon steel pipe 1
A half-split coil chamber 5 was set concentrically on the outer surface side of the butt portion of a and lb. The coil chamber 5 contains a heating coil connected to the transformer 4 and an N2 gas shield mechanism, and is mechanically coupled to the transformer 4 by a hydraulic cylinder 6.

Then, while letting N2 gas flow out from the N2 gas shield mechanism in the coil chamber 5, the carbon steel pipes 1a and 1
N2 gas is passed through the chamber 5 to gas-shield the butt part of the carbon@steel pipes 1a and lb from the inner and outer sides, while the heating coil in the coil chamber 5 is energized to heat the butt part to various temperatures. It was heated and maintained at . The abutting portion thermally expands in the tube axis direction due to heating, and a pressurizing force is applied between the end faces. By changing the support rigidity of the clamps 2a, 2b, the restraining force on the carbon w4 wire pipes 1a, lb was adjusted, and the pressing force applied between the end faces was adjusted. The heating temperature and its holding time were adjusted by a high frequency power source connected to the transformer 4, and the amount of 0□ in the atmosphere was adjusted by a shielding gas meteor.

After joining, a test piece shown in Figure 2 was taken from the joint,
The test piece was subjected to a tensile test to investigate the bonding temperature. The investigation results are shown in Tables 3 and 4 together with the bonding conditions.

A1-2G is an example of the present invention, and both exhibit a bonding strength (base material fracture) of around 40 kg f 7 mm2, even though the roughness of the surfaces to be bonded is adjusted to 100 μmRmax.

On the other hand, A27 has a low bonding strength because the pressing force and the thickness of the insert layer are insufficient.

Furthermore, since the inertness of the bonding atmosphere in A2B is low, the bonding strength is low even though the surface roughness to be bonded is finished to 50 μmRmay. Since the layer thickness of A29 is insufficient, sufficient bonding strength cannot be obtained even if the pressing force is increased to 1.6 kgf/mm''.

In A31 to A44, the insert a is made of powder that does not have the powder composition defined by the present invention, and the bonding strength is low regardless of the pressing force or layer thickness. However, in A38-44, even if the pressing force is increased to 6 kgf/kaku2, sufficient bonding strength is not obtained.

〔Effect of the invention〕

The butt joining method of the present invention uses powder to insert i
, the insert material can be easily and reliably fixed to the surfaces to be joined, regardless of the shape of the surfaces to be joined. Furthermore, excellent bonding strength is guaranteed, and the tolerance range for the roughness of the surfaces to be bonded is wide. Therefore, in on-site construction at piping sites, etc., it is possible to perform joining work with outstanding reliability and workability. The effect can be enjoyed regardless of the pipe diameter, and a particularly large workability improvement effect can be obtained when piping a large diameter pipe of 200A or more.

[Brief explanation of the drawing]

FIG. 1 is an embodiment of the joining method of the present invention (schematic diagram showing the back side,
FIG. 2 is an explanatory diagram of the shape of the test piece. In the figure, la, lb: E tube, 2a, 2b: clamp, 4 Nidransu, 5; coil handle Figure 2 Figure ■ Figure a Q b b

Claims (1)

[Claims] 1. In the steel butt joining method, at least one of the surfaces to be joined has Cr: 10 to 20% and Si: 4 to 10% by weight.
%, B: 1 to 5%, and the remainder substantially consists of Ni to form an insert layer with a layer thickness of 75 to 200 μm, and then the surfaces to be joined are abutted against each other, and the abutted portion is inert. The insert layer is heated in an atmosphere to a temperature exceeding the melting point of the insert layer for 60 seconds or more, and 0.5 kgf is applied to the butt part.
A steel butt joining method characterized by applying a pressing force of /mm^2 or more.