JPH06179093A - Welding method for steel disk part - Google Patents

Abstract

PURPOSE:To efficiently improve stress in the range heated in the vicinity of a weld zone and to improve reliability of the weld zone by cooling rapidly the surface to be treated after the lapse of a time when the temperature difference in the thickness direction of a steel wall is reduced. CONSTITUTION:The interval between a round hole-shaped welding groove 1b provided on steel 1 and the peripheral part of a nozzle stud 2 which is fitting material fitted into this is welded by the weld zone 3. The steel 1 is maintained in a high-temperature state by heat transmission at the time of welding and the surface 7 to be treated is cooled rapidly after the lapse of a time when the temperature difference in the thickness direction of the wall 1a of the steel 1 is reduced. A cooling water supply means 4 for rapid cooling is provided with a water supply pump, etc., supplies the pressurized water in a low- temperature state to a spray nozzle 6 via a water supply pipe 5 and this is jetted in a spray shape as shown by the arrow toward the inside of a base pipe 1. Consequently, labor at the time of executing stress improvement is reduced which can be easily carried out in accordance with welding work.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding a steel disc portion.

[0002]

2. Description of the Related Art When fitting a mounting material such as a disc into a round hole-shaped welding groove formed in a steel material such as a stainless steel plate or a steel pipe, and welding between the welding groove and the mounting material, Due to the heat shrinkage of the weld metal, a tensile residual stress is applied to the weld and its vicinity.

[0003] Conventionally, it has been said that it is effective to carry out a welding operation while cooling a steel material for the purpose of reducing the tensile residual stress caused by the shrinkage of the weld metal and suppressing the occurrence of welding distortion.

[0004]

However, according to the above-mentioned method and the like, the residual welded portion of the mounting material such as a disc cannot be compressed to residual stress, and stress annealing or residual stress after welding is not achieved. Special reprocessing is required to improve stress.

The present invention has been made in view of such circumstances, and an object thereof is to introduce a compressive residual stress by a relatively simple operation.

[0006]

In order to achieve the above object, in the method for welding a steel disk portion according to the present invention, a circular hole-shaped welding groove and a welding groove formed in a steel material are fitted. The process of welding the outer surface of the attached mounting material, and the time to maintain the high temperature state of the steel material due to heat transfer during welding and to reduce the temperature difference in the thickness direction of the wall of the steel material A structure having a step of quenching is adopted.

[0007]

When the weld groove and the attachment material are welded, the welding material heats the steel material and the like to raise the temperature. Immediately after the weld is formed, the temperature difference between the high temperature part and the low temperature part near the steel before heating increases for a short time, but the temperature of the steel wall gradually averages over time. To do.
When the surface to be treated is rapidly cooled when the temperature difference in the wall thickness direction becomes small, stress exceeding the yield point is generated near the rapidly cooled surface based on the temperature difference between the rapidly cooled surface and the internal temperature of the wall. Part of the wall is plastically deformed. Then, when the temperature difference between the inside and the outside of the wall disappears based on the cooling of the wall, the improvement state is achieved in which the compressive residual stress is introduced into the surface to be processed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a welding method for a steel disk portion according to the present invention will be described below with reference to FIGS. In these FIG. 1, reference numeral 1 is a mother pipe (steel material), 2 is a nozzle (mounting material), 3 is a welded portion, 4 is a cooling water supply means, 5 is a water supply pipe, 6 is a spray nozzle, and 7 is a cover. It is the processing side.

The mother tube 1 is, for example, an austenitic stainless steel tube, and a wall (tube wall) 1a is provided with a round hole-shaped welding groove 1b for mounting the nozzle base 2, and the welding groove 1b is formed. 1b, the base portion of the nozzle stub 2 in the fitted state is the welded portion 3
Mounted by.

The cooling water supply means 4 is equipped with a water supply pump or the like, supplies pressurized water in a low temperature state to the spray nozzle 6 via the water supply pipe 5, and is shown by an arrow toward the inner surface of the mother pipe 1. It is to be sprayed like this.

An example of the steps of carrying out the welding method will be described below. The mother tube 1 shown in FIG. 1 is a 12-inch schedule 1
00 (outer diameter 318.5 mm, wall thickness 21.4 mm)
When the nozzle pipe 2 having a small diameter nozzle is attached to the mother pipe 1 and welded, a welding hole 1b having a round hole is formed in the mother pipe 1 and the nozzle 2 is attached to the welding groove 1b. With the base inserted, the weld groove 3 is formed by welding between the welding groove 1b and the outer periphery of the base of the nozzle 2.

At this time, if the ordinary welding is left as it is, a tensile force of ^{20 to} 50 kg / mm ² is pulled in the vicinity of the welded portion 3 (the surface 7 to be treated) as shown by a broken line curve in FIG. The residual stress is applied, which causes stress corrosion cracking and the like.

Therefore, normal welding is carried out before reaching the final layer, and the welding beads fx, fy,
When forming fz, the temperature between passes is set to 80 to 120 ° C., which is slightly higher, and the welding heat input is also set to 10 to 20 kilojoules / cm, which is slightly higher. After the time required for distribution (for example, 1 to 2 minutes, a time set by the thickness of the tube wall of the mother tube 1 as described later), the cooling water supply means 4 is operated to cause the spray nozzle 6 to operate. Cooling water is spouted to cool the inner surface of the mother pipe 1 where the residual stress is to be improved. In this case, the ejection amount of the cooling water is set to, for example, 10 to 20 liters / second, and the cooling is continued until the outer surface temperature becomes close to room temperature (maximum room temperature + 50 ° C.).

The wall 1a of the mother tube 1 is in a high temperature state (100 to 20).
(0 ° C. or higher) and when the temperature difference in the thickness direction of the wall 1a becomes small, the surface to be processed (inner surface of the pipe) 7 is rapidly cooled to cool the wall 1a.
When the temperature is decreased to near the temperature of the cooling water, tensile stress is applied to the vicinity of the surface 7 to be processed of the wall 1a and plastic deformation occurs. Next, when the wall 1a is continuously cooled to reach a low temperature state such as room temperature and the temperature difference between the inside and outside of the wall 1a disappears, a compressive residual stress is introduced into the surface 7 to be processed.

In more detail with reference to FIGS. 3 to 7, as shown in FIG. 3, when the disc-shaped attachment material 2 is attached to the weld groove 1b of the steel material 1 by the weld portion 3, a plurality of weld beads are used. When the welded portion 3 is formed by superimposing the two, the heat input for welding heats the vicinity of the welded portion 3 of the steel material 1 and the attachment material 2. In the temperature distribution immediately after the formation of the final weld bead, as shown by the curve in FIG. 4, the front side has a high temperature and the back side has a low temperature.
Heat is transferred from the high temperature side to the low temperature side with the lapse of time, and a temperature averaging phenomenon occurs in which the temperature distribution changes in the order shown by the curve in FIG.

When the state of the curve is reached, as shown in FIG. 5, the temperature distribution in the radial direction is such that the outer side of the welded portion 3 is heated almost uniformly. The thermal stress (σ1) applied to the high temperature part in this state is the average temperature Tav
Then, approximately, σ1 =-(1/2) Εα (Tav-To) (Equation 1). However, E: modulus of longitudinal elasticity (kg / mm ² ) α: coefficient of linear expansion (° C. ⁻¹ ) To: temperature of low temperature part (° C.) In this state, when one surface (inner surface) of the steel material 1 is rapidly cooled by spray injection of cooling water, the temperature distribution changes from a curve to a curve in FIG. That is, the temperature distribution state of the curve is obtained by rapidly cooling only one surface from the temperature distribution state of the curve.

Thermal stress (σ ₂ ) in the temperature distribution state of the curve
Becomes σ ₂ = Εα (Tav-To) / (1-ν) ... Equation (2). However, ν: Poisson's ratio. Therefore, the combined stress of both is σ = σ ₁ + σ ₂ = (1/2) Εα (Tav-To) {-1 + 2 / (1-ν)} = (1 + ν) Εα (Tav-To) / {2 ( 1-ν)}. In the case of austenitic stainless steel, E = 1.98 × 10 ⁴ kg / mm ² α = 1.68 × 10 ⁻⁵ / ° C. ν = 0.3.

When the temperature difference between the inner and outer layers of the wall is 100 ° C., Tav is about 150 ° C. When the temperature To of the cooling water is 20 ° C., σ = (1 + 0.3) × 1.98 × 10 ⁴ × 1.68 × 10 ⁻⁵ × (150−20) / {2 (1−0.3)} = 40.2 kg / mm ² Is. This stress value is the yield stress of stainless steel σ y =
It greatly exceeds 24 kg / mm ² , and compressive residual stress occurs on the inner surface.

The relationship between strain and stress caused by temperature change will be described with reference to FIG. 7. When the temperature distribution is uniform in the plate thickness direction as shown by Tav in FIG. Although there is a stress-strain relationship located at a point, when the back surface is rapidly cooled, tensile thermal strain exceeding the yield stress occurs on the cooling surface, and the stress-strain distribution corresponding to the temperature distribution of the curve shown in FIG. Then, the point b shifts to the point c. After that, as the whole plate is cooled, from point c to d
In the state after the transition to the point and complete cooling, the state of the curve shown in FIG. 6 (the state where the macroscopic strain is zero) is reached, and a compressive residual stress is generated.

FIG. 8 shows another application example of the welding method for the steel disc portion according to the present invention, in which the weld bead layers in the welded portion 3 are superposed in the pipe axial direction of the mother pipe 1. . Even in this case, with respect to the treated surface (inner surface of the pipe) 7, 8,
Similar to the one embodiment, the residual stress can be improved at a desired location by locally performing water spray or the like and rapidly cooling.

[Other Embodiments] In the present invention, instead of the embodiment, a welded joint having a structure in which the welded portion 3 is formed along the weld groove 1b having a substantially round hole shape is used. Can be applied.

[0022]

EFFECT OF THE INVENTION In the welding method of the steel disk portion according to the present invention, when the steel material is welded in the hole formed in the steel material,
By utilizing the fact that the wall becomes hot due to heat transfer during welding, the residual stress of compression is introduced by rapidly cooling the surface to be treated after the time when the temperature difference in the thickness direction of the steel material becomes small Therefore, the following effects are achieved. (1) By utilizing the heat input of welding, it is possible to efficiently improve the stress only in the heated area in the vicinity of the welded portion with a small number of man-hours and construction period. (2) By utilizing the heat input for welding, it is possible to reduce the labor required for improving the stress and easily perform the operation accompanying the welding work.

[Brief description of drawings]

FIG. 1 is a front cross-sectional view showing an example of a state of implementation of a stress improving method for a pipe welded joint according to the present invention, in which a part of the description is omitted.

FIG. 2 is a stress curve diagram applied in the vicinity of a welded portion by the method shown in FIG.

FIG. 3 is a perspective view in which a part of a welded portion model in which a compressive residual stress is to be introduced is cut away by the stress improving method for a pipe welded joint according to the present invention.

FIG. 4 is a temperature distribution curve diagram of the model of FIG. 3 when the temperature changes.

5 is a temperature distribution curve diagram of a high temperature portion of the model of FIG.

FIG. 6 is a temperature distribution curve diagram of the model of FIG. 3 during rapid cooling.

FIG. 7 is a stress-strain curve diagram of the model of FIG.

FIG. 8 is a front sectional view in which a part of the description is omitted, showing another application example of the stress improving method for a pipe welded joint according to the present invention.

[Explanation of symbols]

 1 mother pipe (steel material) 1a wall (pipe wall) 1b welding groove 2 nozzle base (mounting material) 3 welded portion 4 cooling water supply means 5 water supply pipe 6 spray nozzle 7 treated surface (pipe inner surface) 8 treated surface ( Inner surface of pipe)

Claims (1)

[Claims] 1. A step of welding between a round groove-shaped welding groove formed in a steel material and an outer peripheral portion of a mounting material fitted in the welding groove, and a high temperature state of the steel material due to heat transfer during welding. And a step of rapidly cooling the surface to be treated after a time period during which the temperature difference in the thickness direction of the wall of the steel material becomes small while maintaining the temperature difference.