JPS6176622A - Build-up welding method of subjecting thick-walled structural member - Google Patents

Abstract

PURPOSE:To relieve high residual stress produced in a thick-walled structural member when the member is subjected to a build-up welding by keeping the build-up surface of the member at a low temp. and heating the other side. CONSTITUTION:Corrosion resistant clad steel is joined to one side (inside) of a thick-walled structural member for a nuclear reactor container, etc. by the build-up welding. The build-up surface of the member is kept at a relatively low temp. by cooling, and the other side (outside) is heated to relieve high residual stress produced in the member during the build-up of the clad.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a method for welding and overlaying thick structural members such as PWR reactor vessels, and in particular to a method for welding and overlaying thick structural members such as PWR reactor vessels. Regarding how to reduce

[Conventional technology]

For example, in order to make the inner surface of a PWR reactor vessel corrosion-resistant, SUS clad steel is generally welded overlay as a corrosion-resistant material. In this clad part, very high tensile residual stress is generated by clad welding after welding. Conventionally, quenching by heating from the inner surface has been used as a method to remove this high residual stress, but cladding materials (
Due to the difference in material properties between SVS) and the base material (A553), it is not very effective in reducing high residual stress in the cladding part.

High residual stress in the cladding has recently been brought into focus as a problem of undercrack at the boundary between the cladding material and the base material. As such, research is being conducted in various related fields. Therefore,
Reducing residual stress in the cladding is very important for cracking problems.

[Problem that the invention seeks to solve]

The present invention provides a weld overlay method for reducing the above-mentioned high residual stress, and more specifically, a thick structural member such as a PWR reactor vessel whose inner surface is welded overlaid with clad steel. The present invention provides a method for reducing the high residual stress that occurs during cladding.

[Failure to solve the problem]

The present invention, as a means to solve the above-mentioned problems, consists in cooling the built-up surface of a thick internal structural member such as a nuclear reactor vessel and simultaneously heating the other surface. That is, when welding and overlaying a coated steel material on one side of a thick structural member, after the welding is completed, the structural member is heated from the other side while keeping the overlay surface at a relatively low temperature. Then, the method is used for welding overlay of thick-walled structural members, which is characterized by cooling the entire body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below in comparison with conventional means based on FIGS. 1 to 5 showing an example of an embodiment of the present invention. Note that Figure 1 is a cross-sectional view of the reactor vessel, and Figures 2 to 2 are only diagrams for explaining the mechanism of high tensile residual stress generation in the cladding. It is a diagram in which the parts X, -X, are taken out. Figure 3 shows the changes in the total strain of all the stores with respect to temperature changes.

FIGS. 4 - 4 are diagrams for explaining the residual stress reduction mechanism according to the present invention, and are views taken from Xl-X, which is a part of the reactor vessel in the axial direction of FIG. 1. . FIG. 5 shows the change in the total strain of all stores with respect to temperature changes according to the present invention.

As shown in Fig. 1, clad steel 2 is applied to the inner surfaces of the P, W, and R reactor vessels 1 in order to prevent corrosion of the base metal 3. Clad steel 2 is sequentially overlaid on the base metal 3 in the axial direction for each inner surface circumference. It is welded to cover the entire inner surface of the base material 5. Taking a certain container as an example, the material of the base material 3 is A355 material, and the material of the clad steel 2 is SO3 material.

In addition, the thickness of the plate is approximately 200 mm for the base material, while the cladding is approximately 1/40 of that thickness, and the cladding width is approximately 4 mm.
0. It is. The mechanism of generating high tensile residual stress in the cladding due to cladding welding will be explained. Second
As shown in Figure ■, part of the reactor vessel 1 in the axial direction
Considering X, first of all, the inner surface 4 reaches a very high temperature range due to the cladding. If this inner surface high temperature portion is considered separately from the base material portion 5, the inner surface high temperature portion causes a larger deformation δ than the base material portion, as shown in (2). Since the inner surface high temperature part is a continuous body with the base metal part, the inner surface part generates compressive plastic strain at high temperatures, as shown in (2). In the cooling process after overlaying, the deformation of the inner surface and the base material is as shown in ■ when the two are considered separately, and in the As Wela state,
The inner surface is pulled by the base material as shown in ■, and a high tensile residual stress is generated. Since SaS materials are generally used, the coefficient of glandular expansion is larger than that of the base material A335, so the degree of compression and contraction is large, and the residual stress is even larger. Figure 5 shows the series of changes in the total strain on the inner surface of the entire car. The present invention reduces the high tensile residual stress on the inner surface by heating the outer surface to a certain temperature range or simultaneously cooling the inner surface after the cladding is completed.

The mechanism of reducing residual stress by heating the outer surface or simultaneously cooling the inner surface of the present invention will be explained. As shown in Figure 4 (■), by heating the outer surface, within the thickness of the plate, as shown in (■), the temperature rises at the base material part, while the temperature at the inner part becomes lower. If the inner surface is simultaneously cooled, the temperature difference between the two will further increase. In this temperature distribution, if the two are considered separately as in the case of cladding shown in FIG. 2, the radial deformation of the base material becomes large as shown in (■). Since both the inner surface part and the base material part are continuous bodies, the inner surface part is pulled by the rigid base material part, and tensile stress is generated in the inner surface part. In the case of simultaneous cooling of the inner surface, the difference in deformation between the two becomes even larger, so that the tensile stress also becomes larger. After the heating is stopped, in the cooling process, if the two are considered separately, the shrinkage amount of the high-temperature base material portion is greater than that of the inner surface portion, as shown in (2). Therefore, when the temperature is returned to room temperature, the inner surface is compressed due to the contraction of the rigid base material, as shown in (2).

The series of changes in the total strain during heating according to the present invention for the inner surface is shown by the dotted line in FIG. It is expected that the residual stress on the inner surface will be reduced compared to the As Tel state before heating.

〔Concrete example〕

Hereinafter, the present invention will be explained in detail based on FIGS. 6 to 8.

Figure 6(a) shows a part of the reactor vessel taken out, and Figure 6(b) shows a temperature change, which is a specific example of the present invention, and the change in the total strain of the total reactor with respect to this temperature change. The seventh
As shown in the figure. FIG. 8(a) shows the change in residual stress in the axial direction with respect to temperature change according to the present invention, and FIG. 8(b) shows the change in residual stress in the circumferential direction.

As shown in Fig. 6, a part of the crotch of the reactor vessel is removed, and clad steel (SUB 304 material) 2 is coated on the inner surface of the base material (A533 material) 5, as shown in (a). After successive overlay welding in the axial direction, Tom is applied to the outer surface as shown in 0).
The residual stress was analyzed when ax=300°C and Ti=20°C were applied to the inner surface.

As a result, as shown in FIG. 7, the curve of the total stress curve showed a transition as expected. Still the 8th
As shown in Figures (a) and (b), the residual stress in the As Weld state after cladding welding is extremely large near the cladding, as shown by the solid line, but after residual stress removal treatment, these high residual stresses are The stress has decreased to about A as shown by the dotted line.

〔Effect of the invention〕

As described in detail above, the present invention cools the overlay surface of a thick structural member such as a nuclear reactor vessel and simultaneously heats the other side, thereby reducing the build-up temperature that occurs when building up the cladding of the vessel. This has the effect of reducing residual stress.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the reactor vessel, and Figures 2 - 2 are diagrams for explaining the mechanism of residual stress generation in the cladding. , -X,
This is an extracted figure. Figure 3 shows the change in total strain of the total stress curve with respect to temperature changes. FIGS. 4 - 4 are diagrams for explaining the residual stress reduction mechanism according to the present invention, and are views taken from x4-X, which is a part of the reactor vessel in FIG. 1 in the axial direction. Fifth
The figure shows the evolution of the total strain of the total stress curve with respect to temperature changes according to the present invention. FIG. 6(a) is a diagram showing a part of the reactor vessel taken out, FIG. 6(b) shows the temperature change according to the present invention, and FIG. 7 shows the temperature change based on Ryo 6(b). The graph shows the transition of the total stress curve. Figure 8(a). (b) shows the residual stress change with respect to temperature change according to the present invention. Sub-agent 1) Clear agent Ryo Hagiwara - Figure 3 Figure 5 n- Part (α) Inner surface Figure 8 (b) Inner surface

Claims (1)

[Claims] When welding a coated steel material onto one side of a thick structural member, after the welding is completed, the structural member is heated from the other side while the overlay surface is kept at a relatively low temperature, and then the entire structure is heated. A method for welding overlay of thick structural members, characterized by cooling.