JPS61153226A - Method for improving residual stress in steel plate, or the like - Google Patents

Abstract

PURPOSE:To improve residual stress in steel plate, etc., without being influenced by shape, by heating circumference of a domain to be treated, to cause tensile stress above the yield point near the rim part of said domain, then cooling the heated part to cause residual stress at the domain. CONSTITUTION:Circumference of the domain 2 to be treated of a plane-shaped steel plate 1 is heated, while holding the temp. of the domain 2 to room temp., etc. By expansion of the domain 3, the vicinity of rim part thereof, i.e. that of a boundary part 4 with the domain 3 is stretched in radial direction indicated by an arrow. Force is generated so that the domain 2 is also stretched similarly to the domain 3. In this case, since the sizes at each part of the plate 1 is enlarged at the vicinity of the part 4, the plastic deformation is generated concentratedly near the rim part of the domain 2. Next, if the plate 1 under the state generating thermal expansion and plastic deformation is cooled by natural cooling in state left standing, the pressing force corresponding to the increase of size due to plastic deformation is caused accompanying with thermal contraction of the domain 3, the domain 2 becomes to pressed state, and the state receiving residual pressing stress can be attained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for improving residual stress in steel plates, etc., and particularly relates to a method for improving residual stress in parts of flat plates, large structures, etc. be.

"Prior Art" Generally, it is known that corrosion cracking progresses rapidly in metallic materials such as austenitic stainless steel, which is often used in nuclear power plants, chemical plants, etc., when tensile stress and corrosion factors coexist. It is being

Conventionally, when the metal material is a steel pipe, etc., the pipe is induction heated while cooling water is passed through the pipe to create a temperature difference that causes thermal stress above the yield point on the inner and outer surfaces of the pipe, thereby improving stress. Stress improvement methods have been considered in which residual compressive stress is generated at required joints of pipes, etc.

``Problem to be solved by the invention'' However, although this method is applicable to simple shapes such as straight pipes, it is difficult to apply to large structures with complex shapes, flat plates, etc. Further, there is a problem that it cannot be applied when cooling water cannot be pumped.

The present invention effectively solves the problems of the prior art, and is less affected by shape, and can be applied to a wide range of structures where stress corrosion cracking or fatigue may occur in some parts. The purpose of this invention is to provide a method for improving residual stress.

"Means for Solving the Problems" In order to achieve such an objective, the present invention heats the periphery of a region to be treated to generate tensile stress higher than the yield point near the edge of the region to be treated. After that, the heated part is cooled to generate residual compressive stress in the area to be treated, and by causing plastic deformation in the tensile direction near the edge of the area to be treated, The size of the portion is made large, and the area to be treated is brought into a compressed state by contraction as the heated portion cools.

"Example" Hereinafter, an example to which the method for improving residual stress in steel plates, etc. according to the present invention is applied will be described based on the drawings.

When there is a part of the flat steel plate I shown in FIG. 1 in which the residual stress is to be improved, that is, a region 2 to be treated, the temperature of the region 2 to be treated is maintained at room temperature, etc. 2
heat the surrounding area. When the heating portion (heating region) 3 expands, the vicinity of the edge of the processing region 2, that is, the vicinity of the boundary portion 4 with the heating region 3, moves in the radial direction as shown by the arrows in FIGS. 1 and 2. I'm drawn to it. Therefore, as shown by the solid line in FIG. In the heating area 3, the tensile strength of the material decreases due to high temperature, and when the tensile stress in this area exceeds the yield point, plastic deformation occurs in that area, and the plastic deformation causes the dimensions to slightly increase. In other words, the distance between any two points A and B on the outside of the boundary portion 4 increases by the amount that the dimension increases due to thermal expansion in the heated state, and becomes L + Δ.
L (where ΔI7−αI7ΔT, α: coefficient of linear expansion, T: temperature difference). Then, a force is applied so that the region to be treated 2 is also stretched in the same way as the heating region 3 . In addition, at this time, as shown in FIG. 3, the magnitude of stress in each part of the steel plate l is large near the boundary part 4, so plastic deformation is concentrated near the edge of the treated area 2. I will do it.

Next, when the steel plate l in a state where thermal expansion and plastic deformation has occurred is allowed to cool down naturally, etc., as the heated area 3 thermally contracts, a compressive force corresponding to the increase in dimension due to plastic deformation is generated, and the treated area 2 is in a compressed state as shown by the arrow in FIG. 4, and a residual compressive stress can be applied thereto.

In the example shown in FIG. 1, explanation of the means for maintaining the treated area 2 at room temperature is omitted, but in addition to cooling both sides of the steel plate 1, nozzle components with a large heat capacity are integrated into a part of the steel plate, etc. If the device is installed in a large area, the heat dissipation can be used to maintain a low temperature state or to perform cooling.

In addition, in the example in FIG. 1, the outside of the heating area 3 is expandable and contractible, but if the area of the heating area 3 is large, most of the heating area 3 may be elastically deformed during the heating process. It can be understood that the range of application is wide because it is possible to generate the necessary plastic deformation by generating tensile stress near the edge of the treated region 2 while maintaining the treatment area 2. Therefore, it has the potential to improve stress in many metal structures, parts, etc.

"Effects of the Invention" As explained above, according to the present invention, the periphery of the region to be treated is heated to generate a tensile stress equal to or higher than the yield point near the edge of the region to be treated, and then the heating region is heated. Since the cooling process generates residual compressive stress in the area to be treated, there are fewer restrictions on complex shapes and large structures, the range of application is wide, and workability is high. It is possible to omit sending water, and it is possible to achieve effects such as not being subject to restrictions on cooling water.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is a perspective view illustrating a treated area and a heated area in a steel plate, and
FIG. 3 is a cross-sectional view illustrating the generation of tensile force in the heated region, FIG. 3 is a distribution diagram of stress generated during heating, and FIG. 4 is a sectional view illustrating the state of the steel plate after heat treatment. 1... Steel plate, 2... Treated area, 3...
...Heating area. Figure 2

Claims (1)

[Claims] After heating the periphery of the region to be treated to generate tensile stress equal to or higher than the yield point near the edge of the region to be treated, the heated portion is cooled to generate residual compressive stress in the region to be treated. Features: A method for improving residual stress in steel plates, etc.