JPS591638A - Post-heat treatment method for welded repair parts - Google Patents

Abstract

PURPOSE:To improve the resistance of the repair welded part of steel to stress corrosion cracking, etc. by heating said part in and at the specified region and temp. then cooling forcibly the reparied part and the surface in the peripheral part thereof while continuing heating, ceasing the heating and cooling the entire part down to room temp. CONSTITUTION:The part 6 considered to have stress concentration equal to the stress concentration in the repair welded part 5 of a steel material 1 is reqarded a quasi- repaired part. The range A where the stress therein is made substantially small, for example, the range where the stress is made to about <=10% the max. stress, is determined by stress analysis. The inside of the region apart by about 2 times of the distance (d) from the center of the part 6 up to the circumferential edge of the range A on the outside of said range is determined as a heating range B and the inside of the range B is heated to 580-650 deg.C annealing temp. The hardened part 4 on the lower side of deposited metal 2 is annihilated by such heating and the residual stress in the weld zone is relieved. If the material is heated in this state, the residual stress is generated in the heated part; therefore, only the surface of the range to be decreased is forcibly cooled while the above-described heating is continued. The heating is ceased while the force cooling is continued after the suitable cooling time according to the thickness of the plate and the entire part is cooled down to a room temp.

Description

[Detailed description of the invention] This invention relates to an improved method for post-heat treatment of a welded repaired part of steel.

If defects such as cracks occur locally during the service life of mechanical equipment, etc., the American Society of Mechanical Engineers Boiler and Pressure Vessel Standards (A
SME Code Boiler and Pr-e
ssure Vessel), it is permitted to scrape off that part and fill in the remains with a welded part.

However, this method generates high residual stress in the repaired weld, making it unsuitable for metal materials sensitive to corrosion fatigue, hydrogen embrittlement, or stress corrosion cracking.

In view of the above circumstances, it is an object of the present invention to provide a post-heat treatment method for reducing the tensile stress generated in the weld repaired part or converting it to compressive stress to improve stress corrosion cracking resistance, etc. In a post-heat treatment method applied to.

580 ~ within an area approximately twice the distance from the center of the weld repair part to the periphery of the area where residual stress is to be reduced around it.
By heating to 650°C to eliminate the hardened part on the lower side of the weld metal, the residual stress in the busy weld part is removed, and while the heating is continued, the surface of the weld repair part and its surrounding area is forcibly cooled, and then A post-heat treatment method for a welded repaired part, characterized by stopping heating and cooling the entire part to room temperature.

Fig. 1 shows a case in which a steel material 1 is welded and a weld metal 2 is placed. As the metal 2 and its periphery shrink as they cool from the melting temperature or a temperature close to it, residual stress is generated around the weld metal 2 as shown by curve 3 in Figure 2, causing the weld metal and its surroundings to shrink. A tensile force (10r) is generated in the part. Furthermore, if the weld beads are not placed in an orderly manner, a hardened portion 4 will be formed on the underside of the weld metal 2.

Such defects usually occur in areas where high stress has been generated before repair, and the presence of hardened areas or tensile residual stress indicates properties such as stress corrosion cracking resistance, corrosion fatigue resistance, or hydrogen embrittlement resistance. It is well known that it is undesirable for

By the way, in order to remove the hardened part 4, it is sufficient to heat the part to the annealing temperature, but such local heating causes residual tensile stress in the welded part. Stress cannot be removed.

On the other hand, the present method is explained as follows, taking the nozzle corner of the welded part as an example. As shown in FIGS. Similarly, the portion 6 where stress concentration is thought to occur is considered to be a semi-repaired portion. Next, consider the stress that caused the crack, such as stress due to internal pressure, thermal stress, or residual stress on the surface, and the shape or material of the part where the crack occurred, and perform a stress analysis to calculate the stress until the stress becomes sufficiently small. Determine range A, for example, a range where the maximum stress is approximately 10 inches or less. An area that is twice the distance d from the center of the outer repair portion 6 to the periphery of area A is defined as a heating area B, and the area B is heated to an annealing temperature of 580 to 650°C. For heating, it is preferable to use electric heating, such as by installing an induction coil 7 at the relevant location to perform induction heating, so that temperature control is easy.

This heating section first eliminates the hardened portion 4 on the lower side of the weld metal and removes the residual stress from welding.

If it is cooled in this state, residual stress will be generated in the heated part due to local heating, as in the conventional method. In the method of the present invention, while continuing the above-mentioned heating, only the surface of the area A including the repaired portion and in which the residual stress is to be reduced is forcibly cooled. Forced cooling can be carried out by spraying water or air from the nozzle 8.In order to prevent the cooling medium from acting on parts other than the forced cooling part, a barrier 10 is provided around the forced cooling part. It is best to prevent it from scattering. The cooling time is determined according to the thickness of the material. In other words, considering the temporal change in temperature distribution in the plate thickness direction, the Fourier number aT /12
It is good to choose so that the value is 0.3 to 1 (t: board thickness,
T: heating time, a: temperature conductivity).

In addition, the cooling temperature of the forced cooling section is set at a temperature difference of 1 from the continuous heating section.
Select so that the temperature is 00℃ or higher.

After that, heating is stopped while forced cooling is continued, and the whole is cooled to room temperature.

In this way, in the present invention, only the repaired area is locally cooled first, so the residual stress in the repaired area is reduced to compressive force (
−r). If tensile residual stress is generated around the area, or if this area is located in a place where there is less stress concentration during use, no major harm will occur. The lifespan of can be improved.

[Brief explanation of the drawing]

Figure 1 is a sectional view schematically showing a conventional welded repair part, Figure 2
The figure is a stress distribution diagram showing the distribution state of residual stress after cooling, and FIG. 3 is a sectional view showing an embodiment of the method of the present invention.
FIG. 4 is a front view, and FIG. 5 is a stress distribution diagram showing the residual stress distribution at room temperature. 1... Steel material, 2... Weld metal, 3... Stress, 4
... Hard 2v1-=i part, 5... Repair welding part, 6...

Claims (1)

[Claims] In a post-heat treatment method for a welded repaired part of steel, an area approximately twice the distance from the center of the welded repaired part to the periphery of the area that reduces the residual stress of the candle enclosure is heated at 580 to 650°C.
The welded metal is heated to extinguish the hardened part on the lower side of the weld metal and remove the residual stress in the welded part, and while the heating is continued, the surface of the weld repaired part and its surrounding area is forcibly cooled, and then the heating is stopped. A method for post-heat treatment of a weld repaired part, characterized by cooling the entire part to room temperature.