JPH08333632A - Method for introducing compressive residual stress to metal surface - Google Patents

Abstract

PURPOSE: To prevent the occurrence of defects, such as crack, by introducing compressive residual stress to a metal surface, to prevent the influence of the quality of the material to be treated, and to increase the applicability to the existing material to be treated. CONSTITUTION: The metal surface 1a of a material 1 to be treated is heated into spotted state. Then, a heating point P is successively shifted, and the metal surface 1a in a high-temp. state is cooled rapidly to apply a thermal stress exceeding the yield point. Subsequently, cooling is applied down to uniform temp. to establish compressive residual stress in the metal surface. Spot heating is performed by laser beam, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for introducing a compressive residual stress to a metal surface, and more particularly to introducing a compressive residual stress to a metal surface by spot-like heating and immediately followed by rapid cooling.

[0002]

2. Description of the Related Art Conventionally, as a technique for improving the corrosion resistance of stainless steel, JP-A-1-199919 and JP-A-1-1-1.
99920, JP-A-1-199921 and JP-A-6-1999.
No. -073556 has been proposed, and in all of these techniques, the clad layer is laser-baked on the surface of stainless steel to dramatically improve the corrosion resistance.

[0003]

However, since the clad layer portion is formed by depositing a metal material or the like in a molten state, thermal contraction occurs when the molten metal material or the like solidifies, A tensile residual stress is applied to the surface, and when a crack occurs, the growth of the crack is promoted.

The present invention has been made in view of the above circumstances, and achieves the following objects. Introduce compressive residual stress to the metal surface to prevent the occurrence of defects such as cracks. It is not easily affected by the material of the material to be processed, has a wide range of applications, and is highly practical. Improve applicability to existing materials to be processed.

[0005]

[Means for Solving the Problems]
A spot-like heat is applied by a heat source such as a laser beam to give a large temperature difference between the heating point and the heated portion. At this time, it is desirable to keep an atmosphere of an inert gas around the heating point by interposing a shield gas, and the heating point is in a molten state. By sequentially shifting the heating points, the metal surface is continuously heated, and the metal surface in a high temperature state deviated from the heating point is quickly brought into contact with the refrigerant to rapidly cool the heated point, and the heating point and its vicinity. A thermal stress exceeding the yield point is generated in the vicinity of the metal surface of. For the material to be treated that has been heated and rapidly cooled, the cooling is continued to bring the entire temperature to a uniform temperature, and compressive residual stress is generated on the metal surface. For the material to be treated, it is effective to heat and cool it in a water atmosphere, and in the case of heating it in a gas atmosphere, a shower-like refrigerant may be jetted onto the metal surface to quench it. desirable.
When the corrosion resistance of the material to be treated is required, a technique of forming a clad layer by using a filler rod during heating is added.

[0006]

[Function] When a metal surface is heated in a spot shape by a laser beam or the like, the heating point reaches a molten state, and a molten pool having a small outer diameter and a relatively deep depth is formed. A large temperature difference occurs. When the surrounding atmosphere of the shield gas is set around the heating point, the heating point is isolated from the surrounding environment, the area between the heating point and the heated area becomes uncooled, and the material to be processed is processed in an underwater atmosphere. Even in this case, the temperature difference is provided. When the heating points are sequentially shifted and the metal surface at the heated point is rapidly cooled by the refrigerant, thermal stress due to the transient temperature difference between the heating point and the cooling point causes plastic deformation beyond the yield point. Occurs. At the time of this transition, tensile stress acts on the surface portion to cause plastic deformation, and at the high temperature portion immediately below the surface portion, plastic deformation occurs due to the action of compressive stress. Therefore, in the material to be treated after the treatment, the temperature becomes uniform during cooling such as returning to the normal temperature state, so that stress opposite to that at the time of transition acts on the portion where plastic deformation occurs, and Compressive residual stress is applied to the surface. Further, when the process of introducing the compressive residual stress is performed in a gas atmosphere, the heating point is immediately cooled immediately with a shower-like refrigerant, and then the desired temperature is reduced by continuing the temporary cooling. Installation processing is performed. When a filler rod is used during heating, a clad layer is simultaneously formed and a compressive residual stress is introduced into the surface of the clad layer.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a method for introducing a compressive residual stress to a metal surface according to the present invention will be described below with reference to FIGS.

FIG. 1 shows a state of implementation of the above-described introduction method in the first embodiment. When introducing a compressive residual stress to the metal surface 1a of the material (base material) 1 to be processed, the laser by the laser head 2 is used. The irradiation of the beam L, the isolation of the heating point P by the shield gas curtain 3, the formation of the cladding layer 5 by the supply of the filler rod 4, the rapid cooling of the heating point P by the refrigerant (water) W, etc. are performed in combination. In addition, in FIG.
Reference numeral 6 is a molten pool, and when the laser beam L has a small focal point, a deep (so-called wine glass-like) molten metal portion having a small heating diameter is formed.

For the material 1 to be treated, for example, Inconel material or stainless steel (SUS304 material) is applied,
In this case, the material has a thickness of, for example, 6 mm or more, and is relatively thick in correspondence with the laser output and the heating depth (thick material).
Is applied. Then, in the material 1 to be treated, the metal surface 1a is brought into contact with the water (refrigerant) W, and the laser head 2 is placed opposite to the metal surface 1a.

For the laser head 2, for example, a YAG laser having a laser output of about 3 kW is applied, and He or the like is provided between the laser head 2 and the metal surface 1a so as to surround the irradiation range of the laser beam L. The shielding gas curtain 3 is formed by supplying the shielding gas.

The filler rod 4 forms the clad layer 5 in accordance with the demand for corrosion resistance of the metal surface 1a.
Alloys, etc. are selected.

The steps of implementing the method of introducing the compressive residual stress will be described below with reference to FIGS.

As shown in FIG. 2, the material 1 to be processed before laser irradiation has a temperature distribution in which the temperature (T _M ) is constant in the plate thickness direction of the material.

When the metal surface 1a of the material 1 to be processed is heated in a spot shape by irradiation with the laser beam L, the metal surface 1a
3 is in a molten state, the temperature of the metal surface 1a becomes extremely high as shown by the high temperature on the right side in FIG.
The initial temperature (T _M ) is almost maintained. At the time of the temperature distribution shown in FIG. 3A, the material 1 to be processed will freely expand based on the temperature of each place as shown by the length in the left-right direction of FIG. 3B. However, as described above, when the material 1 to be processed is a thick material, the free expansion of the metal surface 1a is suppressed by most of the material 1 to be processed that retains the initial temperature (T _M ). Therefore, a compressive stress is applied to the molten portion of the metal surface 1a as shown by a tensile stress on the right side in FIG. 3 (c), and a tensile stress is applied immediately below the stress.
It is the formation range of the shield gas curtain 3 and the molten pool 6
In the range where the rapid temperature drop of No. does not occur, the state of FIG. 3C is maintained.

When the laser head 2 is relatively moved in the direction of the arrow in FIG. 1 to sequentially shift the heating points P due to the irradiation of the laser beam L, the refrigerant (water) W is placed on the portion outside the shield gas curtain 3. Contact with each other to rapidly cool (rapidly cool) the metal surface 1a in a high temperature state (molten state), so that a transient phenomenon as shown in FIG. 4 occurs. That is, as shown in FIG. 4A, when the metal surface 1a is rapidly cooled, a portion having a temperature lower than the maximum temperature inside the processing target material 1 is generated. At the time of the temperature distribution shown in FIG. 4A, the material 1 to be processed is based on the temperatures at various points in FIG.
As shown in FIG. 4 (c), free expansion occurs as shown in FIG. 4 (b), but as described above, the portion that maintains the initial temperature (T _M ) suppresses free expansion, and as shown in FIG. 4 (c). In addition, a compressive stress is applied to a portion near the maximum temperature, a tensile stress is applied to the metal surface 1a under the influence of the compressive stress, and a tensile stress is applied to the temperature (T _M ) portion.

In the stress distribution as shown in FIG. 4 (c), if the compressive and tensile stresses are thermal stresses exceeding the yield points corresponding to the respective temperatures, plastic deformation is caused based on these stresses. appear.

Then, as the laser head 2 shown in FIG. 1 moves, the plastically deformed portion is continuously cooled by the coolant W and the workpiece 1 is returned to a normal temperature state. As shown in FIG. 5, the metal surface 1a is compressed based on the fact that the portion of the metal surface 1a that has undergone plastic deformation in the tensile direction is compressed in addition to the overall shrinkage force due to the temperature decrease of the material 1 to be processed. The residual stress can be introduced. Even when the clad layer 5 is formed, a compressive residual stress can be introduced to the surface thereof under the condition that the linear expansion coefficient is similar.

FIG. 6 shows a second embodiment of the method for introducing a compressive residual stress to a metal surface according to the present invention, and shows an implementation situation when the material to be treated 1 is a thin material having a thickness of less than 6 mm, for example. ing. As shown in FIG. 6A, the temperature distribution when the thin material 1 to be processed is heated by the laser beam L is gently formed over the entire thickness of the material 1 to be processed, and immediately after laser irradiation. When the metal surface 1a is cooled, the metal surface 1a is rapidly cooled, so that the temperature of the cooling surface is low and a high temperature portion is left inside the workpiece 1 as shown in FIG. 6 (b). The resulting temperature distribution is shown in Fig. 6
Due to the temperature distribution of (b), the material 1 to be processed will expand freely as shown in FIG. 6 (c), but stress is generated by mutually suppressing free expansion, and these stresses ( For example, when the compressive stress generated by suppressing the expansion of the high temperature part) exceeds the yield point, after cooling, the whole is brought to a uniform temperature, based on the plastic deformation in the compression direction generated inside the material 1 to be treated, As shown in FIG. 6 (d), a compressive residual stress can be introduced into the metal surface 1a.

FIG. 7 shows a third embodiment of the method for introducing a compressive residual stress to a metal surface according to the present invention, in which the material 1 to be treated is an extremely thin material having a thickness of, for example, 2 mm or less, or heat conduction. It shows the implementation status when it is formed of a highly flexible material. Laser beam L for the workpiece 1
The temperature distribution in the case of being heated by means of a small change as shown in FIG. 7 (a), but the rapid cooling of the metal surface 1a immediately after the laser irradiation causes the cooling as shown in FIG. 7 (b). The temperature distribution is such that the temperature of the surface is low and the temperature of the other parts of the material to be processed 1 is high, and the material to be processed 1 is allowed to expand freely as shown in FIG. 7 (c) due to the temperature distribution of FIG. 7 (b). As a result, when these stresses exceed the yield point due to the generation of stresses that suppress free expansion,
As shown in (d), the metal surface 1a is brought into a state in which a compressive residual stress is introduced.

On the other hand, FIG. 8 shows a fourth embodiment of the method of introducing the compressive residual stress to the metal surface according to the present invention, in which the atmosphere around the laser head 2 in the example of FIG. In place of the method described above, the surroundings of the laser head 2 are kept in a gas atmosphere, and the shower-like refrigerant (water) W is jetted from the spray nozzle 8 to the metal surface 1a by water supply from the water supply system 7 to rapidly cool it. Is. In FIG. 8, reference numeral 9 is a laser beam generating means, 10 is a shield gas supply system, and 11 is a wire supply system.

In this case, a shield gas is supplied from the shield gas supply system 10 to leave the tip of the laser head 2 in a shield gas atmosphere, and the metal surface 1a is irradiated with the laser beam L generated by the laser light generating means 9. While irradiating, the heating point P is shifted as shown by the arrow in FIG. 8, while the water is supplied from the water supply system 7, the refrigerant (water) W is ejected in a shower shape from the spray nozzle 8 to rapidly cool the heating point P. It is applied when the cooling action by the refrigerant (water) W ejected from the spray nozzle 8 is sufficient or when the material 1 to be processed is thin.

Even in the fourth embodiment of FIG. 8, when the corrosion resistance of the material 1 to be treated is required, the filler rod 4 is supplied from the wire supply system 11 to the heating point P during heating. , A technique for forming the cladding layer 5 is added.

[0023]

The method of introducing the compressive residual stress to the metal surface according to the present invention has the following effects. (1) The surface of the material to be treated is heated by a laser beam or the like to be in a molten state, and is brought into contact with a coolant while shifting the heating point to quench the material, thereby introducing compressive residual stress to the metal surface and causing cracks or the like. It is possible to prevent the occurrence of defects. (2) Since the compressive residual stress is introduced by utilizing the temperature difference and the thermal expansion difference generated when the surface of the material to be processed is heated in a spot shape, it depends on the thickness and thermal conductivity of the material to be processed. It is not easily affected, and the range of applications can be expanded to enhance its practicality. (3) When the material to be treated is heated, a gas atmosphere is provided around the heating point and is brought into contact with a refrigerant such as water.
The equipment and equipment used is relatively simple and easy to apply,
It can also be applied to the repair of existing materials to be processed. (4) By supplying the filler rod to the heating point, the cladding layer can be formed, and the compressive residual stress can be easily introduced to the surface of the cladding layer.

[Brief description of drawings]

FIG. 1 is a front sectional view showing an implementation state of a first embodiment of a method for introducing a compressive residual stress to a metal surface according to the present invention.

FIG. 2 is a temperature distribution chart of the material to be treated in FIG. 1 before heating.

3A and 3B show a situation when the material to be treated in FIG. 1 is heated, wherein FIG. 3A is a temperature distribution diagram, FIG. 3B is a thermal expansion model diagram, and FIG. 3C is a thermal stress distribution diagram.

4A and 4B show a situation in which the material to be treated in FIG. 1 is water-cooled immediately after heating, (a) is a temperature distribution chart, (b) is a thermal expansion model chart, and (c) is a thermal stress distribution chart. Is.

5 is a residual stress distribution diagram showing a situation after the treatment of the material to be treated in FIG. 1. FIG.

FIG. 6 shows an implementation state of a second embodiment of the method for introducing a compressive residual stress to a metal surface according to the present invention.
Is the temperature distribution diagram during heating, (b) is the temperature distribution diagram during water cooling,
(C) is a model diagram of thermal expansion during water cooling, and (d) is a residual stress distribution diagram showing the state after treatment.

FIG. 7 shows an implementation status of a third embodiment of the method for introducing a compressive residual stress to a metal surface according to the present invention.
Is the temperature distribution diagram during heating, (b) is the temperature distribution diagram during water cooling,
(C) is a model diagram of thermal expansion during water cooling, and (d) is a residual stress distribution diagram showing the state after treatment.

FIG. 8 is a front sectional view with a block diagram showing the fourth embodiment of the method for introducing the compressive residual stress to the metal surface according to the present invention.

[Explanation of symbols]

 1 material to be treated 1a metal surface 2 laser head 3 shield gas curtain 4 filler rod 5 clad layer 6 molten pool 7 water supply system 8 spray nozzle 9 laser light generating means 10 shield gas supply system 11 wire supply system L laser beam P heating point W Refrigerant (water)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location C23C 2/00 C23C 2/00 (72) Inventor Shinobu Sasaki 1 Shin-Nakahara-cho, Isogo-ku, Yokohama-shi, Kanagawa Address Ishikawajima Harima Heavy Industries Co., Ltd. Yokohama Engineering Center

Claims (4)

[Claims] 1. A step of heating a metal surface (1a) of a material (1) to be treated in a spot shape, a step of sequentially shifting a heating point (P) on the metal surface, and a metal surface in a high temperature state deviated from the heating point. A step of bringing the refrigerant (W) into contact with the sample and quenching it to give a thermal stress in the vicinity of the metal surface above the yield point, and a step of cooling the material to be treated to a uniform temperature to generate a compressive residual stress on the metal surface. A method for introducing a compressive residual stress to a metal surface, which comprises: 2. A metal surface (1a) of a material (1) to be treated,
The method of introducing a compressive residual stress to a metal surface according to claim 1, wherein heating is performed in a spot shape by a laser beam. 3. The cooling is performed by interposing a shield gas around the heating point (P) and bringing a refrigerant (W) into contact with the vicinity of the shield gas atmosphere for cooling. Method for Introducing Compressive Residual Stress on Metal Surface of Steel. 4. The material to be treated (1) is heated in a gas atmosphere, and a shower-like coolant (W) is jetted onto the metal surface (1a) to cool it. 2. The method for introducing a compressive residual stress to a metal surface according to 2 or 3.