JP2003113418A - Fatigue life improvement treatment method and long life metal material by it - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve the efficiency of construction and the skill of a constructor in conventional methods for improving fatigue of metal materials to reduce stress concentration and for improving fatigue of metal materials by introducing compressive stress, and An object of the present invention is to provide a new fatigue improvement processing method that solves the problem that quality control cannot be performed because there is no means for measuring the effect after processing. SOLUTION: To improve the fatigue life of a metal material by performing a pretreatment, performing an ultrasonic impact treatment, and then performing a quality assurance inspection on a portion where the fatigue of the metal material becomes a problem. Fatigue life improvement treatment method characterized by the following.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, large welded structures such as bridge girders of bridges, metal welded products such as undercarriage parts of automobiles, and metal materials without welding such as wheels of automobiles. TECHNICAL FIELD The present invention relates to a fatigue life improving treatment method for improving the durability of fatigue cracks in a portion damaged by fatigue and extending the life, and a metal material treated by the treatment method.

[0002]

The durability of metal products is often defined by fatigue. In order to improve such fatigue strength, it is general to increase the cross-section by design to cause a stress phenomenon, but various other fatigue improvement treatment methods have been adopted.

There are roughly two types of fatigue improving treatment methods. First, there are grinding, TIG dressing, etc., in which the stress concentration is reduced by changing the shape of the portion where fatigue is a problem. Further, there are hammer peening, needle peening, shot peening, low temperature transformation molten material, etc., which give a compressive residual stress to a portion where fatigue becomes a problem to reduce a substantial repeated stress range. Among them, hammer peening is said to have both the effect of reducing stress concentration and the effect of introducing compressive stress.

Among the above fatigue improving treatment methods, the effect of the treatment method for reducing stress concentration is visibly apparent,
Actually, in a place where fatigue is a problem, even slight scratches may cause the fatigue strength to worsen. It is necessary and causes a large cost increase.

Also, regarding TIG dressing, a skilled person is required for the work, and when it is used for repairing a bridge in order to apply heat to the application site, hot cracking of the welding material due to stress fluctuation is caused. In order to prevent it, it is necessary to stop the traffic during the work, which is also a major factor of cost increase.

On the other hand, the method of introducing the compressive residual stress is that since the compressive residual stress is invisible, it is difficult to measure the effect after the treatment and it is difficult to guarantee the effect by inspection. It is usually not used in a situation where an engineer with judgment / diagnosis ability cannot be present from a quality control point of view, which is a problem.

Further, in hammer peening, since a large plastic deformation can be given to the processing portion, the trace of the processing can be increased and the processing can be specified after the execution, but
Scratches on the surface during processing may rather cause stress concentration and reduce fatigue strength, and due to the large recoil when giving plastic deformation, the workability is extremely poor, so it is difficult to control finely. , Quality control is very difficult.

Further, when the above-mentioned fatigue improving treatment method for introducing a compressive residual stress is used for repair, at a small time point of 1 mm or less at the initial stage of fatigue crack initiation, a penetrant flaw test, a magnetic particle flaw test, and an eddy current It cannot be detected by the current inspection methods such as flaw detection test, but even if the above fatigue life improvement treatment method is applied in the state where such a crack is left, the progress of the crack cannot be stopped. In addition, it is considered that there is almost no effect of improving fatigue life by introducing compressive residual stress.

[0009] Further, with respect to the low temperature transformation molten material and the case where the compressive residual stress is introduced into the toe portion, the effect is large in the high strength steel, but the effect is almost lost in the low strength steel. As with TIG dressing, there are some problems in construction due to the heat applied by welding, which makes it difficult to use, and it is difficult to measure the effect of the compressive residual stress introduced like other treatment methods. .

[0010]

As described above, the fatigue improvement treatment method for reducing stress concentration mainly has problems in efficiency of construction and skill of the operator, while fatigue improvement treatment by introducing compressive stress. A problem with the treatment method is that it is not possible to measure its effect and perform quality control. Therefore, it is difficult to generally use such a fatigue life improving treatment method.

The present invention has been made in view of the above circumstances, and as a fatigue improving method, ultrasonic waves are applied to the tip end of an amplitude of 20.
Using a tool that vibrates at a frequency of 15 to 60 kHz at a frequency of 15 μm to 60 μm, an ultrasonic shock treatment for peening the metal surface is performed, and the characteristics of the ultrasonic shock treatment given to the metal to be treated are used. The purpose of the present invention is to obtain a fatigue-improving treatment method that achieves a long life and a metal material that has a long life due to the fatigue improvement treatment method by guaranteeing its effect by performing both pretreatment and inspection.

[0012]

In order to solve the above-mentioned problems, the first invention is to subject a portion where fatigue of a metal material is a problem to pretreatment and then ultrasonic impact treatment,
Furthermore, after that, a quality assurance inspection is performed to improve the fatigue life of the metal material.

A second aspect of the present invention is the pretreatment of the first aspect of the present invention, wherein the portion of the metal material subjected to ultrasonic impact treatment and the portion in the vicinity thereof are subjected to plastic working, deformation correction, heat treatment,
Characterized by performing ultrasonic impact treatment after performing a process such as welding that changes the internal metal stress and surface stress, and not performing a process that changes such internal metal stress and surface stress after the ultrasonic impact treatment. And

A third aspect of the present invention is the pretreatment of the first aspect of the invention, wherein the portion of the metal material subjected to ultrasonic impact treatment and the portion in the vicinity thereof are subjected to plastic working, deformation correction, heat treatment,
After performing the process of changing the metal internal stress and surface stress such as welding, non-destructive inspection and ultrasonic impact treatment are performed,
It is characterized in that after the ultrasonic impact treatment, a process of changing such internal stress of metal and surface stress is not performed.

In a fourth aspect of the present invention, in the pretreatment of the first aspect of the invention, a visual inspection, a penetrant flaw detection inspection, a magnetic particle flaw detection inspection, an eddy current flaw detection inspection, etc. are performed on a portion having a fatigue life problem. If a crack is detected, the crack is removed by a grinder or gouging.

Further, in a fifth aspect of the present invention, in the crack removal of the fourth aspect, when the removal depth becomes deeper than 5 mm, the weld overlay is carried out, then smoothed with a grinder, and further visually inspected. Inspection, penetrant inspection, magnetic particle inspection,
It is characterized by conducting an eddy current flaw detection test and confirming that no cracks are detected.

A sixth aspect of the present invention is the ultrasonic impact treatment according to the first aspect, wherein the toe portion, HAZ portion, and welded portion of the welded portion of the metal material are treated so that the shape is stress-concentrated. In addition to deforming so as to prevent the occurrence of cracks, a compressive residual stress is introduced to detoxify the minute defects that are the starting points of fatigue occurrence, and suppress the occurrence of cracks.

A seventh aspect of the present invention is the ultrasonic impact treatment according to the first aspect of the present invention, wherein a treatment is performed on a cut surface of a metal material by sawing, shearing, gas, laser, plasma or the like and the vicinity thereof. In addition to deforming the shape so that stress concentration is unlikely to occur, compressive residual stress is introduced to make harmless to minute defects and extremely hardened parts that are the starting points of fatigue occurrence, and suppress the occurrence of cracks. .

The eighth invention, in the ultrasonic impact treatment of the above-mentioned first invention, introduces compressive stress due to striking using the ultrasonic impact treatment to a crack below the detection limit in the nondestructive inspection, and progresses. It is characterized by stopping.

A ninth aspect of the invention is the ultrasonic impact treatment of the first aspect of the invention, wherein the ultrasonic impact treatment is performed for two or more passes at the same location with respect to the structure and the local portion of the structure where the fatigue crack may occur. By carrying out, the compressive stress due to the impact is introduced into the crack below the detection limit in the nondestructive inspection, and the progress is more reliably stopped.

A tenth aspect of the invention is to perform the quality assurance inspection of the first aspect of the invention by using a molding material such as a dental shape material or scanning with a high precision measuring instrument such as a laser displacement meter. , Take the shape mold after ultrasonic impact treatment,
The processed surface should be approximately the same as the R (radius) of the tool tip of the ultrasonic impact processing used for processing, and that plastic deformation had occurred at a depth of 0.05 mm or more before processing. Is confirmed to improve the shape of the treated part, and to introduce the compressive residual stress to improve the fatigue life.

The eleventh aspect of the invention is to check the ultrasonic impact treatment tip tool when ultrasonic impact treatment is carried out as a steady process in the quality assurance inspection of the first aspect of the invention.
By confirming the equipment output setting and visually confirming the occurrence of plastic deformation in the treated part, confirm that the shape has been improved in the treated part and the fatigue life has been improved by the introduction of compressive residual stress. Characterize

The twelfth aspect of the invention is, in the quality assurance inspection of the first aspect of the invention, in measuring the deformation formed on the metal surface when it is doubtful that the deformation was formed by ultrasonic impact treatment. By observing the texture of the outermost surface of the metal by the sump method on the treated surface and confirming that the texture is finer than other untreated parts, the deformation is formed by ultrasonic impact treatment. The feature is that it is determined.

The thirteenth invention is, in the quality assurance inspection of the first invention, in measuring the deformation formed on the metal surface when it is doubtful that the deformation was formed by ultrasonic impact treatment. By measuring the grain size of the outermost surface of the metal with an ultrasonic grain size measuring device on the treated surface and confirming that the tissue is finer than other untreated parts, the deformation is ultrasonic. It is characterized in that it is formed by impact processing.

Further, the fourteenth invention is, in the quality assurance inspection of the first invention, in measuring the deformation formed on the metal surface when it is doubtful that the deformation was formed by ultrasonic impact treatment. Roughness of the treated surface is measured with a roughness meter or laser displacement meter, and it is confirmed that the surface is smoother in the direction crossing the formed R (radius) than other untreated portions. Thus, it is characterized that the deformation is formed by ultrasonic impact treatment.

The fifteenth aspect of the invention is to measure the deformation formed on the metal surface in the quality assurance inspection of the first aspect, when it is doubtful that the deformation was formed by ultrasonic impact treatment. , The hardness of the treated surface is measured by a Pickers test, etc., and it is confirmed that the surface hardness is 20% or more and less than 100% of that of the other untreated portion, so that the deformation is superb. It is characterized in that it is formed by a sound wave impact process.

The 16th aspect of the present invention is, in the quality assurance inspection of the first aspect of the invention, that when a crack is generated during subsequent use with respect to the ultrasonic impact treatment portion after passing the quality assurance inspection, the inside of the coating film is inspected. The provided microcapsule is characterized in that it breaks at the cracked portion and easily indicates to the outside that cracking has occurred, by applying a paint that leaches out a paint of another color, and shows subsequent cracking. .

The seventeenth invention is characterized in that it is a metal material treated by the fatigue life improving treatment method according to any one of the first to sixteenth inventions.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION The occurrence of fatigue fracture of metal is greatly influenced by stress concentration and residual stress. In a metal material that receives a load, dislocations accumulate in the stress concentration part, which accumulates slip lines and develops into cracks, and after cracks develop, they progress. Residual stress usually exists as a tensile residual stress in a welded part and the like, and it is considered that the effective repetitive stress range is expanded to easily cause a crack and the opening of the generated crack is promoted. Therefore, in order to improve the fatigue life of the metal material, it is necessary to relax the stress concentration and make the residual stress as close to the compression state as possible.

The welded portion of metal has both a sudden change in surface shape and a tensile residual stress, which is the weakest point in terms of fatigue strength. This sudden change in the surface shape acts as a notch, and since it becomes a stress concentration part, plastic deformation is applied to this stress concentration part and it is possible to form a surface formed by a curved surface with a gentle toe radius. The stress concentration part will be relaxed. Further, at this time, if plastic deformation is applied to the metal in the plate thickness direction, the plasticized metal is constrained by the surrounding metal to introduce a compressive force.

Further, the cut end face of metal also has a sudden change portion of the surface and tensile stress and shear stress associated with cutting, which is a weak point of fatigue. This also gives plastic deformation in the direction perpendicular to the end face. Alternatively, the shape can be improved and the compressive stress can be introduced by giving plastic deformation so that the corners of the end faces are curved.

As a means for enabling such plastic working of metal, ultrasonic waves are applied to the tip of an amplitude of 20 μm to 60 μm.
There is a process called ultrasonic impact treatment that performs peening to hit a metal surface with a tool that vibrates at a frequency of 15 μm and a frequency of 15 kHz to 60 kHz. By using this method, it is possible to perform plastic working on the metal surface and introduce compressive residual stress to a depth of about 1.5 mm.

This ultrasonic impact treatment method basically does not change the basic mechanism of hammer peening and fatigue strength improvement, but the impact energy of each impact is reduced to 10,000 times or more per second. The same plastic deformation is realized by applying the impact of. Moreover, since the impact force of each time is small, there is almost no recoil in the equipment, which is very advantageous in terms of usability and workability as compared with hammer peening.

Further, this ultrasonic impact treatment is
Since the metal surface is hit with a very large number of times, it has an effect on the surface of the steel material that the conventional hammer peening does not have. Further, since the hitting energy for each shot is larger than that for shot peening, it brings about an effect which is not available in conventional shot peening.

First, by hitting the surface a large number of times, the uniformity of processing can be obtained. It is known that even with hammer peening, a certain degree of uniformity can be obtained by performing several passes on the same line, but the impact cycle number of ultrasonic impact treatment is 15 to 60 kHz, and the obtained uniformity is hammer peening. If the processing speed is about 0.5 m / min, the metal surface is almost evenly finished and no defects are left.

Further, the surface after the treatment has a remarkable smoothness. Comparing the smoothness of the metal surface before and after the treatment shown in FIGS. 2A and 2B, it is found that the smoothness after the ultrasonic impact treatment is significantly smoother than that after the grinder finishing. Recognize.

Further, it is known that the structure of the metal surface after the treatment is remarkably fined by repeating the plastic working many times by utilizing ultrasonic waves. (Surfa
ceNanocrystallization (SN
C) of metallicMaterials-Pr
orientation of the Concept
behind a New Approach, J.
Master.Sci.Technol.Vol.15 N
o. 3, 1999)

Actually, as a result of applying ultrasonic impact treatment to a steel material for the purpose of improving fatigue, the steel material structure is largely changed before and after the treatment. Such an effect of refining the structure of the steel material is
In particular, the HAZ part near the weld where the structure of the steel material coarsens is remarkable, and the grain size of the HAZ that coarsens up to 100 μm is so small that the grain size is hardly observable after the ultrasonic impact treatment. And a unique steel structure has been achieved by ultrasonic impact treatment.

Further, as the structure of the steel material on the surface of the steel material becomes finer by the ultrasonic impact treatment, the hardness increases.
Fig. 3 shows the hardness distributions of the base metal part, the molten metal part, and the HAZ part after ultrasonic impact treatment. Especially for strength steels often used for welded steel structures, the hardness increases by 20% or more. You can see that In addition, depending on the material and treatment time, the hardness may increase up to about twice as much as before treatment. However, this does not mean that it is hard and brittle martensite, and it is mainly due to fine graining. The effect and work hardening due to the accumulation of dislocations is not an increase in the kind of hardness that causes weld cracking.

Fatigue fracture of a steel sheet consists of crack initiation and propagation. The total of the life of crack initiation and the life of crack propagation is the total life leading to fatigue cracking. In many cases, a crack is generated from a location where stress concentration or residual stress is severe, and the crack that has continued further progresses to eventually break the member. In order to improve the fatigue fracture life of steel sheets,
It is necessary to suppress the occurrence of fatigue cracks and the development of fatigue cracks.

However, normally, once a crack is generated in the steel material, the stress concentration at the crack tip is extremely large, and it is extremely difficult to stop this progress.
For example, even if a stop hole is formed at the tip and the hole is tightened with a high-strength bolt, if a crack tip is left, the crack may propagate inside the bolt and even cut.

Observing the initial fatigue crack, the strain measurement during the fatigue test of the swirl-welded test specimen was performed to observe the initial fatigue crack, which is the state of the crack at the time of occurrence detection. About 10% of the normal fatigue life has passed, and the remaining 90% of the life is the growth life of this crack, which is almost determined unless the crack is removed.

However, cracks in this state cannot be detected by a normal penetration flaw detection test or a magnetic particle flaw detection test. If hammer peening or shot peening, which is a conventional fatigue life improving method, is performed in this state, the treatment is performed while leaving these cracks, so that apparently plastic deformation occurs on the treated surface. However, since the progress of cracks cannot be stopped, the improvement effect is only the reduction of stress concentration due to the shape improvement, and it is considered that the life is hardly extended.

However, if the ultrasonic impact treatment is carried out even in this state, in order to introduce a compressive stress due to plastic deformation to a depth of about 1.5 mm, the crack may be crushed and the tip of the crack may not be opened. it can. Of course, the depth at which compressive stress can be introduced can be as deep as or more than that in hammer peening, but hammer peening has uneven treatment effects, and it is considered that there are many parts to leave without hitting cracks, On the other hand, in the ultrasonic impact treatment, since the number of hits is extremely large as described above, it is possible to uniformly suppress the opening of cracks.

Therefore, in order to effectively obtain the fatigue life improving effect, it is basically necessary to subject the weld metal product to ultrasonic impact treatment to the weld metal portion and the HAZ portion, centering on the toe portion of the weld portion. is there. The interface between the weld metal and the HAZ, which is the weakest point of fatigue, is strengthened against fatigue, and the adverse effects of hot cracking on the surface of the weld metal can be significantly reduced. However, caution is required because it is considered to have little effect on hydrogen cracking at low temperatures.

In order to effectively obtain a fatigue life against the fatigue of a metal, which is a weak point of fatigue without welding, from a cut surface due to saw, shear, gas, laser, plasma, etc. Ultrasonic impact treatment is applied to the end faces. With this, excessive tensile stress entering the end face with cutting,
In addition to relieving shear stress and introducing compressive stress, the stress concentration part such as burrs caused by cutting is shaped into a smooth curved surface by plastic deformation, and especially heat input of gas, laser, plasma etc. It is possible to render the extremely hardened layer, which is generated on the end face by the cutting method accompanied by, harmless. At this time, it is necessary to be careful not to raise the output too much and give harmful deformation to the end face, but this is only possible with ultrasonic impact treatment that has little recoil and is easy to control. , The conventional hammer peening is not feasible, and the shot peening is not efficient.

For such processing at the welded portion, the cut end, etc., one pass is sufficient for the number of treatments on one treatment line, but when it is desired to increase the uniformity or to improve the controllability. If you want to suppress the input power per processing in order to prevent or prevent excessive plastic deformation,
By performing the treatment twice or more on the same line, a more reliable fatigue life improving effect can be obtained.

As described above, the ultrasonic impact treatment causes a unique change in the microstructure of the metal as compared with the effect of the fatigue life improving treatment method of the other compressive stress introduction system. , Hardness, microstructure (grain size)
By observing, it is possible to determine relatively easily whether the trace of the plastic deformation generated on the metal surface is due to the ultrasonic impact treatment.

The surface state after such treatment can be duplicated as in the Sump method to observe the tissue, or can be directly measured by scanning with a displacement meter or the like. The hardness can be easily measured using a Vickers test or the like. Furthermore, if only the particle size is measured, it is easy to use a particle size measuring device using ultrasonic waves.

The degree of stress concentration can be easily achieved by measuring the shape after processing. By observing the condition of the weld toe before and after the treatment, it can be seen that the toe shape is deformed according to the shape of the treated tip tool. The curvature of the curved surface formed by the ultrasonic impact treatment in the stress concentration portion is, of course, the larger the curvature is, the lower the stress concentration coefficient is.However, in the case of the ultrasonic impact treatment, there is a relationship with the compressive stress to be introduced. Empirically, R (radius) is 0.5 mm
Since the fatigue improving effect is high when processing is performed with a tool having a curved surface of about 3.0 mm, the stress concentrated portion is processed with approximately this curvature.

Then, the magnitude of the compressive stress introduced is
It can be inferred by the plastic deformation of the surface before the treatment in the depth direction of the metal after the treatment. Basically, the greater the amount of plastic deformation in the depth direction, the greater the amount of compressive force introduced, but as described above, the amount of plastic deformation formed by ultrasonic impact treatment, and Since the effect of improving fatigue obtained is also related to the curvature of the tool, if R is small, the plastic deformation depth is large, and if R is large, the plastic deformation depth is small, but empirically, R is 0.5 mm to If the plastic deformation depth is about 3.0 mm and about 0.05 mm or more and 1.0 mm or less,
Fatigue improving effect is sufficiently obtained.

It is general and easy to inspect the shape after such treatment by making a duplicate using an amorphous material such as a dental shape material, but scanning with a laser displacement meter or the like. It is also possible to measure directly.

However, in the case where a device for ultrasonic impact treatment is installed in a factory line and a new metal material is produced, the cracks in the pretreatment should be visually inspected at the level of ordinary materials. It can be replaced by checking for the presence or absence of harmful scratches, and also in quality control after processing,
Since the treatment by ultrasonic impact treatment is obvious, check the tip tool of ultrasonic impact treatment, check the output setting, and visually check whether plastic deformation occurs in the product by ultrasonic impact treatment. Can be replaced with only.

In the method of improving the fatigue life of giving a compressive residual stress, it should be noted that the portion of the metal material to be subjected to ultrasonic impact treatment and the portion near the portion which may affect the portion are subjected to ultrasonic wave treatment. To prevent the compressive residual stress introduced by impact treatment from being changed by other processes required for producing the metal material, such as bending, straightening, heat treatment, and plastic deformation, such as welding. is necessary. That is, it is necessary to comply with the order in which the ultrasonic impact treatment is finally performed on the relevant portion after all the processes are completed.

After it is confirmed by the quality assurance inspection that it has a predetermined performance, there is a means for further enhancing the effect. That is, after the treatment, the coating applied to the treated portion has functionality. For coating, microcapsules containing another color of paint can be mixed. This allows the paint inside to be leached out by breaking the microcapsules by an external stimulus to the paint.

As such a functional coating, smart paint (US Pat. No. 5,534,239) capable of indicating the position of the crack by causing the microcapsule to be cracked by the strain generated in the coating when the crack is generated. If you apply what is called) to the place of ultrasonic impact treatment,
It is easy to see and the inspection after use is easy.

FIG. 1 is a flow chart showing the fatigue life improving treatment method of the present invention. Using the characteristics of ultrasonic shock treatment as described above, in order to ensure the fatigue improvement effect, the rules are roughly defined in the order of pretreatment, ultrasonic shock treatment, and quality inspection. .

A fatigue experiment was conducted to confirm the effect obtained by the present invention. In this fatigue experiment, first, fatigue loading was performed until initial fatigue occurred, and then a magnetic particle flaw detection test was performed as a pretreatment.Since no fatigue crack was found at that time, there was no particular fatigue crack removal, etc. The impact treatment was performed, and then the fatigue test was performed again. The fatigue cracks introduced by the first loading are rendered harmless, and the fatigue life is 200 MPa at 300,000 to 150 times.
It has improved more than 10,000 times and more than 5 times.

The feature of the present invention is that since a fatigue crack at an undetectable level can be rendered harmless by introducing plastic deformation and compressive stress at the crack tip, the crack is found unlike the usual method. Even a portion that has not been processed can be treated as a fatigue occurrence preventive measure at the time of inspection. As a result, fatigue can be expected to be improved, so that it is possible to increase the interval between regular inspections related to fatigue of the processed metal product and reduce maintenance costs.

Further, the maintenance cost can be reduced by applying a functional paint which facilitates the crack inspection after the treatment.

As described above, the metal product treated according to the present invention can surely secure the fatigue life of three times or more in the region of the repeated action stress which is usually used.

[0062]

As described above, according to the fatigue life improving method of the present invention and the metal product treated by the fatigue life improving method, a new fatigue life improving treatment method called ultrasonic impact treatment is applied to an appropriate pretreatment and post treatment. By combining with the quality inspection method of No. 1, it is possible to reliably suppress the fatigue generated from the metal surface regardless of new installation, repair, welding, etc., and it is possible to improve the fatigue life. is there. In addition, even if fatigue cracks with small dimensions that cannot be detected by conventional non-destructive inspection are left, the fatigue strength can be improved, so that it is possible to prevent the occurrence of detectable fatigue cracks and prevent the metal This fatigue improvement method can be applied to products, and a functional coating that facilitates the subsequent discovery of cracks can be applied after treatment, which reduces maintenance costs especially for steel structures such as bridges. Is possible.

[Brief description of drawings]

FIG. 1 is a flow chart showing a fatigue life improving treatment method of the present invention.

FIG. 2 is the smoothness of the metal surface after finishing with a grinder,
The figure showing the smoothness of the metal surface after ultrasonic impact processing of the present invention.

FIG. 3 is a diagram comparing the hardness of the metal surface before and after the ultrasonic impact treatment of the present invention.

Continued front page    (72) Inventor Tadashi Ishikawa             20-1 Shintomi, Futtsu City Nippon Steel Co., Ltd.             Inside the surgical development headquarters (72) Inventor Tadashi Kasuya             20-1 Shintomi, Futtsu City Nippon Steel Co., Ltd.             Inside the surgical development headquarters (72) Inventor Koji Honma             20-1 Shintomi, Futtsu City Nippon Steel Co., Ltd.             Inside the surgical development headquarters

Claims (17)

[Claims] 1. A fatigue life of a metal material is improved by performing pretreatment, ultrasonic impact treatment, and quality assurance inspection on a portion where fatigue of the metal material is a problem. A fatigue life improving treatment method characterized by the above. 2. The pretreatment of the fatigue life improving treatment method according to claim 1, wherein a portion of the metal material subjected to ultrasonic impact treatment and a portion in the vicinity thereof are subjected to plastic working, deformation correction, heat treatment,
Characterized by performing ultrasonic impact treatment after performing a process such as welding that changes the internal metal stress and surface stress, and not performing a process that changes such internal metal stress and surface stress after the ultrasonic impact treatment. Fatigue life improvement treatment method. 3. The pretreatment of the fatigue life improving treatment method according to claim 1, wherein a portion of the metal material subjected to ultrasonic impact treatment and a portion in the vicinity thereof are subjected to plastic working, deformation correction, heat treatment,
After performing the process of changing the metal internal stress and surface stress such as welding, non-destructive inspection and ultrasonic impact treatment are performed,
A fatigue life improving method characterized by not performing a process for changing such internal stress and surface stress of metal after ultrasonic impact treatment. 4. In the pretreatment of the fatigue life improving treatment method according to claim 1, after performing a visual inspection, a penetrant flaw detection inspection, a magnetic particle flaw detection inspection, an eddy current flaw detection inspection, etc. on a portion having a fatigue life problem. Then, if a crack is detected, the crack is removed with a grinder or gouging to improve the fatigue life. 5. When removing the cracks in the fatigue life improving treatment method according to claim 4, when the depth of removal becomes as deep as 5 mm or more, after welding build-up, finish smooth with a grinder and further visually Inspection, penetrant inspection, magnetic particle inspection,
Fatigue life improvement treatment method characterized by confirming that cracks are not detected after performing eddy current flaw detection. 6. The ultrasonic impact treatment of the fatigue life improving treatment method according to claim 1, wherein the toe portion, the HAZ portion and the welded portion in the welded portion of the metal material are treated to concentrate the shape of stress. The fatigue life improving treatment method is characterized in that it is deformed so that it does not easily occur, and that compressive residual stress is introduced to detoxify the minute defects that are the starting point of fatigue generation and suppress the generation of cracks. 7. In the ultrasonic impact treatment of the fatigue life improving treatment method according to claim 1, a treatment is performed on a cut surface of a metal material by sawing, shearing, gas, laser, plasma or the like and the vicinity thereof. In addition to deforming the shape so that stress concentration does not easily occur, compressive residual stress is introduced to make harmless to minute defects and extremely hardened parts that are the starting points of fatigue occurrence, and suppress the occurrence of cracks. Fatigue life improvement treatment method. 8. In the ultrasonic impact treatment of the fatigue life improving treatment method according to claim 1, a compressive stress due to impact is introduced into a crack below a detection limit in a nondestructive inspection by using the ultrasonic impact treatment to develop the crack. Fatigue life improvement treatment method characterized by stopping. 9. The ultrasonic impact treatment of the fatigue life improving treatment method according to claim 1, wherein two or more passes of ultrasonic impact treatment are applied to the same portion of a structure or a structure part where a fatigue crack may occur. The fatigue life improving treatment method is characterized by introducing compressive stress due to impact to cracks below the detection limit in non-destructive inspection and stopping the progress more reliably by performing. 10. In the quality assurance inspection of the fatigue life improving treatment method according to claim 1, scanning is performed using a molding material such as a dental shape material or a high precision measuring device such as a laser displacement meter. , Take the shape mold after ultrasonic impact treatment,
The surface of the treated surface is almost the same as the R (radius) of the tool tip of the ultrasonic impact treatment used for the treatment, and plastic deformation occurs at a depth of 0.05 mm or more compared to before treatment. By confirming that, the shape of the treated portion is improved, and it is confirmed that the fatigue life is improved by the introduction of compressive residual stress. 11. In the quality assurance inspection of the fatigue life improving treatment method according to claim 1, when ultrasonic impact treatment is performed as a steady process, confirmation of ultrasonic impact treatment tip tool,
By confirming the equipment output setting and visually confirming the occurrence of plastic deformation in the treated part, confirm that the shape has been improved in the treated part and the fatigue life has been improved by the introduction of compressive residual stress. Fatigue life improvement treatment method characterized by. 12. In the quality assurance inspection of the fatigue life improving treatment method according to claim 1, when it is doubtful that the deformation is formed by ultrasonic impact treatment, the deformation formed on the metal surface is measured. By observing the texture of the outermost surface of the metal by the sump method on the treated surface and confirming that the texture is finer than other untreated parts, the deformation is formed by ultrasonic impact treatment. A method for improving fatigue life, which is characterized by determining the fact. 13. In the quality assurance inspection of the fatigue life improving treatment method according to claim 1, in case of doubt that the deformation is formed by ultrasonic impact treatment, the deformation formed on the metal surface is measured. By measuring the grain size of the outermost surface of the metal with an ultrasonic grain size measuring device on the treated surface and confirming that the tissue is finer than other untreated parts, the deformation is ultrasonic. A fatigue life improving treatment method characterized by determining that it has been formed by impact treatment. 14. In the quality assurance inspection of the fatigue life improving treatment method according to claim 1, in the case of doubt that the deformation was formed by ultrasonic impact treatment, the deformation formed on the metal surface is measured. Roughness of the treated surface is measured with a roughness meter or laser displacement meter, and it is confirmed that the surface is smoother in the direction crossing the formed R (radius) than other untreated portions. Thus, the fatigue life improving method is characterized in that it is determined that the deformation is formed by ultrasonic impact processing. 15. In the quality assurance inspection of the fatigue life improving treatment method according to claim 1, when it is doubtful that the deformation is formed by ultrasonic impact treatment, the deformation formed on the metal surface is measured. , The hardness of the treated surface is measured by a Pickers test, etc., and it is confirmed that the surface hardness is 20% or more and less than 100% of that of the other untreated portion, so that the deformation is superb. A method for improving fatigue life, which is characterized in that it is formed by ultrasonic impact treatment. 16. In the quality assurance inspection of the fatigue life improving treatment method according to claim 1, when a crack is generated in the ultrasonic impact treated portion after passing the quality assurance inspection during subsequent use, the inside of the coating film The provided microcapsule is characterized in that it breaks at the cracked portion and easily indicates to the outside that cracking has occurred, by applying a paint that leaches out a paint of another color, and shows subsequent cracking. Fatigue life improvement treatment method. 17. A metal material treated by the fatigue life improving treatment method according to claim 1.