JPH06246637A - Method for preventing metal thermal fatigue and progress of stress corrosion cracking by zirconia shot blast - Google Patents

Abstract

PURPOSE:To attain both life extension of a shot and rust prevention of a workpiece, in a shot blast used for impeding thermal fatigue, preventing progress of stress corrosion cracking, etc. CONSTITUTION:Surfaces of a workpiece metal are shot blasted by zirconia balls to give compression stress to this metal surface, and by relaxing tensile stress, a fine flaw is prevented from being generated on the surface of the workpiece. Accordingly, by using the zirconia balls 1 to obtain a rust preventing effect, also by excellent toughness, a shot itself can be used over a relatively long period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing thermal fatigue resistance of metal and progress of stress corrosion cracking by zirconia shot blasting.

[0002]

2. Description of the Related Art The peening effect of shot blasting increases the fatigue strength of metal parts and prevents stress corrosion cracking. Therefore, a cold blasting technique by shot blasting for the purpose of such effect exists as a well-known technique. . In general, such blast is mainly made of cast iron or cast steel. Other than this, there are alumina shot, stainless shot, aluminum shot, glass shot, and the like. Conventionally, shot processing has been performed on the stainless steel products by using the above shots such as cast steel and shots made of stainless steel.

[0003]

However, the work piece surface-treated by using the shot as described above had rust at an early stage, and required post-treatment such as pickling. This is because countless minute scratches are generated on the surface of the work piece processed by shots such as cast steel and shots made of stainless steel, and a rust phenomenon is likely to occur. On the other hand, when surface treatment is performed using the above-mentioned alumina shot or glass shot, rust is less generated, but the shot ball is destroyed by one use, and a shot ball newly used each time. It was necessary to select the particle size. Further, the fragments of the destroyed shots are pierced and left on the surface of the work piece subjected to the processing of these shots, and it is necessary to perform a post-treatment such as removing such a residue. In particular, since the glass shot has a relatively small specific gravity, the effect of imparting a compressive stress is small and effective only when used for decorative processing. As described above, in the conventional shot processing, the prevention of rusting and the prevention of damage to the shots have been abandoned as being incompatible with each other. The present invention is intended to solve the above problems.

[0004]

The method for preventing the thermal fatigue resistance of metals and the progress of stress corrosion cracking by zirconia shot blasting according to the first aspect of the present invention is based on
It is characterized in that shot blasting is performed on a metal surface that is a work piece, a compressive stress is applied to this metal surface, and tensile stress is relaxed. In the method for preventing the thermal fatigue resistance and the progress of stress corrosion cracking of metal by the zirconia-based shot blasting according to the second invention of the present application, the zirconia-based ball 1 used in the first invention has yttria or ceria added. It is a substantially spherical one having toughness. Then, a plurality of these zirconia-based balls 1 having a uniform size are formed by a rotary projection method,
Alternatively, the blasting is performed by a suction type or a pressure type method. According to a third aspect of the present invention, there is provided a method for preventing thermal fatigue resistance and progress of stress corrosion cracking of metal by zirconia-based shot blasting according to the first or second aspect, wherein the grain size of the zirconia-based ball 1 is set to Depending on the shape, select between about 0.3 m / mφ and about 1.6 m / mφ. And blast pressure, distance, angle,
For the hose length and nozzle diameter, adjust the plate thickness of the material used and the depth of compressive stress with an Almen gauge, and set appropriate conditions by evaluating in advance with an Almen strip test piece. The plate thickness of the work piece is adjusted within the range of the arc height of about 0.1 to 1.4. A method for preventing thermal fatigue resistance and progress of stress corrosion cracking of metal by a zirconia-based shot blasting according to a fourth invention of the present application is the method according to the first, second or third invention, wherein the zirconia-based ball 1 is blasted and then processed. In order to block the contact with the outside air on the surface of the, the passivation treatment should be carried out by immersing it in an organic paint or an inorganic solvent or by spray-coating these blocking materials. Characterize. A method for preventing thermal fatigue resistance of metal and progress of stress corrosion cracking by zirconia shot blasting according to the fifth invention of the present application is the above-mentioned first, second or third invention, wherein the zirconia ball 1 is blasted and then processed. On the surface of
The sacrificial film that does not affect the work to be coated even if it is deteriorated by contact with the outside air is not formed by the outside air. A method for preventing the thermal fatigue resistance and progress of stress corrosion cracking of metal by zirconia-based shot blasting according to the sixth invention of the present application is the method of the above-mentioned first, second or third invention, wherein the zirconia-based ball 1 is blasted and then processed. On the surface of, a thermal spray coating is formed by metal spraying or ceramic spraying.

[0005]

The method according to the first invention of the present application having the above-mentioned configuration is
In order to improve these factors that cause rust damage after shot processing, the applicant conducted experiments on various shot materials using shot materials, and as a result, the shot processing using the zirconia-based ball 1 showed a higher than expected value. It was discovered that the effect was remarkable. That is, by applying a ball formed of this material called zirconia to a shot, an effect that has not been obtained hitherto can be obtained. This is because the surface of the zirconia ball 1 is smooth,
This is because the surface of the workpiece is not scratched by the shot. Therefore, after shot processing of a stainless steel product, no rust was generated, and the post-treatment which was conventionally required is no longer necessary. Furthermore, the zirconia-based ball 1 itself has excellent toughness, is not broken even after being used about 50 times, and has no wear deformation. Thus, it was possible to impart remarkable durability to shots used to prevent high temperature thermal fatigue cracking or stress corrosive cracking, and further hydrogen induced cracking. In particular, since the zirconia-based ball 1 has strong corrosion resistance and acid resistance even if it is contaminated with oil and acids, it can be reused even in this aspect if it is washed and dried. The method according to the second invention of the present application having the above-mentioned configuration,
Using the zirconia-based ball 1 of the first invention of the present application, a tensile residual stress is applied to a workpiece by a projection method, an air suction method, or a pressure blast method, and the residual stress of the material of the workpiece is relaxed. Made it possible. Therefore, it is possible to use an existing metal structure such as a building as a workpiece to be blasted with the zirconia-based ball 1. In the method according to the third invention of the present application having the above-described configuration, the effects of the first and second inventions are most remarkably obtained with respect to the grain size of the zirconia-based ball 1, the shot device thereof, and the plate thickness of the workpiece. It was possible to set the conditions that can be. In the method according to the fourth invention of the present application having the above configuration, in the first, second, or third invention, a blocking material is interposed between the outside air and the surface of the workpiece after the shot processing. Even when the work piece is used in a corrosive environment or atmosphere, the work piece does not corrode.
The method according to the fifth aspect of the present invention having the above-described configuration is the method according to the first, second or third aspect of the invention, in which after the shot processing, the method itself contacts the outside air between the outside air and the surface of the workpiece. A material that sacrificially deteriorates is interposed, and the surface of the workpiece covered with this material is not affected by the outside air. In the method according to the sixth aspect of the present invention having the above-mentioned configuration, the surface of the workpiece is shielded from corrosive gas or liquid by forming the coating by metal spraying or ceramic spraying.

[0006]

EXAMPLES Examples of the present invention will be specifically described below. Zirconia balls 1 are used as shots for processing to prevent thermal fatigue of metal (a phenomenon that cracks occur by repeated heating and cooling), stress corrosion cracking, and hydrogen-induced cracking by shot blasting. To do. As shown in the enlarged view of FIG. 1, this is about 0.3 m / mφ to about 1.6 m / m depending on the material and shape of the workpiece (not shown) to be shot.
It is a zirconia-based ball 1 having an appropriate size between φ (width X is about 1 m / m 2 in FIG. 1). The zirconia-based ball 1 is a substantially spherical ball having toughness to which yttria, ceria, or the like is added. FIG. 1 shows an almost true sphere, but the shape is not limited to a perfect sphere, and for example, an oval shape, a somewhat elliptical sphere, an ellipsoid, or other substantially spherical sphere other than a perfect sphere. However, it can be implemented.

Then, a plurality of such zirconia-based balls 1 having a uniform size are shot-blasted onto a metal surface which is a workpiece by a rotary projection method, a suction method or a pressure method, A compressive stress is applied to the metal surface, which is the workpiece, to relax the tensile stress. When such a method is used, it is possible to perform on-site processing by selecting an apparatus, and it is possible to carry out the present invention on an existing building or the like. For the blast pressure, distance, angle, hose length, and nozzle diameter, adjust the plate thickness of the material used and the depth of compressive stress with an Almen gauge, and evaluate in advance using an Almen strip test piece. Set in the condition. These evaluations will be described in detail later. Regarding the plate thickness of the work piece, the arc height is about 0.1.
It adjusts within the range of about 1.4 mm.

The workpiece subjected to the shot processing as described above may be used in an environment where corrosion or the like is likely to occur depending on the purpose of use. In such a case, it is desirable to block the contact with the outside air by secondary treatment. Hereinafter, such secondary processing will be described with reference to a suitable example. First, in order to block the contact with the outside air on the surface of the work piece that has been subjected to the above-mentioned shot processing, a method of dipping it in an organic paint or an inorganic solvent or spray coating these blocking materials. Therefore, it is appropriate to perform passivation processing. The above-mentioned inorganic solvent contains an inorganic coating material.

In particular, as long as the work itself can be protected, the structure is not limited to the above-mentioned one, and even if the work itself deteriorates due to contact with the outside air, the influence of the outside air on the workpiece to be coated is not affected. The sacrificial film which is not applied may be formed by a well-known appropriate method.

Furthermore, it is also effective to form a sprayed coating by metal spraying or ceramic spraying on the surface of the workpiece after blasting the zirconia-based balls 1. For example, when exposed to a high temperature thermal fatigue environment, a severe environment of hydrogen-induced cracking, and stress corrosion cracking, a cathodic protection (Al, Al,
Zn, etc.) or a NiCr-based or Hastelloy-based sprayed coating for the purpose of environmental protection is suitable. Furthermore, when corrosion is severe, cermet or ceramic spray is applied to the surface of the corrosion resistant metal of the first layer to the second or third layer,
It is desirable to form a film that blocks corrosive gases and liquids.

Each data obtained by the above configuration and its evaluation method will be described below. First, using the zirconia-based ball 1, various blast pressures, distances, and angles were experimentally changed in the laboratory. In addition, conventional cast steel shots, stainless steel shots, etc. were compared to evaluate the characteristics of zirconia shots.

The first experiment was conducted on stainless steel (SUS30
The surface of 4) was subjected to various shot blasting treatments and exposed indoors, indoors, and outdoors, and the time for rust generation was examined. The results are shown in Table 1.

[0013]

[Table 1]

Table 1 above shows the rust generation state of each SUS material after each shot blasting. In this judgment, the circle mark is normal, the triangle mark with a sharp top has a few cracks, the triangle mark with a sharp bottom has a few cracks, the cross mark is broken, and the cross mark 2
Shows significant cracking. The experimental results of rust generation shown in Table 1 were performed in the atmosphere. “After 24 hours” and “after 168 hours” on the left side of the table are elapsed times after blasting.

In this first experiment, the pressure, distance and nozzle of each blast were the same. The shot materials (A to H) shown in Table 1 above are as follows. That is, the shot sample A is a cast steel shot, and its shape is a sphere having a diameter of about 1 mm. Sample B is a cast iron shot and is a sphere with a diameter of about 1 mm. Sample C is a stainless shot and has a diameter of about 0.8 m.
It is a sphere of m. Sample D is made by adding glass shot to stainless shot. In this case, the stainless shot is a sphere having a diameter of about 0.8 mm, and the glass shot is a sphere having a diameter of about 0.3 mm. Sample E is cast steel shot plus stainless steel shot. In this case, the cast steel shot has a diameter of about 1.0 m.
It is a sphere of m, and the stainless shot has a diameter of about 0.8.
mm sphere. Sample F is a glass shot and is a sphere having a diameter of about 1 mm. Sample G is an alumina shot, which is a sphere having a diameter of 1 mm. Sample H is a zirconia shot, which is a sphere having a diameter of about 1 mm.

As shown in Table 1, rust generation on the surface of stainless steel (SUS304) was good in glass shot, alumina shot, and zirconia shot (synonymous with zirconia-based ball 1; the same applies hereinafter) in the first experiment. When shot blasting is performed on each of these three types, the shot spheres of glass shots and alumina shots are destroyed by one blast, and reuse is impossible unless separated with a sieve (old). , Zirconia shot,
Good without any change. For reference, the characteristics are shown in Table 2 below.

[0017]

[Table 2]

In Table 2, "Hardness" in the "Characteristics" item is a value according to micro-Vickers, and the unit "PPN / Hr" of "empty wear rate" is rotation / hour (hour).
Is shown. Regarding the value of "100" for zirconia in the "Blasting frequency characteristics" item, unlike other materials, it does not mean that destruction occurred after 100 times, but the number of tests was 100 times, during which no destruction occurred. Therefore, it means that the destruction could not be confirmed at least 100 times. Here, "construction of short peening"
(Metal Improvement Company, 6th edition, 1980)
Will be described with reference to.

As generally defined, short peening is a cold working technique intended to increase the fatigue strength of metal parts and prevent stress corrosion cracking. In this short peening, the finished surface is struck with spherical particles under well adjusted conditions. Each short peening ball acts as a small peening hammer. The surface peened by countless impacts results in a layer with residual stress (compressive stress) on the surface, which prevents cracking.

Measuring all the parameters of short peening is both cumbersome and impractical. In order to simplify this, J.K. O. There is a method developed by Mr. Armen. This allows the strength of short peening to be measured, inspected and duplicated. This is based on the following principle.
That is, when one test piece is placed on a holder and subjected to short peening, the test piece warps. In this case, the test piece bulges convexly toward the peened side.

Then, the height of the arc measured by a special gauge (0.008 inch peening strength for A test piece of Almen strip) is defined as the peening strength. Test pieces with three different thicknesses are prepared to measure different strengths. Arc height in A test piece (arc he
ight: If the height of the convexly bulging arc is 0.004 inches or less, use N test pieces. The value for the N test piece is approximately three times that for the A test piece. If the arc height of the A test piece is 0.020 inch or more, the C test piece must be used. The numerical value of the C test piece is A
It becomes about 1/3 of the test piece. 2 and 3 show the test pieces 2 described above. The width a (FIG. 2) is about 76 mm for all N, A and C test pieces, and the height b (FIG. 2) is about 19 mm for all N, A and C test pieces. . The thickness c (Fig. 3) of the test piece 2 is about 0.79 mm for the N test piece.
And the A test piece is about 1.3 mm and the C test piece is about 2.36 mm.

The standard for measuring the strength of peening defines the gauge reading, the arc height, and the type of test piece. It is necessary to define the range of peening strength such as 0.010 to 0.014 A or 0.006 to 0.008 C. All measurements are standard Almen No., 2 gauge (number 2 gauge) as specified in SAE Shot Peening Manual, ANS2430, MILS-13165 (since it did not break, the test was finished at this time). Is used.

The test piece installed on the holder must be placed in the same blast environment as the actual peened part. In fact, if you have a complicated shape, you must use several test pieces and fix them in the same way. 1
After one test, the test piece shall not be reused.

The purpose of controlling shot peening is to apply uniform compressive stress to each of the parts so that the stress is constant quantitatively, and the thickness of the layer to which the compressive stress is applied is also constant. It is to be. It is virtually impossible to measure the stress distribution on the finished surface, so perfect coordination of all of the steps is essential. The stress, depth, and coverage can be controlled by appropriately combining shot material and blast time, blast pressure or wheel speed, nozzle size, blast distance, and blast angle. It is very important that the shot flow and the relative movement of the object be uniform and reproducible.

The magnitude and depth of the residual stress will be described below. As already mentioned, the purpose of short peening is to apply compressive stress to the surface layers. For this purpose, the control method ensures reproducibility of the short peening process. But this method
It does not directly indicate the magnitude of stress or the depth of the layer under stress. The graphs shown in Tables 3 and 4 below show the magnitude and depth of the stress of short peening for steel.

[0026]

[Table 3]

[0027]

[Table 4]

The graph shown in Table 3 above shows the relationship between the residual compressive stress due to shot peening and the tensile strength of steel, with the vertical axis indicating normal hardness (Rockwell 45-5).
Using the shot material of 5), the maximum residual compressive stress at or near the surface after peening is taken, and the abscissa shows the tensile strength and hardness (rockwell) before peening.

The graph shown in Table 4 above shows the relationship between the depth of compressive stress and the peening strength of the Almen strip (steel and titanium alloy), the vertical axis being the hardness of steel and titanium alloy, and the horizontal axis. It is based on the peening strength of Almen strip. The unit of the horizontal axis is millimeter, the upper row of the horizontal axis (C strip) shows the strength by the C test piece, and the lower row of the horizontal axis (A strip) is A.
The strength by the test piece is shown. The scale interval in the lower row of this horizontal axis is 0.005 mm.

Regarding the influence of heat for extending the life,
A test piece bent into a U shape and subjected to stress was shot peened on one side and heated in a magnesium chloride solution on the other side without being processed, to perform a test. The results are shown in Table 5 below.

[0031]

[Table 5]

Table 5 shows SUS by peening processing.
It shows the effect exerted on stress corrosion cracking (SCC) when the 304 test piece is heated to 540 ° C and 585 ° C. "16 hours" and "144 hours" in the "time" item indicate the heating time. In the table, "time for causing SCC" means "time for causing stress corrosion cracking". Further, the processing shown in Note 1 in Table 5 was performed on the A test piece of the Almen strip with a peening strength of 0.008 inch, and the processing shown in Note 2 did not break, so the test was finished at this time. It is a thing (above "Shot Peening Applications" Metal Improvement Co.
(quoted from mpany, Inc.SIXTH EDTION).

Next, stress corrosion cracking was considered and ZrO2 (zirconia: zirconium oxide; hereinafter the same) was evaluated by a second experiment. In this second experiment,
As the test specimen, SUS304 material, which is commonly used, was used. For forming residual stress, the welding rod JIS Z
Since the 3221 D-308 is often used, it conforms to this from the viewpoint of reality. An experiment was conducted using the sample 3 shown in FIGS. 4 and 5. As shown in the figure, the test piece 3 has a cylindrical shape, a thickness d (FIG. 4) of 3 mm, a width e (FIG. 5) of 100 mm, and an outer diameter f (FIG. 5) of 20.
It is 0 mm. Welding did not take grooves at three locations and welding beats were added (groove welding was conducted separately). 4 of FIG. 4 and FIG. 5 shows this weld bead.

In this second experiment, the experimental solution was JI
It was based on the liquid of the 42% magnesium chloride corrosion test method according to SG-0576.

A enamel tank having an internal capacity of 50 liters (inner diameter 390 mm, width 450 mm) was prepared as a test device (not shown). A magnesium chloride solution having a concentration of 42% is contained in the enamel tank. A sub-tank is formed outside the enamel tank to store rapeseed oil. An electric heater is inserted in this sub tank, and the temperature is controlled by an appropriate control means such as a thermostat. By adjusting the temperature of the rapeseed oil in this sub tank, the temperature of the magnesium chloride liquid in the tank of the enamel making tank was 143
It is adjusted to ° C (error range ± 1 ° C). Furthermore, the rapeseed oil in the sub tank outside the enamel tank can be
The magnesium chloride solution was circulated at a low speed and stirred so that the temperature of the magnesium chloride solution did not change.

The consideration regarding the second experiment will be described below. In this second experiment, the specimen 3 shown in FIGS. 4 and 5 was subjected to a continuous immersion test for 24 hours and 48 hours using the above-described experimental apparatus. As a result, cracking occurred as shown in Table 6 below. After being immersed in the enamel bath for 24 hours, the inside of the sample 3 was rubbed with a wire brush and visually observed, but no crack was observed. The cracks of the test pieces could be visually observed on the outer side and the inner side of each test piece after 48 hours of immersion. As described above, in order to prevent the progress of the stress corrosion cracking, in the sample 3 which was not subjected to any processing, remarkable cracking could be confirmed.

[0037]

[Table 6]

Finally, the experiment for preventing the progress of stress corrosion cracking, which was conducted as the third experiment, will be described. By the second experiment, it was confirmed that cracks occur near the weld of SUS304 material which is not subjected to any processing. Therefore, in this section, ZrO2 shot of the present application is applied as a method for preventing the progress, and this effect is to be tested. did.

In this third experiment, the test piece 3 was prepared in the same manner as in the second experiment by subjecting one test piece 3 to three welding beats 4 and one of them was the welding bead 4.
I left it as it was. The other one was blasted with ZrO2 on the surface, and the other one was blasted with ZrO2 on both front and back surfaces.

The third experiment was carried out on the specimen 3 prepared under various processing conditions as shown in Table 7 below.
The effects of shot blasting and silicone resin after shots were considered.

[0041]

[Table 7]

As mentioned above, this Table 7 shows the above ZrO 2
It shows the preparation and evaluation of the shot specimen 3. In this Table 7, "100 w m / m" shown in the columns of "Outside" samples A-2, A-3, and B-2 of the "Processing method" item and the column of the same item "Inside" sample A-3. m
Is the "width e" of 100 mm of the "specimen 3" described above.
(Fig. 5). "Outside" of the item "Processing method"
“Seal” or “251Seal” shown in the column of Sample B-3 and the column of Sample B-2 of “Inside” of the same item means that a silicone resin is applied. For example, "251S
"Eal only twice" means that the silicone resin, product number 251 of Shin-Etsu Chemical Co., Ltd., was applied twice. "Inside" sample C- in the "Processing method" section
"NCH-1" shown in the column of 3 shows the component of the solvent and is Ni-Cr (80-20%). The work piece obtained according to the present invention by the above-described method is a cast iron which has been a problem in the past and causes minute scratches on the work piece surface during shot processing, resulting in rust. Alternatively, it can be confirmed that unlike the shot made of cast steel, the surface is smooth, so that the above-described scratches are not generated on the surface of the workpiece. In addition to such test results, the zirconia-based ball 1 used for shots is excellent in toughness and is a material that has been conventionally considered not to cause rust. Elimination of depositing residue was eliminated.

[0043]

According to the first invention of the present application, it is possible to finish the work piece very smoothly without scratching the surface thereof. Therefore, the rusting phenomenon was significantly reduced. At the same time, since the zirconia-based ball has excellent toughness, its life is not inferior to that of conventional shots made of cast iron or cast steel. Especially cast iron,
Unlike cast steel shots, even if they are contaminated with oil and acids, they can be reused by washing and drying. In this way, it is possible to achieve both prevention of rusting and prevention of breakage, and in addition, it is excellent in that it can be reused due to contamination with acids and the like. From such an effect, a great effect is brought about in terms of cost saving and improvement in economic efficiency. In addition, the second
In the invention of (1), a blasting method suitable for zirconia-based balls is provided, and by adopting these methods, it is necessary to treat existing structures and the like locally. The processing was made possible even in.
According to the third invention of the present application, in the first or second invention, the most suitable condition can be set, and the effect can be efficiently provided. In the fourth invention of the present application, after the shot processing, an appropriate secondary processing is performed to eliminate the influence of the outside air, the atmosphere, or the like, which greatly contributes to prolonging the life of the workpiece. Also in the fifth invention of the present application, after the above-mentioned shot processing, the influence of outside air or atmosphere is eliminated by an appropriate secondary processing, and the life of the workpiece is greatly extended. In the sixth invention of the present application,
The formation of the sprayed coating after the shot processing eliminates the influence of the outside air or the atmosphere and greatly contributes to prolonging the life of the workpiece.

[Brief description of drawings]

FIG. 1 is a schematic overall front view of a plurality of zirconia-based balls 1 used in the present invention.

FIG. 2 is a schematic front view of a test piece used in a first test performed for evaluating the present invention.

FIG. 3 is a schematic plan view of the test piece used in the first test performed for evaluating the present invention.

FIG. 4 is a second and a third performed in evaluating the present invention.
FIG. 3 is a schematic front view of a test piece used in the test of FIG.

FIG. 5 is a second and a third performed in evaluating the present invention.
FIG. 3 is a schematic side view of a test piece used in the test of FIG.

[Explanation of symbols]

 1 Zirconia ball

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shosuke Itomura 1386 Maeda, Urasoe City, Okinawa Prefecture Maeda Housing 7-304

Claims (6)

[Claims] 1. A zirconia-based shot blasting method characterized in that a zirconia-based ball (1) is shot-blasted on a metal surface which is a workpiece, and a compressive stress is applied to the metal surface to relax tensile stress. Method of preventing thermal fatigue and progress of stress corrosion cracking of metals. 2. The zirconia-based ball (1) is a substantially spherical one having a toughness to which yttria, ceria or the like is added, and a plurality of the zirconia-based balls having a uniform size.
(1) is blasted by a rotary projection method, a suction method or a pressure method, and the method for preventing thermal fatigue and progress of stress corrosion cracking of metal by zirconia shot blasting according to claim 1. . 3. The particle size of the zirconia-based balls (1) is about 0.3 m / m depending on the material and shape of the workpiece.
Select from φ to about 1.6 m / mφ, and regarding the blast pressure, distance, angle, hose length, and nozzle diameter, the thickness of the material used and the depth of compressive stress can be measured with an Almen gauge. Adjusted and by Almen strip test piece,
It is assumed that appropriate conditions are set by evaluation in advance, and the plate thickness of the work piece is about arc height 0.1 to 1.
4. The method for preventing the thermal fatigue resistance of metal and the progress of stress corrosion cracking by zirconia shot blasting according to claim 1 or 2, wherein the method is adjusted within the range of 4. 4. After blasting the zirconia-based balls (1),
In order to block the contact with the outside air on the surface of the work piece, it is passivated by immersing it in an organic paint or an inorganic solvent or spray-coating these blocking materials. The method for preventing thermal fatigue resistance and progress of stress corrosion cracking of metal by the zirconia-based shot blasting according to claim 1, 2, or 3. 5. After blasting the zirconia-based balls (1),
A sacrificial film that does not affect the work to be coated on the surface of the work piece even if it is altered by contact with the outside air is formed by an appropriate method. A method for preventing thermal fatigue resistance and progress of stress corrosion cracking of a metal by the zirconia-based shot blasting according to claim 1, 2 or 3. 6. After blasting the zirconia-based balls (1),
A thermal sprayed film formed by metal spraying or ceramic spraying on the surface of the work piece, wherein the metal is thermally fatigued and stress corroded by the zirconia-based shot blasting according to claim 1 or 2. Crack progression prevention method.