JPH06312373A - Shot member - Google Patents

Abstract

PURPOSE:To use shot members in a condition in which processing terms are stable for a long time, by using a spherical polycrystal sintered material having a burst-resistant toughness greater than a specific value, for shot members in a shot-peening process for surface-treatment of a metal article or the like. CONSTITUTION:In a shot-peening process, shot members 1 together with compressed air are jetted from a jet port 2 of a nozzle 3 connected with a supply port for the shot members 1 and a feed port for the compressed air and located a position remote from a workpiece A by a certain distance, so as to collide upon the outer surface of the workpiece A on which concavities and convexities are accordingly formed. In this case, spherical particles of made of polycrystal sintered material such as silicon carbide, silicon nitride, zirconia or thermet, having a fracture toughness (K1C) higher than 3.0MPasq. rt. m. The shot members 1 have a particle size which is for example, 0.3 to 1.6mm, and preferably have a sphericity of higher than 0.9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shot member for spraying a surface of a metal product or the like for surface hardening in a shot peening method.

[0002]

2. Description of the Related Art The shot peening method is a method for accelerating a large number of shot members each having a small grain size by utilizing centrifugal force or placing the shot members on compressed air, whereby mechanical parts or tools represented by springs and screws are used. It is a method of injecting onto the surface of a metal product such as a class (hereinafter abbreviated as a workpiece) to harden the surface. Generally, the structure near the surface of the workpiece is changed and a compressive residual stress is generated. As a method for improving the surface hardness and the fatigue strength, it has been widely used than before.

Further, as the shot member, steel, glass, or ceramic grains having a hardness equal to or higher than the hardness of the workpiece is used (Japanese Patent Laid-Open No. 62-278224, JP-A-62-278224). Sho 61-18397
(See Japanese Patent Publication No. 5).

[0004]

However, conventional shot members made of glass or ceramics have low impact resistance, which indicates the degree of breakage when an impact is applied, and thus have poor durability. However, if it is repeatedly used, wear, chipping, or cracking due to collision with the work piece will occur and the workability will deteriorate, so that there is a problem that the processing conditions are not stable for a long time. Further, the shot member made of steel has a problem that iron rust is generated when it is repeatedly used, the shot member is easily deteriorated, and the rust adheres to the surface of the workpiece.

Further, if the shot member itself has an angular shape, or if the shot member has an angular shape due to wear, chipping, or cracking, the surface of the workpiece may be damaged. It was

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in a shot member for jetting to the surface when the surface hardening treatment of a workpiece is performed by the shot peening method. The fracture toughness (K _1c ) is formed by a spherical polycrystalline sintered body having a fracture toughness (K _1c ) of 3.0 MPa√m or more.

The spherical shape according to the present invention is a shape having no edge portion, and the sphericity is 0.75 (when the radius of the minimum circumscribed circle is 1, the actual minimum radius of the spherical shape is 0.7).
5) or more, and preferably the sphericity is 0.9 or more.

[0008]

According to the present invention, the shot member has a fracture toughness (K
_By using a spherical polycrystalline sintered body having a spherical shape of _1c ) of 3.0 MPa√m or more, it can be used in a state where the processing conditions are stable for a long period of time, and the surface of the workpiece is not scratched.

[0009]

EXAMPLES Examples of the present invention will be described in detail below.

In the shot peening method, as shown in the sectional view of FIG. 1, the shot member 1 is connected to a supply port (not shown) and a compressed air delivery port (not shown) at a position apart from the workpiece A to some extent. The shot member 1 is jetted from the jet port 2 together with the compressed air at an appropriate speed by using the nozzle 3 having the jet port 2 to collide with the surface of the workpiece A so as to form an uneven shape. It is performed by processing into.

Here, the shot member 1 has a fracture toughness (K
_1c ) is a shot member 1 made of a spherical polycrystalline sintered body having a pressure of 3.0 MPa√m or more, and the basis for making them preferable will be described below.

First, it is better that the fracture toughness (K _1c ) indicates that it is less likely to be damaged when an impact is applied. However, if it is less than 3.0 MPa√m, the fracture toughness (K _1c ) of It is preferably 3.0 MPa√m or more, and more preferably 5.0 MPa√m or more, because abrasion, chipping, or cracking due to collision easily occurs and durability deteriorates.

If the shape is other than spherical, a sharp portion is formed, the surface of the workpiece A is likely to be scratched, and cracks or chips are likely to occur during the shot. It is preferably 75 or more, and more preferably spherical with a sphericity of 0.9 or more.

The particle size of the shot member 1 is 0.3 m.
If it is smaller than m, the impact destructive force on the work A is reduced,
On the other hand, if it is larger than 1.6 mm, it is difficult to enter a fine portion, and the number of particles in a certain area is reduced, so that the efficiency of giving energy to the work piece A is reduced,
The thickness is preferably 1.6 mm, and the radius of curvature is preferably 0.15 to 0.8 mm.

Further, if the sintered body is a single crystal, the strength becomes large in one direction and the strength becomes small in the direction perpendicular to the direction of the crystal axis, so that the mechanical strength is stabilized. Therefore, it is preferably a polycrystalline sintered body.

The fracture toughness (K _1c ) is 3.0 MPa√
Examples of the polycrystalline sintered body of m or more include silicon carbide, silicon nitride,
There are ceramics such as zirconia or cermet. Here, the silicon carbide-based ceramics is mainly composed of SiC, and is an oxide of a Group 3a element of the periodic table, Si.
One or more of O ₂ , Al ₂ O ₃ and MgO, or B ₄ C,
C is used as a sintering aid. The silicon nitride ceramics contains Si ₃ N ₄ as a main component and contains an oxide of a Group 3a element such as Y ₂ O ₃ , SiO ₂ , Al ₂ O ₃ and MgO.
One or more of the above are used as sintering aids. Zirconia ceramics contains ZrO ₂ as a main component and contains stabilizers (Y ₂ O ₃ , MgO, CaO, Dy ₂ O ₃ and CeO _2).
Etc.) is added in an appropriate amount, and partially stabilized zirconia containing tetragonal crystals, in particular, partially stabilized zirconia containing 3.0 to 3.8% by weight of MgO as a stabilizer is used. Further, the cermet contains 80 to 99% by weight of a carbonitride composed of elements of Groups 4a, 5a, and 6a of the periodic table such as titanium, niobium, and molybdenum as a hard phase, and other metals such as nickel and cobalt as a binder phase. And in the hard phase 7
About 0% by weight of Ti is TiC, TiN or TiCN
C-TiN type cermet etc. are mentioned.

In the method of manufacturing the shot member 1 made of the above-mentioned material, the raw material powder is adhered to the surface of the core particle by, for example, rolling the raw material powder as a core while spraying a binder or the like on the raw material powder. It is manufactured by forming by a rolling granulation method to form a spherical body of a desired size and firing.

When such a shot member 1 is used,
Since the impact resistance is large, the durability is improved, the processing conditions are stabilized for a long period of time, and the deterioration of the shot member 1 due to iron rust and the adhesion of rust to the surface of the workpiece A are eliminated. Further, since it is spherical, the surface of the work piece A is not scratched.

Further, the hardness of the shot member 1 may be equal to or higher than that of the work A, and the shot member 1 satisfying the following conditions should be more suitable for use. You can

(1) The center line average roughness (Ra) of the surface is set to 0.01 to 0.5 μm or less. This is 0.5 μm
If it is larger than this, the characteristics as an abrasive will come out,
This is because it scratches the surface of the work piece,
This is because if it is smaller than 1 μm, it will flow on the surface.

(2) The specific gravity is 2.0 to 8.0. This is because if it is larger than 8.0, it is difficult to get on the compressed air at the time of injection, and if it is smaller than 2.0, it becomes too light and the efficiency of giving energy to the work piece A is greatly reduced. is there.

(3) The thermal conductivity is set to 4.0 W / m · K or more. This is because if the thermal conductivity is smaller than 4.0 W / m · K, the heat storage of the shot member 1 will proceed and the temperature of the workpiece A will be increased.

(4) The average crystal grain size is 1 to 30 μm, more preferably 1 to 10 μm. This is to maintain high material strength and fracture toughness (K _1c ) as a polycrystalline sintered body.

Experimental Example 1 Here, shot peening was actually performed using the shot member 1 according to this example and a shot member made of glass, chromium molybdenum steel, and alumina ceramics as a comparative example.

The following materials were used as the material of the shot member 1 according to the embodiment.

(1) Silicon Carbide Ceramics A polycrystalline sintered body having a SiC content of 99% by weight, B ₄ C and C as a sintering aid and an average crystal grain size of 10 μm and a Vickers hardness of 24 GPa. , Fracture toughness (K _1c ) is 3.4MP
Silicon carbide ceramics having a√m, specific gravity of 3.2, and thermal conductivity of 62 W / m · K.

(2) Silicon nitride ceramics: Si ₃ N ₄ content: 92% by weight, Y ₂ O ₃ , Al ₂ O ₃
As a sintering aid, a polycrystalline sintered body having an average crystal grain size of 10 μm, a Vickers hardness of 14.5 GPa, a fracture toughness (K _1c ) of 5.7 MPa√m, and a specific gravity of 3. 2. Silicon nitride ceramics with a thermal conductivity of 21 W / mK.

(3) Partially stabilized zirconia ceramics A polycrystalline sintered body having a MgO content of 3.5% by weight, the balance of ZrO ₂ , and an average grain size of 10 μm, a Vickers hardness of 11 GPa and a fracture toughness (K _1c). ) Is 6.7 MPa√m, specific gravity is 6.0, and thermal conductivity is 4 W / m · K, partially stabilized zirconia ceramics.

(4) TiN-based cermet Hard phase 90% by weight, TiN content of TiC, TiC
It is a polycrystalline sintered body having a larger average crystal grain size of 5 μm than N, a Vickers hardness of 15.3 GPa, and a fracture toughness (K
_1c ) is 11 MPa√m, specific gravity is 7.7, thermal conductivity is 8 W
/ M · K TiN-based cermet.

The glass as a comparative example has a Vickers hardness of 6 GPa and a fracture toughness (K _1c ) of 1.5 MPa√.
m and specific gravity of 2.3 were used. The chromium molybdenum steel used had Vickers hardness of 3.0 GPa, fracture toughness (K _1c ) of 3.1 MPa√m, and specific gravity of 8.1. Further, alumina is a polycrystalline sintered body having an Al ₂ O ₃ content of 87% by weight, an average crystal grain size of 10 μm, a Vickers hardness of 12 GPa, a fracture toughness (K _1c ) of 2.9 MPa√m, Specific gravity 3.6, thermal conductivity 17W /
m · K one was used.

The shot member 1 has a sphericity of 0.92, a grain size of 0.8 mm, and a center line average roughness (Ra).
Of 0.3 μm or less is used, and as the work piece A, carbon steel for machine structure having a Vickers hardness of 2.5 GPa is used, the injection port 2 and the work piece A are separated by 5 cm, and the air pressure is 6 kg. The test was conducted under the conditions that the shot member 1 was jetted at a velocity of / cm ² and a jet speed of 25 m / sec.

First, jetting was performed for 30 seconds, and the hardness of the work piece A whose initial Vickers hardness was 2.5 GPa was measured. Next, when the shot members 1 were continuously jetted onto the workpiece A, the time until 50% or more of the shot members 1 became unusable due to cracking or the like was measured. The results are shown in Table 1.

[0033]

[Table 1]

From Table 1, when the shot member 1 of the present invention was used, the Vickers hardness of the processed workpiece A was 2.7.
It was possible to increase the value to 2.8 GPa, and the effect of surface hardening was confirmed. In addition, under the same conditions, it was more effective to use a material having a large specific gravity.

Regarding the usable time, the shot member 1 made of the conventional material can be used only for 50 hours for glass, 150 hours for chrome-molybdenum steel, and 250 hours for alumina ceramics. Since the shot member 1 according to the example can be used for 450 hours or more, it can be seen that the shot member 1 according to the embodiment of the present invention can be used with more stable processing conditions for a long period of time. Furthermore, the fracture toughness (K _1c ) is 5.0MP
When a material of a√m or more is used, it can be used for 500 hours or more, so that the fracture toughness (K _1c ) is 5.
It is more preferable to use a material of 0 MPa√m or more.

After all, the fracture toughness (K _1c ) is 3.0 MPa√
It is understood that the shot member 1 made of spherical polycrystalline ceramics of m or more, and more preferably 5.0 MPa√m or more is preferable.

Experimental Example 2 Next, as an example of the present invention, shot members 1 made of zirconia ceramics and having different sphericities were produced, shot peening was performed for 30 seconds under the same conditions as in Experimental Example 1, and then the workpieces were processed. The surface of the object A was observed with a microscope to check for scratches. Further, shot peening was continuously performed to examine the time (usable time) until 50% or more of shot members 1 became unusable due to cracking or the like. Here, the sphericity is the ratio of the minimum radius of the actual shot member 1 to the radius of the minimum circumscribing circle of the shot member 1, and the closer the sphericity value is to 1, the closer to a perfect sphere. become.

As shown in Table 2, the sphericity is 0.7.
If it is less than 5, it will scratch the work piece A,
This scratch not only reduces the strength of the work piece A, but also the shot member 1 itself is likely to be cracked or chipped, so that the usable time was as short as 300 hours.

On the other hand, when the sphericity is 0.75 or more, the work A is not scratched and the usable time is 450 hours or more, which means that it can be used for a long time.

[0040]

[Table 2]

[0041]

As described above, according to the shot member of the present invention, since the spherical polycrystalline sintered body having the fracture toughness (K _1c ) is 3.0 or more, the shot member itself is chipped. It is possible to provide a shot member that prevents abrasion and wear, can be used in a stable state for a long period of time, and does not scratch the surface of a workpiece.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state where shot peening is performed using a shot member of the present invention.

[Explanation of symbols]

 1: Shot member 2: Jet port 3: Nozzle A: Workpiece

Claims (1)

[Claims] 1. A shot member for jetting onto a surface when surface-treating a metal product or the like by the shot peening method, which has a fracture toughness (K _1c ) of 3.0 MPa√m.
A shot member comprising the above-mentioned spherical polycrystalline sintered body.