JP5299140B2 - MATERIAL OF SHOT PEENING PROJECTION MATERIAL AND METHOD FOR PRODUCING SHOT PEENING PROJECTION MATERIAL - Google Patents

Description

  The present invention relates to a material for a shot peening projection material and a method for manufacturing the shot peening projection material.

  Conventionally, in the production of shot peening projection materials, so-called bearing steel is drawn into wire drawing, this wire drawing is cut to the same length as its diameter, and then projected onto a rigid wall to round the edge. Further, it is known that a predetermined sphericity can be obtained by polishing and then hardening and tempering to obtain a predetermined Vickers hardness (for example, JP-A-2001-79766). See the official gazette).

  However, when the so-called bearing steel is used as the material of the shot peening projection material as it is (for example, high carbon chromium bearing steel SUJ2 defined in Japanese Industrial Standard JIS G4805, the composition is shown in Table 2), There has been a problem that the improvement in productivity cannot be obtained because wire breakage occurs in the process of drawing to obtain a finish line. That is, when a wire breakage occurs in the wire drawing process, the wire drawn at a high speed of about 100 m / min stops, which greatly affects production efficiency. As a result, the productivity of the projection material is also lowered. In particular, when the diameter of the drawn wire becomes thinner than 0.7 mm (for example, about 0.3 mm), the tendency is remarkable, and disconnection frequently occurs in the wire drawing process. That is, a method for manufacturing a shot peening projection material for obtaining an optimum shot peening projection material from a thin finish line has not been established.

The present invention has been made to solve the above problems, and its purpose is to prevent disconnection in the process of drawing a finish line to obtain a finished line in the production of a shot peening projection material. An object of the present invention is to provide a shot peening projection material that can be improved, a finish line, a manufacturing method of a shot peening projection material that can improve productivity, and a projection material produced by the manufacturing method.
That is, in the method for manufacturing a shot peening projection material of the present invention, first, in order to prevent disconnection and ensure cleanliness, a specific shot peening projection material is used, and an appropriate finish line is formed from this material. Secure, maintain the fine carbide state before quenching, and ensure the proper structure after quenching and tempering. Furthermore, the present invention provides a shot peening projection material capable of providing the life of the shot peening projection material and imparting an appropriate compressive residual stress. In addition, the present invention provides a method for producing a shot peening projection material that has good hardenability and is suitable for shot peening.

As a result of intensive studies to solve the above problems, the inventor of the present application, as a first aspect of the present invention, in the material of the shot peening projection material, in mass%, carbon is 0.95 to 1.10%, silicon 0.15 to 0.30%, manganese 0.40% or less, phosphorus 0.020% or less, sulfur 0.010% or less, chromium 1.40 to 1.60%, oxygen 0.0015 %, With the balance being iron and inevitable impurities, the inventors have found that the intended purpose can be achieved, and the present invention has been completed based on such findings.
The reason why such a material is used is to reduce the amount of non-metallic inclusions that degrade the bondability of the base in order to prevent disconnection due to cracks in wire drawing. That is, as compared with the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 2001-79766, it is necessary to reduce the amount of oxidation in order to stably reduce the oxide, and oxygen is extremely reduced to 0.0015% or less. In addition, the upper limit of the amount of silicon is reduced by 17%. Furthermore, manganese and sulfur were reduced to reduce the amount of sulfide, especially MnS. Overall, the upper limit of the content of components other than iron has been tightened. In order to keep the basic carbide amount constant, the carbon amount was the same.

Further, the finish line of the shot peening projection material of the present invention includes a step of drawing the material of the shot peening projection material according to the first aspect of the present invention into a wire material, and annealing and cold drawing the wire material. By repeating the above to make a finished line, the area occupied by the carbide having a particle size of 2 μm or less in the finished line is 80% or more of the area of the entire finished line.
That is, in the present invention, a wire is produced by drawing from an ingot by drawing, and then the wire is drawn by repeating “annealing” and “cold drawing” to form a finished wire. . And the state of the carbide | carbonized_material in the finishing line at this time has the area which the carbide | carbonized_material which is a particle size of 2 micrometers or less occupies 80% or more of the area of the whole finishing line.
In the second aspect of the present invention, the wire obtained by drawing the material of the shot peening projection material according to the first aspect of the present invention is subjected to annealing and cold drawing to obtain a finished line. The reason is that if the wire drawing area reduction ratio is high, the wire is not stretched and breaks easily, so at least the elongation becomes dull and constant, and annealing is performed to remove work hardening, and again This is because it is preferable to perform the drawing while the ductility is recovered.
The reason why the cold drawing is performed is that the expansion of crystal grains occurs in a hot state and the effect of refinement cannot be obtained, so that the process is cold accompanied by work hardening and refinement of crystal grains.
The number of annealing is preferably 3 to 5 times. The drawing area reduction is preferably 10% to 40%.
In the finish line, the area occupied by carbides with a particle size of 2 μm or less is 80% or more of the total area of the finish line. By obtaining an appropriate structure in the thin finish line, it is most suitable for the shot peening projection material. This is to secure an appropriate organization. In addition, the confirmation of the properties on the finish line leads to the improvement of the quality of the final product, and the material is not wasted.

  Here, the finished wire is a fine wire that has been finished and is before cutting, and is obtained by repeating annealing and cold drawing of a wire material obtained by rolling and drawing.

  Further, the finish line is annealed at 720 ° C. or less, thereby preventing coarsening of the carbide of the finish line of the shot peening projection material and maintaining the fine state of the carbide before quenching. As a result, since the fracture strength is increased by refining the crystal grains, it can be ensured that a larger load is applied to the shot peening material. The annealing is preferably performed by heating at 700 ° C. using a bright annealing furnace. By using the bright annealing furnace, there is no generation of oxide scale on the surface of the wire, and the pickling process is not necessary.

Further, the method for producing a shot peening projection material of the present invention includes a step of cutting and plastic working a finish line of the shot peening projection material according to the second aspect of the present invention to form a shot peening material, And a step of quenching and tempering the shot peening material.
According to the present invention, since a finished wire with excellent drawability and confirmed properties is used, a high-productivity and high-quality shot peening projection material can be provided.

Here, the tempering is defined by tempering parameter = T ((21.3−5.8 × [C]) + logt), and C is set as T such that the value is 6200-7300. Here, T: tempering temperature (K), t: tempering time (h), C: carbon content (%). A tempering temperature T, carbon content C, and tempering time t such that the tempering parameter is 6200 to 7300 is preferable because it has features such as preventing coarsening of crystal grains and relaxing processing stress and increasing toughness. .
Moreover, you may have the process of carrying out plastic working further. According to the present invention, since the corners of the projection material are eliminated, there is an advantage that the starting point of destruction hardly occurs during peening. Here, the plastic working to make the shot peening material means that a cut finish line having a short wire shape is made into a round shot peening material shape by plastic working. That is, the shot peening material is not rounded by cutting, polishing, or the like.

Moreover, the manufacturing method of the projection material for shot peening of this invention repeats the process which wire-draws the material of the projection material for shot peening as described in the 1st aspect of this invention to a wire, and annealing and cold drawing. The method includes a step of forming a finish line, a step of cutting and plastically processing the finish line to form a shot peening material, and a step of quenching and tempering the shot peening material.
According to the present invention, there is an advantage of refining crystal grains and restoring toughness after heat treatment.

Furthermore, the manufacturing method of the projection material for shot peening of the present invention is characterized in that the quenching temperature is 820 to 850 ° C. in the manufacturing method of the projection material for shot peening.
According to the present invention, retained austenite is hardly generated, and there is an advantage that a uniform martensite structure can be obtained in the entire material.

The shot peening projection material of the present invention is a shot peening projection material manufactured by the above manufacturing method, and the structure is substantially tempered martensite and the fine carbides are precipitated. The area ratio of carbide is preferably 70% to 95%. This is because when the metal portion that is the bonding layer is reduced, the bonding property of the base is weakened, and when the carbide exceeds 95% and the metal portion is extremely reduced, the carbides are brought into contact with each other. Moreover, when the area ratio of carbide is less than 70%, Vickers hardness HV950 which is a hardness suitable as a projection material for shot peening such as JIS SUJ2 material may not be satisfied. According to this invention, it can be set as the optimal projection material for shot peening.
On the other hand, the carbide particle size is preferably smaller than 2 μm. More preferably, it is 1 to 0.1 μm. This is because if the particle size is 2 μm or more, the influence as a starting point of a crack in the shot of the shot peening projection material becomes large. A particle size of 1 to 0.1 μm is preferable because the exposure from the base is reduced and the influence of carbide is reduced.
In addition, the shot peening projection material of the present invention is, in mass%, 0.95 to 1.10% for carbon, 0.15 to 0.30% for silicon, 0.40% or less for manganese, and 0.8% for phosphorus. 020% or less, sulfur 0.010% or less, chromium 1.40 to 1.60%, oxygen 0.0015% or less, the balance of iron and inevitable impurities, shot peening projection material The material is drawn into a wire, and the drawn wire is repeatedly annealed and cold-drawn to obtain a finished wire, the finished wire is cut and plastically processed to be a shot peening material, and the shot peening material is quenched and tempered. A shot peening projection material manufactured by the method, wherein the structure is composed of fine carbide and tempered martensite, the area ratio of the carbide is 70% to 95%, and further plastic working Therefore it is preferable that the Vickers hardness by adjusting the hardness and 950HV to 1050HV. When the Vickers hardness is 950 HV to 1050 HV, a peening process suitable for a product with high hardness can be performed.

  Since the material of the present invention is a composition material with few disconnections, productivity is improved. In addition, thin lines can be processed at high speed. The finish line of the present invention is suitable for producing a shot peening projection material. The production method of the present invention can produce a projection material having high productivity and quality and suitable for shot peening. The projection material of the present invention is suitable for shot peening.

It is a flow of the manufacturing method of the projection material for shot peening of this invention. It is the microstructure (x1000) using SEM of the finish line for the projection material for shot peening of the present invention. It is the microstructure (x5000) using SEM of the finish line for the projection material for shot peening of the present invention. It is the microstructure (x1000) using SEM of the projection material for shot peening of the present invention. It is the microstructure (x3000) using SEM of the projection material for shot peening of the present invention. It is the microstructure (x1000) using SEM of the projection material for shot peening of the present invention. It is the microstructure (x3000) using SEM of the projection material for shot peening of the present invention. It is a graph showing the particle size distribution of the carbide | carbonized_material of the projection material for shot peening of this invention. It is a graph which shows the relationship between the carbide | carbonized_material area ratio and hardness (composite hardness) of the projection material for shot peening of this invention. (When the composition has high hardness) It is a graph which shows the relationship between the carbide | carbonized_material area ratio and hardness (composite hardness) of the projection material for shot peening of this invention. (When the composition is low hardness)

The inventors of the present application adjust the bearing steel to a composition excellent in the fine wire for the shot peening projection material with respect to the composition of the JIS G4805-SUJ bearing steel, and derive the properties of the composition, thereby performing shot peening from the fine wire. Providing an excellent projection material. Table 1 shows the materials of the shot peening projection material of the present invention. As a comparative example, Table 2 shows conventional SUJ2 materials (JIS standards).

  As shown in Tables 1 and 2, the material of the present invention is limited to a sulfur content of 0.010% or less and oxygen content of 0.0015% or less compared to the composition of JIS G4805-SUJ bearing steel. Therefore, there is little precipitation of inclusions such as sulfides and oxides, so that the cleanliness of the material can be ensured, and the generation of a non-uniform structure that causes disconnection can be prevented. You can do it. For this reason, even if a wire becomes thin, the disconnection in a wire-drawing process can be prevented as much as possible.

  Further, manganese and phosphorus are limited to be lower than the composition of JIS G4805-SUJ bearing steel. These restrictions are preferable in that the generation of retained austenite and the formation of inter-grain ternary compounds are suppressed.

  Moreover, if copper is limited to 0.15% or less, it is preferable in that the carburizing property does not deteriorate.

  Further, if nickel is limited to 0.15% or less, it is preferable in that the carburizing property does not deteriorate.

FIG. 1 shows a flowchart of a method for manufacturing a shot peening projection material using the material of the shot peening projection material of the present invention. Hereinafter, it will be described in detail with reference to FIG. In the flowchart, first, in the first step, a material having the composition specified in Table 1 is prepared. In the second step, the wire is drawn. In the third step, annealing and cold drawing are repeated. Cut in the fourth step.
Plastic working in the fifth step. Quenching and tempering in the sixth step. In some cases, the seventh step is blank.

  Table 3 shows a comparison between the composition of JIS G4805-SUJ bearing steel in Table 2 and Example 1 for the first to third steps. The wire diameter of the drawn material after drawing the wire in the second step was 1.6 mm, and the hardness was HV320.

  In Table 3, in Example 1, in the production of the shot peening projection material, no disconnection occurs in the process of drawing to obtain a finish line. On the other hand, in the comparative example, disconnection occurs in the process of drawing the shot peening projection material to obtain a finish line.

第３工程で焼鈍及び冷間引抜きを繰り返して、ショットピーニング用投射材の仕上げ線を製造した。このとき、仕上げ線の材料となる引き抜き材の線径は１．６ｍｍであり、硬度はＨＶ３２０であった。この材料は、ＨＶ３２０であり、加工硬化していないため、冷間引き抜きが容易にできる。第３工程で焼鈍と冷間引抜きを繰り返す工程では、具体的には、８ｍの光輝（ＢＡ）焼鈍炉を使用して４ｍを７００℃加熱、４ｍを冷却する方法を用いた。
サイズ変遷は、例えば、
径１．６ｍｍ〜１．５ｍｍ〜１．４ｍｍ→（ＢＡ焼鈍）→１．３ｍｍ〜１．２ｍｍ〜１．１ｍｍ〜１．０ｍｍ →（ＢＡ焼鈍）→０．９ｍｍ〜０．８ｍｍ〜０．７５ｍｍ〜０．７ｍｍ →（ＢＡ焼鈍）→ ０．６ｍｍ〜０．５５ｍｍ〜０．５ｍｍ〜０．４５ｍｍ〜０．４ ｍｍ→（ＢＡ焼鈍）→ ０．３５ｍｍ〜０．３ｍｍ（終了）であり、計４回の焼鈍が入っている。

In the third step, annealing and cold drawing were repeated to produce a finish line of the shot peening projection material. At this time, the wire diameter of the drawing material used as the material for the finished wire was 1.6 mm, and the hardness was HV320. This material is HV320 and is not work hardened, so it can be easily cold drawn. In the step of repeating annealing and cold drawing in the third step, specifically, a method of heating 4 m at 700 ° C. using an 8 m bright (BA) annealing furnace and cooling 4 m was used.
The size transition is, for example,
Diameter 1.6 mm to 1.5 mm to 1.4 mm → (BA annealing) → 1.3 mm to 1.2 mm to 1.1 mm to 1.0 mm → (BA annealing) → 0.9 mm to 0.8 mm to 0.75 mm ~ 0.7mm → (BA annealing) → 0.6mm ~ 0.55mm ~ 0.5mm ~ 0.45mm ~ 0.4mm → (BA annealing) → 0.35mm ~ 0.3mm (finish) Contains 4 annealings.

この仕上げ線の組織を確認したところ、粒径２μｍ以下である炭化物の占める面積が仕上げ線全体の面積の８０％以上であった。
本発明のショットピーニング用投射材用の仕上げ線（直径０．３ｍｍのナイタール腐食後）のＳＥＭを用いたミクロ組織を図２に示す。
これにより、ショットピーニング用投射材に優れた仕上げ線の組織が得られたことを確認できた。
このときの仕上げ線の直径は、焼鈍及び冷間引抜きを繰り返して、最終径が０．６ｍｍ以下０．２５ｍｍ以上になるようにする。最終径が０．３ｍｍのとき、ビッカース硬度はＨＶ３５０であった。ビッカース硬度がＨＶ３５０であっても、材料があまり加工硬化していないため、細線においても切断が容易にできる。
なお、本実施例１では、ショットピーニング用投射材としては、直径が０．３ｍｍ乃至０.６ｍｍのものを製造した例を挙げた。しかし、１．０ｍｍ程度までの直径のものはショットピーニングに使用される。但し、本発明の実施例１を使わなくても、すなわち、冷間引抜きと焼鈍とを繰り返さなくても、１．０ｍｍのものは比較的容易に製造が可能である。この意味で、伸線工程は線径が小さくなるほど面倒であることから、本発明は、０.６ｍｍ以下の直径のショットピーニング用投射材（０．６ｍｍ以下の線径の仕上げ線）に好適である。なお、ショットピーニング用投射材の粒径は、たとえば、日本工業規格ＪＩＳ Ｇ５９０４に規定された粒度試験方法を用いて測定する。

When the structure of the finish line was confirmed, the area occupied by the carbide having a particle size of 2 μm or less was 80% or more of the area of the entire finish line.
FIG. 2 shows a microstructure using an SEM of a finish line for a shot peening projection material according to the present invention (after a nital corrosion with a diameter of 0.3 mm).
Thus, it was confirmed that an excellent finish line structure was obtained for the shot peening projection material.
The diameter of the finish line at this time is such that annealing and cold drawing are repeated so that the final diameter is 0.6 mm or less and 0.25 mm or more. When the final diameter was 0.3 mm, the Vickers hardness was HV350. Even if the Vickers hardness is HV350, since the material is not so hard-worked, cutting can be easily performed even for thin wires.
In Example 1, an example in which a shot peening projection material having a diameter of 0.3 mm to 0.6 mm was manufactured was given. However, those having a diameter up to about 1.0 mm are used for shot peening. However, even if it does not use Example 1 of this invention, ie, it does not repeat cold drawing and annealing, a thing of 1.0 mm can be manufactured comparatively easily. In this sense, the wire drawing process is more troublesome as the wire diameter becomes smaller. Therefore, the present invention is suitable for a shot peening projection material having a diameter of 0.6 mm or less (finished wire having a wire diameter of 0.6 mm or less). is there. In addition, the particle size of the shot peening projection material is measured using, for example, a particle size test method defined in Japanese Industrial Standard JIS G5904.

次いで、第４工程で仕上げ線材を切断した。材料ストッパに押し当て、材料のバラツキを抑え定寸にするためバックリング防止ワイヤグリップ装置で固定し切断金型により冷間剪断した。冷間切断装置としてはクランク軸のカム駆動による機械プレス、あるいは油圧、電動プレスが用いられる。ダイイングマシンを使用してもよい。この切断の長さは、仕上げ線の直径と同等から１．５倍の範囲とした。

Next, the finished wire was cut in the fourth step. The material was pressed against the material stopper, fixed with a wire buckling device for preventing buckling, and cold-sheared with a cutting die in order to reduce the variation of the material and make it a constant size. As the cold cutting device, a mechanical press driven by a cam of a crankshaft, or a hydraulic or electric press is used. A dieing machine may be used. The length of this cut was in the range of 1.5 times the diameter of the finish line.

  Plastic working in the fifth step. For example, the shape is made nearly spherical by forging. Alternatively, the corners of the cylinder are rounded by separately colliding with the wall at high speed.

表７に示すように、投射材の寿命は、焼き戻しパラメータを適切に管理することにより改善される。また、投射材の寿命は、介在物の析出による不均一な組成によっても生じるが、本発明では既に粒径２μｍ以下である炭化物の占める面積が仕上げ線全体の面積の８０％以上とされている仕上げ線を用いている（図２）ので、この点でも、投射材の寿命に良い影響を与える。更に、後述するように、ショットピーニング条件を適正にする（ワークと同等以上の投射材の硬さにする等）ことによっても投射材の寿命に良い影響を与える。本発明において投射材のビッカース硬度は直径０．６ｍｍでＨＶ９４０、直径０．３ｍｍでＨＶ９６０であった。ここで、図２aは、直径０．３ｍｍの仕上げ線のＳＥＭ（×１０００）を用いたミクロ組織を示す。図２ｂは、直径０．３ｍｍの仕上げ線のＳＥＭ（×５０００）を用いたミクロ組織を示す。 Quenching and tempering in the sixth step. In Example 1, the structure and hardness are adjusted so as to be suitable for quenching and tempering. The tempering parameter at this time is 6200-7300. Table 7 shows the effect at that time.

As shown in Table 7, the lifetime of the projection material is improved by properly managing the tempering parameters. Further, although the life of the projection material is also caused by a non-uniform composition due to the precipitation of inclusions, in the present invention, the area occupied by the carbide having a particle size of 2 μm or less is already 80% or more of the area of the entire finish line. Since the finish line is used (FIG. 2), this point also has a positive effect on the life of the projection material. Furthermore, as will be described later, making the shot peening conditions appropriate (making the projection material harder than the workpiece or the like) also has a positive effect on the life of the projection material. In the present invention, the Vickers hardness of the projection material was 0.6 mm in diameter and HV940, and 0.3 mm in diameter and HV960. Here, FIG. 2 a shows a microstructure using a SEM (× 1000) of a finishing line having a diameter of 0.3 mm. FIG. 2b shows the microstructure using a SEM (x5000) with a 0.3 mm diameter finished line.

  The results of observing the structure of the projection material obtained in Example 1 and the comparative example will be described below. In the examples, the structure is a fine carbide and tempered martensite structure (Table 8). For this reason, there is an effect that there is little destruction of the projection material which makes inclusions a destruction start point by projection. This was evident by comparing the structure of the projection material before and after use. The microstructure using the SEM of the projection material for shot peening of the present invention after the nital corrosion having a diameter of 0.6 mm (before use) and a diameter of 0.3 mm (after use) is shown in FIGS. Here, FIG. 3 a is a microstructure using a SEM of a projection material having a diameter of 0.6 mm and before use (× 1000). FIG. 3b is a microstructure using a 0.6 mm diameter projection material SEM, before use (x3000). Moreover, FIG. 4 a is a microstructure using a SEM of a projection material having a diameter of 0.3 mm, after use (× 1000). FIG. 4 b is a microstructure using a 0.3 mm diameter projection material SEM, after use (× 3000).

本発明の製造方法で得られた投射材の実施例１と比較例を以下に説明する(表９)。このように、本発明では、焼き入れ温度を８２０℃〜８５０℃とすると炭化物の固溶が適正であった。
図５は、本発明に係る図３ｂのショットピーニング用投射材の炭化物の粒度分布を表すグラフである。炭化物の割合は、各炭化物を投影後、方眼紙を用い面積を求め、求めた面積を平方根にすることにより各炭化物の粒径及びその分布を求めた。平均粒径としては０．８μｍであった。粒径は２．０μｍ以下０．５μｍ以上であった。なお、粒径０．５μｍ未満の炭化物は、実質的に測定が困難であり、測定から除外する。また、平均粒径は、数平均で求めた。

Example 1 and a comparative example of the projection material obtained by the production method of the present invention will be described below (Table 9). Thus, in the present invention, when the quenching temperature is 820 ° C. to 850 ° C., the solid solution of the carbide is appropriate.
FIG. 5 is a graph showing the particle size distribution of the carbide of the shot peening projection material of FIG. 3b according to the present invention. The ratio of carbides was determined by calculating the area using graph paper after projecting each carbide and determining the particle size and distribution of each carbide by taking the obtained area as the square root. The average particle size was 0.8 μm. The particle size was 2.0 μm or less and 0.5 μm or more. Note that carbides having a particle size of less than 0.5 μm are substantially difficult to measure and are excluded from the measurement. Moreover, the average particle diameter was calculated | required by the number average.

Table 10 shows the conditions and results when the shot peening process was performed by actually projecting the workpiece using the projection material of the present invention.
According to the second embodiment, the projection material of the present invention (Vickers hardness is HV950) has a small amount of erosion with respect to a high-hardness workpiece, is easy to work harden the workpiece, and can introduce large residual stress. It was. (Experiment numbers 11-17).
In Experiment Nos. 11 to 17, the Vickers hardness of the projection material was initially 950 HV, but sometimes cured to 1050 HV by use.

Here, the amount of cutting was measured as follows.
<Measurement of amount of cutting>
The diameter of the material to be processed before and after the shot peening treatment was measured using a laser dimension measuring apparatus, and the value calculated by the following equation was used as the amount of cutting. In addition, the amount of cutting was an average value measured n = 10 times, and the measurement site was the center of the shot peening aiming position (maximum amount of cutting).
Cutting amount = (D1-D2) / 2
Dl = Diameter before shot peening
D2 = Diameter after shot peening

The compressive residual stress was measured as follows.
<Method for measuring compressive residual stress>
As a method for measuring the compressive residual stress of the processed product after the shot peening treatment, an X-ray stress measurement method using X-ray diffraction defined in general “JIS B2711” is used as a non-destructive method. Since the sample this time is martensitic steel, the measurement was performed using the characteristic X-ray type = CrKα ray and the X-ray stress coefficient k = −318 [MPa / °].
The measurement site was the center of the shot peening aiming position.
The peak value (= maximum value) of the compressive residual stress is measured by measuring the residual stress distribution after removing the range of almost twice the cross-sectional dimension of the incident X-ray bundle to a predetermined depth by electrolytic polishing. Was determined by

Furthermore, the cross-sectional hardness of the treated product was measured as follows.
<Cross section hardness measurement method>
HV0.3 in the table indicates the value of Vickers hardness of the cross section when the position of 50 μm from the surface of the cross section is measured with an indentation force of 300 g.
In general, a carburized abnormal layer is about 25 μm deep on the surface of the gas carburized product, and the hardness is very low. Even if the location in such a state is measured, the material and heat treatment cannot be evaluated, so the cross-sectional hardness is measured.

<Relative hardness measurement method>
The relative hardness in the table indicates a relative hardness value that is a value obtained by subtracting the hardness of the projection material from the hardness of the surface measured from the surface of the treated product. Since the hardness of the surface is important for selecting the projection material hardness with respect to the cross-sectional hardness for evaluating the material and heat treatment, measurement is performed by dropping an indenter directly on the surface. In addition, the measurement of hardness used the micro Vickers hardness tester (load 500g).
Therefore, in the case of a gas carburized product, the value includes the hardness of the surface abnormal layer. The vacuum carburized product is characterized by the fact that an abnormal surface layer is not formed, but the surface hardness may be lowered depending on the quenching characteristics.

Further, the area ratio of carbide is preferably 70% to 95%. More preferably, it is 80% to 95%. FIG. 6a is a graph showing the relationship between the carbide area ratio and hardness (composite hardness) of the shot peening projection material of the present invention (when the composition has a high hardness). FIG. 6 b is a graph showing the relationship between the carbide area ratio and hardness (composite hardness) of the shot peening projection material of the present invention (when the composition has a low hardness).
From these graphs, it is understood that the Vickers hardness is 920 HV to 1030 HV when the area ratio of the carbide is 70% to 95%. In the case of 950HV, the area ratio of carbide is 70% to 78%.
That is, the hardness HV (m) of the shot peening projection material is given by the following formulas (1) to (3).

そして、式（１）に式（２）と式（３）を代入すると、

Then, substituting Equation (2) and Equation (3) into Equation (1),

炭素量は０．７５％とした。

The carbon content was 0.75%.

This is used as a value near the carbon tolerance limit of the matrix (martensite). Since it is a formula for determining the matrix hardness, the carbon content at this time is set to 0.75%, and the carbides that precipitate beyond the allowable limit are excluded.
Further, residual austenite γR remaining during the heat treatment was considered as follows.

これらから、ショットピーニング用投射材の硬さの複合硬さを求めて、図６ａ、図６ｂに記載した。

From these, the composite hardness of the shot peening projection material was determined and shown in FIGS. 6a and 6b.

On the other hand, in Comparative Example 1, the projection material obtained by rounding the ridge line after cutting the steel wire (the hardness is HV700, the material is, for example, mass%, carbon 0.81%, manganese 0.48%, silicon 0.23%, Phosphorus 0.012%, sulfur 0.004%, and inevitable impurities (abbreviated as CCW type) are high-concentration carburized steels (steel grades suitable for carbide-dispersed carburization and have a Vickers hardness of 880 to 990 HV). A large residual stress could not be introduced into the hardness workpiece (Experiment No. 8). In the present invention, experiment number 15 corresponds.
Since the cemented carbide projection material (Vickers hardness is HV1380), which is Comparative Example 2, is too hard and has a large amount of carving work (SCM420H: hardened steel), the working pressure is used for peening. There is a limit (Experiment No. 10). In the present invention, experiment number 11 corresponds.

As described above, according to the present invention, in the production of a shot peening projection material, the shot peening projection material can be improved in productivity by preventing wire breakage in the step of drawing to obtain a finish line. It is possible to provide a method for producing a projection material for shot peening that can improve the material, finish line, and productivity, and a projection material produced by the production method.
Further, according to the present invention, it is possible to provide a shot peening projection material capable of providing the life of the shot peening projection material and applying appropriate compressive residual stress. In addition, according to the present invention, it is possible to provide a method for manufacturing a shot peening projection material that has good hardenability and is suitable for shot peening.

This application is based on Japanese Patent Application No. 2008-046967 filed on February 28, 2008 in Japan and Japanese Patent Application No. 2008-169971 filed on June 30, 2008, the contents of which are incorporated herein by reference. A part of it is formed.
The present invention will also be more fully understood from the following detailed description. However, the detailed description and specific examples are preferred embodiments of the present invention and are described for illustrative purposes only. This is because various changes and modifications will be apparent to those skilled in the art from this detailed description.
The applicant does not intend to contribute any of the described embodiments to the public, and the disclosed modifications and alternatives that may not be included in the scope of the claims are equivalent. It is part of the invention under discussion.
In this specification or in the claims, the use of nouns and similar directives should be interpreted to include both the singular and the plural unless specifically stated otherwise or clearly denied by context. The use of any examples or exemplary terms provided herein (eg, “etc.”) is merely intended to facilitate the description of the invention and is not specifically recited in the claims. As long as it does not limit the scope of the present invention.

Claims (3)

In mass%, carbon is 0.95 to 1.10%, silicon is 0.15 to 0.30%, manganese is 0.40% or less, phosphorus is 0.020% or less, sulfur is 0.010% or less, A material for a shot peening projection material containing 1.40 to 1.60% chromium and 0.0015% or less oxygen, and the balance consisting of iron and inevitable impurities ,
A step of drawing the wire;
A process of repeating annealing and cold drawing to finish lines,
Cutting the finish line and plastic working it into a shot peening material;
And quenching and tempering the shot peening material,
The quenching temperature of the quenching is 820-850 ° C.,
Tempering parameter in the tempering = T ((21.3-5.8 × [C]) + logt) is 6200-7300, where T: tempering temperature (K), t: tempering time (h), C: carbon content (% )
A method for producing a shot peening projection material, comprising: The number of annealing is 3 to 5 times,
  The manufacturing method of the projection material for shot peening of Claim 1. The area reduction rate of the wire drawing step is 10% to 40%.
  The manufacturing method of the projection material for shot peening of Claim 1 or Claim 2.

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