JPH0592368A - Manufacture of steel group shot - Google Patents

Abstract

PURPOSE:To provide a method of stably manufacturing shots having a hardness which is greater than that of a conventional one, and a hardness and a particle size which are relatively uniform, and which can hard crack. CONSTITUTION:There is carried out a manufacturing method comprising a heat treatment step of heat-treating a steel wire so as to obtain a drawn wire having a perlite structure in its entirety, a drawing step of drawing the drawn wire so as to reduce the diameter of the wire to a predetermined value in order to obtain a mechanically hardened drawn wire, a cutting step of cutting this drawn wire by a predetermined length so as to obtain shot blanks, and an external press step of applying an external pressure to the shot blanks so as to round the edge parts of the shot blanks while hardening the same. Thereafter, there may be carried out a low temperature heat-treatment process in which the shot blanks are heated up to a temperature less than a recrystallization temperature, and are then hardened under distortion-aging effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing iron-based shot particles used in shot pinning for improving the strength of automobile gears and the like.

[0002]

2. Description of the Related Art It is known that it is desirable to use shot particles having a high hardness in order to impart an effective residual compressive stress to the gears for automobiles in order to improve their fatigue strength. Shot Peaning App
licenses ”MetalIprovemen
Company t (1980)). Therefore, for example, when strengthening a carburized and quenched part, the surface hardness of the part (Hv650
Up to 850)), it is necessary to use shot particles having a hardness comparable to that of Hv70.
Some of the materials up to about 0 have been put into practical use ("Material Testing Technology" Vol. 34 No. 2 (1989.4)).

As a conventional method for producing a cut wire shot, a conventional high hardness shot grain is drawn into a wire having a predetermined diameter by drawing a steel wire material, and the wire is cut into a predetermined length, and then a wall is cut. It has been obtained by imparting a roundness to the edge portion by projecting it on the surface of the metal, and then performing heat treatment such as quenching and tempering (Japanese Patent Laid-Open No. 63-196380).
Publication).

As a still shot manufacturing method, cast iron is granulated by an atomizing method and then quenched and
It was also obtained by performing heat treatment for tempering and then sieving.

[0005]

However, the shot particles obtained by the above conventional manufacturing method are practically Hv700.
However, even if the hardness is as high as this, the hardness and the particle size vary greatly, and cracks easily occur. That is, in the conventional method for producing a cut wire shot, since the shot grain material cut into the predetermined diameter and the predetermined length is subjected to the heat treatment for the purpose of increasing the hardness, each shot grain material is likely to aggregate during the heat treatment. Therefore, in this method, heat is not easily applied to the shot grain material present inside the agglomerate, and the adhered state of steam or the like during the heat treatment varies depending on the degree of agglomeration, and the heat treatment becomes incomplete, and the Hv 700 It was difficult to manufacture only the ones, and it was easy to manufacture the ones with large variations in hardness. And, the shot particles thus obtained were those of high hardness that were more likely to crack earlier than those of low hardness,
Due to large variations in hardness, large variations in particle size were likely to occur.

Further, in the conventional steel shot manufacturing method, since the cast iron is granulated by the atomizing method, the dendrite structure and defects due to this are inevitable, and cast iron contains a large amount of carbon for the purpose of increasing hardness. As a result, defects were more likely to occur, and it was possible to manufacture only products up to Hv 700, and it was easy to manufacture products that were easily broken. And the high hardness shot particles thus obtained are
Since it is easily cracked during production and use, the particle size also tends to vary greatly.

Therefore, according to the conventional manufacturing method, only shot grains having a limited number of applicable parts can be produced. Even if such shot grains are applied, the shot-peening quality varies due to large variations in hardness and particle size. -There was a problem in that it was necessary to frequently measure and manage the arc height, which is a measure of the training effect. Further, in the conventional manufacturing method, since it is necessary to screen out the non-standardized shot particles in order to make the particle diameter uniform, the manufacturing cost rises, and the manufactured shot particles need to be screened at the time of use. As a result, the amount of consumption increases and the processing cost also rises.

The present invention has been made in view of the above-described problems, and an object thereof is to stably produce shot grains having higher hardness than conventional ones, less variation in hardness and grain size, and less likely to break. In the provision of the manufacturing method.

[0009]

The first method for producing iron-based shot grains according to the present invention is a heat treatment step for obtaining a wire drawing material in which the entire structure is almost pearlite by heat treating the steel wire material. And a drawing step of reducing the wire drawing material to a predetermined diameter to obtain a work-hardened wire, and cutting the wire drawing into a predetermined length to obtain a shot grain material. It is characterized by comprising a cutting step and an external pressure step of imparting a roundness to the edge portion and applying work hardening by applying an external pressure to the shot grain material.

In the second method for producing iron-based shot grains of the present invention, a steel wire material having a carbon content of 0.7 to 1.0% by weight is heat-treated, so that the entire structure is expanded to be pearlite. A heat treatment step for obtaining a wire material, a drawing step for reducing the wire drawing material to a predetermined diameter to obtain a work-hardened wire, and a cutting step for cutting the wire into a predetermined length. A cutting step of obtaining a first shot grain material, an external pressure step of applying a pressure to the first shot grain material to give a rounded edge portion and a work-hardened second shot grain material, It is characterized by comprising a low temperature heat treatment step of heating the second shot grain material at a temperature equal to or lower than the recrystallization temperature and performing strain age hardening.

In the heat treatment step, the steel wire material is heat treated to obtain a wire drawing material in which the entire structure is almost pearlite. A commercially available steel wire material can be adopted. When the diameter of the steel wire material is too large to be suitable for heat treatment, it is possible to perform the heat treatment after the steel wire material has a small diameter by wire drawing. Also, Hv70
In order to produce shot grains of about 0 or more, carbon of 0.
A steel wire material containing 7 to 1.0% by weight can be adopted. If the carbon content in the steel wire material is less than 0.7% by weight, the entire structure is hardly pallitized and the hardness is not sufficiently improved. If the carbon content exceeds 1.0% by weight, the drawing process becomes difficult. Further, the heat treatment can be performed by patenting.

[0012] In the drawing step, wire-drawing is carried out to reduce the wire-drawing material to a predetermined diameter to obtain a work-hardened wire. The wire drawing process can be performed at room temperature. By this step, it is possible to draw a wire with a thin diameter up to a target diameter. In the cutting step, the shot grain material is obtained by cutting the wire drawing into a predetermined length. After that, when the low temperature heat treatment step is performed subsequent to the external pressure step, this shot grain material is referred to as a first shot grain material.

In the external pressure step, an external pressure is applied to the shot grain material or the first shot grain material so that the edge portion is rounded and work hardened. As a means for applying an external pressure, a means for projecting the shot grain material or the first shot grain material onto a wall or the like can be adopted. In this way, shot grains are obtained. However, when the low temperature heat treatment step is further performed thereafter, the shot grains obtained here are referred to as the second shot grain material.

In the low temperature heat treatment step, the second shot grain material is heated at a temperature not higher than the recrystallization temperature to be strain age hardened. As the low temperature heat treatment step, bluing can be adopted. Thus, according to the production method of the present invention, Hv6
Iron-based shot particles of 50 or more, and Hv of 700 or more can be obtained if necessary.

[0015]

The shot grains produced by the method for producing iron-based shot grains of the present invention are rich in toughness and hardly cracked because the entire structure is almost pearlite in the heat treatment step.
That is, since it is not granulated by the atomizing method, it does not have a dendrite structure and defects caused thereby.
Further, work hardening occurs due to the tensile stress in the drawing step, and further work hardening occurs due to the compressive stress in the external pressure step. Therefore, the shot grains produced are
Due to being lightened, work hardening of tensile stress, and work hardening of compressive stress, high hardness is guaranteed and it is hard to crack. Further, in this manufacturing method, since the heat treatment is performed before the granulation, the variation in hardness is not increased by inducing the agglomeration of each shot grain material during the heat treatment, and the degree of pearlization in the heat treatment step can be adjusted. By adjusting the cross-section reduction rate during the drawing process and the degree of the external pressure process,
Uniformity of hardness of each grain is guaranteed. Further, the uniformity of the particle size is guaranteed by adjusting the diameter and length of the wire drawing in the drawing process and the cutting process.

In addition, a large number of dislocations are introduced in the shot grains (second shot grain material) obtained through the drawing process and the external pressure process, but when the low temperature heat treatment process is performed after the external pressure process, Nitrogen, carbon, etc. in the air or the second shot grain material move to this transition line as solute atoms,
The hardness is further increased because the transition is fixed by this solute atom.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. (Example 1) First, carbon 0.81% by weight, manganese 0.
A cylindrical steel wire material (Φ 5.5 mm) composed of 48% by weight, 0.23% by weight of silicon, 0.012% by weight of phosphorus, 0.004% by weight of sulfur, and remaining weight% of iron was prepared. Since this steel wire material has a diameter so large that it is not suitable for heat treatment, it is mechanically descaled and then subjected to a film treatment of boric acid and then at a wire drawing process of 350 m / min. It was drawn out to make a thin steel wire material of Φ2.92 mm.
With this thin steel wire material, an austenitizing temperature of 900 ° C,
A lead patenting process as a heat treatment was performed under the condition of a lead bath temperature of 550 ° C. In this way, a wire drawing material was obtained in which the entire structure was almost pearlite. The hardness of this wire drawing material is
It was Hv395.

Next, as a drawing step, the wire drawing material was subjected to wire drawing. First, descaling is performed by pickling at room temperature with hydrochloric acid, and then a coating treatment of phosphate is applied, followed by drawing at 400 m / min for wire drawing to obtain a wire with a diameter of 0.87 mm. did. The hardness of this wire drawing is
The maximum Hv 678, the minimum Hv 605, the average Hv 644, and the variation (R = range) 73 are obtained, and it can be seen that work hardening is performed.

Thereafter, as a cutting step, the wire drawing is cut into a length of 0.87 mm by using a cutting machine to obtain Φ 0.8.
A (first) shot grain material having a length of 7 mm and a length of 0.87 mm was obtained. Then, an external pressure was applied to the (first) shot grain material as an external pressure step. As the external pressure, the (first) shot grain material was projected 200 times on the wall made of wear-resistant steel under the condition of 57 m / s. In this way, shot grains having rounded edges (second shot grain material) were obtained. The hardness of this shot grain is maximum Hv 759, minimum Hv 705, average Hv 727, and R54, and it can be seen that the shot grains are work-hardened. (Example 2) Columnar steel composed of 0.82% by weight of carbon, 0.49% by weight of manganese, 0.18% by weight of silicon, 0.007% by weight of phosphorus, 0.003% by weight of sulfur, and remaining weight% of iron. The wire material (Φ5.5 mm) is Φ2.85 as in the first embodiment.
mm steel wire material. Then, as in Example 1, heat treatment was performed. The hardness of the wire drawing material after heat treatment is H
It was v410.

Further, as in the first embodiment, Φ0.80 mm
Was drawn. The hardness of this drawn wire was maximum Hv684, minimum Hv603, average Hv647, and R81. Then, in the same manner as in Example 1, a length of 0.80 mm was cut to obtain a shot grain material. This shot grain material was subjected to the external pressure process in the same manner as in Example 1 to obtain shot grains. The hardness of this shot grain was maximum Hv770, minimum Hv703, average Hv735, and R67. (Example 3) Shot grains were manufactured in the same manner as in Example 2 except that the number of projections on the wall was 100 times. The hardness of this shot grain is maximum Hv729, minimum Hv630, and average Hv.
It was 678 and R99.

Example 4 The same steel wire material as in Example 1 was used as a thin steel wire material with a diameter of 2.27 mm in the same manner as in Example 1, and heat treatment was performed as in Example 1. The hardness of the wire drawing material after the heat treatment was Hv439. Further, similarly to Example 1, the wire was drawn with Φ0.60 mm. The hardness of this wire drawing is
Maximum Hv656, Minimum Hv607, Average Hv631, R
It was 49.

Then, as in the first embodiment, the length is 0.60.
It cut | disconnected to mm and obtained the shot grain raw material. This shot grain material was subjected to the external pressure process in the same manner as in Example 1 to obtain shot grains. The hardness of this shot grain was maximum Hv744, minimum Hv709, average Hv731, and R65. Therefore, it is understood that the shot particles manufactured by the manufacturing methods of Examples 1 to 4 have Hv of 700 or more and can be applied to various parts. (Example 5) The shot grains (second shot grain material) obtained in Example 1 were subjected to a low temperature heat treatment step at 300 ° C and 20 ° C.
After uniformly heating for a minute, it was air-cooled. The hardness of the shot particles thus obtained was maximum Hv809, minimum Hv752, average Hv774, and R57. Therefore, it can be seen that the hardness of the shot grains subjected to the low temperature heat treatment step in Example 5 is increased by Hv47 on average as compared with the shot grains of Example 1. (Evaluation) (1) The metallographic structure of the shot particles obtained by the manufacturing method of Example 1 is shown in FIG. FIG. 8 shows a metal structure of a conventional high hardness steel shot (hereinafter, referred to as shot grains of Comparative Example 1).
Shown in. Further, the metallographic structure of a conventional high hardness cut wire shot (hereinafter, referred to as shot grains of Comparative Example 2) is shown in FIG.
Shown in.

It can be seen from FIG. 7 that the shot grains of Example 1 have a pearlite structure in which the entire structure is work-hardened and are unlikely to crack. On the other hand, from FIG. 8, it can be seen that the shot grains of Comparative Example 1 have cavities of casting defects having a dendrite structure. Further, it is understood from FIG. 9 that the shot grains of Comparative Example 2 have an incomplete quenching / tempering structure. (2) The shot grains of Example 1, Example 5, Comparative Example 1 and Comparative Example 2 were used to compare hardness and uniformity of hardness. The hardness distribution of the shot grains of Example 1 is shown in FIG. 1 and Example 5.
2 shows the hardness distribution of the shot particles of Comparative Example 1, FIG. 3 shows the hardness distribution of the shot particles of Comparative Example 1, and FIG. 4 shows the hardness distribution of the shot particles of Comparative Example 2.

As a result, it can be seen that the hardnesses of Examples 1 and 5 are smaller than those of Comparative Examples 1 and 2. Further, it can be seen that the hardness of Example 5 is higher than that of Example 1. (3) The shot grains of Example 1 and Comparative Example 1 were used to compare the uniformity of grain size. The particle size distributions of shot particles of Example 1 and Comparative Example 1 are also shown in FIG.

As a result, it can be seen that the shot grains of Example 1 have smaller variations in grain size than those of Comparative Example 1. Therefore, it can be seen that the manufacturing method of Example 1 does not require sieving broken shot particles in order to make the particle diameter uniform, and thus the manufacturing cost can be reduced. (4) Using the shot particles of Example 1 and Comparative Example 1, shot pinning was performed on a hypoid gear (Hv750) under the same conditions, and the input torque (kgf · m) and the number of load repetitions (times) until breakage were performed. The fatigue strength was measured by.
Results are shown in FIG.

From these results, the shot grains of Example 1 were
It can be seen that the fatigue strength which is slightly superior to that of Comparative Example 1 can be imparted. (5) The shot grains of Example 1 and Comparative Example 1 were used to confirm the stability and consumption of arc height by an actual machine test. As a result, it was found that in the shot grains of Example 1, the variation range of the arc height was 0.06, which was reduced to 2/3 as compared with the shot grains of Comparative Example 1. Therefore, it can be understood that the application of the shot grains of Example 1 can solve the problem that the shot pinning quality is stable and the arc height measurement / management must be frequently performed.

Further, the consumption amount of shot particles in Example 1 was about 1/7 of that in Comparative Example 1. this is,
This is because the shot particles of Example 1 are less likely to be broken during use and have a uniform hardness and particle size as compared with those of Comparative Example 1, and thus it is difficult to reduce the weight by sieving. Therefore, it is understood that the processing cost can be reduced. (6) Using the shot particles of Example 1, Example 5, and Comparative Example 1, the amount of wear was confirmed by an actual machine test.

As a result, the shot grains of Example 5 have an average Hv50 higher than that of Example 1, but
The amount of consumption is about 1/7 as compared with that of Comparative Example 1,
The amount of wear was almost the same as that of Example 1. this is,
This is because the shot particles of Example 5 are less likely to break during use and have uniform hardness and particle size as compared with those of Comparative Example 1 as in Example 1, and thus it is difficult to reduce the weight by sieving. .. Therefore, it is understood that the shot grains of Example 5 can also reduce the processing cost.

[0029]

As described above in detail, in the method for producing iron-based shot particles of the present invention, after the entire structure is almost pearlite, wire drawing is performed to work-harden it by tensile stress. Since it is cut later, the edge portion is rounded by applying an external pressure and the work is hardened by the compressive stress, it is possible to manufacture shot grains having a small hardness variation and a high hardness, which is hard to break. Further, when the shot grains are further heated at a temperature equal to or lower than the recrystallization temperature, the shot grains are strain age-hardened, and the shot grains having higher hardness can be manufactured.

Therefore, in this manufacturing method, since the shot grains maintain the toughness and hardness due to the pearlite structure and work hardening, the Hv70 is maintained even if the carbon amount is not increased so much.
About 0 or more shot grains can be produced, and the produced shot grains can be applied to various parts. Further, even if the produced shot grains are used repeatedly, the variations in hardness and grain size in the production lot are small, so that the shot pinning quality can be preferably maintained, and it is necessary to frequently perform the arc height measurement / management. Absent.

Further, in this manufacturing method, since it is not necessary to sift out in order to make the particle diameter uniform, the manufacturing cost can be reduced, and the manufactured shot particles are difficult to break and need to be sifted during use. Since it is not present, the wear amount of shot particles is reduced and the processing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a graph showing a hardness distribution of shot particles in Example 1.

FIG. 2 is a graph showing a hardness distribution of shot particles in Example 5.

3 is a graph showing a hardness distribution of shot particles in Comparative Example 1. FIG.

FIG. 4 is a graph showing a hardness distribution of shot particles of Comparative Example 2.

5 is a graph showing the particle size distribution of shot particles of Example 1 and Comparative Example 1. FIG.

FIG. 6 is a graph showing the fatigue strength of hypoid gears using the shot particles of Example 1 and Comparative Example 1.

FIG. 7 shows a metallographic structure of shot grains of Example 1 320.
It is a micrograph with a magnification of 2.

8 shows a metallographic structure of shot grains of Comparative Example 1 320. FIG.
It is a micrograph with a magnification of 2.

FIG. 9 shows a metallographic structure of shot grains of Comparative Example 320.
It is a micrograph with a magnification of 2.

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[Procedure amendment]

[Submission date] November 16, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Figure 7]

[Fig. 2]

[Figure 3]

[Figure 4]

[Figure 8]

[Figure 9]

[Figure 5]

[Figure 6]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akio Takahashi, Toyota city, Toyota city, Aichi prefecture, Toyota Motor Co., Ltd. (72) Inventor, Seikichi Hadano, Toyota city, Aichi prefecture, Toyota city, Toyota car company (72) Inventor Michihiro Suzuki 1 Toyota-cho, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Kazumi Kito, 481 Toyama Seijo, Ama Prefecture, Shibu Village, Niigata, Tofu Steel Co., Ltd. (72) Inventor Yoshihiro Watanabe 14 Yamayama, Kaifu-gun, Aichi Omagane 48 Otori 481 Toyo Seiko Co., Ltd.

Claims (2)

[Claims] Claim: What is claimed is: 1. A steel wire material is heat-treated to obtain a wire drawing material in which the entire structure is almost pearlite, and a wire drawing work is performed to reduce the wire drawing material to a predetermined diameter. A drawing step for obtaining a hardened wire, a cutting step for cutting the wire into a predetermined length to obtain a shot grain material, and an external pressure applied to the shot grain material to round the edge portion. An iron-based shot grain manufacturing method, which comprises an external pressure step of applying and working hardening. 2. A heat treatment step for obtaining a wire drawing material in which the entire structure is almost pearlite by heat treating a steel wire material containing 0.7 to 1.0% by weight of carbon, and the wire drawing material having a predetermined diameter. A drawing process for obtaining a work-hardened wire by performing a wire drawing process for reducing the wire to a predetermined length, and a cutting process for cutting the wire into a predetermined length to obtain a first shot grain material; By applying external pressure to the shot grain material,
Second work-hardened second with rounded edges
An iron-based shot grain manufacturing method comprising: an external pressure step of obtaining a shot grain raw material; and a low temperature heat treatment step of heating the second shot grain raw material at a temperature equal to or lower than a recrystallization temperature to perform strain age hardening.