JPWO2019188120A1 - Shot used for blasting - Google Patents

Abstract

The present disclosure is a shot used for blasting, in which C: 0.20 to 0.50% by mass, Si: 0.50 to 1.10% by mass, and Mn: 0.50 to 1. It is composed of an iron-based alloy containing 15% by mass, and the mass ratio of C to Si is 0.30 to 0.75, the mass ratio of C to Mn is 0.30 to 0.75, and the mass ratio of Si to Mn is 0. For shots of .70 to 1.60 and Vickers hardness of HV400 to 800.

Description

The present disclosure relates to shots used for blasting.

Shot blasting is used for removing sand from castings after casting, deburring metal products, and removing scales such as rust. Shot blasting is a processing method in which particles called shots are projected toward a work piece. Iron-based particles are often used as shots.

Patent Document 1 describes as additive elements C: 0.80 to 1.10% by mass, Si: 0.50 to 1.00% by mass, Mn: 0.50 to 1.00% by mass, Cr: 0.10. Shots containing ~ 0.30% by weight and the balance being Fe (containing unavoidable impurities) are disclosed. Since shots are used repeatedly until they are worn to a size that is not suitable for shot blasting, it is desired that shots with less wear (longer life) be introduced.

The hardness of the shot is selected according to the physical characteristics of the work and the purpose of shot blasting. It is desired to establish a manufacturing method for manufacturing shots having various hardnesses.

Japanese Unexamined Patent Publication No. 53-75156

The present disclosure has been made in view of the above circumstances, and an object of the present invention is to provide a shot having a long life and various hardness because the cleaning efficiency is not easily impaired.

The shot according to one form of the present disclosure is a shot used for blasting. The shot is composed of an iron-based alloy containing C: 0.25 to 0.50% by mass, Si: 0.50 to 1.10% by mass, and Mn: 0.50 to 1.15% by mass as additive elements. .. Further, in the shot, the mass ratio of C to Si (C / Si) was 0.30 to 0.75, the mass ratio of C to Mn (C / Mn) was 0.30 to 0.75, and the mass ratio of Si to Mn was 0.30 to 0.75. The mass ratio (Si / Mn) is 0.70 to 1.60. The Vickers hardness of the shot is HV400 to 800 (specified in JIS Z 2244: 2009).

In one embodiment, the total content of C, Si and Mn (C + Si + Mn) may be 1.80 to 2.40% by mass.

In one embodiment, the iron-based alloy further comprises 0.30 to 1.0% by mass of at least one element selected from the group consisting of Cr, Ni, Cu, Mo, Al, B, V, Nb and Ti. It may be included.

In one embodiment, the shot may be substantially formed from the tempered martensite phase.

In one embodiment, the number of particles with blow holes may be 5% or less of the total shot.

In one embodiment, when the length of the particles in the longitudinal direction is L and the maximum diameter in the direction orthogonal to the longitudinal direction is S, the number of particles having an L / S of 2.0 or more is 5 for the entire shot. It may be less than or equal to%.

According to one embodiment of the present disclosure, a shot having a long life and various hardness is provided because the cleaning efficiency is not easily impaired.

FIG. 1 shows the results of observing the cross sections of the shots of Example 1 and Comparative Example with a scanning electron microscope.

The shot according to one embodiment of the present disclosure is a shot made of a four-component iron-based alloy containing C, Si and Mn as additive elements. Alternatively, it can be said that the shot according to one embodiment of the present disclosure is a shot containing particles made of an iron-based alloy, and the iron-based alloy contains C, Si, and Mn as additive elements. The shot (iron-based alloy) may contain other unavoidable impurities.

Hereinafter, the shot of one embodiment will be described in detail by taking the case of producing a shot by the water atomizing method as an example. Unless otherwise specified,% in the following description indicates mass%.

<Melting process>
Raw materials for shots (Fe, C, Si, Mn, etc.) weighed so as to have a predetermined composition are put into a melting furnace and heated to 1600 to 1750 ° C. to melt them into a molten metal.

Fe is the element that is the basis of the shot.

C is an element that affects hardness. As the C concentration increases, the shot becomes harder and the cleaning ability increases, but the toughness decreases in proportion to the C concentration. A decrease in toughness leads to a decrease in life. Considering the hardness and life required as a shot, the content of C in the iron-based alloy is 0.25 to 0.50% by mass, but it may be 0.30 to 0.45% by mass, and is 0. It may be 35 to 0.45% by mass.

Si has the effect of removing oxygen in the molten metal of the raw material. Oxygen contained in the molten metal inhibits the spheroidization of particles during granulation by the atomizing method. When the Si concentration is high, the deoxidizing effect is high, so that spherical particles can be easily obtained, but the toughness decreases in proportion to the Si concentration. Further, by removing oxygen in the molten metal, it is possible to reduce internal defects called blow holes. C also has a deoxidizing effect, but considering the life, it is difficult to add an amount of C that can sufficiently obtain the deoxidizing effect. Considering the deoxidizing effect and the life, the content of Si in the iron-based alloy is 0.50 to 1.10% by mass, but it may be 0.55 to 1.05% by mass, and 0.60. It may be ~ 1.00% by mass.

Mn has the effect of improving the quenchability of the granulated particles and the effect of shifting the pearlite nose in the TTT diagram to the right to lower the critical cooling rate. By quenching, the hardness required for a shot can be obtained. The structure of the particles is transformed by quenching, and at this time, it is required to have a structure having homogeneous and fine crystal grains. The quenching conditions are adjusted so that such a structure can be obtained, but in the case of fine particles such as shots, it is necessary to adjust the quenching conditions delicately. By adding Mn to the alloy, the allowable value of quenching conditions is widened, and the conditions can be easily adjusted. This facilitates the introduction of a structure having homogeneous and fine (for example, 2 to 10 μm) crystal grains throughout the granulated particles. As a result, the particles have excellent toughness, so that the life of the shot is improved. However, since Mn is an expensive metal, increasing the concentration leads to an increase in the production cost of shots. Considering the quenching effect and cost, the content of Mn in the iron-based alloy is 0.50 to 1.15% by mass, but may be 0.55 to 1.00% by mass, 0.60. It may be ~ 0.95% by mass.

Further, when the content of C in the iron-based alloy is a mass%, the content of Si is b mass%, and the content of Mn is c mass%, the synergies of the additive elements C, Si, and Mn are obtained. Considering the effect, each mass ratio and the like are as follows.
Although a / b (mass ratio of C to Si) is 0.30 to 0.75, it may be 0.35 to 0.60 or 0.40 to 0.50.
Although a / c (mass ratio of C to Mn) is 0.30 to 0.75, it may be 0.35 to 0.60 or 0.40 to 0.50.
The b / c (mass ratio of Si to Mn) is 0.70 to 1.60, but may be 0.80 to 1.40 or 0.99 to 1.20.
The a + b + c (total content of C, Si, and Mn) is preferably 1.80 to 2.40% by mass, but may be 1.85 to 2.25% by mass, and 1.90 to 2.25% by mass. It may be 10% by mass.

The iron-based alloy may further contain at least one element selected from the group consisting of Cr, Ni, Cu, Mo, Al, B, V, Nb and Ti. These other additive elements are added for the purpose of complementing the effects of Si and Mn, and the effects shown below can be obtained by the addition. However, if the concentration of these other additive elements is too high, problems such as a decrease in hardness, a decrease in life, and insufficient spheroidization tend to occur. Therefore, the content of these other additive elements in the iron-based alloy (when a plurality of elements are added, the total content thereof) may be adjusted to be 0.30 to 1.0% by mass.

Cr has an effect of improving hardenability and an effect of shifting the pearlite nose in the TTT diagram to the right to lower the critical cooling rate. If the concentration of Cr is too low, these effects cannot be sufficiently obtained, and if it is too high, the toughness of the shot tends to decrease. In consideration of these, the Cr content in the iron-based alloy may be adjusted to be 0.3 to 1.0% by mass.

Ni and Cu have the effect of improving hardenability and life while suppressing inhibition of spheroidization by oxygen. If the concentrations of Ni and Cu are too low, these effects cannot be sufficiently obtained, and if they are too high, the toughness tends to decrease. In consideration of these, the total content of Ni and Cu in the iron-based alloy may be adjusted to be 0.4 to 1.0% by mass. Although Ni is slightly superior to Cu in exhibiting the above effects, it is an expensive material, so the composition ratio of Ni and Cu is determined in consideration of the effects and cost.

Mo has the effect of reducing the variation of each particle in structure and hardness, the effect of improving hardenability, and the effect of shifting the pearlite nose in the TTT diagram to the right to lower the critical cooling rate. .. If the concentration of Mo is too low, these effects tend not to be sufficiently obtained. Further, since Mo is an expensive material, if the concentration of Mo is too high, the demerit due to the increase in cost becomes larger than the merit that these effects can be obtained. In consideration of these, the content of Mo in the iron-based alloy may be adjusted to be 0.1 to 0.3% by mass.

Al has an effect of removing oxygen in the molten metal of the raw material to promote spheroidization of particles and an effect of reducing blow holes. If the concentration of Al is too low, these effects cannot be sufficiently obtained, and if it is too high, spheroidization tends to be inhibited. In consideration of these, the content of Al in the iron-based alloy may be adjusted to be 0.04 to 0.12% by mass.

B has an effect of improving hardenability and an effect of improving the life. If the concentration of B is too low, these effects cannot be sufficiently obtained, and if it is too high, the life tends to be shortened. In consideration of these, the content of B in the iron-based alloy may be adjusted to be 0.01 to 0.05% by mass.

V, Nb and Ti have the effect of improving the life. If the concentration of these elements is too low, the effect cannot be sufficiently obtained, and if the concentration is too high, the life tends to be shortened. In consideration of these, the total content of V, Nb and Ti in the iron-based alloy may be adjusted to be 0.05 to 0.5% by mass.

<Granulation process>
A granulated product (spherical body) is obtained by dropping the raw material molten metal from a nozzle at the bottom of the melting tank and injecting high-pressure water toward the molten metal.

Oxygen in the molten metal becomes a factor that inhibits the spheroidization of particles during granulation. The shot of one embodiment is formed from a molten metal containing Si as a raw material. Since oxygen in the molten raw material is removed by Si, spheroidization of particles can be promoted by using such a raw material.

In addition, oxygen in the molten metal causes blow holes. Blow holes are generated when oxygen in the molten raw material is not released into the atmosphere when the raw material is solidified, but is contained as bubbles inside the particles. By using Si as a raw material, oxygen in the molten material can be removed and blow holes can be reduced.

<Quenching process>
Since the granulated product produced as described above contains C, it is harder than Fe. However, it is necessary to further improve the hardness in order to use it as a shot. The granulated product produced in the granulation step is dried by a rotary kiln or the like, heated to 800 to 900 ° C., held for about 1 hour, and then dropped into water for quenching. Thereby, the hardness of the granulated product can be increased.

Since the granulated product contains Mn, the hardenability is improved. Further, in the granulated product, the pearlite nose in the TTT diagram is shifted to the right, so that the critical cooling rate is lowered. Further, when quenching is performed, the structure of the granulated product becomes finer, so that the toughness is improved. That is, such a granulated product can be used as a shot with less wear (longer life).

<Tempering process>
The granulated product that has undergone the quenching step is heated at 300 to 600 ° C. for about 0.5 to 2.0 hours, and then slowly cooled to perform tempering. Thereby, the granulated product can be adjusted to a desired hardness, and the toughness of the granulated product lowered by the quenching step can be improved.

By going through the quenching step and the tempering step, a fine and uniform structure is introduced into the granulated product. In particular, the texture of the particles contained in the shot of one embodiment is substantially formed primarily from the tempered martensite phase. The crystal grain size in the tempered martensite phase is about 0.5 to 10 μm. Particles having such a structure have high toughness even when an impact load is repeatedly applied during blasting, so that wear is suppressed.

<Classification process>
Sieve the granulated product after the quenching process using a vibrating sieve or the like. As a result, particles having a predetermined diameter are classified.

<Recovery process>
Through the steps of inspecting the shape, hardness, etc. of the classified particles, a shot containing particles having a predetermined diameter can be obtained.

The Vickers hardness of the shot (particle) of one embodiment is HV400-800. From the viewpoint of blast workability and life, the HV may be 400 to 650 or 400 to 500. The standard deviation of HV can be HV50 or less. Since the shot of one embodiment has a specific composition, it has sufficient hardness as a shot, and the variation in hardness for each particle is extremely small. Due to the extremely small variation in hardness, the finished quality is stable during blasting.

In the shot of one embodiment, when the length of the particles in the longitudinal direction is L and the maximum diameter in the direction orthogonal to the longitudinal direction is S, the number of particles having an L / S of 2.0 or more is the entire shot. It may be 5% or less of. Since the shot of one embodiment has a specific composition, it contains a large amount of uniformly spheroidized particles, and the finished quality is stable during blasting. The number of the particles may be 1% or less of the whole shot, or 0.1% or less.

In the shot of one embodiment, the number of particles having blow holes may be 5% or less of the total shot. Here, the particles having blow holes mean that the area ratio of the bubbles in the cross section is 10% or more of the area of the cross section, and the wall surface of the bubbles is gentle. The blow hole is the starting point for shot damage during blasting. Since the shot of one embodiment has a specific composition, the number of particles having blow holes is extremely small and the life is long. The number of the particles may be 3% or less of the entire shot, or 1% or less.

In the shot of one embodiment, the number of particles having cracks may be 5% or less of the total shot. Here, the particle having a crack means that the length of the crack in the cross section is 3 times or more the width of the crack and the length of the crack is 20% or more of the minimum diameter in the cross section. The crack is the starting point for the shot to be damaged during the blasting process. Since the shot of one embodiment has a specific composition, the number of particles having cracks is extremely small and the life is long. The number of the particles may be 3% or less of the entire shot, or 1% or less.

In the shot of one embodiment, the average particle size of the contained particles may be 0.1 to 1.5 mm. If the average particle size is within this range, the life of the shot tends to be long. Here, the average particle size is a value measured by sieving using a JIS Z 8801 standard sieve. The average particle size may be 0.1 to 1.0 mm, 0.15 to 0.75 mm, or 0.2 to 0.45 mm.

The apparent density of the shots of one embodiment may be 7.45 g / cm ³ or more. This makes it easier to obtain collision energy with the work piece during blasting, so it is easy to sufficiently grind the work piece.

[Example]
Next, the test results for confirming the effect of the shot of one embodiment will be described.
First, various shots made of iron-based alloys having the compounding ratios shown in Table 1 were prepared by using the water atomization method. X in Table 1 indicates the content (total content) of the additive element selected from the group consisting of Cr, Ni, Cu, Mo, Al, B, V, Nb and Ti.

The obtained particles were classified to obtain shots having desired particle diameters (φ0.3 mm, φ0.6 mm, φ1.0 mm). The shots having each particle size were prepared as follows.
φ0.3 mm: Passed through a 0.425 mm sieve and remained on a 0.355 mm sieve.
φ0.6 mm: Passed through a 0.710 mm sieve and remained on a 0.600 mm sieve.
φ1.0 mm: Passed through a 1.180 mm sieve and remained on a 1.000 mm sieve.

(1) Measurement of Vickers hardness After the shot particles were embedded in the resin, they were polished so that the center of the cross section was exposed on the surface. The Vickers hardness was measured for 10 shots according to the above-mentioned standard (JIS Z 2244: 2009), and the average value was taken as the hardness of the shots. The results are shown in Table 2.

(2) Measurement of apparent density Measurement was performed according to JIS Z0311: 2004. Specifically, about 10 g of shots was placed in a specific gravity bottle (volume: 50 ml), and the mass was measured. Next, distilled water was charged into a specific gravity bottle to remove air bubbles inside, and then the mass was measured. The apparent density was calculated from these masses. This operation was performed twice, and the average value was taken as the apparent density of the shot. The results are shown in Table 2.

(3) Verification of defects (blow holes) After the shot particles were embedded in the resin, they were polished so that the center of the cross section was exposed on the surface. The cross section of 100 shots was observed with a projector, the number of shots in which the above-mentioned blow hole was present as a defect was measured, and the ratio was calculated. The results are shown in Table 2.

(4) Verification of sphericity After spreading the particles of the shot on a glass plate, the length L in the longitudinal direction of the particles and the maximum diameter S in the direction orthogonal to the longitudinal direction are measured for 100 shots with a microscope. Observed by. Then, the number of particles having an L / S of 2.0 or more was measured, and the ratio (particle shape defect rate) was calculated. The results are shown in Table 2.

(5) Evaluation of life The 100 g of the manufactured shot was put into a life test device (manufactured by Ervin: The Test Ervin Machine) and projected toward a steel material (HRC65) at a projection speed of 60 m / s. The shots after projection were collected, the collected shots were classified by a sieve (0.300 mm, 0.500 mm or 0.850 mm), and the weight of the shots remaining on the sieve was weighed. This operation was repeated until the amount of shots remaining on the sieve was 10 g, and the curve showing the relationship between the number of collisions obtained by this test and the residual rate of shots was integrated, and this value was used as the lifetime value. The results are shown in Table 2.

A comparative example is a shot having a conventional composition. It was found that the shots of Examples 1 to 10 had a longer life than the shots of Comparative Example.

In addition, the cross sections of the shots of Example 1 and Comparative Example were observed with a scanning electron microscope. As shown in FIG. 1, in the shot of the example, the structure mainly formed from the refined tempered martensite phase was observed, whereas in the shot of the comparative example, the unrefined martensite was observed. Tissues formed primarily from the site phase were observed.

The shot of one embodiment has a hardness required for cleaning and has a long life, so that it has an extremely large industrial value. This shot can be used for any blasting process.

Although the water atomization method has been described as an example of the shot production method of one embodiment, another method such as a gas atomization method or a disc atomization method may be adopted.

Claims (6)

A shot used for blasting
It is composed of an iron-based alloy containing C: 0.25 to 0.50% by mass, Si: 0.50 to 1.10% by mass, and Mn: 0.50 to 1.15% by mass as additive elements.
The mass ratio of the C to the Si is 0.30 to 0.75, the mass ratio of the C to the Mn is 0.30 to 0.75, and the mass ratio of the Si to the Mn is 0.70 to 1. 60
A shot with a Vickers hardness of HV400-800. The shot according to claim 1, wherein the total content of the C, the Si, and the Mn is 1.80 to 2.40% by mass. Claim that the iron-based alloy further contains 0.30 to 1.0% by mass of at least one element selected from the group consisting of Cr, Ni, Cu, Mo, Al, B, V, Nb and Ti. The shot according to 1 or 2. The shot according to any one of claims 1 to 3, which is substantially formed from the tempered martensite phase. The shot according to any one of claims 1 to 4, wherein the number of particles having blow holes is 5% or less of the entire shot. When the length of the particles in the longitudinal direction is L and the maximum diameter in the direction orthogonal to the longitudinal direction is S, the number of particles having an L / S of 2.0 or more is 5% or less of the entire shot. The shot according to any one of claims 1 to 5.

Images