CN111278603A

CN111278603A - Shot for shot peening

Info

Publication number: CN111278603A
Application number: CN201980005353.1A
Authority: CN
Inventors: 加藤佑人; 石川政行; 田沼直也; 谷口隼人
Original assignee: Sintokogio Ltd
Current assignee: Sintokogio Ltd
Priority date: 2018-03-28
Filing date: 2019-03-08
Publication date: 2020-06-12
Also published as: DE112019000550T5; JP7205535B2; TW201942381A; US20210069864A1; WO2019188120A1; JPWO2019188120A1

Abstract

The invention relates to a shot, which is used for shot blasting and comprises a component containing C: 0.20 to 0.50 mass%, Si: 0.50 to 1.10 mass% and Mn: 0.50 to 1.15 mass% of an iron-based alloy as an additive element, wherein 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, the mass ratio of Si to Mn is 0.70 to 1.60, and the Vickers hardness is HV400 to 800.

Description

Shot for shot peening

Technical Field

The invention relates to a shot for shot peening.

Background

Shot blasting may be used for shakeout of cast products after casting, deburring of metal products, and removal of scale (scale) such as rust. Shot blasting is a processing method in which particles called shot are projected onto a workpiece. Iron-based particles are often used as the shot.

Patent document 1 discloses a composition containing C: 0.80 to 1.10 mass%, Si: 0.50 to 1.00 mass%, Mn: 0.50 to 1.00 mass%, Cr: 0.10 to 0.30 mass% of a pellet containing an additive element and the balance Fe (containing unavoidable impurities). Since the projectile is repeatedly used until it is worn to a size unsuitable for shot blasting, it is desired to have a (long-life) projectile with less wear.

The hardness of the shot is selected according to the physical properties of the workpiece and the purpose of shot blasting. It is desirable to establish a manufacturing method for manufacturing shot having a variety of hardnesses.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 53-75156

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a shot which is not easily damaged in grinding and sweeping efficiency, has a long life, and has various hardnesses.

A shot according to an embodiment of the present invention is a shot for shot peening. The pill is prepared from a mixture of C: 0.20 to 0.50 mass%, Si: 0.50 to 1.10 mass% and Mn: 0.50 to 1.15 mass% of an iron-based alloy as an additive element. In the pellet, the mass ratio of C to Si (C/Si) is 0.30 to 0.75, the mass ratio of C to Mn (C/Mn) is 0.30 to 0.75, and the mass ratio of Si to Mn (Si/Mn) is 0.70 to 1.60. The Vickers hardness of the pellet is HV 400-800 (prescribed in JIS Z2244: 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 may further contain 0.30 to 1.0 mass% of at least 1 element selected from the group consisting of Cr, Ni, Cu, Mo, Al, B, V, Nb, and Ti.

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

In one embodiment, the number of particles having pores may be 5% or less of the total amount of the pellet.

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 may be 5% or less of the entire pellet.

According to one embodiment of the present invention, there can be provided a long-life projectile having various hardnesses, since the grinding and sweeping efficiency is not easily impaired.

Drawings

Fig. 1 shows the results of observing the cross section of each pellet of example 1 and comparative example with a scanning electron microscope.

Detailed Description

The shot of one embodiment of the present invention is a shot made of a 4-component iron-based alloy containing C, Si and Mn as an additive element. Alternatively, the pellet according to one embodiment of the present invention may be referred to as a pellet as follows: contains particles composed of an iron-based alloy containing C, Si and Mn as additive elements. Other inevitable impurities may be contained in the shot (iron-based alloy).

Hereinafter, a description will be given of a projectile of an embodiment by taking a case where the projectile is produced by a water atomization method as an example. Unless otherwise specified, the% in the following description means mass%.

< melting step >

Raw materials (Fe, C, Si, Mn, etc.) of the shot weighed so as to have a predetermined composition are charged into a melting furnace, heated to 1600 to 1750 ℃, and melted to prepare a melt.

Fe is an element that becomes the basis of the pellet.

C is an element that affects hardness. If the concentration of C is high, the shot becomes hard, and therefore the grinding and sweeping ability becomes high, but the toughness decreases in proportion to the concentration of C. The decrease in toughness leads to a decrease in life. In consideration of the hardness and the life required for the shot, the content of C in the iron-based alloy may be 0.20 to 0.50 mass%, or may be 0.30 to 0.45 mass%, or may be 0.35 to 0.45 mass%.

Si has an effect of removing oxygen in the raw material melt. When granulation is performed by the atomization method, the oxygen contained in the raw material melt hinders the spheroidization of particles. If the concentration of Si is high, the deoxidation effect is high, and therefore spherical particles are easily obtained, but toughness decreases in proportion to the concentration of Si. Further, by removing oxygen from the raw material melt, internal defects called blowholes can be reduced. C also has a deoxidizing effect, but if the lifetime is taken into consideration, it is difficult to add C in an amount that can sufficiently obtain the deoxidizing effect. In view of the deoxidation effect and the life, the content of Si in the iron-based alloy may be 0.50 to 1.10 mass%, or may be 0.55 to 1.05 mass%, or may be 0.60 to 1.00 mass%.

Mn has an effect of improving the hardenability of the granulated particles and an effect of moving the pearlite nose in the TTT diagram to the right side to reduce the critical cooling rate. By quenching, the hardness required for the shot can be obtained. The structure of the particles is transformed by quenching, but in this case, it is required to form a structure having homogeneous and fine crystal grains. The quenching conditions are adjusted to obtain such a structure, but in the case of fine particles such as shot, fine adjustment of the quenching conditions is required. By adding Mn to the alloy, the allowable value of the quenching condition is increased, and the condition can be easily adjusted. This makes it easy to introduce a structure having homogeneous and fine (e.g., 2 to 10 μm) crystal grains into the whole granulated particles. As a result, the pellets have excellent toughness, and therefore, the life of the pellet is improved. However, since Mn is an expensive metal, if the concentration is increased, the production cost of the shot increases. In view of the quenching effect and cost, the content of Mn in the iron-based alloy may be 0.50 to 1.15 mass%, or 0.55 to 1.00 mass%, or 0.60 to 0.95 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 mass ratios are as follows in consideration of synergistic effects of C, Si and Mn as additive elements.

a/b (mass ratio of C to Si) is 0.30 to 0.75, or 0.35 to 0.60, or 0.40 to 0.50.

a/C (mass ratio of C to Mn) is 0.30 to 0.75, or 0.35 to 0.60, or 0.40 to 0.50.

b/c (mass ratio of Si to Mn) is 0.70 to 1.60, or 0.80 to 1.40, or 0.90 to 1.20.

The a + b + c (total content of C, Si and Mn) is preferably 1.80 to 2.40 mass%, may be 1.85 to 2.25 mass%, and may be 1.90 to 2.10 mass%.

The iron-based alloy may further contain at least 1 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 following effects can be obtained by the addition. However, if the concentration of these other additive elements is too high, there is a tendency that problems such as a decrease in hardness, a decrease in lifetime, and insufficient spheroidization occur. Therefore, the content of these other additive elements (the total content thereof in the case of adding a plurality of elements) in the iron-based alloy can be adjusted to 0.30 to 1.0 mass%.

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

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

Mo has an effect of reducing the structure of each particle and uneven hardness, an effect of improving hardenability, and an effect of moving the pearlite nose in the TTT diagram to the right side to reduce 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 disadvantage due to the increase in cost is greater than the advantage that these effects can be obtained. In view of these, the content of Mo in the iron-based alloy can be adjusted to 0.1 to 0.3 mass%.

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

B has the effect of improving the hardenability and the 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 lifetime tends to be decreased. In view of these, the content of B in the iron-based alloy can be adjusted to 0.01 to 0.05 mass%.

V, Nb and Ti have the effect of increasing the lifetime. If the concentration of these elements is too low, the effect cannot be sufficiently obtained, and if it is too high, the lifetime tends to be reduced. In view of these, the total content of V, Nb and Ti in the iron-based alloy can be adjusted to 0.05 to 0.5 mass%.

< granulation step >

The raw material melt is dropped from a nozzle at the bottom of the melting tank, and high-pressure water is sprayed onto the melt, thereby obtaining granulated materials (spherical bodies).

Oxygen in the raw material melt becomes a factor that inhibits spheroidization of particles at the time of granulation. The shot of an embodiment is formed from a melt containing Si as a raw material. Since oxygen in the raw material melt is removed by Si, the use of such a raw material can promote the spheroidization of particles.

Further, oxygen in the raw material melt causes pores. The blowholes are generated because oxygen in the raw material melt is not released into the atmosphere at the time of solidification of the raw material and is contained in the particles in the form of bubbles. By using Si as a raw material, oxygen in the raw material melt is removed, and pores can be reduced.

< quenching step >

The granules produced as described above contain C, and are therefore harder than Fe. However, when used as a pellet, the hardness needs to be further increased. The granulated material produced in the granulation step is dried in a rotary kiln or the like, heated to 800 to 900 ℃ and held for about 1 hour, and then put into water to be quenched. This can increase the hardness of the granulated substance.

Since Mn is contained in the granulated product, hardenability is improved. In addition, the pearlite nose in the TTT diagram of the granulated product moves to the right, and therefore the critical cooling rate decreases. Further, the structure of the granulated product is refined during quenching, and therefore, the toughness is improved. That is, such a granulated substance can be used as a shot with less wear (having a long life).

< tempering step >

Tempering is performed by: the granulated material after the quenching step is heated at 300 to 600 ℃ for about 0.5 to 2.0 hours, and then slowly cooled. This makes it possible to adjust the hardness of the granulated material to a desired level and to improve the toughness of the granulated material that is reduced in the quenching step.

The fine and uniform structure is introduced into the granulated substance through the quenching step and the tempering step. In particular, the structure of the particles contained in the shot of one embodiment is substantially formed mainly of the tempered martensite phase. The grain size of the tempered martensite phase is about 0.5 to 10 μm. Even if impact load is repeatedly applied to particles having such a structure during shot peening, wear is suppressed because of high toughness.

< fractionation step >

The granulated material after the quenching step is sieved with a vibrating sieve or the like. Thereby, particles having a predetermined diameter are classified.

< recovery step >

The pellet containing the particles having a predetermined diameter is obtained through the steps of inspecting the shape, hardness, and the like of the classified particles.

One embodiment of the pellet (particle) has a Vickers hardness of HV400 to 800. From the viewpoint of shot peening workability and life, the HV may be 400 to 650, or 400 to 500. The standard deviation of HV may be HV50 or less. The pellet of one embodiment has a sufficient hardness as a pellet because of its specific composition, and the variation in hardness of each particle is extremely small. Since the unevenness in hardness is extremely small, the finished quality is stable during shot peening.

In the pellet 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 may be 5% or less of the entire pellet. 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 in the shot peening process. The number of the particles may be 1% or less of the total amount of the pellet, or may be 0.1% or less.

In the pellet of one embodiment, the number of particles having pores may be 5% or less of the entire pellet. Here, the particles having pores mean particles in which the area ratio of bubbles in the cross section is 10% or more of the area of the cross section and the wall surfaces of the bubbles are flat. The blowholes serve as starting points of shot breakage during shot peening. The pellet of one embodiment has a specific composition, and therefore, the number of particles having pores is extremely small, and the life is long. The number of the particles may be 3% or less of the total amount of the pellet, or may be 1% or less.

In the pellet of one embodiment, the number of particles having cracks may be 5% or less of the entire pellet. Here, the particle having a crack means a particle in which 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 of the cross section. The cracks become starting points of shot breakage at the time of shot peening. The shot of one embodiment has a specific composition, and therefore, 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 total amount of the pellet, or may be 1% or less.

In the pellet of one embodiment, the average particle diameter of the contained particles may be 0.1 to 1.5 mm. When the average particle diameter is within this range, the life of the pellet tends to be long. Here, the average particle diameter is a value measured by sieving using a JIS Z8801 reference sieve. The average particle size may be 0.1 to 1.0mm, or 0.15 to 0.75mm, or 0.2 to 0.45 mm.

The projectile of an embodiment may have an apparent density of 7.45g/cm³The above. This makes it easy to obtain collision energy with respect to the workpiece during shot peening, and therefore, the workpiece can be sufficiently ground.

Examples

Next, test results for confirming the effect of the pellet of one embodiment will be described.

First, various kinds of pellets made of an iron-based alloy having the compounding ratio shown in table 1 were produced by a water atomization method. X in Table 1 represents the content (total content) of an additive element selected from Cr, Ni, Cu, Mo, Al, B, V, Nb and Ti.

Classifying the obtained particles to obtain particles having a desired particle diameter

The pill of (1). Pellets having each particle size were prepared as follows.

Passing through a 0.425mm sieve, leaving pellets on the 0.355mm sieve.

Passing through a 0.710mm sieve, leaving the pellets on the 0.600mm sieve.

Passing through a 1.180mm sieve, pellets remained on the 1.000mm sieve.

(1) Measurement of Vickers hardness

After the particles of the shot were embedded in the resin, the surface was polished so that the center of the cross section was exposed. The Vickers hardness was measured for 10 shots according to the above standard (JIS Z2244: 2009), and the average value was taken as the hardness of the shot. The results are shown in Table 2.

(2) Determination of apparent Density

According to JIS Z0311: 2004, the measurement was carried out. Specifically, about 10g of the pellets were charged into a pycnometer (volume: 50ml) and the mass was measured. Then, the mass was measured by filling a pycnometer with distilled water and removing air bubbles inside. The apparent density was calculated from these masses. This operation was performed 2 times, and the average value was defined as the apparent density of the shot. The results are shown in Table 2.

(3) Verification of defects (air holes)

After the particles of the shot were embedded in the resin, the surface was polished so that the center of the cross section was exposed. The cross section was observed for 100 shots by a projector, and the number of shots having the above-mentioned air holes as defects was measured to calculate the ratio thereof. The results are shown in Table 2.

(4) Verification of sphericity

After the pellet particles were spread 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 were observed for 100 pellets by a microscope. 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 lifetime

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

The comparative example is a pellet having a conventional composition. It is understood that the life of the pellets of examples 1 to 10 is longer than that of the pellets of comparative example.

[ Table 1]

[ Table 2]

In addition, the cross section of each pellet of example 1 and comparative example was observed by a scanning electron microscope. As shown in fig. 1, in the shot of the example, a refined structure mainly composed of a tempered martensite phase was observed, whereas in the shot of the comparative example, a structure mainly composed of a martensite phase was observed, which was not refined.

Industrial applicability

The projectile of one embodiment is extremely valuable in industry because it has the hardness required for grinding and sweeping and has a long life. The shot can be used for all shot peening.

The method for producing a pellet according to one embodiment has been described by taking a water atomization method as an example, but other methods such as a gas atomization method and a disc atomization method may be employed.

Claims

1. A shot for shot-peening,

consists of a mixture of C: 0.20 to 0.50 mass%, Si: 0.50 to 1.10 mass% and Mn: 0.50 to 1.15% by mass of an iron-based alloy as an additive element,

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 0.70 to 1.60,

the Vickers hardness of the projectile is HV 400-800.

2. The pellet according to claim 1, wherein the total content of C, Si and Mn is 1.80 to 2.40% by mass.

3. The shot according to claim 1 or 2, wherein the iron-based alloy further contains 0.30 to 1.0 mass% of at least 1 element selected from the group consisting of Cr, Ni, Cu, Mo, Al, B, V, Nb, and Ti.

4. A projectile in accordance with any one of claims 1 to 3, formed substantially of a tempered martensite phase.

5. The pellet according to any one of claims 1 to 4, wherein the number of the particles having pores is 5% or less of the entire pellet.

6. The pellet according to any one of claims 1 to 5, wherein when L represents a length of the particles in a longitudinal direction and S represents a maximum diameter in a direction orthogonal to the longitudinal direction, the number of particles having an L/S of 2.0 or more is 5% or less of the entire pellet.