KR102130490B1 - Fe-based Metal Parts Producing Method Used For Automobile Steering Wheel - Google Patents

Abstract

The present invention relates to a method for manufacturing iron-based metal parts used in automobile steering devices. More specifically, the present invention relates to a method for manufacturing iron-based metal parts used in an automobile steering apparatus using iron-based metal granulated powder. In more detail, the slurry liquefaction step, the mixture of iron-based metal powder is introduced and stirred, granulation step, molding step, sintering step, finishing step, iron-based metal parts used in automobile steering apparatus using iron-based metal granulated powder It's about how.

Description

Fer-based Metal Parts Producing Method Used For Automobile Steering Wheel

The present invention relates to a method for manufacturing iron-based metal parts used in automobile steering devices. More specifically, the present invention relates to a method for manufacturing iron-based metal parts used in an automobile steering apparatus using iron-based metal granulated powder. In more detail, the slurry liquefaction step, the mixture of iron-based metal powder is introduced and stirred, granulation step, molding step, sintering step, finishing step, iron-based metal parts used in automobile steering apparatus using iron-based metal granulated powder It's about how.

Powder metallurgy products such as camshafts, connecting rods, crankshaft chains, and gears that require high strength and high density in automotive parts are mixed powdered Fe-Cu, Fe-Cu-C and alloyed Fe-Ni-Mo-C , Fe-Ni-Mo-C, and the like.

However, in Non-Patent Documents 1 to 3, in order to increase their density, warm forming, two-stage press sintering, sinter forging, metal injection molding (MIM), etc. must be performed as an additional special treatment process. It has theoretical density. Due to this, there is a problem that the manufacturing cost of parts increases.

In the manufacture of metal powder metallurgy for automobile parts, there is also an attempt to manufacture a high performance composite metal matrix composite (MMC) with improved physical properties compared to the original base by adding a dispersoid to the matrix.

A method of manufacturing a heat-resistant steel component comprising a degreasing step as a prior art is described in Patent Document 1.

As a reinforcing material, it may be made of metal or ceramic, and its shape may be various, such as particles, whiskers, or fibers. For example, by adding particles such as SiC, Al ₂ O ₃ , B ₄ C, or fibers such as C, SiC to the Al powder, wear and fatigue properties of the Al metal can be improved.

In addition, when Ni-Mn-B is added to the Fe matrix, it is possible to significantly increase the mechanical strength of the iron alloy by forming a two-step liquid phase during sintering, thereby densifying it, but may cause problems such as elongation.

(Non-Patent Document 1) Okuno, T. and Yashiro, N., "The Improvement in Strength of Sintered Machine Parts," NTN Technical review , No. 82, 2014, pp. 21-25.

(Non-Patent Document 2) Fujiki, A., "The Present Status of PM Automotive Parts", Materia Japan . Vol. 53, No. 12, 2014, pp. 608-611.

(Non-Patent Document 3) Gun, T. and Simsir, M., "Investigation of Mechanical Properties of Fe-Based Metal Matrix Composites by Warm Compaction for Gear Production," ACTA PHYSICA POLONICA A, Vol. 131, No. 3, 2017, pp. 443-447.

(Patent Document 1) Korean Patent Registration No. 10-1202462

Tungsten carbide as a Fe-based reinforcing material in high-strength iron-based composite materials has a specific gravity of 15.6, a melting point of 2870°C, and an elastic modulus of 600 GPa, which is significantly higher than that of iron. The strength properties of the iron-based composite material with a new composition to which carbide is added are still insufficient.

In view of the above problems, the present invention is a method for manufacturing a new iron-based metal part that overcomes the limitations of the prior art, by mixing a certain amount of tungsten carbide and boron in an iron-based metal powder, through sintering density and particle coarsening. An object of the present invention is to provide a method for manufacturing iron-based metal parts used in a steering system for automobiles using an iron-based metal granulated powder capable of obtaining high specific gravity, high tensile strength and high elastic modulus.

The present invention is a first step of liquefying the slurry to be mixed by adding a binder, a plasticizer, an antifoaming agent to a solvent; A second step of introducing and stirring a mixture of an iron-based metal powder containing iron-based metal powder, tungsten carbide and boron into the liquefied slurry; The mixture of the iron-based metal powder of the second step is vacuum sealed with a nozzle and sprayed into a spray drying chamber where hot air at a temperature of 100 to 300° C. is supplied at a flow rate of 5 to 30 m ³ /min to prepare and granulate the iron-based metal granule powder. Third step; A fourth step of filling and molding the iron-based metal granule powder into a mold to manufacture and mold a molded article; A fifth step of sintering the molded article at a temperature of 1,100 to 1,400°C in the sintering furnace and then cooling to manufacture the sintered article; It is to provide a method for manufacturing an iron-based metal component used in an automobile steering apparatus using an iron-based metal granulated powder, comprising a sixth step of machining the sintered product to adjust dimensions.

In addition, in one embodiment of the present invention, the mixture of the iron-based metal powder, if the content of the iron-based metal powder is Fe mass part, the content of tungsten carbide is WC mass part, and the content of boron is B mass part, the following relational expression is satisfied. It is to provide a method for manufacturing an iron-based metal component used in an automobile steering apparatus using an iron-based metal granule powder, characterized in that.

(Equation 1) Fe / WC = 2.4 ~ 8.5

(Equation 2) WC / B = 10 ~ 250

In addition, according to an embodiment of the present invention, when the tensile strength of the iron-based metal component using the iron-based metal granule powder is TS (MPa), and the elongation is E (%), the iron-based system is characterized in that the following relationship is satisfied. It is to provide a method for manufacturing iron-based metal parts used in an automobile steering apparatus using metal granulated powder.

(Equation 3) TS / E = 85 ~ 95

In addition, an embodiment of the present invention, the iron-based metal powder has an average particle diameter of 5 ~ 30㎛, the distribution of particle size is 3 ~ 50㎛, the compression molding is carried out at a pressure of 1.0 ~ 10ton / cm ² , The iron-based metal granulated powder is to provide a method for manufacturing iron-based metal parts used in an automobile steering apparatus using an iron-based metal granulated powder having an average particle diameter of 100 to 200 μm.

The present invention is used in an automobile steering apparatus using an iron-based metal granulated powder capable of obtaining a high specific gravity, high tensile strength and a high modulus of elasticity by mixing a specific content of tungsten carbide and boron in an iron-based metal powder through sintering density and particle coarsening. It is intended to provide a method for manufacturing iron-based metal parts.

1 shows an embodiment of a method for manufacturing an iron-based metal component used in an automobile steering apparatus using an iron-based metal granule powder of the present invention.
Figure 2 shows the principle of the mixing process for mixing the raw materials.
3 shows an example of an injection device.
4 shows an example of a specimen produced by a molding process.
5 shows a photograph of an example of a sintering apparatus.
6 shows a scanning electron microscope photograph of the starting material powder.
7 shows the density change of the composite material specimens according to the sintering temperature.
8 shows a photograph of a specimen for analysis of a tensile specimen.
9 shows a microstructure photograph of a specimen sintered at a specific temperature.
10 shows the EDS analysis results of the specimen sintered at a specific temperature.

Powder metallurgy is a method of compressing a metal powder and then sintering it.

After the metal powder is mixed with a binder, which is a binder, and compressed to form an ingot, a molding step is performed to produce a product in a shape designed through cutting or press processing. A sintering step is performed in which the product subjected to the forming step is heated in a sintering furnace. The finishing step of grinding or cutting the product that has undergone the sintering step according to the designed dimensions is performed.

According to the powder metallurgy method, a coarse powder of 50 to 200 µm is used, so that the mechanical properties of the product, i.e., density, strength, hardness, etc., cannot be obtained to be used as a driving component (rotor and cam ring) for power steering of automobiles. In this way, when the iron-based metal powder is compressed into a mold in the molding step, the compressive strength may be increased to improve mechanical properties, but in this case, since the mold is damaged, it is limited to increase the compressive strength. Therefore, a post process such as forging or heat treatment is required.

In addition, in the powder metallurgy method, a powder having a coarse particle size (50 to 200 µm) should be used to secure moldability and produce a uniform product. These coarse powders form large pores at the time of molding, and these large pores act as a factor to lower densification.

Therefore, fine metal powder applied to metal injection molding may be used, but when applied to the powder metallurgy method, it is a fine particle whose average particle diameter is only 5~10㎛, so it can be used in the mold with cohesion between particles. Density unevenness occurs during molding because it is not densely packed.

In addition, since the filling amount is not constant, the uniformity of the product decreases. In addition, the finer the powder, the more stress it is in the powder state because it is less likely to cause plastic deformation, which is a factor that can cause cracks during heat treatment, and the fine powder smaller than the tolerance between the molds leads to damage to the mold. It is difficult to apply powder metallurgy.

The powder injection molding method using the fine metal powder is as follows.

The mixing step of mixing the metal powder and the binder, which is a binder, is performed in a mixer, and the mixture that has undergone the mixing step is injected into an injection molding machine, and compression molding is performed.

Since the product subjected to the injection molding step is heated in a degreasing furnace, a degreasing step for removing the binder must be included. A sintering step is performed in which the product subjected to the degreasing step is heated in a sintering furnace. The finishing step of grinding or cutting the product that has undergone the sintering step according to the designed dimensions is performed.

The reason for the degreasing step is that the wax and the polymer are used as a binder in order to improve the fluidity of the metal powder in the injection molding machine, since these waxes and polymers may remain as carbon during heat treatment under conditions of an inert atmosphere. This is because there is a need to remove it through the degreasing step.

In the step of degreasing according to the metal powder injection molding method, about 12 to 60 hours should be heated to room temperature to 1,000°C. As a result, productivity decreases and fuel costs increase, which increases production costs. In addition, while the powder metallurgy method has a shrinkage rate of 1 to 5%, the shrinkage range of the powder injection molding method is 12 to 22%, and the shrinkage is quite large, and it is not easy to control the shrinkage in three dimensions.

The present invention is a first step of liquefying the slurry to be mixed by adding a binder, a plasticizer, an antifoaming agent to a solvent; A second step of introducing and stirring a mixture of an iron-based metal powder containing iron-based metal powder, tungsten carbide and boron into the liquefied slurry; The mixture of the iron-based metal powder of the second step is vacuum sealed with a nozzle and sprayed into a spray drying chamber where hot air at a temperature of 100 to 300° C. is supplied at a flow rate of 5 to 30 m ³ /min to prepare and granulate the iron-based metal granule powder. Third step; A fourth step of filling and molding the iron-based metal granule powder into a mold to manufacture and mold a molded article; A fifth step of sintering the molded article at a temperature of 1,100 to 1,400°C in the sintering furnace and then cooling to manufacture the sintered article; It is to provide a method for manufacturing an iron-based metal component used in an automobile steering apparatus using an iron-based metal granule powder, comprising a sixth step of machining the sintered product to adjust dimensions.

For the mixture of the iron-based metal powder, for example, iron-based metal powder 75 mass% to 85 mass%, tungsten carbide powder 10 mass% to 25 mass%, boron powder content of 0.1 mass% to 1 mass% can be used.

In the present invention, by applying an iron-based metal powder having an average particle diameter of 5 to 30 μm of iron-based metal powder and 90% or more of the powder having a particle size distribution of 3 to 50 μm to the powder metallurgy, mechanical properties are found in the casting process or injection molding. ), and wants to improve productivity and reduce production costs.

Granulate iron-based metal powder (average particle size 5~30㎛), particle size distribution 3~50㎛ (more than 90% of the powder) to an average particle size of 100~200㎛ to evenly fill in the mold like the existing powder metallurgy method , After filling the powder metallurgy mold using granulated powder, press molding and sintering.

Iron-based metal granule powder is additionally iron (Fe), carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), chromium (Cr), molybdenum (Mo), copper (Cu) ), any one or two or more selected from nickel (Ni).

As the granulated fine powder is molded, it is uniformly distributed, and the uniformly distributed fine powder provides a relatively large sintering driving force, so it is an iron system suitable for use in automobile parts such as rotors or cam rings for power steering of automobiles during the sintering process. Metal parts can be manufactured. It is possible to improve the mechanical properties due to density improvement.

In addition, since the degreasing step can be reduced or omitted compared to the powder injection molding method using the fine powder, the productivity can be improved and the process time can be saved, thereby reducing production costs.

That is, the iron-based metal fine powder can be granulated and applied to the powder metallurgy process, and as a result, an iron-based metal component capable of minimizing the processing amount while having properties similar to the properties of the cast material can be manufactured.

In addition, the iron-based metal powder was oxidized in the granulation (granule) process of agglomerating and spheroidizing the iron-based metal powder, and the oxidized iron-based metal powder was reduced in the molding process. In the (Granule) process, an additive such as a binder is added to the solvent in advance, mixed, and then the iron-based metal powder is added to the solvent, so that the pre-mixed binder, plasticizer, antifoaming agent and other additives combine with the iron-based metal powder to coat the surface. Can be prevented.

1 shows an embodiment of a method for manufacturing an iron-based metal component used in an automobile steering apparatus using an iron-based metal granule powder of the present invention. Looking at the present invention in more detail step by step as follows.

(1) liquefaction, stirring and granulation steps;

The mixing process for mixing the raw materials uses the principle shown in FIG. 2. For example, a high-speed planetary mixer is a mechanical device that can generate a very large centrifugal force and agitation power by simultaneously rotating and rotating at a high speed in a mixing vessel, regardless of the specific gravity of the metal powder. Mix uniformly and quickly.

In the slurry preparation step, an iron-based metal powder and a slurry material are prepared. The iron-based metal powder is a fine powder, having an average particle diameter of 5 to 30 μm and a particle size distribution of 3 to 50 μm (90% or more of the powder). Use that.

As the granulated fine powder is molded, it is uniformly distributed, and the uniformly distributed fine powder provides a relatively large sintering driving force, so it is an iron system suitable for use in automobile parts such as rotors or cam rings for power steering of automobiles during the sintering process. Metal parts can be manufactured. In addition, it is possible to improve mechanical properties due to density improvement.

In particular, the mixture of iron-based metal powders, if the content of the iron-based metal powder is Fe parts by mass, the content of tungsten carbide powder by WC parts by mass, and the content of boron powder by B parts by mass, it is preferable to satisfy the following relationship.

(Equation 1) Fe / WC = 2.4 ~ 8.5

(Equation 2) WC / B = 10 ~ 250

Here, when the range of the above (formula 1) and (formula 2) is satisfied, that is, when the range of Fe / WC is from 2.4 to 8.5, the range of WC / B is 10 to 250, more preferably 50 to 150 In this case, the sintering density at the iron-based matrix is increased, and may be effective for liquid phase sintering to promote particle coarsening. In addition, the mechanical properties such as tensile strength are excellent due to the iron-based metal powder.

The iron-based metal powder of the present invention has an average particle diameter of 5 to 30 μm and a particle size distribution of 3 to 50 μm. When the iron-based metal powder is 5 μm or less, the iron-based metal powder is used as a gravity during the granulation process. Precipitation can be reduced, but oxidation is relatively large due to the increase in the specific surface area of the powder, and when compression molding requires large power for plastic deformation, and when the iron-based metal powder is 30 µm or more, the iron-based metal powder is used in the granulation process. Precipitation due to gravity occurs in the slurry state, making it difficult to secure a uniform granulated (granular) particle size, and large granular powders cause abnormal grain growth and large pores during sintering after molding, which hinders densification during sintering, thereby relatively high density. And mechanical properties due to stress concentration due to large pores may deteriorate.

The slurry material is composed of a liquid that enables the iron-based metal powder to be sprayed with fluidity, and includes a binder to aggregate the iron-based metal powder.

The liquid and the binder are volatile, and the liquid may use pure water, ethanol, or the like, and an organic binder, an inorganic binder, or an organic/inorganic hybrid binder may be used as the binder.

As the organic binder, polyvinyl butyral or polyvinyl alcohol may be used.

As an inorganic binder, a compound in which silica and various inorganic components are combined for use in iron-based metal granule powder can be used, and a core can be produced by using a curing reaction of an inorganic binder, to improve tensile strength and elongation The ratio of silicone-inorganic components can be adjusted.

Unlike organic binders, inorganic binders are recognized for eco-friendliness because the amount of harmful gas generated is close to zero, and have many advantages such as adhesion and dispersion.

As the inorganic binder, one or a mixture thereof selected from the group consisting of sodium silicate, alumina silicate, and calcium silicate can be preferably used.

When an organic-inorganic hybrid binder is used, it is possible to impart more binding force during granulation than an organic binder. For example, a binder of a compound represented by the following formula can be preferably used.

Here, n can use 5 to 10, more preferably n can use 7, R is an acrylic group or an epoxy group, and more preferably an epoxy group in terms of tensile strength and elongation.

Further, a compound of the following formula can be preferably used as a plasticizer.

Here, n may use 100 to 1,000. An antifoaming agent can be used as a conventional antifoaming agent, and there is no particular problem in molding because only a binder and a plasticizer are imparted to the surface of the iron-based metal powder, but when the molding is difficult to take out of the mold, it is lubricated. Lubricants are also added to impart properties.

When using a non-aqueous ethanol as a solvent, it is for suppressing oxidation of the iron-based metal powder, and when using pure water, oxidation is greater than ethanol, and when using pure water as a solvent, the oxidizing layer is reduced using a reducing atmosphere during sintering. Should do.

As a component for granulation of the iron-based metal powder, 1 to 3 parts by mass of the binder, 0.5 to 1 parts by mass of the plasticizer, and 0.5 to 1 parts by mass of the antifoaming agent can be preferably used compared to 100 parts by weight of the solvent.

In the mixing step, the binder is first dissolved in a solution, and then a slurry material, a binder, a plasticizer, and an antifoaming agent are introduced into the stock solution supplying device and mixed. Thereafter, the iron-based metal powder is put into a stock solution supplying device and mixed and dispersed. Of course, various mixer types can be used. At this time, as an example, the mixing step is performed for 30 minutes to 1 hour.

When the iron-based metal particles of the stock solution in the stock solution supply device are large or the dispersion is not sufficient, additional crushing and dispersion may be performed in a stock solution atomization device equipped with a metal ball or a ceramic ball. In addition, as a method of spray drying, a spray nozzle is installed inside the spray drying chamber shown in FIG. 3, and the stock solution is sprayed upward by the spray nozzle. At this time, the pressure in the spray drying chamber should be kept under a vacuum. In order to maintain such a vacuum state, the exhaust device located under the nozzle of the spray drying chamber exhausts the hot air supplied in the spray drying chamber and the solvent vaporized by the hot air.

The stock solution sprayed by the nozzle is dispersed in the form of a droplet in the upper direction of the spray drying chamber, and the spherical slurry is dried as it is, and the solvent is volatilized and spherical granular powder is formed. At this time, the granular powder is in a state in which a plurality of particles of the iron-based metal powder are bound by the binding force of the binder and the cohesive force of the powder (the power of Van der Waals).

The granular powder in which a plurality of particles of the iron-based metal powder are combined is dropped to the lower part of the spray drying chamber by weight, and the granular powder is withdrawn by a product recovery device installed at the lower part of the spray drying chamber.

At this time, the temperature of the injected hot air is 100 to 300°C, and is supplied at a flow rate of 5 to 30 m 3 /min. The average particle size of the granular powder particles thus formed is 100 to 200 µm, but when the granular powder particles are 100 µm or less, the fluidity of the powder decreases due to the cohesion between the granular powders, and accordingly, the reproducibility of filling may decrease. .

In addition, when the granular powder particles are 200 μm or more, the recovery rate of the powder may decrease. The main reason for preventing oxidation even when iron-based metal powder is added to the solvent (water) in the granulation (granule) process is that the binder, plasticizer, and antifoaming agent are added at the moment the metal powder enters the solvent by adding an additive such as a binder in advance to the solvent. Since it coats the surface with iron-based metal powder, oxidation is prevented.

When using a solvent such as non-aqueous ethanol to prevent oxidation, the cost of equipment increases accordingly, and the raw material (solvent) cost increases, resulting in an increase in manufacturing cost, but reducing the oxide layer during molding or reducing it while sintering In order to solve the oxidation problem, if the solvent is granulated (granulated) using water (aqueous), the solvent cost can be lowered and oxidation inhibition is possible.

(2) Forming step

In the forming step, the granulated powder is filled in a mold of a press machine so as to be a disk or block-shaped ingot and compression molded. At this time, since the particles of the granular powder have a diameter of 10 times larger than the particles of the iron-based metal powder and have a spherical shape, fluidity is excellent by gravity. Therefore, there is an advantage of evenly filling the inside of the mold.

After that, it is molded using a press machine, so that the shape of the molded product is completed according to the product being commercialized. That is, when the granule powder is filled in a mold of a press machine so as to be a disk or block-shaped ingot, and the compression molding is performed, the granular powder has an advantage in that the divided fine metal powder is evenly filled in the mold. .

After the block shape is molded in this way, it is molded into various shapes such as a ring shape by using a press machine to produce a shape of a molded product.

4 shows an example of a specimen produced by a molding process.

(3) Sintering step

In the sintering step, the molded product is maintained in a hydrogen and nitrogen atmosphere at 1,100 to 1,400°C in a sintering furnace for 18 minutes to 3 hours, and then cooled at room temperature to produce a sintered product.

The binder is volatilized and removed from the sintering furnace. In particular, when polyvinyl butyral is used, it is volatilized by heating in the sintering furnace due to its characteristics and is more easily removed. At this time, sintering in an N2 100% atmosphere is preferable in that oxidation due to the introduction of oxygen and other gases is prevented.

5 shows a photograph of the sintering apparatus.

(4) Finishing step

In the finishing step, the dimension is adjusted by grinding or cutting the sintered product manufactured in the sintering step to the correct dimension. The finishing method is not limited.

When the iron-based metal parts used in the steering system for automobiles using the manufactured iron-based metal granulated powder have a tensile strength of TS (MPa) and an elongation of E (%), the following relational expression It is preferable to satisfy.

(Equation 3) TS / E = 85 ~ 95

That is, the range of TS/E is preferably 85 to 95. When the range of TS/E is less than 85, deformation is apt to occur, and when the range of TS/E exceeds 95, the ductility of the iron-based metal parts is insufficient, so it is easy to break.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[Experimental Example]

1. Specimen preparation

* Liquefaction, stirring and granulation steps

In Example 1, 79.8 wt% of iron-based metal powder and 20 wt% of tungsten carbide powder and 0.2 wt% of boron powder were uniformly mixed with a high-speed planetary stirrer. And, in Comparative Example 1, 79.8 wt% of iron-based metal powder and 20.2 wt% of tungsten carbide powder were uniformly mixed with a high-speed planetary stirrer.

Fe (purity 99.4%) was used as the average particle size of 30 µm (Example 1) and 100 µm (Comparative Example 1), and tungsten carbide (purity 99.95%) powder was used as a single particle size of 4 µm. The average particle size of the boron (purity 91.6%) powder was 0.8 µm, and it was divided into those with and without components.

6 is a scanning electron microscope photograph of the starting raw material powder, wherein the main raw material particles show a generally spherical shape.

Specifically, FIG. 6(a) is a scanning electron microscope photograph of an iron-based metal powder of 30 μm, FIG. 6(b) is a scanning electron microscope photograph of an iron-based metal powder of 100 μm, and FIG. 6(c) is a tungsten carbide It is a scanning electron microscope photograph, and FIG. 6(d) is a scanning electron microscope photograph of Boron.

Table 1 shows the weight composition ratio of the composition of the mixture of the iron-based metal powder used for preparing the composite specimen.

ratio Example 1 Comparative Example 1 Fe / WC 3.99 3.95 WC/B 100 -

100 g of a mixture of iron-based metal powder was placed in a mixed solvent of 100 ml of ethanol solvent, 1.0 ml of polyvinyl butyral, and 1.0 ml of polyethylene glycol, and mixed for 1 hour. The slurry was sprayed into the spray drying chamber, and hot air at 130°C was supplied. As a result, it was confirmed that the granulated powder was formed.

* Molding stage

In order to optimize the properties of the spray dried powder and the product production process, uniaxial pressure molding was performed, and the molding pressure was tested at 250 ton/cm2, respectively.

* Sintering step

The press-molded molded body was sintered in a high-temperature vacuum batch furnace and a continuous furnace, and sintered at a sintering temperature of 1,300°C for 75 min. Sintering was performed in a hydrogen or nitrogen-hydrogen atmosphere. This sintered body was produced in accordance with the MPIF standard in the form of a tensile specimen.

2 Characteristic evaluation

The sintered specimen was first measured for apparent density using an electric densimeter. The theoretical density (D) of the alloy composed of component 1 (weight W ₁ , density D ₁ ) and component 2 (weight W ₂ , density D ₂ ) can be expressed as the following equation.

This value is applied to the sintered body having a density of 100% without any pores after sintering, and in practice, it is relatively low compared to the theoretical density since pores are included. Tensile strength, elastic modulus and elongation of the sintered specimen were measured by a universal material tester (10 tons). The microstructure was etched after polishing, and observed with an optical microscope, and the surface shape and composition ratio were analyzed with a scanning electron microscope and EDS, respectively.

3. Density change

7 shows the density change of the composite material specimens according to the sintering temperature. As the sintering temperature increased, the density of both specimens increased. In particular, the specimen of Example 1 already exhibited a sintering density of 8.01 g/cm 3 at 1150°C.

The theoretical density for a mixture of iron-based metal powder (79.8wt%) and tungsten carbide powder (20.2wt%) is about 　8.73g/cm3. Therefore, the relative density of the sintered specimens in the range of 1150 to 1300°C is 80.6% to 99.1% and 　91.1% to the specimens of Comparative Example 1 (coarse Fe powder without B) and those of Example 1 (fine Fe powder with B), respectively. It was 99.7%. From these results, it can be seen that the sintering density and the sintering rate increase as the size of the initial iron-based metal powder decreases with the addition of the boron component as a starting material for manufacturing the iron-based metal powder and tungsten carbide composite.

8 was prepared for the analysis of tensile specimens. Here, F13 shows Comparative Example 1 and F22 shows Example 1.

4. Tensile strength and elastic modulus

Table 2 below shows the tensile test characteristic values for each sintered specimen. Comparative Example 1 having a composition of iron powder having a large particle size shows a tensile strength of 200 MPa, an elongation of 1.8% and an elastic modulus of 130 GPa at a sintering temperature of 1300°C, whereas in the case of Example 1 in which iron powder having a small particle size and 0.2% boron are added The tensile strength was about 500 MPa at 1300°C, the elongation was 5.5%, and the elastic modulus was about 190 GPa. Table 3 below shows the results for the ratio TS/E.

Therefore, when the iron powder having a small particle size is used together with the addition of boron, the mechanical properties of the composite material can be greatly improved. In general, since the sintered body has an increase in elastic modulus or tensile strength according to the density, the high tensile strength and elastic modulus values of the specimen of Example 1 compared to Comparative Example 1 are large due to the increased density in Example 1. On the other hand, the effect of increasing the modulus of elasticity of the composite material can be explained by the rule of mixtures as shown in the following equation.

_Comp = _m · V _m E E + E _p · V _p

Here, the elastic modulus E _m and the volume fraction V _m are the main components as the main component, and the elastic modulus E _p and the volume fraction V _p are the additive component elements.

tensile strength(MPa) Elastic Modulus (GPa) Elongation(%) Comparative Example 1 200 130 1.8 Example 1 500 190 5.5

TS / E ratio Comparative Example 1 111.1 Example 1 90.9

5. Microstructure

In the case of the specimen of Comparative Example 1 having large initial iron particles, even after sintering at 1300°C, the average particle diameter did not occur to about 100㎛, and although the pores were slightly reduced compared to the 1150°C sintered body, the large pores were still present. On the other hand, in the case of the specimen of Example 1 in which the initial particles were small and boron was added, the iron particles grew relatively coarse and grew over 100 μm, and in some cases large particles of several hundred μm were also observed. In the EDS analysis, the tungsten carbide particles were distributed in the grains or grain boundaries of the iron crystals without changing the size depending on the sintering temperature. 9 is a microstructure photograph of the specimen of Comparative Example 1 and the specimen of Example 1 sintered at various temperatures. Figure 10 shows the EDS analysis results of the S2 specimen sintered at 1300 ℃. Here, S1 is a specimen of Comparative Example 1, S2 is a specimen of Example 1.

In this way, in the sample without boron, the grain growth of iron particles was suppressed due to the grain boundary movement by tungsten carbide, but the iron particles grew rapidly with the addition of boron, which effectively improved the grain growth of iron. It may be because it has not been suppressed.

From the microstructure results, in the preparation of the iron-tungsten carbide composite, there is little solubility between iron and tungsten carbide in the manufacture of iron-tungsten carbide composites, showing only an increase in “density” due to “solid-phase sintering” of iron particles. (liquid phase sintering), which seems to effectively contribute to density increase and particle growth (coarsening) due to densification. Looking at the phase equilibrium of iron-boron, it forms a molten phase at about 1175 °C. In general, in the liquid sintering state, not only the speed of particle growth is increased by reducing the contact angle between particles, but also densification by the liquid phase and over-particle growth by the liquid film occurs.

That is, it was confirmed that the iron-tungsten carbide composite material is very effective in increasing density and strength compared to pure iron-based powder metallurgy. By using the boron component as an additive to the iron powder raw material having smaller sized initial particles, the density of the sintered body is greatly increased, and its mechanical properties are further improved. In the preparation of the iron-tungsten carbide composite, the components of the additive boron actually contribute to the effect of promoting liquid sintering of the iron particles.

Claims (4)

A first step of liquefying the slurry by adding a binder, a plasticizer, and an antifoaming agent to the solvent;
A second step of introducing and stirring a mixture of an iron-based metal powder containing iron-based metal powder, tungsten carbide and boron into the liquefied slurry;
The mixture of the iron-based metal powder of the second step is vacuum sealed with a nozzle and sprayed into a spray drying chamber where hot air at a temperature of 100 to 300° C. is supplied at a flow rate of 5 to 30 m ³ /min to prepare and granulate the iron-based metal granule powder. Third step;
A fourth step of filling and molding the iron-based metal granule powder into a mold to manufacture and mold a molded article;
A fifth step of manufacturing the sintered product by sintering the molded product at a temperature of 1,100 to 1,400°C in a N ₂ 100% atmosphere of the sintering furnace, and then cooling;
Comprising a sixth step of processing the sintered product to adjust the dimensions to finish,
The mixture of the iron-based metal powder is the iron-based metal powder, characterized in that if the content of the iron-based metal powder is Fe parts by mass, the content of tungsten carbide is WC parts by mass, and the content of boron is B parts by mass, Method for manufacturing iron-based metal parts used in used automobile steering devices.
(Equation 1) Fe / WC = 2.4 ~ 8.5
(Equation 2) WC / B = 10 ~ 250 delete The method according to claim 1,
If the tensile strength of the iron-based metal component using the iron-based metal granule powder is TS (MPa), and the elongation is E (%), it is used in an automobile steering apparatus using the iron-based metal granule powder, characterized in that the following relational expression is satisfied. Iron-based metal parts manufacturing method.
(Equation 3) TS / E = 85 ~ 95 The method according to claim 1 or 3,
The iron-based metal powder has an average particle diameter of 5 to 30㎛, and a particle size distribution of 3 to 50㎛,
The compression molding is carried out at a pressure of 1.0 ~ 10ton / cm ² ,
The iron-based metal granule powder is a method for manufacturing iron-based metal parts used in an automobile steering apparatus using an iron-based metal granule powder, characterized in that the average particle diameter is 100 ~ 200㎛.

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