KR102663665B1 - Iron-based powder for powder metallurgy and method for producing same - Google Patents

Abstract

The present invention relates to an iron-based powder for powder metallurgy applied to sintered parts for automobiles requiring high wear resistance and a method for manufacturing the same.
Meanwhile, the method of manufacturing iron-based powder for powder metallurgy according to an embodiment of the present invention is a method of manufacturing iron-based powder for powder metallurgy used in the manufacture of automobile parts, and is a method of manufacturing iron-based powder for powder metallurgy, which contains chromium (Cr), nickel (Ni), and molybdenum ( Setting a target content for each alloy component of the iron-based powder containing Mo), phosphorus (P), silicon (Si), iron (Fe) and other unavoidable impurities; Increasing the target content of chromium (Cr), phosphorus (P), and silicon (Si) by 0.5 to 45%, and preparing an ingot with a content corresponding to the target content of nickel (Ni) and molybdenum (Mo); ; preparing molten steel by melting the ingot; It includes manufacturing iron-based powder using the molten steel.

Description

Iron-based powder for powder metallurgy and its manufacturing method {IRON-BASED POWDER FOR POWDER METALLURGY AND METHOD FOR PRODUCING SAME}

The present invention relates to an iron-based powder for powder metallurgy and a method for manufacturing the same, and more specifically, to an iron-based powder for powder metallurgy applied to sintered parts for automobiles requiring high wear resistance and a method for manufacturing the same.

In general, iron-based powder is manufactured by mixing and dissolving scrap iron scrap and molten iron produced in the iron making process in a steelmaking furnace to prepare molten steel adjusted to the desired component content, and then supplying the molten steel to a tundish using water injection equipment. These iron-based powders are used for various purposes, such as raw materials for powder metallurgy and various additives for manufacturing automobile parts, etc.

Recently, in the automobile industry, research has been actively conducted on materials that require high wear resistance for engine or transmission parts applications in accordance with the trend of high output and high performance of engines.

In line with this trend, research on the application of powder materials to automotive sintered parts that can achieve high wear resistance is being activated, and for this, the need to develop a manufacturing process for multi-component alloy powders containing Cr, Mo, Ni, etc. is emerging.

The content described as background technology above is only for understanding the background to the present invention, and should not be taken as an admission that it corresponds to prior art already known to those skilled in the art.

Public Patent No. 10-2016-0002089 (2016.01.07)

The present invention provides an iron-based powder for powder metallurgy that can improve the target content hit rate of alloy components with very high affinity for oxygen, such as Cr and Si components, and a method for manufacturing the same.

In addition, an iron-based powder for powder metallurgy applied to sintered parts for automobiles requiring high wear resistance and a method for manufacturing the same are provided.

The iron-based powder for powder metallurgy according to an embodiment of the present invention is an iron-based powder for powder metallurgy used in the manufacture of automobile parts, and has chromium (Cr): 7 to 9%, nickel (Ni): 1.5 to 1.5% by weight. 2.5%, molybdenum (Mo): 1.6 to 2.2%, phosphorus (P): 0.3 to 0.7%, silicon (Si): 0.5 to 1.1%, the remainder contains iron (Fe) and other inevitable impurities.

The iron-based powder further contains oxygen (O): 0.2% or less.

The molding density of the iron-based powder is characterized in that it is 6.2 g/cm3 or more at a pressure of 600 MPa.

The iron-based powder further contains boron (B): 0.001 to 0.01%.

The hardness of the iron-based powder is preferably 60 HRC or more, and the wear rate is preferably 10 mg/M or less.

Meanwhile, the method of manufacturing iron-based powder for powder metallurgy according to an embodiment of the present invention is a method of manufacturing iron-based powder for powder metallurgy used in the manufacture of automobile parts, and includes chromium (Cr), nickel (Ni), molybdenum ( Setting a target content for each alloy component of the iron-based powder containing Mo), phosphorus (P), silicon (Si), iron (Fe) and other unavoidable impurities; Increasing the target content of chromium (Cr), phosphorus (P), and silicon (Si) by 0.5 to 45%, and preparing an ingot with a content corresponding to the target content of nickel (Ni) and molybdenum (Mo); ; preparing molten steel by melting the ingot; It includes manufacturing iron-based powder using the molten steel.

In the step of setting the target content for the alloy component, the target content of each alloy component is expressed in weight%, chromium (Cr): 7 to 9%, nickel (Ni): 1.5 to 2.5%, molybdenum (Mo): 1.6. ~ 2.2%, phosphorus (P): 0.3 ~ 0.7%, silicon (Si): 0.5 ~ 1.1%, the remainder being iron (Fe).

In the step of preparing the ingot, the ingot is characterized in that it further contains manganese (Mn): 0.2 to 0.45%.

In the step of preparing the molten steel, a deoxidizing agent is added at least once while dissolving the ingot.

The deoxidizer is aluminum (Al), and the deoxidizer is added so that the aluminum (Al) content in the final molten steel is 0.1% or less.

In the step of preparing the molten steel, the melting temperature of the ingot is 1590 to 1630°C.

In the step of preparing the molten steel, 0.001 to 0.01% of boron (B) is added to the molten steel while the ingot is melting.

The step of manufacturing the iron-based powder is characterized in that the iron-based powder is manufactured by a water injection method or a gas injection method, and the molten steel is maintained at 1540 to 1560° C. before manufacturing the iron-based powder.

After the step of manufacturing the iron-based powder, the step of heat treating the iron-based powder is further included.

The step of heat treating the iron-based powder is characterized in that it is performed at a heat treatment temperature of 400 to 600 ° C. in a reducing atmosphere.

According to an embodiment of the present invention, in order to meet the target content of the alloy component, the target alloy component can be adjusted by manufacturing iron-based powder using an ingot in which the content of each component is adjusted according to the oxygen affinity of the alloy component. The quality of iron-based powder can be improved.

Additionally, the recovery rate of each component can be improved by adding manganese (Mn) to the ingot.

Additionally, the wear resistance of iron-based powder can be improved by adding an appropriate amount of boron (B) during dissolution of the ingot.

1 is a flowchart showing the manufacturing steps of iron-based powder for powder metallurgy according to an embodiment of the present invention;
Figure 2 is a photograph showing the state of powder particles according to comparative examples and examples.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below and will be implemented in various different forms. These embodiments only serve to ensure that the disclosure of the present invention is complete and to fully convey the scope of the invention to those skilled in the art. This is provided to inform you.

The iron-based powder for powder metallurgy according to an embodiment of the present invention is an iron-based powder prepared for manufacturing automobile parts requiring high wear resistance by a sintering method, and is divided into weight percent to satisfy the required characteristics of camshaft cam lobe parts. , Chromium (Cr): 7 ~ 9%, Nickel (Ni): 1.5 ~ 2.5%, Molybdenum (Mo): 1.6 ~ 2.2%, Phosphorus (P): 0.3 ~ 0.7%, Silicon (Si): 0.5 ~ 1.1% , it is desirable to contain the remaining iron (Fe) and other inevitable impurities.

In addition, it is preferable that the iron-based powder is controlled to contain oxygen (O) in the range of 0.2% or less.

The iron-based powder having the above composition must have a molding density of 6.2 g/cm3 or more at a pressure of 600 MPa in order to be applied to cam lobe parts. If the molding density is less than 6.2g/cm3, a higher molding pressure is required to secure the target molding density, and the springback (dimensional expansion rate due to elastic recovery) that occurs at this time increases, affecting the dimensional change rate of the inner/outer diameter of the cam lobe. Because of this, assembly with the shaft deteriorates. In addition, when the molding density is less than 6.2 g/cm3, a high temperature sintering process of 1,200°C or more is required to secure the target sintering density of 7.2 g/cm3 or more, resulting in an increase in manufacturing costs.

Therefore, it is desirable that the molding characteristics of the iron-based powder proposed in the present invention satisfy a molding density of 6.2 g/cm3 or more at a pressure of 600 MPa.

In addition, the iron-based powder preferably contains 0.001 to 0.01% of boron (B) to improve hardness and wear resistance.

Boron (B) is an element that shows excellent hardenability improvement even with the addition of a small amount. Boron (B) increases hardenability by suppressing the nucleation of proeutectoid ferrite. Therefore, it is desirable to limit the boron content to 0.001 to 0.01% so that hardness and wear resistance can be improved by the addition of boron (B).

Accordingly, the hardness of the iron-based powder can be 60 HRC or more, and the wear rate can be 10 mg/M or less.

A method for manufacturing the metal powder for powder metallurgy formed as described above will be described.

Figure 1 is a flowchart showing the manufacturing steps of iron-based powder for powder metallurgy according to an embodiment of the present invention.

As shown in the drawing, the method for manufacturing iron-based powder for powder metallurgy according to an embodiment of the present invention includes chromium (Cr), nickel (Ni), molybdenum (Mo), phosphorus (P), silicon (Si), and iron ( Setting a target content for each alloy component of the iron-based powder containing Fe) and other unavoidable impurities; Increasing the target content of chromium (Cr), phosphorus (P), and silicon (Si) by 0.5 to 45%, and preparing an ingot with a content corresponding to the target content of nickel (Ni) and molybdenum (Mo); ; preparing molten steel by melting the ingot; It includes manufacturing iron-based powder using the molten steel.

Each step is explained in detail.

1. Step of setting target content for each alloy component

This is a step of setting the target content of each alloy component constituting the iron powder. In this embodiment, in order to satisfy the required characteristics of the camshaft cam lobe parts, chromium (Cr): 7 to 9%, nickel (Ni) is set in weight%. ): 1.5 to 2.5%, molybdenum (Mo): 1.6 to 2.2%, phosphorus (P): 0.3 to 0.7%, silicon (Si): 0.5 to 1.1%, and the remaining iron (Fe).

2. Steps to prepare ingots

Prepare an ingot containing chromium (Cr), nickel (Ni), molybdenum (Mo), phosphorus (P), silicon (Si), and iron (Fe).

At this time, the content of each alloy component is adjusted compared to the target content according to its affinity with oxygen.

For example, alloy components with high affinity for oxygen, such as chromium (Cr), phosphorus (P), and silicon (Si), increase the content by 0.5 to 45% compared to the target content, and nickel (Ni) and molybdenum (Mo) For alloy elements with very low affinity for oxygen, the content is adjusted to correspond to the target content.

For example, the Cr component in the ingot is increased by 0.5 to 3% based on the target content of 7 to 9% of the final iron-based powder, and the Si component is increased by 20% based on the target content of 0.5 to 1.1% of the final iron-based powder. The content of each component was designed by increasing it to ~ 45%, and the P component was increased to 10 ~ 16% based on the target content of 0.3 ~ 0.7% of the final iron powder.

At this time, the Ni and Mo components had very low affinity for oxygen, so they were designed to have the same content based on the target content of the final iron powder.

Meanwhile, in order to improve the recovery rate of each alloy component, an additional 0.2 to 0.45% by weight of Mn component can be added to the ingot. When Mn is added in an amount of 0.2 to 0.45%, the recovery rate of each component can be improved to 80 to 95%. However, if Mn is added in excess of 0.45%, the Mn component may remain in the iron-based powder and reduce moldability within the powder, so it is preferable to limit the Mn content to 0.2 to 0.45%.

3. Steps to prepare molten steel

Prepare molten steel to form iron-based powder by dissolving the ingot.

The ingot is melted in the air, and the melting temperature is preferably maintained at 1590 to 1630°C. In this embodiment, the melting process was carried out using an induction furnace, but in addition to this induction furnace process, it can also be applied to arc furnaces, reverberatory furnaces, etc. that are carried out in an atmospheric atmosphere.

On the other hand, when the oxygen content in the iron-based powder used in the camshaft cam lobe exceeds 0.2%, the moldability decreases during molding and inclusions are formed in the powder, which has a significant adverse effect on the properties of the part. Therefore, the melting temperature of molten steel, which affects the content of oxygen in the powder, is preferably maintained at 1590 to 1630°C, preferably 1590 to 1610°C. If the melting temperature of the molten steel is lower than the suggested temperature, smooth dissolution of the alloy components does not occur, and if the melting temperature of the molten steel is higher than the suggested temperature, the oxygen content in the powder increases, which may cause a problem of lowering the molding density. .

Additionally, if a deoxidizing agent is added while dissolving the ingot, the production of oxides due to Cr and P, which have high oxygen affinity, can be controlled during dissolution of the ingot.

It is desirable to add the deoxidizer more than once while dissolving the ingot. And aluminum (Al) can be used as a deoxidizer.

For example, while dissolving the ingot, aluminum (Al) can be added as a deoxidizer at least once to several times. However, the input amount is adjusted so that the Al content in the final molten steel satisfies 0.1% or less. Preferably, 30 to 50% of the total weight of the deoxidizer is added when the ingot is 30 to 50% dissolved, and the remaining deoxidizer is added after the ingot is completely dissolved.

When the deoxidizer is added in several batches, aluminum (Al) combines with oxygen in the molten steel to form Al oxide, and rises to the surface of the molten steel together with Si oxide to form an upper film. Accordingly, it is effective in lowering the amount of dissolved oxygen in molten steel.

At this time, the reason why the amount of deoxidizer is proposed to be 0.1% is because if the amount of deoxidizer is more than 0.1%, impurities formed by aluminum in the powder below may be mixed or encroach on the tundish nozzle, causing clogging.

Meanwhile, in this embodiment, in order to improve the hardness and wear resistance of the iron-based powder, 0.001 to 0.01% of boron (B) can be added to the molten steel while the ingot is melting. At this time, it is desirable to add boron (B) during melting of the ingot so that it has a uniform chemical composition throughout the molten steel.

4. Steps for manufacturing iron-based powder

Iron-based powder in powder form is manufactured using the prepared molten steel.

At this time, water atomization or gas atomization can be applied as a method of manufacturing iron-based powder in powder form using molten steel. However, in this embodiment, the water injection method is used for explanation.

So, the prepared molten steel is moved to the tundish for water injection. At this time, it is desirable to maintain the temperature of the molten steel in the tundish at 1540 to 1560°C. The water injection process time is determined by the amount of molten steel manufactured, but takes from a minimum of 10 minutes to a maximum of 90 minutes. In this embodiment, the water injection process time is 15 minutes, and if the temperature of the molten steel in the tundish is not maintained at 1540 to 1560°C, the oxygen content in the molten steel increases during the water injection process, and the oxygen content in the final powder reaches the target maximum. If it is contained more than the value, the moldability of iron-based powder deteriorates. In addition, if the molten steel temperature is managed below 1540°C to lower the oxygen content, cooling of the molten steel may occur, solidification may occur, and clogging of the tundish nozzle may occur, making it difficult to manufacture normal powder.

The molten steel, which is moved to the tundish and maintained at its temperature, flows into the water injection facility through the tundish nozzle and is powdered through the water injection process.

The iron-based powder prepared in this way is dehydrated and dried.

5. Step of heat treatment of iron-based powder

The manufactured iron-based powder can be subjected to a subsequent heat treatment process to ensure moldability. The heat treatment temperature is 400 to 600°C. Through heat treatment, the content of oxygen in the powder can be reduced, thereby improving formability.

However, if the heat treatment temperature is higher than 600°C, the powder may be reoxidized due to the oxidizing property of chromium, which may cause the oxygen content to increase.

Meanwhile, heat treatment is preferably performed in a reducing atmosphere to prevent re-oxidation of alloy components. In this example, a mixed gas of nitrogen (30%) and hydrogen (70%) was used, but 100% hydrogen, methane, ammonia decomposition gas, natural gas decomposition gas, etc. that create a reducing atmosphere can be used as the atmospheric gas. .

Next, the present invention will be explained through comparative examples and examples.

First, the recovery rate and molding density of each component according to the addition of manganese (Mn) were measured.

For each sample, the addition and content of manganese were changed as shown in Table 1 below, and the recovery rate and molding density of each alloy component were measured accordingly and are shown in Table 1.

division Mn content recovery rate Molded density (g/cc) Cr Si P Mo Ni (at 600MPa molding) No. One Not added 75 67 81 98 97 6.29 No. 2 0.20% added 80 81 89 99 97 6.28 No. 3 0.45% added 95 88 92 97 98 6.27 No. 4 0.50% added 98 93 92 98 97 6.13

As can be seen in Table 1, the recovery rate of each alloy component increased when Mn was added compared to when Mn was not added. However, if the added content of Mn exceeds 0.45%, the Mn component may remain in the powder and reduce moldability, so it is preferable to limit the content to 0.2 to 0.45%.

Next, changes in oxygen content and molding density in the powder according to the melting temperature of the ingot were measured.

The dissolution temperature of each sample was changed as shown in Table 2 below, and the oxygen content and molding density in the powder were measured accordingly and are shown in Table 2.

division Dissolution temperature℃ Oxygen component in powder
(%) Molded density (g/cc)
(at 600MPa molding) No. 5 1600 0.17 6.29 No. 6 1630 0.21 6.2 No. 7 1670 0.23 6.18

As can be seen in Table 3, when the dissolution temperature increases, the oxygen content in the powder increases and the molding density decreases. Therefore, it is desirable to maintain the melting temperature of molten steel at 1590 to 1630°C, preferably 1590 to 1610°C.

Next, the formation of impurities in the final powder was observed depending on the amount of Al, a deoxidizing agent, added during dissolution of the ingot.

Figure 2 is a photograph showing the state of powder particles according to comparative examples and examples. Figure 2 (a) is an SEM photograph of iron-based powder with Al added at less than 0.1%, and (b) is an SEM photograph showing Al at more than 0.1%. This is an SEM photo of the iron-based powder added.

As can be seen in Figure 2, impurities due to Al were not observed in the iron-based powder containing less than 0.1% of Al, but impurities due to Al were observed in the iron-based powder containing more than 0.1% of Al.

Therefore, when more than 0.1% of Al is added, impurities formed by Al may be mixed into the powder or encroach on the tundish nozzle, causing clogging.

Next, changes in the properties of the sintered body according to the amount of boron (B) added were measured.

For each sample, the input amount of boron (B) was changed as shown in Table 3 below, and the hardness, wear rate, and Charpy impact strength of the sintered body manufactured using the iron-based powder produced accordingly were measured, and the results are shown in Table 3. indicated. At this time, the wear rate was expressed as weight loss per meter by grinding the sample with a force of 42N using 80 mesh sandpaper and averaging the weight plasticity of the sample.

division B input amount
(%) Hardness
(HRC) wear rate
(mg/M) Charpy impact strength
(J) No. 8 Not added 58 10.032 71 No. 9 0.005 65 9.053 63 No. 10 0.01 71 8.174 52 No. 11 0.02 92 5.321 25

As can be seen in Table 3, hardness and wear resistance increase as boron (B) is added, but if more than 0.01% is added, the impact strength rapidly decreases and may be easily broken, so in this example, the amount of boron (B) added is the maximum. It is desirable to limit the value to 0.01%.

Next, changes in oxygen content and molding density in the powder according to heat treatment temperature during heat treatment were measured.

For each sample, the heat treatment temperature was changed as shown in Table 4 below, and the oxygen content and molding density in the powder were measured accordingly and are shown in Table 4.

division heat treatment temperature
(℃) Oxygen content in powder
(%) Molded density (g/cc)
(at 600MPa molding) No. 12 Not in progress 0.17 6.29 No. 13 200 0.17 6.29 No. 14 300 0.16 6.29 No. 15 400 0.15 6.31 No. 16 600 0.12 6.33 No. 17 700 0.28 6.15

As can be seen in Table 4, it was confirmed that as heat treatment was performed, the content of oxygen in the powder decreased and the molding density increased. However, when the heat treatment temperature exceeded 600°C, it was confirmed that re-oxidation occurred within the iron-based powder due to the oxidizing property of chromium, and the oxygen component increased.

Although the present invention has been described with reference to the accompanying drawings and the above-described preferred embodiments, the present invention is not limited thereto and is limited by the claims described below. Accordingly, those skilled in the art can make various changes and modifications to the present invention without departing from the technical spirit of the claims described later.

Claims (15)

delete delete delete delete delete A method of manufacturing iron-based powder for powder metallurgy used in the manufacture of automobile parts,
Setting the target content for each alloy component of iron-based powder containing chromium (Cr), nickel (Ni), molybdenum (Mo), phosphorus (P), silicon (Si), iron (Fe), and other unavoidable impurities. and;
The content of chromium (Cr), phosphorus (P), and silicon (Si) is increased by 0.5 to 45% in weight percent compared to the target content, and the ingot is made with a content corresponding to the target content of nickel (Ni) and molybdenum (Mo). Preparation steps;
preparing molten steel by melting the ingot;
Comprising the step of manufacturing iron-based powder using the molten steel,
In the step of preparing the molten steel, the melting temperature of the ingot is 1590 to 1630°C,
In the step of manufacturing the iron-based powder, the iron-based powder is manufactured by a water injection method or a gas injection method, and the molten steel is maintained at 1540 to 1560 ° C. before manufacturing the iron-based powder,
After the step of manufacturing the iron-based powder, the step of heat-treating the iron-based powder is further included,
A method of producing iron-based powder for powder metallurgy, characterized in that the step of heat-treating the iron-based powder is carried out at a heat treatment temperature of 400 to 600° C. in a reducing atmosphere. In claim 6,
In the step of setting the target content for the alloy component, the target content of each alloy component is expressed in weight%, chromium (Cr): 7 to 9%, nickel (Ni): 1.5 to 2.5%, molybdenum (Mo): 1.6. ~ 2.2%, phosphorus (P): 0.3 ~ 0.7%, silicon (Si): 0.5 ~ 1.1%, the remainder being iron (Fe).
In claim 7,
In the step of preparing the ingot, the ingot further contains manganese (Mn): 0.2 to 0.45% by weight.
In claim 6,
In the step of preparing the molten steel,
A method for producing iron-based powder for powder metallurgy, characterized in that a deoxidizing agent is added at least once while dissolving the ingot.
In claim 9,
The deoxidizer is aluminum (Al), and the deoxidizer is added so that the content of aluminum (Al) in the final molten steel is 0.1% or less in weight percent.
delete In claim 6,
In the step of preparing the molten steel, a method for producing iron-based powder for powder metallurgy, characterized in that 0.001 to 0.01% by weight of boron (B) is added to the molten steel while the ingot is melting.
delete delete delete

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