SINTERED MATERIAL FOR ALUMINUM DIE CASTING AND MANUFACTURING METHOD THEREOF

Abstract

A sintered material for aluminum die casting can prevent the strength from being lowered even after steam treatment. The sintered material for aluminum die casting is a sintered material used as an insert at the time of aluminum die casting, and contains Cr: 0.71 to 0.97 wt %, Mo: 0.10 to 0.20 wt %, and C: 0.64 to 0.87 wt %, with the remainder being Fe and other unavoidable impurities.

Claims

1. A sintered material used as an insert in aluminum die casting, the sintered material comprising: Cr: 0.71 to 0.97 wt %; Mo: 0.10 to 0.20 wt %; and C: 0.64 to 0.87 wt %; wherein the remainder comprises Fe and other unavoidable impurities.

2. The sintered material of claim 1, further comprising one or two or more selected from the group consisting of Mn, Ni and S; wherein a total content of Mn, Ni and S is in a range of 0.15 to 0.45 wt %.

3. The sintered material of claim 1, wherein the sintered material does not contain Cu.

4. The sintered material of claim 1, wherein the sintered material has a yield strength of 400 MPa or more, and a fatigue strength of 150 MPa or more.

5. The sintered material of claim 1, wherein the sintered material has a density of 6.8 to 7.2 g/cm3.

6. The sintered material of claim 1, wherein on a surface of the sintered material, a surface protective layer made of iron oxide is formed.

7. The sintered material of claim 6, wherein Cu is not crystallized in the surface protective layer.

8. A method of manufacturing a sintered material for aluminum die casting, the method comprising: preparing an iron-based pre-alloy powder containing chromium (Cr) and molybdenum (Mo); preparing an iron-based pre-alloy mixture by mixing carbon powder, a functional additive, and a lubricant with the iron-based pre-alloy powder; preparing a molded material by molding the iron-based pre-alloy mixture; preparing a sintered material by sintering the molded material; and steam-treating the sintered material; wherein the iron-based pre-alloy powder further includes Mn, Ni, and S; and wherein a total content of Mn, Ni and S is in a range of 0.15 to 0.45 wt %.

9. The method of claim 8, wherein the iron-based pre-alloy powder contains Cr: 0.72 to 0.98 wt %, and Mo: 0.10 to 0.20 wt %, wherein the remainder comprises Fe and other unavoidable impurities.

10. (canceled)

11. The method of claim 8, wherein the iron-based pre-alloy powder does not contain Cu.

12. The method of claim 8, wherein the iron-based pre-alloy mixture is prepared by mixing a functional additive and a lubricant with the iron-based pre-alloy powder, so that the iron-based pre-alloy mixture contains Cr: 0.71 to 0.97 wt %, Mo: 0.10 to 0.20 wt %, C: 0.63 to 0.87 wt %, functional additive: 0.10 to 0.20 wt %, and lubricant: 0.54 to 0.66 wt %, wherein the remainder comprises Fe and other unavoidable impurities.

13. The method of claim 8, wherein the sintered material contains Cr: 0.71 to 0.97 wt %, Mo: 0.10 to 0.20 wt %, C: 0.64 to 0.87 wt %, and functional additive: 0.10 to 0.20 wt %, wherein the remainder comprises Fe and other unavoidable impurities.

14. The method of claim 8, wherein the preparing of the sintered material comprises sintering the molded material at a temperature of 1100 to 1150? C. for 20 to 60 minutes in a nitrogen and hydrogen mixed gas atmosphere, and then air-cooling the molded material.

15. The method of claim 8, wherein the steam-treating of the sintered material comprises treating the sintered material in a steam atmosphere at a temperature of 400 to 600? C. for 30 to 60 minutes.

16. The method of claim 15, wherein in the steam-treating of the sintered material, on a surface of the sintered material, a surface protective layer made of iron oxide is formed.

17. The method of claim 16, wherein in the steam-treating of the sintered material, Cu is not crystallized in the surface protective layer.

18. The method of claim 8, wherein after the steam-treating of the sintered material, the microstructure of the sintered material is pearlite.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0039] FIG. 1A is a photograph showing a fracture surface of a fatigue test piece according to a Comparative Example.

[0040] FIG. 1B is a photograph showing the fracture surface of the fatigue test piece according to an Example.

[0041] FIG. 2 is a photograph showing the EDS check result of analyzing the fracture surface components of the fatigue test piece according to a Comparative Example.

[0042] FIG. 3A is an SEM image showing the microstructure of a Comparative Example.

[0043] FIG. 3B is an SEM image showing the microstructure of an Example.

DETAILED DESCRIPTION

[0044] Hereinafter, exemplary embodiments disclosed herein will be described with reference to the accompanying drawings, in which identical or like components are given like reference numerals regardless of drawing numbers, and description thereof will not be repeated.

[0045] Suffixes for components, module, unit and part used in the following description, will be given or used in place of each other taking only easiness of specification preparation into consideration, and they do not have distinguishable meanings or roles by themselves.

[0046] In describing the embodiments disclosed herein, it is noted that the detailed description for related known arts may be omitted herein so as not to obscure essential points of the disclosure. Further, the accompanying drawings are intended to facilitate a better understanding of examples disclosed herein, and the technical spirit disclosed herein is not limited by the accompanying drawings, and rather should be construed as including all the modifications, equivalents and substitutes within the technical idea and technical scope of the disclosure.

[0047] The terms including ordinal number such as, first, second and the like may be used to explain various components, but the components should not be limited by these terms. Said terms are used in order only to distinguish one component from another component.

[0048] Further, when one component is referred to as being connected or accessed to another element, it should be understood that the one component may be directly connected or accessed to the other component or any intervening component may also be present therebetween. Contrarily, when one component is referred to as being directly connected or directly accessed to another component, it should be understood as that no other element is present therebetween.

[0049] Singular expressions may include the meaning of plural expressions unless the context clearly indicates otherwise.

[0050] Terms such as include (or comprise), have (or be prepared with), and the like are intended to indicate that features, numbers, steps, operations, components, parts, or combinations thereof written in the following description exist, and thus should not be understood as that the possibility of existence or addition of one or more different features, numbers, steps, operations, components, parts, or combinations thereof is excluded in advance.

[0051] The sintered material for aluminum die casting according to an embodiment of the present disclosure is a material used as an insert during aluminum die casting, and may be applied to engine parts of an internal combustion engine that must maintain excellent fatigue strength while achieving weight reduction. For example, a cylinder block, a piston pin, a bed plate, and the like constituting an engine of an internal combustion engine may be manufactured by aluminum die casting using the sintered material according to the present disclosure.

[0052] Such sintered material may be manufactured by mixing the iron-based pre-alloy powder with a carbon powder, a functional additive, and a lubricant. However, the lubricant is vaporized during the process of sintering the sintered material, so that it does not remain in the final sintered material.

[0053] Therefore, the sintered material for aluminum die casting according to an embodiment of the present disclosure contains Cr: 0.71 to 0.97 wt %, Mo: 0.10 to 0.20 wt %, and C: 0.64 to 0.87 wt %, with the remainder being Fe and other unavoidable impurities.

[0054] Additionally, the sintered material may further contain one or two or more kinds selected from the group consisting of Mn, Ni and S in order to secure physical properties. In this case, the total content of Mn, Ni and S is preferably in a range of 0.15 to 0.45 wt %.

[0055] In addition, the sintered material may contain the functional additive at a level of 0.10 to 0.20 wt %. In this case, various functional additives may be applied as the functional additive to secure physical properties, formability, and processability of the sintered material.

[0056] Meanwhile, Cr and Mo, which are the main alloy elements of the pre-alloy iron-based powder forming the sintered material, are components contained to secure rigidity in structural parts, and are alloy elements that stabilize pearlite which is the microstructure of the pre-alloy iron-based powder.

[0057] So, when Cr and Mo are contained less than the presented content range, the pearlite, which is a microstructure, is not stably formed, and, when they are contained more than the presented content range, the effect of improving the physical properties is inadequate, and there is a problem in that the formability is lowered or the production cost of the sintered material is increased.

[0058] Additionally, C is a material manufactured in the form of carbon powder separately from the pre-alloy iron-based powder and mixed with the pre-alloy iron-based powder, and is an additive element that stabilizes the pearlite along with Cr and Mo.

[0059] So, when C is contained less than the presented content range, the pearlite, which is a microstructure, is not stably formed, and when it is contained more than the presented content range, there is a problem in that the formability is lowered.

[0060] Meanwhile, the sintered material according to the present embodiment preferably does not contain Cu. Therefore, when an insert for aluminum die casting is manufactured using the sintered material, and when the insert is steam-treated for aluminum die casting, it is possible to fundamentally prevent the crystallization of Cu in a temperature range during the steam treatment. In addition, it is possible to fundamentally prevent Cu from being precipitated in the heating temperature section during the preheating of the insert.

[0061] And, on the surface of the sintered material according to the present embodiment, a surface protective layer made of iron oxide such as Fe.sub.3O.sub.4 is formed by the steam treatment. Therefore, it is possible to solve the problem that the residues in the pores inside the sintered material are vaporized or air bubbles are transferred to the inside of the molten metal during the preheating and die casting process for aluminum die casting using the sintered material.

[0062] In addition, it is characterized that Cu is not crystallized on the surface protective layer.

[0063] By adjusting the components of the sintered material as described above, the sintered material can maintain a yield strength of 400 MPa or more and a fatigue strength of 150 MPa or more.

[0064] And, the sintered material preferably has a density of 6.8 to 7.2 g/cm.sup.3.

[0065] A method for manufacturing the sintered material as described above will be described.

[0066] A method of manufacturing a sintered material for aluminum die casting according to an embodiment of the present disclosure includes preparing an iron-based pre-alloy powder containing chromium (Cr) and molybdenum (Mo), preparing an iron-based pre-alloy mixture by mixing carbon powder, a functional additive, and a lubricant with the iron-based pre-alloy powder, preparing a molded material by molding the iron-based pre-alloy mixture, preparing a sintered material by sintering the molded material, and steam-treating the sintered material.

[0067] The preparing of the iron-based pre-alloy powder is a step of preparing the iron-based pre-alloy powder constituting the sintered material.

[0068] In this case, the iron-based pre-alloy powder preferably contains Cr: 0.72 to 0.98 wt %, and Mo: 0.10 to 0.20 wt %, with the remainder being Fe and other unavoidable impurities.

[0069] And, the iron-based pre-alloy powder may further include one or two or more kinds selected from the group consisting of Mn, Ni, and S. In this case, the total content of Mn, Ni and S is preferably kept in a range of 0.15 to 0.45 wt %.

[0070] In particular, the iron-based pre-alloy powder preferably does not contain Cu in order to fundamentally prevent the problems caused by the inclusion of Cu.

[0071] The preparing of the iron-based pre-alloy mixture is a step of mixing the carbon powder, the functional additive and the lubricant with the iron-based pre-alloy to form the sintered material.

[0072] In this case, the iron-based pre-alloy mixture is obtained by measuring the contents of the carbon powder, the functional additive and the lubricant and mixing them with the iron-based pre-alloy powder, so that the iron-based pre-alloy mixture contains Cr: 0.71 to 0.97 wt %, Mo: 0.10 to 0.20 wt %, C: 0.63 to 0.87 wt %, functional additive: 0.10 to 0.20 wt %, and lubricant: 0.54 to 0.66 wt %, with the remainder being Fe and other unavoidable impurities.

[0073] The preparing of the molded material is a step of molding the iron-based pre-alloy mixture into a predetermined shape. For example, the iron-based pre-alloy mixture is press-molded to manufacture an insert of a desired shape.

[0074] The preparing of the sintered material is a step of sintering the molded product formed into a predetermined shape.

[0075] The atmosphere for sintering the molded material is carried out in a mixed gas atmosphere of nitrogen and hydrogen. At this time, the mixing ratio of nitrogen and hydrogen is preferably maintained in the range of 90%?10%: 10%?10%.

[0076] In addition, the molded material is preferably maintained at a temperature of 1100 to 1150? C. for 20 to 60 minutes, and then cooled in air cooling conditions.

[0077] The steam-treating of the sintered material includes forming a surface protective layer made of iron oxide on the surface of the sintered material by steam-treating the sintered material on which the sintering and the cooling have been completed.

[0078] At this time, the steam treatment is preferably performed by treating the sintered material in a steam atmosphere at a temperature of 400 to 600? C. for 30 to 60 minutes.

[0079] In the sintered material that has been steam-treated in this way, Cu is not crystallized on the surface protective layer, and the surface protective layer is made of iron oxide such as Fe.sub.3O.sub.4.

[0080] And, the microstructure of the sintered material is formed in pearlite.

[0081] Next, the present disclosure will be described through Comparative Examples, and Examples.

[0082] First, the existing materials applied to Comparative Examples, and Examples used an iron-based pre-alloy mixture whose composition was adjusted to Fe-3Cu-0.7C by mixing Cu powder and C powder with iron-based powder, and the inventive material used an iron-based pre-alloy mixture whose composition was adjusted to Fe-0.85Cr-0.15Mo-0.75C by mixing iron-based pre-alloy powder containing Cr and Mo with C powder. At this time, the existing material and the inventive material were each mixed with 0.15 wt % of a functional additive and 0.6 wt % of a lubricant.

[0083] And, after preparing the sintered materials while changing the density according to the adjustment of the pressing force of the molding, the presence or absence of steam treatment, and the type of atmospheric gas of the sintering as shown in Table 1 below, density, Young's modulus, yield strength, tensile strength and fatigue strength of the respective sintered materials were measured, and the results are shown together in Table 1.

TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Comparative Item Example 1 Example 2 Example 3 Example 4 Example 1 Example 2 Material quality Existing Existing Inventive Inventive Inventive Inventive material material material material material material Steam-treatment ? ? ? ? Sintering gas ENDO ENDO ENDO N2:H2 N2:H2 N2:H2 Density (g/cm.sup.3) 6.97 7.03 7.04 6.96 7.04 7.16 Young's 125 135 135 125 135 144 modulus (GPa) Yield 430 421 385 391 418 442 strength (MPa) Tensile 580 485 394 476 454 492 strength (MPa) Fatigue 165 105 100 160 150 170 strength (MPa)

[0084] As can be seen from Table 1, it was confirmed that the Young's modulus proportionally changed according to the change in density in Comparative Examples and Examples.

[0085] Meanwhile, in the case of Comparative Example 1 which used an existing material containing Cu, but was not subjected to the steam treatment, and employed ENDO as the sintering gas, it was confirmed that the yield strength and the tensile strength were excellent, and that the fatigue strength was not lowered.

[0086] However, in the case of Comparative Example 2 which used an existing material containing Cu, but was subjected to the steam treatment, and employed ENDO as the sintering gas, it was confirmed that the yield strength and the tensile strength were excellent, but that the fatigue strength was significantly lowered.

[0087] And, in the case of Comparative Example 3 which used an inventive material not containing Cu, and was subjected to the steam treatment, and employed ENDO as the sintering gas, it could be confirmed that the yield strength and the tensile strength were lowered, and particularly that the fatigue strength was significantly lowered.

[0088] Additionally, in the case of Comparative Example 4 which used an inventive material not containing Cu, but was not subjected to the steam treatment, and employed a mixed gas of nitrogen and hydrogen as the sintering gas, it was confirmed that the tensile strength and fatigue strength were excellent, but that the yield strength was lowered.

[0089] Meanwhile, in the case of Examples 1 and 2 which used a mixed gas of nitrogen and hydrogen as a sintering gas and was subjected to the steam treatment while using an inventive material that does not contain Cu, it was confirmed that the yield strength, the tensile strength and the fatigue strength were all excellent. In particular, it was confirmed that Examples 1 and 2 both had a yield strength of 400 MPa or more, and a fatigue strength of 150 MPa or more.

[0090] Next, the fracture surfaces of the sintered materials manufactured according to the component change of the sintered material were compared.

[0091] First, after measuring the fatigue strengths of the sintered materials manufactured according to Comparative Example 2 and Example 1, the fracture surfaces were observed, and the fracture surface component of Comparative Example 2 was analyzed.

[0092] FIG. 1A is a photograph showing the fracture surface of the fatigue test piece according to Comparative Example 2, FIG. 1B is a photograph showing the fracture surface of the fatigue test piece according to Example 1, and FIG. 2 is a photograph showing the EDS check result of analyzing the fracture surface components of the fatigue test piece according to the Comparative Example.

[0093] Comparing FIGS. 1A and 1B, in Comparative Example 2, a relatively large number of coarse pores were observed on its fracture surface. Contrarily, it could be confirmed that Example 1 had less and finer pores than Comparative Example 2.

[0094] In addition, as can be seen in FIG. 2, in Comparative Example 2, although the Cu content was adjusted to 3 wt %, it was confirmed that the Cu content was detected as 11.2 wt % at the fracture surface, so it can be inferred that during the sintering process, a significant amount of Cu was crystallized on the surface of the powder, which caused the defect.

[0095] Next, in order to find out the microstructures of the sintered materials according to Comparative Examples and Examples, the microstructures of Comparative Example 2 and Example 1 were observed, and the results are shown in FIGS. 3A and 3B.

[0096] FIG. 3A is an SEM image showing the microstructure of the Comparative Example, and FIG. 3B is an SEM image showing the microstructure of the Example.

[0097] As can be seen from FIGS. 3A and 3B, it could be confirmed that pearlite was formed as a microstructure in both the sintered materials according to Comparative Example 2 and Example 1.

[0098] Next, the change in strength according to the component change of the iron-based pre-alloy mixture was investigated.

[0099] At this time, the inventive material basically employed an iron-based pre-alloy mixture whose composition was adjusted to Fe-0.85Cr-0.15Mo-0.75C by mixing an iron-based pre-alloy powder containing Cr and Mo with a C powder, and Examples were prepared, in which the contents of C, Cr and Mo had been varied. At this time, the existing material and the inventive material were each mixed with 0.15 wt % of a functional additive and 0.6 wt % of a lubricant.

[0100] And, the sintered materials were prepared while changing the density according to the adjustment of the pressing force during the molding as shown in Table 2 below, and then the yield strength and tensile strength thereof were measured, and the results are shown together in Table 2.

TABLE-US-00002 TABLE 2 Item Example 3 Example 4 Example 5 Example 6 Material quality Inventive Inventive Inventive Inventive material material material material Changed composition 0.67C 0.75Cr 0.11Mo Steam-treatment ? ? ? ? Sintering gas N.sub.2:H.sub.2 N.sub.2:H.sub.2 N.sub.2:H.sub.2 N.sub.2:H.sub.2 Density (g/cm.sup.3) 7.01 7.04 7.03 6.83 Yield strength (MPa) 415 421 427 409 Tensile strength (MPa) 438 444 459 431

[0101] As can be seen in Table 2, it could be confirmed that all of Examples 3 to 6 in which the density was maintained and the contents were changed within the ranges of the components and contents presented in the present disclosure maintained excellent yield strength and tensile strength. In particular, it was confirmed that all of Examples 3 to 6 maintained a yield strength of 400 MPa or more.

[0102] Although the present disclosure has been described with reference to the accompanying drawings and the above-described preferred embodiments, the present disclosure is not limited thereto, but limited by the following claims. Accordingly, those of ordinary skill in the art can variously change and modify the present disclosure within a scope which does not depart from the technical idea of the claims to be described later.