Die-casting die steel and production method thereof

Abstract

The invention relates to die-casting die steel which comprises the following elements in percentage by mass: 0.32%-0.45% of C, 1.35%-1.65% of Cr, 0.3%-0.6% of Mn, 0.15%-0.25% of Mo, 0.01%-0.03% of Si, 0.005%-0.012% of V, 0.7%-1.1% of AL, 0.1%-0.3% of Ni and the balance of Fe. The invention further relates to a production method of the die-casting die steel, and the production method comprises the following steps: burdening the components in percentage by weight and then putting the components into an electric furnace; smelting in a protective atmosphere to obtain a melt; the melt is subjected to heat preservation for 2.5 h to 3 h under the condition of 1570 DEG C to 1650 DEG C, vacuum die-casting forming is conducted, a casting is obtained, the casting is subjected to multidirectional forging machining, and a forging stock is obtained; performing high-temperature annealing on the forging stock; the annealed forging stock is subjected to rough machining, quenching and tempering treatment; and the tempered forging stock is subjected to finish machining and nitriding treatment, so that the die steel has better thermal conductivity and high toughness, the material can generate toughness deformation response under frequent high temperature and high pressure, the deformation of the product is reduced, the high-temperature wear resistance is improved through a good nitriding layer structure, and thus the service life of the product is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of die steel, and more particularly to a die-casting die steel and a production method thereof. Background Art

[0002] Mold steel can be roughly divided into three categories: cold working mold steel, hot working mold steel and plastic mold steel. At present, hot deformation molds have to withstand huge mechanical stress and thermal stress when manufacturing die-casting products. The current mold steel usually contains more carbide-forming elements and higher alloying elements, resulting in insufficient toughness. The material is prone to cracking when subjected to high-temperature thermal expansion or large thrust extrusion deformation. There is a slight deformation during the tempering process, and the decarburization layer cannot be completely cleaned. Secondly, there is also the problem of insufficient thermal conductivity. Under frequent high temperature and high pressure, the elastic limit of the material is exceeded. Under the continuous action of the internal stress of the material, internal cracks are easily formed, and then rapidly expand and crack, eventually leading to failure.

[0003] The Chinese patent with publication number CN109136765A discloses a hot working die steel and a preparation method thereof, comprising the following alloy elements: C 0.35-0.42%, Si 0.80-1.20%, Mn 0.30-0.60%, Cr 2.50-3.50%, Mo 2.30-3.20%, V 0.45~0.65%, P<0.015%, S<0.002%, Fe balance, the prepared steel has the advantages of high thermal stability, thermal strength and good toughness, etc., which meets the high temperature performance requirements of the current mold manufacturing for its materials, but the steel contains high carbide-forming elements such as Cr, Mo, Si, and V. The precipitation of carbides at high temperatures will form a network, and the material is prone to fatigue cracking during use, which shortens the life of the mold; the alloy component content is high, the Si element content is high, and the thermal conductivity of the material is poor, so the overall welding performance is poor, it is easy to crack, and the machining performance is poor, there is a slight deformation during the tempering process, and the decarburization layer cannot be completely cleaned; the nitriding performance is poor, it is not easy to nitridate, resulting in insufficient toughness and brittle cracking. Summary of the invention

[0004] The purpose of the present invention is to provide a die-casting die steel in view of the deficiencies in the prior art, comprising the following elements in percentage by mass: C: 0.32%-0.45%, Cr: 1.35%-1.65%, Mn: 0.3%-0.6%, Mo: 0.15%-0.25%, Si: 0.01%-0.03%, V: 0.005%-0.012%, Al: 0.7%-1.1%, Ni: 0.1%-0.3%, Fe balance, by reducing the content of alloy elements and Si, it is not easy to form network carbides on the surface when working at high temperature, it is not easy to fatigue cracking, and the decarburized layer can be thoroughly cleaned; at the same time, in order to improve the hardness of the product, the product is tempered to improve the hardness of the product, so that the hardness of the die steel after tempering is more suitable for mechanical processing, and the welding performance is improved; in addition, by adding the Al element, the product is rapidly nitrided, the hardness gradient of the nitrided surface layer is reduced, and the toughness of the product is sufficient to withstand high-temperature expansion and strong extrusion deformation. The material hardness is suitable as the matrix hardness. After surface nitriding, the surface hardness is strengthened and the thermal conductivity of the material is improved.

[0005] Another object of the present invention is to provide a production method for die-casting die steel in view of the deficiencies in the prior art, comprising the steps of: mixing the weight percentages of the constituent elements and placing them in an electric furnace, smelting them under a protective atmosphere to obtain a melt; keeping the melt at 1570°C-1650°C for 2.5-3h, vacuum die-casting to obtain a casting, and performing multi-directional forging processing on the casting to obtain a forging blank; performing high-temperature annealing on the forging blank; quenching and tempering the annealed forging blank; and nitriding the tempered forging blank to make the die steel have better thermal conductivity and high toughness. Under frequent high temperature and high pressure, the material can produce tough deformation response, reduce the deformation of the product, and a good nitrided layer structure increases high-temperature wear resistance, thereby extending the service life of the product.

[0006] The technical solutions of the present invention are as follows:

[0007] A die-casting die steel comprises the following elements in percentage by mass: C: 0.32%-0.45%, Cr: 1.35%-1.65%, Mn: 0.3%-0.6%, Mo: 0.15%-0.25%, Si: 0.01%-0.03%, V: 0.005%-0.012%, Al: 0.7%-1.1%, Ni: 0.1%-0.3%, and Fe as a remainder.

[0008] A method for producing die-casting die steel comprises the following steps in sequence:

[0009] S1, after mixing the weight percentage of each component element, put it into an electric furnace and smelt it under a protective atmosphere to obtain a melt;

[0010] S2, keeping the melt at 1570°C-1650°C for 2.5h-3h, vacuum die-casting to obtain a casting, and multi-directional forging the casting to obtain a forging blank;

[0011] S3, high temperature annealing of the forging blank;

[0012] S4, rough machining, quenching and tempering the annealed forging blank;

[0013] S5. Perform fine machining and nitriding on the tempered forging blank.

[0014] As a preferred embodiment, in S1, the temperature of the electric furnace is 1570°C-1650°C.

[0015] As a preferred embodiment, in S3, the annealing temperature is 1250°C to 1280°C, and the heat preservation time is 8h-10h.

[0016] As a preferred embodiment, in S4, the quenching temperature is 920°C-960°C, and the heat preservation time is 30min-40min.

[0017] As a preferred embodiment, in S4, the tempering temperature is 580°C-600°C, and the tempering times are 2-3 times.

[0018] As a preferred embodiment, in S4, the hardness of the forging blank after tempering is 30HRC-36HRC.

[0019] As a preferred embodiment, in S5, the depth of the nitrided layer of the forging blank is 0.6 mm-0.8 mm.

[0020] As a preferred embodiment, in S5, the hardness of the nitrided layer of the forging blank from the surface to 0.2 mm is greater than 1000 HV.

[0021] As a preference, in S5, the hardness gradient of the nitride layer decreases to a core hardness of 300HV-330HV.

[0022] The beneficial effects of the present invention are

[0023] 1. The present invention reduces the content of alloy elements and Si, so that the surface of the product is not easy to form network carbides when working at high temperature, is not easy to fatigue cracking, and the decarburized layer can be thoroughly cleaned; at the same time, in order to improve the hardness of the product, the product is tempered to improve the hardness of the product, so that the hardness of the mold steel after tempering is more suitable for mechanical processing, and the welding performance and thermal conductivity are improved; in addition, by adding Al elements, the product is quickly nitrided, and the hardness gradient of the nitrided surface layer decreases, so that the toughness of the product is sufficient to withstand high-temperature expansion and strong extrusion deformation; by adding Ni, the hardness of the product is improved without affecting its toughness, and the hardness of the product is suitable as the matrix hardness. After surface nitriding, the surface hardness is strengthened to better cope with friction and high-temperature working conditions.

[0024] In summary, the present invention has the advantages of high temperature resistance and high toughness, and is suitable for the technical field of die steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below in conjunction with the accompanying drawings:

[0026] Figure 1 Graphs showing test results of four embodiments;

[0027] Figure 2 This is the microstructure metallographic diagram of conventional die steel after quenching and tempering;

[0028] Figure 3 This is a metallographic diagram of the mold steel raw material structure in the embodiment of the present invention;

[0029] Figure 4 This is the metallographic diagram of the nitrided structure of conventional die steel;

[0030] Figure 5 This is a metallographic diagram of the nitrided structure of the die steel in the embodiment of the present invention; DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings.

[0032] Embodiment 1

[0033] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0034] A die-casting die steel comprises the following elements in percentage by mass: C: 0.32%-0.45%, Cr: 1.35%-1.65%, Mn: 0.3%-0.6%, Mo: 0.15%-0.25%, Si: 0.01%-0.03%, V: 0.005%-0.012%, Al: 0.7%-1.1%, Ni: 0.1%-0.3%, and Fe as a remainder.

[0035] A method for producing die-casting die steel comprises the following steps in sequence:

[0036] S1. Put 0.35% C, 1.35% Cr, 0.3% Mn, 0.15% Mo, 0.01% Si, 0.005% V, 0.7% Al and 0.1% Ni into an electric furnace at 1570°C and smelt under a protective atmosphere to obtain a melt;

[0037] S2, keeping the melt at 1570°C for 2.5 hours, vacuum die-casting to obtain a casting, and multi-directional forging the casting to obtain a forging blank;

[0038] S3, annealing the forging blank at 1250°C and keeping it warm for 8h;

[0039] S4, rough machining the annealed forging blank, quenching at 920°C, keeping warm for 30min, tempering at 580°C, and tempering twice;

[0040] S5. Perform fine machining and nitriding on the tempered forging blank.

[0041] Finally, the performance test of the mold steel finally obtained in this embodiment was carried out. The test items included hardness, nitriding depth, nitriding surface hardness, core hardness, and fracture toughness. The test results are shown in the attached Figure 1 .

[0042] Embodiment 2

[0043] A method for producing die-casting die steel comprises the following steps in sequence:

[0044] S1. Put 0.35% C, 1.55% Cr, 0.5% Mn, 0.15% Mo, 0.01% Si, 0.01% V, 0.7% Al and 0.1% Ni into an electric furnace at 1570°C and smelt under a protective atmosphere to obtain a melt;

[0045] S2, keeping the melt at 1570°C for 2.5 hours, vacuum die-casting to obtain a casting, and multi-directional forging the casting to obtain a forging blank;

[0046] S3, annealing the forging blank at 1250°C and keeping it warm for 8h;

[0047] S4, rough machining the annealed forging blank, quenching at 920°C, keeping warm for 30 minutes, tempering at 580°C, and tempering twice;

[0048] S5. Perform fine machining and nitriding on the tempered forging blank.

[0049] Finally, the performance test of the mold steel finally obtained in this embodiment was carried out. The test items included hardness, nitriding depth, nitriding surface hardness, core hardness, and fracture toughness. The test results are shown in the attached Figure 1 .

[0050] Embodiment 3

[0051] A method for producing die-casting die steel comprises the following steps in sequence:

[0052] S1. Put 0.35% C, 1.65% Cr, 0.6% Mn, 0.2% Mo, 0.03% Si, 0.01% V, 0.85% Al and 0.2% Ni into an electric furnace at 1650°C and smelt under a protective atmosphere to obtain a melt;

[0053] S2, keeping the melt at 1650° C. for 2.5 hours, vacuum die-casting to obtain a casting, and multi-directional forging the casting to obtain a forging blank;

[0054] S3, annealing the forging blank at 1280°C for 8 hours;

[0055] S4, rough machining the annealed forging blank, quenching at 960°C, keeping warm for 30 minutes, tempering at 600°C, and tempering for 3 times;

[0056] S5. Perform fine machining and nitriding on the tempered forging blank.

[0057] Finally, the performance test of the mold steel finally obtained in this embodiment was carried out. The test items included hardness, nitriding depth, nitriding surface hardness, core hardness, and fracture toughness. The test results are shown in the attached Figure 1 .

[0058] Embodiment 4

[0059] A method for producing die-casting die steel comprises the following steps in sequence:

[0060] S1. Put 0.45% C, 1.65% Cr, 0.6% Mn, 0.25% Mo, 0.03% Si, 0.12% V, 1.1% Al and 0.3% Ni into an electric furnace at 1650°C and smelt under a protective atmosphere to obtain a melt;

[0061] S2, keeping the melt at 1650° C. for 2.5 hours, vacuum die-casting to obtain a casting, and multi-directional forging the casting to obtain a forging blank;

[0062] S3, annealing the forging blank at 1280°C for 8 hours;

[0063] S4, rough machining the annealed forging blank, quenching at 960°C, keeping warm for 30 minutes, tempering at 600°C, and tempering for 3 times;

[0064] S5. Perform fine machining and nitriding on the tempered forging blank.

[0065] Finally, the performance test of the mold steel finally obtained in this embodiment was carried out. The test items included hardness, nitriding depth, nitriding surface hardness, core hardness, and fracture toughness. The test results are shown in the attached Figure 1 .

[0066] From the attached Figure 1 The following conclusions can be drawn from the test data: by reducing the content of alloy elements and Si, it is not easy for the product to form network carbides on the surface when working at high temperatures, it is not easy to fatigue crack, and the decarburized layer can be thoroughly cleaned; at the same time, in order to improve the hardness of the product, the product is tempered to improve the hardness of the product, so that the hardness of the mold steel after tempering is more suitable for mechanical processing, and the welding performance and thermal conductivity are improved; in addition, by adding Al elements, the product is quickly nitrided, and the hardness gradient of the nitrided surface layer decreases, so that the toughness of the product is sufficient to withstand high-temperature expansion and strong extrusion deformation; by adding Ni, the hardness of the product is increased without affecting its toughness. The hardness of the product is suitable as the matrix hardness. After surface nitriding, the surface hardness is strengthened to better cope with friction and high-temperature working conditions.

[0067] from Figure 2 The microstructure of conventional mold steel after quenching and tempering shows that carbides precipitate to form a network at high temperature, which is prone to fatigue cracking during use. Figure 3 It can be seen that the mold steel in the embodiment of the present invention has less carbide-forming elements, so it is not easy to form network carbides on the surface when working at high temperature. Figure 4 It can be seen from the figure that after nitriding, conventional die steel has strong notch sensitivity and there are micro cracks with a depth of 0.1 mm on the surface of the nitrided layer. During use, these cracks are often used as crack sources and crack rapidly, causing the product to fail prematurely. Figure 5 It can be seen that the mold steel in the embodiment of the present invention is not prone to microcracks after nitriding, and the nitriding speed is fast and the nitriding depth is deep.

[0068] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by the terms "front and back", "left and right", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or component referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the invention.

[0069] Of course, in the present technical solution, those skilled in the art should understand that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the element may be multiple, and the term "one" should not be understood as a limitation on the quantity.

[0070] The above description in conjunction with the accompanying drawings is only a preferred embodiment of the present invention, but the present invention is not limited to the above embodiment. It should be pointed out that for those skilled in the art, various modifications and improvements can be made without departing from the structure of the present invention, which should also be regarded as the scope of protection of the present invention and will not affect the effect and practicality of the implementation of the present invention.

Claims

1. A die-casting die steel, characterized in that: Including the element composition by mass percentage: C: 0.32%-0.45%, Cr: 1.35%-1.65%, Mn: 0.3%-0.6%, Mo: 0.15%-0.25%, Si: 0.01%-0.03%, V: 0.005%-0.012%, Al: 0.7%-1.1%, Ni: 0.1%-0.3%, Fe balance.

2. The method for producing die-casting die steel according to claim 1, characterized in that: The following steps are included in sequence: S1, after mixing the weight percentage of each component element, put it into an electric furnace and smelt it under a protective atmosphere to obtain a melt; S2, keeping the melt at 1570°C-1650°C for 2.5h-3h, vacuum die-casting to obtain a casting, and multi-directional forging the casting to obtain a forging blank; S3, high temperature annealing of the forging blank; S4, rough machining, quenching and tempering the annealed forging blank; S5. Perform fine machining and nitriding on the tempered forging blank.

3. The method for producing die-casting die steel according to claim 2, characterized in that: In S1, the temperature of the electric furnace is 1570°C-1650°C.

4. The method for producing die-casting die steel according to claim 2, characterized in that: In S3, the annealing temperature is 1250°C to 1280°C, and the temperature is kept for 8h-10h.

5. The method for producing die-casting die steel according to claim 2, characterized in that: In S4, the quenching temperature is 920°C-960°C, and the temperature is kept for 30min-40min.

6. The method for producing a die-casting die steel according to claim 2, characterized in that: In S4, the tempering temperature is 580°C-600°C, and the tempering times are 2-3 times.

7. The method for producing die-casting die steel according to claim 2, characterized in that: In S4, the hardness of the forging blank after tempering is 30HRC-36HRC.

8. The method for producing die-casting die steel according to claim 2, characterized in that: In S5, the depth of the nitrided layer of the forging blank is 0.6 mm-0.8 mm.

9. The method for producing die-casting die steel according to claim 2, characterized in that: In S5, the hardness of the nitrided layer of the forging blank from the surface to 0.2 mm is greater than 1000 HV.

10. The method for producing die-casting die steel according to claim 2, characterized in that: In S5, the hardness gradient of the nitride layer decreases to a core hardness of 300 HV-330 HV.

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