Preparation method of powder metallurgy tool steel and tool steel

Abstract

The invention provides a preparation method of powder metallurgy tool steel and the powder metallurgy tool steel. The preparation method comprises the following steps: S1, preparing materials according to an element ratio, adding tool steel raw materials into a smelting ladle, heating and smelting into molten steel, adding casting powder into the molten steel, removing floating impurities, and adding a secondary deoxidizing agent for deoxidizing; s2, the deoxidized molten steel is poured into a medium-frequency induction furnace to be refined, and the medium-frequency induction furnace is covered with alkaline casting powder; s3, the molten steel obtained after the step S2 is completed is atomized and sprayed out of the medium-frequency induction furnace; and S4, collecting atomized and formed powder, and performing hot isostatic pressing to prepare a steel ingot.

Description

Technical Field

[0001] The present invention relates to the field of tool steel, and in particular to a method for preparing powder metallurgy tool steel. The present invention also relates to a tool steel prepared by the method. Background Art

[0002] Powder metallurgy tool steel is a high-grade steel made by forging and rolling a dense steel billet made by powder metallurgy method (such as hot isostatic pressing of atomized powder under vacuum packaging). It has the advantages of small heat treatment deformation, good forging and grinding performance, etc.

[0003] Due to the advantages of powder metallurgy technology, it has become the key to solving new material problems and plays a vital role in the development of new materials. Powder metallurgy is an emerging material preparation technology. Modern powder metallurgy emerged in the late 19th century and early 20th century. By the 1930s, a complete set of powder metallurgy technology was gradually formed, industrial production began to take shape, and research on the process and its mechanism also achieved certain results. In the mid-20th century, powder metallurgy production technology developed rapidly, and the application field of products continued to expand, becoming an important part of modern industry. On this basis, in order to adapt to the higher requirements of material properties and forming technology put forward by the rapid development of science and technology, a number of new powder metallurgy processes have been developed, including: hot isostatic pressing, combustion synthesis, rapid solidification, and spray forming. Summary of the invention

[0004] In view of this, the present invention proposes a method for preparing powder metallurgy tool steel to refine the tool steel structure and improve the impact toughness and wear resistance of the tool steel.

[0005] A method for preparing powder metallurgy tool steel, the method comprising the following steps:

[0006] S1. Prepare materials according to the element ratio, add tool steel raw materials into the melting ladle, heat and smelt into molten steel, add protective slag to the molten steel, remove floating impurities, and add secondary deoxidizer for deoxidation;

[0007] S2, pouring the deoxidized molten steel into a medium frequency induction furnace for refining, and covering the medium frequency induction furnace with alkaline protective slag;

[0008] S3, spraying the molten steel after step S2 from the medium frequency induction furnace in atomized form;

[0009] S4. Collect the atomized powder and hot isostatically press it into a steel ingot.

[0010] Furthermore, the heating temperature in step S1 is 200-500° C. above the liquidus temperature of the steel.

[0011] Furthermore, in step S2, the initial electromagnetic induction frequency during refining in the medium frequency induction furnace is 1500-2000 Hz, the alkaline protective slag added during smelting at this frequency is CaO, Al2O3 and SiO2, and the smelting time is 90-100 min;

[0012] Then switch the electromagnetic induction frequency to 500-900Hz. The alkaline protective slag added during smelting at this frequency is CaF2 and silicon aluminum barium calcium composite deoxidizer, and the smelting time is 60-75min;

[0013] Finally, the electromagnetic induction frequency is switched to 1000-1300 Hz. The alkaline protective slag added during smelting at this frequency is MgO and CaF2, and the smelting time is 40-55 minutes.

[0014] Furthermore, the atomization pressure of the molten steel in step S3 is 180-200 MPa.

[0015] Furthermore, the process of hot isostatic pressing to form the steel ingot in step S4 includes placing the metal powder into a bag under a protective atmosphere, vacuum degassing and sealing the bag, and hot isostatic pressing the bag.

[0016] Furthermore, the protective atmosphere adopts argon.

[0017] Furthermore, the vacuum degassing temperature of the jacket is 310-390°C and the pressure is <10Pa.

[0018] Furthermore, the temperature of hot isostatic pressing is 1350-1500° C., and the pressure is 115-135 MPa.

[0019] Furthermore, the steel grade of the powder metallurgy tool steel is HOPT15M.

[0020] The present invention also provides a powder metallurgy tool steel prepared by adopting the above-mentioned preparation method of powder metallurgy tool steel.

[0021] The preparation method of the powder metallurgy tool steel of the present invention adopts medium frequency electromagnetic induction refining, and is directly atomized and formed by a medium frequency induction furnace without passing through a tundish, and is combined with a hot isostatic pressing process, so that the prepared tool steel has a uniform and fine structure, high hardness and high wear resistance, and good plasticity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0023] Figure 1 The metallographic diagram described in Example 1 of the present invention;

[0024] Figure 2The metallographic diagram described in Example 2 of the present invention;

[0025] Figure 3 This is the metallographic diagram described in Example 5 of the present invention. DETAILED DESCRIPTION

[0026] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0027] The experimental methods in the following examples are conventional methods unless otherwise specified. The experimental materials used in the following examples are purchased from conventional markets unless otherwise specified. In addition, unless otherwise specified in this example, the terms and processes involved in this example are understood in accordance with the general knowledge and conventional methods in the prior art.

[0028] The present invention relates to a method for preparing powder metallurgy tool steel, which specifically comprises the following steps:

[0029] A method for preparing powder metallurgy tool steel, the method comprising the following steps:

[0030] S1. Prepare materials according to the element ratio, add tool steel raw materials into the melting ladle, heat to 200-500℃ above the liquidus temperature of the steel grade to smelt into molten steel, add protective slag to the molten steel to remove floating impurities, and add secondary deoxidizer for deoxidation. The weight ratio of protective slag is 25-30 parts of CaO, 10-15 parts of CaF2, 15-20 parts of Al2O3, and 20-25 parts of SiO2, and the amount of protective slag added is 2-5% of the weight of molten steel. The secondary deoxidizer is silicon aluminum barium deoxidizer, and the amount of secondary deoxidizer added is 0.03-0.08% of the weight of molten steel. The deoxidation capacity of silicon barium alloy is better than that of aluminum, and it can effectively replace aluminum for deep deoxidation. The deoxidation efficiency of barium-containing silicon alloy is not as good as that of pure aluminum, but it can accelerate the removal of inclusions from molten steel. This is mainly because barium oxide will not form high-melting point spinel with aluminum oxide, but can form low-melting point barium-containing silicate. The barium-silicon molar ratio of the preferred silicon-aluminum-barium deoxidizer of the present invention is 1:(3.3-5).

[0031] S2. Pour the deoxidized molten steel into a medium frequency induction furnace for refining, and cover the medium frequency induction furnace with alkaline protective slag. During this step of refining, set the initial electromagnetic induction frequency to 1500-2000Hz. The alkaline protective slag added during smelting at this frequency is CaO, Al2O3 and SiO2, and the smelting time is 90-100min; then switch the electromagnetic induction frequency to 500-900Hz. The alkaline protective slag added during smelting at this frequency is CaF2 and silicon aluminum barium calcium composite deoxidizer, and the smelting time is 60-75min; finally switch the electromagnetic induction frequency to 1000-1300Hz. The alkaline protective slag added during smelting at this frequency is MgO and CaF2, and the smelting time is 40-55min

[0032] S3, spraying the molten steel after step S2 from the medium frequency induction furnace in an atomized manner, adjusting the opening of the nozzle so that the atomization pressure of the molten steel is 180-200Mpa.

[0033] S4, collecting the powder formed by atomization, putting the metal powder into a bag under a protective atmosphere, vacuum degassing and sealing the bag, and hot isostatic pressing the bag into a steel ingot. The protective atmosphere uses argon, the vacuum degassing temperature of the bag is 310-390°C, the pressure is less than 10Pa, the hot isostatic pressing temperature is 1350-1500°C, and the pressure is 115-135MPa.

[0034] The steel grade of the powder metallurgy tool steel applicable to the present invention is HOPT15M.

[0035] The preparation method of the powder metallurgy tool steel of the present invention adopts medium frequency electromagnetic induction refining, and is directly atomized and formed by a medium frequency induction furnace without passing through a tundish, and is combined with a hot isostatic pressing process, so that the prepared tool steel has a uniform and fine structure, high hardness and high wear resistance, and good plasticity.

[0036] Example 1

[0037] The present embodiment relates to a method for preparing a powder metallurgy tool steel, comprising the following steps:

[0038] S1. Prepare materials according to the element ratio, add tool steel raw materials into the melting ladle, heat to 500℃ above the liquidus temperature of the steel grade to smelt into molten steel, add protective slag to the molten steel to remove floating impurities, and add secondary deoxidizer for deoxidation. The weight ratio of protective slag is 30 parts of CaO, 15 parts of CaF2, 20 parts of Al2O3, and 25 parts of SiO2, and the amount of protective slag added is 5% of the weight of the molten steel. The secondary deoxidizer is a silicon aluminum barium deoxidizer, and the amount of the secondary deoxidizer added is 0.08% of the weight of the molten steel. The molar ratio of barium to silicon of the silicon aluminum barium deoxidizer is 1:5.

[0039] S2. Pour the deoxidized molten steel into a medium frequency induction furnace for refining, and cover the medium frequency induction furnace with alkaline protective slag. During this step of refining, set the initial electromagnetic induction frequency to 2000Hz. The alkaline protective slag added during smelting at this frequency is CaO, Al2O3 and SiO2, and the smelting time is 90min; then switch the electromagnetic induction frequency to 900Hz. The alkaline protective slag added during smelting at this frequency is CaF2 and silicon aluminum barium calcium composite deoxidizer, and the smelting time is 60min; finally switch the electromagnetic induction frequency to 1300Hz. The alkaline protective slag added during smelting at this frequency is MgO and CaF2, and the smelting time is 40min.

[0040] S3. After step S2, the molten steel is sprayed out from the medium frequency induction furnace in atomized form, and the opening of the nozzle is adjusted so that the atomization pressure of the molten steel is 200 MPa.

[0041] S4, collecting the powder formed by atomization, putting the metal powder into a bag under a protective atmosphere, vacuum degassing and sealing the bag, and hot isostatic pressing the bag into a steel ingot. The protective atmosphere uses argon, the vacuum degassing temperature of the bag is 390°C, the pressure is less than 10Pa, the hot isostatic pressing temperature is 1500°C, and the pressure is 135MPa.

[0042] The steel grade of the powder metallurgy tool steel applicable to this embodiment is HOPT15M.

[0043] Example 2

[0044] The present embodiment relates to a method for preparing a powder metallurgy tool steel, comprising the following steps:

[0045] S1. Prepare materials according to the element ratio, add tool steel raw materials into the melting ladle, heat to 200℃ above the liquidus temperature of the steel grade to smelt into molten steel, add protective slag to the molten steel to remove floating impurities, and add secondary deoxidizer for deoxidation. The weight ratio of protective slag is 25 parts of CaO, 10 parts of CaF2, 15 parts of Al2O3, and 20 parts of SiO2, and the amount of protective slag added is 2% of the weight of the molten steel. The secondary deoxidizer is a silicon aluminum barium deoxidizer, and the amount of the secondary deoxidizer added is 0.03% of the weight of the molten steel. The molar ratio of barium to silicon of the silicon aluminum barium deoxidizer is 1:3.3.

[0046] S2. Pour the deoxidized molten steel into a medium frequency induction furnace for refining, and cover the medium frequency induction furnace with alkaline protective slag. When refining in this step, set the initial electromagnetic induction frequency to 1500Hz. The alkaline protective slag added during smelting at this frequency is CaO, Al2O3 and SiO2, and the smelting time is 100min; then switch the electromagnetic induction frequency to 500Hz. The alkaline protective slag added during smelting at this frequency is CaF2 and silicon aluminum barium calcium composite deoxidizer, and the smelting time is 75min; finally switch the electromagnetic induction frequency to 1000Hz. The alkaline protective slag added during smelting at this frequency is MgO and CaF2, and the smelting time is 55min.

[0047] S3. After step S2, the molten steel is sprayed out from the medium frequency induction furnace in an atomized manner, and the opening of the nozzle is adjusted so that the atomization pressure of the molten steel is 180 MPa.

[0048] S4, collecting the powder formed by atomization, putting the metal powder into a bag under a protective atmosphere, vacuum degassing and sealing the bag, and hot isostatic pressing the bag into a steel ingot. The protective atmosphere uses argon, the vacuum degassing temperature of the bag is 310°C, the pressure is less than 10Pa, the hot isostatic pressing temperature is 1350°C, and the pressure is 115MPa.

[0049] The steel grade of the powder metallurgy tool steel applicable to this embodiment is HOPT15M.

[0050] Example 3

[0051] The present embodiment relates to a method for preparing a powder metallurgy tool steel, comprising the following steps:

[0052] S1. Prepare materials according to the element ratio, add tool steel raw materials into the melting ladle, heat to 300℃ above the liquidus temperature of the steel grade to smelt into molten steel, add protective slag to the molten steel to remove floating impurities, and add secondary deoxidizer for deoxidation. The weight ratio of protective slag is 28 parts of CaO, 13 parts of CaF2, 18 parts of Al2O3, and 22 parts of SiO2, and the amount of protective slag added is 3% of the weight of the molten steel. The secondary deoxidizer is a silicon aluminum barium deoxidizer, and the amount of the secondary deoxidizer added is 0.07% of the weight of the molten steel. The molar ratio of barium to silicon of the silicon aluminum barium deoxidizer is 1:3.9.

[0053] S2. Pour the deoxidized molten steel into a medium frequency induction furnace for refining, and cover the medium frequency induction furnace with alkaline protective slag. During this step of refining, set the initial electromagnetic induction frequency to 1800Hz. The alkaline protective slag added during smelting at this frequency is CaO, Al2O3 and SiO2, and the smelting time is 95min; then switch the electromagnetic induction frequency to 650Hz. The alkaline protective slag added during smelting at this frequency is CaF2 and silicon aluminum barium calcium composite deoxidizer, and the smelting time is 70min; finally switch the electromagnetic induction frequency to 1200Hz. The alkaline protective slag added during smelting at this frequency is MgO and CaF2, and the smelting time is 45min.

[0054] S3. After step S2, the molten steel is sprayed out from the medium frequency induction furnace in an atomized manner, and the opening of the nozzle is adjusted so that the atomization pressure of the molten steel is 185 MPa.

[0055] S4, collecting the powder formed by atomization, putting the metal powder into a bag under a protective atmosphere, vacuum degassing and sealing the bag, and hot isostatic pressing the bag into a steel ingot. The protective atmosphere uses argon, the vacuum degassing temperature of the bag is 350°C, the pressure is less than 10Pa, the hot isostatic pressing temperature is 1380°C, and the pressure is 130MPa.

[0056] The steel grade of the powder metallurgy tool steel applicable to this embodiment is HOPT15M.

[0057] Example 4

[0058] The present embodiment relates to a method for preparing a powder metallurgy tool steel, comprising the following steps:

[0059] S1. Prepare materials according to the element ratio, add tool steel raw materials into the melting ladle, heat to 450℃ above the liquidus temperature of the steel grade to smelt into molten steel, add protective slag to the molten steel to remove floating impurities, and add secondary deoxidizer for deoxidation. The weight ratio of protective slag is 26 parts of CaO, 12 parts of CaF2, 19 parts of Al2O3, and 24 parts of SiO2, and the amount of protective slag added is 4.5% of the weight of molten steel. The secondary deoxidizer is a silicon aluminum barium deoxidizer, and the amount of the secondary deoxidizer added is 0.06% of the weight of the molten steel. The molar ratio of barium to silicon of the silicon aluminum barium deoxidizer is 1:4.

[0060] S2. Pour the deoxidized molten steel into a medium frequency induction furnace for refining, and cover the medium frequency induction furnace with alkaline protective slag. When refining in this step, set the initial electromagnetic induction frequency to 1800Hz. The alkaline protective slag added during smelting at this frequency is CaO, Al2O3 and SiO2, and the smelting time is 95min; then switch the electromagnetic induction frequency to 800Hz. The alkaline protective slag added during smelting at this frequency is CaF2 and silicon aluminum barium calcium composite deoxidizer, and the smelting time is 65min; finally switch the electromagnetic induction frequency to 1250Hz. The alkaline protective slag added during smelting at this frequency is MgO and CaF2, and the smelting time is 45min.

[0061] S3. After step S2, the molten steel is sprayed out from the medium frequency induction furnace in atomized form, and the opening of the nozzle is adjusted so that the atomization pressure of the molten steel is 190 MPa.

[0062] S4, collecting the powder formed by atomization, putting the metal powder into a bag under a protective atmosphere, vacuum degassing and sealing the bag, and hot isostatic pressing the bag into a steel ingot. The protective atmosphere uses argon, the vacuum degassing temperature of the bag is 350°C, the pressure is less than 10Pa, and the hot isostatic pressing temperature is 1450°C and the pressure is 130MPa.

[0063] The steel grade of the powder metallurgy tool steel applicable to this embodiment is HOPT15M.

[0064] Example 5

[0065] The present embodiment relates to a method for preparing a powder metallurgy tool steel, comprising the following steps:

[0066] S1. Prepare materials according to the element ratio, add tool steel raw materials into the melting ladle, heat to 380℃ above the liquidus temperature of the steel grade to smelt into molten steel, add protective slag to the molten steel to remove floating impurities, and add secondary deoxidizer for deoxidation. The weight ratio of protective slag is 27 parts of CaO, 13 parts of CaF2, 18 parts of Al2O3, and 23 parts of SiO2, and the amount of protective slag added is 3.5% of the weight of molten steel. The secondary deoxidizer is a silicon aluminum barium deoxidizer, and the amount of the secondary deoxidizer added is 0.07% of the weight of the molten steel. The molar ratio of barium to silicon of the silicon aluminum barium deoxidizer is 1:3.8.

[0067] S2. Pour the deoxidized molten steel into a medium frequency induction furnace for refining, and cover the medium frequency induction furnace with alkaline protective slag. When refining in this step, set the initial electromagnetic induction frequency to 1900Hz. The alkaline protective slag added during smelting at this frequency is CaO, Al2O3 and SiO2, and the smelting time is 90min; then switch the electromagnetic induction frequency to 800Hz. The alkaline protective slag added during smelting at this frequency is CaF2 and silicon aluminum barium calcium composite deoxidizer, and the smelting time is 60min; finally switch the electromagnetic induction frequency to 1150Hz. The alkaline protective slag added during smelting at this frequency is MgO and CaF2, and the smelting time is 50min.

[0068] S3. After step S2, the molten steel is sprayed out from the medium frequency induction furnace in an atomized manner, and the opening of the nozzle is adjusted so that the atomization pressure of the molten steel is 185 MPa.

[0069] S4, collecting the powder formed by atomization, putting the metal powder into a bag under a protective atmosphere, vacuum degassing and sealing the bag, and hot isostatic pressing the bag into a steel ingot. The protective atmosphere uses argon, the vacuum degassing temperature of the bag is 380°C, the pressure is less than 10Pa, the hot isostatic pressing temperature is 1390°C, and the pressure is 135MPaa.

[0070] The steel grade of the powder metallurgy tool steel applicable to this embodiment is HOPT15M.

[0071] Comparative Example 1

[0072] The preparation method of a powder metallurgy tool steel in this comparative example is basically the same as that in Example 3, except that the secondary deoxidizer in step S1 of this comparative example is a ferrosilicon deoxidizer.

[0073] Comparative Example 2

[0074] The preparation method of a powder metallurgy tool steel in this comparative example is basically the same as that in Example 3, except that the frequency of the medium frequency induction furnace during refining in step S2 of this comparative example is kept constant at 1800 Hz.

[0075] Comparative Example 3

[0076] The preparation method of a powder metallurgy tool steel in this comparative example is basically the same as that in Example 3, except that the atomization pressure in step S3 of this comparative example is 170 MPa.

[0077] Comparative Example 4

[0078] The preparation method of a powder metallurgy tool steel in this comparative example is basically the same as that in Example 3, except that the temperature of hot isostatic pressing in step S4 of this comparative example is 1300° C. and the pressure is 110 MPa.

[0079] Comparative Example 5

[0080] The preparation method of a powder metallurgy tool steel in this comparative example is basically the same as that in Example 5, except that the frequency of the medium frequency induction furnace during refining in step S2 of this comparative example is kept constant at 1900 Hz.

[0081] Comparative Example 6

[0082] The preparation method of a powder metallurgy tool steel in this comparative example is basically the same as that in Example 5, except that the atomization pressure in step S3 of this comparative example is 165 MPa.

[0083] The preparation method of the powder metallurgy tool steel of the present invention adopts medium frequency electromagnetic induction refining, and multi-frequency regulation is used to divide the refining process into three stages. Different slag systems are used in different stages with different smelting times to further improve the purity and deoxidation level of the molten steel. The powder is directly atomized and formed by a medium frequency induction furnace without passing through a tundish. The powder particle size can be controlled in a smaller range by controlling the atomizing gas pressure. In combination with the hot isostatic pressing process, the tool steel obtained can have a uniform and fine structure, high purity, high hardness and high wear resistance, and good plasticity.

[0084] The above embodiments and comparative examples were subjected to impact toughness test, wear test and corrosion resistance test, and the test results are shown in the following table:

[0085]

[0086] The above-mentioned embodiments show that the impact toughness, wear resistance and corrosion resistance of the tool steel prepared by the preparation method of the present invention are better than those of the comparative examples, and the tool steel has excellent comprehensive performance.

[0087] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0088] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A method for preparing powder metallurgy tool steel, characterized in that: The preparation method comprises the following steps: S1. Prepare materials according to the element ratio, add tool steel raw materials into the melting ladle, heat and smelt into molten steel, add protective slag to the molten steel, remove floating impurities, and add secondary deoxidizer for deoxidation; S2, pouring the deoxidized molten steel into a medium frequency induction furnace for refining, and covering the medium frequency induction furnace with alkaline protective slag; S3, spraying the molten steel after step S2 from the medium frequency induction furnace in atomized form; S4. Collect the atomized powder and hot isostatically press it into a steel ingot.

2. The powder metallurgy tool steel according to claim 1, characterized in that: The heating temperature in step S1 is 200-500° C. above the liquidus temperature of the steel.

3. The powder metallurgy tool steel according to claim 1, characterized in that: In step S2, the initial electromagnetic induction frequency of the medium frequency induction furnace is 1500-2000 Hz, the alkaline protective slag added during smelting at this frequency is CaO, Al2O3 and SiO2, and the smelting time is 90-100 min; Then switch the electromagnetic induction frequency to 500-900Hz. The alkaline protective slag added during smelting at this frequency is CaF2 and silicon aluminum barium calcium composite deoxidizer, and the smelting time is 60-75min; Finally, the electromagnetic induction frequency is switched to 1000-1300 Hz. The alkaline protective slag added during smelting at this frequency is MgO and CaF2, and the smelting time is 40-55 minutes.

4. The powder metallurgy tool steel according to claim 1, characterized in that: The atomization pressure of the molten steel in step S3 is 180-200 MPa.

5. The powder metallurgy tool steel according to claim 1, characterized in that: The process of hot isostatic pressing to form a steel ingot in step S4 includes placing metal powder into a bag under a protective atmosphere, vacuum degassing and sealing the bag, and hot isostatic pressing the bag.

6. The powder metallurgy tool steel according to claim 5, characterized in that: The protective atmosphere used was argon.

7. The powder metallurgy tool steel according to claim 5, characterized in that: The vacuum degassing temperature of the package is 310-390℃, and the pressure is less than 10Pa.

8. The powder metallurgy tool steel according to claim 5, characterized in that: The temperature of hot isostatic pressing is 1350-1500°C and the pressure is 115-135MPa.

9. The powder metallurgy tool steel according to any one of claims 1 to 8, characterized in that: The steel grade of the powder metallurgy tool steel is HOPT15M.

10. A powder metallurgy tool steel prepared by the method for preparing powder metallurgy tool steel according to any one of claims 1 to 9.

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