A method for preparing high-titanium content powder metallurgy high-speed steel

Abstract

The invention discloses a method for preparing a powder metallurgy high-speed steel with a high titanium content, and in particular relates to a method for hardening the powder metallurgy high-speed steel by in-situ generating titanium-rich carbon (nitride) during the sintering process. The invention forms a metastable material by high-energy ball milling of high-speed steel pre-alloy powder and titanium source powder, and then uniformly mixes with carbon black and a forming agent and cold presses the material, and sintering is performed in a vacuum or low-pressure nitrogen atmosphere to obtain a powder metallurgy high-speed steel with a titanium content of 2 to 9 wt.%. During the sintering process, titanium and carbon (nitrogen) react in-situ to generate dispersed, nearly spherical strong carbon (nitride), which can enable the sintered high-speed steel to maintain a high strength while improving hardness and wear resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder metallurgy high-speed steel preparation, and specifically relates to a method for preparing powder metallurgy high-speed steel with high titanium content, and more particularly to a method for hardening powder metallurgy high-speed steel by in-situ generating titanium-rich carbon (nitride) during sintering. Background Art

[0002] As a kind of ledeburite steel, high speed steel has high hardness, wear resistance, good combination of strength and toughness, and corresponding high temperature working performance. It has become the preferred material for manufacturing various modern cutting tools and molds, especially cutting tools with complex shapes. Compared with traditional cast and forged high speed steel, the preparation of powder metallurgy high speed steel by sintering pre-alloyed powder can inhibit segregation, and has fine grains, uniform carbide distribution, higher strength, toughness and wear resistance.

[0003] With the increasing use of difficult-to-process materials such as titanium alloys, special performance steels, and high-temperature alloys, the modern machining industry has put forward higher requirements for the mechanical properties of tool and die materials, such as hardness, wear resistance, strength, and impact toughness. Powder metallurgy high-speed steel often competes with cemented carbide for use as cutting tool materials. Compared with superhard tool materials, the relatively low manufacturing cost and high toughness of powder metallurgy high-speed steel are more acceptable, but the hardness and wear resistance of powder metallurgy high-speed steel need to be further improved compared with superhard tool materials. Hard carbide particles are often used to reinforce high-speed steel, and the use of the two composites is expected to combine their respective advantages. TiC (or TiCN) is a typical hard reinforcement particle with high hardness and thermal stability. Its composite with high-speed steel has great potential to improve the red hardness and adhesion resistance of the material. However, after mixing TiC (or TiCN) particles into high-speed steel powder, high-speed steel is prepared by forming and sintering. There are problems such as particles are not easy to disperse, carbides often gather at grain boundaries after sintering, and poor bonding with the matrix interface, which significantly reduces the strength and toughness of the material. Due to the strong affinity between Ti and C, only a small amount of Ti is usually added as an inoculant during steel smelting. Too much Ti will form coarse carbides in the melt, and the Ti element is also easily oxidized and burned at high temperatures. Therefore, whether it is conventional smelting of high-speed steel or manufacturing of high-speed steel powder, it is difficult to increase the Ti content in the steel, and it is impossible to directly form a large amount of Ti carbides in the steel. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing powder metallurgy high-speed steel with high titanium content, in view of the fact that the content of strong carbides in traditional high-speed steel casting and forging / powder metallurgy high-speed steel is insufficient, and the hardness and other properties are difficult to meet the processing requirements of difficult-to-process materials such as titanium alloys, special performance steels, and high-temperature alloys; and it is difficult to increase the Ti content and form a large number of Ti-rich carbides in traditional high-speed steel casting and forging / powder metallurgy high-speed steel, and it is difficult to make the reinforcement phase uniformly distributed after sintering after adding TiC (or TiCN) particles to the high-speed steel powder, which significantly reduces the strength and toughness of the material. The powder metallurgy high-speed steel prepared by the preparation method of the present invention has a titanium content greater than 1%, and has the characteristics of high density and high mechanical properties.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] The invention discloses a preparation method of powder metallurgy high-speed steel with high titanium content. The method comprises the following steps: high-energy ball milling is performed on pre-alloyed high-speed steel raw material powder and titanium source powder to form a metastable powder with supersaturated solid solution of Ti, and then the powder is mixed with carbon powder and a forming agent to obtain a raw material mixed powder, and the raw material mixed powder is pressed to obtain a green body, and the green body is sintered in a vacuum environment or a low-pressure nitrogen atmosphere to obtain a powder metallurgy high-speed steel with in-situ generated titanium-rich carbide or carbonitride.

[0007] The preparation method of the present invention firstly adopts high-energy ball milling of pre-alloyed high-speed steel raw material powder and titanium source powder to form a metastable powder with supersaturated solid solution of Ti. The inventors have found that the Ti element can be solid-dissolved in the high-speed steel powder by mechanical alloying, and then after the powder is formed and sintered, a dispersed Ti-rich carbon (nitride) is formed in situ, and the size and morphology of the carbon (nitride) are controllable, and the interface bonding strength with the matrix is ​​high, which can significantly improve the hardness and wear resistance while maintaining or slightly reducing the toughness of the high-speed steel.

[0008] As a preferred embodiment, the present invention provides a method for preparing high-titanium content powder metallurgy high-speed steel: the high-speed steel raw material powder is selected from one of high-speed steel T15 powder, high-speed steel T42 powder, high-speed steel M2 powder, high-speed steel M3:2 powder and high-speed steel M4 powder.

[0009] The high-speed steel raw material powders used in the present invention are all commercially available high-speed steel pre-alloyed powders.

[0010] As a preferred embodiment, the present invention discloses a method for preparing high-titanium content powder metallurgy high-speed steel, wherein the titanium source powder is titanium powder and / or titanium-iron master alloy powder. The titanium source powder in the present invention adopts commercially available titanium source powder.

[0011] As a preferred solution, the present invention discloses a method for preparing high-titanium content powder metallurgy high-speed steel, wherein the titanium source powder is added in an amount of 2-9% of the mass of the raw material mixed powder in terms of titanium. The titanium content is controlled within this range, and the performance of the final obtained material is optimal. If the amount of titanium source powder added is too much, the carbide content formed is more, and the plastic toughness loss of the high-speed steel is relatively large; if the amount added is too little, the hardness improvement is not obvious.

[0012] As a further preferred solution, the titanium powder is hydrogenated dehydrogenated titanium powder. The amount of the added titanium powder is 2-9% of the mass of the raw material mixed powder. The inventors found that hydrogenated dehydrogenated titanium powder has a small particle size, is easier to mechanically alloy, and has a low oxygen content. The powder metallurgy high-speed steel obtained by using it as a raw material has better performance.

[0013] As a further preferred solution, the titanium-iron master alloy powder is FeTi70-A powder. Since the Ti content of FeTi70-A powder is 70%, the added amount thereof is 3-13% of the mass of the raw material mixed powder.

[0014] As a preferred embodiment, the present invention discloses a method for preparing a powder metallurgy high-speed steel with a high titanium content, wherein the high-energy ball milling is carried out under a protective atmosphere, the ball-to-material ratio is 10-15:1, the rotation speed of the high-energy ball milling is 200-400 rpm, and the time of the high-energy ball milling is 24-48 hours. By adopting the above-mentioned ball milling process, the Ti element can be mechanically alloyed in the high-speed steel matrix, breaking through the solid solubility limit of the Ti element in the high-speed steel matrix, and forming a metastable powder of Ti supersaturated solid solution. On the one hand, Ti is evenly distributed in the iron matrix, laying a good foundation for the in-situ dispersion and precipitation of Ti-rich carbon (nitride) during the sintering process; on the other hand, the activity of Ti is reduced, and the difficulty of reducing metal oxides is reduced. In addition, the particle size of the powder after high-energy ball milling is reduced, the metal oxides are fully reduced in a vacuum atmosphere, the sintering activity is increased, and the sintering densification of the formed green body is promoted.

[0015] In a further preferred embodiment, during the high-ball milling, the milling jar and the grinding balls are both made of stainless steel.

[0016] As a preferred embodiment, the present invention discloses a method for preparing high-titanium content powder metallurgy high-speed steel, wherein the carbon powder is colloidal graphite, and the particle size of the carbon powder is 1 to 3 μm. The inventors have found that the colloidal graphite with the above particle size can be better dispersed in the mixed powder, thereby facilitating the in-situ formation of titanium-rich carbides or carbonitrides during sintering.

[0017] As a preferred solution, the present invention discloses a method for preparing high-titanium content powder metallurgy high-speed steel, wherein the amount of carbon powder added is 0.8-2.5% of the mass of the raw material mixed powder. The performance is optimal when the content of carbon powder is controlled within this range. If the content of carbon powder is too small, it is not conducive to the full formation of carbides by Ti, and if it is too much, it will cause coarse carbides, which is harmful to mechanical properties.

[0018] As a preferred embodiment, the present invention discloses a method for preparing high-titanium content powder metallurgy high-speed steel, wherein the molding agent is polyethylene glycol 4000, and the addition amount of the polyethylene glycol 4000 is 1-2% of the mass of the raw material mixed powder.

[0019] As a preferred embodiment, the present invention discloses a method for preparing high-titanium content powder metallurgy high-speed steel: the pressing and forming method is cold pressing, and the pressing and forming pressure is 100-200 MPa.

[0020] As a preferred embodiment, the present invention discloses a method for preparing a high titanium content powder metallurgy high speed steel: when sintering in a vacuum environment, the vacuum degree is ≤10 -2 Pa, the sintering temperature is 1140-1220℃, and the sintering time is 60-120min.

[0021] Titanium-rich carbide-reinforced powder metallurgy high-speed steel is formed under a vacuum environment.

[0022] As a preferred embodiment, the present invention discloses a method for preparing a high-titanium content powder metallurgy high-speed steel: when sintering in a low-pressure nitrogen atmosphere, the temperature is first raised to the sintering temperature under vacuum, and then nitrogen is introduced to make the nitrogen atmosphere pressure 10 2 ~10 4 Pa, the sintering temperature is 1120~1200℃, and the sintering time is 60-120min. High-purity nitrogen is used in the actual operation process.

[0023] In a low-pressure nitrogen atmosphere, nitrogen can replace part of the carbon in high-speed steel and form a carbonitride strengthening phase with titanium.

[0024] The present invention discloses a method for preparing high-titanium content powder metallurgy high-speed steel, comprising the following steps:

[0025] Step 1

[0026] Weigh high-speed steel raw material powder and titanium source powder, with Ti element accounting for 2-9wt.% of the raw material mixed powder, place the two powders in a ball mill, then evacuate, fill with inert gas, such as argon, and seal. Mechanically alloy the titanium element through high-energy ball milling to form a metastable powder of supersaturated solid solution of the titanium element, then add 0.8-2.5wt.% of carbon powder and 1-2wt.% of polyethylene glycol 4000 to the ball mill, add an appropriate amount of anhydrous ethanol and wet mill, place the mixed powder in a vacuum drying oven to completely dry, and then pass through a 100-mesh standard sieve.

[0027] Step 2

[0028] The ball-milled mixed powder is molded using a press at a pressure of 100 to 200 MPa.

[0029] Step 3

[0030] The pressed green body is placed in a vacuum chamber with a degree of vacuum better than 10 -2 Pa atmosphere, the sintering temperature is 1140 ~ 1220 ℃, the holding time is 60-120min; or firstly heat to 1120 ~ 1200 ℃ under vacuum, and then introduce nitrogen to keep the nitrogen pressure in the furnace at 10 2 ~10 4 Pa, sintering for 60-120min, and then cooling with the furnace to obtain powder metallurgy high-speed steel with high titanium content.

[0031] The invention can produce blanks with various complicated shapes through common die pressing.

[0032] A high-titanium content powder metallurgy high-speed steel prepared by the above-mentioned method of the present invention has a titanium content of 2 to 9wt.%. During the sintering process, titanium and carbon (nitrogen) react in situ to form dispersed and nearly spherical carbon (nitride), which can enable the sintered high-speed steel to maintain a high strength while improving hardness and wear resistance.

[0033] Principles and advantages

[0034] The present invention mechanically alloys the Ti element in the high-speed steel matrix by high-energy ball milling high-speed steel raw material powder and titanium source powder under an inert atmosphere, breaking through the solid solubility limit of the Ti element in the high-speed steel matrix. On the one hand, the Ti is evenly distributed in the iron matrix, laying a good foundation for the in-situ dispersion and precipitation of Ti-rich carbon (nitride) during the sintering process; on the other hand, the activity of Ti is reduced, and the difficulty of reducing the metal oxide is reduced. In addition, the particle size of the powder after high-energy ball milling is reduced, the metal oxide is fully reduced in a vacuum atmosphere, the sintering activity is increased, and the sintering densification of the formed green body is promoted.

[0035] The present invention can also use a low-pressure nitrogen atmosphere during the sintering and heat preservation stage. The nitrogen element can replace part of the carbon in the high-speed steel and form a carbonitride strengthening phase with titanium and vanadium; and the excess carbon dissolves into the matrix, which can reduce the temperature of liquid phase generation, thereby reducing the sintering densification temperature.

[0036] In summary, the present invention increases the solid solubility limit of the Ti element and the sintering activity of the powder by high-energy ball milling of high-speed steel raw material powder and titanium source powder. During the powder sintering process, Ti-rich carbon (nitride) is generated by in-situ reaction to strengthen the matrix, thereby obtaining a powder metallurgy high-speed steel sintered body with high density and high mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a scanning electron microscope photograph of the sintered state of the high-titanium content powder metallurgy high-speed steel prepared in Example 5 of the present invention. From the figure, it can be seen that nearly spherical Ti-rich carbides are dispersed in the powder metallurgy high-speed steel matrix. DETAILED DESCRIPTION

[0038] Example 1

[0039] Step 1

[0040] Weigh high-speed steel raw material powder and titanium source powder. The high-speed steel raw material powder is ordinary M2 high-speed steel powder on the market, and the titanium source powder is hydrogenated dehydrogenated titanium powder, accounting for 9% of the mass of the raw material mixed powder. The two powders are placed in a ball mill, and then evacuated and filled with argon to seal. The ball mill is placed on a planetary ball mill for high-energy ball milling. During high-energy ball milling, stainless steel ball mills and grinding balls are used, and the ball-to-material ratio is controlled to be 10:1. The speed of the high-energy ball mill is 200rpm, and the high-energy ball milling time is 48h to fully alloy the Ti element. Then add 2.5wt.% of carbon powder and 2wt.% of polyethylene glycol 4000 to the ball mill, and add an appropriate amount of anhydrous ethanol and wet ball mill. The evenly mixed powder is placed in a central control drying oven to completely dry, and then passed through a 100-mesh standard sieve to obtain an evenly mixed raw material mixed powder.

[0041] Step 2

[0042] The ball-milled mixed raw material powder was pressed into a mold using a press machine at a pressure of 200 MPa.

[0043] Step 3

[0044] The pressed green body is placed in a vacuum chamber with a degree of vacuum better than 10 -2 The steel was sintered in an atmosphere of Pa at a temperature of 1220°C for 120 minutes and then cooled to room temperature. The density of the sintered high-speed steel reached 98.3% and the hardness reached 64HRC.

[0045] Example 2

[0046] The other conditions are consistent with those in the embodiment, except that: the sintering is carried out in a low-pressure nitrogen atmosphere, the pressure is 10 4 Pa, sintering temperature is 1200℃. The density of sintered high speed steel reaches 98.7% and hardness reaches 65HRC.

[0047] Example 3

[0048] Step 1

[0049] Weigh high-speed steel raw material powder and titanium source powder. The high-speed steel raw material powder is ordinary M2 high-speed steel powder on the market, and the titanium source powder is FeTi70-A powder, which accounts for 8% of the mass of the raw material mixed powder. The two powders are placed in a ball mill, and then vacuumed and filled with argon to seal. The ball mill is placed on a planetary ball mill for high-energy ball milling. During high-energy ball milling, stainless steel ball mills and grinding balls are used, and the ball-to-material ratio is controlled to be 10:1. The speed of the high-energy ball mill is 300rpm, and the time of high-energy ball milling is 32h to fully alloy the Ti element. Then add 1.5wt.% of carbon powder and 2wt.% of polyethylene glycol 4000 to the ball mill, and add an appropriate amount of anhydrous ethanol and wet ball mill. The evenly mixed powder is placed in a central control drying oven for complete drying, and then passed through a 100-mesh standard sieve to obtain an evenly mixed raw material mixed powder.

[0050] Step 2

[0051] The raw material mixed powder after ball milling is molded by a press machine at a pressure of 150 MPa.

[0052] Step 3

[0053] The pressed green body is placed in a vacuum chamber with a degree of vacuum better than 10 -2 The steel was sintered in an atmosphere of Pa at a temperature of 1180°C for 90 minutes and then cooled to room temperature. The density of the sintered high-speed steel reached 98.5% and the hardness reached 62HRC.

[0054] Example 4

[0055] The other conditions are the same as those in the embodiment, except that the sintering is carried out in a low-pressure nitrogen atmosphere with a pressure of 10 4 Pa, sintering temperature is 1170℃. The density of sintered high speed steel reaches 98.9% and hardness reaches 63HRC.

[0056] Comparative Example 1

[0057] Other conditions are consistent with the embodiment, except that the M2 high-speed steel powder and the FeTi70-A powder are only mixed but not high-energy ball milled, the density of the sintered high-speed steel is less than 98%, and the carbides in the microstructure are irregular in shape, coarse and evenly distributed.

[0058] Example 5

[0059] Step 1

[0060] Weigh high-speed steel raw material powder and titanium source powder. The high-speed steel raw material powder is ordinary M2 high-speed steel powder on the market, and the titanium source powder is hydrogenated dehydrogenated titanium powder, accounting for 2% of the mass of the raw material mixed powder. The two powders are placed in a ball mill, and then evacuated and filled with argon to seal. The ball mill is placed on a planetary ball mill for high-energy ball milling. During high-energy ball milling, stainless steel ball mills and grinding balls are used, and the ball-to-material ratio is controlled to be 15:1. The speed of the high-energy ball mill is 400rpm, and the high-energy ball milling time is 24h to fully alloy the Ti element. Then add 0.8wt.% of carbon powder and 2wt.% of polyethylene glycol 4000 to the ball mill, and add an appropriate amount of anhydrous ethanol and wet ball mill. The evenly mixed powder is placed in a central control drying oven for complete drying, and then passed through a 100-mesh standard sieve to obtain an evenly mixed raw material mixed powder.

[0061] Step 2

[0062] The raw material mixed powder after ball milling is molded by a press machine at a pressure of 100 MPa.

[0063] Step 3

[0064] The pressed green body is placed in a vacuum chamber with a degree of vacuum better than 10 -2 The steel was sintered in an atmosphere of Pa at a temperature of 1140°C for 60 minutes and then cooled to room temperature. The density of the sintered high-speed steel reached 99.0% and the hardness reached 59HRC.

[0065] Example 6

[0066] The other conditions are the same as those in the embodiment, except that the sintering is carried out in a low-pressure nitrogen atmosphere with a pressure of 10 4 Pa, sintering temperature is 1120℃. The density of sintered high speed steel reaches 99.2% and hardness reaches 60HRC.

Claims

1. A method for preparing high titanium content powder metallurgy high speed steel, characterized in that: The pre-alloyed high-speed steel raw material powder and titanium source powder are subjected to high-energy ball milling to form a metastable powder with supersaturated solid solution of Ti, which is then mixed with carbon powder and a forming agent to obtain a raw material mixed powder, which is pressed to obtain a green body, and the green body is sintered in a vacuum environment or a low-pressure nitrogen atmosphere to obtain a powder metallurgy high-speed steel with in-situ generated titanium-rich carbide or carbonitride; The titanium source powder is hydrogenated dehydrogenated titanium powder and / or titanium-iron master alloy powder; The amount of the titanium source powder added is 2-9% of the mass of the raw material mixed powder in terms of titanium; The high-energy ball milling is carried out under a protective atmosphere, the ball-to-material ratio is 10-15:1, the rotation speed of the high-energy ball milling is 200-400 rpm, and the high-energy ball milling time is 24-48 h; When sintering in vacuum environment, the vacuum degree is ≤10 -2 Pa, the sintering temperature is 1140~1220℃, and the sintering time is 60-120 min; When sintering in a low-pressure nitrogen atmosphere, first heat to the sintering temperature under vacuum, then introduce nitrogen to make the nitrogen atmosphere pressure 10 2 ~10 4 Pa, the sintering temperature is 1120~1200℃, and the sintering time is 60-120 min.

2. The method for preparing a high titanium content powder metallurgy high speed steel according to claim 1, characterized in that: The high-speed steel raw material powder is selected from one of high-speed steel T15 powder, high-speed steel T42 powder, high-speed steel M2 powder, high-speed steel M3:2 powder and high-speed steel M4 powder.

3. The method for preparing a high titanium content powder metallurgy high speed steel according to claim 2, characterized in that: The titanium-iron master alloy powder is FeTi70-A powder.

4. A method for preparing a high titanium content powder metallurgy high speed steel according to any one of claims 1 to 3, characterized in that: The high-energy ball milling is carried out under a protective atmosphere, the ball-to-material ratio is 10-15:1, the rotation speed of the high-energy ball milling is 200-400 rpm, and the high-energy ball milling time is 24-48 h; During the high-energy ball milling, the ball milling jar and the grinding balls are made of stainless steel.

5. The method for preparing a high titanium content powder metallurgy high speed steel according to any one of claims 1 to 3, characterized in that: The carbon powder is colloidal graphite, and the particle size of the carbon powder is 1-3 μm; The amount of carbon powder added is 0.8-2.5% of the mass of the raw material mixed powder.

6. A method for preparing a high titanium content powder metallurgy high speed steel according to any one of claims 1 to 3, characterized in that: The molding agent is polyethylene glycol 4000, and the addition amount of the polyethylene glycol 4000 is 1-2% of the mass of the raw material mixed powder.

7. A method for preparing a high titanium content powder metallurgy high speed steel according to any one of claims 1 to 3, characterized in that: The pressing method is cold pressing, and the pressing pressure is 100-200 MPa.

Images