Carbon-free high speed steel and powder metallurgical production method and use thereof

Abstract

The application belongs to the field of high-speed steel, and specifically discloses a carbon-free high-speed steel, which comprises a steel base body and intermetallic compounds dispersedly distributed in the base body; the intermetallic compounds comprise mu phase, sigma phase, B2 phase and gamma prime phase; the mu phase comprises at least one of Fe7W6, Fe7Mo6, Co7W6 and Co7Mo6; the sigma phase comprises FeCrMo; the B2 phase comprises FeAl; the gamma prime phase comprises at least one of Ni3Al and Co3Al; in the carbon-free high-speed steel, the mass percentage of each element is as follows: Co: 10-30%, Mo: 5-20%, W: 2-10%, the total content of Cr, Ni and Al: 7-22%, and the balance is Fe; the mass ratio of Cr, Ni and Al: 1-3:1-2:1-2. The application also discloses preparation and application of the carbon-free high-speed steel. The application innovatively proposes a brand-new carbon-free high-speed steel, which can realize synergistic strengthening, and can make the high-speed steel have excellent hot hardness, red hardness and high thermal conductivity, and excellent water corrosion resistance and high-temperature oxidation resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of alloy, in particular to the technical field of high speed steel preparation. BACKGROUND

[0002] Traditional high speed steel is mainly composed of high wear-resistant and high-hardness carbide and excellent toughness steel matrix. High speed steel has many advantages such as high red hardness, good wear resistance, good combination of strength and toughness, and performance adjustment by heat treatment, and has unique advantages in manufacturing complex thin blades and impact-resistant cutters, high-performance cold working dies, rolls, high-temperature bearings, etc. However, as a high-alloy ledeburite steel, high speed steel has coarse organization and serious alloy element segregation. The development of powder metallurgy large equipment obtains powder metallurgy high speed steel with fine and uniform organization by gas atomization + HIP process, but high speed steel with high hardness and high wear resistance by adding high carbon still has obvious performance short board: 1) high tendency of decarburization at high temperature during heat treatment, and hardening and deformation of the material during quenching, high tendency of thermal cracking, and difficult to correct the size and shape change by pressure straightening and machining; 2) based on the secondary hardening mechanism of tempering carbide precipitation, the highest temperature corresponding to the peak value of tempering hardness is 560-570℃, and the hardness of over-tempered state decreases sharply; 3) due to the addition of a large amount of carbon and carbide forming elements, the thermal conductivity is low (such as ASP30 thermal conductivity at room temperature is 22 W / (m.K)). Due to the above-mentioned shortcomings of traditional high speed steel, its application in high temperature and severe working conditions is greatly limited. For example, in the field of cutting tools for difficult-to-machine materials such as titanium alloy, high-temperature alloy and stainless steel, high speed steel is obviously difficult to perform, while cemented carbide is weak in the above-mentioned difficult-to-machine materials due to its poor oxidation resistance and insufficient toughness. Therefore, it is urgent to develop cutting tool materials with high thermal conductivity and good hot hardness for difficult-to-machine materials such as titanium alloy, high-temperature alloy and stainless steel.

[0003] Patent CN111793773A discloses a carbon-free high-speed steel hardened by Laves phase and mu phase, which realizes hardening by in-situ precipitation of dispersedly distributed nanoscale intermetallic compounds. The precipitated phase generated by in-situ reaction of transition elements and refractory elements has high diffusion activation energy and good thermal stability, which endows the material with excellent thermal hardness and red hardness. The carbon-free high-speed steel with coherent strain hardening obtained by high-density nanoscale intermetallic compound precipitation is expected to be suitable for tool materials for machining of difficult-to-machine metals such as titanium alloy, high-temperature alloy and stainless steel. However, the carbon-free high-speed steel still has deficiencies in complex application conditions, especially in wet milling and cutting conditions. The microstructure distribution of the carbon-free high-speed steel is that intermetallic compounds are dispersedly distributed in the ferrite matrix, and the corrosion potential difference between the ferrite matrix and the intermetallic compounds is large, which leads to poor corrosion resistance of the carbon-free high-speed steel. In addition, the elements (Al, Ni and Cr) prone to form passive film are not present in the composition ratio, which can easily cause corrosion of the tool in wet conditions and humid environment, thereby leading to failure of the tool. In addition, the main component of the carbon-free high-speed steel is iron, although its high-temperature performance is outstanding, but the loose ferric oxide oxide film layer on the surface in the high-temperature environment service is difficult to hinder the diffusion of oxygen to the matrix, thereby causing continuous oxidation of the material and loose shedding of the surface layer.

[0004] In summary, the existing carbon-free high-speed steel is difficult to balance high room temperature, high temperature hardness, toughness, corrosion resistance and oxidation resistance. SUMMARY

[0005] In order to solve the problem that the carbon-free high-speed steel is difficult to balance room temperature, high temperature hardness, corrosion resistance and oxidation resistance, the first object of the present application is to provide a carbon-free powder metallurgy high-speed steel, which aims to provide a carbon-free high-speed steel that balances excellent hardness, corrosion resistance and high-temperature oxidation resistance.

[0006] The second object of the present application is to provide a preparation method of the high-speed steel, which aims to prepare a new high-speed steel that balances excellent hardness, corrosion resistance and oxidation resistance.

[0007] The third object of the present application is to provide an application of the carbon-free high-speed steel in preparing alloy products.

[0008] For the carbon-free powder metallurgy high-speed steel, in order to improve its corrosion resistance and high-temperature oxidation resistance, its hardness and toughness are often sacrificed, and it is difficult to balance high room temperature, high temperature hardness, high corrosion resistance and high-temperature oxidation resistance. In view of this problem, the present application provides the following solutions:

[0009] A carbon-free high-speed steel, comprising a steel matrix and intermetallic compounds dispersedly distributed in the matrix;

[0010] The intermetallic compound comprises a mu phase, a sigma phase, a B2 phase and a gamma' phase, wherein the mu phase comprises at least one of Fe7W6, Fe7Mo6, Co7W6 and Co7Mo6; the sigma phase comprises FeCrMo; the B2 phase comprises FeAl; and the gamma' phase comprises at least one of Ni3Al and Co3Al.

[0011] In the carbon-free high-speed steel, the mass percentage of each element is as follows: Co: 10-30%, Mo: 5-20%, W: 2-10%, wherein the total content of Cr, Ni and Al is 7-22%, and the balance is Fe.

[0012] The mass ratio of Cr, Ni and Al is 1-3:1-2:1-2.

[0013] In view of the problem that the carbon-free high-speed steel is difficult to balance high hardness, high temperature hardness, corrosion resistance and oxidation resistance during high temperature service, the application innovatively provides a carbon-free high-speed steel which is synergistically reinforced by a mu phase, a sigma phase, a B2 phase and a gamma' phase, and further based on the joint control of the element ratio between the intermetallic compounds, the synergistic reinforcement can be realized, and the high-speed steel can have excellent hot hardness, red hardness and high thermal conductivity, and excellent water corrosion resistance and high temperature oxidation resistance.

[0014] In the application, the joint control of the composition and element ratio of the carbon-free high-speed steel which is synergistically reinforced by the intermetallic compounds of the mu phase, the sigma phase, the B2 phase and the gamma' phase is the key to realize the synergistic reinforcement and balance the excellent hardness, corrosion resistance and high temperature oxidation resistance of the high-speed steel.

[0015] Preferably, the intermetallic compound mu phase has micron-sized sintered primary phases (≤5 microns) and nanometer-sized secondary precipitated phases (≤100 nanometers), the sigma phase is a micron-sized phase (≤5 microns), and the B2 phase and the gamma' phase are nanometer-sized phases (≤200 nanometers).

[0016] The mu phase comprises Fe7W6, Fe7Mo6, Co7W6 and Co7Mo6; the sigma phase is FeCrMo; the B2 phase is FeAl; and the gamma' phase is Ni3Al and Co3Al.

[0017] Preferably, in the carbon-free high-speed steel, the mass percentage of each element is as follows: Co: 13-27%, Mo: 10-18%, W: 4-8%, wherein the total content of Cr, Ni and Al is 8-19%, and the balance is Fe.

[0018] Preferably, Co: 18-26%, Mo: 12-17%, W: 4-7%, wherein the total content of Cr, Ni and Al is 11-19%, and the balance is Fe.

[0019] More preferably, Co: 21-25%, Mo: 13-16%, W: 4-6%, wherein the total content of Cr, Ni and Al is 12-16%, and the balance is Fe;

[0020] Preferably, the mass ratio of Cr, Ni, and Al is 1.5–2:1:1;

[0021] Preferably, the carbon-free high-speed steel is allowed to contain unavoidable impurities, and the impurity content is preferably below 0.02%.

[0022] In a preferred embodiment, the carbon-free high-speed steel has a hardness of 63-70 HRC, a bending strength of 2300-3400 MPa, and an impact toughness of 6-14 J / cm. 2 The fracture toughness is 24–38 MPa.m. 1 / 2 The corrosion rate measured in deionized water is less than 7 × 10⁻⁶. - 3 mm / a, after continuous oxidation at 700℃ in a muffle furnace for 100 hours, the weight gain due to oxidation is less than 2×10. -4 g / cm 2 .

[0023] A further preferred embodiment is that the carbon-free high-speed steel has a hardness of 65-70 HRC, a bending strength of 2700-3400 MPa, and an impact toughness of 9-14 J / cm. 2 The fracture toughness is 28–38 MPa.m. 1 / 2 The corrosion rate measured in deionized water is less than 4 × 10⁻⁶. -3 After continuous oxidation at 700℃ for 100 hours in a muffle furnace, the oxidation weight gain is less than 1.3 × 10 mm / a. -4 g / cm 2 .

[0024] This invention also aims to provide a powder metallurgy preparation method for the aforementioned carbon-free high-speed steel, comprising the following steps:

[0025] Step (1): Ingredients

[0026] Prepare the required raw material powder containing metal powder A and reinforcing additives according to the element content of the carbon-free high-speed steel described above;

[0027] The metal powder A is a powder containing elemental metals such as cobalt, molybdenum, tungsten, and iron, or an alloy powder containing two or more of these metals.

[0028] The reinforcing additive is an alloy powder capable of providing the required mass ratio of Cr, Ni, and Al;

[0029] Step (2): Shaping and sintering

[0030] The raw material powder is shaped, compacted, and sintered to obtain a sintered compact;

[0031] Step (3): deformation annealing

[0032] The sintered compact is preheated and deformed at 1150-1230°C, and then air-cooled to obtain a deformed compact, which is then annealed at 800-900°C and cooled in the furnace to obtain an annealed deformed compact;

[0033] Step (4): solid solution

[0034] The annealed deformed compact in step (3) is subjected to solid solution treatment, and then aged after cooling to room temperature, to obtain the carbon-free high-speed steel.

[0035] In view of the problems in the preparation of the carbon-free high-speed steel according to the characteristics of the present application, such as difficulty in forming intermetallic compounds corresponding to μ phase, σ phase, B2 phase and γ' phase, difficulty in controlling grain size, and difficulty in regulating the uniform distribution state, the present application innovatively performs powder metallurgy treatment with the aid of reinforcing additives, and controls the synergistic combination of Cr, Ni and Al elements in the reinforcing additives, the proportion, alloying form, and the temperature of the sintering, thermal deformation, solid solution treatment and other steps in the powder metallurgy process, to promote the formation of composite intermetallic compounds of μ phase, σ phase, B2 phase and γ' phase, and improve the grain size and uniform distribution state, thereby improving the prepared carbon-free high-speed steel with excellent hardness, corrosion resistance and high-temperature oxidation resistance.

[0036] In the present application, the metal powder A can be a metal single-element powder of cobalt, molybdenum, tungsten or iron.

[0037] The metal powder in step (1) is a commercial high-purity (>99.8%) ultra-fine (average particle size <4 μm) powder. The Fe powder can be, for example, a carbonyl iron powder.

[0038] In the present application, the composition, proportion and alloying use of the reinforcing additive are one of the keys to the formation of μ phase, σ phase, B2 phase and γ' phase, and the improvement of their distribution and synergistic strengthening.

[0039] In the reinforcing additive, the mass ratio of Cr, Ni and Al is 1-3:1-2:1-2; further preferably 1.5-2:1:1.

[0040] Preferably, the reinforcing additive in step (1) is a quaternary entropy alloy powder containing Fe, Cr, Ni and Al; preferably, the content of Fe in the reinforcing additive is 40-60 wt%.

[0041] Further preferably, the reinforcing additive in step (1) is Fe 0.5 (Cr x Niy Al 1-x-y ) 0.5 x is 0.4-0.5, and y is 0.25-0.285.

[0042] The present application researches and finds that the functional additive is added in the form of the medium entropy alloy, the proportion of the combined elements can unexpectedly realize synergy, can be beneficial to form the mu phase, sigma phase, B2 phase and gamma' phase, and can synergistically improve the comprehensive performance of the obtained carbon-free high-speed steel.

[0043] In the present application, the forming treatment can be carried out based on the known process, for example, the raw material powder and the forming agent are ball milled and mixed, and then pressed into a shape;

[0044] The forming agent can be a forming agent known in the industry, for example, can be at least one of paraffin, PEG and stearic acid, and the addition amount can be adjusted as needed, considering the processing effect and cost, and the addition amount can be 3-6% of the mass percentage of the powder.

[0045] In the present application, the ball milling in step (1) can be planetary ball milling and drum ball milling. The grinding balls are selected from cemented carbide balls, the grinding medium is anhydrous ethanol, the ball-to-material ratio is (4-6):1, the rotation speed is 220-300 r / min when using planetary ball milling, and the ball milling time is 60-72 h; when using drum ball milling, the rotation speed is 100-140 r / min, and the ball milling time is 96-120 h. Considering the mixing efficiency, drum ball milling is preferably used.

[0046] In the present application, the uniformly mixed powder in step (1) is dried by negative pressure stirring after ball milling to obtain a slurry, the drying temperature is slightly higher than the boiling point of alcohol, and the powder after drying is cooled to room temperature, sieved and vacuum packaged.

[0047] In the present application, the process parameters of the pressing in step (1) are: a pressing pressure of 100-200 MPa, a pressure holding time of 30-60 seconds, and the pressing can be one of die pressing and cold isostatic pressing. The die pressing can be one-way pressing or two-way pressing, and two-way die pressing is preferably selected.

[0048] In the present application, the sintering process in step (2) can be vacuum sintering, hydrogen atmosphere and pressure sintering. Considering the preparation cost and process control of the material, vacuum sintering is preferably used.

[0049] In the present application, the vacuum sintering process in step (2) is: sintering is carried out by stage heating, a 300-600 DEG C debinding platform is set, an 1100-1200 DEG C alloying and sintering shrinkage densification platform is set, and the final sintering temperature is 1320-1380 DEG C to complete the densification, the holding time is 2-3 h. The vacuum degree during sintering is controlled at 0.001 Pa-0.01 Pa, and finally slowly cooled to room temperature with the furnace.

[0050] In the present application, the hot working deformation amount in step (3) is 60-80%, and the hot deformation is completed by multiple passes, and after each pass is completed, the furnace is returned and kept for 5-10 min, and the temperature at the end of each pass is controlled to be higher than 900 DEG C, and the hot deformation can be one of hot rolling, free forging and die forging. Preferably, hot rolling is used to ensure flatness.

[0051] In the present application, the solid solution treatment in step (4) is protected by vacuum atmosphere or nitrogen atmosphere, the solid solution treatment temperature is 1180-1250 DEG C, the solid solution treatment time is 60-120 min, and the rapid cooling is oil cooling or air cooling. Preferably, vacuum solid solution treatment is used, and rapid oil cooling is used to room temperature.

[0052] In the present application, the aging treatment in step (4) is carried out in a muffle furnace, the temperature is 560-660 DEG C, the single aging time is 1-2 h, and the number of times is 1-3 times.

[0053] In the technical scheme of the present application, the composition and relative content of transition metal components and refractory elements are the basis for realizing the composite strengthening of multiple intermetallic compounds, and the content, form and distribution of the four strengthening phases of mu phase, sigma phase, B2 phase and gamma prime phase need to be controlled by the overall process. The present application uses a combination of strengthening additives and powder metallurgy processes such as sintering, annealing, solid solution, aging and temperature control in stages, which is beneficial to promote the formation of intermetallic compounds including mu phase, sigma phase, B2 phase and gamma prime phase, and improve their distribution and grain size. Not only that, but also it is beneficial to ensure the appropriate solid solution amount, aging hardening capacity, and thus improve the hardness, corrosion resistance and high temperature oxidation resistance of the prepared carbon-free high speed steel.

[0054] The present application has the following advantages:

[0055] 1. The present application provides a special mu phase, sigma phase, B2 phase and gamma prime phase composite reinforced carbon-free high speed steel, which is based on the combination of the synergistic intermetallic compounds and the proportion, which can realize synergistic reinforcement, so that the carbon-free high speed steel has high strength and toughness, excellent red hardness and thermal hardness, and good corrosion resistance and oxidation resistance. Compared with the carbon-free high speed steel disclosed in CN111793773A, the high speed steel of the present application not only retains excellent high temperature performance, but also greatly improves the corrosion resistance and oxidation resistance of the material.

[0056] 2、The application innovatively carries out powder metallurgy treatment with the aid of reinforcing additives, and based on the synergistic control of Cr, Ni and Al elements, proportion, alloying form in the reinforcing additives and temperature of powder metallurgy process conditions such as sintering, deformation and solid solution, thereby promoting the formation of mu phase, sigma phase, B2 phase and gamma prime phase composite intermetallic compounds, and improving the grain and uniform dispersion state, and further improving the prepared carbon-free high-speed steel with excellent hardness, corrosion resistance and high-temperature oxidation resistance. In addition, the whole process flow is simple and the cost is low, and the repeatability is strong. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 and Figure 2 The microstructure diagram of the carbon-free high-speed steel prepared in Example 1;

[0058] Figure 3 The microstructure diagram of the carbon-free high-speed steel prepared in Comparative Example 4; DETAILED DESCRIPTION

[0059] The application will be further described below in the technical scheme of the application combined with specific examples, but the protection scope of the application is not limited to the following examples.

[0060] In the following cases of the application, the element proportion of the chemical formula of the medium-entropy alloy as the additive refers to the mass ratio of the elements. For example, when the additive is Fe 0.5 (Cr 0.5 Ni 0.25 Al 0.25 ) 0.5 medium-entropy alloy powder, the mass ratio of Cr:Ni:Al therein is 0.5:0.25:0.25, and the mass ratio of Fe and (total amount of Cr-Ni-Al) is 0.5:0.5.

[0061] Example 1

[0062] A multi-phase intermetallic compound composite hardening high-performance carbon-free powder metallurgy high-speed steel is prepared, and the steps are as follows:

[0063] Step 1: batching

[0064] The raw material powder is weighed according to the designed formula, wherein the mass percentage composition of the high-speed steel is: Co: 25%, Mo: 14%, W: 5%, the total weight of Cr-Ni-Al is 16%, the impurity content is less than 0.02%, and the balance is Fe. The preparation method is as follows: first, the Fe powder, Co powder, Mo powder, W powder and additive (Fe 0.5 (Cr 0.5 Ni 0.25 Al 0.25 ) 0.5Medium-entropy alloy powder)

[0065] Step 2: forming

[0066] Add paraffin wax as a forming agent to the raw material powder in step 1 at a powder mass of 4wt%, and mix for 72h using a planetary ball mill; the powder slurry after ball milling is dried using negative pressure, and the drying temperature is slightly higher than the boiling point of alcohol. The dried and sieved powder is bidirectionally pressed at a pressure of 180MPa, and the holding time is 30 seconds;

[0067] Step 3: sintering

[0068] Sinter the green body formed by pressing in a vacuum sintering furnace, set a 300-600℃ debinding platform, use carrier gas for debinding, the protective atmosphere is Ar gas, a 1100-1200℃ alloying and sintering shrinkage densification platform, the final sintering temperature is 1360℃, and the holding time is 2h, then cool to room temperature in the furnace.

[0069] Step 4: deformation annealing

[0070] Heat the sintered body at 1180℃ for 2h, then hot roll, the thickness reduction is 75%, the thickness reduction in each rolling pass is not more than 15%, and the final hot rolling temperature is higher than 900℃; anneal the hot rolled deformed body at 880℃ for 3h, then cool to room temperature in the furnace.

[0071] Step 5: solution and aging treatment

[0072] Perform solution and aging treatment on the hot rolled deformed body; the solution treatment temperature is 1230℃, the holding time is 90min, and then rapidly oil cooled to room temperature; the aging treatment temperature is 620℃, and the single holding time is 1h, then take out and air cool to room temperature, repeat the aging twice to obtain a carbon-free high speed steel with multiple intermetallic compound composite strengthening. The microstructure of the carbon-free high speed steel obtained in Example 1 is shown in Figures 1 and 2, and there are micron-sized primary μ phase and σ phase uniformly distributed in the matrix, wherein the σ phase is elongated along the grain boundary, and the primary μ phase is dispersedly distributed in the grain, while the intragranular strengthening nanoscale μ phase, γ' phase and B2 phase are difficult to identify in the figure due to their small size.

[0073] Test the prepared material, and the mechanical property detection standards are bending strength, impact toughness, and hardness test:

[0074] GB / T 3851-2015, GB / T 5318-2017, GB / T 9097-2016;

[0075] After testing, the mechanical properties of the above prepared high speed steel are: the hardness at room temperature is 68.9HRC, the bending strength is 3174MPa, the impact toughness is 9.9J / cm 2 , and the fracture toughness is 31.2MPa.m1 / 2 The corrosion rate in deionized water was 2.9 x 10 -3 mm / a, and the oxidation weight gain after continuous oxidation at 700°C in a muffle furnace for 100 hours was 8 x 10 -5 g / cm 2 .

[0076] Example 2

[0077] Example 2, compared with Example 1, still uses Fe 0.5 (Cr 0.5 Ni 0.25 Al 0.25 ) 0.5 entropy alloy powder as an additive, wherein the mass percentage composition of the high-speed steel is: Co: 21%, Mo: 13%, W: 4%, the total weight of Cr-Ni-Al is 12%, the impurity content is less than 0.02%, and the balance is Fe.

[0078] The mechanical properties of the high-speed steel prepared above were detected as follows: hardness was 66.8 HRC, bending strength was 3321 MPa, impact toughness was 12.8 J / cm 2 , fracture toughness was 35.4 MPa.m 1 / 2 , the corrosion rate in deionized water was 3.9 x 10 - 3 mm / a, and the oxidation weight gain after continuous oxidation at 700°C in a muffle furnace for 100 hours was 1.2 x 10 -4 g / cm 2 .

[0079] Example 3

[0080] A multi-phase intermetallic compound composite hardening high-performance carbon-free powder metallurgy high-speed steel was prepared, and the raw material powder was weighed according to the design formula, wherein the mass percentage composition of the high-speed steel was: Co: 18%, Mo: 12%, W: 4%, the total weight of Cr-Ni-Al was 10.5%, the impurity content was less than 0.02%, and the balance was Fe. The preparation method is as follows:

[0081] Step 1: batching

[0082] First, the Fe powder, Co powder, Mo powder, W powder, Fe 0.5 (Cr 0.43 Ni 0.285 Al 0.285 ) 0.5 entropy alloy powder,

[0083] Step 2: forming

[0084] The powder mass 4wt% of paraffin wax is added as a forming agent, and the planetary ball mill is used for wet grinding mixing for 72h; the powder slurry after ball milling is dried under negative pressure, and the drying temperature is slightly higher than the boiling point of alcohol; the sieved powder is bidirectionally pressed under a pressure of 180MPa, and the pressure holding time is 30 seconds;

[0085] Step 3: sintering

[0086] The green body formed by pressing is sintered in a vacuum sintering furnace, a 300-600℃ debinding platform is set, carrier gas debinding is used in the debinding stage, the protective atmosphere is Ar gas, a 1100-1200℃ alloying and sintering shrinkage densification platform is set, the final sintering temperature is 1330℃, and the sintering is cooled to room temperature after holding for 2h.

[0087] Step 4: deformation annealing

[0088] Then, the sintered blank is heated at 1180℃ and held for 2h, and then hot-rolled, the thickness reduction of hot rolling is 80%, the thickness reduction of hot rolling pass is not more than 15%, and the final hot rolling temperature is higher than 900℃; the hot-rolled deformed blank is annealed at 880℃ for 3h and then cooled to room temperature in the furnace.

[0089] Step 5: solution and aging treatment

[0090] Finally, the hot-rolled deformed blank is subjected to solution and aging treatment; the solution treatment temperature is 1200℃, the holding time is 70min, and then the solution treated blank is rapidly oil-cooled to room temperature; the aging treatment temperature is 600℃, the blank is taken out after single holding for 1h and then air-cooled to room temperature, and the aging is repeated twice to obtain a carbon-free high-speed steel with multiple intermetallic compound composite strengthening. It is detected that the mechanical properties of the high-speed steel prepared above are: hardness is 65.2HRC, bending strength is 2789MPa, impact toughness is 13.6J / cm 2 , and fracture toughness is 37.1MPa.m 1 / 2 The corrosion rate measured in deionized water is 6.2x10 -3 mm / a, and the oxidation weight gain after continuous oxidation in a muffle furnace at 700℃ for 100h is 1.8x10 -4 g / cm 2 .

[0091] Example 4

[0092] Compared with Example 3, Example 4 still uses Fe 0.5 (Cr 0.43 Ni 0.285 Al 0.285 ) 0.5The medium-entropy alloy powder is used as an additive, and the high-speed steel has a mass percentage composition of Co: 26%, Mo: 17%, W: 7%, Cr-Ni-Al total weight of 17.5%, impurity content less than 0.02%, and the balance of Fe.

[0093] The high-speed steel prepared above has the following mechanical properties: hardness of 69.1 HRC, bending strength of 2987 MPa, impact toughness of 7.8 J / cm 2 , and fracture toughness of 25.6 MPa.m 1 / 2 . The corrosion rate in deionized water is 1.9 x 10 - 3 mm / a, and the oxidation weight gain after continuous oxidation in a muffle furnace at 700 DEG C for 100 hours is 5 x 10 -5 g / cm 2 .

[0094] Example 5

[0095] Compared with Example 1, the high-speed steel still has a mass percentage composition of Fe 0.5 (Cr 0.5 Ni 0.25 Al 0.25 ) 0.5 The medium-entropy alloy powder is used as an additive, and the high-speed steel has a mass percentage composition of Co: 12%, Mo: 10%, W: 3%, Cr-Ni-Al total weight of 8%, impurity content less than 0.02%, and the balance of Fe.

[0096] The high-speed steel prepared above has the following mechanical properties: hardness of 65.6 HRC, bending strength of 2874 MPa, impact toughness of 15.2 J / cm 2 , and fracture toughness of 38.4 MPa.m 1 / 2 . The corrosion rate in deionized water is 7.3 x 10 - 3 mm / a, and the oxidation weight gain after continuous oxidation in a muffle furnace at 700 DEG C for 100 hours is 2.1 x 10 -4 g / cm 2 .

[0097] Comparative Example 1

[0098] Compared with Example 1, the only difference is that the total element content of Cr-Ni-Al is reduced to 3.5%. Other operations and parameters are the same as those in Example 1.

[0099] The high-speed steel prepared above has the following mechanical properties: hardness of 68.2 HRC, bending strength of 3024 MPa, impact toughness of 10.4 J / cm 2 , and fracture toughness of 30.5 MPa.m 1 / 2The corrosion rate in deionized water was 5.8 x 10 - 2 mm / a, and the oxidation weight gain after continuous oxidation at 700°C in a muffle furnace for 100 hours was 1.1 x 10 -3 g / cm 2 .

[0100] Comparative Example 2

[0101] Compared with Example 1, the only difference was that the total element content of Cr-Ni-Al was increased to 28%. Other operations and parameters were the same as in Example 1.

[0102] The mechanical properties of the high-speed steel prepared above were detected to be: hardness 61.7 HRC, bending strength 2315 MPa, impact toughness 4.4 J / cm 2 , and fracture toughness 21.4 MPa.m 1 / 2 . The corrosion rate in deionized water was 6 x 10 -4 mm / a, and the oxidation weight gain after continuous oxidation at 700°C in a muffle furnace for 100 hours was 4 x 10 -5 g / cm 2 . (Although a large amount of Cr, Ni and Al elements were added to obtain a significant improvement in the corrosion resistance and oxidation resistance of the carbon-free high-speed steel, the hardness of the carbon-free high-speed steel at room temperature was reduced, and the brittleness of the material was significantly increased, and excessive addition had an adverse effect on the mechanical properties of the carbon-free high-speed steel.)

[0103] Comparative Example 3

[0104] Compared with Example 1, the only difference was that the Fe 0.5 (Cr 0.5 Ni 0.25 Al 0.25 ) 0.5 entropy alloy powder was not added, and other operations and parameters were the same as in Example 1.

[0105] The mechanical properties of the high-speed steel prepared above were detected to be: hardness 69.1 HRC, bending strength 3067 MPa, impact toughness 7.9 J / cm 2 , and fracture toughness 28.4 MPa.m 1 / 2 . The corrosion rate in deionized water was 1.5 x 10 - 1 mm / a, and the oxidation weight gain after continuous oxidation at 700°C in a muffle furnace for 100 hours was 7.4 x 10 -3 g / cm 2 .

[0106] Comparative Example 4

[0107] Comparing with Example 1, the only difference is that the additive is Ni and Al, and is added in the form of simple substance, the weight ratio and total content of Ni and Al in the additive are the same as Example 1, and other operations and parameters are also the same as Example 1.

[0108] The mechanical properties of the high speed steel prepared above are: hardness 67.5 HRC, bending strength 2798 MPa, impact toughness 8.8 J / cm 2 , and fracture toughness 32.1 MPa.m 1 / 2 The corrosion rate in deionized water is 3.4 x 10 - 2 mm / a, and the oxidation weight gain after continuous oxidation at 700°C in a muffle furnace for 100 hours is 2.2 x 10 -3 g / cm 2

[0109] Comparative Example 5

[0110] Comparing with Example 1, the only difference is that the additive is used in the form of simple substance with the same weight ratio, and other operations and parameters are the same as Example 1.

[0111] The mechanical properties of the high speed steel prepared above are: hardness 67.8 HRC, bending strength 2867 MPa, impact toughness 7.3 J / cm 2 , and fracture toughness 26.5 MPa.m 1 / 2 The corrosion rate in deionized water is 5.3 x 10 - 3 mm / a, and the oxidation weight gain after continuous oxidation at 700°C in a muffle furnace for 100 hours is 1.1 x 10 -4 g / cm 2 .

[0112] From the results of Comparative Example 5 and Example 1, it can be seen that the addition of Cr, Ni and Al in the form of element powder causes the oxidation resistance and corrosion resistance to be not as good as the addition of alloy powder due to partial oxidation. In addition, the product after partial oxidation causes the mechanical properties of the carbon-free high speed steel to decrease slightly.

[0113] Table 1 Comparison of properties of carbon-free high speed steels prepared in examples and comparative examples

[0114]

[0115]

[0116] It can be known from the performance comparison of the examples and the comparative examples that the carbon-free powder metallurgy high-speed steel co-strengthened by multiphase intermetallic compounds prepared by the application has the characteristics of high hardness, high strength and toughness, corrosion resistance and oxidation resistance. Compared with the carbon-free high-speed steel without adding chromium, nickel and aluminum, the corrosion resistance and oxidation resistance are greatly improved, and the excellent high-strength hardening characteristics of the carbon-free high-speed steel itself are retained. In the application, the addition of Cr, Ni and Al elements can significantly improve the corrosion resistance and oxidation resistance of the carbon-free high-speed steel, but the content of Cr, Ni and Al elements still needs to be controlled in a suitable composition range to retain the excellent room temperature and high-temperature hardness and high mechanical properties of the carbon-free high-speed steel. In addition, the addition of Cr, Ni and Al in the form of pre-alloyed entropy alloy powder can effectively avoid the oxidation problem in the process, so as to better alloy with the matrix. In summary, the high-performance carbon-free powder metallurgy high-speed steel prepared by the application can better meet the requirements of cutting tool materials in corrosive and oxidizing working conditions.

Claims

1. A carbon-free high-speed steel, characterized in that, Includes a steel matrix and intermetallic compounds dispersed in the matrix; The intermetallic compound includes a μ phase, a σ phase, a B2 phase, and a γ' phase, wherein the μ phase includes at least one of Fe7W6, Fe7Mo6, Co7W6, and Co7Mo6; the σ phase includes FeCrMo; the B2 phase includes FeAl; and the γ' phase includes at least one of Ni3Al and Co3Al. The carbon-free high-speed steel contains the following mass percentages of elements: Co: 10~30%, Mo: 5~20%, W: 2~10%, with the total content of Cr, Ni, and Al being 7~22%, and the balance being Fe. The mass ratio of Cr, Ni, and Al is 1~3:1~2:1~2.

2. The carbon-free high-speed steel as described in claim 1, characterized in that, The μ phase includes Fe7W6, Fe7Mo6, Co7W6 and Co7Mo6; the σ phase is FeCrMo; the B2 phase is FeAl; and the γ' phase is Ni3Al and Co3Al.

3. The carbon-free high-speed steel as described in claim 1, characterized in that, The carbon-free high-speed steel contains the following mass percentages of elements: Co: 13-27%, Mo: 10-18%, W: 4-8%, with a total content of Cr, Ni, and Al of 8-19%, and the balance being Fe.

4. The carbon-free high-speed steel as described in claim 3, characterized in that, Co: 18~26%, Mo: 12~17%, W: 4~7%, with the total content of Cr, Ni and Al being 11~19%, and the balance being Fe.

5. The carbon-free high-speed steel as described in claim 3, characterized in that, Co: 21~25%, Mo: 13~16%, W: 4~6%, of which the total content of Cr, Ni and Al is 12~16%, and the balance is Fe.

6. The carbon-free high-speed steel as described in claim 1, characterized in that, The mass ratio of Cr, Ni, and Al is 1.5~2:1:

1.

7. The carbon-free high-speed steel as described in claim 1, characterized in that, The carbon-free high-speed steel is allowed to contain unavoidable impurities, with the impurity content being below 0.02%.

8. The carbon-free high-speed steel according to any one of claims 1 to 7, characterized in that, The carbon-free high-speed steel has a hardness of 63-70 HRC, a bending strength of 2300-3400 MPa, and an impact toughness of 6-14 J / cm. 2 The fracture toughness is 24~38 MPa.m 1 / 2 The corrosion rate measured in deionized water is less than 7 × 10⁻⁶. -3 mm / a, after continuous oxidation at 700℃ for 100 hours, the oxidative weight gain is less than 2×10. -4 g / cm 2 .

9. The carbon-free high-speed steel as described in claim 8, characterized in that, The carbon-free high-speed steel has a hardness of 65-70 HRC, a bending strength of 2700-3400 MPa, and an impact toughness of 9-14 J / cm. 2 The fracture toughness is 28~38 MPa.m 1 / 2 The corrosion rate measured in deionized water is less than 4 × 10⁻⁶. -3 mm / a, after continuous oxidation at 700℃ for 100 hours, the oxidative weight gain is less than 1.3×10. -4 g / cm 2 .

10. A powder metallurgy preparation method for carbon-free high-speed steel according to any one of claims 1 to 9, characterized in that the steps include... include: Step (1): Ingredients Prepare the required raw material powder containing metal powder A and reinforcing additives according to the element content of the carbon-free high-speed steel described above; The metal powder A is a powder containing elemental metals such as cobalt, molybdenum, tungsten, and iron, or an alloy powder containing two or more of these metals. The reinforcing additive is an alloy powder capable of providing the required mass ratio of Cr, Ni, and Al; Step (2): Shaping and sintering The raw material powder is shaped, pressed, and sintered to obtain a sintered blank; Step (3): Deformation annealing The sintered billet is preheated and hot deformed at 1150~1230℃ and then air-cooled to obtain a deformed billet. After being held at 800~900℃ for annealing, it is cooled in the furnace to obtain an annealed deformed billet. Step (4): Solution treatment The annealed deformed billet described in step (3) is subjected to solution treatment, cooled to room temperature, and then aged to obtain the carbon-free high-speed steel.

11. The powder metallurgy preparation method according to claim 10, characterized in that, In the reinforcing additive, the mass ratio of Cr, Ni, and Al is 1~3:1~2:1~2.

12. The powder metallurgy preparation method according to claim 10, characterized in that, The reinforcing additive mentioned in step (1) is a quaternary medium-entropy alloy powder containing Fe, Cr, Ni and Al.

13. The powder metallurgy preparation method according to claim 12, characterized in that, The Fe content in the aforementioned reinforcing additive is 40-60 wt%.

14. The powder metallurgy preparation method according to claim 10, characterized in that, The reinforcing additive mentioned in step (1) is Fe 0.5 (Cr x Ni y Al 1-x-y ) 0.5 x is 0.4~0.5, and y is 0.25~0.

285.

15. The powder metallurgy preparation method according to claim 10, characterized in that, The molding stage involves: ball milling and mixing the raw material powder and molding agent, followed by pressing and molding. The molding agent is at least one of paraffin, PEG and stearic acid; The weight of the molding agent is 3-6% of the weight of the raw material powder; The pressure during the pressing and molding stage is 100~200MPa, and the holding time is 30~60 seconds.

16. The powder metallurgy preparation method according to claim 10, characterized in that, In step (2), the sintering process is vacuum sintering, hydrogen atmosphere sintering, or pressure sintering; The vacuum sintering stage includes a first holding stage at 300~600℃, a second holding stage at 1100~1200℃, and a third holding stage at 1320~1380℃, with the vacuum degree controlled at 0.001Pa~0.01Pa during the sintering process.

17. The powder metallurgy preparation method according to claim 10, characterized in that, In step (3), the amount of hot deformation is 60~80%, and the hot deformation is completed in multiple passes. After each pass of deformation is completed, the furnace is returned to the furnace for 5~10 minutes of heat preservation. The temperature at the end of each pass of hot deformation is controlled to be higher than 900℃.

18. The powder metallurgy preparation method according to claim 10, characterized in that, In step (4), the solution treatment is carried out under vacuum or nitrogen atmosphere protection, the solution treatment temperature is 1180~1250℃, and the solution treatment time is 60~120min.

19. The powder metallurgy preparation method according to claim 10, characterized in that, Cooling is achieved using either oil cooling or air cooling.

20. The powder metallurgy preparation method according to claim 10, characterized in that, In step (4), the temperature of the aging process is 560~660℃, the aging time is 1~2h, and the number of times is 1~3.

21. The application of the carbon-free high-speed steel according to any one of claims 1 to 9 or the carbon-free high-speed steel prepared by the powder metallurgy method according to any one of claims 10 to 20, characterized in that, The carbon-free high-speed steel is prepared into alloy products.

22. The application as described in claim 21, characterized in that, The alloy product in question is a cutting tool.

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