High speed steel and method for producing the same

Abstract

The application provides a high-speed steel and a preparation method thereof, and the chemical components of the high-speed steel include the following in percentage by mass: C: 0.86-0.90%, Si: 0.20-0.45%, Mn: 0.20-0.40%, Cr: 7.00-7.50%, W: 5.00-5.50%, Mo: 1.70-2.20%, V: 1.50-1.90%, Co: 0.50-2.00%, and the balance is Fe and impurities. The high-speed steel is designed through alloy components, and through the organic cooperation of W+Mo, the Co element is added to improve the quenching property of heat treatment, the design principle of multi-element compound, and the mechanism of the precipitation and growth of different element carbides in the solidification process, so that the steel has excellent high wear resistance and high corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of steel alloy materials technology, and particularly to a high-speed steel. This invention also relates to a method for preparing the aforementioned high-speed steel. Background Technology

[0002] The screw is the most important working component of an extruder, often referred to as its "heart," and it's equally crucial in the injection molding industry. The appropriate selection of the screw directly impacts the performance of both the extruder and injection molding machine, as well as the quality of the finished products. Under certain harsh operating conditions, tools or components not only experience wear from direct contact with hard abrasive particles in the moving parts or working medium, but also suffer from corrosion from moisture, acids, or other corrosive agents. On one hand, the presence of hard reinforcing phases such as ceramic particles and glass fibers in the plastic exacerbates wear on these components; on the other hand, corrosive components in the plastic also cause chemical corrosion. To ensure a long service life for components used in these special conditions, the tool steel used must possess high wear resistance and corrosion resistance. Furthermore, tool steel used in this field must also have good strength and toughness to withstand the pressure and torsional forces of the operating conditions, and to facilitate machining to the required shapes and sizes, it must also possess sufficient machinability and grindability. Summary of the Invention

[0003] In view of this, the present invention aims to provide a high-speed steel to improve its wear resistance and corrosion resistance.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0005] A high-speed steel, wherein the chemical composition of the high-speed steel comprises, by mass percentage: C: 0.86-0.90%, Si: 0.20-0.45%, Mn: 0.20-0.40%, Cr: 7.00-7.50%, W: 5.00-5.50%, Mo: 1.70-2.20%, V: 1.50-1.90%, Co: 0.50-2.00%, with the balance being Fe and impurities.

[0006] Furthermore, the impurities include S, and S: ≤0.015%.

[0007] Furthermore, the impurities include P, and P: ≤0.030%.

[0008] Furthermore, the impurities include N, and N ≤ 0.006%.

[0009] Furthermore, the M6C carbide content of the high-speed steel accounts for 3.5-4.1% by volume.

[0010] Furthermore, the M of the high-speed steel23 The C6 carbide content is 10.3-11.1% by volume.

[0011] Furthermore, the MC carbide content of the high-speed steel accounts for 1.9-2.1% by volume.

[0012] This invention also proposes a method for preparing high-speed steel, which includes the following steps:

[0013] S1. Preparing steel ingots;

[0014] S2. Anneal the steel ingot prepared in S1, and then heat it to above the recrystallization temperature;

[0015] S3. Forge the steel ingot, then anneal it with residual heat, and roll it into flat steel;

[0016] S4. Perform spheroidizing annealing treatment on the flat steel.

[0017] Furthermore, the steel ingot preparation in step S1 involves refining the molten alloy in an LF furnace, degassing it under vacuum in a VD furnace, and casting it into a steel ingot; or refining the molten alloy in an ESH furnace and preparing the steel ingot in a jet furnace.

[0018] Furthermore, the spheroidizing annealing in step S4 includes the following steps:

[0019] S401. The flat steel is heated to 770-790℃ at a rate of 90-100℃ / h and held at that temperature;

[0020] S402. Heat to 880-890℃ at a rate of 90-100℃ / h and hold at that temperature;

[0021] S403. Rapidly cool to 770-790℃ at a rate of ≥50℃ / h;

[0022] S404. Slowly cool to 670-690℃;

[0023] S405 is cooled to 550℃ in the furnace before being unloaded.

[0024] This invention, through the design of alloy composition and the organic combination of W and Mo, along with the addition of Co to improve heat treatment hardenability, adopts a multi-component composite design principle. It comprehensively considers the precipitation and growth mechanisms of different elemental carbides during solidification, resulting in a steel grade with excellent high wear resistance and high corrosion resistance. In this invention, specific chemical compositions and ratios are necessary conditions for achieving its wear resistance performance. The functions and principles of each chemical component are as follows:

[0025] Specifically, in this invention, the carbon (C) content needs to be controlled between 0.86% and 0.90%. Its function is as one of the constituent elements of carbides, with some elements dissolved in the matrix to improve the matrix strength. The C content should not exceed 0.90% to ensure that ledeburite structure is not generated or is minimally generated during the solidification process of the molten steel, and it also helps control the amount of MC carbides and carbide segregation. The C content should not be less than 0.86% to ensure that appropriate hardness is achieved after heat treatment.

[0026] The role of tungsten (W) is that it is a carbide-forming element, forming M6C carbides with carbon. These carbides inhibit grain growth, improving the high-temperature hardness and wear resistance of the steel. The W content should not exceed 5.50% to ensure minimal formation of M6C skeletal ledeburite during solidification, preventing difficulty in breaking down the structure during later hot working and affecting the steel's plasticity. The W content should not be less than 5.00% to ensure sufficient carbide formation, improving the steel's wear resistance and red hardness. The optimal control of W and C content results in an M6C carbide volume fraction of 3.5%-4.1% for this steel grade.

[0027] The role of molybdenum (Mo): Mo is a carbide-forming element. Under non-equilibrium cooling conditions, the carbides formed by Mo undergo a phase transition, producing metastable M2C carbides. These plate-like and fan-shaped M2C carbides decompose into fine M6C+MC particles during forging heating and holding after solidification and cooling, making them easier to distribute evenly. This increases the toughness and thermoplasticity of the steel, improves the stability of the carbides, and enhances the strength and wear resistance of the steel. Therefore, the Mo content in this invention is controlled at 1.70-2.20%.

[0028] The equivalent relationship between W (tungsten), Mo (molybdenum), and C (carbon) in forming carbides is that 1.0% W is equivalent to 1.8% Mo. W and Mo can be substituted for each other. This invention controls the W equivalent [W] = W + Mo / 1.8, 4.44 ≤ [W] ≤ 5.32, and W equivalent ≥ 4.44 to ensure that the M6C content at room temperature after heat treatment is greater than 3.5%, and W equivalent ≤ 5.32 to ensure that the M6C carbides precipitated in the liquid phase are ≤ 2.6%. This results in materials with high wear resistance while reducing the probability of complex carbide formation during smelting.

[0029] The role of Cr (chromium): Cr can promote M 23 The precipitation of C6 carbides, along with the partial dissolution of Cr in the matrix, primarily improves the hardenability and tempering hardness of the steel. In this invention, the Cr content is 7.00–7.50%, preferably M. 23 The volume fraction of C6 carbides is 10.3%-11.1%.

[0030] The role of vanadium (V) is that it is a strong carbide-forming element, forming proeutectic and eutectic MC during solidification. As the V content increases, the difference between the precipitation temperature of proeutectic MC and eutectic MC becomes larger, resulting in larger proeutectic MC particles. Considering both the quenching and tempering hardness of the steel and the MC particle size, the V content in this invention is 1.50-1.90%, and the V and C content is preferably controlled to achieve a MC carbide volume fraction of 1.9-2.1% in this steel grade.

[0031] Si (silicon) element strengthens ferrite, enhances the secondary hardening ability of steel during heat treatment, reduces the critical cooling rate of steel, and improves the hardenability of steel. In this invention, the content of Si element is controlled at 0.20-0.45%.

[0032] The presence of manganese (Mn) makes cutting easier and helps improve the quality of the machined surface. Sulfur (S) is a metal inclusion-forming element. To mitigate the harmful effects of S forming low-melting-point non-metallic inclusions with Fe and other elements, an appropriate amount of Mn is controlled to form MnS. However, MnS extends and distributes along the rolling direction, reducing toughness in that direction. Therefore, the lower the S content, the better. In this invention, the S content is controlled at ≤0.015%, and the Mn content is controlled at 0.20-0.40%.

[0033] Co (cobalt) forms a continuous solid solution with iron. During use, Co inhibits and delays the precipitation and aggregation of carbides from other elements, significantly improving the hot strength and high-temperature hardness of steel, and enhancing the hardenability of the material. In this invention, the Co content is controlled between 0.50% and 2.00%.

[0034] The role of nitrogen (N) is that it has a stronger affinity for v (V) in steel than carbon (C). It partially replaces c atoms in MC (methyl monoxide) to form m(CN)-type carbonitrides. The incorporation of nitrogen increases the precipitation temperature and ΔT value of the proeutectic carbides, thereby increasing the size of the primary MC carbides. To reduce the particle size of MC carbides, this invention requires controlling the N content to be ≤0.006%. Attached Figure Description

[0035] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0036] Figure 1 This is a scanning electron microscope (SEM) image of the high-speed steel described in Embodiment 1 of the present invention.

[0037] Figure 2 This is a scanning electron microscope (SEM) image of the high-speed steel described in Embodiment 2 of the present invention. Detailed Implementation

[0038] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0039] A high-speed steel, wherein the chemical composition of the high-speed steel comprises, by mass percentage: C: 0.86-0.90%, Si: 0.20-0.45%, Mn: 0.20-0.40%, Cr: 7.00-7.50%, W: 5.00-5.50%, Mo: 1.70-2.20%, V: 1.50-1.90%, Co: 0.50-2.00%, with the balance being Fe and impurities.

[0040] The S content in the impurities is preferably ≤0.015%, the P content is preferably ≤0.030%, and the N content is preferably ≤0.006%.

[0041] The method for preparing high-speed steel according to the present invention specifically includes the following steps:

[0042] S1. Preparation of steel ingots. There are two methods for preparing steel ingots: one is to melt the alloy and recycled material in a neutral crucible and pour it into a ladle, then refine it in an LF furnace, degas it under vacuum in a VD furnace, and cast it into F435 steel ingots; the other is to melt the alloy and recycled material in a neutral crucible and pour it into a ladle, then refine it in an ESH furnace and prepare it into φ360 diameter steel ingots using a jet furnace.

[0043] S2. Anneal the steel ingot prepared in S1, and then heat it to above the recrystallization temperature, which can be set to 1160-1170℃.

[0044] S3. The steel ingot is forged into 140 square billets using a precision forging machine, then subjected to residual heat annealing at 750-770℃, and rolled into φ12-72 round bars using a φ600 rolling mill;

[0045] S4. Perform spheroidizing annealing on the round steel. Spheroidizing annealing preferably includes the following steps:

[0046] The flat steel is heated to 770-790℃ at a rate of 90-100℃ / h and held for 6-8 hours; then heated to 880-890℃ at a rate of 90-100℃ / h and held for 5.5-7 hours; then rapidly cooled to 770-790℃ at a rate of ≥50℃ / h; then slowly cooled to 670-690℃ and held for 9-11 hours; finally, all heat dissipation vents are opened, and the flat steel is cooled in the furnace to 550℃ before being removed from the furnace.

[0047] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0048] Example 1

[0049] This embodiment relates to a high-speed steel and its preparation method, comprising the following components by mass percentage: 0.87% C, 0.30% Si, 0.30% Mn, 0.025% P, 0.012% S, 7.35% Cr, 1.85% Mo, 5.25% W, 1.65% V, 0.80% Co, with the balance being iron.

[0050] Its preparation method includes the following steps:

[0051] S1. The alloy and scrap are melted in a neutral crucible and poured into a ladle. After ESH ladle refining, the alloy is spray-formed and directly deposited into steel ingots.

[0052] S2. After annealing, the steel ingot from the previous step is heated in a ring furnace at a temperature of 1165-1170℃ for homogenization.

[0053] S3. The steel ingot is forged into 140 square billets using a precision forging machine. After residual heat annealing at 760℃, the billets are rolled into φ62-73 round bars using a rolling mill.

[0054] S4. The round steel is heated to 780℃ at a rate of 90℃ / h and held for 8 hours; then heated to 880℃ at a rate of 90℃ / h and held for 7 hours; then rapidly cooled to 780℃ at a rate of 50℃ / h; finally, slowly cooled to 680℃ and held for 11 hours; all heat dissipation vents are opened, and the steel is cooled in the furnace to 550℃ before being removed from the furnace. After straightening and machining, the steel is inspected, and the electron micrograph is shown below. Figure 1 As shown.

[0055] The steel product prepared in this embodiment was oil quenched at 1100℃ and tempered at 550℃. After tempering, the hardness reached 62HRC, the grain size reached grade 11, and the impact toughness was 36J. The high-speed steel prepared in this embodiment has an M6C carbide content of 3.6% by volume, an M23C6 carbide content of 10.7% by volume, and an MC carbide content of 2.0% by volume.

[0056] Example 2

[0057] This embodiment relates to a high-speed steel and its preparation method, comprising the following components by mass percentage: 0.88% C, 0.35% Si, 0.30% Mn, 0.025% P, 0.012% S, 7.40% Cr, 1.80% Mo, 5.30% W, 1.70% V, 1.0% Co, with the balance being iron.

[0058] Its preparation method includes the following steps:

[0059] S1. The alloy and scrap are melted in a neutral crucible and poured into a ladle. After being refined in an LF furnace and degassed in a VD vacuum, it is cast into a 435Kg ingot.

[0060] S2. After annealing, the steel ingot from the previous step is heated in a ring furnace at a temperature of 1160-1165℃ for homogenization.

[0061] S3. The steel ingot is forged into 140 square billets using a precision forging machine. After residual heat annealing at 760℃, the billets are rolled into φ62-73 round bars using a rolling mill.

[0062] S4. The round steel is heated to 780℃ at a rate of 100℃ / h and held for 6 hours; then heated to 890℃ at a rate of 100℃ / h and held for 5.5 hours; rapidly cooled to 780℃ at a rate of 55℃ / h; slowly cooled to 680℃ and held for 9 hours; all heat dissipation vents are opened, and the steel is cooled in the furnace to 550℃ before being removed from the furnace. The straightened steel sheet is then scanned by electron microscopy, and the electron micrograph is shown below. Figure 2 As shown.

[0063] The steel product prepared in this embodiment was oil quenched at 1180℃ and tempered at 550℃. After tempering, the hardness reached 66HRC, the grain size reached grade 11, and the impact toughness was 28J. The high-speed steel prepared in this embodiment has an M6C carbide content of 3.9% by volume, an M23C6 carbide content of 10.8% by volume, and an MC carbide content of 1.9% by volume.

[0064] Example 3

[0065] This embodiment relates to a high-speed steel and its preparation method, comprising the following components by mass percentage: 0.90% C, 0.20% Si, 0.20% Mn, 0.020% P, 0.010% S, 7% Cr, 1.7% Mo, 5% W, 1.5% V, 0.50% Co, with the balance being iron.

[0066] Its preparation method includes the following steps:

[0067] S1. The alloy and scrap are melted in a neutral crucible and poured into a ladle. After ESH ladle refining, the alloy is spray-formed and directly deposited into steel ingots.

[0068] S2. After annealing, the steel ingot from the previous step is heated in a ring furnace at a temperature of 1165-1170℃ for homogenization.

[0069] S3. The steel ingot is forged into 140 square billets using a precision forging machine. After residual heat annealing at 760℃, the billets are rolled into φ62-73 round bars using a rolling mill.

[0070] S4. Heat the round steel to 780℃ at a rate of 90℃ / h and hold for 8 hours; heat to 880℃ at a rate of 90℃ / h and hold for 7 hours; rapidly cool to 780℃ at a rate of 50℃ / h; slowly cool to 680℃ and hold for 11 hours; open all heat dissipation vents and cool to 550℃ in the furnace before removing from the furnace.

[0071] The steel product prepared in this embodiment was oil quenched at 1120℃ and tempered at 550℃. After tempering, the hardness reached 64.5 HRC, the grain size reached grade 11, and the impact toughness was 30 J. The high-speed steel prepared in this embodiment has an M6C carbide content of 3.7% by volume, an M23C6 carbide content of 10.7% by volume, and an MC carbide content of 2.0% by volume.

[0072] Example 4

[0073] This embodiment relates to a high-speed steel and its preparation method, comprising the following components by mass percentage: 0.87% C, 0.45% Si, 0.40% Mn, 0.015% P, 0.01% S, 7.5% Cr, 2.2% Mo, 5.5% W, 1.9% V, 2% Co, with the balance being iron.

[0074] Its preparation method includes the following steps:

[0075] S1. The alloy and scrap are melted in a neutral crucible and poured into a ladle. After being refined in an LF furnace and degassed in a VD vacuum, the mixture is cast into a 435Kg ingot.

[0076] S2. After annealing, the steel ingot from the previous step is heated in a ring furnace at a temperature of 1160-1165℃ for homogenization.

[0077] S3. The steel ingot is forged into 140 square billets using a precision forging machine. After residual heat annealing at 760℃, the billets are rolled into φ62-73 round bars using a rolling mill.

[0078] S4. Heat the round steel to 780℃ at a rate of 90℃ / h and hold for 8 hours; heat to 880℃ at a rate of 90℃ / h and hold for 7 hours; slowly cool to 680℃ at a rate of 30℃ / h; open all heat dissipation vents and cool in the furnace to 550℃ before removing from the furnace. Straighten the steel and then inspect it.

[0079] The steel product prepared in this embodiment was oil quenched at 1160℃ and tempered at 550℃. After tempering, the hardness reached 66HRC, the grain size reached grade 11, and the impact toughness was 32J. The high-speed steel prepared in this embodiment has an M6C carbide content of 3.8% by volume, an M23C6 carbide content of 10.7% by volume, and an MC carbide content of 2.1% by volume.

[0080] Comparative Example 1

[0081] This embodiment relates to a high-speed steel and its preparation method, comprising the following components by mass percentage: 0.86% C, 0.30% Si, 0.30% Mn, 0.025% P, 0.012% S, 4.00% Cr, 5.00% Mo, 6.00% W, 1.80% V, with the balance being iron.

[0082] Its preparation method includes the following steps:

[0083] S1. The alloy and scrap are melted in a neutral crucible and poured into a ladle. After being refined in an LF furnace and degassed in a VD vacuum, the mixture is cast into a 435Kg ingot.

[0084] S2. After annealing, the steel ingot from the previous step is heated in a ring furnace at a temperature of 1165-1170℃ to homogenize it.

[0085] S4. Heat the round steel to 780℃ at a rate of 90℃ / h and hold for 8 hours; heat to 880℃ at a rate of 90℃ / h and hold for 7 hours; rapidly cool to 780℃ at a rate of 50℃ / h; slowly cool to 680℃ and hold for 11 hours; open all heat dissipation vents and cool in the furnace to 550℃ before removing from the furnace. Straighten the steel and machine it for inspection.

[0086] The steel product prepared in this embodiment was oil quenched at 1160℃ and tempered at 550℃. After tempering, the hardness reached 62HRC, the grain size reached grade 11, and the impact toughness was 32J. The high-speed steel prepared in this embodiment has an M6C carbide content of 3.2% by volume, an M23C6 carbide content of 8.7% by volume, and an MC carbide content of 1.5% by volume.

[0087] Comparative Example 2

[0088] This embodiment relates to a high-speed steel and its preparation method, comprising the following components by mass percentage: 0.90% C, 0.20% Si, 0.20% Mn, 0.020% P, 0.010% S, 7% Cr, 1.7% Mo, 5% W, 1.5% V, 0.50% Co, with the balance being iron.

[0089] Its preparation method includes the following steps:

[0090] S1. The alloy and scrap are melted in a neutral crucible and poured into a ladle, and then smelted and cast into F435 ingots over a period of 20 tons.

[0091] S2. After annealing, the steel ingot from the previous step is heated in a ring furnace at a temperature of 1140-1150℃.

[0092] S3. The steel ingot is forged into 140 square billets using a precision forging machine. After residual heat annealing at 760℃, the billets are rolled into φ62-73 round bars using a rolling mill.

[0093] S4. Heat the round steel to 780℃ at a rate of 90℃ / h and hold for 8 hours; heat to 880℃ at a rate of 90℃ / h and hold for 7 hours; rapidly cool to 780℃ at a rate of 50℃ / h; slowly cool to 680℃ and hold for 11 hours; open all heat dissipation vents and cool to 550℃ in the furnace before removing from the furnace.

[0094] The steel product prepared in this embodiment was oil quenched at 1120℃ and tempered at 550℃. After tempering, the hardness reached 64.5 HRC, the grain size reached grade 10, and the impact toughness was 23 J. The high-speed steel prepared in this embodiment has an M6C carbide content of 3.5% by volume, an M23C6 carbide content of 10.2% by volume, and an MC carbide content of 2.0% by volume.

[0095] The steels of the above embodiments and comparative examples were subjected to performance tests, and the test data are shown in Table 1 below.

[0096] Table 1

[0097] Hardness after tempering Grain size Impact toughness <![CDATA[M6C content]]> <![CDATA[M 23 C6 content]]> MC content Example 1 62HRC Level 11 36J 3.6％ 10.7％ 2.0％ Example 2 66HRC Level 11 28J 3.9％ 10.8％ 1.9％ Example 3 64.5 HRC Level 11 30J 3.8％ 10.7％ 2.0％ Example 4 64HRC Level 11 27J 3.5％ 10.5％ 1.9％ Comparative Example 1 62HRC Level 11 32J 3.2％ 8.7％ 1.5％ Comparative Example 2 64.5 HRC Level 10 23J 3.5％ 10.7％ 1.9％

[0098] The test data of each embodiment of the present invention are better than those of the comparative examples. Comparative example 1 shows that the hardness and toughness of the present invention are better than those of M2 produced by conventional smelting. Comparative example 2 shows that the grain size of the present invention is finer and the impact energy is higher after heat treatment compared with the traditional ingot casting process.

[0099] In the description of this specification, embodiments of the present invention are given. It is to be understood that the above embodiments are exemplary and should not be construed as limiting the invention. Without contradiction, those skilled in the art can combine, integrate, substitute and modify the features of the different embodiments or examples described in this specification.

Claims

1. A method for preparing high-speed steel, characterized in that: The chemical composition of the high-speed steel, by mass percentage, includes: C: 0.86-0.90%, Si: 0.20-0.45%, Mn: 0.20-0.40%, Cr: 7.00-7.50%, W: 5.00-5.50%, Mo: 1.70-2.20%, V: 1.50-1.90%, Co: 0.50-2.00%, with the balance being Fe and impurities; The high-speed steel has an M6C carbide content of 3.5-4.1% by volume. The M of the high-speed steel 23 The C6 carbide content is 10.3-11.1% by volume; The high-speed steel has an MC carbide content of 1.9-2.1% by volume. The method includes the following steps: S1. Preparing steel ingots; S2. Anneal the steel ingot prepared in S1, and then heat it to above the recrystallization temperature; S3. Forge the steel ingot, then anneal it with residual heat, and roll it into round steel. S4. The round steel is subjected to spheroidizing annealing treatment; The heating temperature in step S2 is between 1160-1170°C.

2. The method for preparing high-speed steel according to claim 1, characterized in that: The impurities include S, and S: ≤0.015%.

3. The method for preparing high-speed steel according to claim 1, characterized in that: The impurities include P, and P: ≤0.030%.

4. The method for preparing high-speed steel according to claim 1, characterized in that: The impurities include N, and N ≤ 0.006%.

5. The method for preparing high-speed steel according to claim 1, characterized in that: The steel ingot preparation in step S1 involves refining the molten alloy in an LF furnace, degassing it in a VD furnace under vacuum, and then casting it into a steel ingot; or refining the molten alloy in an ESH furnace and then preparing the steel ingot in a jet furnace.

6. The method for preparing high-speed steel according to claim 1, characterized in that, Step S4, the spheroidizing annealing, includes the following steps: S401. The round steel is heated to 770-790℃ at a rate of 90-100℃ / h and held at that temperature; S402. Heat to 880-890℃ at a rate of 90-100℃ / h and hold at that temperature; S403. Rapidly cool to 770-790℃ at a rate of ≥50℃ / h; S404. Slowly cool to 670-690℃; S405 is cooled to 550℃ in the furnace before being unloaded.

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