Efficient and energy-saving production method of high-performance tool steel

Abstract

The invention provides a high preparation and production method, which comprises the following steps: carrying out primary smelting by using a converter, carrying out vacuum refining, carrying out rapid continuous casting to form a primary blank, carrying out spheroidizing annealing treatment, carrying out hot isostatic pressing on the primary blank subjected to spheroidizing annealing treatment, lightly forging the primary blank, carrying out repeated hot forging, carrying out stress relief annealing, carrying out finish machining on the primary blank, quenching and carrying out isothermal aging treatment, after the components and the performance of the part are inspected to be qualified, finishing and warehousing are conducted, the part comprises the following standard chemical components in percentage by mass: 0.35-0.45% of C, 4.5-5.0% of Ni, 9.0-10% of Cr, 2.5-3.2% of Mo, 7.0-8.5% of Co, 0.015-0.020% of Ti, 0.5-0.6% of Si, 0.05-0.10% of Mn, 0.015-0.035% of Ce, less than or equal to 1% of Nb, less than or equal to 0.002% of P, less than or equal to 0.025% of S and the balance of matrix Fe and inevitable impurities, and the standard performance indexes of the part include the normal-temperature mechanical performance standard and the high-temperature performance standard. Wherein the normal-temperature mechanical properties Rm are larger than or equal to 1000 MPa, Rp0.2 is larger than or equal to 1180 MPa, A is larger than or equal to 10%, Z is larger than or equal to 20%, Kv is larger than or equal to 45 J, the grain size is grade 5, the high-temperature performance index Curie temperature ranges from 500 DEG C to 760 DEG C, and the red hardness at the temperature of 500 DEG C to 700 DEG C is larger than 60 HRC.

Description

[Technical Field]

[0001] This invention relates to the field of high alloy smelting, and more specifically to a highly efficient and energy-saving method for producing tool steel. [Background Technology]

[0002] With the rapid development of heavy industrial manufacturing fields such as military equipment and aerospace processing, the demand for special properties of high-speed tool steel, such as high hardness, high wear resistance, and high-temperature magnetic retention, is increasing. This type of steel is widely used in tools, molds, and some special parts. However, the development of this high-value steel material is difficult and the price is high, often requiring imports, which limits the further development of this type of material. Therefore, exploring and developing high-speed tool steel with excellent comprehensive properties has become an important research hotspot in the field of materials today.

[0003] As industrial production development requires the continuous development of different new steel grades, new requirements are constantly being put forward for their performance and other aspects. To this end, countries around the world have actively developed new types of steel with various characteristics to meet different performance requirements in recent years. The development of modern manufacturing industry has put forward higher requirements for the performance of high-performance steel. Countries around the world mainly adopt the following two approaches to improve performance: one is to optimize existing compositions and develop new steel grades, and the other is to improve production processes and update process control technologies.

[0004] Because of its high carbon content and the presence of a large number of alloying elements such as Ni, Cr, Mo, V, and Ce, this type of steel is prone to forming white spots and network carbides. It usually requires complex smelting and forming processes as well as special heat treatment processes, such as repeated forging and annealing, to reduce the white spot spheroidization structure and break down the sensitivity to network carbides.

[0005] The purpose of this invention is to provide an efficient preparation and production method for tool steel, so as to solve the problems mentioned in the background art, such as: high alloy content makes it prone to cracking, uneven microstructure and low performance during production.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a high-efficiency and energy-saving production method for high-performance tool steel, wherein the chemical composition (mass percentage) is: C: 0.35-0.45%, Ni: 4.5-5.0%, Cr: 9.0-10%, Al: 0.010-0.040%, Mo: 2.5-3.2%, Co: 7.0-8.5%, Ti: 0.015-0.020%, Si: 0.5-0.6%, Mn: 0.05-0.10%, Ce: 0.015-0.035%, Nb: ≤1%, P: ≤0.002%, S: ≤0.025%, with the remainder being matrix Fe and unavoidable impurities, and the hardenability DI value is controlled within the range of 54-63mm to reduce the tendency of the steel to crack.

[0007] The preparation method of the present invention is as follows: First, the scrap steel and iron are pretreated by converter steel (1) to reach the composition. Then, the pretreated steel (1) is vacuum refined (2) by vacuum drawing. Alloy elements and rare earth elements are added to reach the composition requirements. The billet is then quickly cast into a billet (3). The billet (3) is then spheroidized and annealed (4) to reach a spheroidization rate of more than 85%. After entering hot isostatic pressing (5), it is repeatedly hot forged and stress-relief annealed (6) and finished (7). Then, it is quenched and isothermal aged (8) to reach the mechanical performance index requirements (9). Finally, it is finished and put into storage (10).

[0008] The steel pretreatment (1) involves adding scrap steel and molten iron to the converter, blowing oxygen, injecting carbon powder, adding dephosphorizing agent to regulate the carbon, sulfur and phosphorus content in the steel, adding rare earth Ce, and achieving the design composition requirements (by mass fraction, the molten steel contains C at 0.35-0.65%, Si at 0.4-0.6%, rare earth Ce at 0.015-0.035%, P at less than 0.020% and / or S ≤ 0.0020%), followed by vacuum refining (2).

[0009] The vacuum refining (2) involves pre-treating the molten steel (1) and quickly transferring it to a vacuum refining furnace. Under vacuum, molybdenum, chromium, cobalt, manganese, nickel, titanium, niobium, and silicon are added in proportion to alloy the molten steel. The process is then checked to ensure that the design composition requirements are met. The process also includes further dehydrogenation and deoxidation treatment before the initial billet (3) is quickly cast.

[0010] The rapid continuous casting into a preliminary billet (3) involves rapidly casting the vacuum refining (2) into a designed blank, which then enters spheroidizing annealing (4).

[0011] The spheroidizing annealing (4) involves placing the cast billet (3) into a zoned heat treatment furnace (15), which is set up in the direction from feeding to discharging as follows: heating zone (780±20℃, time 370min±30min), holding zone (780±10℃, time 150min±30min), rapid cooling zone (610±20℃, time 90min±30min), isothermal zone (610±10℃, time 450±30min), and slow cooling zone (580±10℃, time 330±30min). The billet is then air-cooled to below 120℃. The uniformity of the metallographic structure reaches HV hardness difference ≤ 5HV, and the spheroidization rate inside the billet alloy reaches more than 85%. The billet then enters hot isostatic pressing (5).

[0012] The hot isostatic pressing (5) involves placing the spheroidized annealed blank into a vacuum hot press furnace (17) for hot isostatic pressing. The heating temperature is set to 1200-1500℃, the pressure is set to 1.0-1.5MPa, and the time is 1.5-2h. The blank then undergoes repeated hot forging and annealing (6).

[0013] The repeated hot forging and annealing (6) process involves lightly forging the alloy part after hot isostatic pressing (5), followed by repeated hot forging and annealing (6) in a vacuum annealing furnace. The hot forging temperature is 1150±50℃, and the stress-relief annealing temperature is set to 870±20℃. After holding at this temperature for 8±1.5h, the part is homogenized and then subjected to finishing (7). Finally, it is quenched and isothermal aged (8).

[0014] The quenching and isothermal aging (8) involves placing the forgings that have undergone repeated hot forging and annealing (6) into a vacuum quenching furnace for quenching and tempering. The quenching temperatures are 1120℃-1210℃, the quenching holding time is 5min, and the cooling method is oil cooling. After quenching, the blank is further tempered in a vacuum tempering furnace. Three tempering processes are used, with tempering temperatures of 540℃-570℃ and holding time of 1.5h. Then, isothermal aging is performed at 550±10℃ for 10±2min before inspection (9).

[0015] The inspection (9) includes room temperature mechanical property testing and high temperature performance testing. The room temperature mechanical properties are Rm≥1000MPa, Rp0.2≥1180MPa, A≥10%, Z≥20%, Kv≥45J, and grain size grade 5. The high temperature performance indicators are Curie temperature around 500℃-760℃ and red hardness greater than 60HRC at 500℃-700℃. After the performance inspection is qualified, the product is finished (10), packaged and stored for future use.

[0016] Compared with the prior art, the present invention provides a high-efficiency preparation and production method, which has the following beneficial effects:

[0017] 1. The alloying elements in this preparation method are composed of chromium, cobalt, manganese, molybdenum, nickel, niobium and silicon. The carbon content is high and the alloy composition exceeds 20%. In addition, a special heat treatment process is used to make the prepared parts have good performance at both room temperature and high temperature.

[0018] 2. The hot isostatic pressing process is adopted to maintain the parts with excellent mechanical properties and good surface and internal cavity dimensional accuracy comparable to forgings.

[0019] 3. The integrated manufacturing process from smelting to continuous casting and then to forging was disclosed. Heat treatment was carried out in a zoned heat treatment furnace, realizing the environmentally friendly mass production of high-performance parts. [Attached Image Description]

[0020] Appendix Figure 1 This is a schematic diagram of a high-efficiency and energy-saving production method for high-performance tool steel according to the present invention.

[0021] Appendix Figure 2 This is a schematic diagram of a production line for a high-efficiency and energy-saving production method of high-performance tool steel according to the present invention.

[0022] Appendix Figure 3 This is a metallographic structure diagram after isothermal aging in an embodiment of the present invention.

[0023] In the diagram: 1. Steel pretreatment; 2. Vacuum refining; 3. Casting of initial billet; 4. Spheroidizing annealing; 5. Hot isostatic pressing; 6. Repeated hot forging + annealing; 7. Finishing; 8. Quenching + isothermal aging; 9. Inspection; 10. Finishing and warehousing; 11. Converter; 12. Vacuum refining furnace; 13. Continuous casting machine; 14. Initial billet; 15. Zoned heat treatment furnace one; 16. Conveyor belt; 17. Vacuum hot isostatic pressing furnace; 18. Finished parts; 19. Zoned vacuum heat treatment furnace two; 20. Inspection room; 21. Machining workshop; 22. Insulation door; 23. Annealing furnace; 24. Quenching furnace; 25. Inspection room; 26. Aging furnace; 27. Packaging and warehousing.

Detailed Implementation Methods

[0024] The present invention will be further described below with reference to the accompanying drawings.

[0025] Appendix Figures 1-3 The accompanying drawings are for illustrative purposes only. The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] The invention provides, for example Figure 1-3 The method for producing a high-performance tool steel with high efficiency and energy saving is shown. The chemical composition (mass percentage) is as follows: C: 0.35-0.45%, Ni: 4.5-5.0%, Cr: 9.0-10%, Al: 0.010-0.040%, Mo: 2.5-3.2%, Co: 7.0-8.5%, Ti: 0.015-0.020%, Si: 0.5-0.6%, Mn: 0.05-0.10%, Ce: 0.015-0.035%, Nb: ≤1%, P: ≤0.002%, S: ≤0.025%, with the remainder being the matrix Fe and unavoidable impurities. The hardenability DI value is controlled within the range of 54-63mm to reduce the tendency of the steel to crack.

[0027] like Figure 1-3As shown, the preparation method of the alloy of the present invention is as follows: First, the scrap steel and iron are pretreated by converter steel (1) to reach the composition. Then, the pretreated steel (1) is vacuum refined (2) by vacuuming. Alloy elements and rare earth elements are added to reach the composition requirements. The steel is then quickly cast into a billet (3). The billet (3) is then spheroidized and annealed (4) to reach a spheroidization rate of more than 85%. After entering hot isostatic pressing (5), it is repeatedly hot forged and stress-relief annealed (6) and finished (7). Then, it is quenched and isothermal aged (8) to reach the mechanical performance index requirements (9). Finally, it is finished and put into storage (10).

[0028] like Figure 1-2 As shown, the steel pretreatment (1) involves adding scrap steel and molten iron to the converter, blowing oxygen, injecting carbon powder, adding dephosphorizing agent to regulate the carbon, sulfur and phosphorus content in the steel, adding rare earth Ce, and achieving the design composition requirements (by mass fraction, the molten steel contains C at 0.35-0.65%, Si at 0.4-0.6%, rare earth Ce at 0.015-0.035%, P at less than 0.020% and / or S ≤ 0.0020%), followed by vacuum refining (2).

[0029] like Figure 1-2 As shown, the vacuum refining (2) involves pre-treating the molten steel (1) and quickly transferring it to a vacuum refining furnace. Under vacuum, molybdenum, chromium, cobalt, manganese, nickel, titanium, niobium, and silicon are added in proportion to alloy the molten steel. The process is then checked to ensure that the design composition requirements are met. The process also includes further dehydrogenation and deoxidation treatment before the initial billet (3) is quickly cast.

[0030] like Figure 1-2 As shown, the rapid continuous casting into a preliminary billet (3) is to rapidly cast the vacuum refining (2) into a designed blank and then enter the spheroidizing annealing (4).

[0031] like Figure 1-2 As shown, the spheroidizing annealing (4) places the cast billet (3) into the partitioned heat treatment furnace (15), and sets it into a heating zone (780±20℃, time 370min±30min), a holding zone (780±10℃, time 150min±30min), a rapid cooling zone (610±20℃, time 90min±30min), an isothermal zone (610±10℃, time 450±30min), and a slow cooling zone (580±10℃, time 330±30min) according to the direction from feeding to discharging. Then it is air-cooled to below 120℃. The uniformity of the metallographic structure reaches HV hardness difference ≤5HV, and the spheroidization rate inside the billet alloy reaches more than 85%. Then it enters the hot isostatic pressing (5).

[0032] Preferably, the spheroidizing annealing is carried out in a partitioned heat treatment furnace (15), which is divided into at least two independently temperature-controlled furnace chambers. The furnace chambers are equipped with openable insulated doors (22), and the furnace chambers are also provided with a conveyor belt (16) for automatic transfer of heat-treated parts between the furnace chambers.

[0033] The hot isostatic pressing (5) involves placing the spheroidized annealed blank into a vacuum hot press furnace (17) for hot isostatic pressing. The heating temperature is set to 1200-1500℃, the pressure is set to 1.0-1.5MPa, and the time is 1.5-2h. The blank then undergoes repeated hot forging and annealing (6).

[0034] Preferably, the vacuum hot press furnace (17) and the partitioned heat treatment furnace (15) are arranged adjacent to each other in the process flow sequence, and an automatic conveyor belt is also provided between the furnaces for automatic transfer of parts between the furnaces.

[0035] like Figure 1-2 As shown, the repeated hot forging and annealing (6) is to first lightly forge the alloy part after hot isostatic pressing (5), and then repeatedly hot forge and anneal (6) in a vacuum annealing furnace. The hot forging temperature is 1150±50℃, and the stress relief annealing temperature is set to 870±20℃. After holding at 8±1.5h for homogenization and stress relief annealing, the part is then finished (7) and then quenched and isothermal aging (8).

[0036] The quenching and isothermal aging (8) involves placing the forgings that have undergone repeated hot forging and annealing (6) into a vacuum quenching furnace for quenching and tempering. The quenching temperatures are 1120℃-1210℃, the quenching holding time is 5min, and the cooling method is oil cooling. After quenching, the blank is further tempered in a vacuum tempering furnace. Three tempering processes are used, with tempering temperatures of 540℃-570℃ and holding time of 1.5h. Then, isothermal aging is performed at 550±10℃ for 10±2min before inspection (9).

[0037] Preferably, the vacuum annealing furnace is formed by the annealing furnace chamber (23) of the partitioned vacuum heat treatment furnace two (19), and the vacuum quenching furnace and vacuum tempering furnace are formed by the quenching furnace chamber (24) of the partitioned vacuum heat treatment furnace two (19). The furnace chamber partition of the partitioned vacuum heat treatment furnace two (19) also includes an isothermal aging furnace chamber (26). The furnace chamber partitions are arranged adjacently according to the process flow sequence, and an automatic conveyor belt (16) is also provided between the furnace chambers for automatic transfer of parts between the furnaces.

[0038] The inspection (9) includes room temperature mechanical property testing and high temperature performance testing. The room temperature mechanical properties are Rm≥1000MPa, Rp0.2≥1180MPa, A≥10%, Z≥20%, Kv≥45J, and grain size grade 5. The high temperature performance indicators are Curie temperature around 500℃-760℃ and red hardness greater than 60HRC at 500℃-700℃. After the performance inspection is qualified, the product is finished (10) and put into storage for future use.

[0039] Preferably, all heat treatments of the present invention are carried out in a partitioned heat treatment furnace, wherein the partitioned heat treatment furnace one (15) and the partitioned vacuum heat treatment furnace two (19) are divided into at least two independently temperature-controlled furnace chambers, and the furnace chambers are equipped with openable insulated doors (22), and the furnace chambers are also provided with a conveyor belt (16) for automatic transfer of heat-treated parts between the furnace chambers.

[0040] Figure 3 The image shows the metallographic structure of a Φ40 gear obtained in this embodiment of the invention, located 20 mm from the center line. As can be seen from the image, the gear is mainly composed of tempered sorbite with good uniformity.

[0041] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-performance tool steel production method with high efficiency and energy saving, the chemical composition of which is (mass percentage) C: 0.35-0.45%, Ni: 4.5-5.0%, Cr: 9.0-10%, Al: 0.010-0.040%, Mo: 2.5-3.2%, Co: 7.0-8.5%, Ti: 0.015-0.020%, Si: 0.5-0.6%, Mn: 0.05-0.10%, Ce: 0.015-0.035%, Nb: ≤1%, P: ≤0.002%, S: ≤0.025%, and the rest is base Fe and inevitable impurities, and the hardenability DI value is controlled in the range of 54-63 mm to reduce the tendency of brittle cracking of the steel grade.

2. The method of claim 1, wherein the high-performance tool steel is produced with high efficiency and energy saving, and the method is characterized in that, The preparation method steps are as follows: first, the scrap steel and iron are pretreated in the converter (1) to achieve the composition, then the molten steel is vacuum refined (2) by vacuumizing and adding alloying elements and rare earth elements to achieve the composition requirement, and then rapidly continuous casting into the initial blank (3), then spheroidizing annealing treatment (4) is performed on the initial blank (3) to achieve a spheroidizing rate of more than 85%, then hot isostatic pressing (5) is performed, then repeated hot forging, stress relief annealing (6) and finishing (7) are performed, then quenching and isothermal aging (8) are performed, then inspection (9) is performed to achieve the mechanical property index requirement, and then finishing and storage (10) are performed.

3. The method of claim 2, wherein the high-performance tool steel is produced by the following steps: The molten steel pretreatment (1) is carried out by adding scrap steel and molten iron in the converter, blowing oxygen, spraying carbon powder, adding dephosphorizing agent to control the carbon, sulfur and phosphorus content in the steel, adding rare earth Ce, and achieving the design composition requirement (in mass fraction, the direct molten steel contains C in the range of 0.35-0.65%, Si in the range of 0.4-0.6%, rare earth Ce in the range of 0.015-0.035%, P less than 0.020% and / or S less than 0.0020%), and then vacuum refining (2) is performed. ​ 4. The method of claim 3, wherein the high-performance tool steel is produced by the following steps of: The vacuum refining (2) is to rapidly transfer the molten steel pretreatment (1) to the vacuum refining furnace, vacuumize, and add molybdenum, chromium, cobalt, manganese, nickel, titanium, niobium and silicon elements to alloy the molten steel according to the proportion, and then inspect to achieve the design composition requirement, and further hydrogen removal and deoxidation treatment process is performed, and then the initial blank (3) is rapidly cast. ​ 5. The method of claim 4, wherein the high-performance tool steel is produced by the following steps: The initial blank (3) is rapidly cast into the designed blank by the vacuum refining (2), and then spheroidizing annealing (4) is performed. ​ 6. The method of claim 5, wherein the high-performance tool steel is produced with high efficiency and energy saving. The spheroidizing annealing (4) is to place the initial blank (3) into the partitioned heat treatment furnace (15), and set the temperature rising zone (780±20℃, time 370min±30min), the holding zone (temperature 780±10℃, time 150min±30min), the fast cooling zone (610±20℃, time 90min±30min), the isothermal zone (610±10℃, time 450±30min), and the slow cooling zone (580±10℃, time 330±30min) according to the direction from feeding to discharging, and then air cool to below 120℃, the metallographic structure uniformity reaches HV hardness difference ≤5HV, the spheroidizing rate of the blank alloy reaches more than 85%, and then the hot isostatic pressing (5) is performed.

7. The method of claim 6, wherein the high-performance tool steel is produced by the following steps: The hot isostatic pressing (5) is to put the spheroidizing annealed blank into a vacuum hot pressing furnace (17) for hot isostatic pressing process, the heating temperature is set to 1200-1500℃, the pressure is set to 1.0-1.5MPa, and the time is 1.5-2h, then it enters the repeated hot forging and annealing (6), the annealing is carried out in the annealing furnace chamber (23) of the partition vacuum heat treatment furnace two (19). ​ 8. The method of claim 7, wherein the high-performance tool steel is produced by the following steps: The repeated hot forging and annealing (6) is to first lightly forge the alloy piece after the hot isostatic pressing (5), then carry out the repeated hot forging and annealing (6) process in the vacuum annealing furnace, the hot forging temperature is 1150±50℃, the stress relief annealing temperature is set to 870±20℃ for 8±1.5h, after the uniformizing stress relief annealing, it enters the finish machining (7), then it enters the quenching and isothermal aging (8), the quenching is carried out in the quenching furnace chamber (24) and the isothermal aging furnace chamber (26) of the partition vacuum heat treatment furnace two (19). ​ 9. The method of claim 8, wherein the high-performance tool steel is produced by the following steps: The quenching and isothermal aging (8) is to put the forged piece after the repeated hot forging and annealing (6) into the vacuum quenching furnace for quenching and tempering, the quenching temperature is 1120-1210℃, the quenching holding time is 5min, the cooling mode is oil cooling, after the quenching, the blank is continuously treated by the vacuum tempering furnace for tempering, three times of tempering are adopted, the tempering temperatures are 540-570℃, the holding time is 1.5h, then it enters the 550±10℃ isothermal aging for 10±2min, and then it enters the inspection (9). ​ 10. The method of claim 9, wherein the high performance tool steel is produced by the following steps: The inspection (9) includes the normal temperature mechanical property detection and the high temperature property detection, wherein the normal temperature mechanical property Rm≥1000MPa, Rp0.2≥1180MPa, A≥10%, Z≥20%, Kv≥45J, the grain size is 5, the high temperature property index Curie temperature is about 500-760℃, the 500-700℃ red hardness is greater than 60HRC, after the performance inspection is qualified, it enters the finishing (10) for shaping and storage for standby. ​

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