A preparation method and casting device of a static spacer bushing cast high-speed steel composite roller

Abstract

This invention discloses a method and casting apparatus for preparing a statically spaced high-speed steel composite roll, belonging to the field of metallurgical roll manufacturing technology. The casting apparatus includes a movable workstation trolley, a base box, a spacer positioning end cover, a water-cooled crystallizer, a spacer, a CNC casting table, a weighing casting machine, a ladle, a dedicated casting pipe for the working layer, a riser box closing lifting arm, and a riser box. The water-cooled crystallizer is positioned above the base box, and the spacer is located inside the water-cooled crystallizer, with the interior of the spacer forming a core cavity. The dedicated casting pipe for the working layer on the weighing casting machine extends between the water-cooled crystallizer and the spacer, and a core-filling pouring cup is provided at the top of the riser box. During preparation, the base box is first shaped, and the spacer and water-cooled crystallizer are installed. After inert gas protection, molten high-speed steel is statically poured between the water-cooled crystallizer and the spacer. After the working layer solidifies, the box is closed, and the core molten steel is poured. The composite roll is obtained through slow cooling, annealing, rough machining, heat treatment, and finish machining.

Description

Technical Field

[0001] This invention relates to the field of metallurgical roll manufacturing technology, and in particular to a method for preparing a statically spaced high-speed steel composite roll and a casting apparatus. Background Technology

[0002] Currently, the two mature international processes suitable for mass production of high-speed steel rolls are centrifugal casting and CPC (continuous cladding casting). CPC casting was invented by Nippon Steel in Japan, which has long held a monopoly on this technology. High-speed steel rolls manufactured using this process possess a perfect metallic microstructure in their working layer, and their performance is unmatched by centrifugally cast rolls. Many domestic roll companies and institutions have made numerous efforts to develop domestically produced CPC technology, but without success. Therefore, inventing a new casting process suitable for domestic production conditions, capable of achieving working layer casting quality comparable to CPC casting, is of paramount importance.

[0003] The existing centrifugally cast high-speed steel rolls have the following shortcomings: 1. Due to the extremely high centrifugal force multiple of about 100 in the casting working layer, coupled with the high alloy content and the difference in alloy mass density in the working layer, the distribution of the working layer is uneven on the inside and outside of the cross-section. The tungsten alloy content is higher towards the outside, while the vanadium alloy content is lower, resulting in radial component segregation and cracks, and uneven wear resistance.

[0004] 2. Since centrifugal casting relies on metal molds for cooling, the temperature rise of the molds in the later stage of cooling leads to insufficient undercooling of the molten steel in high-speed steel. The carbide structure in the working layer of hot-rolled strip rolls becomes coarser towards the inner radial direction, resulting in a certain hardness gradient in the working layer. 3. When centrifugal casting pours molten steel into the working layer, the high-speed rotation of the cold mold causes the molten steel to splash at an instantaneous speed. The high-temperature molten steel comes into contact with the air, artificially creating oxidation of the molten steel and deteriorating its quality.

[0005] 4. The inner wall of the roll mold (cold type) is sprayed with heat-insulating coating before casting, and anti-oxidation protective slag is added after casting. These factors all affect the quality of the metallurgical bonding between the inner and outer layers, and the so-called failure of flaw detection is due to this.

[0006] Therefore, developing a high-speed steel composite roll that is feasible to produce, has a metallographic structure that meets the CPC process level, and performs similarly is of great engineering value to my country's roll manufacturing industry. Summary of the Invention

[0007] To address the problems of compositional segregation and cracking, uneven radial wear resistance, and unsatisfactory yield in existing high-speed steel rolls, this invention provides a high-speed steel composite roll and its preparation method. Before casting, a low-melting-point metal spacer as a transition layer and a water-cooled crystallizer are implanted. Molten iron is then poured into the working layer to achieve bonding between the working layer and the transition layer. Next, a riser box is closed, and molten iron is poured into the core to achieve bonding between the core and the transition layer. This method satisfies the requirements for high mechanical properties in the working layer, high strength and toughness in the core, and good interfacial metallurgical bonding, meeting the casting needs of small and medium-sized roll blanks. Simultaneously, this process and equipment can also be used to produce high-chromium ferrochrome and other composite rolls. Technical solution

[0008] Process Flow Process planning, bottom box design (with pre-installed metal sleeve), bottom box placement at the casting machine station, crystallizer placement at the casting machine station and merging with the bottom box, riser box placement at the preparation casting station, batching and melting of molten steel, pouring of molten steel into the working layer, merging of riser box, pouring of core molten steel, unpacking, inspection of roll blanks, annealing, rough machining, non-destructive testing, heat treatment (quenching + tempering), finish machining, and comprehensive physical property testing. (1) Chemical composition of high-speed steel working layer (wt%): C: 1.5~2.0; Cr: 4.0~6.0; Mo: 3.5–5.0; W: 1.0~4.5; V: 4.0~6.0; Si: 0.3~0.8; Mn: 0.4~0.9; Nb: 0.1~3.5; N: 0.02~0.06; P≤0.025, S≤0.015; The balance is Fe and unavoidable impurities.

[0009] (2) Chemical composition of the core matrix steel (wt%): C: 1.3~1.50; Cr: 0.15~0.4; Si: 1.6~2.5; Mn: 0.5~1.0; Ni: 0.5~1.0; The balance is Fe and unavoidable impurities.

[0010] Deterioration treatment Organizational structure characteristics The microstructure of the high-speed steel working layer consists of fine tempered martensite + uniformly dispersed MC, M2C, M6C, and M23 C6 and M7C3 type carbides, without network or segregation; The transition layer is a flat and dense metallurgical bonding layer, free of pores, inclusions, and shrinkage, with an interfacial bonding strength ≥600MPa; The core is tempered sorbite with a small amount of bainite, with a good balance of strength and toughness. After heat treatment, the strength is ≥700MPa, and it can withstand large torque and impact loads.

[0011] Preparation method (1) Casting machine and its performance functions Positioning of the bottom box for roll casting; The rolling mill is automatically weighed in real time during the casting process to control the casting speed.

[0012] During the pouring of the working layer, the pouring cup system is automatically controlled in real time to rise with the liquid level.

[0013] Monitor the temperature and changes of the metal spacer.

[0014] Automatic control of the crystallizer cooling water.

[0015] Automatic control of protective gas output; The riser box is automatically closed.

[0016] After the working layer solidifies and cools, it is moved out of the casting station to prepare for the casting of the next roll.

[0017] High-speed steel working layer casting process control The roll base box, which has been placed with the crystallizer, is positioned at the casting machine station.

[0018] Connect the water circuit and the protective gas circuit of the crystallizer, and pass water and gas through to replace the air in the inner and outer cavities with argon gas until the casting is completed.

[0019] Move the pouring cup and pouring system down to the lowest pouring position.

[0020] Set the pouring time for the working layer.

[0021] The high-speed steel molten steel is melted by medium frequency induction melting and then refined by argon blowing at the bottom of the furnace. It is then poured into the crystallizer at 1460-1480℃.

[0022] The riser box is located on the crystallizer.

[0023] (3) Core molten steel casting The core molten iron is poured again according to the time specified in the process, so that the solidification and shrinkage of the outer layer and the core feeding are synchronized, forming a strong metallurgical bonding interface.

[0024] (4) Post-cast slow cooling and stress-relief annealing Spheroidizing annealing: Hold at 820-840℃ for 4-8 hours, furnace cool to below 600℃ and then air cool to improve machinability; roughing Because the riser end of the roll body is covered by the core metal material and the inclusions in the working layer float to this point, the allowance in this area is slightly larger than that in centrifugal machining, so attention should be paid to this during rough machining.

[0025] (6) Heat treatment process The process is the same as centrifugal casting.

[0026] Test items: Chemical composition: The finished product composition of the working layer and the finished product composition of the core. In particular, the radial composition, hardness, and metallographic structure of the working layer.

[0027] Hardness: As-cast hardness, hardness of finished product after heat treatment, especially the radial hardness variation of the working layer.

[0028] Tensile test: After casting, take a tensile specimen from the riser end, and perform a tensile test after heat treatment.

[0029] Metallography: Metallographic features of the working layer and core after heat treatment. In particular, the radial metallographic changes in the working layer.

[0030] Final performance: (1) Surface hardness of working layer: HSD 83~88; (2) Core hardness: HSD33~45; (3) Core strength: 350MPa (4) Impact energy AKv ≥ 40J (5) Interface bonding strength ≥ 450 MPa (6) No cracks, no segregation, no interface defects, meeting the requirements for long-term stable use of large double roller mills.

[0031] Compared with related technologies, the preparation method and casting apparatus for statically spaced high-speed steel composite rolls provided by the present invention have the following advantages: 1. Using a static tangential gating method with rapid forced cooling in a crystallizer results in a uniform composition of the high-speed steel working layer, eliminating compositional segregation caused by centrifugal rollers, and producing small-sized and well-dispersed primary phase carbides. The as-cast state exhibits no network of carbides. 2. The casting tooling crystallizer has no coating adhering to it, so there is no coating to contaminate the molten steel and generate new inclusions; 3. After metallurgical composite processing, the partial melting of the interlayer prevents excessive melting of the working layer by molten iron in the core of individual centrifugal rolls, which could lead to thinning of the working layer, insufficient toughness due to increased core alloy content, or poor bonding. 4. During casting, it is protected by inert gas, eliminating the need for glass protective slag. This results in fewer inclusions in the bonding layer, improving the bonding strength of the metal materials in each layer of the roll blank and the pass rate after non-destructive testing. At the same time, there is no severe oxidation of the working layer steel caused by centrifugal casting.

[0032] 5. Because the roll body is poured from bottom to top, the inclusions in the molten steel float to the end face of the riser and are removed by machining.

[0033] 6. Because the core of the roll is made of ductile iron cast iron, the ductile iron core has low thermal expansion and low thermal convexity, resulting in good roll threading performance. This avoids the shortcomings of CPC cast high-speed steel rolls and expands the number of mill stands in which rolls produced by this process can be used. Attached Figure Description

[0034] Figure 1 A schematic diagram of the casting device structure for static spacer casting of high-speed steel composite rolls provided by the present invention.

[0035] The following are labeled in the diagram: 1. CNC pouring table; 2. Weighing pouring machine; 3. Ladle; 4. Core-filling pouring cup; 5. Riser box; 6. Molding sand; 7. Special pouring pipe for working layer; 8. Isolation sleeve; 9. Core cavity; 10. Water-cooled crystallizer; 11. Solidified molten steel in working layer; 12. Isolation sleeve positioning end cap; 13. Bottom box; 14. Molding sand; 15. Movable workstation trolley; 16. Crystallizer cooling water circuit; 17. Riser box closing lifting arm; 18. Protective gas pipeline. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] In the specific implementation process, such as Figure 1 As shown, a casting device for statically casting high-speed steel composite rolls with a diaphragm includes a CNC casting table 1, a weighing casting machine 2, a ladle 3, a core-filling pouring cup 4, a riser box 5, molding sand 6, a special pouring pipe for the working layer 7, a diaphragm 8, a core cavity 9, a water-cooled crystallizer 10, solidified molten steel in the working layer 11, a positioning end cap for the diaphragm 12, a bottom box 13, molding sand 14, a movable workstation trolley 15, a cooling water circuit for the crystallizer 16, a rising box closing lifting arm 17, and a protective gas pipeline 18.

[0038] A base box 13 is placed on top of the movable workstation trolley 15. The base box 13 is filled with molding sand 14. An isolation sleeve positioning end cap 12 is set on top of the base box 13. The isolation sleeve positioning end cap 12 positions and supports the isolation sleeve 8 at the bottom. A water-cooled crystallizer 10 is set on top of the isolation sleeve positioning end cap 12. The isolation sleeve 8 is placed inside the water-cooled crystallizer 10. The isolation sleeve 8 is made of low melting point metal material. The internal space of the isolation sleeve 8 forms the core cavity 9. The annular gap between the water-cooled crystallizer 10 and the isolation sleeve 8 forms the working layer casting cavity. The outer wall of the water-cooled crystallizer 10 is connected to the crystallizer cooling water channel 16. The inlet and outlet of the crystallizer cooling water channel 16 are connected to the outer wall of the water-cooled crystallizer 10 to form a circulating cooling circuit. The outlet of the protective gas pipeline 18 is set at the bottom position between the water-cooled crystallizer 10 and the isolation sleeve 8. The protective gas pipeline 18 is connected to an external argon gas source.

[0039] A CNC pouring platform 1 is fixedly installed on one side of the movable workstation trolley 15. A weighing pouring machine 2 is installed on the top of the CNC pouring platform 1. A ladle 3 is installed above the weighing pouring machine 2. The ladle 3 is used to hold high-speed molten steel after medium-frequency induction melting and bottom argon blowing refining. A special pouring pipe 7 for the working layer is connected to the weighing pouring machine 2. The outlet end of the special pouring pipe 7 for the working layer extends to the bottom of the working layer pouring cavity between the water-cooled crystallizer 10 and the isolation sleeve 8. During the pouring process, the weighing pouring machine 2 weighs the weight of the molten steel injected into the cavity in real time and automatically controls the steel output flow rate of the ladle 3 according to the set pouring speed.

[0040] On the other side of the movable workstation trolley 15, a riser box assembling lifting arm 17 is set. A riser box 5 is fixedly installed on the riser box assembling lifting arm 17. The riser box 5 is filled with molding sand 6. A core-filling pouring cup 4 is installed on the top of the riser box 5. The riser box assembling lifting arm 17 drives the riser box 5 to move up and down in the vertical direction. The movable workstation trolley 15 moves in the horizontal direction to the pouring station or the assembly station.

[0041] When preparing high-speed steel composite rolls using the above casting device, the bottom box 13 is first placed on the movable work station trolley 15, the bottom box 13 is filled with molding sand 14, and the isolation sleeve positioning end cap 12, the isolation sleeve 8 and the water-cooled crystallizer 10 are placed on top of the bottom box 13 in sequence. The core cavity 9 is formed inside the isolation sleeve 8, and the inner wall of the water-cooled crystallizer 10 is an uncoated metal wall.

[0042] The movable workstation trolley 15 is moved horizontally to the casting station on one side of the CNC casting table 1, and the crystallizer cooling water circuit 16 and the protective gas circuit 18 are connected. The crystallizer cooling water circuit 16 circulates cooling water into the outer wall of the water-cooled crystallizer 10, and the protective gas circuit 18 circulates argon into the bottom of the casting cavity of the working layer between the water-cooled crystallizer 10 and the isolation sleeve 8. The argon completely replaces the air in the cavity from bottom to top, and argon is continuously circulated as a protective atmosphere throughout the casting process.

[0043] After high-speed steel molten steel is melted by medium-frequency induction melting and argon blowing at the bottom of the furnace, the temperature of the molten steel is controlled at 1460-1480℃. The molten steel in the ladle 3 is injected into the working layer casting cavity between the water-cooled crystallizer 10 and the isolation sleeve 8 by a static pouring method through the weighing pouring machine 2 and / or the working layer special pouring pipe 7. During the pouring process, the weighing pouring machine 2 weighs the molten steel in real time and controls the pouring speed, while monitoring the temperature change of the isolation sleeve 8 in real time. The pouring stops when the molten steel level slowly rises from bottom to top to the upper plane of the water-cooled crystallizer 10. During the pouring process, cooling water is continuously circulated into the water-cooled crystallizer 10 for forced cooling. During the pouring process of the working layer molten steel, the heated part of the isolation sleeve 8 melts and forms a metallurgical bond with the working layer.

[0044] After the working layer of molten steel solidifies, a solidified molten steel 11 is formed in the working layer. The movable work station trolley 15 is moved horizontally to the box closing position on one side of the riser box closing lifting arm 17. The riser box closing lifting arm 17 is started to close the riser box 5 above the water-cooled crystallizer 10. The molding sand 6 filled inside the riser box 5 and the core filling pouring cup 4 at the top form the core pouring channel.

[0045] After the working layer molten steel solidifies and shrinks to the predetermined time, the core molten steel is poured into the riser box 5 through the core filling pouring cup 4. The core molten steel enters the core cavity 9 through the sprue formed by the molding sand 6 in the riser box 5, realizing the metallurgical bonding between the core and the working layer. During the core molten steel pouring process, the solidification and shrinkage of the working layer and the core feeding are carried out simultaneously.

[0046] After casting, the roll blank undergoes slow cooling followed by stress-relief annealing using a spheroidizing annealing process at a temperature of 820–840℃ for 4–8 hours. It is then furnace-cooled to below 600℃ and subsequently air-cooled. After annealing, the roll blank is removed from the box and inspected. If the inspection is successful, the riser end of the roll body is rough-machined to remove inclusions from the working layer. After rough machining, non-destructive testing is performed. If the inspection is successful, quenching and tempering are then carried out sequentially. After heat treatment, the roll undergoes finishing to obtain a high-speed steel composite roll. The surface hardness of the working layer of the roll is HSD 83-88, the core hardness is HSD 33-45, the core strength is not less than 350MPa, the impact energy AKv is not less than 40J, and the interface bonding strength is not less than 450MPa. The roll is free of cracks, segregation, and interface defects. The microstructure of the working layer consists of a tempered martensite matrix with uniformly dispersed MC, M2C, M6C, and M... 23 C5 and M7C3 type carbides are free of network carbides and compositional segregation. The transition layer between the working layer and the core is a flat and dense metallurgical bonding layer with no porosity, inclusions and shrinkage defects at the interface.

[0047] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A casting apparatus for statically casting high-speed steel composite rolls with spacers, characterized in that, It includes a CNC pouring table, a weighing pouring machine, a ladle, a core-filling pouring cup, a riser box, molding sand, a special pouring pipe for the working layer, an isolation sleeve, a core cavity, a water-cooled crystallizer, solidified molten steel in the working layer, an isolation sleeve positioning end cap, a bottom box, molding sand, a movable workstation trolley, a crystallizer cooling water circuit, a riser box closing lifting arm, and protective gas pipelines; The movable workstation trolley is equipped with a base box, which contains molding sand. An isolation sleeve positioning end cover is located above the base box. A water-cooled crystallizer is located above the isolation sleeve positioning end cover. An isolation sleeve is installed inside the water-cooled crystallizer. The isolation sleeve contains a core cavity. The working layer of solidified molten steel is located between the water-cooled crystallizer and the isolation sleeve. A crystallizer cooling water circuit is connected to the water-cooled crystallizer. A protective gas pipeline is provided between the water-cooled crystallizer and the isolation sleeve. A CNC casting platform is provided on one side of the movable workstation trolley. A weighing casting machine is provided on the top of the CNC casting platform. A molten steel ladle is provided above the weighing casting machine. A special casting pipe for the working layer is provided on the weighing casting machine. The special casting pipe for the working layer extends to the space between the water-cooled crystallizer and the isolation sleeve. On the other side of the movable workstation trolley is a riser box closing lifting arm, on which a riser box is mounted, a core-filling pouring cup is mounted on the top of the riser box, and molding sand is contained inside the riser box.

2. The casting apparatus for statically casting high-speed steel composite rolls with spacers according to claim 1, characterized in that, The inner wall of the water-cooled crystallizer is an uncoated metal wall, and the isolation sleeve is a low-melting-point metal sleeve. The isolation sleeve partially melts during the casting process of the working layer and forms a metallurgical bond with the working layer.

3. The casting apparatus for statically casting high-speed steel composite rolls with spacers according to claim 1, characterized in that, The weighing and casting machine is used to weigh the molten steel in real time during the casting process and control the casting speed; the outlet of the protective gas pipeline is located at the bottom between the water-cooled crystallizer and the isolation sleeve, and is used to introduce inert gas into the cavity to replace the air; the cooling water flow rate of the crystallizer cooling water circuit is adjusted according to the temperature monitoring signal of the isolation sleeve.

4. The casting apparatus for statically casting high-speed steel composite rolls with spacers according to claim 1, characterized in that, The riser box moves vertically relative to the movable workstation trolley via the riser box closing lifting arm. The movable workstation trolley moves horizontally to the pouring station or the box closing station. The isolation sleeve positioning end cover is located between the bottom box and the isolation sleeve and is used for bottom positioning and support of the isolation sleeve.

5. A method for preparing high-speed steel composite rolls using the casting apparatus described in claims 1 to 4, characterized in that, Includes the following steps: Step 1: Place the base box on the movable workstation trolley, fill the base box with molding sand, and install the isolation sleeve positioning end cap, isolation sleeve and water-cooled crystallizer in sequence on the top of the base box, forming the core cavity inside the isolation sleeve. Step 2: Move the movable workstation trolley to the casting station, connect the cooling water circuit and protective gas pipeline of the crystallizer, and introduce inert gas into the cavity between the water-cooled crystallizer and the isolation sleeve to replace the air. Staticly pour the high-speed steel molten steel into the space between the water-cooled crystallizer and the isolation sleeve through the special casting pipe of the working layer until the liquid level of the molten steel rises to the upper plane of the water-cooled crystallizer. During the casting process, the casting speed is controlled by the weighing casting machine, and the temperature change of the isolation sleeve is monitored in real time. Step 3: After the molten steel in the working layer solidifies, the riser box, which is filled with molding sand and has a core-filling pouring cup on top, is placed above the water-cooled crystallizer by the riser box closing lifting arm. Step 4: After the working layer molten steel solidifies and shrinks to the predetermined time, pour the core molten steel into the core filling pouring cup, so that the core molten steel enters the core cavity and achieves metallurgical bonding between the core and the working layer. Step 5: After casting, slow cooling and stress-relief annealing are performed, followed by unpacking, rough machining, heat treatment and finish machining to obtain high-speed steel composite rolls.

6. The method for preparing a statically spaced high-speed steel composite roll according to claim 5, characterized in that, In step two, the pouring temperature of the high-speed steel molten steel is 1460-1480℃. During the pouring process, cooling water is continuously introduced into the water-cooled crystallizer for forced cooling, and argon gas is introduced throughout the pouring process as a protective atmosphere.

7. The method for preparing a statically spaced high-speed steel composite roll according to claim 5, characterized in that, In step five, the stress-relief annealing is spheroidizing annealing, with an annealing temperature of 820-840℃ and a holding time of 4-8 hours, followed by furnace cooling to below 600℃ and then air cooling; the heat treatment is quenching and tempering treatment performed sequentially.

8. The method for preparing a statically spaced high-speed steel composite roll according to claim 5, characterized in that, The chemical composition of the high-speed steel molten steel, by mass percentage, is as follows: C: 1.5–2.0%, Cr: 4.0–6.0%, Mo: 3.5–5.0%, W: 1.0–4.5%, V: 4.0–6.0%, Si: 0.3–0.8%, Mn: 0.4–0.9%, Nb: 0.1–3.5%, N: 0.02–0.06%, P≤0.025%, S≤0.015%, with the balance being Fe and unavoidable impurities; The chemical composition of the core molten steel, by mass percentage, is: C: 1.3-1.50%, Cr: 0.15-0.4%, Si: 1.6-2.5%, Mn: 0.5-1.0%, Ni: 0.5-1.0%, with the balance being Fe and unavoidable impurities.

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