Radial forging forming method for high-thermal-strength steel hollow stepped shaft core component

Abstract

The present application relates to a kind of high heat-resistant steel core component hollow stepped shaft radial forging forming method, comprising the following steps: electroslag remelted ingot is prepared by extrusion forming straight pipe blank—straight pipe blank is shrunk by radial pipe forging into shrunk pipe blank—shrunk pipe blank is made into hollow stepped pipe blank by core rod radial hollow forging—hollow stepped pipe blank is made into stepped shaft forging by radial forging with straight rod—stepped shaft forging annealing—stepped shaft forging is drilled to hollow stepped shaft by straight rod drilling mode.This application meets the high heat-resistant steel hollow stepped forging in the forging process Inner hole outer circle simultaneously reach large deformation, increase deformation degree, especially with rod forming stage, with small deformation to achieve large deformation degree, deformation process time is short, realize deformation under constant temperature, the whole deformation is easy to realize dynamic recrystallization, easy to control high heat-resistant steel carbide precipitation and distribution, solve the technical difficulty that forging deformation process organization homogenization low, high temperature strength, low temperature impact simultaneously reach requirement.

Description

Technical Field

[0001] This invention belongs to the field of material forming, and specifically relates to a radial forging method for a hollow stepped shaft of a high heat-strength steel core component. Background Technology

[0002] In recent years, my country's equipment manufacturing industry has developed rapidly, creating an urgent need to extend the service life of high-end equipment's pressure-bearing hollow core components. These components operate in harsh environments, requiring solutions for alternating load impact toughness at low temperatures and high-temperature performance stability under high temperature and pressure. This necessitates sufficiently high high-temperature strength to ensure the components do not deform under high temperature and pressure, while simultaneously possessing high impact toughness at both room temperature and low temperatures (-40℃) to prevent brittle fracture under alternating loads. To address this, drawing on the material properties of 25Cr3Mo3NiNbZr and 40CrNi4Mo1V, a high-thermal-strength material, 30Cr2Ni3MoWV, was developed. This material possesses high room-temperature strength, high low-temperature impact toughness, and high-temperature strength, making it a key material for manufacturing pressure-bearing hollow core components for heavy equipment. The product blanks are formed from electroslag remelted steel ingots through hot working. Because the alloy content of carbide-forming elements reaches over 4.5%, it exacerbates the dendritic structure and carbide segregation of the electroslag remelted steel ingots, increasing the difficulty of simultaneously meeting the technical requirements for low-temperature impact and high-temperature strength. Hollow components are formed using a forging + drilling and boring method. Due to the large blank size, high forging deformation resistance, narrow forging temperature range, long forging time, and uneven forging temperature, the core shift near the inner hole is small, making it difficult to overcome the challenges of uniform carbide precipitation and uniform grain structure. This inherited inhomogeneity is difficult to resolve through heat treatment, resulting in unstable product performance, particularly affecting low-temperature impact toughness and high-temperature strength. Therefore, a forming method that deforms both the inner hole and the outer circle simultaneously is required to effectively break up coarse carbides and dendrites and improve their distribution. However, when using hollow extrusion forging composite forming, due to the high alloy content of high heat-strength steel and the narrow forging temperature range, the long length of the forging and the large temperature drop during hollow forging with a mandrel in the precision forging machine cause the deformation resistance to exceed the forging capacity of the equipment, resulting in the mandrel seizing up and making it impossible to achieve radial hollow forging forming. Summary of the Invention

[0003] This invention provides a radial forging method for hollow stepped shafts of high heat-strength steel core components. The technical problem to be solved is: for manufacturing 30Cr2Ni3MoWV high heat-strength steel hollow component blanks, the traditional forging method has the problem of low impact performance, and the new hollow extrusion forging composite forming method has the problem of difficulty in realizing hollow forging.

[0004] To solve the above technical problems, the present invention provides a radial forging method for a hollow stepped shaft of a heat-resistant steel core component, characterized by the following steps:

[0005] S1. Electroslag remelted steel ingots are extruded into straight tube billets;

[0006] S2. Straight tube blanks are radially forged into tube-shrinking tube blanks.

[0007] S3. The tube blank is radially hollow forged by a mandrel to form a hollow stepped tube blank.

[0008] S4. Hollow stepped tube blanks are radially forged into stepped shaft forgings using straight bars.

[0009] S5, Annealing of stepped shaft forgings;

[0010] S6. The straight bar is drilled out to form a hollow stepped shaft by drilling the hole in the stepped shaft forging.

[0011] Beneficial Effects: This invention combines the accumulated experience and deformation effects from performance testing of 30Cr2Ni3MoWV high-strength and high-toughness steel forgings manufactured using different methods, identifying key points in the manufacturing process. It proposes a radial forging method for hollow stepped shafts of high-heat-strength steel core components, integrating tube shrinking, hollow forging, and bar forging into a single radial forging process. This achieves the hollow forging effect, ensuring that the inner and outer diameters of the high-heat-strength steel hollow stepped forgings simultaneously achieve large deformations during the forging process, increasing the degree of deformation. Particularly in the bar forming stage, it achieves a large degree of deformation with a small amount of deformation. The deformation process is short, achieving deformation under isothermal conditions. The entire deformation process facilitates dynamic recrystallization, making it easier to control the precipitation and distribution of carbides in high-heat-strength steel. It solves the technical difficulties of achieving low microstructure homogeneity, high-temperature strength, and low-temperature impact simultaneously during the forging deformation process. After heat treatment, the core component blank achieves a high-temperature yield strength Rp0.2≥260MPa at 700℃, a low-temperature impact AKV≥20J at -40℃, and a room-temperature yield strength Rp0.1≥1150MPa at 20℃.

[0012] This invention effectively solves the shortcomings of traditional hot-formed high-heat-strength steel forgings, overcomes the difficulty of hollow radial forging, and achieves an innovative forming technology that ensures the comprehensive performance of the core component of the high-heat-strength steel hollow stepped shaft meets the requirements. Attached Figure Description

[0013] Figure 1 Schematic diagram of electroslag remelted steel ingots being extruded into straight tube billets;

[0014] Figure 2 : Schematic diagram of radial tube shrinking forging forming of tube shrinking billet;

[0015] Figure 3 Schematic diagram of hollow tube blank formed by mandrel hollow forging;

[0016] Figure 4 Schematic diagram of a stepped forging;

[0017] Figure 5Schematic diagram of annealing curve for stepped shaft forging. Detailed Implementation

[0018] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below.

[0019] The present invention proposes a radial forging method for a hollow stepped shaft core component made of high heat-strength steel, comprising the following steps: preparing a straight tube blank by extrusion of an electroslag remelted steel ingot; forging the straight tube blank into a tube blank by radial tube shrinking forging; forging the tube blank into a hollow stepped tube blank by radial hollow forging with a mandrel; forging the hollow stepped tube blank into a stepped shaft forging by radial forging with a straight bar; annealing the stepped shaft forging; and drilling the straight bar out of the stepped shaft forging to form a hollow stepped shaft.

[0020] Specifically as follows:

[0021] S1. Electroslag remelted steel ingots are extruded into straight tube billets for preparation.

[0022] 30Cr2Ni3MoWV electroslag remelted steel ingots are extruded into straight tube billets using an extrusion press. The dimensions of the straight tube billets are: D*d*L (D, d, and L are the outer diameter, inner diameter, and length of the straight tube billet, respectively). The wall thickness of the straight tube billet must satisfy (Dd) / 2=(0.25-0.375)D, and D≤620mm. See attached figure. Figure 1 .

[0023] S2. Straight tube blanks are radially reduced and forged into reduced tube blanks.

[0024] The 30Cr2Ni3MoWV straight tube billet was preheated and heated to 1150±10℃, with a holding time of 0.8h-1.2h per 100mm of outer diameter. It was then forged on a precision forging mill using a 10° inlet flat hammer for reduction. The diameter reduction *n* was controlled according to (d-d1)-(25-45mm). When *n* < 45mm, it was forged in one pass; when *n* ≥ 45mm, it was forged in two passes. After forging, it was reheated in the furnace. *d1* is the diameter of the mandrel used for hollow forging. The shape and dimensions of the reduced tube billet are shown in the appendix. Figure 2 .

[0025] S3. The tube blank is radially hollow-forged into a hollow stepped tube blank using a mandrel.

[0026] The 30Cr2Ni3MoWV tube blank is heated to 1240±10℃ and held at 1.5h-2.0h / 100mm for outer diameter. It is then forged on a precision forging mill using an 8° inlet hollow forging hammer and a mandrel with an outer diameter of d1, requiring d1-d2 = 30-60mm (d2 is the inner diameter of the stepped shaft forging). The hollow forging produces a hollow stepped tube blank. The dimensions of the hollow stepped tube blank are controlled by ensuring the maximum difference in forging ratio between each step is within 0.8. See the attached document for the shape and dimensions of the hollow stepped tube blank. Figure 3 .

[0027] S4. Hollow stepped tube blanks are radially forged into stepped shaft forgings using strip bars.

[0028] Prepare a straight bar with a diameter of d2 (the inner diameter of the stepped shaft forging) and a length equal to the length of the stepped shaft forging plus 400 mm. The hollow stepped tube blank is heated to 1080±10℃ for 1.2-1.5 hours per 100 mm of outer diameter. Remove the hollow stepped tube blank from one end and clamp it with a manipulator. Insert the straight bar completely into the inner diameter of the hollow stepped tube blank from the other end, leaving a 150 mm protrusion on the end face. Forge using a hollow forging process, forming in one pass with a forming ratio ≥1.5. See the attached figure for the shape and dimensions of the stepped shaft forging. Figure 4 .

[0029] S5, Forging Annealing

[0030] After forging, the surface temperature is air-cooled to 400℃-480℃, and then placed in the furnace at 600℃-650℃. After entering the furnace, the surface is held at 650±10℃ for 3 hours. The annealing process curve is attached. Figure 5 .

[0031] S6, Drilling and boring to remove straight rods

[0032] Drilling and boring method for stepped shaft forging to remove straight bar and form hollow stepped shaft

[0033] This radial forging process, which integrates tube shrinking, hollow forging, and strip forging, allows for simultaneous large deformation of the inner and outer diameters of the high-heat-strength steel hollow stepped shaft forging during the forging process. This ensures that the core hollow stepped shaft component meets requirements for high-temperature strength, low-temperature impact resistance, and room-temperature strength. It overcomes the technical challenges of achieving low microstructure homogeneity during the forging deformation process while simultaneously meeting the requirements for high-temperature strength and low-temperature impact resistance.

[0034] Using this invention, hollow stepped shafts of high heat-strength steel forgings with different specifications, including outer diameters of 250-400mm, hole diameters of 110mm-180mm, and lengths of ≤11000mm, can be produced, laying the foundation for improving the comprehensive performance of high heat-strength steel.

[0035] Its characteristics lie in the fact that the inner hole and outer circle are deformed simultaneously in each process of forging, which increases the degree of deformation, achieves a large degree of deformation with a small amount of deformation, the deformation process is short, deformation is achieved under constant temperature conditions, the entire deformation is easy to achieve dynamic recrystallization, and it is easy to control the precipitation and distribution of carbides in high heat strength steel.

[0036] Example:

[0037] Specifications and dimensions of large hollow stepped shaft forgings:

[0038] Φ385*3350+Φ335*2650+Φ305*900Φ285*2220+320*460 / Φ100, unit mm.

[0039] 1. Preparation of straight tube billets for extrusion from high heat-strength steel ingots;

[0040] High-heat-strength steel is produced using atmosphere-protected electroslag remelted steel ingots. Ingot dimensions: φ995 / φ1008mm × 1910mm, weight 11800kg. The ingot is charged into the furnace at a temperature ≤500℃, held for at least 4 hours, then preheated to 850℃~900℃ at a rate ≤60℃ / h, held at this temperature for at least 8 hours, then reheated to 1260±10℃ and held for 35 hours. After holding, the furnace temperature is reduced to 1230℃ before the ingot is removed. The ingot surface is descaled with water, then upset in a 1200mm upsetting cylinder, pierced with a φ355mm piercing needle, with an upsetting ratio of 1.53. The ingot is then returned to the furnace for reheating at 1230-20℃, held for at least 9 hours. The blanks were extruded into Φ620±5×Φ250±5×4000±50mm blanks using a Φ630mm extrusion die and a 250mm mandrel in a 1200mm extrusion cylinder.

[0041] Perform annealing.

[0042] 2. Straight tube blanks are forged by tube reduction on a precision forging machine.

[0043] After the inner hole of the straight tube billet is machined to remove oxide scale, an anti-oxidation coating is applied to the inner hole, and the inner hole is sealed with aluminum silicate asbestos. The billet is preheated in the furnace at a furnace temperature ≤550℃, held at 500℃-550℃ for 3 hours, then heated to 700℃-800℃ for further preheating, and held at this temperature for at least 5 hours. The final heating temperature is 1150℃, and the holding time is 6.0 hours. After holding, the tube is forged by tube reduction, with a reduction of 85mm. The dimensions after tube reduction forging are: Φ535*Φ200*4500.

[0044] 3. Radial hollow forging of precision forging mandrel

[0045] After forging, the inner hole of the billet is sealed with aluminum silicate asbestos and immediately returned to the original furnace. The temperature is rapidly raised to 1240-20℃ and held for 4.0 hours. After being taken out of the furnace for forging, suitable glass powder is sprayed into the inner hole, and lubricant is applied to the mandrel. The billet is inserted into the mandrel and rotated. Then, hollow forging is performed. A Φ150mm mandrel is used for forging. One end is forged into a Φ410*Φ150*1920 section, and then forged into a Φ440*Φ150*1620 section. The remaining part is forged into a Φ458*Φ150*2300 section, with a total length of about 5840mm. The forging ratios are 1.62, 1.38, and 1.26 respectively. After forging, the billet is returned to the furnace for heating.

[0046] 4. Forging with bars on a precision forging machine

[0047] Φ100mm×11100mm bars were prepared for use in forming and forging. The billet was returned to the furnace for heating to 1080℃ and held for 4 hours. After holding, the billet was removed for forging. After being placed on a press, the Φ100mm bar was inserted for forging using a hollow forging method. The Φ410*Φ150*1920 section was forged into a tube Φ320*460+Φ285*2220+Φ305*900, the Φ440*Φ150*1620 section was forged into a tube Φ335*2650, and the Φ458*Φ150*2300 section was forged into a tube Φ385. The forging ratios were 1.572.04, 1.75, 1.674, and 1.355, respectively.

[0048] 5. After forging, annealing is performed, followed by internal drilling and boring.

[0049] 6) Inspection: The forgings undergo rough machining and heat treatment.

[0050] (1) High-magnification tissue detection and analysis

[0051] After rough machining, the forgings undergo quenching and tempering heat treatment, and are tested in total.

[0052] (3) Performance testing and analysis

[0053] After rough machining and tempering, the forgings were tested at both ends. The room temperature yield strength Rp0.1 was between 1154 MPa and 11174 MPa, the low temperature impact at -40℃ was between 21.0 J and 27.2 J, and the impact difference of the same specimen was less than 6 J. The high temperature yield strength at 700℃ Rp0.2 was ≥260 MPa.

[0054]

[0055] This invention utilizes an integrated radial forging process combining tube shrinking, hollow forging, and bar forging to achieve simultaneous deformation of the inner and outer diameters in each process. This allows for a large degree of deformation with a small amount of deformation, achieving deformation under constant temperature conditions within a short time, and enabling dynamic recrystallization throughout the entire deformation process. Verification using this method with two forgings showed that the high-heat-strength steel exhibits a room-temperature yield strength Rp0.1 between 1154 MPa and 11174 MPa, a low-temperature impact strength at -40℃ between 21.0 J and 27.2 J, with the impact difference between the same specimens less than 6 J, and a high-temperature yield strength Rp0.2 at 700℃ ≥ 260 MPa.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for radial forging of a hollow stepped shaft for a heat-resistant steel core component, characterized in that: Includes the following steps: S1. 30Cr2Ni3MoWV electroslag remelted steel ingots are extruded to form straight tube billets; S2. Straight tube blanks are radially shrunk and forged into shrunk tube blanks; wherein, shrunk forging is carried out on a precision forging machine, and the diameter reduction n is controlled according to (d-d1)-(25-45)mm. When the reduction n<45mm, one pass is used for shrunk forging. When the reduction n≥45mm, it is divided into two passes for shrunk forging. After forging, the tube blanks are reheated in the furnace. d1 is the diameter of the mandrel used for hollow forging, and d is the inner diameter of the straight tube blank. S3. The tube blank is radially hollow-forged into a hollow stepped tube blank using a mandrel. The tube blank is heated to 1240±10℃ and held at this temperature for 1.5h-2.0h / 100mm of outer diameter. A hollow forging hammer and a mandrel with an outer diameter of d1 are used on a precision forging machine, requiring d1-d2=30-60mm, where d2 is the inner diameter of the stepped shaft forging. The hollow forging produces a hollow stepped tube blank. The dimensions of the hollow stepped tube blank are controlled based on the maximum difference of the forging ratio of each step being within 0.

8. S4. Hollow stepped tube blanks are radially forged into stepped shaft forgings using straight bars. S5, Annealing of stepped shaft forgings; S6. Hollow stepped shafts are obtained by drilling away the straight bar using a stepped shaft forging drilling method.

2. The radial forging method for a hollow stepped shaft of a heat-resistant steel core component according to claim 1, characterized in that: In S5, after forging, the surface temperature is air-cooled to 400℃-480℃, the furnace temperature is 600℃-650℃, the furnace temperature after entering the furnace is 650±10℃, and the holding time is 3h.

3. The radial forging method for a hollow stepped shaft of a heat-resistant steel core component according to claim 1, characterized in that: In S1, the dimensions of the straight tube blank are: D d L, D, d, and L are the outer diameter, inner diameter, and length of the straight tube blank, respectively. The wall thickness of the straight tube blank must satisfy (Dd) / 2 = (0.25 - 0.375)D, and D ≤ 620 mm.

4. The radial forging method for a hollow stepped shaft of a heat-resistant steel core component according to claim 1, characterized in that: In S2, the straight tube blank is preheated and heated to a temperature of 1150±10℃, and the holding time is 0.8h-1.2h / 100mm for the outer diameter.

5. The radial forging method for a hollow stepped shaft of a heat-resistant steel core component according to claim 1, characterized in that: In S2, a 10° inlet flat hammer head tube shrinking forging is adopted.

6. The radial forging method for a hollow stepped shaft of a heat-resistant steel core component according to claim 1, characterized in that: In S3, an 8° inlet hollow forging hammerhead is used on the precision forging machine.

7. The radial forging method for a hollow stepped shaft of a heat-resistant steel core component according to claim 1, characterized in that: In S4, a straight bar with an inner diameter d2 of the stepped shaft forging is prepared. The heating temperature of the hollow stepped tube blank is 1080±10℃, and the holding time is 1.2h-1.5h / 100mm according to the outer diameter. The hollow stepped tube blank is taken out and clamped by the manipulator at one end. The straight bar is inserted into the inner hole of the hollow stepped tube blank from the other end. The hollow forging process is used for forging, and the forging is formed in one pass with a forming forging ratio ≥1.5.

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