A method for manufacturing an alloy steel forging for a Christmas tree wellhead

Abstract

The application discloses a kind of alloy steel forgings manufacturing methods for Christmas tree wellhead, and technical solution points are as follows:Step S1, prepare alloy material, get blank;Step S2, forging heating, blank is sent into furnace, and heated to 1230 DEG C±14 DEG C;Step S3, forging, including the following steps: first step: light rolling external circle;Second step: blank axial deformation;Third step: radial deformation is carried out;Fourth step carries out chord deformation, fifth step: punch;Sixth step: ring rolling, get workpiece;Step S4, performance heat treatment: quenching: workpiece is into furnace and heated to 600-650 DEG C and kept, heated to 899-940 DEG C and kept, then water cooling;Tempering: workpiece is into furnace and heated to 650-680 DEG C and kept, then air cooling, the advantages of the present application lie in ensuring that material anisotropy is uniform.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of low alloy structural steel, in particular to a manufacturing method of alloy steel forge piece for Christmas tree wellhead. BACKGROUND

[0002] At present, the Christmas tree equipment is an important equipment for oil and gas exploitation, which is composed of a casing head, a tubing head and a Christmas tree, and has a sealing element arranged thereon. The sealing element is used to connect a casing string and a tubing string, and seal the annular space between each layer of casing and the tubing. The Christmas tree equipment can control the pressure and flow rate of the wellhead, and is also used in special operations such as acidizing and fracturing, water injection and testing. The Christmas tree equipment is mainly made of alloy forge pieces.

[0003] However, in the underground working environment, the Christmas tree equipment parts are in a complex stress environment, mainly subjected to axial and radial stress, and also subjected to tangential shear force, and the stress and shear force in each direction are different. If the anisotropy of the material is not uniform, the load bearing capacity of the material in each direction will be different, which will easily lead to excessive consumption of the material and affect the service life of the equipment. Therefore, at present, it is necessary to improve the uniformity of the anisotropy of the material to ensure that the performance of the material in each direction meets the design requirements. SUMMARY

[0004] In view of the above-mentioned shortcomings of the prior art, the present application aims to provide a manufacturing method of alloy steel forge piece for Christmas tree wellhead, which has the advantage of ensuring the uniformity of the anisotropy of the material.

[0005] The above technical object of the present application is achieved by the following technical solution:

[0006] A manufacturing method of alloy steel forge piece for Christmas tree wellhead, comprising the following steps:

[0007] Step S1, preparing an alloy material to obtain a blank;

[0008] Step S2, forging heating, sending the blank into a furnace and heating to 1230℃±14℃;

[0009] Step S3, forging, including the following working steps:

[0010] First step: light rolling of the outer circle;

[0011] Second step: axial deformation of the blank, one upsetting of the forge piece to H=0.8D, one elongation to H1=2D1, two upsetting to H2=0.8D2, rolling, flat end face, and back to the furnace for heat preservation, wherein H is the height of the blank, D is the outer diameter of the blank, H1 is the height of the blank after one elongation, D1 is the outer diameter of the blank after one elongation, H2 is the height of the blank after two upsetting, and D2 is the outer diameter of the blank after two upsetting; and recording the forging ratio a1=(D1 / D)2 +(D2 / D1) 2 ,

[0012] Third step: the blank is turned over by 90°, radial deformation is carried out, secondary lengthening is carried out to H3=2D3, and then tertiary upsetting is carried out to H4=0.8D4, H3 is the height of the blank after secondary lengthening, D3 is the outer diameter of the blank after secondary lengthening, H4 is the height of the blank after tertiary upsetting, and D4 is the outer diameter of the blank after tertiary upsetting; the forging ratio a2=(D3 / D2) is recorded 2 +(D4 / D3) 2 ,

[0013] Fourth step: the blank is turned over by 90°, chordal deformation is carried out, tertiary lengthening is carried out to H5=2D5, and then quaternary upsetting is carried out to H6=0.8D6, H5 is the height of the blank after tertiary lengthening, D5 is the outer diameter of the blank after tertiary lengthening, H6 is the height of the blank after quaternary upsetting, and D6 is the outer diameter of the blank after quaternary upsetting; the forging ratio a3=(D6 / D5) is recorded 2 +(D5 / D4) 2 ,

[0014] The forging ratio of the blank after ejection is a=a 1+ a 2+ a 3， a>8, and is less than 15;

[0015] Fifth step: punching;

[0016] Sixth step: ring rolling, to obtain a workpiece;

[0017] Step S4, performance heat treatment:

[0018] Quenching: the workpiece is put into a furnace and heated to 600-650 DEG C and kept, heated to 899-940 DEG C and kept, and then water-cooled;

[0019] Tempering: the workpiece is put into a furnace and heated to 650-680 DEG C and kept, and then air-cooled.

[0020] Further, in the fifth step of step S3, the punching inner diameter size is deformed by 20% from the final design size.

[0021] Further, in the quenching of step S4, the workpiece is loaded into the furnace at ≤100 DEG C.

[0022] Further, in the quenching of step S4, the holding time of the 600-650 DEG C stage and the 899-940 DEG C stage is T / 40+2-3h, wherein T is the diameter of the equivalent circle of the thickest part of the workpiece.

[0023] Further, in the quenching of step S4, the temperature rising speed of 600-650 DEG C stage is ≤80 DEG C / h, the temperature rising speed of 899-940 DEG C stage is ≤120 DEG C / h, and the furnace temperature uniformity satisfies ±10 DEG C.

[0024] Further, in the quenching of step S4, the cooling water temperature is ≤30 DEG C, the circulating water flow rate is 30-50 mm / s, swinging is carried out after entering the water, the swinging time is not less than 15 min, and tempering treatment is carried out after water cooling for 2-3 h.

[0025] Further, in the quenching of step S4, the total weight of the quenching water tank is ≥10 * the weight of the workpiece.

[0026] Further, in the tempering of step S4, the workpiece is loaded into the furnace at ≤300 DEG C, the temperature rising speed is ≤100 DEG C / h, and the furnace temperature uniformity satisfies ±8 DEG C.

[0027] Further, in the tempering of step S4, the holding time is T / 25+2-3 h.

[0028] Further, in step S1, the alloy material comprises components in percentage by weight: C 0.10%-0.15%, Mn 0.30%-0.60%, Cr 2.20%-2.50%, Mo 0.87%-1.13%, P 0.01%, S 0.01%, Si 0.15%-0.50%, Ni 0.45%-0.5%, V 0.02%-0.03%, Cu ≤0.25%, Ti 0.025%, Al 0.020%-0.04%, Nb 0.01%, Sn 0.02%, Sb 0.03%, As 0.03%, Pb 0.01%, Bi 0.01%, B 0.001%, N 0.012%, carbon equivalent CEQ 0.90-0.93%, and the balance is Fe.

[0029] In summary, the present application has the following beneficial effects:

[0030] 1. The forging controls the upsetting frequency and the upsetting ratio, and the upsetting is carried out from the chord direction, the radial direction and the axial direction, so that the coarse grain structure at the center of the blank is fully broken, the internal structure of the material is more compact, the grain is finer, then the metal is driven to flow to the outer edge from the chord direction and the radial direction, the uniformity and the grain refinement degree are improved, the stress distribution of the material is more uniform, the anisotropy of the material is uniform, and the toughness of the forging is good.

[0031] 2. In the free forging, the inner hole is expanded, the metal flow gradually flows along the radial direction, the material uniformity is reduced, and in the process of deformation, the gas pores in the material are as far as possible to be eliminated and the inclusions are as far as possible to be crushed, so that the quality of the material is improved, and the forging deformation is avoided.

[0032] 3. After quenching, the original alpha phase in the alloy is mainly transformed into martensite, and part of the alpha phase is retained as residual austenite, which has good strength and toughness, and forms carbide precipitates at the grain boundaries, which helps to inhibit intergranular corrosion and reduce the generation of stress corrosion cracks, inhibit the generation of stress corrosion cracks, and reduce the defects of the alloy.

[0033] 4. After tempering, the martensite in the alloy begins to decompose and transform into ferrite and a certain amount of residual austenite. With the increase of tempering temperature and time, the amount of residual austenite also increases accordingly, and the tempering structure has better toughness and impact resistance, but its hardness and strength are lower than that of the quenched structure, and the tempering temperature window and holding time need to be strictly controlled to balance the strength and toughness.

[0034] 5. Control the content of Ni and improve the corrosion resistance, inhibit the generation of intergranular corrosion and cracks, and if the content of Ni is too high, it will also lead to the increase of the thermal expansion coefficient of the alloy, reduce the strength and tensile properties of the alloy, and increase the medium carbon equivalent of the alloy. The carbon and chromium form carbon chromium carbide, which can increase the hardness and strength of the alloy. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is the metallographic phase diagram of the forging obtained in Example 1.

[0036] Figure 2 is the metallographic phase diagram of the forging obtained in Example 2.

[0037] Figure 3 is the metallographic phase diagram of the forging obtained in Example 3.

[0038] Figure 4 is the metallographic phase diagram of the forging obtained in Example 4.

[0039] Figure 5 is the metallographic phase diagram of the forging obtained in Comparative Example 1.

[0040] Figure 6 is the metallographic phase diagram of the forging obtained in Comparative Example 2.

[0041] Figure 7 is the metallographic phase diagram of the forging obtained in Comparative Example 3.

[0042] Figure 8 is the metallographic phase diagram of the forging obtained in Comparative Example 4. DETAILED DESCRIPTION

[0043] Example 1:

[0044] A manufacturing method of an alloy steel forging for a Christmas tree wellhead, comprising the following steps:

[0045] Step S1, preparing an alloy material to obtain a blank. The alloy material includes components in percentage by weight: C 0.10-0.15%, Mn 0.30-0.60%, Cr 2.20-2.50%, Mo 0.87-1.13%, P 0.01%, S 0.01%, Si 0.15-0.50%, Ni 0.45-0.5%, V 0.02-0.03%, Cu ≤0.25%, Ti 0.025%, Al 0.020-0.04%, Nb 0.01%, Sn 0.02%, Sb 0.03%, As 0.03%, Pb 0.01%, Bi 0.01%, B 0.001%, N 0.012%, carbon equivalent CEQ 0.90-0.93%.

[0046] Step S2, forging heating, sending the blank into a furnace and heating to 1216℃, strictly controlling the temperature window to avoid overheating to cause high-temperature ferrite.

[0047] Step S3, forging, including the following working steps:

[0048] First step: light rolling of the outer circle;

[0049] Second step: axial deformation of the blank, the original height of the forging is H0, the forging is once upset to H=0.8D, once elongated to H1=2D1, twice upset to H2=0.8D2. Rolling, flat end face, back to the furnace for heat preservation, and the forging ratio a1 is recorded, which is required to be greater than 3 and not more than 6.

[0050] Wherein H is the height of the blank, D is the outer diameter of the blank, H1 is the height of the blank after once elongation, D1 is the outer diameter of the blank after once elongation, H2 is the height of the blank after twice upsetting, and D2 is the outer diameter of the blank after twice upsetting. The final forging temperature is guaranteed to be ≥850℃.

[0051] Wherein the specific sizes are:

[0052] The blank size in the embodiment is

[0053] H0=1688mm;

[0054] D=1105mm;

[0055] H=885mm;

[0056] D1=814mm;

[0057] H1=1630mm;

[0058] D2=1105mm;

[0059] H2=885mm;

[0060] After calculation, a1=(D1 / D)2 +(D2 / D1) 2 = (1105 / 814)2+ (1105 / 814)2= 3.68.

[0061] Third step: the blank is turned over 90°, radial deformation is carried out, secondary lengthening is carried out to H3=2D3, and then tertiary upsetting is carried out to H4=0.8D4, H3 is the height of the blank after secondary lengthening, D3 is the outer diameter of the blank after secondary lengthening, H4 is the height of the blank after tertiary upsetting, D4 is the outer diameter of the blank after tertiary upsetting, and the forging ratio a2 is required to be greater than 3, and is not more than 6 at most.

[0062] In which the specific sizes are:

[0063] In this embodiment, the blank size is

[0064] D3=814mm;

[0065] H3=1630mm;

[0066] D4=1105mm;

[0067] H4=885mm;

[0068] After calculation a2=(D3 / D2) 2 +(D4 / D3) 2 = (1105 / 814)2+ (1105 / 814)2= 3.68.

[0069] Fourth step: the blank is turned over 90°, chordal deformation is carried out, tertiary lengthening is carried out to H5=2D5, and then quaternary upsetting is carried out, H5 is the height of the blank after tertiary lengthening, D5 is the outer diameter of the blank after tertiary lengthening, H6 is the height of the blank after quaternary upsetting, and D6 is the outer diameter of the blank after quaternary upsetting, and the forging ratio a3 is required to be greater than 3, and is not more than 6 at most.

[0070] In this embodiment, the blank size is:

[0071] D5=814mm;

[0072] H5=1630mm;

[0073] D6=1058mm;

[0074] H6=965mm;

[0075] After calculation a3=(D6 / D5) 2 +(D5 / D4) 2 = (1058 / 814)2+ (1105 / 814)2= 3.52.

[0076] The forging ratio of the ejection is a=a1+a2+a3=3.68+3.68+3.38=10.74, the final calculation of the forging ratio is a>8 and less than 15.

[0077] The fifth step is punching, punching with a punch of 300 mm, reaming to Φ250 mm core rod to the final size, the deformation of the size before reaming and the final size is 20%.

[0078] The size of the forging after punching is: φ1222mm*φ670mm*956mm.

[0079] The sixth step is to roll the ring to the forming size to obtain the workpiece.

[0080] The forming size of the workpiece is: Φ1383mm / Φ907mm×933mm.

[0081] Step S4, performance heat treatment:

[0082] Quenching: first, the workpiece is ≤100℃ into the furnace, the workpiece is heated to 600℃, the heating rate is ≤80℃ / h, the heating rate is 70℃ / h, the holding time is T / 40+2-3h, where T is the diameter of the equivalent circle of the thickest part of the workpiece.

[0083] In this embodiment, T= (1380-910) / 2=235mm, the calculated holding time is 235 / 40+2=7.875h, which is rounded to 8h.

[0084] Then heat to 899℃ and hold, the heating rate is ≤80℃ / h, the heating rate is 70℃ / h, the holding time is T / 40+2-3h, where T is the diameter of the equivalent circle of the thickest part of the workpiece.

[0085] The furnace temperature uniformity is ±10℃, then water cooling, the cooling water temperature is ≤30℃, the circulating water flow rate is 30-50mm / s, after entering the water, swing for not less than 15min, water cooling for 2-3h, then tempering treatment, and the total weight of the quenching water tank is ≥10*the weight of the workpiece.

[0086] In this embodiment, the weight of the workpiece is 6660kg, and the total weight of the quenching water tank is 600 tons.

[0087] Tempering: the workpiece is ≤300℃ into the furnace, the workpiece is heated to 650℃, the heating rate is ≤100℃ / h, the heating rate is 90℃ / h, the furnace temperature uniformity is ±8℃, the holding time is T / 25+2-3h, then air cooling.

[0088] In this embodiment, T is 235mm, the calculated holding time is 235 / 25+2=9.4+2=11.4h, which is rounded to 12h.

[0089] Example 2

[0090] The difference between the embodiment 1 and the embodiment 2 is that:

[0091] Step S4, performance heat treatment:

[0092] Quenching: first, the workpiece is ≤100℃ loaded into the furnace, the workpiece is heated to 620℃ in the furnace, the heating rate is ≤80℃ / h, the heating rate is 70℃ / h, and the holding time is T / 40+2-3h, wherein T is the diameter of the equivalent circle at the thickest part of the workpiece.

[0093] In this embodiment, T is 235mm, and the holding time is calculated as 235 / 40+2=7.875h, which is rounded to 8h.

[0094] Then, it is heated to 910℃ and held, the heating rate is ≤80℃ / h, the heating rate is 70℃ / h, and the holding time is T / 40+2-3h, wherein T is the diameter of the equivalent circle at the thickest part of the workpiece. The furnace temperature uniformity is ±10℃.

[0095] In this embodiment, T is 235mm, and the holding time is calculated as 235 / 40+2=7.875h, which is rounded to 8h.

[0096] Then, water cooling, the cooling water temperature is ≤30℃, the circulating water flow rate is 30-50mm / s, after entering the water, it is oscillated, the oscillation time is not less than 15min, and after water cooling for 2-3h, it is tempered, and the total weight of the quenching water tank is ≥10*the weight of the workpiece.

[0097] In this embodiment, the weight of the workpiece is 6660kg, and the total weight of the quenching water tank is 600 tons.

[0098] Tempering: the workpiece is ≤300℃ loaded into the furnace, the workpiece is heated to 660℃ in the furnace, the heating rate is ≤100℃ / h, the heating rate is 90℃ / h, the furnace temperature uniformity is ±8℃, the holding time is T / 25+2-3h, and then air cooling.

[0099] In this embodiment, T is 235mm, and the holding time is calculated as 12h.

[0100] Example 3

[0101] The difference between the embodiment 1 and the embodiment 3 is that:

[0102] Step S4, performance heat treatment:

[0103] Quenching: first, the workpiece ≤100 ℃ into the furnace, the workpiece into the furnace to 640 ℃, the heating rate ≤80 ℃ / h, the heating rate is 70 ℃ / h, the holding time is T / 40+2-3h, wherein T is the diameter of the equivalent circle of the thickest part of the workpiece. Then heated to 920 ℃, the heating rate ≤80 ℃ / h, the heating rate is 70 ℃ / h, the holding time is T / 40+2-3h, wherein T is the diameter of the equivalent circle of the thickest part of the workpiece, the furnace temperature uniformity ±10 ℃, then water cooling, cooling water temperature ≤30 ℃, circulating water flow rate 30-50 mm / s, after entering the water swing, swing time not less than 15 min, water cooling 2-3h after tempering treatment, and the total weight of the quenching tank ≥10*workpiece weight.

[0104] Tempering: the workpiece is ≤300 ℃ into the furnace, the workpiece into the furnace to 660 ℃, the heating rate ≤100 ℃ / h, the heating rate is 90 ℃ / h, the furnace temperature uniformity meets ±8 ℃, the holding time is T / 25+2-3h, then air cooling.

[0105] Example 4:

[0106] The difference between the steps of example 1 is:

[0107] Step S4, performance heat treatment:

[0108] Quenching: first, the workpiece ≤100 ℃ into the furnace, the workpiece into the furnace to 650 ℃, the heating rate ≤80 ℃ / h, the heating rate is 70 ℃ / h, the holding time is T / 40+2-3h, wherein T is the diameter of the equivalent circle of the thickest part of the workpiece.

[0109] In this embodiment, T is 235 mm, and the calculated holding time is 8h.

[0110] Then heated to 940 ℃, the heating rate ≤80 ℃ / h, the heating rate is 70 ℃ / h, the holding time is T / 40+2-3h, wherein T is the diameter of the equivalent circle of the thickest part of the workpiece, the furnace temperature uniformity ±10 ℃.

[0111] In this embodiment, T is 235 mm, and the calculated holding time is 8h.

[0112] Then water cooling, cooling water temperature ≤30 ℃, circulating water flow rate 30-50 mm / s, after entering the water swing, swing time not less than 15 min, water cooling 2-3h after tempering treatment, and the total weight of the quenching tank ≥10*workpiece weight.

[0113] In this embodiment, the weight of the workpiece is 6660 kg, and the total weight of the quenching tank is 600 tons.

[0114] Tempering: the workpiece is charged into the furnace at ≤300℃, the workpiece is heated to 680℃ in the furnace, the heating rate is ≤100℃ / h, the heating rate is 90℃ / h, the furnace temperature uniformity meets ±8℃, the holding time is T / 25+2-3h, and then air cooling.

[0115] In this embodiment, T is 235mm, and the calculated holding time is 8h.

[0116] Comparative Example 1:

[0117] The difference between this comparative example and Example 1 is that this comparative example uses traditional forging means, specifically:

[0118] First step: light rolling, the blank size is

[0119] Second step: (the workpiece is once upset to a height of 885, and the blank size is once elongated to a height of 1630, and the blank size is twice upset to a height of 885, and the blank size is rolled, and the blank size is The forging ratio a is 3.68.

[0120] Comparative Example 2:

[0121] The difference between this comparative example and Example 1 is that:

[0122] Step S3, forging, including the following steps:

[0123] First step: light rolling;

[0124] Second step: blank axial deformation, the workpiece is once upset to once elongated to twice upset to rolled, flat end face, reheat, and the calculated forging ratio a1 is 2.4.

[0125] Third step: the blank is turned over 90°, radial deformation is performed, and twice elongation is performed to and then three times upsetting is performed to The forging ratio a2 is 2.4.

[0126] Fourth step: the blank is turned over 90°, chordwise deformation is performed, and three times elongation is performed to and then four times upsetting is performed to The forging ratio a3 is 2.43.

[0127] The forging ratio of the blank is a=a1+a2+a3=7.23, and the final calculated forging ratio is a<8.

[0128] Comparative Example 3:

[0129] The difference from Example 1 is that:

[0130] Quenching: the forged piece is heated to 930℃, the holding time is 12h, then water cooling, the cooling water temperature is ≤30℃, the circulating water flow rate is 30-50mm / s, after entering the water, swing for not less than 15min, after water cooling for 2-3h, tempering treatment is carried out, and the total weight of the quenching tank is ≥10*the weight of the workpiece.

[0131] Comparative Example 4:

[0132] The difference from Example 1 is that:

[0133] Normalizing: the forged piece is heated to 910℃, the holding time is 10h.

[0134] Alloy comprehensive performance detection:

[0135] Experimental group: samples from Example 1-4 are taken, recorded as experimental group 1-4. Samples from Comparative Example 1-4 are taken, recorded as experimental group 5-8.

[0136] Details are shown in Table 1.

[0137]

[0138] Table 1

[0139] Detection result analysis:

[0140] (1) From the performance of the forged pieces of experimental group 1-4, the tensile strength is above 900MPa, the yield strength is above 790MPa, the impact energy is increased by 30-100%, under the premise of meeting the use requirements, there are higher performance indexes under the macro, which proves that the microstructure of the forged piece is refined, and it is proved that the coarse grain structure is fully broken and the grain refinement is completed during forging; and the impact energy index is more than 70J, which means that the inclusions, segregation, internal cracks and other defects in the forged piece are less, which means that the brittleness of the forged piece is low and the toughness is good.

[0141] (2) Comparing experimental group 1 and experimental group 5, the main difference is the different forging methods, the tensile strength difference is nearly 50MPa, and the yield strength difference is nearly 90MPa, which means that the coarse grain crushing in experimental group 1 is more complete.

[0142] (3) Comparing experimental group 1 and experimental group 6, the main difference is the different forging ratios, the tensile strength difference is nearly 100MPa, and the yield strength difference is nearly 90-120MPa, which means that when the forging deformation cannot reach the specific requirement window, it cannot well drive the metal to flow to the three-way outer edge, further improving the uniformity and grain refinement degree.

[0143] (4) Compared between experimental group 1 and experimental group 7, the main difference is the quenching parameter, the tensile strength of which is nearly 60 MPa, and the yield strength of which is nearly 60 MPa, from the side of the quenching parameter affecting the process of martensitic transformation, using the process window of example 1, controlling the transformation degree of α phase, ensuring the residual austenite, improving the strength and toughness of the forging.

[0144] (5) Compared between experimental group 1 and experimental group 8, the main difference is the normalizing parameter, the tensile strength of which is nearly 70 MPa, and the yield strength of which is nearly 70 MPa, by finding the most suitable tempering temperature window and holding time, controlling the proportion of residual austenite, completing the strengthening of strength and toughness.

[0145] Metallographic detection:

[0146] Specification: 100 μm.

[0147] Requirement: grain size 5 or above 5.

[0148] Experimental group 1: the structure is as shown in Figure 1 , the grain size is 9, and there is no crack, looseness and porosity and other defects.

[0149] Experimental group 2: the structure is as shown in Figure 2 , the grain size is 8, and there is no crack, looseness and porosity and other defects.

[0150] Experimental group 3: the structure is as shown in Figure 3 , the grain size is 8, and there is no crack, looseness and porosity and other defects.

[0151] Experimental group 4: the structure is as shown in Figure 4 , the grain size is 8, and there is no crack, looseness and porosity and other defects.

[0152] Experimental group 5: the structure is as shown in Figure 5 , the grain size is 7, and the grain is relatively thick, and there is no crack, looseness and porosity and other defects.

[0153] Experimental group 6: the structure is as shown in Figure 6 , the grain size is 7, and the grain is relatively thick, and there is no crack, looseness and porosity and other defects.

[0154] Experimental group 7: the structure is as shown in Figure 7 , the grain size is 7, and the grain is relatively thick, and there is no crack, looseness and porosity and other defects.

[0155] Experimental group 8: the structure is as shown in Figure 8 , the grain size is 7, and the grain is relatively thick, and there is no crack, looseness and porosity and other defects.

[0156] Any combination of the technical features in the above-described embodiments can be made, and for the sake of brevity, not all possible combinations are described, however, as long as the combination of the technical features does not exist in contradiction, it shall be considered within the scope of the present disclosure.

[0157] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it shall not be understood as a limitation on the patent scope of the present application. It shall be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these shall be within the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A method for manufacturing an alloy steel forging for the wellhead of an oil well, characterized in that, Includes the following steps: Step S1: Prepare alloy materials to obtain a billet; Step S2, forging heating: the billet is sent into the furnace and heated to 1230℃±14℃; Step S3, forging, includes the following steps: Step 1: Gently roll the outer circle; Step 2: Axial deformation of the billet. The forging is first upset to H=0.8D, first drawn to H1=2D1, second upset to H2=0.8D2, rounded, end face flattened, and then heat-treated in the furnace. Here, H is the billet height, D is the billet outer diameter, H1 is the billet height after the first drawing, D1 is the billet outer diameter after the first drawing, H2 is the billet height after the second upset, and D2 is the billet outer diameter after the second upset. Record the forging ratio a1 = (D1 / D). 2 +(D2 / D1) 2 , Step 3: Rotate the billet 90° for radial deformation, then draw it twice to H3=2D3, followed by upsetting it three times to H4=0.8D4. H3 is the billet height after the second drawing, D3 is the billet outer diameter after the second drawing, H4 is the billet height after the third upsetting, and D4 is the billet outer diameter after the third upsetting. Record the forging ratio a2=(D3 / D2). 2 +(D4 / D3) 2 , Step 4: Rotate the billet 90° and perform chordal deformation, drawing it three times until H5 = 2D5, then upsetting it four times until H6 = 0.8D6. H5 is the billet height after three drawing stages, D5 is the billet outer diameter after three drawing stages, H6 is the billet height after four upsetting stages, and D6 is the billet outer diameter after four upsetting stages. Record the forging ratio a3 = (D6 / D5). 2 +(D5 / D4) 2 , The forging ratio of the billet is a = a1 + a2 + a 3， a > 8 and less than 15; Step 5: Punching; Step 6: Rolling the ring to obtain the workpiece; Step S4, Performance Heat Treatment: Quenching: The workpiece is placed in the furnace and heated to 600-650℃ and held, then heated to 899-940℃ and held, and then water-cooled; Tempering: The workpiece is placed in the furnace and heated to 650-680℃ and held at that temperature, then air-cooled; In the quenching process of step S4, the workpiece is loaded into the furnace at ≤100℃, and the holding time for the 600~650℃ and 899~940℃ stages is T / 40+2~3h, where T is the diameter of the equivalent circle at the thickest part of the workpiece. The heating rate for the 600~650℃ stage is ≤80℃ / h, and the heating rate for the 899~940℃ stage is ≤120℃ / h. The furnace temperature uniformity meets ±10℃, the cooling water temperature is ≤30℃, the circulating water flow rate is 30~50mm / s, and the workpiece is oscillated after immersion in the water for no less than 15min. After water cooling for 2~3h, tempering is performed. The total weight of the quenching water tank is ≥10×the weight of the workpiece. In the tempering process of step S4, the workpiece is loaded into the furnace at ≤300℃, the heating rate is ≤100℃ / h, the furnace temperature uniformity meets ±8℃, and the holding time is T / 25+2~3h. In step S1, the alloy material comprises the following components by weight percentage: C 0.10%~0.15%, Mn 0.30%~0.60%, Cr 2.20%~2.50%, Mo 0.87%~1.13%, P 0.01%; S 0.01%; Si 0.15%~0.50%, Ni 0.45%~0.5%, V 0.02%~0.03%, Cu ≤0.25%, Ti 0.025%, Al 0.020%~0.04%, Nb 0.01%, Sn 0.02%, Sb 0.03%, As 0.03%, Pb 0.01%, Bi 0.01%, B 0.001%, N 0.012%, carbon equivalent CEQ 0.90~0.93%, and the balance being Fe.

2. The method for manufacturing an alloy steel forging for an oil wellhead according to claim 1, characterized in that: In the fifth step of step S3, the inner diameter of the punch is reduced to a deformation of 20% from the final design size.

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