Process for producing large-diameter super-thick-wall seamless steel pipes by hot rolling and multiple continuous reducing

Abstract

The application relates to a production method of a large-diameter super-thick-wall seamless steel pipe by hot rolling multiple continuous reducing processes, and relates to the field of the skew rolling technology of the seamless steel pipe. The large-diameter super-thick-wall seamless steel pipe is obtained by performing the following processes on-line by hot rolling: once skew rolling piercing and reducing rolling, twice skew rolling piercing and reducing rolling, skew rolling pipe reducing, skew rolling reducing and smoothing, and on-line diameter fixing (reducing). The physicochemical comprehensive performance and the grain size grade of the large-diameter (D / S<=14.5) super-thick-wall seamless steel pipe produced by the method meet the standard requirements, and the steel pipe quality has high straightness and size precision.

Description

Technical Field

[0001] This invention relates to the field of seamless steel pipe skew rolling technology, specifically to a process production method for hot rolling multiple continuous diameter reduction rolling of large-diameter ultra-thick-walled seamless steel pipes. Background Technology

[0002] Traditional seamless steel pipe production lines include skew rolling piercing mills, reducing mills (optional), skew rolling tube mills, skew rolling leveling mills, and sizing mills. The production process is generally as follows: solid tube blanks with an outer diameter less than or equal to or close to that of the finished steel pipe are sequentially passed through the skew rolling piercing mill for diameter expansion, the skew rolling tube mill, and the skew rolling leveling mill for piercing and diameter expansion, and finally sizing by the sizing mill to obtain the finished seamless steel pipe.

[0003] For large-diameter, ultra-thick (D / S=6~11, where D is the outer diameter of the steel pipe and S is the wall thickness of the steel pipe) seamless steel pipes, in the application of traditional skew rolling process, in order to comply with the total elongation control requirements in GB / T5310 standard 6.2.3.3, the process technology setting basically adopts (forged billet or rolled billet) to match the technical characteristics of skew rolling diameter expansion and to stably ensure the quality of the produced products; therefore, the purchase cost of the (forged billet or rolled billet) round tube billet raw material selected in the early stage is relatively large.

[0004] However, with the continuous development of the national nuclear power, boiler, and thermal power industries, the demand for large-diameter, ultra-thick-walled seamless steel pipes for special supercritical and ultra-high pressure applications is increasing. Existing seamless steel pipe production lines generally employ equal-diameter or expanded-diameter piercing rolling processes for hot rolling, skew rolling tube forming, and skew rolling for uniform metal elongation. Under the hot-rolled skew rolling deformation elongation state, the original process parameters, such as the guide plate spacing, become problematic. If the guide plate spacing is too small, only equal-diameter or expanded-diameter rolling is possible, and the diameter reduction deformation process cannot be achieved. If the guide plate spacing is too large, the pressure and friction on the tool guide plates are significantly increased, and the guide plates are prone to metal adhesion and welding. This results in spiral scratches or spiral-covered peeling defects on the outer surface of the steel pipe during rotational deformation. Furthermore, the tool guide plates wear out rapidly and are subject to significant consumption, limiting the production of large-diameter (D / S=6~11, where D is the outer diameter of the steel pipe and S is the wall thickness) seamless steel pipes. Processing of ultra-thick-walled seamless steel pipes.

[0005] However, if a large-diameter continuously cast billet is used for hot rolling and multiple continuous diameter reduction production, the requirement of total process elongation of 3 to 5.2 can be met, which complies with the total elongation control provisions of GB / T5310 standard 6.2.3.3. Furthermore, the outer diameter of the piercing roll is easier to reduce, the rolling resistance of the guide plate to small elongation metal deformation is also reduced, the piercing roll quality is stable, the wear and consumption of the tool guide plate is reduced, and the service life is extended.

[0006] However, the existing skew rolling piercing mill, reducing mill (optional), skew rolling tube mill, and skew rolling leveling mill in the production line are mainly used for equal diameter or expansion rolling, which cannot meet the production needs of large diameter ultra-thick wall seamless steel pipes. If multiple continuous reducing equipment are newly configured, the purchase cost will be expensive. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies that use multiple skew rolling mills for continuous diameter reduction rolling. This invention provides a method for producing large-diameter, ultra-thick-walled seamless steel pipes by sequentially processing large-diameter continuously cast round billets as substitutes for forged billets (rolled billets) through skew rolling diameter reduction and piercing, skew rolling secondary diameter reduction and piercing, skew rolling diameter reduction and pipe rolling, skew rolling diameter reduction leveling, and online sizing. This production method complies with the total elongation control requirements in GB / T5310 standard 6.2.3.3, and produces large-diameter (D / S=6~11) ultra-thick-walled seamless steel pipes with high quality and dimensional accuracy. It is suitable for producing seamless steel pipes with an outer diameter of Ø615~914mm.

[0008] A method for producing large-diameter, ultra-thick-walled seamless steel pipes using a hot-rolling, multi-stage continuous diameter reduction process, characterized by the following steps:

[0009] Step 1) Place the diameter D 坯 The continuously cast solid round tube billet is heated to a temperature range of 1230±50℃, and then subjected to a single skew rolling reduction and piercing rolling process to obtain a capillary tube with an outer diameter of D1 and a temperature of 1160℃~1220℃, where the outer diameter range is D1=D 坯 -D 坯 * (0.02~0.045);

[0010] The diameter D of the continuously cast round tube blank 坯 It satisfies formula (1)

[0011] ;

[0012] Where D is the outer diameter of the formed seamless steel pipe, and S is the wall thickness of the formed seamless steel pipe;

[0013] Step 2) The tube is subjected to secondary skew rolling to reduce its diameter and pierce, resulting in a rough tube with an outer diameter of D2 and a temperature of 1100℃~1160℃, where the outer diameter range is D2=D1-D1*(0.02~0.045).

[0014] Step 3) The rough tube obtained in Step 2) is subjected to skew rolling to reduce its diameter, resulting in a rough tube with an outer diameter of D3 and a temperature of 1040℃~1100℃, where the outer diameter range is D3=D2-D2*(0.02~0.045).

[0015] Step 4) The rough tube obtained in Step 3) is subjected to skew rolling to reduce the diameter and smooth the tube, resulting in a rough tube with an outer diameter of D4 and a temperature of 980℃~1040℃, where the outer diameter range D4=D3-D3*(0.02~0.045).

[0016] Step 5) Based on the residual heat of the rough tube after diameter reduction and equalization in Step 4), the rough tube is heated with controlled temperature, and the temperature of the rough tube is controlled at 910℃~1020℃.

[0017] Step 6) The rough tube with temperature controlled at 910℃~1020℃ is longitudinally sized and rolled to obtain a finished seamless steel tube with an outer diameter of D and a temperature of 820℃~930℃.

[0018] Furthermore, the outer diameter and wall thickness of the finished seamless steel pipe meet the formula: D / S=6~11, and the outer diameter of the finished seamless steel pipe is Ø615~914mm; D is the outer diameter of the formed seamless steel pipe, and S is the wall thickness of the steel pipe.

[0019] Furthermore, the specifications of the continuously cast solid round tube billet in step 1) are: diameter of Ø700mm~Ø1100mm, length of 1900mm~4600mm, and total heating time of 24.5h~45h.

[0020] Furthermore, in steps 1) and 2), a two-roll skew rolling mill is used for a first-stage skew rolling reduction piercing and a second-stage skew rolling reduction piercing.

[0021] Furthermore, in step 3), a two-roll skew rolling mill with tapered rolls is used for skew rolling to reduce the diameter; in step 4), a two-roll skew rolling mill is used for skew rolling to reduce the diameter and level the surface.

[0022] Furthermore, in step 5), 18 continuous medium-frequency coil heating furnaces are used for through-type temperature control heating, with a total heating time of 8 min to 20 min.

[0023] Furthermore, in step 6), a three-roll five-stand sizing mill is used to perform longitudinal sizing rolling on the rough tube.

[0024] Furthermore, in the single-stage skew rolling reduction piercing process of the two-roll skew rolling mill, the cone angle of the roll inlet section is... a 入1 ,length l 1-1 All should satisfy the formula (2) for the reduction amount of the maximum incoming material diameter.

[0025] ;

[0026] The two-roll skew rolling mill has a tapered section at the roll inlet during the secondary skew rolling reduction piercing process. a 入1 ,length l1-1 All should satisfy the formula (3) for the reduction amount of the maximum incoming material diameter.

[0027] ;

[0028] The cone angle of the roll inlet section of the two-roll skew rolling mill a 入2 ,length l 1-2 All should satisfy the formula (4) for the reduction amount of the maximum incoming material diameter.

[0029] ;

[0030] The cone angle of the roll inlet section of the two-roll skew rolling mill a 入3 ,length l 1-3 All should satisfy the formula (5) for the reduction amount of the maximum incoming material diameter.

[0031] .

[0032] Furthermore, in steps 1) and 2), the position d1 of the guide plate compression belt in the two-roll skew rolling mill corresponds radially to the position z2-1 of the throat of the roll compression belt, and the exit angle of the guide plate... a 2-1 ≤ Corresponding roll exit angle a 出1 , a 2-1 = a 出1 – (0°~0.5°);

[0033] In step 3), the position d2 of the guide plate compression belt of the two-roll skew rolling mill corresponds radially to the position z2-2 at the throat of the compression belt in the deformation zone. The exit angle of the guide plate... a 2-2 ≤ Corresponding roll exit angle a 出2 , a 2-2 = a 出2 – (0°~0.5°);

[0034] Step 4) The radial positions of the guide plate compression belt d3 and the throat of the compression belt in the deformation zone of the two-roll skew rolling mill correspond to each other. The exit angle of the guide plate... a 2-3 ≤ Corresponding roll exit angle a 出3 , a 2-3 =a 出3 –(0°~0.5°).

[0035] Furthermore, in steps 1) and 2), the wall reduction amount of the first skew rolling and the second piercing rolling is controlled to be ≤5mm; in step 3), the wall reduction amount of the diameter reduction rolling is controlled to be ≤4mm; and in step 4), the wall reduction amount of the skew rolling diameter reduction is controlled to be ≤4mm.

[0036] The beneficial effects of this invention are:

[0037] In this invention, the guide plate compression strip positions of the two-roll skew rolling mill, two-roll skew rolling tube mill, and two-roll skew rolling sizing mill correspond radially to the throat positions of the roll compression strips. This weakens the pressure friction force at the guide plate compression strip position when the metal in the throat area, pressed down by the small guide plate spacing, undergoes elliptical longitudinal elongation under the pressure of the roll mandrel. Simultaneously, the guide plate exit cone angle is smaller than the roll exit cone angle, satisfying the formula: a 2= a 出 – (0°~0.5°), thus effectively limiting the extension of the transverse deformation of the steel pipe. Combined with the ≤ wall reduction value range, the outer diameter of the through rolling can be effectively controlled. At the same time, the rolling resistance of the guide plate to small elongation metal deformation will also be reduced, the through rolling quality will be stable, the wear and consumption of the tool guide plate will be reduced, and the service life will be extended, overcoming the defects of the existing technology.

[0038] The process production method of the present invention involves partial structural modifications to the existing skew rolling and diameter expansion equipment, enabling the equipment to be adapted to the continuous skew rolling and diameter reduction deformation process. This overcomes the shortcomings of existing multiple skew rolling mill units that cannot perform continuous diameter reduction rolling, and the modification cost is low, eliminating the need to purchase a new production line at a high price.

[0039] Meanwhile, this invention also broadens the selection requirements for raw materials of large-diameter (D / S=6~11) ultra-thick-walled seamless steel pipes; large-diameter continuously cast billets can be used as raw materials, and existing forging (rolling) billet raw material processes can also be taken into account; at the same time, in terms of energy saving, compared with the previous technology of forging and rolling square billets or cast billets to obtain round billets (forging billets or rolling billets), it directly saves about 2,000 yuan / ton of comprehensive manufacturing cost of raw material forging billets (rolling billets); and saves about 35 days of production cycle for processing forging billet (rolling billet) materials.

[0040] The production method of this invention complies with the total elongation control requirements in GB / T5310 standard 6.2.3.3. The produced large-diameter (D / S=6~11) ultra-thick-walled seamless steel pipes have good quality and high dimensional accuracy. It is suitable for the production of seamless steel pipes with an outer diameter of Ø615~914mm. At the same time, large-diameter continuous casting billets can be used as raw materials, and existing forging (rolling) billet raw material processes can also be taken into account. The steel pipes have high dimensional accuracy. Attached Figure Description

[0041] Figure 1 A spatial arrangement diagram of the rolls and guide plates in the diameter reduction rolling process of a two-roll skew rolling mill for invention.

[0042] Figure 2 A longitudinal center section view of the guide plate during the diameter reduction rolling process in a two-roll skew rolling mill.

[0043] Figure 3 A spatial arrangement diagram of the rolls and guide plates in the diameter reduction rolling process of a two-roll skew rolling mill with conical rolls for invention.

[0044] Figure 4 A longitudinal section of the center profile of the guide plate during the diameter reduction rolling process of a tapered roll two-roll skew rolling mill.

[0045] Figure 5 A spatial arrangement diagram of the rolls and guide plates during the diameter reduction rolling process in a two-roll skew rolling mill for invention.

[0046] Figure 6 A longitudinal center section view of the guide plate during the diameter reduction rolling process in a two-roll skew rolling mill.

[0047] Figure 7 This is a schematic diagram of the billet's first bite-in state during a single skew rolling reduction and piercing rolling process.

[0048] Figure 8 This is a schematic diagram of the workpiece's first bite-in state during the secondary skew rolling reduction and piercing rolling process.

[0049] Figure 9 This is a schematic diagram of the billet biting state during the skew rolling reduction tube process.

[0050] Figure 10 This is a schematic diagram of the workpiece biting state during the skew rolling diameter reduction and straightening process. Detailed Implementation

[0051] This invention provides a method for producing large-diameter, ultra-thick-walled seamless steel pipes using a hot-rolling, multi-stage continuous diameter reduction process. The method includes the following steps:

[0052] 1) Heating of tube blank:

[0053] Step 1) Place the diameter D 坯The continuously cast round tube billet is placed in a 35-meter ring furnace for heating. The specifications of the continuously cast solid round tube billet (preferably a continuously cast solid round tube billet, but forging or rolling billets can also be used) range from (diameter Ø700mm~Ø1100mm × length 1900mm~4600mm). The total heating time is generally 24.5 h~45 h depending on the steel grade and diameter. The heating temperature is in the range of 1230±50℃.

[0054] 2) Single-stage diameter reduction piercing:

[0055] After being heated and held at a certain temperature, the continuously cast round tube billet is subjected to a single skew rolling reduction piercing process using a two-roll skew rolling mill to obtain a tube with an outer diameter of D1 and a temperature of 1160℃~1220℃, where the outer diameter range is D1=D 坯 -D 坯 * (0.02~0.045);

[0056] The diameter D of the continuously cast round tube blank 坯 It satisfies formula (1)

[0057] ;

[0058] Where D is the outer diameter of the formed seamless steel pipe, and S is the wall thickness of the formed seamless steel pipe;

[0059] 3) Secondary diameter reduction perforation:

[0060] The tube after the first skew rolling reduction and piercing is subjected to a second skew rolling reduction and piercing process using a two-roll skew rolling mill to obtain a rough tube with an outer diameter of D2 and a temperature of 1100℃~1160℃, where the outer diameter range is D2=D1-D1*(0.02~0.045).

[0061] 4) Bias-rolled reducing tube:

[0062] The rough tube is rolled into a diameter reduction tube by a two-roll skew rolling mill with conical rolls to obtain a rough tube with an outer diameter of D3 and a temperature of 1040℃~1100℃, where the outer diameter range is D3=D2-D2*(0.02~0.045).

[0063] 5) Cross rolling, diameter reduction and leveling

[0064] The rough tube is subjected to skew rolling and diameter reduction by a two-roll skew rolling mill to obtain a rough tube with an outer diameter of D4 and a temperature of 980℃~1040℃, wherein the outer diameter range D4=D3-D3*(0.02~0.045).

[0065] 6) Temperature-controlled heating

[0066] The raw pipe is heated through a continuous medium-frequency coil heating furnace group of 18 units with temperature control, with a total heating time of 8 min to 20 min and a controlled temperature range of 910℃ to 1020℃.

[0067] 7) Online sizing

[0068] The rough tube, which is controlled at a temperature of 910℃~1020℃ in step 6), is longitudinally rolled by a three-roll five-stand sizing mill to obtain a finished seamless steel tube with an outer diameter of D and a temperature range of 820℃~930℃. The size of the major semi-axis, minor semi-axis and average diameter of the elliptical hole formed by the three rolls of the first to fifth groups of the three-roll five-stand sizing mill with different hole types is shown in Table 1.

[0069] Table 1. Specifications of the pass profiles for a three-roll, five-stand sizing mill (unit: mm)

[0070]

[0071] In the process of this invention, the mandrels used in the two-roll skew rolling piercing mill, the two-roll skew rolling tube mill, and the two-roll skew rolling leveling mill are all designed and configured according to the design standards of the piercing mill mandrel.

[0072] In the process of this invention, in steps 2) and 3), the wall reduction amount of the first skew rolling and the second piercing rolling is controlled to be ≤5mm; in step 4), the wall reduction amount of the skew rolling tube is controlled to be ≤4mm; and in step 5), the wall reduction amount of the skew rolling uniformization is controlled to be ≤4mm.

[0073] like Figure 1-10 The two-roll skew rolling mill, two-roll skew rolling tube mill, and two-roll skew rolling sizing mill in the process of the present invention are all equipped with a pair of rolls and a pair of guide plates, which are all existing known equipment. The rolls of the two-roll skew rolling mill, two-roll skew rolling tube mill, and two-roll skew rolling sizing mill are all tapered rolls. The position d1 of the guide plate compression belt in the two-roll skew rolling mill corresponds to the radial position of the throat z2-1 of the roll compression belt. The exit angle of the guide plate is... a 2-1 ≤ Corresponding roll exit angle a 出1 , a 2-1 = a 出1 – (0°~0.5°).

[0074] The guide plate compression belt position d2 of the two-roll skew rolling mill corresponds radially to the throat position z2-2 of the compression belt in the deformation zone. The exit angle of the guide plate... a 2-2 ≤ Corresponding roll exit angle a 出2 ,a 2-2 = a 出2 – (0°~0.5°).

[0075] The radial positions of the guide plate compression belt d3 and the throat of the roll compression belt z2-3 in the two-roll skew rolling mill correspond to each other. The exit angle of the guide plate... a 2-3 ≤ Corresponding roll exit angle a 出3 , a 2-3 = a 出3 – (0°~0.5°).

[0076] The purpose of controlling the exit angle of the guide plate is to effectively control the outer diameter during the reduction rolling process by adjusting the guide plate spacing parameters in conjunction with the small elongation deformation of the metal.

[0077] The two-roll skew rolling mill has a cone angle at the entrance section of the middle rolls in the single skew rolling reduction piercing process. a 入1 ,length l 1-1 All should satisfy the formula (2) for the reduction amount of the maximum incoming material diameter.

[0078] ;

[0079] The two-roll skew rolling mill has a cone angle at the entrance section of the middle rolls during the secondary skew rolling reduction piercing process. a 入1 ,length l 1-1 All should satisfy the formula (3) for the reduction amount of the maximum incoming material diameter.

[0080] ;

[0081] The cone angle of the roll inlet section of the two-roll skew rolling mill a 入2 ,length l 1-2 All should satisfy the formula (4) for the reduction amount of the maximum incoming material diameter.

[0082] ;

[0083] The cone angle of the roll inlet section of the two-roll skew rolling mill described in the text a 入3 ,length l 1-3 All should satisfy the formula (5) for the reduction amount of the maximum incoming material diameter.

[0084] .

[0085] In this invention, the process roll exit angles of the two-roll skew rolling mill, the two-roll skew rolling tube mill, and the two-roll skew rolling leveling mill are configured and used at 2.5° to 4°. This is the roll exit angle commonly used by many steel pipe companies in China for diameter expansion piercing and diameter expansion rolling. It is a method of diameter reduction piercing invented based on the existing process roll exit angle facilities. Beyond 4°, it is generally a pure diameter expansion process, making diameter reduction rolling difficult.

[0086] First Embodiment

[0087] This embodiment uses a continuously cast round tube billet with finished specifications of Ø914×120mm, steel grade P91, and diameter of Ø1100mm (the billet diameter satisfies the formula). This embodiment will be described in detail below.

[0088] The process in this embodiment is as follows:

[0089] 1) The Ø1100mm continuous casting round tube billet is placed in a 35-meter ring furnace and heated at 1230±50℃ for 38.5 h~45 h. Then, it is subjected to a one-time skew rolling reduction piercing rolling through a two-roll skew rolling mill to obtain a tube with an outer diameter of D1, a temperature of 1160℃~1220℃ and a wall thickness of 133mm, D1=1066mm;

[0090] 2) The tube is subjected to secondary skew rolling and piercing by a two-roll skew rolling mill to obtain a rough tube with an outer diameter of D2, a temperature of 1100℃~1160℃ and a wall thickness of 128mm, where D2=1032mm.

[0091] 3) The rough tube is rolled by a two-roll skew rolling mill to reduce its diameter, resulting in a rough tube with an outer diameter of D3, a temperature of 1040℃~1100℃, and a wall thickness of 124mm, where D3=1008mm.

[0092] 4) Step 3) The obtained rough tube is subjected to skew rolling and diameter reduction through a two-roll skew rolling mill to obtain a rough tube with an outer diameter of D4, a temperature of 980℃~1040℃ and a wall thickness of 120mm, where D4=985mm.

[0093] 5) Step 4) The obtained rough tube is heated by 18 continuous medium frequency coil heating furnaces with controlled temperature. The total heating time is generally 18±2 min depending on the steel grade and diameter, and the temperature of the rough tube is controlled and guaranteed to be 910℃~1020℃.

[0094] 6) The raw tube that has been heated under controlled temperature is longitudinally rolled through a three-roll five-stand sizing mill (see Table 1 for the roll pass data) to obtain a hot finished steel pipe with an outer diameter of Ø928.8mm, a temperature of 820℃~930℃ and a wall thickness of 120.5mm. After cooling, the outer diameter is Ø915.9mm.

[0095] As a further explanation of this embodiment, this embodiment is a modification of an existing seamless steel pipe diameter expansion production line to realize the diameter reduction process of the present invention. The original production line includes an Ø800 two-roll skew rolling mill, an Ø960 two-roll skew rolling mill, a Julong leveling mill, a continuous medium-frequency coil heating furnace group, and an Ø914 three-roll sizing mill. The Ø914 three-roll sizing mill is configured with matching die frames according to the commonly used national standard finished product outer diameter, including die sets of (711 mm, 762 mm, 813 mm, 864 mm, 914 mm); non-standard finished product outer diameter matching die sets suitable for finished product outer diameters in the range of Ø615~914 mm can also be configured as needed.

[0096] In this embodiment, the mandrels used in the two-roll skew rolling mill, the two-roll skew rolling tube mill, and the two-conical roll skew rolling mill are all designed and configured according to the design standards for piercing mill mandrels.

[0097] In this embodiment, the rolls and guide plates of the two-roll skew rolling mill, the two-roll skew rolling tube mill, and the two-roll skew rolling leveling mill have all been reconfigured as required. The primary skew rolling diameter reduction piercing process and the secondary skew rolling diameter reduction piercing process are both completed using the two-roll skew rolling mill. The specific configuration parameters are as follows:

[0098] As shown in Figure 1-10, the cone angle of the roll inlet section of the two-roll skew rolling mill is... a 入1 =3°, length l 1-1 =1550mm, when the rolls of the two two-roll skew rolling mills are pressed down, the distance between the compression strips is c1, c1=957mm. In a single skew rolling reduction piercing process, when the two rolls are pressed down, the length of the roll surface between the first bite point of the billet and the compression strip of the rolls is... =1366.17mm, of which (This is common knowledge) l 1-1 > l 2-1 Simultaneously satisfy the formula Ensure the tube blank is successfully bitten in.

[0099] In the secondary skew rolling reduction piercing process, when the two secondary piercing rolls are pressed down, the length of the roll surface between the workpiece's first bite point and the roll compression zone is... (This is common knowledge) l 1-1 >l 2-2 Simultaneously satisfy the formula This ensures the workpiece is successfully engaged.

[0100] The cone angle of the roll inlet section of a two-roll skew rolling mill a 入2 =3°, length l 1-2 =1150mm, given that the distance between the compression strips of the two rolls of the two-roll skew rolling mill is c2 when the two rolls are pressing down, c2=930mm, calculate the roll surface length between the workpiece's first bite point and the roll compression strip when the two rolls of the two-roll skew rolling mill are pressing down. (This is common knowledge) l 1-2 > l 2-3 Simultaneously satisfy the formula This ensures the workpiece is successfully engaged.

[0101] The cone angle of the roll inlet section of the two-roll skew rolling mill a 入3 =3°, length l 1-3 =1150mm, assuming the distance between the compression strips of the two rolls of the two-roll skew rolling mill is c3 when the two rolls are pressed down, c3=908.4mm, calculate the roll surface length between the workpiece's first bite point and the roll compression strip when the two rolls of the two-roll skew rolling mill are pressed down. (This is common knowledge) l 1-3 > l 2-4 Simultaneously satisfy the formula This ensures the workpiece is successfully engaged.

[0102] In a two-roll skew rolling mill, the position d1 of the guide plate compression belt corresponds radially to the position z2-1 at the throat of the roll compression belt. The exit angle of the guide plate... a 2-1 =2.8°, roll exit angle a 出1 =3°, satisfying the formula a 2-1 = a 出1 –(0°~0.5°) requirements.

[0103] In a two-roll skew rolling mill, the guide plate compression belt position d2 corresponds radially to the throat position z2-2 of the roll compression belt. The exit angle of the guide plate... a 2-2 =3.2°, roll exit angle a出2 =3.5°, which satisfies the formula a 2-2 = a 出2 – (0°~0.5°) requirements.

[0104] In the two-roll skew rolling mill, the guide plate compression belt position d3 corresponds radially to the throat position z2-3 of the roll compression belt. The exit angle of the guide plate... a 2-3 =2.7°, roll exit angle a 出3 =3°, satisfying the formula a 2-3 = a 出3 –(0°~0.5°) requirements.

[0105] The detailed process parameters for the first embodiment are shown in Table 2 below:

[0106] Table 2 shows the specific process parameters for the first embodiment (unit: mm).

[0107]

[0108] Second Embodiment

[0109] This embodiment uses a continuously cast round tube billet with finished specifications of Ø615×56mm, steel grade P92, and diameter of Ø750mm (the billet diameter satisfies the formula). Using the example of , this embodiment will be described in detail.

[0110] The process in this embodiment is as follows:

[0111] 1) The Ø750mm continuous casting round tube billet is placed in a 35-meter ring furnace and heated at 1230±50℃ for 26 h~30 h. Then, it is subjected to a one-time skew rolling reduction piercing rolling through a two-roll skew rolling mill to obtain a tube with an outer diameter of D1, a temperature of 1160℃~1220℃, and a wall thickness of 63mm, where D1=733mm.

[0112] 2) The tube is subjected to secondary skew rolling and diameter reduction piercing rolling through a two-roll skew rolling mill to obtain a rough tube with an outer diameter of D2, a temperature of 1100℃~1160℃ and a wall thickness of 60mm, where D2=712mm.

[0113] 3) The rough tube is rolled into a diameter reduction tube by a two-roll skew rolling mill to obtain a rough tube with an outer diameter of D3, a temperature of 1040℃~1100℃ and a wall thickness of 58mm, D3=687mm;

[0114] 4) Step 3) The obtained rough tube is subjected to skew rolling and diameter reduction through a two-roll skew rolling mill to obtain a rough tube with an outer diameter of D4, a temperature of 980℃~1040℃ and a wall thickness of 56mm, D4=662mm.

[0115] 5) Step 4) The obtained rough tube is heated by 18 continuous medium frequency coil heating furnaces with controlled temperature (ignoring the temperature drop during transportation). The total heating time is generally 10±2 min depending on the steel grade and diameter, and the temperature of the rough tube is controlled and guaranteed to be between 910℃ and 1020℃.

[0116] 6) The raw tube that has been heated under controlled temperature is longitudinally rolled through a three-roll five-stand sizing mill (pass data are shown in Table 1) to obtain a hot finished steel pipe with an outer diameter of Ø625.6mm, a temperature of 820℃~930℃ and a wall thickness of 56.6mm. After cooling, the outer diameter is Ø619mm.

[0117] This embodiment achieves the diameter reduction process of the present invention by modifying a seamless steel pipe diameter expansion production line. The original production line includes an Ø800 two-roll skew rolling mill, an Ø960 two-roll skew rolling mill, a giant sizing mill, a continuous medium-frequency coil heating furnace group, and an Ø914 three-roll sizing mill. The Ø914 three-roll sizing mill is configured with a frame according to the production size requirements of seamless steel pipes with finished product specifications of Ø615×56mm.

[0118] In this embodiment, the mandrels used in the two-roll skew rolling piercing mill, the two-roll skew rolling tube mill, and the two-conical roll skew rolling mill are all designed and configured according to the design standards of the piercing mill mandrel. The first skew rolling diameter reduction piercing process and the second skew rolling diameter reduction piercing process are both completed by the two-roll skew rolling piercing mill.

[0119] In this embodiment, the rolls and guide plates of the two-roll skew rolling mill, the two-roll skew rolling tube mill, and the two-roll skew rolling leveling mill have all been reconfigured as required. The specific configuration parameters are as follows:

[0120] As shown in Figure 1-10, the cone angle of the roll inlet section of the two-roll skew rolling mill is... a 入1 =3°, length l 1-1 =1550mm, when the rolls of the two two-roll skew rolling mill are pressed down, the distance between the compression strips is c1, c1=652.5mm. In a single skew rolling reduction piercing process, when the two rolls are pressed down, the roll surface length between the first bite point of the billet and the roll compression strip is... (This is common knowledge) l 1-1 > l 2-1 Simultaneously satisfy the formula This ensures that the billet is successfully bitten in.

[0121] In the secondary skew rolling reduction piercing process, when the two secondary piercing rolls are pressed down, the length of the roll surface between the workpiece's primary bite point and the compression zone of the secondary piercing rolls is... ,in (This is common knowledge) l 1-1 > l 2-2 Simultaneously satisfy the formula This ensures the workpiece is successfully engaged.

[0122] The cone angle of the roll inlet section of a two-roll skew rolling mill a 入2 =3°, length l 1-2 =1150mm, setting the distance between the compression strips of the two rolls of the two-roll skew rolling mill to be c2 when the two rolls are pressing down, c2=640.8mm, calculate the roll surface length between the workpiece's first bite point and the compression strip of the skew rolling mill roll when the two rolls of the two-roll skew rolling mill are pressing down. (This is common knowledge) l 1-2 > l 2-3 Simultaneously satisfy the formula This ensures the workpiece is successfully engaged.

[0123] The cone angle of the roll inlet section of the two-roll skew rolling mill a 入3 =3°, length l 1-3 =1150mm, assuming the distance between the compression strips of the two rolls of the two-roll skew rolling mill is c3 when the two rolls are pressed down, c3=618.3mm, calculate the roll surface length between the workpiece's first bite point and the roll compression strip when the two rolls of the two-roll skew rolling mill are pressed down. (This is common knowledge) l 1-3 > l 2-4 Simultaneously satisfy the formula This ensures the workpiece is successfully engaged.

[0124] In a two-roll skew rolling mill, the position d1 of the guide plate compression belt corresponds radially to the position z2-1 at the throat of the roll compression belt. The exit angle of the guide plate... a 2-1 =2.8°, roll exit angle a 出1 =3°, satisfying the formula a 2-1 = a 出1–(0°~0.5°) requirements.

[0125] In a two-roll skew rolling mill, the guide plate compression belt position d2 corresponds radially to the throat position z2-2 of the roll compression belt. The exit angle of the guide plate... a 2-2 =3.2°, roll exit angle a 出2 =3.5°, which satisfies the formula a 2-2 = a 出2 – (0°~0.5°) requirements.

[0126] In the two-roll skew rolling mill, the guide plate compression belt position d3 corresponds radially to the throat position z2-3 of the roll compression belt. The exit angle of the guide plate... a 2-3 =2.7°, roll exit angle a 出3 =3°, satisfying the formula a 2-3 = a 出3 –(0°~0.5°) requirements.

[0127] The detailed process parameters for the second embodiment are shown in Table 3 below:

[0128] Table 3 shows the specific process parameter data for the second embodiment (unit: mm).

[0129]

[0130] According to the finished product inspection, the nominal wall thickness S deviation range of the seamless steel pipes prepared in the first and second embodiments is ≤ ±8%, and the nominal outer diameter D deviation range is 0 to +7mm. The finished seamless steel pipes have high dimensional accuracy and meet the tolerance requirements specified in the standard. The total elongation of the deformation caused by the process method meets the requirements of (6.2.3.3 Total Elongation Control in GB / T5310 standard).

[0131] As can be seen from the above embodiments, the large-diameter (D / S=6~11) ultra-thick-walled seamless steel pipes produced by the multiple continuous diameter reduction process of the present invention are suitable for the production of seamless steel pipes with an outer diameter of Ø615~914mm. The total diameter reduction is large and the total process elongation is controlled within the range of 3~5.2, which meets the total elongation control requirements of 6.2.3.3 in GB / T5310 standard. In terms of product specification and dimensional accuracy, the longitudinal rolling of the sizing mill during the forming process can eliminate the straightness of the spiral ripples on the outer surface caused by the deformation of the two-roll skew rolling to the greatest extent. After comprehensive finished product inspection, the seamless steel pipes have high dimensional accuracy, the process method is reasonable and reliable, and the cost reduction effect is significant.

[0132] In summary, the hot-rolled continuous diameter reduction process of this invention, combined with subsequent online controlled cooling technology or heat treatment technology for different materials, can fully meet the various technical requirements of the standards for the dimensional accuracy and comprehensive physical and chemical properties of ultra-high pressure large-diameter ultra-thick-walled seamless steel pipes such as boiler tubes and thermal power and chemical pipes.

[0133] Although the invention has been described in conjunction with embodiments, it will be apparent to those skilled in the art that various modifications may be made to the above embodiments without departing from the spirit and scope of the claims.

[0134] Table 4 shows the specific product group spacing configuration of this invention (unit: mm).

[0135]

[0136] According to Table 4, the corresponding tube blank can be directly selected based on the finished product specifications.

Claims

1. A method for producing large-diameter, ultra-thick-walled seamless steel pipes using a hot-rolling, multi-stage continuous diameter reduction process, characterized in that... Includes the following steps: Step 1) Place the diameter D 坯 The continuously cast solid round tube billet is heated to a temperature range of 1230±50℃, and then subjected to a single skew rolling reduction and piercing rolling process to obtain a capillary tube with an outer diameter of D1 and a temperature of 1160℃~1220℃, where the outer diameter range is D1=D 坯 -D 坯 * (0.02~0.045); The diameter D of the circular tube blank 坯 It satisfies formula (1) （1） Where D is the outer diameter of the formed seamless steel pipe, and S is the wall thickness of the formed seamless steel pipe; Step 2) The tube is subjected to secondary skew rolling to reduce its diameter and pierce, resulting in a rough tube with an outer diameter of D2 and a temperature of 1100℃~1160℃, where the outer diameter range is D2=D1-D1*(0.02~0.045). Step 3) The rough tube obtained in Step 2) is subjected to skew rolling to reduce its diameter, resulting in a rough tube with an outer diameter of D3 and a temperature of 1040℃~1100℃, where the outer diameter range is D3=D2-D2*(0.02~0.045). Step 4) The rough tube obtained in Step 3) is subjected to skew rolling to reduce the diameter and smooth the tube, resulting in a rough tube with an outer diameter of D4 and a temperature of 980℃~1040℃, where the outer diameter range D4=D3-D3*(0.02~0.045). Step 5) Based on the residual heat of the rough tube after diameter reduction and equalization in Step 4), the rough tube is heated with controlled temperature, and the temperature of the rough tube is controlled at 910℃~1020℃. Step 6) The rough tube with temperature controlled at 910℃~1020℃ is longitudinally sized and rolled to obtain a finished seamless steel tube with an outer diameter of D and a temperature of 820℃~930℃. In steps 1) and 2), a two-roll skew rolling mill is used for one-stage skew rolling and two-stage skew rolling to reduce diameter and pierce the diameter. In step 3), a two-roll skew rolling mill is used for skew rolling to reduce the diameter; in step 4), a two-roll skew rolling mill is used for skew rolling to reduce the diameter and level the surface. In the single-stage skew rolling reduction piercing process of the two-roll skew rolling mill, the cone angle α of the roll inlet section is... 入1 Length l 1-1 All should satisfy the formula (2) for the reduction amount of the maximum incoming material diameter. (2); In the secondary skew rolling reduction piercing process of the two-roll skew rolling mill, the cone angle α of the roll inlet section is... 入1 Length l 1-1 All should satisfy the formula (3) for the reduction amount of the maximum incoming material diameter. (3); The cone angle α at the roll inlet section of the two-roll skew rolling mill is... 入2 Length l 1-2 All should satisfy the formula (4) for the reduction amount of the maximum incoming material diameter. （4）； The cone angle α at the roll inlet section of the two-roll skew rolling mill is... 入3 Length l 1-3 All should satisfy the formula (5) for the reduction amount of the maximum incoming material diameter. （5）。 2. The production method of large-diameter ultra-thick-walled seamless steel pipe by hot rolling multiple continuous diameter reduction process according to claim 1, characterized in that: The outer diameter and wall thickness of the finished seamless steel pipe meet the formula: D / S=6~11, and the outer diameter of the finished seamless steel pipe is Ø615~914mm.

3. The production method of large-diameter ultra-thick-walled seamless steel pipe by hot rolling multiple continuous diameter reduction process according to claim 1, characterized in that: The specifications of the solid round tube billet in step 1) are: diameter Ø700mm~Ø1100mm, length 1900mm~4600mm, and total heating time 24.5h~45h.

4. The production method of large-diameter ultra-thick-walled seamless steel pipe by hot rolling multiple continuous diameter reduction process according to claim 1, characterized in that: In step 5), 18 continuous medium-frequency coil heating furnaces are used for through-type temperature control heating, with a total heating time of 8 min to 20 min.

5. The production method of large-diameter ultra-thick-walled seamless steel pipe by hot rolling multiple continuous diameter reduction process according to claim 1, characterized in that: In step 6), a three-roll five-stand sizing mill is used to longitudinally sizing the rough tube.

6. The production method of large-diameter ultra-thick-walled seamless steel pipe by hot rolling multiple continuous diameter reduction process according to claim 1, characterized in that: In steps 1) and 2), the position d1 of the guide plate compression belt in the two-roll skew rolling mill corresponds radially to the position z2-1 at the throat of the roll compression belt, and the exit angle α of the guide plate... 2-1 ≤ Corresponding roll exit angle a 出1 a 2-1 =a 出1 – (0°~0.5°); In step 3), the position d2 of the guide plate compression belt of the two-roll skew rolling mill corresponds to the radial position of z2-2 at the throat of the compression belt in the deformation zone, and the exit angle α of the guide plate. 2-2 ≤ Corresponding roll exit angle a 出2 a 2-2 =a 出2 – (0°~0.5°); Step 4) The position d3 of the guide plate compression belt of the two-roll skew rolling mill corresponds radially to the position z2-3 of the throat of the compression belt in the deformation zone. The exit angle α of the guide plate... 2-3 ≤ Corresponding roll exit angle a 出3 a 2-3 =a 出3 – (0°~0.5°).

7. The production method of large-diameter ultra-thick-walled seamless steel pipe by hot rolling multiple continuous diameter reduction process according to claim 1, characterized in that: In steps 1) and 2), the wall reduction amount of the first skew rolling diameter reduction piercing and the second skew rolling diameter reduction piercing is controlled to be ≤5mm; in step 3), the wall reduction amount of the skew rolling diameter reduction is controlled to be ≤4mm; in step 4), the wall reduction amount of the skew rolling diameter reduction leveling is controlled to be ≤4mm.

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