A preparation method of bimetallic oil and gas composite pipe X65 / 2205

Abstract

The invention discloses a preparation method of a bimetallic oil and gas composite pipe X65 / 2205. The raw materials are sequentially subjected to converter smelting, LF furnace refining, RH degassing, casting continuous casting billet, hot extrusion, rolling, cyclic temperature change, normalizing and tempering according to the ingredients. The casting continuous casting billet adopts a centrifugal casting method to remove impurities such as lighter metal oxides and slag; the hot extrusion temperature is 500-600°C, the extrusion strength is 700-900MPa, and the plasticity of the pipe is increased; the cyclic temperature change interval is selected between 100-960°C to obtain a refined austenite grain structure, and after three cycles, the grain size can reach 11. The good metallurgical combination of the bimetallic material enables the oil and gas pipeline to have the strength of X65 steel and the corrosion resistance of 2205 duplex stainless steel. The normalizing and tempering treatments continuously reduce the supersaturation of carbon in the martensite in the composite pipe, weaken the lattice distortion, and reduce the residual stress, thereby improving the comprehensive performance of the composite pipe.

Description

Technical Field

[0001] The invention relates to the field of metal material manufacturing, and in particular to a method for preparing a bimetallic oil and gas composite pipe X65 / 2205. Background Art

[0002] Marine oil and gas resources are an important part of oil and gas resources and an important direction for future oil and gas resource exploitation. With the continuous increase in world energy consumption and the reduction of land-based oil and gas resources, oil and gas development has moved from land to sea, and the proportion of marine oil and gas resources has continued to increase. At present, marine oil and gas reserves account for 30%-40% of global reserves, and deep-sea oil and gas production will increase by more than 300% in the next ten years. A large part of marine oil and gas resources are distributed in deep-water areas with a water depth of 1000m or even more than 2000m, and a dedicated deep-sea oil and gas production and transportation system needs to be built for exploitation; among them, deep-sea oil and gas transmission pipelines, as a major form of marine oil and gas storage and transportation, are an indispensable lifeline for the development and production of offshore oil and gas fields, and are also the safest, most economical, and least environmentally destructive way of transporting oil and gas.

[0003] During their service, deep-sea pipelines will face a variety of complex and harsh conditions such as plastic deformation, extremely high water pressure and strong corrosion. This requires that the material has high strength and toughness while also having multiple properties such as strain resistance, crush resistance and corrosion resistance. Usually, a single material is difficult to meet multiple design requirements. Taking highly corrosion-resistant nickel-based alloy seamless steel pipes as an example, only 1 / 3 of this material is used to solve internal corrosion problems, and the remaining 2 / 3 of the material is only used as structural support materials, resulting in a huge waste of resources. In recent years, my country has made certain progress in the research and development of steel plates, steel pipes and other materials for marine oil and gas pipelines, laying the foundation for the research and development of composite pipelines.

[0004] At present, the forming process of bimetallic composite pipes on the domestic market remains at the level of mechanical compounding (spinning, drawing, bulging, rolling, etc.), and has the following disadvantages: (1) The bonding strength between the inner layer and the outer layer is insufficient, and it cannot undergo subsequent deformation with a large deformation amount; (2) Due to the capacity of the equipment used to manufacture such composite steel pipes, the composite pipes with relatively thick coatings cannot solve the bonding problem of the two layers; (3) For pipes whose coating metals are required to have highly corrosion-resistant materials, the corrosion-resistant materials of the coatings are difficult to make into corresponding seamless steel pipes. Summary of the invention

[0005] The main purpose of the present invention is to provide a preparation method of bimetallic oil and gas composite pipe X65 / 2205, so that the oil and gas pipeline meets the strength and corrosion resistance requirements; by improving the heat treatment process, ultra-fine austenite grains are obtained, so that the strength and toughness of the bimetallic oil and gas composite pipe are further improved.

[0006] The technical solution to achieve the purpose of the present invention is:

[0007] A method for preparing a bimetallic oil and gas composite pipe X65 / 2205, wherein the composite pipe is composed of a double-layer metal pipe, wherein the outer metal pipe is X65 grade pipeline steel, and its chemical composition mass percentage is as follows: C: 0.09-0.20%; Si: 0.3-0.4%; Mn: ≤1.5%; P: ≤0.015%; S: ≤0.003%; Cr: 0.05-0.062%; Ni: 0.011%; Mo: 0.005%; V: 0.111%; the rest are Fe elements and Inevitable impurity elements; the inner metal tube is 2205 duplex stainless steel, and its chemical composition mass percentage is as follows: C: 0.015~0.024%; Si: 0.412~0.572%; Mn: ≤1.7%; P: ≤0.01%; S: ≤0.002%; Cr: 22.8%; Ni: 4.36~5.76%; Mo: 3.12%; V: 0.024%; N: 0.13%; the rest are Fe elements and inevitable impurity elements; it is specifically prepared by the following steps:

[0008] The outer metal tube and the inner metal tube are prepared according to their chemical compositions, and the raw materials are sequentially smelted in a converter, refined in a LF furnace, degassed in RH, cast into continuous casting billets, hot extruded, rolled, cyclically temperature-changed, normalized, and tempered to obtain the bimetallic oil and gas composite pipe, wherein in the step of casting the continuous casting billet, a centrifugal casting method is adopted for casting, the outer layer is cast first, and then the inner layer is cast after the outer layer is cast, and the composition of the inner and outer layers is controlled by controlling the rotation speed of the centrifuge during the casting process; in the cyclic temperature-changing step, the casting is heated to an austenitizing temperature of 940-960°C at a heating rate of 30°C / min, the holding time is 5min, and then the casting is rapidly cooled to 80-100°C at a cooling rate of 250°C / s, and repeated 1-3 times.

[0009] Preferably, in the hot extrusion step, the temperature is controlled at 500-600°C, and the extrusion strength is 700-900 MPa. The extrusion strength can vary according to the temperature. The higher the temperature, the lower the extrusion strength.

[0010] Preferably, in the rolling step, a planetary tube mill is used; the rough rolling area adopts the R1 rough rolling mill with no pass and the R2 rough rolling mill with 5 passes; the finishing area adopts the F2 no pass mode; the rolling speed is 8~10m / min, the rotation speed of the turntable is 225~250rpm, the rough rolling mill outlet temperature is controlled at 1000~1050℃, the finishing rolling inlet temperature is less than 980℃, and the final rolling temperature is controlled at 820±15℃.

[0011] Preferably, in the normalizing step, the temperature of the heating furnace is controlled at 280-300°C, the casting is placed, firstly the temperature is increased to 450-500°C at a heating rate of 100°C / h, kept warm for 1 hour, then the temperature is increased to 570-600°C at a heating rate of 100°C / h, kept warm for 2 hours, and finally air / wind cooling is used to cool to room temperature.

[0012] Preferably, in the tempering step, the furnace temperature of the heating furnace is controlled at 280-300°C, the casting is placed, firstly the temperature is increased to 360-400°C at a heating rate of 100°C / h, kept warm for 1 hour, then the temperature is increased to 670-700°C at a heating rate of 100°C / h, kept warm for 2-4 hours, and finally air-cooled to room temperature.

[0013] Compared with the prior art, the present invention has the following advantages: (1) a double-layer oil and gas composite pipe structure is adopted to make full use of the service characteristics of different materials, meet the service strength while avoiding material performance waste, and the cost is relatively low; (2) X65 steel and 2205 duplex stainless steel can form a good metallurgical bond to meet the strength and corrosion resistance requirements of oil and gas pipelines; (3) the selection of centrifugal casting method, under large centrifugal force, lighter metal oxides, slag and other impurities will be squeezed to the surface or center of the casting, so that the impurities can be removed during processing or de-gating to obtain high-quality castings; (4) refined austenite grains are obtained through cyclic temperature change, and the finer the grains, the better the strength and toughness; (5) through normalizing and tempering treatment, the supersaturation of martensitic carbon in X65 / 2205 is reduced, the lattice distortion is weakened, and the residual stress is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A flow chart of a method for preparing a bimetallic oil and gas composite pipe provided by the present invention.

[0015] Figure 2 A cyclic temperature variation curve of a method for preparing a bimetallic oil and gas composite pipe provided by the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0017] A bimetallic oil and gas composite pipe is composed of X65 steel (outer layer) and 2205 duplex stainless steel (inner layer);

[0018] The composition of X65 steel pipe is as follows by weight: C: 0.156%; Si: 0.329%; Mn: 1.45%; P: 0.011%; S: 0.004%; Cr: 0.062%; Ni: 0.011%; Mo: 0.005%; V: 0.111%; the rest are Fe elements and unavoidable impurity elements;

[0019] The composition of 2205 duplex stainless steel pipe is as follows by weight percentage: C: 0.024%; Si: 0.572%; Mn: 1.63%; P: 0.009%; S: 0.001%; ​​Cr: 22.8%; Ni: 5.76%; Mo: 3.12%; V: 0.024%; N: 0.13; the rest are Fe elements and unavoidable impurity elements;

[0020] C: Increases the hardenability, strength and hardness of the material, but reduces plasticity and toughness, increases the tough-brittle transition temperature, and deteriorates the welding performance of the steel pipe. The present invention selects different carbon contents according to the hardness to be achieved by the product. The present invention controls its content to be 0.10-0.40%.

[0021] Mn: It is an element that improves the hardenability of steel and plays a role in solid solution strengthening to improve the strength and hardness of steel. However, excessive Mn can easily reduce the plasticity, toughness and weldability of steel. In order to achieve the matching of strength, plasticity and toughness, the Mn content of the present invention is controlled at 0.50-1.70%.

[0022] P: deteriorates the welding performance of steel and reduces the plasticity and toughness of steel. In the present invention, the P content is controlled to ≤0.015%;

[0023] S: Strip-shaped sulfide inclusions will increase the crack sensitivity of steel during heat treatment and welding. The S content of the present invention is controlled to ≤0.005%;

[0024] Cr: increases the hardenability, corrosion resistance and toughness of the material. The present invention controls the Cr content to ≤22.8%.

[0025] Ni: Ni element can ensure the existence of austenite and improve the stability of reversed austenite. During the deformation process, reversed austenite, as a soft phase in the organization, can absorb part of the strain energy to improve the low-temperature toughness of the material, and can reduce the tough-brittle transition temperature of the material to ensure the safety of the material at low temperatures. The Ni content of the present invention is controlled at 0.01-6%.

[0026] Mo: can expand the austenite phase region, delay the transformation of austenite to ferrite, and promote the formation of acicular ferrite. However, Mo is a precious metal element, which is not conducive to cost reduction. In the present invention, Mo is controlled within 0.005-3.12%. Example 1

[0027] Please refer to Figure 1 ,in Figure 1 The present invention provides a flow chart of a method for preparing a bimetallic oil and gas composite pipe. The method comprises the following steps:

[0028] A bimetallic oil and gas composite pipe is composed of X65 steel (outer layer) and 2205 duplex stainless steel (inner layer); the components of the X65 steel pipe are as follows by weight: C: 0.156%; Si: 0.329%; Mn: 1.45%; P: 0.011%; S: 0.004%; Cr: 0.062%; Ni: 0.011%; Mo: 0.005%; V: 0.111%; the rest are Fe elements and inevitable impurity elements; the components of the 2205 duplex stainless steel pipe are as follows by weight: C: 0.024%; Si: 0.572%; Mn: 1.63%; P: 0.009%; S: 0.001%; ​​Cr: 22.8%; Ni: 5.76%; Mo: 3.12%; V: 0.024%; N: 0.13; the rest are Fe elements and inevitable impurity elements;

[0029] The processing technology of the steel pipe includes the following steps which are performed in sequence: the smelting raw materials are successively smelted in a converter, refined in an LF furnace, degassed in RH, poured into continuous casting billets, hot extruded, rolled, cycled temperature change, normalized, and tempered.

[0030] In the step of casting the continuous casting billet, the casting material is prepared, X65 steel grade material is selected as the outer layer casting material of the pipeline steel pipe, and 2205 steel material is selected as the inner layer material of the pipeline steel pipe.

[0031] In the step of casting the continuous casting billet, a centrifugal casting method is adopted to cast the outer layer first, and then the inner layer is cast after the outer layer is cast. During the casting process, the composition of the inner and outer layers is strictly controlled by controlling the rotation speed of the centrifuge.

[0032] In the hot extrusion step, the cast steel pipe is hot extruded, the temperature is controlled at 500-600°C, and the extrusion strength is 700-900MPa. The extrusion strength can be adjusted according to the temperature. The higher the temperature, the lower the extrusion strength.

[0033] In the rolling step, the hot-extruded steel pipe is rolled using a planetary tube mill; the rough rolling area adopts the R1 rough rolling mill with no pass and the R2 rough rolling mill with 5 passes; the finishing area adopts the F2 no pass mode; the rolling speed is 10m / min, the rotation speed of the turntable is 250rpm, the rough rolling mill outlet temperature is controlled at 1000-1050°C, the finishing rolling inlet temperature should be less than 980°C, and the final rolling temperature is controlled at 820±15°C.

[0034] In the above-mentioned step of cyclic temperature change, the rolled pipe is placed in a high-power electric induction heater to make the pipe reach the austenitizing temperature of 940-960°C (30°C / min) in a short time, and the temperature is kept for 5 minutes, and then rapidly cooled to 80-100°C (250°C / s). Repeat once, such as Figure 2 shown.

[0035] In the normalizing step, the furnace temperature is controlled at 280-300°C and the casting is placed therein. The temperature is first increased to 450-500°C at a heating rate of 100°C / h and kept warm for 1 hour. The temperature is then increased to 570-600°C at a heating rate of 100°C / h and kept warm for 2 hours. Finally, air / wind cooling is used to cool the casting to room temperature.

[0036] In the tempering step, the furnace temperature of the heating furnace is controlled at 280-300°C and the casting is placed therein. The temperature is firstly increased to 360-400°C at a heating rate of 100°C / h and kept at that temperature for 1 hour. The temperature is then increased to 670-700°C at a heating rate of 100°C / h and kept at that temperature for 3 hours. Finally, the casting is air-cooled to room temperature. Example 2

[0037] Please refer to Figure 1 ,in Figure 1 The present invention provides a flow chart of a method for preparing a bimetallic oil and gas composite pipe. The method comprises the following steps:

[0038] A bimetallic oil and gas composite pipe is composed of X65 steel (outer layer) and 2205 duplex stainless steel (inner layer); the components of the X65 steel pipe are as follows by weight: C: 0.156%; Si: 0.329%; Mn: 1.45%; P: 0.011%; S: 0.004%; Cr: 0.062%; Ni: 0.011%; Mo: 0.005%; V: 0.111%; the rest are Fe elements and inevitable impurity elements; the components of the 2205 duplex stainless steel pipe are as follows by weight: C: 0.024%; Si: 0.572%; Mn: 1.63%; P: 0.009%; S: 0.001%; ​​Cr: 22.8%; Ni: 5.76%; Mo: 3.12%; V: 0.024%; N: 0.13; the rest are Fe elements and inevitable impurity elements;

[0039] The processing technology of the steel pipe includes the following steps which are performed in sequence: the smelting raw materials are successively smelted in a converter, refined in an LF furnace, degassed in RH, poured into continuous casting billets, hot extruded, rolled, cycled temperature change, normalized, and tempered.

[0040] In the step of casting the continuous casting billet, the casting material is prepared, X65 steel grade material is selected as the outer layer casting material of the pipeline steel pipe, and 2205 steel material is selected as the inner layer material of the pipeline steel pipe.

[0041] In the step of casting the continuous casting billet, a centrifugal casting method is adopted to cast the outer layer first, and then the inner layer is cast after the outer layer is cast. During the casting process, the composition of the inner and outer layers is strictly controlled by controlling the rotation speed of the centrifuge.

[0042] In the hot extrusion step, the cast steel pipe is hot extruded, the temperature is controlled at 500-600°C, and the extrusion strength is 700-900MPa. The extrusion strength can be adjusted according to the temperature. The higher the temperature, the lower the extrusion strength.

[0043] In the rolling step, the hot-extruded steel pipe is rolled using a planetary tube mill; the rough rolling area adopts the R1 rough rolling mill with no pass and the R2 rough rolling mill with 5 passes; the finishing area adopts the F2 no pass mode; the rolling speed is 10m / min, the rotation speed of the turntable is 250rpm, the rough rolling mill outlet temperature is controlled at 1000-1050°C, the finishing rolling inlet temperature should be less than 980°C, and the final rolling temperature is controlled at 820±15°C.

[0044] In the step of cyclic temperature change, the rolled pipe is placed in a high-power electric induction heater to make the pipe reach the austenitizing temperature of 940-960°C (30°C / min) in a short time, and the holding time is 5 minutes, and then it is rapidly cooled to 80-100°C (250°C / s). Repeat twice, as shown in 2.

[0045] In the normalizing step, the furnace temperature of the heating furnace is controlled at 280-300°C and the casting is placed therein. The temperature is first increased to 450-500°C at a heating rate of 100°C / h and kept warm for 1 hour. The temperature is then increased to 570-600°C at a heating rate of 100°C / h and kept warm for 2 hours. Finally, the casting is cooled to room temperature by air / wind cooling.

[0046] In the tempering step, the furnace temperature of the heating furnace is controlled at 280-300°C and the casting is placed therein. The temperature is firstly increased to 360-400°C at a heating rate of 100°C / h and kept at that temperature for 1 hour. The temperature is then increased to 670-700°C at a heating rate of 100°C / h and kept at that temperature for 3 hours. Finally, the casting is air-cooled to room temperature. Example 3

[0047] Please refer to Figure 1 ,in Figure 1 The present invention provides a flow chart of a method for preparing a bimetallic oil and gas composite pipe. The method comprises the following steps:

[0048] A bimetallic oil and gas composite pipe is composed of X65 steel (outer layer) and 2205 duplex stainless steel (inner layer); the components of the X65 steel pipe are as follows by weight: C: 0.156%; Si: 0.329%; Mn: 1.45%; P: 0.011%; S: 0.004%; Cr: 0.062%; Ni: 0.011%; Mo: 0.005%; V: 0.111%; the rest are Fe elements and inevitable impurity elements; the components of the 2205 duplex stainless steel pipe are as follows by weight: C: 0.024%; Si: 0.572%; Mn: 1.63%; P: 0.009%; S: 0.001%; ​​Cr: 22.8%; Ni: 5.76%; Mo: 3.12%; V: 0.024%; N: 0.13; the rest are Fe elements and inevitable impurity elements;

[0049] The processing technology of the steel pipe includes the following steps which are performed in sequence: the smelting raw materials are successively smelted in a converter, refined in an LF furnace, degassed in RH, poured into continuous casting billets, hot extruded, rolled, cycled temperature change, normalized, and tempered.

[0050] In the step of casting the continuous casting billet, the casting material is prepared, X65 steel grade material is selected as the outer layer casting material of the pipeline steel pipe, and 2205 steel material is selected as the inner layer material of the pipeline steel pipe.

[0051] In the step of casting the continuous casting billet, a centrifugal casting method is adopted to cast the outer layer first, and then the inner layer is cast after the outer layer is cast. During the casting process, the composition of the inner and outer layers is strictly controlled by controlling the rotation speed of the centrifuge.

[0052] In the hot extrusion step, the cast steel pipe is hot extruded, the temperature is controlled at 500-600°C, and the extrusion strength is 700-900MPa. The extrusion strength can be adjusted according to the temperature. The higher the temperature, the lower the extrusion strength.

[0053] In the rolling step, the hot-extruded steel pipe is rolled using a planetary tube mill; the rough rolling area adopts the R1 rough rolling mill with no pass and the R2 rough rolling mill with 5 passes; the finishing area adopts the F2 no pass mode; the rolling speed is 10m / min, the rotation speed of the turntable is 250rpm, the rough rolling mill outlet temperature is controlled at 1000-1050°C, the finishing rolling inlet temperature should be less than 980°C, and the final rolling temperature is controlled at 820±15°C.

[0054] In the above-mentioned step of cyclic temperature change, the rolled pipe is placed in a high-power electric induction heater to make the pipe reach the austenitizing temperature of 940-960°C (30°C / min) in a short time, and the temperature is kept for 5 minutes, and then rapidly cooled to 80-100°C (250°C / s). Repeat 3 times. Figure 2 shown.

[0055] In the normalizing step, the furnace temperature of the heating furnace is controlled at 280-300°C and the casting is placed therein. The temperature is first increased to 450-500°C at a heating rate of 100°C / h and kept warm for 1 hour. The temperature is then increased to 570-600°C at a heating rate of 100°C / h and kept warm for 2 hours. Finally, the casting is cooled to room temperature by air / wind cooling.

[0056] In the tempering step, the furnace temperature of the heating furnace is controlled at 280-300°C and the casting is placed therein. The temperature is firstly increased to 360-400°C at a heating rate of 100°C / h and kept at that temperature for 1 hour. The temperature is then increased to 670-700°C at a heating rate of 100°C / h and kept at that temperature for 3 hours. Finally, the casting is air-cooled to room temperature.

[0057] The main mechanical properties of X65 / 2205 steel after the implementation case treatment are shown in Table 1

[0058] Table 1 Main mechanical properties of bimetallic oil and gas composite pipe X65 / 2205

[0059] project Tensile strength(MPa) Yield strength (MPa) Impact energy (J) Grain size grade Example 1 518 327 365 6 Example 2 570 361 290 10 Example 3 610 400 366 11

[0060] From the data in Table 1, it can be seen that the bimetallic oil and gas composite pipe composed of X65 and 2205 has both the strength of X65 steel and the corrosion resistance of 2205 duplex stainless steel. Under the heat treatment method of rapid cycle heating and cooling, the austenite grains are refined each time they are heated, and the nucleation rate of the next austenitization is increased. At the same time, the undissolved fine carbides during rapid heating not only hinder the growth of austenite grains, but also become the non-spontaneous core of austenite, resulting in further refinement of austenite. In addition, normalizing and tempering treatments continuously reduce the supersaturation of carbon in martensite in X65 steel, weaken the degree of lattice distortion, and reduce residual stress. Thereby improving the strength and toughness of the bimetallic oil and gas composite pipe.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing bimetallic oil and gas composite pipe X65 / 2205, characterized in that: The composite pipe is composed of a double-layer metal pipe, wherein the outer metal pipe is X65 grade pipeline steel, and its chemical composition by mass percentage is as follows: C: 0.09-0.20%; Si: 0.3-0.4%; Mn: ≤1.5%; P: ≤0.015%; S: ≤0.003%; Cr: 0.05-0.062%; Ni: 0.011%; Mo: 0.005%; V: 0.111%; the rest is Fe element and unavoidable impurity elements; the inner layer The metal tube is 2205 duplex stainless steel, and its chemical composition mass percentage is as follows: C: 0.015-0.024%; Si: 0.412-0.572%; Mn: ≤1.7%; P: ≤0.01%; S: ≤0.002%; Cr: 22.8%; Ni: 4.36-5.76%; Mo: 3.12%; V: 0.024%; N: 0.13%; the rest are Fe elements and unavoidable impurity elements; it is specifically prepared by the following steps: The outer metal tube and the inner metal tube are respectively prepared according to their chemical compositions, and the raw materials are successively smelted in a converter, refined in an LF furnace, degassed in RH, cast into continuous casting billets, hot extruded, rolled, cyclically temperature-changed, normalized, and tempered to obtain the bimetallic oil and gas composite pipe, wherein in the step of casting the continuous casting billet, a centrifugal casting method is used for casting, the outer layer is cast first, and the inner layer is cast after the outer layer is cast, and the composition of the inner and outer layers is controlled by controlling the rotation speed of the centrifuge during the casting process; in the cyclic temperature-changing step, the casting is heated to an austenitizing temperature of 940-960°C at a heating rate of 30°C / min, the holding time is 5min, and then rapidly cooled to 80-100°C at a cooling rate of 250°C / s, and repeated 1-3 times; The normalizing step is: control the furnace temperature of the heating furnace at 280-300°C, put the casting in, first heat it to 450-500°C at a heating rate of 100°C / h, keep it warm for 1 hour, then heat it to 570-600°C at a heating rate of 100°C / h, keep it warm for 2 hours, and finally cool it to room temperature by air / wind cooling.

2. The method according to claim 1, characterized in that In the hot extrusion step, the temperature is controlled at 500-600° C. and the extrusion strength is 700-900 MPa.

3. The method according to claim 1, characterized in that In the rolling step, a planetary tube mill is used; the rough rolling area adopts the R1 rough rolling mill with no pass and the R2 rough rolling mill with 5 passes; the finishing area adopts the F2 no pass mode; the rolling speed is 8-10m / min, the rotation speed of the turntable is 225-250rpm, the outlet temperature of the rough rolling mill is controlled at 1000-1050℃, the inlet temperature of the finishing rolling is less than 980℃, and the final rolling temperature is controlled at 820±15℃.

4. The method according to claim 1, characterized in that In the tempering step, the furnace temperature of the heating furnace is controlled at 280-300°C, and the casting is placed. The temperature is first increased to 360-400°C at a heating rate of 100°C / h and kept warm for 1 hour. The temperature is then increased to 670-700°C at a heating rate of 100°C / h and kept warm for 2-4 hours. Finally, the casting is air-cooled to room temperature.

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