Preparation method of precise seamless steel tube for drill rod of rotary drilling rig

Abstract

The invention discloses a preparation method of a precise seamless steel tube for a drill rod of a rotary drilling rig, and relates to the field of steel tubes. Comprising the following steps that raw materials are prepared and smelted, molten iron or high-purity waste steel with low phosphorus content, low sulfur content and low gas content is selected as a main raw material, and then the main raw material is subjected to external refining, component fine adjustment and continuous casting and blank treatment; hot piercing is carried out, specifically, the continuous casting round billet is loaded into an annular heating furnace, a multi-section heating system is adopted for heating, and then hot piercing treatment is carried out in a two-roller skew rolling piercing machine; hot rolling extension is conducted, specifically, the perforated tubular billet is rapidly fed into an online heating furnace, and then rolling is conducted on a multi-rack retained core rod or full-floating core rod continuous pipe rolling machine; and sizing / reducing, and rapidly heating. The steel pipe has rigidity, strength and humanity, the fatigue life of the steel pipe is prolonged, meanwhile, the surface smoothness of an inner hole is high, the dimensional tolerance of the inner diameter and the outer diameter is accurate, the wall thickness uniformity is high, the straightness is good, and in addition, the steel pipe also has high internal cleanliness and good wear resistance.

Description

Technical Field

[0001] This invention relates to the field of steel pipes, and more particularly to a method for preparing precision seamless steel pipes for rotary drilling rigs. Background Technology

[0002] Rotary drilling rigs, as key equipment in modern foundation engineering construction, subject their drill rods to enormous tensile, compressive, torsional, and impact loads during operation, and operate in complex and harsh environments (such as underground mud and rock cuttings). The main body of the drill rod is a critical load-bearing component, and its performance directly affects the efficiency and safety of the entire machine. The requirements for the steel pipe mainly include:

[0003] Extremely high strength and toughness: It can withstand huge tensile and compressive stresses and impact loads, especially when transmitting large torques, requiring high torsional strength and good toughness to prevent brittle fracture.

[0004] Excellent fatigue performance: It must have excellent resistance to fatigue cracking when subjected to repeated alternating loads.

[0005] Precise geometric dimensions: high surface finish of the inner hole, accurate tolerance of inner and outer diameters, high uniformity of wall thickness, and good straightness are crucial for the connection accuracy, sealing performance, and uniformity of stress distribution of the drill pipe assembly.

[0006] Good wear resistance: resists erosion and abrasion from mud and rock cuttings.

[0007] High internal cleanliness: prevents inclusions and other defects from becoming fatigue crack sources.

[0008] However, existing steel pipes cannot simultaneously meet the above requirements. Therefore, this invention proposes a method for preparing precision seamless steel pipes for rotary drilling rigs. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for preparing precision seamless steel pipes for rotary drilling rigs.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for manufacturing a precision seamless steel pipe for rotary drilling rig drill rods includes the following steps:

[0012] S1: Raw material preparation and smelting. Select molten iron or high-purity scrap steel with low phosphorus, low sulfur and low gas content as the main raw materials, and then carry out ladle refining, composition fine-tuning and continuous casting, and billet processing steps respectively.

[0013] S2: Hot piercing, the continuously cast round billet is loaded into the annular heating furnace and heated using a multi-stage heating system, and then hot piercing is performed on the two-roll skew rolling piercing mill.

[0014] S3: Hot rolling extension, the pierced tube is quickly fed into an online heating furnace, and then rolled on a multi-stand limited mandrel or fully floating mandrel continuous rolling mill;

[0015] S4: Sizing / reducing. After rapid heating, if the size is close to the finished product or the size requirement before cold drawing, use a multi-stand two-roll sizing / reducing machine for micro-tension or tensionless sizing. If a larger reduction in outer diameter is required, use a tension reducing machine for diameter reduction.

[0016] S5: Pickling and lubrication, sawing to remove the irregular ends of the hot-rolled pipe, then shot blasting or sandblasting the inner and outer surfaces of the steel pipe to remove the iron oxide scale, then pickling with an acid solution, then neutralizing with a weak alkaline solution, and then passivating with phosphate.

[0017] S6: Lubricant coating. A water-soluble phosphate coating agent is applied to the inner surface of the steel pipe, and a high-viscosity metal soap-based lubricant is applied to the outer surface, followed by drying.

[0018] S7: Cold drawing adjustment, cold drawing is performed using a cycle of cold drawing - intermediate heat treatment - cold drawing;

[0019] S8: Finished product heat treatment, quenching and tempering treatment of cold-drawn steel pipes;

[0020] S9: Straightening and quality inspection. The steel pipe is straightened by hot straightening or cold straightening, then cut to length, chamfered, and then inspected for quality.

[0021] Preferably: In step S1:

[0022] Low phosphorus means phosphorus content ≤ 0.015%;

[0023] Low sulfur is defined as sulfur content ≤ 0.010%;

[0024] Low gas content: O≤20ppm, N≤60ppm, H≤2ppm.

[0025] Preferably, in step S1, the ladle refining step is as follows:

[0026] S11: Melt the main raw material in an electric arc furnace or converter;

[0027] S12: Transferred to the ladle refining furnace for deoxidation and desulfurization: Add aluminum wire and / or silicon-calcium wire to the molten steel for deep deoxidation, control the slag basicity CaO / SiO2 to 3.0-4.0, and blow argon and stir for strong desulfurization for ≥15 minutes to ensure that the sulfur content is finally reduced to S≤0.005%.

[0028] S13: Transfer to a vacuum degassing furnace or circulating degassing furnace for vacuum degassing treatment: Place the molten steel in a vacuum chamber with a vacuum degree ≤67Pa and treat for ≥15 minutes.

[0029] Preferably: In step S2:

[0030] The multi-stage heating system is as follows: preheating stage 750-900℃, heating stage 1200-1250℃, and soaking stage 1220-1280℃;

[0031] Heating time is d is the billet diameter, in mm;

[0032] The two-roll skew rolling mill has a feed angle β of 8°-12°, a rolling angle γ of 6°-10°, a roll speed of 80-150 rpm, and an elongation coefficient μ of 3.5-6.0.

[0033] Preferably, in step S3, the heating temperature of the online heating furnace is 1100-1150℃, and the heating time is... to d is the capillary diameter, in mm.

[0034] Preferably, in step S4, if the total reduction rate of the sizing is ≤10%, the size is close to the size requirement of the finished product or before cold drawing; otherwise, the outer diameter is reduced by a large margin.

[0035] Preferably, in step S5, the pickling solution is a hydrochloric acid solution with a concentration of 10%-20% or a sulfuric acid solution with a concentration of 10%-15%, and the pickling temperature is 55-70℃.

[0036] The neutralizing weak alkaline solution is sodium carbonate or a 1%-3% sodium hydroxide solution.

[0037] Preferably, in step S6, the thickness of the inner surface coating is 5-15 μm, and the thickness of the outer surface coating is 0.05-0.15 mm.

[0038] Preferably, in step S8, the quenching process is as follows:

[0039] S81a: Heating, heat the finished product to 30-50°C above the steel's complete austenitization temperature, and hold for [time missing]. to d is the diameter of the steel pipe, in mm;

[0040] S82a: Cooling and quenching, using multiple nozzles for high-pressure injection catalysis, nozzle pressure ≥5 bar, quenching medium is quenching oil or polymer aqueous solution with a concentration of 8%-15%.

[0041] Preferably, in step S8, tempering is performed at least 4 hours after quenching, and the tempering includes the following steps:

[0042] S81b: Heating, under a nitrogen-protected atmosphere, at a heating rate of ≥100℃ / h to 450-550℃, holding time is... to d is the diameter of the steel pipe, in mm;

[0043] S82b: Cool, temper, and remove from the furnace; air cool to room temperature.

[0044] The beneficial effects of this invention are as follows:

[0045] 1. The steel pipe of the present invention has high rigidity and durability, and its fatigue life is improved. At the same time, it has high surface smoothness of inner hole, accurate tolerance of inner and outer diameter, high uniformity of wall thickness, good straightness, high internal cleanliness and good wear resistance. Attached Figure Description

[0046] Figure 1 This is a flowchart illustrating a method for preparing precision seamless steel pipes for rotary drilling rigs, as proposed in this invention. Detailed Implementation

[0047] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0048] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection or setting, a detachable connection or setting, or an integral connection or setting. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0049] Example 1:

[0050] A method for manufacturing precision seamless steel pipes for rotary drilling rigs includes the following steps:

[0051] S1: Raw material preparation and smelting. Select molten iron or high-purity scrap steel with low phosphorus, low sulfur and low gas content as the main raw materials, and then carry out ladle refining, composition fine-tuning and continuous casting, and billet processing steps respectively.

[0052] S2: Hot piercing, the continuously cast round billet is loaded into the annular heating furnace and heated using a multi-stage heating system, and then hot piercing is performed on the two-roll skew rolling piercing mill.

[0053] S3: Hot rolling extension, the pierced tube is quickly fed into an online heating furnace, and then rolled on a multi-stand limited mandrel or fully floating mandrel continuous rolling mill;

[0054] S4: Sizing / reducing. After rapid heating, if the size is close to the finished product or the size requirement before cold drawing, use a multi-stand two-roll sizing / reducing machine for micro-tension or tensionless sizing. If a larger reduction in outer diameter is required, use a tension reducing machine for diameter reduction.

[0055] S5: Pickling and lubrication, sawing to remove the irregular ends of the hot-rolled pipe, then shot blasting or sandblasting the inner and outer surfaces of the steel pipe to remove the iron oxide scale, then pickling with an acid solution, then neutralizing with a weak alkaline solution, and then passivating with phosphate.

[0056] S6: Lubricant coating. A water-soluble phosphate coating agent is applied to the inner surface of the steel pipe, and a high-viscosity metal soap-based lubricant is applied to the outer surface, followed by drying.

[0057] S7: Cold drawing adjustment, cold drawing is performed using a cycle of cold drawing - intermediate heat treatment - cold drawing;

[0058] S8: Finished product heat treatment, quenching and tempering treatment of cold-drawn steel pipes;

[0059] S9: Straightening and quality inspection. The steel pipe is straightened by hot straightening or cold straightening, then cut to length, chamfered, and then inspected for quality.

[0060] In step S1:

[0061] Low phosphorus means phosphorus content ≤ 0.015%;

[0062] Low sulfur is defined as sulfur content ≤ 0.010%;

[0063] Low gas content: O≤20ppm, N≤60ppm, H≤2ppm.

[0064] In step S1, the ladle refining step is as follows:

[0065] S11: Melt the main raw material in an electric arc furnace or converter;

[0066] S12: Transferred to the ladle refining furnace for deoxidation and desulfurization: Add aluminum wire and / or silicon-calcium wire to the molten steel for deep deoxidation, control the slag basicity CaO / SiO2 to 3.0-4.0, and blow argon and stir for strong desulfurization for ≥15 minutes to ensure that the sulfur content is finally reduced to S≤0.005%.

[0067] S13: Transfer to a vacuum degassing furnace or circulating degassing furnace for vacuum degassing treatment: Place the molten steel in a vacuum chamber with a vacuum degree ≤67Pa and treat for ≥15 minutes.

[0068] In step S2:

[0069] The multi-stage heating system is as follows: preheating stage 750℃, heating stage 1200℃, and soaking stage 1220℃;

[0070] Heating time is d is the billet diameter, in mm;

[0071] The two-roll skew rolling mill has a feed angle β of 8°, a rolling angle γ of 6°, a roll speed of 80 rpm, and an elongation coefficient μ of 3.5.

[0072] In step S3, the heating temperature of the online heating furnace is 1100℃, and the heating time is... d is the capillary diameter, in mm.

[0073] In step S4, if the total reduction rate of the sizing is ≤10%, the size is close to the size requirement of the finished product or before cold drawing; otherwise, the outer diameter is reduced by a large margin.

[0074] In step S5, the pickling solution is a 10% hydrochloric acid solution or a 10% sulfuric acid solution, and the pickling temperature is 55°C.

[0075] The neutralizing weak alkaline solution is sodium carbonate or a 1% sodium hydroxide solution.

[0076] In step S6, the inner surface coating thickness is 5 μm and the outer surface coating thickness is 0.05 mm.

[0077] In step S8, the quenching process is as follows:

[0078] S81a: Heating, heating the finished product to 30°C above the steel's complete austenitization temperature, holding for [time missing]. d is the diameter of the steel pipe, in mm;

[0079] S82a: Cooling and quenching, using multiple nozzles for high-pressure injection catalysis, nozzle pressure ≥5 bar, quenching medium is quenching oil or 8% polymer aqueous solution.

[0080] In step S8, tempering is performed at least 4 hours after quenching, and includes the following steps:

[0081] S81b: Heating, under a nitrogen-protected atmosphere, at a heating rate of ≥100℃ / h to 450-550℃, holding time is... d is the diameter of the steel pipe, in mm;

[0082] S82b: Cool, temper, and remove from the furnace; air cool to room temperature.

[0083] Example 2:

[0084] A method for manufacturing precision seamless steel pipes for rotary drilling rigs includes the following steps:

[0085] S1: Raw material preparation and smelting. Select molten iron or high-purity scrap steel with low phosphorus, low sulfur and low gas content as the main raw materials, and then carry out ladle refining, composition fine-tuning and continuous casting, and billet processing steps respectively.

[0086] S2: Hot piercing, the continuously cast round billet is loaded into the annular heating furnace and heated using a multi-stage heating system, and then hot piercing is performed on the two-roll skew rolling piercing mill.

[0087] S3: Hot rolling extension, the pierced tube is quickly fed into an online heating furnace, and then rolled on a multi-stand limited mandrel or fully floating mandrel continuous rolling mill;

[0088] S4: Sizing / reducing. After rapid heating, if the size is close to the finished product or the size requirement before cold drawing, use a multi-stand two-roll sizing / reducing machine for micro-tension or tensionless sizing. If a larger reduction in outer diameter is required, use a tension reducing machine for diameter reduction.

[0089] S5: Pickling and lubrication, sawing to remove the irregular ends of the hot-rolled pipe, then shot blasting or sandblasting the inner and outer surfaces of the steel pipe to remove the iron oxide scale, then pickling with an acid solution, then neutralizing with a weak alkaline solution, and then passivating with phosphate.

[0090] S6: Lubricant coating. A water-soluble phosphate coating agent is applied to the inner surface of the steel pipe, and a high-viscosity metal soap-based lubricant is applied to the outer surface, followed by drying.

[0091] S7: Cold drawing adjustment, cold drawing is performed using a cycle of cold drawing - intermediate heat treatment - cold drawing;

[0092] S8: Finished product heat treatment, quenching and tempering treatment of cold-drawn steel pipes;

[0093] S9: Straightening and quality inspection. The steel pipe is straightened by hot straightening or cold straightening, then cut to length, chamfered, and then inspected for quality.

[0094] In step S1:

[0095] Low phosphorus means phosphorus content ≤ 0.015%;

[0096] Low sulfur is defined as sulfur content ≤ 0.010%;

[0097] Low gas content: O≤20ppm, N≤60ppm, H≤2ppm.

[0098] In step S1, the ladle refining step is as follows:

[0099] S11: Melt the main raw material in an electric arc furnace or converter;

[0100] S12: Transferred to the ladle refining furnace for deoxidation and desulfurization: Add aluminum wire and / or silicon-calcium wire to the molten steel for deep deoxidation, control the slag basicity CaO / SiO2 to 4.0, and blow argon and stir for strong desulfurization for ≥15 minutes to ensure that the sulfur content is finally reduced to S≤0.005%.

[0101] S13: Transfer to a vacuum degassing furnace or circulating degassing furnace for vacuum degassing treatment: Place the molten steel in a vacuum chamber with a vacuum degree ≤67Pa and treat for ≥15 minutes.

[0102] In step S2:

[0103] The multi-stage heating system is as follows: preheating stage 900℃, heating stage 1250℃, and soaking stage 1280℃;

[0104] Heating time is d is the billet diameter, in mm;

[0105] The two-roll skew rolling mill has a feed angle β of 12°, a rolling angle γ of 10°, a roll speed of 150 rpm, and an elongation coefficient μ of 6.0.

[0106] In step S3, the heating temperature of the online heating furnace is 1150℃, and the heating time is... d is the capillary diameter, in mm.

[0107] In step S4, if the total reduction rate of the sizing is ≤10%, the size is close to the size requirement of the finished product or before cold drawing; otherwise, the outer diameter is reduced by a large margin.

[0108] In step S5, the pickling solution is a 20% hydrochloric acid solution or a 15% sulfuric acid solution, and the pickling temperature is 70°C.

[0109] The neutralizing weak alkaline solution is sodium carbonate or a 3% sodium hydroxide solution.

[0110] In step S6, the inner surface coating thickness is 15 μm and the outer surface coating thickness is 0.15 mm.

[0111] In step S8, the quenching process is as follows:

[0112] S81a: Heating, heating the finished product to 50°C above the steel's complete austenitization temperature, holding for [time missing]. d is the diameter of the steel pipe, in mm;

[0113] S82a: Cooling and quenching, using multiple nozzles for high-pressure injection catalysis, nozzle pressure ≥ 5 bar, quenching medium is quenching oil or a 15% polymer aqueous solution.

[0114] In step S8, tempering is performed at least 4 hours after quenching, and includes the following steps:

[0115] S81b: Heating, under a nitrogen-protected atmosphere, at a heating rate of ≥100℃ / h to 450-550℃, holding time is... d is the diameter of the steel pipe, in mm;

[0116] S82b: Cool, temper, and remove from the furnace; air cool to room temperature.

[0117] Example 3:

[0118] A method for manufacturing precision seamless steel pipes for rotary drilling rigs includes the following steps:

[0119] S1: Raw material preparation and smelting. Select molten iron or high-purity scrap steel with low phosphorus, low sulfur and low gas content as the main raw materials, and then carry out ladle refining, composition fine-tuning and continuous casting, and billet processing steps respectively.

[0120] S2: Hot piercing, the continuously cast round billet is loaded into the annular heating furnace and heated using a multi-stage heating system, and then hot piercing is performed on the two-roll skew rolling piercing mill.

[0121] S3: Hot rolling extension, the pierced tube is quickly fed into an online heating furnace, and then rolled on a multi-stand limited mandrel or fully floating mandrel continuous rolling mill;

[0122] S4: Sizing / reducing. After rapid heating, if the size is close to the finished product or the size requirement before cold drawing, use a multi-stand two-roll sizing / reducing machine for micro-tension or tensionless sizing. If a larger reduction in outer diameter is required, use a tension reducing machine for diameter reduction.

[0123] S5: Pickling and lubrication, sawing to remove the irregular ends of the hot-rolled pipe, then shot blasting or sandblasting the inner and outer surfaces of the steel pipe to remove the iron oxide scale, then pickling with an acid solution, then neutralizing with a weak alkaline solution, and then passivating with phosphate.

[0124] S6: Lubricant coating. A water-soluble phosphate coating agent is applied to the inner surface of the steel pipe, and a high-viscosity metal soap-based lubricant is applied to the outer surface, followed by drying.

[0125] S7: Cold drawing adjustment, cold drawing is performed using a cycle of cold drawing - intermediate heat treatment - cold drawing;

[0126] S8: Finished product heat treatment, quenching and tempering treatment of cold-drawn steel pipes;

[0127] S9: Straightening and quality inspection. The steel pipe is straightened by hot straightening or cold straightening, then cut to length, chamfered, and then inspected for quality.

[0128] In step S1:

[0129] Low phosphorus means phosphorus content ≤ 0.015%;

[0130] Low sulfur is defined as sulfur content ≤ 0.010%;

[0131] Low gas content: O≤20ppm, N≤60ppm, H≤2ppm.

[0132] In step S1, the ladle refining step is as follows:

[0133] S11: Melt the main raw material in an electric arc furnace or converter;

[0134] S12: Transferred to the ladle refining furnace for deoxidation and desulfurization: Add aluminum wire and / or silicon-calcium wire to the molten steel for deep deoxidation, control the slag basicity CaO / SiO2 to 3.5, and blow argon and stir for strong desulfurization for ≥15 minutes to ensure that the sulfur content is finally reduced to S≤0.005%.

[0135] S13: Transfer to a vacuum degassing furnace or circulating degassing furnace for vacuum degassing treatment: Place the molten steel in a vacuum chamber with a vacuum degree ≤67Pa and treat for ≥15 minutes.

[0136] In step S2:

[0137] The multi-stage heating system is as follows: preheating stage 825℃, heating stage 1225℃, and soaking stage 1260℃.

[0138] The heating time is dmin, where d is the billet diameter in mm;

[0139] The two-roll skew rolling mill has a feed angle β of 10°, a rolling angle γ of 8°, a roll speed of 110 rpm, and an elongation coefficient μ of 3.5-6.0.

[0140] In step S3, the heating temperature of the online heating furnace is 1125℃, and the heating time is... d is the capillary diameter, in mm.

[0141] In step S4, if the total reduction rate of the sizing is ≤10%, the size is close to the size requirement of the finished product or before cold drawing; otherwise, the outer diameter is reduced by a large margin.

[0142] In step S5, the pickling solution is a 15% hydrochloric acid solution or a 12.5% ​​sulfuric acid solution, and the pickling temperature is 62.5℃.

[0143] The neutralizing weak alkaline solution is sodium carbonate or a 2% sodium hydroxide solution.

[0144] In step S6, the inner surface coating thickness is 10 μm and the outer surface coating thickness is 0.1 mm.

[0145] In step S8, the quenching process is as follows:

[0146] S81a: Heating, heating the finished product to 40°C above the steel's complete austenitization temperature, holding for [time missing]. d is the diameter of the steel pipe, in mm;

[0147] S82a: Cooling and quenching, using multiple nozzles for high-pressure injection catalysis, nozzle pressure ≥ 5 bar, quenching medium is quenching oil or a polymer aqueous solution with a concentration of 11%.

[0148] In step S8, tempering is performed at least 4 hours after quenching, and includes the following steps:

[0149] S81b: Heating, under a nitrogen-protected atmosphere, at a heating rate of ≥100℃ / h to 500℃, holding time is... d is the diameter of the steel pipe, in mm;

[0150] S82b: Cool, temper, and remove from the furnace; air cool to room temperature.

[0151] Using a Ф130mm×15mm×6000mm drill pipe made of 42CrMo as the main material, mechanical property tests and life-cycle economic tests were conducted on the preparation method of this invention, traditional hot-rolled pipe + quenching and tempering, and imported equivalent products. The tests were repeated with multiple identical products, and the results are shown in Tables 1 and 2.

[0152] Table 1: Mechanical Property Tests

[0153]

[0154]

[0155] Table 2: Economic Performance Tests Throughout the Life Cycle

[0156]

[0157]

[0158] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for manufacturing precision seamless steel pipes for rotary drilling rigs, characterized in that, Includes the following steps: S1: Raw material preparation and smelting. Select molten iron or high-purity scrap steel with low phosphorus, low sulfur and low gas content as the main raw materials, and then carry out ladle refining, composition fine-tuning and continuous casting, and billet processing steps respectively. S2: Hot piercing, the continuously cast round billet is loaded into the annular heating furnace and heated using a multi-stage heating system, and then hot piercing is performed on the two-roll skew rolling piercing mill. S3: Hot rolling extension, the pierced tube is quickly fed into an online heating furnace, and then rolled on a multi-stand limited mandrel or fully floating mandrel continuous rolling mill; S4: Sizing / reducing. After rapid heating, if the size is close to the finished product or the size requirement before cold drawing, use a multi-stand two-roll sizing / reducing machine for micro-tension or tensionless sizing. If a larger reduction in outer diameter is required, use a tension reducing machine for diameter reduction. S5: Pickling and lubrication, sawing to remove the irregular ends of the hot-rolled pipe, then shot blasting or sandblasting the inner and outer surfaces of the steel pipe to remove the iron oxide scale, then pickling with an acid solution, then neutralizing with a weak alkaline solution, and then passivating with phosphate. S6: Lubricant coating. A water-soluble phosphate coating agent is applied to the inner surface of the steel pipe, and a high-viscosity metal soap-based lubricant is applied to the outer surface, followed by drying. S7: Cold drawing adjustment, cold drawing is performed using a cycle of cold drawing - intermediate heat treatment - cold drawing; S8: Finished product heat treatment, quenching and tempering treatment of cold-drawn steel pipes; S9: Straightening and quality inspection. The steel pipe is straightened by hot straightening or cold straightening, then cut to length, chamfered, and then inspected for quality.

2. The method for preparing a precision seamless steel pipe for rotary drilling rig drill rods according to claim 1, characterized in that, In step S1: Low phosphorus means phosphorus content ≤ 0.015%; Low sulfur is defined as sulfur content ≤ 0.010%; Low gas content: O≤20ppm, N≤60ppm, H≤2ppm.

3. The method for preparing a precision seamless steel pipe for rotary drilling rig drill rods according to claim 1, characterized in that, In step S1, the ladle refining step is as follows: S11: Melt the main raw material in an electric arc furnace or converter; S12: Transferred to the ladle refining furnace for deoxidation and desulfurization: Add aluminum wire and / or silicon-calcium wire to the molten steel for deep deoxidation, control the slag basicity CaO / SiO2 to 3.0-4.0, and blow argon and stir for strong desulfurization for ≥15 minutes to ensure that the sulfur content is finally reduced to S≤0.005%. S13: Transfer to a vacuum degassing furnace or circulating degassing furnace for vacuum degassing treatment: Place the molten steel in a vacuum chamber with a vacuum degree ≤67Pa and treat for ≥15 minutes.

4. The method for preparing a precision seamless steel pipe for rotary drilling rig drill rods according to claim 1, characterized in that, In step S2: The multi-stage heating system is as follows: preheating stage 750-900℃, heating stage 1200-1250℃, and soaking stage 1220-1280℃; Heating time is d is the billet diameter, in mm; The two-roll skew rolling mill has a feed angle β of 8°-12°, a rolling angle γ of 6°-10°, a roll speed of 80-150 rpm, and an elongation coefficient μ of 3.5-6.

0.

5. The method for preparing a precision seamless steel pipe for rotary drilling rig drill rods according to claim 1, characterized in that, In step S3, the heating temperature of the online heating furnace is 1100-1150℃, and the heating time is... to d is the capillary diameter, in mm.

6. The method for preparing a precision seamless steel pipe for rotary drilling rig drill rods according to claim 1, characterized in that, In step S4, if the total reduction rate of the sizing is ≤10%, the size is close to the size requirement of the finished product or before cold drawing; otherwise, the outer diameter is reduced by a large margin.

7. The method for preparing a precision seamless steel pipe for rotary drilling rig drill rods according to claim 1, characterized in that, In step S5, the pickling solution is a hydrochloric acid solution with a concentration of 10%-20% or a sulfuric acid solution with a concentration of 10%-15%, and the pickling temperature is 55-70℃. The neutralizing weak alkaline solution is sodium carbonate or a 1%-3% sodium hydroxide solution.

8. The method for preparing a precision seamless steel pipe for rotary drilling rig drill rods according to claim 1, characterized in that, In step S6, the inner surface coating thickness is 5-15 μm, and the outer surface coating thickness is 0.05-0.15 mm.

9. The method for preparing a precision seamless steel pipe for rotary drilling rig drill rods according to claim 1, characterized in that, In step S8, the quenching process is as follows: S81a: Heating, heat the finished product to 30-50°C above the steel's complete austenitization temperature, and hold for [time missing]. to d is the diameter of the steel pipe, in mm; S82a: Cooling and quenching, using multiple nozzles for high-pressure injection catalysis, nozzle pressure ≥5 bar, quenching medium is quenching oil or polymer aqueous solution with a concentration of 8%-15%.

10. The method for preparing a precision seamless steel pipe for rotary drilling rig drill rods according to claim 1, characterized in that, In step S8, tempering is performed at least 4 hours after quenching, and includes the following steps: S81b: Heating, under a nitrogen-protected atmosphere, at a heating rate of ≥100℃ / h to 450-550℃, holding time is... to d is the diameter of the steel pipe, in mm; S82b: Cool, temper, and remove from the furnace; air cool to room temperature.

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