Ultra-fine grain seamless steel pipe and cold machining manufacturing method thereof

Abstract

The invention provides a cold machining manufacturing method of an ultra-fine grain seamless steel pipe. The method comprises the following steps: firstly, selecting a low-alloy structural steel billet with specific components, which comprises C, Si, Mn and microalloy elements of Nb, V and Ti, and heating, perforating and hot-rolling to prepare a pierced billet; and then multi-pass cold deformation treatment is carried out, 5-8 times of cold drawing or cold rolling is carried out on the pierced billet, the deformation of each pass is not lower than 30%, the cold drawing or cold rolling is carried out at the room temperature at the specific speed, and natural cooling is carried out between the passes. Recrystallization annealing is carried out after each pass of cold deformation, heat preservation is carried out for 1-2 hours at the temperature of 650-750 DEG C, and then controlled cooling is carried out. And finally, a finished product is obtained through straightening, head and tail cutting and nondestructive testing. According to the method, through cyclic cooperation of multi-pass cold deformation and recrystallization annealing and the effect of synergistically inhibiting grain growth of microalloy elements, the internal structure of the steel pipe is fully refined and homogenized, and then the comprehensive mechanical properties of the strength and toughness of the finished seamless steel pipe are remarkably improved; and meanwhile, the technological process is stable and controllable, and the product surface quality is excellent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal material processing and pipe manufacturing, in particular to an ultra-fine-grained seamless steel pipe and a cold processing manufacturing method thereof. BACKGROUND

[0002] The seamless steel pipe is widely used in key fields such as mechanical manufacturing, energy and chemical industry and building structure due to its good comprehensive mechanical properties and service reliability. With the increasing requirements of modern industry on equipment lightweight and safety performance, the traditional seamless steel pipe is difficult to meet the use requirements of high-end structural parts in terms of strength and toughness matching.

[0003] Grain refinement is an effective way to improve the strength and toughness of metal materials. At present, the industry mainly relies on hot deformation controlled rolling or normalizing treatment and other hot processing techniques to realize grain refinement, but such methods have obvious limitations: on the one hand, the grain refinement degree in the hot processing process is limited, and it is difficult to stably obtain an ultra-fine-grained structure; on the other hand, high-temperature processes are prone to cause defects such as oxidation and decarburization on the surface of the steel pipe, and have high requirements on equipment and control, which affects the uniformity and stability of product quality.

[0004] In addition, although some technologies attempt to add micro-alloying elements to assist in grain refinement, there are problems such as unreasonable element ratio and insufficient coordination with deformation process, and the grain inhibition effect of micro-alloying is not fully utilized. Therefore, how to realize sufficient grain refinement and guarantee the uniformity and stability of product performance without high-temperature defects has become a technical difficulty to be broken through in the field. SUMMARY

[0005] In view of the above technical problems in the related art, the present application provides an ultra-fine-grained seamless steel pipe and a cold processing manufacturing method thereof, which can overcome the above shortcomings of the prior art.

[0006] To achieve the above technical purposes, the technical solution of the present application is as follows: A cold processing manufacturing method of an ultra-fine-grained seamless steel pipe; The cold processing manufacturing method of the ultra-fine-grained seamless steel pipe comprises the following steps: S1. Raw pipe preparation: selecting a low-alloy structural steel billet, the chemical composition of the billet is as follows in terms of mass percentage: C: 0.10-0.20%, Si: 0.15-0.35%, Mn: 0.80-1.20%, Nb: 0.05-0.10%, V: 0.03-0.08%, Ti: 0.02-0.07%, P≤0.030%, S≤0.020%, the rest being Fe and unavoidable impurities, and the total mass percentage of the three micro-alloying elements Nb, V and Ti is 0.05-0.15%; the billet is heated, perforated and hot-rolled into a rough pipe; S2. Multi-pass cold deformation treatment: the pipe blank is subjected to 5-8 times of cold drawing or cold rolling deformation, the deformation amount of each pass is not less than 30% in terms of cross-sectional area shrinkage, the pipe blank is subjected to lubrication treatment before each deformation, the deformation temperature is room temperature, the deformation rate is 0.5-2 m / s, and the steel pipe is naturally cooled to room temperature between adjacent deformation passes; S3. Recrystallization annealing treatment: after each cold deformation pass is completed, the steel pipe is subjected to recrystallization annealing, the annealing temperature is 650-750℃, the holding time is 1-2 h, and then the steel pipe is cooled to below 300℃ in the furnace and then air-cooled to room temperature; the recrystallization annealing treatment is carried out under nitrogen protection to avoid decarburization and surface oxidation of the steel pipe; S4. Finished product treatment: the steel pipe treated in step S3 is subjected to straightening, head and tail cutting and non-destructive testing to obtain a finished product of an ultra-fine-grained seamless steel pipe.

[0007] Further, the outer diameter of the pipe blank in step S1 is 50-150 mm, and the wall thickness is 5-20 mm.

[0008] Further, the lubrication treatment in step S2 uses a graphite-based lubricating grease or a molybdenum disulfide lubricating film.

[0009] Further, the holding time of the recrystallization annealing in step S3 is adjusted according to the wall thickness of the steel pipe, and the greater the wall thickness, the longer the holding time.

[0010] Further, the lubrication treatment in step S2 includes lubrication treatment of the inner surface and the outer surface of the pipe blank respectively.

[0011] Further, the non-destructive testing in step S4 includes ultrasonic testing or eddy current testing.

[0012] According to another aspect of the present application, an ultra-fine-grained seamless steel pipe is provided. The grain size of the ultra-fine-grained seamless steel pipe reaches 12 or more, the tensile strength is ≥600 MPa, the yield strength is ≥450 MPa, and the impact energy at -20℃ is ≥50 J.

[0013] Further, the surface of the seamless steel pipe is free of oxidation and decarburization.

[0014] Further, the ultra-fine-grained seamless steel pipe is used for mechanical structural parts, hydraulic system parts or building steel structural parts.

[0015] The present application has the following advantages: through the combination of multi-pass cold deformation and recrystallization annealing, and with the synergistic effect of micro-alloy elements to inhibit grain growth, the internal structure of the steel pipe is fully refined and homogenized, thereby significantly improving the comprehensive mechanical properties of the finished product of the seamless steel pipe in terms of strength and toughness, while ensuring stable and controllable process and excellent surface quality of the product. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a process flow diagram of a cold working manufacturing method for an ultrafine grain seamless steel pipe according to an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention; obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] A cold working manufacturing method for an ultrafine-grained seamless steel pipe according to an embodiment of the present invention includes the following steps: S1. Raw material tube preparation: Low-alloy structural steel billets are selected, and the chemical composition of the billets, by mass percentage, is as follows: C: 0.10-0.20%, Si: 0.15-0.35%, Mn: 0.80-1.20%, Nb: 0.05-0.10%, V: 0.03-0.08%, Ti: 0.02-0.07%, P≤0.030%, S≤0.020%, with the remainder being Fe and unavoidable impurities, and the total mass percentage of the three microalloying elements Nb, V, and Ti is 0.05-0.15%; the billets are heated, pierced, and hot-rolled to form rough tubes; S2. Multi-pass cold deformation treatment: The rough tube is subjected to 5-8 cold drawing or cold rolling deformations. The deformation amount of each pass is not less than 30% based on the cross-sectional area shrinkage rate. The rough tube is lubricated before each deformation. The deformation temperature is room temperature and the deformation rate is 0.5-2m / s. The steel tube is naturally cooled to room temperature between adjacent deformation passes. S3. Recrystallization annealing: After each cold deformation pass, the steel pipe is subjected to recrystallization annealing at a temperature of 650-750℃ and a holding time of 1-2 hours. Then, it is cooled in the furnace to below 300℃ and then air-cooled to room temperature. The recrystallization annealing process is protected by nitrogen to avoid decarburization and surface oxidation of the steel pipe. S4. Finished product processing: The steel pipe processed in step S3 is straightened, its ends are cut off, and non-destructive testing is performed to obtain the finished ultra-fine grain seamless steel pipe.

[0020] According to an embodiment of the present invention, a cold working manufacturing method for an ultrafine grain seamless steel pipe is described. In a specific embodiment, the outer diameter of the rough pipe in step S1 is 50-150 mm, and the wall thickness is 5-20 mm.

[0021] According to an embodiment of the present invention, a cold working manufacturing method for an ultrafine grain seamless steel pipe is described. In a specific embodiment, the lubricant used in the lubrication treatment in step S2 is a graphite-based grease or a molybdenum disulfide lubricating film.

[0022] According to an embodiment of the present invention, a cold working manufacturing method for an ultrafine grain seamless steel pipe is described. In a specific embodiment, the holding time of recrystallization annealing in step S3 is adjusted according to the wall thickness of the steel pipe. The greater the wall thickness, the longer the holding time.

[0023] According to an embodiment of the present invention, a cold working manufacturing method for an ultrafine grain seamless steel pipe is described. In a specific embodiment, the lubrication treatment in step S2 includes lubricating the inner and outer surfaces of the rough pipe respectively.

[0024] According to an embodiment of the present invention, a cold working manufacturing method for an ultrafine grain seamless steel pipe is described. In a specific embodiment, the non-destructive testing in step S4 includes ultrasonic testing or eddy current testing.

[0025] Secondly, according to an embodiment of the present invention, an ultra-fine grain seamless steel pipe has a grain size of grade 12 or above, a tensile strength ≥600MPa, a yield strength ≥450MPa, and an impact absorption energy ≥50J at -20℃.

[0026] According to an embodiment of the present invention, in a specific embodiment, the surface of the seamless steel pipe is free from oxidation and decarburization.

[0027] According to an embodiment of the present invention, an ultra-fine grain seamless steel pipe is used in a specific embodiment for mechanical structural components, hydraulic system pipes, or building steel structural components.

[0028] To facilitate understanding of the above technical solutions of the present invention, the following detailed description of the above technical solutions of the present invention will be provided through specific usage methods.

[0029] In practical application, the cold working manufacturing method for an ultra-fine grain seamless steel pipe according to the present invention includes the following steps: 1. Preparation of raw material tubes: Low-alloy structural steel billets are selected, and the chemical composition of the billets, by mass percentage, is as follows: C: 0.10-0.20%, Si: 0.15-0.35%, Mn: 0.80-1.20%, Nb: 0.05-0.10%, V: 0.03-0.08%, Ti: 0.02-0.07%, P≤0.030%, S≤0.020%, with the remainder being Fe and unavoidable impurities. The total mass percentage of the three microalloying elements, Nb, V, and Ti, is 0.05-0.15%. The billets are heated, pierced, and hot-rolled into rough tubes. The outer diameter of the rough tubes is 50-150 mm, and the wall thickness is 5-20 mm.

[0030] 2. Multi-pass cold deformation treatment: The rough tube is subjected to 5-8 cold drawing or cold rolling deformations, with each deformation amount (based on cross-sectional area shrinkage) not less than 30%. Before each deformation pass, the rough tube is lubricated; graphite-based grease or molybdenum disulfide lubricating film can be used as the lubricant. The deformation process is carried out at room temperature, with the deformation rate controlled at 0.5-2 m / s. Between adjacent deformation passes, the steel tube is allowed to cool naturally to room temperature in air.

[0031] 3. Recrystallization annealing treatment: After each cold deformation pass, the steel pipe undergoes recrystallization annealing. The annealing temperature is 650-750℃, and the holding time is 1-2 hours. The holding time can be adjusted according to the wall thickness of the steel pipe; for thicker walls, the holding time should be appropriately extended. After holding, the pipe is cooled in the furnace to below 300℃, and then air-cooled to room temperature. Furthermore, nitrogen protection is used in the annealing process to prevent decarburization and surface oxidation of the steel pipe.

[0032] 4. Finished product processing: After the final cold deformation and recrystallization annealing, the steel pipe is straightened, its ends are cut off, and non-destructive testing is performed. The non-destructive testing includes ultrasonic testing or eddy current testing. After removing defective parts, the finished ultra-fine grain seamless steel pipe is obtained.

[0033] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0034] Example 1 This embodiment provides a cold working manufacturing method for ultra-fine grain seamless steel pipes, the specific steps of which are as follows: S1. Raw Material Pipe Preparation: A steel billet with the following chemical composition by mass percentage: C: 0.15%, Si: 0.25%, Mn: 1.00%, Nb: 0.08%, V: 0.05%, Ti: 0.02%, P: 0.025%, S: 0.015%, with the remainder being Fe. The steel billet is heated to 1250℃, pierced, and hot-rolled to produce a rough pipe with an outer diameter of 80mm and a wall thickness of 10mm.

[0035] S2. Multi-pass cold deformation treatment: The rough tube undergoes 6 passes of cold drawing deformation, with each pass involving a deformation of 32%. Before each pass, graphite-based grease is applied to the inner surface of the rough tube, and a molybdenum disulfide lubricating film is sprayed onto the outer surface for lubrication. The cold drawing rate is 1 m / s, and the process is carried out at room temperature. Between adjacent passes, the steel tube is allowed to cool naturally to room temperature.

[0036] S3. Recrystallization annealing treatment: After each cold drawing is completed, the steel pipe is placed in the annealing furnace and held at 700℃ for 1.5h. Then, it is cooled with the furnace to below 300℃ and then taken out of the furnace and air-cooled to room temperature.

[0037] S4. Finished product processing: The annealed steel pipe is straightened, and the ends are cut off. Then, ultrasonic testing is performed to obtain the finished seamless steel pipe.

[0038] According to the test results, the finished seamless steel pipe obtained in this embodiment has a grain size of grade 13, a tensile strength of 620MPa, a yield strength of 460MPa, and an impact absorption energy of 55J at -20℃.

[0039] Example 2 This embodiment provides another cold working manufacturing method for ultra-fine grain seamless steel pipes, the specific steps of which are as follows: Raw material tube preparation: A steel billet with the following chemical composition by mass percentage: C: 0.12%, Si: 0.18%, Mn: 0.90%, Nb: 0.05%, V: 0.06%, Ti: 0.04%, P: 0.020%, S: 0.010%, with the remainder being Fe. The steel billet was heated to 1200℃, pierced, and hot-rolled to produce a rough tube with an outer diameter of 120mm and a wall thickness of 15mm.

[0040] Multi-pass cold deformation treatment: The rough tube undergoes 8 passes of cold rolling deformation, with each pass involving a deformation of 30-35% (average deformation of 32%). Lubrication is performed before each pass of cold rolling, and the cold rolling speed is 1.5 m / s, carried out at room temperature. The steel tube is allowed to cool naturally to room temperature between adjacent passes.

[0041] Recrystallization annealing treatment: After each cold rolling pass, the steel pipe is held at 680℃ for 2 hours, then cooled in the furnace to 280℃ and then air-cooled to room temperature.

[0042] Finished product processing: The steel pipe is straightened, the ends are cut off, and then eddy current testing is performed to obtain the finished seamless steel pipe.

[0043] According to the test results, the finished seamless steel pipe obtained in this embodiment has a grain size of 12.5, a tensile strength of 610MPa, a yield strength of 455MPa, and an impact absorption energy of 52J at -20℃.

[0044] Comparative Example Seamless steel pipes were produced using a traditional hot rolling and normalizing process, with the same chemical composition of the raw materials as in Example 1. After hot rolling, the steel billets were normalized at 880°C, held at that temperature for 1 hour, and then air-cooled.

[0045] Tests showed that the finished seamless steel pipe produced by the comparative method had a grain size of grade 9, a tensile strength of 500 MPa, a yield strength of 380 MPa, and an impact absorption energy of 35 J at -20℃.

[0046] A comparison of the performance data from the examples and comparative examples shows that the seamless steel pipes produced by the method of the present invention are significantly superior to those produced by traditional processes in terms of grain size, strength, and toughness, fully demonstrating the technical advantages of the method of the present invention.

[0047] In summary, compared with the prior art, the present invention has the following beneficial effects: By adopting a process route that combines multi-pass cold deformation and recrystallization annealing, and by utilizing the synergistic effect of Nb, V, and Ti microalloying elements, grain growth can be effectively suppressed and grain nucleation can be promoted, resulting in seamless steel pipes with ultra-fine grain structure and a grain size that can stably reach level 12 or above.

[0048] The ultrafine-grained seamless steel pipe prepared by the above method exhibits excellent comprehensive mechanical properties. Its tensile strength is not less than 600 MPa, its yield strength is not less than 450 MPa, and its impact absorption energy at a low temperature of -20℃ is not less than 50 J. Compared with seamless steel pipes prepared by traditional hot working processes, the product of this invention shows a significant increase in strength of approximately 20-30% and a significant increase in toughness of approximately 30-40%, achieving a good balance between high strength and high toughness.

[0049] The cold working deformation and recrystallization annealing process used in this invention has key parameters such as deformation amount, deformation rate, annealing temperature and holding time that are easy to control precisely, thereby ensuring the stability and reproducibility of the production process and facilitating large-scale mass production.

[0050] Because the main processing is carried out at room temperature, the surface oxidation and decarburization problems caused by high-temperature heating are avoided, resulting in excellent surface quality of the finished steel pipes. At the same time, this process ensures the uniformity of the product's internal structure and mechanical properties, enabling it to meet the stringent performance requirements of various high-end fields such as mechanical structures, hydraulic systems, and building steel structures.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cold-working manufacturing method for ultra-fine grain seamless steel pipes, characterized in that, Includes the following steps: S1. Raw material tube preparation: Low-alloy structural steel billets are selected, and the chemical composition of the billets, by mass percentage, is as follows: C: 0.10-0.20%, Si: 0.15-0.35%, Mn: 0.80-1.20%, Nb: 0.05-0.10%, V: 0.03-0.08%, Ti: 0.02-0.07%, P≤0.030%, S≤0.020%, with the remainder being Fe and unavoidable impurities, and the total mass percentage of the three microalloying elements Nb, V, and Ti is 0.05-0.15%; the billets are heated, pierced, and hot-rolled to form rough tubes; S2. Multi-pass cold deformation treatment: The rough tube is subjected to 5-8 cold drawing or cold rolling deformations. The deformation amount of each pass is not less than 30% based on the cross-sectional area shrinkage rate. The rough tube is lubricated before each deformation. The deformation temperature is room temperature and the deformation rate is 0.5-2m / s. The steel tube is naturally cooled to room temperature between adjacent deformation passes. S3. Recrystallization annealing: After each cold deformation pass, the steel pipe is subjected to recrystallization annealing at a temperature of 650-750℃ and a holding time of 1-2 hours. Then, it is cooled in the furnace to below 300℃ and then air-cooled to room temperature. The recrystallization annealing process is protected by nitrogen to avoid decarburization and surface oxidation of the steel pipe. S4. Finished product processing: The steel pipe processed in step S3 is straightened, its ends are cut off, and non-destructive testing is performed to obtain the finished ultra-fine grain seamless steel pipe.

2. The cold working manufacturing method for an ultrafine-grained seamless steel pipe according to claim 1, characterized in that, The outer diameter of the rough tube mentioned in step S1 is 50-150mm, and the wall thickness is 5-20mm.

3. The cold working manufacturing method for an ultrafine-grained seamless steel pipe according to claim 1, characterized in that, The lubricant used in the lubrication treatment in step S2 is graphite-based grease or molybdenum disulfide lubricating film.

4. The cold working manufacturing method for an ultrafine-grained seamless steel pipe according to claim 1, characterized in that, The holding time for recrystallization annealing in step S3 is adjusted according to the wall thickness of the steel pipe; the greater the wall thickness, the longer the holding time.

5. The cold working manufacturing method for an ultrafine-grained seamless steel pipe according to claim 3, characterized in that, The lubrication treatment in step S2 includes lubricating the inner and outer surfaces of the rough pipe respectively.

6. The cold working manufacturing method of an ultrafine-grained seamless steel pipe according to claim 1, characterized in that, The non-destructive testing described in step S4 includes ultrasonic testing or eddy current testing.

7. A seamless steel pipe with ultra-fine grains, characterized in that, The ultrafine grain seamless steel pipe is prepared by the manufacturing method of any one of claims 1 to 6, and its grain size reaches grade 12 or above, tensile strength ≥600MPa, yield strength ≥450MPa, and impact absorption energy at -20℃ ≥50J.

8. The ultra-fine grain seamless steel pipe according to claim 7, characterized in that, The surface of the seamless steel pipe is free from oxidation and decarburization.

9. The ultra-fine grain seamless steel pipe according to claim 7, characterized in that, The ultra-fine grain seamless steel pipe is used for mechanical structural components, hydraulic system pipes, or building steel structural components.

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