A production process for ultra-fine seamless steel pipe

Abstract

A production process for ultra-fine seamless steel pipes, relating to the technical field of seamless steel pipe manufacturing. The specific steps are as follows: S1, tempering the hollow tube billet or hot-rolled rough pipe produced by centrifugal casting; S2, cold-rolling the steel pipe after the tempering treatment in step S1 through a cold rolling mill for 1 to 4 times, followed by recrystallization annealing to recrystallize and soften the steel pipe; S3, repeating step S2 3 to 10 times to obtain an ultra-fine seamless steel pipe of a set size. The present invention can completely transform the overall casting structure into a rolling structure, or use a hot-rolled rough pipe, and subsequently use a cold rolling + recrystallization softening cycle process to obtain an ultra-fine tempered seamless steel pipe. The process is simple, highly operable, and requires a small investment in equipment. It is a manufacturing method for producing high-quality ultra-fine tempered seamless steel pipes in a short process.

Description

Technical Field

[0001] The invention relates to the technical field of seamless steel pipe manufacturing, in particular to a production process of ultra-fine seamless steel pipe. Background Art

[0002] The size and orientation of metal structure grains have a great influence on the mechanical properties of metal materials. Refining the structure is an effective means to improve the strength, toughness and plasticity of steel materials. There are also many methods for grain refinement.

[0003] In the traditional method, the process of promoting grain refinement by increasing the cooling rate and increasing the supercooling, low-temperature pouring, mechanical stirring, etc. has limited effect and is difficult to implement. Moreover, when the mechanical stirring intensity is too high, it is easy to draw in air and impurities during the solidification process to form shrinkage holes, segregation and other defects, which greatly affect the mechanical properties of the metal material. The chemical treatment method is to add a small amount of special chemical elements as a modifier or inoculant to the molten metal to increase the heterogeneous nucleation rate or inhibit the growth of grains. It is currently widely used in industrial production, but it is costly and has a complicated preparation process. In addition, the addition of heterogeneities to alloys or pure metals often causes alloy solution contamination or inoculation failure.

[0004] The electric field force is used to cause the relative movement of the liquid and solid phases, promote the breakage of dendrites and increase the number of grains to refine the grains. This process method can achieve pollution-free grain refinement because it has no contact with metal materials.

[0005] Relevant data show that various electric field grain refinement technologies and magnetic field grain refinement technologies can achieve the purpose of refining the grains of solidified structures well, while the existing pulse current grain refinement devices only process the natural solidification of molten metal and cannot obtain a structure with consistent grain orientation while refining the grains.

[0006] In the traditional method, cyclic quenching treatment can also be used to refine the grains. Cyclic quenching treatment is repeated rapid heating (to the austenitizing temperature) and cooling. The specific process is to heat the steel from room temperature to a temperature slightly higher than Ac3, keep it warm for a short time at a lower austenitizing temperature, and then quickly quench and cool it to room temperature, and repeat this process. Each cycle of the austenite grains will be refined to a certain extent, thereby obtaining a fine austenite grain structure. Studies have shown that the refinement effect is best when the cycle is 3 to 4 times; the refinement effect is not obvious when the cycle is more than 5 times. The basic requirement is that the heating and cooling speeds must be quite fast. When rapid heating and rapid cooling cannot be achieved, the grains cannot be significantly refined. This method is suitable for all steels that can be hardened by austenitizing and quenching.

[0007] However, the present invention can improve the comprehensive performance of the steel pipe and save the amount of alloy addition, and thus has broad application prospects in the steel industry. Summary of the invention

[0008] The purpose of the present invention is to provide a production process for ultra-fine seamless steel pipes, which can effectively solve the problems in the background technology.

[0009] The technical solution to achieve the above purpose is:

[0010] A production process for an ultra-fine seamless steel pipe, characterized in that the specific steps are as follows:

[0011] S1. Performing quenching and tempering treatment on the centrifugally cast hollow tube billet or hot rolled rough tube;

[0012] S2, cold rolling the steel pipe after the quenching and tempering treatment in step S1 through a cold rolling mill for 1 to 4 passes, and then softening annealing to recrystallize and soften the steel pipe;

[0013] S3. Repeat step S2 3 to 10 times to obtain an ultra-fine seamless steel pipe of a set size.

[0014] Furthermore, the annealing temperature is greater than 360° C. and is at least 40° C. lower than the tempering temperature in the heat treatment process in step S1.

[0015] Beneficial effects of the present invention:

[0016] The present invention can completely transform the overall casting structure into a rolling structure, or use a hot-rolled rough pipe, and then use a cold rolling + recrystallization softening cycle process to obtain an ultra-fine quenched and tempered seamless steel pipe. The process is simple, highly operable, and requires a small investment in equipment. It is a short-process manufacturing method for producing high-quality ultra-fine quenched and tempered seamless steel pipes.

[0017] The present invention adopts a process route of first tempering and then cold rolling and annealing, which effectively avoids the limitations of pure hot working grain refinement and pure heat treatment grain refinement, and the limited degree of grain refinement. The rough pipe is tempered to obtain a tempered structure, and then a cyclic processing method combining cold rolling and recrystallization annealing is performed to gradually crush and refine the tempered grains until an ultra-fine tempered structure is obtained. The comprehensive performance of the steel pipe can be improved and the amount of alloy addition can be saved, so it has broad application prospects in the steel industry. DETAILED DESCRIPTION Example 1

[0018] This example takes the production of φ535mm 30MnV tube blank as an example to further illustrate the technical solution of the present invention, and the specific steps are as follows:

[0019] The centrifugally cast hollow tube blank of φ600*50mm (diameter*wall thickness) is subjected to tempering treatment, specifically, it is heated to 890℃ in a quenching furnace and water-cooled quenched, the water temperature is ≤50℃, the inside and outside of the tube are water-cooled at the same time, and the water is cooled to the steel tube temperature ≤50℃, and then it is tempered, and the tempering temperature is 680℃.

[0020] The first cold rolling was carried out in two passes through the cold rolling mill, with each cold rolling reducing the wall by 3 mm. After cold rolling, the steel was kept at 550°C for 130 minutes and then air-cooled to room temperature.

[0021] The steel sheet was cold rolled twice in the second cold rolling process, with a wall reduction of 4 mm each time. After cold rolling, it was kept at 550°C for 110 minutes and then air-cooled to room temperature.

[0022] The third cold rolling is performed in two passes through the cold rolling mill, and the wall reduction is 5mm each time; after cold rolling, it is kept at 550℃ for 80min, and then air-cooled to room temperature;

[0023] The steel sheet was cold rolled for the fourth time in a cold rolling mill, and the wall reduction was 5 mm. After cold rolling, the steel sheet was kept at 550°C for 60 minutes, and then air-cooled to room temperature.

[0024] The obtained seamless steel pipe has the specifications of φ535*21mm (diameter*wall thickness).

[0025] In this example, centrifugal casting rough tube is used to combine quenching and tempering with cold rolling + recrystallization annealing, which can convert the cast structure into a processed structure and obtain an ultra-fine (grain size ≥ 8 levels) quenched and tempered steel pipe. Example 2

[0026] This example takes the production of φ825mm 40Cr2Ni2Mo tube blank as an example to further illustrate the technical solution of the present invention, and the specific steps are as follows:

[0027] The hot-rolled rough pipe of φ900*60mm (diameter*wall thickness) is subjected to tempering treatment. Specifically, it is heated to 840℃ in a quenching furnace and then quenched, the water temperature is ≤50℃, and the inside and outside of the pipe are simultaneously water-cooled + quenched by double liquid quenching liquid until the steel pipe temperature is ≤50℃, and then tempered at 660℃.

[0028] The first cold rolling is performed twice by the cold rolling mill, with each cold rolling reducing the wall by 6 mm. After cold rolling, the temperature is kept at 520°C for 190 minutes and then air-cooled to room temperature.

[0029] The second cold rolling was performed in two passes, with a wall reduction of 5 mm each time. After cold rolling, the temperature was kept at 520 °C for 150 min and then air-cooled to room temperature.

[0030] The third cold rolling was performed in two passes, with each cold rolling reducing the wall thickness by 4 mm. After cold rolling, the temperature was kept at 520°C for 120 min and then air-cooled to room temperature.

[0031] The obtained seamless steel pipe has the specifications of φ825*30mm (diameter*wall thickness).

[0032] In this example, a hot-rolled rough tube is selected and tempered in combination with cold rolling + recrystallization annealing. The hot-rolled tempered structure is gradually broken during the cold rolling process to obtain an ultra-fine (grain size ≥ 9 levels) tempered steel tube. The grains are much finer than the grain size of about 6 levels obtained by traditional hot processing + tempering.

Claims

1. A production process for ultra-fine seamless steel pipe, characterized in that: The specific steps are as follows S1. quenching and tempering the hollow tube blank of 30MnV centrifugally cast or the hot-rolled rough tube of 40Cr2Ni2Mo to obtain a quenched and tempered structure; S2, cold rolling the steel pipe after the quenching and tempering treatment in step S1 through a cold rolling mill for 1 to 4 times, and then recrystallization annealing to soften the steel pipe; the annealing temperature is >360°C and is 40°C lower than the tempering temperature in the quenching and tempering treatment process in step S1; S3 and step S2 are repeated 3 to 10 times, so that the quenched and tempered grains are gradually crushed and refined until an ultra-fine quenched and tempered structure is obtained, and an ultra-fine seamless steel pipe of a set size is obtained.