CN115488184A

CN115488184A - Hot perforation method for niobium-containing austenitic stainless steel hollow billet

Info

Publication number: CN115488184A
Application number: CN202211110541.0A
Authority: CN
Inventors: 方旭东; 孙铭山; 赵建伟; 夏焱
Original assignee: Shanxi Taigang Stainless Steel Co Ltd
Current assignee: Shanxi Taigang Stainless Steel Co Ltd
Priority date: 2022-09-13
Filing date: 2022-09-13
Publication date: 2022-12-20

Abstract

The invention discloses a hot perforation method of a niobium-containing austenitic stainless steel capillary, which comprises the following steps: preparing a circular tube blank; sending the round pipe blank into a heating furnace for three-section continuous heating treatment; perforating the round pipe blank subjected to the heating treatment by using a hot perforating machine; wherein, the three-stage continuous heating treatment comprises: heating the round pipe blank to 850 ℃ in a preheating section of a heating furnace for heat preservation; heating the round pipe blank to 1100 ℃ in a heating section of a heating furnace for heat preservation, and then heating to 1250-1280 ℃ for heat preservation; the round pipe billet is cooled to 1120-1150 ℃ in a soaking section of a heating furnace for heat preservation. The hot perforation method can effectively avoid the quality defects of the niobium-containing austenitic stainless steel capillary such as the cracking of the whole inner wall and the cracking of the tail part.

Description

Hot perforation method for niobium-containing austenitic stainless steel hollow billet

Technical Field

The invention relates to the technical field of stainless steel processing, in particular to a hot perforating method of a niobium-containing austenitic stainless steel capillary.

Background

In order to improve the power generation efficiency and reduce the emission, the steam temperature and pressure parameters of the coal-fired power plant are continuously improved, the traditional materials cannot meet the requirements of a unit boiler, and a large amount of high-performance niobium-containing austenitic stainless steel seamless steel pipes are needed. Compared with the conventional austenitic stainless steel, the niobium-containing austenitic stainless steel contains a large amount of niobium and nitrogen (0.4 percent Nb and 0.1-0.3 percent N), can precipitate nano-sized MX and NbCrN in the service process, can well disperse and distribute in a matrix, can block dislocation movement, can improve precipitation strengthening effect and creep resistance, and can improve the high-temperature resistance of the austenitic stainless steel. However, austenitic stainless steels containing niobium present a number of difficulties during the production of seamless tubes, the most important of which is the problem of cracking of the inner walls of the tubular billet. Fig. 1 and fig. 2 show the appearance of the cracking defect of the inner wall of the niobium-containing austenitic stainless steel hot-punched capillary, wherein fig. 1 shows the appearance of the cracking of the whole branch of the hot-punched capillary, and fig. 2 shows the appearance of the cracking of the tail of the hot-punched capillary. The tubular billet produced by the hot perforation method has the rejection rate of more than 50 percent due to the cracking of the inner wall, so that the finished product rate is low, the manufacturing cost is high, and the production of the tubular billet made of the material is severely restricted.

Disclosure of Invention

In view of the above problems, the present invention aims to provide a hot-piercing method for austenitic stainless steel hollow billets containing niobium, so as to avoid quality defects such as inner wall branch cracking and tail cracking.

Specifically, the invention is realized by the following technical scheme:

a hot perforation method of a niobium-containing austenitic stainless steel hollow billet comprises the following steps:

step S1, preparing a round pipe blank;

s2, conveying the round pipe blank into a heating furnace to carry out three-section type continuous heating treatment;

s3, perforating the circular tube blank subjected to the heating treatment by using a hot perforating machine;

wherein, step S2 further comprises:

step S201, heating the round pipe blank to 850 ℃ in a preheating section of a heating furnace for heat preservation;

step S202, heating the circular tube blank to 1100 ℃ in a heating section of a heating furnace for heat preservation, and then heating to 1250-1280 ℃ for heat preservation;

and step S203, cooling the round pipe blank to 1120-1150 ℃ in a soaking section of a heating furnace, and preserving heat.

Optionally, in step S201, the temperature of the round pipe blank is increased to 850 ℃ at a speed of not more than 300 ℃/h in the preheating section of the heating furnace, and the holding time is 1.0-1.5 min/mm.

Optionally, in step S202, the temperature of the round pipe blank is raised to 1100 ℃ at a speed of not less than 600 ℃/h in the heating section of the heating furnace, the heat preservation time is 0.5-0.8 min/mm, and then the temperature is raised to 1250-1280 ℃ at a speed of not less than 600 ℃/h, and the heat preservation time is 1.0-1.5 min/mm.

Optionally, in step S203, the holding time of the round pipe blank in the soaking section of the heating furnace is 0.8 to 1.0min/mm.

Alternatively, in step S3, the ovality factor of the hot-piercing machine is 1.06 to 1.15.

Alternatively, in step S3, the roll rotation speed R of the hot piercing mill is set in accordance with the diameter D of the round pipe billet:

when D is more than or equal to 65 and less than or equal to 85mm, the rotating speed R of the roller is more than or equal to 40R/min and less than or equal to 50R/min;

when 85-inch fabric D is less than or equal to 110mm, the roller rotating speed R is more than 20R/min and less than or equal to 30R/min;

when the size D of the all-in-one rolls is less than or equal to 110mm, the rotating speed R of the rolls is less than or equal to 20R/min and more than or equal to 15R/min.

Alternatively, in step S3, the feed angle of the hot-piercing machine is 8.5 ⁰ ～10 ⁰ 。

Optionally, in step S1, performing internal quality flaw detection on the round pipe blank according to GB/T4162-2008, with the round pipe blank qualification grade being class B; the heart macroscopic structure of the round tube blank is detected according to GB/T1979-2001, and the central loose grade of the round tube blank is below 1.0 grade.

Optionally, in step S1, the non-metallic inclusions of the circular tube blank are inspected according to GB/T10561-2005, and the thick and thin inclusions of the non-metallic inclusions of sulfide, oxide, silicate, punctate and spherical are respectively no more than 1.5, and the total is no more than 5.5.

Optionally, in step S1, the round tube blank is subjected to a peeling process and optionally a local thinning process to make the round tube blank surface defect-free.

Compared with the prior art, the hot perforation method of the niobium-containing austenitic stainless steel capillary has at least the following beneficial effects:

the surface quality and the structure of the tubular billet produced by the hot perforation method of the niobium-containing austenitic stainless steel tubular billet are good, and the tubular billet can be used for cold machining production of seamless tubes.

The hot piercing method of the niobium-containing austenitic stainless steel tubular billet adopts the tubular billet produced by the round tube billet, and the rejection rate caused by internal cracking is controlled within 5 percent.

Drawings

FIG. 1 shows the morphology of the whole branch crack of niobium-containing austenitic stainless steel hot-punched capillary;

FIG. 2 shows the appearance of cracking at the tail of a niobium-containing austenitic stainless steel hot-punched capillary;

FIG. 3 shows the microstructure of the dendritic main cracks in the cracking zone of the inner wall of the niobium-containing austenitic stainless steel hot-punched capillary;

FIG. 4 shows a micro-crack microstructure of a cracked region of the inner wall of a niobium-containing austenitic stainless steel hot-pierced capillary;

FIG. 5 shows another micro-crack microstructure of the inner wall crack region of a niobium-containing austenitic stainless steel hot-pierced capillary;

FIG. 6 shows an energy spectrum curve of a crack defect in the inner wall of a niobium-containing austenitic stainless steel hot-piercing capillary;

FIG. 7 shows macroscopic segregation of round pipe billets at low magnification;

FIG. 8 shows the inner wall microcracks that occur in the deformed band of hot-perforated tubulars.

Detailed Description

The invention will be described in detail with reference to the following detailed description for fully understanding the objects, features and effects of the invention. The process of the present invention employs conventional methods or apparatus in the art, except as described below. The following noun terms have meanings commonly understood by those skilled in the art unless otherwise specified.

Aiming at the problem that the capillary produced by a hot perforation method has serious inner wall cracking, the inventor of the invention carries out deep research and finds that the cracked areas of the inner wall of the capillary are all near the wall thickness of about 1/4 of the inner wall, the cracked areas are all composed of dendritic main cracks and a plurality of cluster micro cracks with similar positions, and the micro cracks are mainly formed by gathering, connecting and penetrating the micro cracks characterized by weak oxidation of grain boundaries. Fig. 3 shows the micro-morphology of the dendritic main cracks in the internal crack region of the hot-punched capillary, fig. 4 shows the micro-morphology of one micro-crack in the internal crack region of the hot-punched capillary, fig. 5 shows the micro-morphology of another micro-crack in the internal crack region of the hot-punched capillary, and fig. 6 shows the energy spectrum curve of the crack defect on the inner wall of the hot-punched capillary. By combining the hot working characteristics of the niobium-containing austenitic stainless steel and the analysis of the pipe-making process parameters on the production site, the internal crack defect of the hollow billet is generated in the hot piercing process and is mainly related to solidification structure segregation of the circular pipe billet and cracking caused by unreasonable hot piercing process parameters. For example, fig. 7 shows that the low-power macrosegregation of the circular tube blank can reach 60.07 percent; FIG. 8 shows the inner wall microcracks that occur in the deformed band of hot-perforated tubulars.

In order to solve the problem of cracking of the existing niobium-containing austenitic stainless steel hot-piercing capillary, the invention provides a hot-piercing method of the niobium-containing austenitic stainless steel capillary on the basis of providing a circular tube blank quality requirement meeting the hot-piercing process, and selecting proper hot-piercing process parameters to avoid quality defects such as cracking of the whole inner wall and cracking of the tail.

The hot-piercing method of the present invention is directed to a niobium-containing austenitic stainless steel hot-piercing capillary tube which may have the following elemental composition (in weight%):

0.04 to 0.13 percent of C, less than or equal to 0.5 percent of Si, less than or equal to 2.0 percent of Mn, less than or equal to 0.045 percent of P, less than or equal to 0.030 percent of S, 18.0 to 25.0 percent of Cr, 8.0 to 23.0 percent of Ni, 0.2 to 1.0 percent of Nb and 0.05 to 0.35 percent of N; and optionally, one or more of Cu 2.0-4.0%, B0.001-0.01% and Al 0.03-0.3%; and the balance Fe and inevitable impurities.

For example, the elemental composition (wt%) of the round tube blanks used in the following examples is: 0.08 percent of C, less than or equal to 0.24 percent of Si, less than or equal to 0.87 percent of Mn, less than or equal to 0.0026 percent of P, less than or equal to 0.001 percent of S, 18.8 percent of Cr, 9.2 percent of Ni, 0.45 percent of Nb, 0.11 percent of N, 2.9 percent of Cu, 0.007 percent of B and 0.11 percent of Al. Of course, this is only exemplary, and the hot-piercing method of the present invention is also applicable to the production of other niobium-containing austenitic stainless steel hot-pierced capillaries conforming to the above-described composition.

The inventor finds that the niobium-containing austenitic stainless steel has the following characteristics: (1) the heat distortion resistance is large, and at 1100-1200 ℃, the heat distortion resistance is 2 times that of carbon steel and alloy steel and 1.5 times that of the traditional austenitic stainless steel; (2) the deformation temperature range is narrow, and the optimal processing temperature window is concentrated within 200 ℃. (3) Because of containing higher niobium, a large amount of niobium compounds precipitated in deformation have stronger pinning effect on deformed tissues, and the material presents obvious work hardening characteristics. (4) Large thermal expansion coefficient and low thermal conductivity.

In order to avoid the quality defects of internal cracking and the like of the tubular billet in the hot piercing of the niobium-containing austenitic stainless steel, the main process measures of the hot piercing method of the niobium-containing austenitic stainless steel tubular billet comprise a special screening and processing method of a round tube billet, a heating process of the round tube billet, hot piercing process parameter measures and the like. The total process route of hot perforation production is as follows: preparing a round pipe blank → drilling a centering hole → heating the pipe blank → hot piercing → quenching → straightening → acid washing → inspecting.

Specifically, the hot-piercing method for the austenitic stainless steel capillary containing niobium comprises the following steps:

step S1: preparing a circular tube blank.

In order to prevent a large amount of hot piercing waste products caused by insufficient metallurgical quality of the round tube blank, before hot piercing, round tube blank preparation work is carried out, and the hot piercing method specifically comprises the following steps: and screening out the round pipe blank capable of meeting the requirements of the hot piercing process as the round pipe blank before hot piercing by adopting internal quality inspection means such as flaw detection, low-power inspection, high-power inspection and the like and combining an appearance quality inspection method.

The inventor finds that the hot piercing process has high requirements on the metallurgical quality of the round tube blank. The metallurgical quality seriously affects the yield of the hot-punched tubular billet. The niobium-containing austenitic stainless steel contains a large amount of niobium and nitrogen (for example, 0.4% Nb and 0.1% to 0.3% by weight), and in the process of solidifying the molten steel from a liquid to a solid, a large amount of unevenly distributed large-size niobium compounds (NbN and NbCrN) are formed at the solidified end, and when the casting process is not controlled properly, the washed niobium compounds are interlaced and coact with severe porosity and shrinkage cavities formed in the later stage of solidification due to incomplete feeding of the molten steel, thereby further destroying the continuity of the metal and becoming a crack source for cracks in the hot-piercing hollow billet of the circular tube blank. In addition, the coarse and fine inclusions with large sizes, such as sulfides, oxides, silicates and lattice non-deformation inclusions, formed in the smelting process can also become crack sources in the deformation process due to the difference of the deformation capacity of the inclusions and the metal body, so that the capillary tube is cracked after perforation. And the macroscopic defects of cracks, folding, scabbing, pits and the like on the surface of the circular tube blank cause the surface defects of the tubular billet after hot piercing, so that the repair modulus is increased, and the scrapping risk is increased. Therefore, as a pipe making process, a proper method is adopted to screen out the round pipe blank with good metallurgical quality meeting the requirements of the hot piercing process, and the method is very important for improving the yield of the tubular billet and improving the surface quality stability of the inner wall and the outer wall of the tubular billet.

In a preferred embodiment, the preparing the round tube blank specifically comprises:

step S101: and (3) carrying out internal quality flaw detection on the round pipe blank according to GB/T4162-2008 'ultrasonic detection method for forged and rolled steel bars', wherein the qualified grade of the round pipe blank is grade B.

Step S102: the center macrostructure of the circular tube blank is not allowed to have shrinkage cavity defects, so the circular tube blank is allowed to have center porosity below 1.0 grade according to the detection of GB/T1979-2001 structural steel macrostructure defect rating chart.

Step S103: the non-metallic inclusion (namely high power) of the round tube blank is inspected according to GB/T10561-2005 'microscopic inspection method of determination standard rating diagram of content of non-metallic inclusion in steel', and the round tube blank meets the following conditions as qualified: nonmetallic inclusions of sulfide (group A), nonmetallic inclusions of oxide (group B), nonmetallic inclusions of silicate (group C) and non-metallic inclusions of point shape (group A)Class D) of coarse and fine non-metallic inclusions (class D) of not more than 1.5 grade _S Class) is less than or equal to 1.5 grade, and the sum of the various non-metallic inclusions is less than or equal to 5.5 grade.

Step S104: through the detection of the steps, the round pipe billets meeting the requirements are screened out and are round pipe billets with good metallurgical quality, the round pipe billets are used as raw materials to be peeled, the defects of cracks, folds, scabs, pits and the like which are visible to naked eyes are not allowed on the surfaces of the peeled round pipe billets, if the defects exist, the defects need to be locally ground, and the grinding depth of the local defects is ensured: width: length is equal to 1.

And (4) obtaining the round tube blank with a defect-free surface through peeling treatment and optional local grinding treatment. And (3) carrying out saw cutting blanking on the circular tube blank according to the specification and the single weight of the hollow billet and the yield for the next treatment.

In the present invention, it is considered that the surface of the circular blank is free from fine scratches, indentations, pits, and surface cracks of not more than 0.2mm, which are not more than half the tolerance in terms of actual dimensions, i.e., the surface of the circular blank is free from defects.

It should be noted that, the steps S101, S102, and S103 are only for distinguishing the steps and are not for limiting the sequence of the steps. In actual production, the step sequence can be determined by the person skilled in the art according to actual needs.

Step S2: and (3) sending the circular tube blank into a heating furnace for three-stage continuous heating treatment.

The inventor has found through research that a reasonable heating system is the key to ensure that the material is in an optimal thermoplastic zone during the hot perforation process. The niobium-containing austenitic stainless steel contains a large amount of alloy elements such as Cr, ni, cu, nb and the like, and compared with carbon steel and low alloy steel, the niobium-containing austenitic stainless steel has the advantages of large thermal expansion coefficient, low thermal conductivity and reasonable heating speed, and can improve the heating efficiency and prevent heating stress cracks from generating on the premise of ensuring the heating quality. In addition, the reasonable heating temperature has obvious effect on dissolving the amount of large-size niobium compounds (NbN and NbCrN) and improving the form of the niobium compounds, and the natural plasticity of the material is increased. The proper holding time is beneficial to improving the temperature uniformity of the material before deformation, and if the holding time is too long, abnormal growth of crystal grains is caused, and the ductility of the material is deteriorated.

In order to ensure that the circular tube blank is always in the optimal thermoplastic zone in the hot piercing process and improve the heating quality, the circular tube blank is heated in a three-section continuous heating mode.

In a preferred embodiment, the three-stage continuous heat treatment comprises, in order:

step S201: and (4) heating in a preheating section.

The round tube blank is heated to 850 ℃ from room temperature at the preheating section of the heating furnace at the speed of no more than 300 ℃/h (for example, 300 ℃/h, 250 ℃/h, 200 ℃/h and the like), the heat preservation time is 1.0-1.5 min/mm according to the diameter of the round tube blank, namely the heat preservation time = (1.0-1.5) min xD, D is the diameter of the round tube blank, and the unit is millimeter.

The inventor finds that the austenitic stainless steel containing niobium has large thermal expansion coefficient and low thermal conductivity, and in order to prevent serious heating stress generated by overhigh heating speed, after the round tube blank enters a heating furnace, the heating speed is strictly controlled to prevent larger stress from being generated, so that the round tube blank is slowly heated to 850 ℃ at the temperature of less than or equal to 300 ℃/h for heat preservation, and the heat preservation time is 1.0-1.5 min/mm according to the diameter of the tube blank, thereby gradually eliminating the internal and external temperature difference of the round tube blank in the heating process.

Step S202: and heating in a heating section.

The circular tube blank is heated up to 1100 ℃ in a heating section of a heating furnace at a speed of not less than 600 ℃/h (for example, 600 ℃/h, 650 ℃/h, 700 ℃/h and the like), the heat preservation time is 0.5-0.8 min/mm according to the diameter of the circular tube blank, then the temperature is raised to 1250-1280 ℃ at a speed of not less than 600 ℃/h (for example, 600 ℃/h, 650 ℃/h, 700 ℃/h and the like), and the heat preservation time is 1.0-1.5 min/mm according to the diameter of the circular tube blank.

The inventor researches and discovers that in order to maximally dissolve the amount of large-size niobium compounds (NbN and NbCrN) formed in the solidification process and change the precipitate form and reduce the adverse effect of the niobium compounds accumulated in the core part of the circular tube blank on hot piercing, the steel is heated to 1250-1280 ℃, a part of large-size niobium compounds are dissolved, and the thermoplasticity of the material is improved, different from the conventional austenitic stainless steel (such as TP 310) containing high Cr and Ni contents. In order to improve the heating quality, the circular tube blank with the steel temperature exceeding 850 ℃ after being preheated can be quickly heated to 1100 ℃ for proper heat preservation according to the temperature being more than or equal to 600 ℃/h, the heat preservation time is 0.5-0.8 min/mm according to the diameter of the circular tube blank, after the internal temperature and the external temperature are uniform, the temperature is raised to 1250-1280 ℃ according to the temperature being more than or equal to 600 ℃/h for heat preservation, the heat preservation time is 1.0-1.5 min/mm according to the diameter of the circular tube blank, and the amount of the niobium compound can be effectively reduced by 30-50 percent.

Step S203: heating in a soaking section.

The temperature of the round pipe blank is reduced to 1120-1150 ℃ in the soaking section of the heating furnace for heat preservation, and the heat preservation time is 0.8-1.0 min/mm according to the diameter calculation of the round pipe blank.

The soaking section is the last heating stage before hot working and is the key heating for ensuring the normal operation of hot perforation. Combining the results of the thermal simulation tensile test, the reduction of area of the material increases with the increase of temperature, the thermoplasticity is obviously improved, and the tensile strength is continuously reduced. The reduction of area is increased to about 60% at 1000 ℃ and above; the temperature is continuously increased to 1200 ℃, and the reduction of area of the material is almost kept unchanged, which shows that the material keeps good thermoplasticity; when the deformation temperature exceeds 1250 ℃, the reduction of area of the material is sharply reduced, and when the reduction of area is reduced to 1300 ℃, the reduction of area is reduced to below 5 percent, and the thermoplasticity of the material is sharply deteriorated. Therefore, it is inferred that the optimum thermoplastic range of such a material is 1000 to 1200 ℃, and the material should be kept in this temperature range during hot working, and hot working at 1000 ℃ or lower is avoided as much as possible, and hot working at 1250 ℃ or higher is prohibited.

Through the intensive research of the inventor, the heating target temperature before tapping is controlled to be 1120-1150 ℃, and the material can be ensured to be within 1250 ℃ to complete deformation in the hot perforation process. According to the requirement of rolling rhythm, the round pipe blank enters a soaking section to be heated and insulated, the temperature inside and outside the round pipe blank is slowly reduced to 1120-1150 ℃ from 1250-1280 ℃ along with the extension of the insulation time, the insulation time is calculated according to the diameter of the round pipe blank to be 0.8-1.0 min/mm, and tapping hot piercing is carried out when the temperature difference of steel is less than or equal to 10 ℃. The specific cooling rate can be reasonably selected by those skilled in the art according to actual production conditions, and is not limited herein.

In the production process of the tubular billet, the three-section continuous heating treatment is adopted for the circular billet, so that the residual stress caused by the prior hot working can be eliminated; on the other hand, the method is used for reducing the phenomenon that undissolved large-size niobium compounds (NbN and NbCrN) become crack sources in the hot working process by dissolving the amount of the large-size niobium compounds (NbN and NbCrN), thereby increasing the natural plasticity of the material; thirdly, because of adopting high temperature heat preservation for a certain time, large-size niobium compounds (NbN and NbCrN) are dissolved in the matrix, the content of Nb in the matrix is increased, and the secondary precipitated NbC in the subsequent hot perforation process can pin the deformed structure and refine grains.

And step S3: and (4) perforating the round pipe blank after the heating treatment by using a hot perforating machine.

The inventor finds that the niobium-containing austenitic stainless steel contains high niobium, and a large amount of fine niobium compounds (MX phases) precipitated during deformation have a strong pinning effect on a deformation structure, so that the niobium-containing austenitic stainless steel material has obvious work hardening characteristics. In the hot piercing process, at the stage that the round pipe blank is bitten into a roller, under the action of periodic variable pressure stress and tangential shear stress of the roller, the material is obviously processed and hardened along with the increase of deformation, so that microcracks are generated in the material before the material enters the roller throat, and the microcracks generated by the processing and hardening are gradually gathered, connected and penetrated to form serious inner wall cracks along with the proceeding of rolling and the combined action of a subsequent top. Therefore, the key to reducing the inner hole cracks is to prevent core microcracks from occurring before the round tube billet enters the roll throat after the first bite. The process parameters influenced mainly include: ovality factor (guide plate distance/roll distance), roll speed, feed angle (roll inclination).

In a preferred embodiment, the hot-piercing machine is configured as follows:

ellipticity coefficient: 1.06-1.15.

The roll gap directly influences the diameter reduction rate of the round tube blank, and is a key parameter for ensuring the secondary biting and forming the hole cavity of the hot piercing. If the rolling reduction is less than 10%, secondary biting is difficult. The reduction rate of more than 16% causes the formation of seizing and cavities in advance. The guide plate distance determines the ovality of the rolled piece in the deformation zone, and is one of the key parameters which can be controlled in the actual production. Compared with other stainless steels, austenitic stainless steels containing niobium have relatively low hot workability and are prone to hardening cracks in the core of the tube blank during the working process. Through practical research, the roll distance is actually controlled to be 10% -13%, a guide plate is installed in production and is adjusted or replaced at any time according to the wear degree, and the ovality coefficient is controlled to be 1.06-1.15, such as 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14 or 1.15, so that hot perforation can be guaranteed, and the quality of the inner wall of the capillary and the production efficiency can be improved.

Roller rotation speed: for the same piercing mill, the number of roll revolutions affects the rolling speed and the temperature rise effect of the tube deformation. When the rotating speed of the roller is high, the rolling speed is high, the temperature rise at the tail part of the hollow billet is higher, local overburning is often caused, and cracks on the inner wall appear. When the rotating speed of the roller is too low, the deformation temperature is reduced too much, the deformation resistance is increased, and the perforation cannot be finished smoothly. For the niobium-containing austenitic stainless steel, multiple theoretical calculations, experiments and production practice researches are carried out, and the rotating speed R of the roller is selected as follows according to the difference of the diameter D of the circular tube blank:

Feed angle (roll inclination): 8.5 ⁰ ～10 ⁰ E.g. 8.5 ⁰ 、8.8 ⁰ 、9.0 ⁰ 、9.2 ⁰ 、9.4 ⁰ 、9.6 ⁰ 、9.8 ⁰ 、10 ⁰ And the like.

The hot piercer feed angle is usually fixed at 8 ⁰ When a steel pipe having a thin wall thickness is produced in the hot piercing process, the surface quality of the capillary is improved as the number of times of rolling with rolls increases during the rotation. For austenitic stainless steels containing niobium, by choosing a larger feed angle, one canGreatly reduces the times of the grinding and rolling of the rolling piece by the roller and reduces the rolling time. Through practical research, the feed angle is adjusted to 8.5 ⁰ ～10 ⁰ The internal cracking rate can be obviously reduced.

The sequence of the other process steps of the hot perforation method of the present invention, such as centering, quenching, straightening, pickling, inspecting, etc., and the process conditions and the related schemes in the prior art can be referred to, and the present invention is not limited in particular.

Examples

The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. The experimental methods without specifying specific conditions in the following examples were selected according to the conventional methods and conditions, or according to the commercial instructions.

Example 1:

the specification of the round pipe blank is phi 110mm, the length is 1890mm, and the specification of the target tubular billet is phi 114 multiplied by 15mm. The total process route is as follows: preparing a round pipe blank → drilling a centering hole → heating the pipe blank → hot piercing → quenching → straightening → acid washing → inspecting. The method comprises the following specific steps:

1. preparation of round tube billet

Flaw detection, low power, high power and surface quality detection are respectively carried out on the round tube blanks according to GB/T4162-2008-B grade, GB/T1979-2001 and GB/T10561-2005, and blanking and punching centering holes are carried out on the tube blanks qualified by screening. The blanking length carries out single-length or multiple-length blanking on the pipe blank according to the single-branch weight and the finished product pipe yield, the blanking length is 1890 mm/branch, and a centering hole is drilled at one end of the blanking pipe blank.

2. Heating of

Heating is carried out according to a three-stage heating method.

A preheating section: preheating the tube blank, heating the tube blank from room temperature to 850 ℃, controlling the heating speed set by temperature rise according to 200 ℃/hour, and preserving heat for 2.5 hours after the temperature reaches 850 ℃.

A heating section: quickly heating to 1100 deg.C at a speed of not less than 600 deg.C/min, holding for 1 hr, and quickly heating to 1250 deg.C at a speed of not less than 600 deg.C/min, and holding for 120min.

A soaking section: and (4) cooling to 1140 ℃ along with the furnace, preserving the heat for 1.5 hours, and then tapping.

3. Thermal perforation

Ovality coefficient (disc distance/roll distance): 1.07

Roller rotation speed: 28/min

Feed angle 9 ⁰

By adopting the process, the rejection rate of the produced pierced billet caused by the internal cracking is 2.1%.

Example 2:

the specification of the round tube blank is phi 85mm, the length is 8000mm, and the specification of the target tubular billet is phi 89 multiplied by 10mm. The total process route is as follows: preparing a round pipe blank → drilling a centering hole → heating the pipe blank → hot piercing → quenching → straightening → acid washing → inspecting. The method comprises the following specific steps:

1. preparation of round tube billet

Flaw detection, low power, high power and surface quality detection are respectively carried out on the round tube blanks according to GB/T4162-2008-B grade, GB/T1979-2001 and GB/T10561-2005, and blanking and punching centering holes are carried out on the tube blanks qualified by screening. The blanking length carries out single-length or multiple-length blanking on the pipe blank according to the single-count weight and the yield of the finished pipe. And punching a centering hole at one end of the blanking pipe blank.

2. Heating of

Heating is carried out according to a three-stage heating method.

A preheating section: preheating the tube blank, heating the tube blank from room temperature to 850 ℃, controlling the heating speed set by temperature rise according to 260 ℃/hour, and preserving heat for 2 hours after the temperature reaches 850 ℃.

A heating section: quickly heating to 1100 deg.C at a speed of not less than 600 deg.C/min, holding for 50 min, and quickly heating to 1250 deg.C at a speed of not less than 600 deg.C/min, and holding for 100 min.

A soaking section: cooling to 1150 deg.c, maintaining for 70 min and tapping.

3. Thermal perforation

Ovality coefficient (disc distance/roll distance): 1.08

Roller rotation speed: 40r/min

Feed angle 8.5 ⁰

By adopting the process, the rejection rate of the produced pierced billet caused by the internal cracking is 3.4%.

Example 3:

the specification of the round pipe billet is phi 130mm, the length is 6000mm, and the specification of the target tubular billet is 135 multiplied by 18mm. The total process route is as follows: preparing a round pipe blank → drilling a centering hole → heating the pipe blank → hot piercing → water quenching → straightening → acid washing → inspecting. The method comprises the following specific steps:

4. preparation of round tube billet

5. Heating of

Heating according to a three-stage heating method.

A preheating section: preheating the tube blank, heating the tube blank from room temperature to 850 ℃, controlling the heating speed set by temperature rise according to 260 ℃/hour, and preserving heat for 130 minutes after the temperature reaches 850 ℃.

A heating section: quickly heating to 1100 deg.C at a speed of not less than 600 deg.C/min, holding for 70 min, and quickly heating to 1250 deg.C at a speed of not less than 600 deg.C/min, and holding for 150 min.

A soaking section: cooling to 1150 deg.c with the furnace, maintaining for 110 min and tapping.

6. Thermal perforation

Ovality coefficient (disc distance/roll distance): 1.07

Roller rotation speed: 18r/min

Feed angle 9.5 ⁰

By adopting the process, the rejection rate of the produced pierced billet caused by the internal cracking is 0%.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other substitutions, modifications, combinations, changes, simplifications, etc., which are made without departing from the spirit and principle of the present invention, should be construed as equivalents and included in the protection scope of the present invention.

Claims

1. A hot perforation method for a niobium-containing austenitic stainless steel hollow billet is characterized by comprising the following steps:

step S1, preparing a round pipe blank;

s3, perforating the round pipe blank subjected to the heating treatment by using a hot perforating machine;

wherein, step S2 further comprises:

2. The hot piercing method according to claim 1, wherein in step S201, the round pipe blank is heated to 850 ℃ at a rate of not more than 300 ℃/h in the preheating section of the heating furnace, and the holding time is 1.0 to 1.5min/mm.

3. The hot piercing method according to claim 1, wherein in step S202, the round pipe blank is heated up to 1100 ℃ at a rate of not less than 600 ℃/h in the heating zone of the heating furnace, and the holding time is 0.5 to 0.8min/mm, and then heated up to 1250 to 1280 ℃ at a rate of not less than 600 ℃/h, and the holding time is 1.0 to 1.5min/mm.

4. The hot piercing method according to claim 1, wherein in step S203, the holding time of the round pipe billet in the soaking section of the heating furnace is 0.8 to 1.0min/mm.

5. The thermal piercing method according to claim 1, wherein in step S3, an ovality coefficient of the thermal piercing machine is 1.06 to 1.15.

6. A hot piercing method as claimed in claim 1, wherein in step S3, the roll rotation speed R of the hot piercing mill is set in accordance with the diameter D of the round pipe billet:

when D is more than or equal to 85mm and less than or equal to 110mm, the roller rotating speed R is more than 20R/min and less than or equal to 30R/min;

7. The thermal piercing method according to claim 1, wherein in step S3, a feed angle of the thermal piercing machine is 8.5 ⁰ ～10 ⁰ 。

8. A hot piercing method according to claim 1, characterized in that in step S1, the round pipe billet is subjected to internal quality flaw detection according to GB/T4162-2008, and the round pipe billet pass grade is class B; the heart macroscopic structure of the round tube blank is detected according to GB/T1979-2001, and the central loose grade of the round tube blank is below 1.0 grade.

9. The hot piercing method according to claim 1, wherein in step S1, the nonmetallic inclusions of the round pipe billet are inspected in accordance with GB/T10561-2005, and the coarse and fine types of the nonmetallic inclusions of sulfide type, the nonmetallic inclusions of oxide type, the nonmetallic inclusions of silicate type, the nonmetallic inclusions of point type and the nonmetallic inclusions of spherical type are respectively not more than 1.5 grades, and the total is not more than 5.5 grades.

10. A hot-piercing method according to claim 1, characterized in that in step S1 the round tube billet is subjected to a peeling treatment and optionally a local thinning treatment to render the round tube billet surface free of defects.