CN116765136A - Forging and rolling method for austenitic stainless steel pipe - Google Patents

Abstract

The invention discloses a forging and rolling method of austenitic stainless steel pipes, which belongs to the technical field of austenitic stainless steel pipe manufacturing. In view of the problem that it is difficult to take into account both size and grain size in the production of austenitic stainless steel pipes, the present invention provides a forging and rolling method for austenitic stainless steel pipes, which includes forging preliminary forming: forging electroslag ingots to form preliminary forming blanks, and the preliminary forming The diameter of the billet is determined based on the total elongation ratio requirements of the hot-rolled pipe and the target size of the pipe. The grain size of the initially formed billet is determined based on the target grain size of the pipe and the amount of rolling deformation. Hot rolling forming: The initially formed billet is processed in sequence. Drilling of positioning holes, cross-rolling and perforation and finishing rolling form the formed pipe. The elongation ratio of each time is determined according to the total elongation ratio of the pipe and the number of processes; cooling and shaping: the formed pipe is cooled to form the target pipe. The invention can produce austenitic stainless steel pipes taking into account both size and grain size.

Description

A kind of austenitic stainless steel pipe forging and rolling method

Technical field

The invention relates to the field of manufacturing austenitic stainless steel pipes, and in particular to a forging and rolling method of austenitic stainless steel pipes.

Background technique

For the manufacturing of stainless steel pipes, there are currently three main manufacturing methods: rolling, free forging and direct cutting.

For austenitic stainless steel pipes, due to their material characteristics, it is difficult to effectively improve the product grain size through heat treatment processes such as solid solution. Therefore, for pipes with high requirements on grain size, the grain size must be effectively controlled during the forging or rolling process.

The method of direct cutting of bar or cylindrical materials not only has low material utilization rate, but also has large machining allowance and low economy.

The size specifications that can be produced for forged pipes are limited, the machining allowance in the diameter direction is large, the material utilization rate is not high, the processing cost is high, and the length of the forged pipe is short, generally only pipes with a length of less than 5m can be produced, and the production efficiency of the forging operation is low , has high requirements for the control of the forging process. During the forging process, uneven deformation is prone to occur, and problems such as local coarse grains and mixed crystals occur, resulting in products that cannot meet the requirements.

Hot-rolled pipes are generally rolled using continuous casting billets, which have high production efficiency, accurate margin control, and low processing volume. However, due to limitations of rolling production characteristics, hot-rolled pipes exhibit uneven grain size along the rolling direction. Especially for large-size stainless steel pipes and when the grain size requirements are high, the grain size of hot-rolled pipes is difficult to meet the requirements.

Contents of the invention

In order to solve the related problem of difficulty in balancing size and grain size in the production of austenitic stainless steel pipes, the present invention provides a forging and rolling method of austenitic stainless steel pipes. The technical solution is:

An austenitic stainless steel pipe forging and rolling method, including:

Forging preliminary forming: The electroslag ingot is forged to form a preliminary forming blank, and the diameter of the preliminary forming blank is determined according to the total elongation ratio requirement of the hot-rolled pipe and the target size of the pipe. The grain size of the preliminary forming blank is based on the target grain size of the pipe. The degree and rolling deformation are determined;

Hot rolling forming: The preliminary forming blank is sequentially drilled with positioning holes, cross-rolled and perforated, and finished rolled to form a formed pipe. The elongation ratio of each time is determined according to the total elongation ratio of the pipe and the number of processes;

Cooling and shaping: The formed pipe is water-cooled within 5 minutes to form the target pipe.

Using the above technical solution, forging is used in the initial forming stage to refine the grains and obtain a uniform forged structure to ensure the grain size of subsequent pipe forming; hot rolling is used in the forming stage to ensure the pipe size, especially the length; Rapid cooling and shaping by water cooling prevents the pipe grains from coarsening or mixed crystals due to high waste heat, so that the final pipe meets both size and grain size requirements.

In a preferred embodiment of the present invention, the forging preliminary forming includes:

Before forging, the electroslag ingot is kept at a temperature of 1150°C to 1220°C for 60h to 120h.

Using the above technical solution, high-temperature diffusion of steel ingots is achieved, macro-segregation of steel ingots is improved, and the unevenness of the recrystallized structure is reduced, thereby ensuring the grain size of the final pipe.

In a preferred embodiment of the present invention, the forging preliminary forming includes:

The electroslag ingot is subjected to upsetting twice and drawing twice to form a steel billet, and the upsetting ratio is ≥ 2 and the drawing ratio is ≥ 2;

After the steel billet is returned to the furnace and heated and kept at 1150°C to 1180°C, the upper flat anvil and the lower V-shaped anvil are used to elongate the steel billet into the preliminary blank with a cross-sectional diameter of D0 through a deformation of 35% to 55%. , the initially formed blank satisfies:

(D0 ² -d0 ² )×L0×0.99=(D ² -d ² )×L,

The total elongation ratio of the pipe = L/L0,

Wherein, D0 is the diameter of the initially formed blank, d0 is the diameter of the positioning hole, L0 is the length of the initially formed blank, D is the outer diameter of the target pipe, d is the inner diameter of the target pipe, L is the length of the target pipe.

Using the above technical solution, through two upsetting and two elongation, the steel billet is fully and effectively compacted and broken as-cast dendrites; through the upper flat anvil and lower V-shaped anvil elongation, the internal grains of the steel billet are obtained for the first time. The overall refinement makes the grain size of the initially formed blank reach 2-3 levels.

In a preferred embodiment of the present invention, the diameter of the positioning hole is 80mm-120mm.

In a preferred embodiment of the present invention, the hot rolling forming includes:

The initially formed blank is subjected to two cross-rolling piercings and one finish rolling in sequence, and the total elongation ratio of the pipe is 2.4 to 3.2. The elongation ratio of the first cross-rolling and piercing is 1.1 to 1.3, and the second cross-rolling and piercing is The elongation ratio is 2.0~2.2, and the elongation ratio of the finishing rolling pass is 1.07~1.1.

In a preferred embodiment of the present invention, the hot rolling forming includes:

The preformed blank after drilling the positioning holes and before cross-rolling and perforation is first heated to 1100±10°C and held for 2 hours, and then rapidly heated to 1240±10°C, for example within 1 hour, and held for 4 to 6 hours.

In a preferred embodiment of the present invention, the initially formed blank after the first cross-rolling and piercing is heated to 1100°C to 1150°C for heat preservation, and then the temperature is raised to 1200°C to 1240°C for heat preservation, and then the second inclined rolling is performed. Rolled and perforated.

In a preferred embodiment of the present invention, the diameter reduction rate of the finishing rolling passes is 2.6% to 3.0%.

In a preferred embodiment of the present invention, after the initial forging forming and before the hot rolling forming, it includes:

Surface treatment: The initially formed blank is subjected to surface peeling treatment, and surface cracks are subjected to carbon arc gouging and grinding and polishing, and the length:width:depth of the pits formed after grinding and polishing is 10:6:1.

Another technical solution is:

An austenitic stainless steel pipe produced by any of the above forging and rolling methods, and the diameter D of the pipe is Φ500~Φ900mm, the wall thickness T is 30mm-70mm, the length L≥4000mm, and the full cross-section grain Degree ≥ level 4.

Using the above technical solution, the pipe obtained takes into account both size and grain size, meeting the demand for large-sized austenitic stainless steel pipes with uniform grains and high grain size.

Description of drawings

Figure 1 is a schematic diagram of the dimensions of a 5.6-ton electroslag ingot;

Figure 2 is a schematic diagram of the dimensions of the initially formed blank;

Figure 3 is a schematic diagram of the initially formed blank after drilling of positioning holes;

Figure 4 shows the heating curve during hot rolling forming;

Figure 5 is a schematic diagram of the first cross-rolling perforation;

Figure 6 is a schematic diagram of the second cross-rolling perforation;

Figure 7 is a schematic diagram of the finishing rolling process;

Figure 8 is a grain size metallographic diagram of the formed target pipe.

Detailed ways

The content of the present invention can be more easily understood with reference to the following detailed description of the preferred implementation methods of the present invention and the included examples. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the event of conflict, the definitions in this specification shall prevail. As used herein, the term "prepared from" is synonymous with "comprising." As used herein, the terms "includes," "includes," "has," "contains," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or device that includes listed elements need not be limited to those elements, but may include other elements not expressly listed or inherent to such composition, step, method, article, or device. elements.

The conjunction "consisting of" excludes any unspecified elements, steps or components. If used in a claim, this phrase will close the claim so that it does not contain materials other than those described except for the usual impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim rather than immediately following the subject matter, it is limited only to the elements described in that clause; other elements are not excluded from the claim as a whole beyond the requirements.

When an amount, concentration, or other value or parameter is expressed in terms of a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose any upper range limit or preferred value and any lower range limit. or any pairing of preferred values, whether or not that range is individually disclosed. For example, when the range "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4," "1 to 3," "1 to 2," "1 to 2, and 4 to 5." , "1 to 3 and 5" etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include the endpoints thereof and all integers and fractions within the range.

The singular includes the plural unless the context clearly indicates otherwise. "Optional" or "any" means that the matter or event subsequently described may or may not occur, and the description includes circumstances in which the event occurs and circumstances in which the event does not occur.

Approximate terms in the description and claims are used to modify quantities, indicating that the present invention is not limited to the specific quantity, but also includes acceptable modifications that are close to the quantity without causing changes in the relevant basic functions. Correspondingly, the use of "about", "approximately", etc. to modify a numerical value means that the present invention is not limited to the precise numerical value. In some instances, approximate terms may correspond to the precision of the instrument used to measure the value. In the specification and claims of this application, range definitions may be combined and/or interchanged, and if not stated otherwise such ranges include all subranges subsumed therebetween.

In addition, the indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirements (ie, the number of occurrences) of the elements or components. Therefore "a" or "an" should be read to include one or at least one, and the singular form of an element or component also includes the plural form, unless it is obvious that the singular form is intended.

An austenitic stainless steel pipe forging and rolling method. This method can take into account the size and grain size requirements of the pipe through the "forging + rolling" forming process. It is especially suitable for the production of large diameters, wall thicknesses and lengths, and grain size. Pipes with high requirements, such as thick-walled pipes with a diameter D of Φ500~Φ900mm, a wall thickness T of 30mm-70mm, and a length ≥4000mm, can be produced using this method to make their grains uniform, the overall grain size of the pipes high, and the pipes The grain size of the full cross-section is ≥4.

The following dimensions will be This method will be explained in detail using target pipes with a grain size of ≥4 and a grain size difference of no more than 2 as an example. It can be understood that this method can not only produce pipes of this size, but also can produce/> etc.

This method includes:

S1 forging preliminary forming: Forge the electroslag ingot shown in Figure 1 to form a preliminary forming blank as shown in Figure 2, and the diameter of the preliminary forming blank is determined according to the total elongation ratio requirements of the hot-rolled pipe and the target size of the pipe. The grain size of the blank is determined based on the target grain size of the pipe and the amount of rolling deformation. Specifically, the grain size of the initially formed blank is 2-3, which can provide uniform grains and structures for subsequent hot-rolled pipes, as well as grain size differences that comply with mining regulations.

In order to meet this grain size requirement, the specific steps of initial forging forming may include:

Before S11 forging, the bottom 60mm of the Φ800×1200mm electroslag ingot is cut off and then heated in the furnace and kept at a temperature of 1150°C to 1220°C for 60h to 120h, thereby achieving high-temperature diffusion of the steel ingot, improving the macrosegregation of the steel ingot, and reducing the recrystallized structure. Inhomogeneity, thereby ensuring the grain size of the final tube.

S12 electroslag ingots are heated evenly and quickly come out of the furnace. The electroslag ingots are quickly and continuously upset twice and drawn twice through a hydraulic press to form a steel billet. The upsetting ratio is ≥2 and the drawing ratio is ≥2, so that the steel billet is fully effective. Ground compaction and fragmentation of as-cast dendrites.

After the steel billet is refurbished and heated and kept at 1150°C to 1180°C, the upper flat anvil and the lower V-shaped anvil are used to elongate the steel billet into a preformed blank with a cross-sectional diameter of D0 through a deformation of 35% to 55%, so that the internal grains of the steel billet The first overall refinement is obtained, a uniform forged structure is obtained, and the grain size of the initially formed blank can reach 2-3 levels, providing a better foundation for the final pipe grain size. The V-shaped anvil can adopt an angle of 100° to 120°, more preferably 100°. This angle has a good match with the process of a blank with a diameter of 650mm, and the core stress state and strain effect obtained during forging are the best, which is conducive to obtaining Uniform grains.

The initial forming blank satisfies:

(D0 ² -d0 ² )×L0×0.99=(D ² -d ² )×L,

The total elongation ratio of the pipe = L/L0,

Among them, D0 is the diameter of the initially formed blank, d0 is the diameter of the positioning hole, L0 is the length of the initially formed blank, D is the outer diameter of the target pipe, d is the inner diameter of the target pipe, and L is the length of the target pipe.

S2 hot rolling forming: The initially formed blank is sequentially drilled with positioning holes (to form the blank as shown in Figure 3), cross-rolled and perforated (to form the blank as shown in Figures 5 and 6) and finish rolling, forming the shape as shown in Figure 7 For the formed pipe shown, the elongation ratio each time is determined based on the total elongation ratio of the pipe and the number of processes. Hot rolling production allows precise control of pipe size.

The diameter of the positioning hole can be 80mm-120mm, for example, it can be 80mm, 100mm or 120mm. The size of the target pipe is 100mm through holes can be used, which size can reduce the deformation resistance of stainless steel materials.

For pipes with grain size requirements of ≥4 and unidirectional rolling, the total elongation ratio is set at 2.4~3.2, the elongation ratio of the first cross-rolling and perforation is 1.1~1.3, and the elongation ratio of the second cross-rolling and perforation is 2.0 ~2.2, the elongation ratio of the finishing rolling pass is 1.07~1.1. If the elongation ratio is too small, the size will not meet the standard. If the elongation ratio is too high, the deformation resistance will increase, causing damage to the equipment. Specifically, the size of the target pipe is The elongation ratio of the first cross-rolling and piercing pass can be 1.3, the elongation ratio of the second cross-rolling and piercing pass can be 2.0, the elongation ratio of the finishing rolling pass can be 1.1, and the total elongation ratio can be 2.7. Therefore, according to the above formula and elongation ratio requirements, the size design of the initial forming blank can be/> The difference part takes into account that the former is processed/> For the later rolled tube blanks, it is also considered that before the first piercing, the heat preservation time is longer and there will be fire loss. The fire loss here is set as 1%.

Hot rolling forming can specifically include:

S21 is shown in Figure 4. The preformed blank after drilling the positioning holes and before cross-rolling and perforation is first heated to 1100±10℃, holding time 2h, and then rapidly heated to 1240±10℃, for example within 1h, and holding time 4~6h.

Since the billet needs to be rolled with a large rolling ratio in the future, the billet has high deformation resistance. By heating and maintaining heat, the plasticity of the billet can be improved and the load requirements of the rolling equipment can be reduced. At a lower temperature level, the internal heat of the billet is first carried out to increase the overall temperature and plasticity of the billet. At this temperature level, the grain growth rate is very slow and the grains will not grow significantly; long-term heating in the high-temperature stage can The plasticity of the billet is quickly further improved, and since subsequent rolling will improve the grain size of the bar again, the impact is controllable.

The S22 preliminary forming billet is quickly released from the furnace, and the preliminary forming billet is subjected to two cross-rolling and piercing operations and one finishing rolling in sequence. The cross-rolling and piercing is performed by a cross-rolling unit, and the finishing rolling is performed by a finishing rolling unit. The finishing rolling unit includes multiple groups of alternating vertical and horizontal forming groups. Roller.

The period from the time when the initially formed blank is released from the furnace to the start of piercing must be ≤300 seconds. If it exceeds the time limit, it must be returned to the furnace and refired. As shown in Figure 5, after the first cross-rolling and piercing, the blank is rolled into a pipe with an outer diameter D1, an inner diameter d1, and a length L1. The elongation ratio of the first cross-rolling and piercing is L1/L0. In this embodiment, it is specifically: outer diameter A pipe with a wall thickness of 165mm and a length of 2100mm has a deformation of 20%.

After the first cross-rolling and piercing, the preformed blank is heated to 1050°C to 1120°C for insulation, for example, 1100°C for 1 hour, and then heated to 1200°C to 1240°C for insulation, for example, 1220°C ± 10°C for 2 hours, and then the second step is performed. Cross-rolled perforation. Since the temperature of the initially formed billet has dropped after the first piercing, the deformation resistance has increased; the reheating will improve the plasticity of the tube billet and enable large deformation rolling in the next pass. As shown in Figure 6, after the second cross-rolling and piercing, the blank is rolled into a pipe with an outer diameter D2, an inner diameter d2, and a length L2. The elongation ratio of the second cross-rolling and piercing is L2/L1. In this embodiment, specifically the outer diameter A pipe with a wall thickness of 60mm and a length of 4200mm has a deformation of 53%.

As shown in Figure 7, after finishing rolling, the blank is rolled once into a pipe with a diameter of D, an inner diameter of d, and a length of L. The finishing elongation ratio is L/L2. The diameter reduction rate of the finishing rolling passes is 2.6% to 3.0%. The purpose of finishing rolling passes is mainly to control the inner and outer diameter dimensions, and the elongation ratio should not be too large. It also increases radial deformation and reduces the anisotropy of hot-rolled pipes. The specific process of finish rolling can be as follows: first, place glass powder in the inner hole of the cross-rolled and perforated tube blank to facilitate rolling by the finishing mill; then quickly send the cross-rolled and perforated tube blank to the finishing rolling unit, and pass through the finishing rolling unit. Multiple sets of alternating vertical and horizontal forming rolls roll the tube blank into the target size at one time. of pipes.

Through this hot rolling forming step, it is ensured that the rolling process does not exceed the preset process window, thereby achieving controllable process, obtaining hot-rolled pipes with stable quality, and finally obtaining austenitic stainless steel pipes that meet the grain size requirements.

It can be understood that the billet size during the hot rolling process satisfies:

(D1 ² -d1 ² )×L1=(D2 ² -d2 ² )×L2=(D ² -d ² )×L×0.99.

S3 cooling shaping: cooling the formed pipe to avoid coarsening or mixed crystals of the pipe grains due to high waste heat. It should be noted that the shorter the cooling time of the formed pipe transfer, the better, for example within 5 minutes, specifically 2 minutes, 3 minutes, 4 minutes, etc., so as to improve the shaping effect; at the same time, the faster the cooling rate, the better, for example, using water cooling .

The austenitic stainless steel pipes produced by this method were sampled for grain size testing. The grain sizes were all above level 4, and the grain morphology was generally uniformly distributed. The grain size metallographic diagram is shown in Figure 8.

In a preferred embodiment of the present invention, after the initial forging forming in S1 and before the hot rolling forming in S2, it includes:

Surface treatment: The surface of the initially formed blank is peeled, and the surface cracks are subjected to carbon arc gouging and grinding and polishing. The length:width:depth of the pits formed after grinding and polishing is 10:6:1, thus making subsequent rolling easier. Folding and cracks will not occur when rolling, and it is easier to obtain a surface close to the shape of a pipe after rolling the dimples with this length-width-depth ratio.

Specifically: 80% of the forging surface is machined to make it white, and the remaining black parts are ground and polished with a pneumatic grinding wheel; for deep crack defects, carbon arc gouging is used to remove the defects. Then the surface of the carbon planer is polished, and the "length: width: depth" of the polished pits meets the requirements of "10:6:1".

It is obvious to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be regarded as illustrative and non-restrictive from any point of view, and the scope of the present invention is defined by the appended claims rather than the above description, and it is therefore intended that all claims falling within the claims All changes within the meaning and scope of equivalent elements are included in the present invention.

Claims (10)

1. A method of forging an austenitic stainless steel pipe, comprising:

forging and preliminary shaping: forging an electroslag ingot to form a primary formed blank, wherein the diameter of the primary formed blank is determined according to the total extension ratio requirement of a hot rolled pipe and the target size of the pipe, and the grain size of the primary formed blank is determined according to the target grain size and the rolling deformation of the pipe;

hot rolling and forming: sequentially performing positioning hole punching treatment, oblique rolling perforation and finish rolling on the primary formed blank to form a formed pipe, wherein the extension ratio of each time is determined according to the total extension ratio of the pipe and the working procedure times;

cooling and shaping: and cooling the formed pipe to form a target pipe.

2. The austenitic stainless steel pipe forging method as recited in claim 1, wherein the forging preliminary forming includes:

before forging, the electroslag ingot is insulated for 60-120 hours at 1150-1220 ℃.

3. The austenitic stainless steel pipe forging method as recited in claim 1, wherein the forging preliminary forming comprises:

upsetting the electroslag ingot twice and drawing twice to form a steel billet, wherein the upsetting ratio is more than or equal to 2, and the drawing ratio is more than or equal to 2;

after the billet is returned to the furnace and heated at 1150-1180 ℃, an upper flat anvil and a lower V-shaped anvil are adopted, the billet is drawn into the primary formed billet with the section diameter of D0 by the deformation of 35-55%, and the primary formed billet meets the following conditions:

(D0 ² -d0 ² )×L0×0.99＝(D ² -d ² )×L，

the total elongation of the tubing = L/L0,

wherein D0 is the diameter of the primary formed blank, D0 is the diameter of the positioning hole, L0 is the length of the primary formed blank, D is the outer diameter of the target pipe, D is the inner diameter of the target pipe, and L is the length of the target pipe.

4. The method of forging and rolling austenitic stainless steel pipe according to claim 3, wherein the diameter of the positioning hole is 80mm to 120mm.

5. The austenitic stainless steel pipe forging method according to claim 1, wherein the hot rolling forming comprises:

and sequentially carrying out two oblique rolling perforation and one finish rolling on the primary formed blank, wherein the total extension ratio of the pipe is 2.4-3.2, the extension ratio of the first oblique rolling perforation is 1.1-1.3, the extension ratio of the second oblique rolling perforation is 2.0-2.2, and the extension ratio of the finish rolling pass is 1.07-1.1.

6. The austenitic stainless steel pipe forging method according to claim 5, wherein the hot rolling forming comprises:

and heating the primary formed blank after positioning hole punching and before cross rolling perforation to 1100+/-10 ℃, preserving heat for 2 hours, then rapidly heating to 1240+/-10 ℃, for example, within 1 hour, and preserving heat for 4-6 hours.

7. The forging and rolling method for austenitic stainless steel pipes according to claim 6, wherein the primary formed blank after the first piercing by diagonal rolling is heated to 1100-1150 ℃ for heat preservation, then heated to 1200-1240 ℃ for heat preservation, and then the second piercing by diagonal rolling is performed.

8. The method of forging and rolling austenitic stainless steel pipes according to claim 5, wherein the reduction ratio of the finish rolling pass is 2.6% to 3.0%.

9. The austenitic stainless steel pipe forging method according to claim 1, characterized by comprising, after the forging preliminary forming and before the hot rolling forming:

surface treatment: carrying out surface skinning treatment on the primary formed blank, carrying out carbon arc gouging and polishing treatment on surface cracks, and forming pit lengths after polishing: width: the depth is 10:6:1.

10. An austenitic stainless steel pipe is characterized in that the pipe is produced by adopting the forging and rolling method according to any one of claims 1-9, wherein the diameter D of the pipe is phi 500-phi 900mm, the wall thickness T is 30-70 mm, the length L is more than or equal to 4000mm, and the full-section grain size is more than or equal to 4 grade.