Manufacturing method of HR3C super-thick seamless pipe for power plant superheater

Abstract

The application belongs to the field of seamless pipe processing and relates to a HR3C super-thick seamless pipe processing and manufacturing method for power station superheaters; the technical scheme comprises the following steps: perforating round steel, surface cleaning, cold rolling of the blank pipe, heat treatment and degreasing treatment; the round steel is heated to 1200 DEG C, then perforated by using a perforator, the included angle between the perforation roller and the roller center is 8 DEG during the perforation process, the rolling speed is 260-270 r / min, and the blank pipe is prepared; the blank pipe is straightened and pickled, and surface defects are cleaned; the blank pipe is rolled by using a cold rolling pipe machine, the ratio of the diameter of the large head of the mandrel of the cold rolling pipe machine to the diameter of the sizing section is 1-2.5; the blank pipe after the cold rolling is subjected to degreasing treatment; the blank pipe after the degreasing treatment is subjected to heat treatment; the method for perforating the round steel further comprises the following steps: the round steel is heated to 1200±10 DEG C, and the heating time is kept for 6 hours.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of seamless pipe processing, and relates to a manufacturing method of HR3C super-thick seamless pipe for power station superheater. BACKGROUND

[0002] HR3C (25Cr-20Ni-Nb-N) steel is a new type of austenitic heat-resistant steel successfully developed by adding 0.2-0.6% of Nb and 0.15-0.35% of N on the basis of 25Cr-20N type TP310H steel, and improving the creep strength of the material through solid solution strengthening and precipitation strengthening. Especially, the precipitation strengthening of carbides and carbonitrides of Nb precipitated during service increases the creep rupture strength of the material to 181 MPa. When the metal wall temperature is 650℃, the high-temperature stress-rupture strength of the material can reach about twice that of TP310H. The HR3C super-thick seamless steel pipe is mainly applied in the last superheater and the thick frequency superheater, and meets the higher pressure requirement of the last superheater and the thick frequency superheater, and the high-temperature superheater and reheater components manufactured at a temperature not higher than 700℃. The high strength and high hardness of the HR3C material determine that the processes such as piercing, cold rolling and heat treatment are difficult in the pipe manufacturing process, especially the production process of the super-thick seamless pipe (the diameter-wall ratio is between 2 and 3) introduced in the present application, which is more difficult. The composition of HR3C is as follows:

[0003] Table 1 Composition of HR3C

[0004]

[0005] At present, the diameter-wall ratio of the finished pipe made of HR3C material mainly concentrates on 3-20, such as The super-thick wall seamless finished pipe with a diameter-wall ratio less than 3 exceeds the equipment capacity, and is mainly processed by multi-pass cold drawing, for example 17mm and the like. Due to the development of high pressure of the ultra-supercritical power station boiler, the super-thick seamless steel pipe becomes a necessary product, and the multi-pass cold drawing not only has a long processing route, but also has a low yield due to the multiple passes, and the grain size difference is large due to the multi-pass heat treatment, so that the performance cannot be guaranteed. Therefore, the development of the super-thick seamless steel pipe process is a common goal of the user and the company. The product has the basic characteristics different from the ordinary specifications, such as small diameter, large weight per meter, small inner hole and super-thick wall, and the like, and especially the use of the super-limit and the equipment capacity exceeding the limit in the production and manufacturing process brings difficulties to the development of the product.

[0006] Considering the requirements of the grain size difference, mechanical properties of the pipe wall thickness of the superheater of the thermal power unit, the existing equipment capacity and the existing process which cannot be referenced, the production process of the super-thick seamless steel pipe with a diameter-wall ratio less than 3 of the HR3C pipe material is designed as follows: piercing + two cold rolling passes + one cold drawing pass.

[0007] The method solves the problems of the small deformation amount of the super-thick hollow pipe in the production process, the difficulty of directly rolling the super-thick pipe into a finished product, and the uneven grain of the super-thick pipe in heat treatment. SUMMARY

[0008] To overcome the defects in the above related technology, the application provides a HR3C super-thick seamless pipe processing and manufacturing method for a superheater of a power station. The HR3C super-thick seamless pipe processing and manufacturing method for the superheater of the power station is suitable for a super-thick seamless pipe processed by HR3C stainless steel. The HR3C super-thick seamless pipe processing and manufacturing method for the superheater of the power station comprises the following steps: perforating a round steel, surface cleaning, cold rolling of a hollow pipe, heat treatment, and degreasing treatment. The round steel is heated to 1200 DEG C, and then perforated by a perforating machine. The center angle between the perforating roller and the roller center is 8 DEG, and the rolling speed is 260-270 r / min, so as to prepare the hollow pipe. The hollow pipe is straightened and pickled, and the surface defects are cleaned. The hollow pipe is rolled by a cold rolling pipe machine. The ratio of the big head diameter of the mandrel of the cold rolling pipe machine to the diameter of the sizing section is 1-2.5. The hollow pipe after the cold rolling is subjected to the degreasing treatment. The hollow pipe after the degreasing treatment is subjected to the heat treatment.

[0009] The method for perforating the round steel further comprises the following steps: heating the round steel to 1200±10 DEG C, and keeping the heating time for 6 hours.

[0010] The cold rolling of the hollow pipe further comprises the following steps:

[0011] The first pass cold rolling is rolled by the cold rolling pipe machine. The ratio of the big head diameter of the mandrel of the cold rolling pipe machine to the diameter of the sizing section is 1-2.5 in the first pass cold rolling.

[0012] The second pass cold rolling is rolled by the cold rolling pipe machine. The ratio of the big head diameter of the mandrel of the cold rolling pipe machine to the diameter of the sizing section is 1-2.5 in the second pass cold rolling.

[0013] The rolling speed of the cold rolling pipe machine is 30 times / min, and the feed amount is 3-3.5 mm.

[0014] After the cold rolling of the hollow pipe, the HR3C super-thick seamless pipe processing and manufacturing method for the superheater of the power station further comprises once drawing of the cold-rolled hollow pipe.

[0015] The cold rolling of the hollow pipe further comprises the following steps:

[0016] The heat treatment of the hollow pipe after the first pass cold rolling comprises the following steps: heating the hollow pipe to 1220±15 DEG C, and keeping the temperature for 55±2 min.

[0017] The process of heat treating the hollow pipe after the second pass of cold rolling comprises heating the hollow pipe to 1200±15 DEG C and keeping the temperature for 52±2 min.

[0018] The method for manufacturing the HR3C extra-thick seamless pipe further comprises, after the first drawing of the cold-rolled hollow pipe, a process of heat treating the first-drawn hollow pipe, which comprises heating the hollow pipe to 1200±15 DEG C and keeping the temperature for 50±2 min.

[0019] The present application has the following advantages:

[0020] 1. The present application provides a method for manufacturing a high-nickel alloy HR3C extra-thick seamless pipe, which provides a solution in the case of insufficient manufacturing capacity. The produced extra-thick pipe meets the requirements of higher temperature and higher pressure of a boiler power station. Meanwhile, the technical difficulties of uncontrolled wall thickness (thick-walled pipe drawing has a wall-thinning phenomenon) and poor grain size of the finished product caused by multi-pass drawing of the high-nickel alloy HR3C extra-thick seamless pipe are solved, the machining amount of the extra-thick pipe is effectively reduced, and the performance fully meets the requirements of national standards and the design requirements of a boiler power station.

[0021] 2. The present application adjusts the rotating speed of the piercing roller, which is adjusted from the original 300-320 rpm to 260-270 rpm. The rotating speed of the roller is reduced to reduce the self-rotation speed of the round steel, improve the centering of the piercing plug and the round steel, reduce the occurrence of wall deviation, and stabilize the piercing. Too small rotating speed of the roller can easily cause too large temperature drop of the round steel during the piercing process, which affects the piercing quality.

[0022] The included angle between the piercing roller and the roller center is reduced from the original 12° to 8°. The included angle of the roller is reduced to reduce the feeding speed of the round steel during the piercing process, greatly reduce the rolling force, stabilize the plug rod, and improve the centering.

[0023] By taking the above measures, the defects of small piercing plug rod are solved, and the quality problem of piercing wall deviation is also solved, with the wall deviation being less than 1.5 mm.

[0024] For the same size of round steel, the hollow pipe size after piercing is not the same, the elongation is not consistent, and the deformation heat generated during the deformation process is also not consistent. Therefore, the heating temperature of the round steel is uncertain. For the Φ114*22 mm small deformation size after piercing, the piercing temperature and heating time need to be re-determined to solve the quality problems of piercing roll jamming and internal cracking.

[0025] 3. The piercing temperature is 1200±10 DEG C and the heating time is 6 hours. The rolling is stable, the piercing plug rod runs smoothly, and the inner and outer surface quality is not a problem.

[0026] Through the test, the piercing temperature is 1170±15℃ and the heating time is 5 hours, the piercing process is difficult to bite in, the rolling is unstable, and the core rod is bent. The temperature of the round steel measured during the piercing process reaches 30°, which is larger than the temperature drop of the ordinary specification. The piercing temperature is 1220±10℃ and the heating time is 6 hours, the piercing is normally bitten in, the rolling is stable, the piercing top rod runs smoothly, but the inner surface produces internal cracks, and the proportion of internal cracks reaches 12%.

[0027] 4、The present application is aimed at designing a core rod for a rough pipe, and performing multi-pass cold rolling, avoiding multi-pass drawing process, which can avoid the case that the grain difference is large after multi-pass drawing and heat treatment, and the performance cannot be guaranteed.

[0028] 5、The present application adopts one-time drawing process, and the wall thickness of the ordinary specification drawing process will increase, and the wall thickness of the air drawing will decrease by 1mm, which does not occur in the actual production process. The wall thickness of the one-time drawing process is 17.3-17.7mm, which meets the tolerance requirements of the finished product. If the drawing is two or more times, the wall thickness of the finished product does not meet the tolerance requirements, and the HR3C extra-thick pipe cannot control the wall thickness in multi-pass drawing to complete batch production. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technical solutions, the drawings needed to be used in the embodiments or the related technical solution description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0030] Figure 1 It is the surface graph of the rough pipe in the present application when the rolling speed is 55 times / min and the feed amount is 2.5mm in the rough pipe cold rolling process;

[0031] Figure 2 It is the cross-sectional view of the rough pipe after one cold drawing in the present application;

[0032] Figure 3 It is the grain graph of the outer surface of the rough pipe after one cold drawing in the present application;

[0033] Figure 4 It is the grain graph of the inner surface of the rough pipe after one cold drawing in the present application;

[0034] Figure 5 It is the cross-sectional view of the seamless steel pipe after multi-pass cold drawing in the present application. DETAILED DESCRIPTION

[0035] In order to make the above object, characteristics and advantages of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0036] In the description of the present application, it should be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0037] The terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "multiple" is two or more.

[0038] Embodiment 1

[0039] The specific manufacturing process of the present application includes the following steps:

[0040] Φ110mm round steel is perforated to prepare Φ114*22mm hollow pipe.

[0041] The Φ114*22mm hollow pipe is subjected to the first pass cold rolling operation to prepare Φ89*19mm hollow pipe.

[0042] The Φ89*19mm hollow pipe is subjected to the second pass cold rolling operation to prepare Φ57*18mm hollow pipe.

[0043] The Φ57*18mm hollow pipe is subjected to one pass cold drawing operation to prepare Φ51*18mm seamless steel pipe.

[0044] The following describes the main key process technical difficulties and quality key control points:

[0045] 1. Piercing

[0046] Φ114*22mm high nickel alloy HR3C piercing rolling force is big, but the ejector rod uses Φ60 specification, Φ60 ejector rod is the specification of piercing Φ65 outer diameter, breaking the limit of tool, the smaller the piercing top, the more unstable the piercing process, causing the ejector rod bending, the top and round steel can not be centered, and the piercing blank wall is serious.

[0047] Take measures:

[0048] Adjust the speed of the piercing roll, the speed is adjusted from 300-320 rpm to 260-270 rpm, reduce the speed of the roll to reduce the speed of the round steel, improve the centering of the piercing top and the round steel, reduce the wall deviation and stabilize the piercing. Too small roll speed can cause too much round steel temperature drop during piercing process, affecting the piercing quality.

[0049] Reduce the angle between the piercing roll and the roll center, the angle is adjusted from 12° to 8°, reduce the angle of the roll, reduce the round steel feeding speed during the piercing process, greatly reduce the rolling force, stabilize the ejector rod and improve the centering.

[0050] By taking the above measures, the defects of small piercing ejector rod are solved, and the piercing wall deviation quality problem is solved, and the wall deviation is less than 1.5mm.

[0051] The same specification round steel, the piercing blank specification is not the same, the elongation is not consistent, and the deformation heat generated during the deformation process is not consistent, so the round steel heating temperature is uncertain. Piercing Φ114*22mm small deformation specification, need to redevelop piercing temperature and heating time, solve the piercing roll jam, internal crack and other quality problems.

[0052] Table two piercing deformation comparison

[0053]

[0054] Piercing temperature test:

[0055] The first piercing temperature is 1170±15℃ and the heating time is 5 hours, the piercing process is difficult to bite, the rolling is unstable, causing the core rod bending. The round steel temperature reaches 30° during the piercing process, which is larger than the ordinary specification.

[0056] The second piercing temperature is 1200±10℃ and the heating time is 6 hours, the piercing is normal bite, the rolling is stable, the piercing ejector rod runs smoothly, and the internal and external surface quality is good.

[0057] The third piercing temperature is 1220±10℃ and the heating time is 6 hours, the piercing is normal bite, the rolling is stable, the piercing ejector rod runs smoothly, but the internal surface produces internal crack, the internal crack ratio reaches 12%.

[0058] The HR3C small deformation thick wall pipe piercing temperature is controlled at 1200±10°, the heating time is 6 hours, and the given piercing temperature range is small. The high piercing temperature ensures that the steel pipe temperature is above the solid solution temperature after piercing, and improves the mechanical properties of the blank pipe.

[0059] 2. Cold rolling process

[0060] First pass cold rolling: the Φ114*22mm blank pipe is rolled into a Φ89*18.5mm blank pipe.

[0061] Second pass cold rolling: the Φ89*19mm blank pipe is rolled into a Φ57*18.5mm blank pipe.

[0062] Table three cold rolling inner diameter, mandrel comparison

[0063]

[0064]

[0065] The following measures are taken for the problems of steel pipe and tool mismatch, insufficient wall reduction, and mandrel curve design.

[0066] Measures taken:

[0067] The first cold rolling reports the mandrel specification as Φ114*22—Φ89*18.5, ensuring that the steel pipe inner diameter Φ52mm after cold rolling can meet the minimum 3mm gap requirement of the next rolling mandrel, and the steel pipe can pass through the mandrel for rolling to meet the process design requirements. It also ensures that the semi-finished product wall thickness is greater than the finished product wall thickness, otherwise it cannot be rolled. In the actual production process, the cold rolling outer diameter is adjusted to Φ88.7-88.8mm, and the mandrel position is adjusted backward, which can ensure that the wall thickness meets the requirement of 19mm, and ensures that the finished product wall reduction is normally rolled.

[0068] The second pass cold rolling mandrel design is according to Φ89*19—Φ57*18, which can ensure that the mandrel diameter and the diameter of the sizing section are less than 2.5, and the mandrel curve design is not a problem, and can be normally rolled. In the actual rolling process, the cold rolling outer diameter is adjusted to Φ57.6-57.8mm, and the mandrel position is adjusted backward, which can ensure that the cold rolling wall thickness is greater than or equal to 18.3mm, and ensures that the wall thickness reduction during the finished product drawing process can also meet the tolerance requirements.

[0069] For the HR3C thick seamless pipe cold rolling process, high rolling speed and small feed amount rolling parameters, large rolling speed and small feed parameters are the pipe being rolled more frequently and more times in the unit length of the mandrel, which is easy to cause HR3C cold rolling work hardening, cold rolling plasticity deterioration, and produce surface transverse cracks, surface cracks and other defects.

[0070] Measures taken:

[0071] Low rolling speed and large feed can reduce the rolling times in unit length, reduce work hardening and reduce surface cracking.

[0072] Adjusting the semi-finished product heat treatment process and changing the mechanical properties of HR3C semi-finished product are beneficial to cold deformation.

[0073] Table Four Cold Rolling Parameter Comparison

[0074]

[0075] 3. Drawing Process

[0076] Φ57*18.5mm raw pipe is drawn to Φ51*18mm seamless steel pipe through one pass.

[0077] Wall thickness reduction occurs during the drawing of HR3C extra-thick (tube diameter to wall ratio ≤5) seamless steel pipe. Through the test process, the following wall thickness changes are obtained. Wall thickness increase occurs during the drawing process of ordinary specifications, and the wall thickness of the empty drawing is reduced by 1mm, which does not occur in the actual production process. The wall thickness of this process is reduced by 17.3-17.7mm in one pass, which meets the tolerance requirements of the finished product. If two passes are drawn, the wall thickness of the finished product does not meet the tolerance requirements, and the wall thickness of HR3C extra-thick pipe cannot be controlled during multi-pass drawing, which cannot complete batch production.

[0078] Table Five: Wall Thickness Change

[0079]

[0080] 4. Heat Treatment Process

[0081] The heat treatment process is mainly to ensure the cold working performance of the semi-finished product and the mechanical properties and grain extremum of the finished product meet the requirements. The following is the design of the heat treatment process system for different deformation amounts and heat treatment purposes in each pass.

[0082] Table Three Cold Rolling Inner Diameter and Core Rod Comparison

[0083]

[0084] Measures taken:

[0085] The high temperature and long holding time of the heat treatment after the first pass of cold rolling is to solve the mechanical properties of the next pass of cold rolling, reduce the yield strength and tensile strength of HR3C material, and improve the elongation.

[0086] The total deformation of the second pass of cold rolling is large, but the wall thickness reduction is small, the diameter reduction is large, which leads to inconsistent wall thickness deformation in the radial direction of the steel pipe, and different grain crushing, reducing the heat treatment temperature and shortening the holding time can solve the technical problem of the grain extremum of the final product being greater than 3, and also meet the small deformation of the empty drawing to the mechanical properties of HR3C.

[0087] The third pass empty drawing is due to the small diameter-wall ratio of the pipe material, the drawing deformation is along with the pipe material being drawn out, the steel pipe is contacted with the outer die to generate friction force by the outer metal layer, the resistance is large, the metal flow is slow, the metal flow speed in the radial direction is inconsistent, the wall thickness is reduced. And the grain change of the outer layer of the wall thickness is larger than that of the inner layer of the wall thickness, the heat treatment temperature and the actual situation need to be adjusted to ensure the grain extreme difference of the finished product after heat treatment.

[0088] After the method of the application is implemented, not only the required Φ51*18mm thick wall pipe is obtained, but also the wall thickness is uniform, the inner and outer surfaces are smooth and consistent, the size precision is high, the yield reaches more than 87%, and after heat treatment, the grain size of the inner and outer surfaces is uniform, the extreme difference is small, and the design requirements are met.

[0089] Comparative example 1

[0090] Using multi-pass drawing, the 51*18mm pipe multi-pass process is produced:

[0091] The Φ110mm round steel is perforated;

[0092] Multi-pass drawing operation, each drawing operation forms the following rough pipe in turn: Φ104*20mm rough pipe, Φ94*18 rough pipe, Φ84*18 rough pipe, Φ74*18mm rough pipe, Φ65*17.8mm rough pipe, Φ60*17mm rough pipe, Φ55*(16.5-17)mm rough pipe, Φ51*(16.5-17)mm rough pipe.

[0093] Using multi-pass drawing process, the wall thickness requirement of 18mm cannot be accurately met, only negative difference can be achieved, and the qualified rate is low.

[0094] At the same time, the inner and outer surfaces are rough after cold rolling, the grains always extend in a single direction, and the mechanical properties are unstable. Due to multi-pass cold drawing, multiple heat treatment softening is necessary, so the grain extreme difference is large due to multiple heat treatment. The inner surface is rough, the inner hole is not cleaned after heat treatment, and the surface defects increase after cold drawing, increasing the rework. The comprehensive yield is less than 70%.

[0095] In the description of the present specification, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0096] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for manufacturing a HR3C extra thick seamless pipe for a superheater of a power plant, which is suitable for an extra thick seamless pipe manufactured using HR3C stainless steel, characterized in that, The power station superheater HR3C extra-thick seamless pipe manufacturing method comprises the following steps: Perforating the round steel, heating the round steel to 1200 DEG C, and using a perforator to perform perforation, wherein the angle between the perforation roller and the roller center is 8 DEG, the rolling speed is 260-270 r / min, and a blank pipe is prepared; Surface cleaning, straightening and pickling the blank pipe, and cleaning the surface defects; Cold rolling the blank pipe, wherein the ratio of the diameter of the large head of the mandrel of the cold rolling pipe machine to the diameter of the sizing section is 1-2.5; Degreasing treatment is performed on the cold-rolled blank pipe; Heat treatment is performed on the degreased blank pipe; The method of perforating the round steel further comprises heating the round steel to 1200±10 DEG C and maintaining the heating time for 6 hours; The rolling speed of the cold rolling pipe machine is 30 times / min, and the feed amount is 3-3.5 mm; After the cold rolling of the blank pipe, the power station superheater HR3C extra-thick seamless pipe manufacturing method further comprises once drawing of the cold-rolled blank pipe; The cold rolling of the blank pipe further comprises: After the first pass of cold rolling, the blank pipe is heat treated, and the heat treatment process after the first pass of cold rolling comprises heating the blank pipe to 1220±15 DEG C and maintaining the temperature for 55±2 min; After the second pass of cold rolling, the blank pipe is heat treated, and the heat treatment process after the second pass of cold rolling comprises heating the blank pipe to 1200±15 DEG C and maintaining the temperature for 52±2 min; After the once drawing of the cold-rolled blank pipe, the power station superheater HR3C extra-thick seamless pipe manufacturing method further comprises heat treatment of the once-drawn blank pipe, and the heat treatment process of the once-drawn blank pipe comprises heating the blank pipe to 1200±15 DEG C and maintaining the temperature for 50±2 min.

2. The method of claim 1, wherein the HR3C extra heavy seamless pipe for a superheater of a power plant is manufactured by the steps of: The cold rolling of the blank pipe further comprises: The first pass of cold rolling is performed by using a cold rolling pipe machine, and the ratio of the diameter of the large head of the mandrel of the cold rolling pipe machine to the diameter of the sizing section is 1-2.5 in the first pass of cold rolling; The second pass of cold rolling is performed by using a cold rolling pipe machine, and the ratio of the diameter of the large head of the mandrel of the cold rolling pipe machine to the diameter of the sizing section is 1-2.5 in the second pass of cold rolling.

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