Pipe die submerged arc surfacing remanufacturing method and system for improving thermal fatigue performance

Abstract

The invention discloses a pipe die submerged arc surfacing remanufacturing method and system capable of improving the thermal fatigue performance, and the method comprises the following steps: 1, pretreatment: removing thermal fatigue cracks, cracks and wear scratches on the inner wall of a pipe die by adopting a turning or boring process, the method comprises the following steps of (1) pre-treating a pipe die, (2) pre-heating at low temperature: pre-heating a to-be-welded part of the pre-treated pipe die by adopting a high-frequency induction heating module, (3) carrying out submerged arc surfacing, (4) carrying out subarea induction tempering treatment on the surfaced pipe die, firstly turning or boring all thermal fatigue cracks, cracks, abrasion scratches and high-temperature oxidation fatigue layers on the inner wall of the pipe die, and then carrying out tempering treatment on the pipe die. A low-temperature preheating welding wire formula is adopted, crack resistance is achieved under low heat input, a good structure is formed, curved surface self-adaptive welding is achieved, powder is automatically added in the welding process, welding slag is automatically cleaned, dotting is conducted after welding, stress is released, and longitudinal or transverse cracks are effectively avoided. And tempering the pipe die repaired by surfacing after welding, and carrying out ultrasonic scanning and residual stress testing.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of pipe mold remanufacturing, and particularly relates to a pipe mold submerged arc welding remanufacturing method and system for improving thermal fatigue performance. BACKGROUND

[0002] The centrifugal cast iron pipe mold, referred to as a "pipe mold" for short, is made of 21crmo10 steel, which is a kind of hot work die steel. The pipe mold is a key component for casting cast iron pipes on a centrifugal casting machine and is a consumable mold with a large demand.

[0003] Thermal fatigue is the main failure mode of the pipe mold. Due to the harsh service environment, the molten iron (1300-1450℃) is applied to the inner wall of the pipe mold due to the centrifugal effect, causing the temperature of the inner wall of the pipe mold to rise sharply, while the outer surface is cooled by circulating water to reduce the temperature. The change in temperature causes the alternating change of stress, and after a period of service, thermal fatigue will occur, eventually forming a large area of cracks, especially at the pipe mold spout end, which bears the most molten iron and is the most serious crack area. If the cracks are not treated, not only will cracks occur, but even local fractures may occur, causing the molten iron to leak and splash, which is very dangerous. During service, the pipe mold is repeatedly affected by rapid heating and rapid cooling, and when the limit thermal stress or external force impact is exceeded, irreversible plastic deformation will occur. After the molten iron in the pipe mold cools and solidifies, the centrifugal cast iron pipe (cast pipe) is formed. When the draw tool pulls out the cast pipe from the mold, wear phenomena are prone to occur, and long-term use without maintenance will cause serious scratches and wear. During the production of ductile cast iron pipes, the pipe mold, as a key tooling mold, is subjected to the alternating action of high-temperature molten iron and cooling water for a long time, resulting in thermal fatigue cracks on the inner wall. In the prior art, the pipe mold develops thermal fatigue cracks on the inner wall due to rapid heating and cooling during the centrifugal casting process. After traditional submerged arc welding repair, the pipe mold can only produce 150-200 cast pipes before failing. Currently, pipe mold repair mainly uses the following methods:

[0004] 1. Submerged arc welding technology: the current main technology for repairing pipe molds: that is, using submerged arc welding wire to repair layer by layer. Submerged arc welding has high efficiency and speed, and low cost compared with laser technology, but the welding layer is mostly coarse Widmanstatten structure, which can easily cause thermal fatigue cracks again under high temperature, rapid cooling and rapid heating conditions, reducing the fatigue resistance of the pipe mold and causing premature failure.

[0005] 2. Laser cladding technology: with the gradual maturity of laser technology, laser cladding repair technology has a higher and higher proportion in the repair market. It has good quality, highly dense material organization, almost no defects, and no complicated procedures, and does not require preheating before welding and high-temperature tempering after welding. However, the key to restricting its development is the high cost of equipment and the slow repair speed compared with submerged arc welding, which is relatively low in efficiency.

[0006] 3. A few departments use thermal spraying technology and manual electrode or wire surfacing, which cannot meet the requirements of national standards, industry standards and industrial use, and has been basically abandoned. The tube mold repair needs to meet the following performance. SUMMARY

[0007] The purpose of the present application is to provide a tube mold submerged arc surfacing remanufacturing method and system to improve the thermal fatigue performance, so as to solve the problems in the background art.

[0008] To achieve the above-mentioned purpose, the present application provides the following technical solution: a tube mold submerged arc surfacing remanufacturing method to improve the thermal fatigue performance, comprising the following steps:

[0009] Step one, pretreatment: using turning or boring process to remove the thermal fatigue cracks, cracks, wear scratches and high temperature oxidation fatigue layer on the inner wall of the tube mold, removing the thickness of 5.8-6.2mm, making the surface roughness Ra of the inner wall of the tube mold ≤6.3μm, and using magnetic powder detection, coloring detection or eddy current detection method to detect the cracks on the inner wall of the tube mold after pretreatment, if cracks are detected, continue to locally turn or bore until no cracks are detected, and then clean the inner wall of the tube mold to remove the oxides, oil stains and dust on the inner wall surface, eliminate the surface layer failure organization and potential crack defects of the base material, and ensure the metallurgical bonding reliability of the subsequent surfacing layer and the base material, and provide a clean and smooth substrate for surfacing;

[0010] Step two, low temperature preheating: using high frequency induction heating module to preheat the tube mold to be welded part after pretreatment, the preheating temperature is controlled at 240-270℃, and the preheating holding time is 4.0-5.5 hours, which can reduce the thermal stress of the base material and the surfacing layer, inhibit the generation of cold cracks, provide a stable thermal environment for the subsequent surfacing process, and avoid the sudden change of heat input leading to organizational defects;

[0011] Step three, submerged arc surfacing: using Cr-W-Ni series welding wire, the base component of the welding wire meets: Cr14.2±0.5%, W3.0±0.3%, Ni9.5±0.5%(mass fraction), and nano Al□O3 particles are added to the welding wire to reduce the hot crack sensitivity, and TiC particles are added to improve the wear resistance and corrosion resistance of the surfacing metal, through alloy component regulation and particle addition, the thermal stability, toughness of the surfacing metal is optimized, the hot crack sensitivity is reduced, and the wear resistance and corrosion resistance of the surfacing layer are improved;

[0012] An intelligent power supply and wire feeding system is used, the intelligent power supply is equipped with an expert database, the molten pool image and voltage fluctuation signal obtained by molten pool monitoring are used to adjust the welding current, voltage and wire feeding speed in real time, the heat input is kept stable, the welding parameters are dynamically adapted according to the real-time state of the molten pool, the heat input is kept stable, and the formation defects of the surfacing layer caused by parameter fluctuation are avoided;

[0013] An infrared thermometer and an intelligent power supply form a temperature control closed loop control: the infrared thermometer monitors the molten pool temperature and interlayer temperature in real time, if the temperature is higher than 270℃, the intelligent power supply automatically reduces the welding current or increases the welding speed; if the temperature is lower than 240℃, the intelligent power supply automatically increases the welding current or reduces the welding speed; at the same time, through the additional active cooling device, the total heat input and the repeated heating of the heat affected zone (HAZ) are reduced, the width of the HAZ is reduced, the molten pool and interlayer temperature are stabilized in a reasonable range, the total heat input and the repeated heating of the heat affected zone are reduced, the width of the heat affected zone is reduced, and the toughness is reduced due to the coarsening of the organization.

[0014] Adopting curved surface adaptive welding: integrating a laser scanner to feedback the welding gun posture in real time, keeping the normal angle between the welding wire and the pipe mold surface at 85°±2°; and based on the pipe mold curvature radius R (unit: m), adjusting the welding current I and the welding speed V in real time, the adjustment formula is: I=I0·(1+0.2 / R), V=V0·(1-0.15 / R), where I0 is the reference current and V0 is the reference speed, ensuring the stability of the angle between the welding wire and the pipe mold surface during curved surface welding, adjusting the welding parameters for different curvature pipe molds, and ensuring the uniform thickness and quality consistency of the cladding layer.

[0015] Step four, the cladded pipe mold is subjected to zoned induction tempering treatment, the tempering temperature is 530-580℃, the holding time is 4.0-5.5 hours, after tempering, air cooling to room temperature, and quenching the pipe mold after tempering, so that the hardness of the cladding layer reaches HRC52-55, the pipe mold after welding and treatment is subjected to finishing, so that the pipe mold size and precision meet the specified requirements, ultrasonic scanning (probe frequency 5MHz) and X-ray diffraction method (sin 2 ψ method) are used for nondestructive testing and residual stress testing respectively; and production testing is carried out, after continuous production of 300 cast pipes, the maximum crack length of the cladding layer is ≤0.8mm, the welding residual stress is released, the cladding layer organization stability and hardness (up to HRC52-55) are controlled, the pipe mold size precision is ensured, internal defects are checked, crack resistance potential is evaluated, and the remanufactured pipe mold hot fatigue performance is verified to meet the standards.

[0016] Preferably, in step three, the particle size of the nano Al2O3 particles is 50-100nm, the addition amount is 4-7wt%, and the nano Al2O3 particles are mixed into the welding wire after pre-dispersion by mechanical alloying, realizing uniform dispersion of nano Al2O3 in the welding wire (avoiding agglomeration to cause cladding layer defects), strengthening the interface bonding between the welding wire and the base body, and stably playing the role of reducing the hot crack sensitivity.

[0017] Preferably, in step three, the TiC particles are added in an amount of 2-5wt%, and the TiC particles are pre-dispersed by mechanical alloying and mixed with nano-Al2O3 particles in the welding wire to improve the wear resistance of the surfacing layer while avoiding the increase of brittleness, to realize the synergistic dispersion of TiC and nano-Al2O3, and to simultaneously play the functions of crack resistance, wear resistance, and corrosion resistance, and to optimize the comprehensive service performance of the surfacing layer.

[0018] Preferably, in step three, the flux used is modified SJ101 flux (in accordance with GB / T5293), 10wt% CaF2 and 2wt% TiO2 are added in the modified SJ101 flux, the slag basicity BIIW = 1.8-2.2, and the weight ratio of the welding wire to the flux is 0.85-1.05, to improve the flowability, detachability, and arc stability of the slag, to ensure the protection of the molten pool by the slag (to reduce defects such as pores), to match the surfacing fusion requirements, and to ensure the uniformity of the composition and the forming quality of the surfacing layer.

[0019] Preferably, in step three, the inner wall of the pipe mold is treated by dotting during the surfacing process to release thermal stress, a multi-layer and multi-pass welding process is used to control the thickness of each layer to reduce heat input, and at the same time, an automatic powder feeding device is used to deliver alloy powder to the molten pool, and a slag automatic cleaning device is used to clean the slag in real time, to actively release thermal stress and avoid crack propagation, to reduce single-pass heat input to reduce the risk of cumulative thermal stress and repeated heating of the heat-affected zone, to accurately control the composition of the surfacing layer and avoid the influence of slag inclusions, and to improve the surfacing efficiency and quality consistency.

[0020] A pipe mold submerged arc surfacing remanufacturing system for improving thermal fatigue performance, comprising the following devices: a stepless speed regulation automatic roller frame, a welding gun, the pipe mold is placed on the stepless speed regulation automatic roller frame, a water cooling ring is arranged at the front end of the stepless speed regulation automatic roller frame, and one end of the pipe mold is inserted into the water cooling ring, a high-frequency induction heating module is also arranged at the front end of the stepless speed regulation automatic roller frame, to provide stable support and adjustable speed rotation power for the pipe mold (to adapt to pipe molds of different diameters), to control the temperature of the end of the pipe mold to avoid overheating, to accurately preheat the to-be-welded part of the pipe mold, to constitute an automatic basic system of "support-preheat-surfacing", and to ensure the stability of the remanufacturing process.

[0021] Preferably, the slag automatic cleaning device comprises a slag collecting box connected to the front end of the stepless speed regulation automatic roller frame, a cyclone separator is arranged on the surface of the slag collecting box, one end of the cyclone separator is connected with a high-pressure centrifugal fan through a pipeline, one end of the high-pressure centrifugal fan is connected with a high-temperature wear-resistant hose, and one end of the high-temperature wear-resistant hose extends into the pipe mold, to realize the real-time collection, efficient separation, and centralized storage of the slag in the pipe mold through negative pressure driving, to avoid the pollution of the slag to the surfacing environment, and to ensure the continuous performance of the surfacing process.

[0022] Preferably, the welding gun bottom is connected with a mounting rack, the welding gun is arranged at one end of the high-temperature wear-resistant hose, the infrared temperature measuring instrument is arranged on the mounting rack, and the laser scanner is arranged at the top of the mounting rack, so that the welding gun, the infrared temperature measuring instrument and the laser scanner are integrated and cooperated, the molten pool and the interlayer temperature are accurately monitored at a short distance (signals are provided for the temperature control closed loop), the pipe mold curved surface is comprehensively scanned (welding gun posture data is fed back), and the surfacing precision is improved.

[0023] Preferably, the molten pool monitoring is arranged on the mounting rack, the molten pool image and the voltage fluctuation signal are stably collected at a short distance, reliable basis is provided for real-time fine adjustment of the intelligent power supply welding parameter, and the molten pool stability and the surfacing layer quality are guaranteed.

[0024] Preferably, the welding slag collecting box is connected with an upper powder hopper, one end of the bottom of the upper powder hopper is connected with a powder feeding pipe, and the joint of the powder feeding pipe and the upper powder hopper is provided with a powder adding and conveying module; one end of the powder feeding pipe extends into the pipe mold, the alloy powder can be continuously stored in the surfacing process, the powder conveying amount is accurately controlled through the powder adding and conveying module, the powder is accurately sent to the molten pool, and the accuracy of surfacing layer composition regulation and control is guaranteed.

[0025] Compared with the prior art, the present application has the following beneficial effects: firstly, all thermal fatigue cracks, cracks, wear scratches, high-temperature oxidation fatigue layers on the inner wall of the pipe mold are removed or bored, a low-temperature preheating welding wire formula is used, cracks are resisted under low heat input, and good organization is formed; Al□O□ nanoparticles are added to reduce thermal crack sensitivity; TiC particles are added to further improve the wear resistance and corrosion resistance of the surfacing metal; an intelligent power supply and a wire feeding system are used, the current and voltage are real-time fine adjusted according to the molten pool image and voltage fluctuation, and the heat input is kept stable; infrared temperature measurement and temperature control closed loop control are used to monitor the molten pool temperature and interlayer temperature in real time, the total heat input and the repeated heating of HAZ are greatly reduced through active cooling, the HAZ width is minimized, the HAZ organization is prevented from being coarsened, the base material strength and toughness are maintained, the workpiece deformation is significantly reduced, the curved surface is adaptively welded, the laser scanner is integrated to feed back the welding gun posture in real time, the normal included angle between the welding wire and the pipe mold surface is kept at 85°±2°; the welding process is automatically powered and the welding slag is automatically cleaned, the welding efficiency is improved, and the quality and consistency of the surfacing layer are improved; the workpiece is marked after welding, stress is released, and longitudinal or transverse cracks are effectively avoided; the surfacing repaired pipe mold is tempered after welding, finally machined to the specified size and precision, and ultrasonic scanning and residual stress testing are performed. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a structure schematic view of the stepless speed regulation automatic roller frame of the present application;

[0027] Figure 2 It is a structure schematic view of the welding gun, the laser scanner and the molten pool monitoring of the present application;

[0028] Figure 3 The system control schematic diagram of the present application;

[0029] Figure 4 The pipe mold pattern after dotting of the present application;

[0030] Figure 5 The pipe mold dotting detail drawing of the present application.

[0031] In the figure: 1, stepless speed regulation automatic roller frame; 2, high-frequency induction heating module; 3, infrared temperature measuring instrument; 4, molten pool monitoring; 5, laser scanner; 6, welding gun; 7, pipe mold; 8, water-cooling ring; 9, welding slag collection box; 10, cyclone separator; 11, high-pressure centrifugal fan; 12, high-temperature wear-resistant hose; 13, powder feeding hopper; 14, powder feeding pipe; 15, powder feeding and conveying module. DETAILED DESCRIPTION

[0032] 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 of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0033] In the description of the present application, it should be noted that, unless otherwise explicitly specified and limited, the terms "mounting", "provided with", "sleeved", "sleeved", "connected" and the like should be understood in a broad sense, for example, "connected" can be fixedly connected, or can be detachably connected, or integrally connected, can be mechanically connected, or electrically connected, can be directly connected, or indirectly connected through an intermediate medium, can be the communication between two elements, and those skilled in the art can understand the specific meaning of the above terms in the present application according to the specific circumstances.

[0034] The present application provides a pipe mold submerged arc welding remanufacturing method for improving thermal fatigue performance, as shown in Figures 1-5 The present application provides a pipe mold submerged arc welding remanufacturing method for improving thermal fatigue performance, as shown in

[0035] Step one, pretreatment: remove the thermal fatigue cracks, cracks, wear scratches and high-temperature oxidation fatigue layer (remove thickness 5.8-6.2mm) on the inner wall of the pipe mold 7 through turning or boring process, realize the function of "eliminating the failure of the surface layer of the base material, ensuring the reliability of the metallurgical bonding between the subsequent surfacing layer and the base material"; simultaneously control the surface roughness Ra≤6.3μm of the inner wall of the pipe mold 7 to provide a flat base for surfacing; adopt magnetic powder flaw detection, coloring flaw detection or eddy current detection method to detect the cracks on the inner wall after pretreatment, eliminate the potential cracking hazards through "defect secondary removal" mechanism (if cracks are detected, continue to locally turn / bore until there are no cracks); finally clean the inner wall to remove oxides, oil stains and dust, so as to avoid the influence of impurities on the bonding quality of the surfacing layer.

[0036] Step two, low temperature preheating: use high-frequency induction heating module 2 to preheat the pipe mold 7 to be welded after pretreatment, through the parameter design of "240-270℃ low temperature interval + 4.0-5.5 hours holding", realize the function of "reducing the thermal stress between the base material and the surfacing layer, inhibiting the generation of cold cracks", at the same time, provide a stable thermal environment for the subsequent surfacing process, avoid the sudden change of heat input leading to organizational defects.

[0037] Step three, submerged arc surfacing:

[0038] Welding wire design: adopt Cr-W-Ni series welding wire (Cr14.2±0.5%, W3.0±0.3%, Ni9.5±0.5%, mass fraction), through the alloy composition control to optimize the thermal stability and toughness of the surfacing metal; synchronously add nano Al□O3 particles (reduce thermal crack sensitivity) and TiC particles (improve wear resistance and corrosion resistance), realize the function of "simultaneous improvement of crack resistance and service performance".

[0039] Intelligent control: use intelligent power supply and wire feeding system equipped with expert database, through the molten pool image and voltage fluctuation signal obtained by molten pool monitoring (4), real-time adjust welding current, voltage and wire feeding speed, realize the function of "dynamic adaptation of molten pool state, maintain stable heat input", avoid the forming defects of surfacing layer caused by parameter fluctuation.

[0040] Temperature control closed loop: form a closed loop control with infrared thermometer 3 and intelligent power supply, through "decrease flow / increase speed at high temperature, increase flow / decrease speed at low temperature" dynamic adjustment, ensure that the molten pool temperature and interlayer temperature are stable in the range of 240-270℃; synchronously match additional active cooling device, realize the function of "reducing total heat input and repeated heating of heat affected zone (HAZ)", and then reduce the width of HAZ, avoid the toughness decline caused by HAZ organizational coarsening.

[0041] Surface adaptation: the integrated laser scanner 5 feeds back the posture of the welding torch 6 in real time, keeps the normal angle between the welding wire and the surface of the pipe mold 7 at 85°±2°, and ensures the uniform thickness of the cladding layer during curved surface welding; based on the curvature radius R (unit: m) of the pipe mold 7, the welding parameters are adjusted in real time through the formula I=I0·(1+0.2 / R), V=V0·(1-0.15 / R) (I0 is the reference current, and V0 is the reference speed), to realize the functions of “adapting to the welding requirements of pipe molds with different curvatures, and ensuring the consistency of cladding quality”.

[0042] Step four, post-welding treatment and detection:

[0043] Heat treatment: the cladded pipe mold 7 is subjected to zoned induction tempering (530-580℃, holding for 4.0-5.5 hours) to realize the functions of “releasing welding residual stress and regulating the stability of cladding layer structure”; after tempering, air cooling to room temperature, and then quenching to make the hardness of the cladding layer reach HRC52-55, to ensure the wear resistance;

[0044] Finishing and verification: the post-welding pipe mold 7 is finished to ensure that the size and precision meet the use requirements; ultrasonic scanning (probe frequency 5MHz) is used for non-destructive testing (to check internal defects), X-ray diffraction (sin 2 ψ method) is used to test residual stress (to evaluate the anti-cracking potential); through the service verification of “continuous production of 300 cast pipes”, it is ensured that the maximum crack length of the cladding layer is ≤0.8mm, to realize the function of “verifying that the remanufactured pipe mold meets the standard of hot fatigue performance”.

[0045] In step three, the particle size of the nano Al□O□ particles is 50-100nm (this particle size range can realize uniform dispersion of the particles in the welding wire, avoiding defects in the cladding layer caused by agglomeration), and the addition amount is 4-7wt% (adapted to the composition of Cr-W-Ni welding wire, balanced anti-cracking property and mechanical property); and after pre-dispersion by mechanical alloying, they are mixed into the welding wire, to realize the effect of “strengthening the interface bonding between the particles and the welding wire matrix, and improving the stability of anti-cracking function”.

[0046] In step three, the addition amount of TiC particles is 2-5wt% (this addition amount can improve wear resistance while avoiding excessive increase of cladding layer brittleness); and after pre-dispersion by mechanical alloying, they are mixed into the welding wire together with nano Al□O3 particles, to realize the effect of “two kinds of particles synergistically dispersed, synchronously exerting anti-cracking, wear-resistant and corrosion-resistant functions”, optimizing the comprehensive service performance of the cladding layer.

[0047] In step three, the modified SJ101 flux (in line with GB / T5293) is used by adding 10wt% CaF2 (to reduce the melting point of the slag, improve the fluidity and removability of the slag) and 2wt% TiO2 (to enhance the stability of the electric arc and regulate the metallurgical effect of the slag), so that the slag basicity BIIW = 1.8-2.2 (to ensure the protective effect of the slag on the molten pool and reduce defects such as pores); the weight ratio of the welding wire and the flux is set to 0.85-1.05 to realize the functions of "matching the fusion requirements of the overlaying process, ensuring the uniformity of the composition of the overlaying layer and the forming quality".

[0048] In step three, the overlaying process is optimized by the following auxiliary means: dot processing: the inner wall of the pipe mold 7 is processed by dotting to realize the functions of "actively releasing thermal stress and avoiding crack propagation caused by stress concentration";

[0049] Multi-layer and multi-pass welding: control the thickness of each layer of overlaying to realize the functions of "reducing single-pass heat input, reducing cumulative thermal stress and the risk of repeated heating of HAZ";

[0050] Automatic auxiliary device: the alloy powder is delivered to the molten pool by the automatic powder feeding device (to accurately regulate the composition of the overlaying layer), and the welding slag is cleaned in real time by the automatic slag cleaning device (to avoid the influence of slag inclusions on the subsequent welding pass), which together realizes the functions of "improving the efficiency and quality consistency of the overlaying process".

[0051] A pipe mold submerged arc overlaying remanufacturing system for improving thermal fatigue performance includes the following core devices and functions: stepless speed regulation automatic roller stand 1 provides stable support and adjustable speed rotation power for the pipe mold 7, adapts to the welding requirements of pipe molds of different diameters, realizes the functions of "ensuring the stability of the pipe mold axis and ensuring the uniformity of the overlaying process", and welding gun 6: as the core of the overlaying execution, realizes the functions of "accurately delivering the welding wire and flux to the molten pool and completing the forming of the overlaying layer";

[0052] Water-cooled ring 8: arranged at the front end of the stepless speed regulation automatic roller stand 1, one end of the pipe mold 7 is inserted into it, and the function of "controlling the temperature of the end of the pipe mold and avoiding stress concentration caused by overheating of the end" is realized through circulating cooling, high-frequency induction heating module 2: arranged at the front end of the stepless speed regulation automatic roller stand 1, realizes the function of "accurately preheating the pipe mold to be welded part, and provides a heat environment meeting the temperature requirements for overlaying", and each device cooperates to form an automatic basic system of "pipe mold support-preheating-overlaying", ensuring the stability of the remanufacturing process.

[0053] The slag automatic cleaning device includes: slag collection box 9, which is the core of slag collection and realizes the functions of "collecting slag and avoiding pollution of the overlaying environment";

[0054] Cyclone separator 10: arranged on the surface of the slag collection box 9, realizes the functions of "high-efficiency separation of slag and gas and improves the efficiency of slag collection" through centrifugal force.

[0055] High-pressure centrifugal fan 11: connected with cyclone separator 10 through pipeline, provides negative pressure power, realizes the function of "driving the flow of pipe mold slag to the collection box";

[0056] High-temperature wear-resistant hose 12: one end is connected with high-pressure centrifugal fan 11, the other end extends into pipe mold 7, resists high temperature in surfacing area, realizes the function of "stably conveying slag and avoiding pipeline damage", and cooperates with the above-mentioned devices to realize the function of "real-time and efficient slag cleaning to ensure the continuous surfacing process".

[0057] The welding gun 6 is connected with the mounting bracket at the bottom, and the welding gun 6 is arranged at one end of the high-temperature wear-resistant hose 12; the infrared temperature measuring instrument 3 is installed on the mounting bracket, realizes the function of "close-range and real-time monitoring of molten pool and interlayer temperature to provide accurate signals for temperature control closed loop"; the laser scanner 5 is arranged at the top of the mounting bracket, realizes the function of "comprehensive scanning of pipe mold curved surface and real-time feedback of welding gun posture adjustment data"; the three are integrated in the mounting bracket, forming a "welding execution-temperature monitoring-posture detection" cooperative unit, which improves the surfacing precision.

[0058] The molten pool monitoring 4 is installed on the mounting bracket, realizes the function of "close-range and stable acquisition of molten pool image and voltage fluctuation signal to provide reliable basis for real-time fine adjustment of welding parameters by intelligent power supply", and guarantees the stability of molten pool and the quality of surfacing layer. The upper powder hopper 13 is connected to the slag collection box 9, which is used for storing alloy powder, realizes the function of "providing continuous powder supply for the surfacing process"; one end of the bottom of the upper powder hopper 13 is connected with the powder feeding pipe 14, and a powder feeding module 15 is arranged at the connection position, realizes the function of "precise control of powder feeding amount to ensure stable powder supply according to process requirements"; one end of the powder feeding pipe 14 extends into the pipe mold 7, realizes the function of "precise delivery of alloy powder to the molten pool to avoid loss or pollution in the delivery process", and guarantees the precision of composition control of the surfacing layer.

[0059] The pipe mold submerged arc surfacing remanufacturing method and system for improving thermal fatigue performance, through the travelling crane, the pipe mold 7 to be remanufactured is hoisted to the pair of rollers of the stepless speed regulation automatic roller frame 1, the roller spacing is adjusted according to the diameter (φ500-2000mm) of the pipe mold 7, the axis of the pipe mold 7 is aligned with the center axis of the roller frame, one end of the pipe mold 7 is slowly inserted into the annular hollow structure of the water cooling ring 8 (the insertion depth is 100-150mm), the circulating cooling system of the water cooling ring 8 is started, 30-40℃ industrial cooling water is circulated, and the thermal protection barrier of the end of the pipe mold is pre-established (to avoid overheating of the end during subsequent preheating / surfacing);

[0060] Then start the roller frame motor, at a low speed of 0.5 r / min, to run the test, and detect the tube mold rotation eccentricity (requirements ≤0.1 mm / m) through the laser centering instrument. If the eccentricity is out of tolerance, adjust the roller position until the tube mold rotation linear speed is uniform (error ≤±5%), to provide a "dynamic stability reference" for subsequent operations.

[0061] And move the high-frequency induction heating module 2, so that the induction coil surrounds the outside of the tube mold 7 to be welded area (coil and tube mold outer wall distance 5-8 mm), connect the temperature sensor and calibrate (ensure the temperature measurement error ≤±5℃), and move the installation rack integrated with the welding gun 6, infrared thermometer 3 and laser scanner 5 to one end of the tube mold, adjust the height and angle of the installation rack, so that the welding gun 6 is aligned with the tube mold 7 inner wall to be welded starting position, the laser scanner 5 starts preheating scanning, and the initial curvature radius R of the tube mold 7 inner wall is obtained (as the basis for subsequent parameter adjustment), the molten pool monitoring 4 is started, the focal length of the high-definition camera is calibrated (ensure the molten pool image definition ≥1080P) and the voltage sensor (sampling frequency 1 kHz, error ≤±0.1V), and the standard parameters (such as molten pool length threshold 15 mm, arc voltage range 28-32V) are recorded into the image processing system;

[0062] The preset proportion of alloy powder (such as nano Al□O□5wt%+TiC3wt%) is loaded into the upward powder hopper 13, and the bottom vibration device (50Hz) is started to prevent agglomeration. The screw rod of the powder feeding module 15 (servo motor driven screw rod pump) is run empty to calibrate the conveying amount, and one end of the powder feeding pipe 14 is fixed to the front of the molten pool 30-50 mm (aligned with the center of the molten pool);

[0063] Start the slag automatic cleaning device, check the connection sealing of the high-pressure centrifugal fan 11, high-temperature wear-resistant hose 12 and cyclone separator 10, and run at -50kPa negative pressure to ensure that there is no leakage in the air flow channel;

[0064] The high-frequency induction heating module 2 is connected to a 20kHz high-frequency current, which generates eddy current in the surface layer (2-5mm depth) of the tube mold inner wall by electromagnetic induction principle. The eddy current joule heat makes the temperature of the area to be welded rise rapidly (temperature rise rate 10-15℃ / min), and the temperature sensor feeds back the tube mold temperature in real time. When the temperature rises to 240-270℃, the module automatically switches to the heat preservation mode (reduces the current output to 60% of the rated value), and the roller frame 1 rotates the tube mold at a speed of 1 r / min to ensure that the temperature of the tube mold 7 inner wall is uniform in the circumferential direction (temperature difference ≤±3℃). During the heat preservation process, the water-cooled ring sleeve 8 continues to operate, and the circulating water controls the temperature of the end of the tube mold 7 to be 150-200℃ (to avoid stress concentration caused by too large temperature difference between the end and the area to be welded), and the heat preservation time is set to 4.5 hours (adjust according to the thickness of the tube mold, increase 0.5 hours for every 10mm increase in thickness);

[0065] 10 minutes before the end of the heat preservation, start the infrared thermometer 3 to measure the temperature of multiple points on the inner wall of the pipe mold (1 point per 100 mm), if there is a local area with a temperature lower than 240°C, increase the current of the induction coil in the local area by 10% to compensate for the heat, and ensure that the overall temperature of the area to be welded meets the standard.

[0066] Then start the intelligent welding power supply and output the initial parameters (current I□=400A, voltage V□=30V, wire feeding speed 8m / min), the welding torch 6 starts to feed wire and flux (modified SJ101 flux, weight ratio of wire to flux 1:1), at the same time, the roller frame 1 is accelerated to 2r / min (adjust according to the diameter of the pipe mold to ensure that the weld width is 15-20mm), the mounting frame moves at a constant speed of 8mm / min along the axis of the pipe mold, and the spiral surfacing is started;

[0067] The laser scanner 5 scans the curved surface of the inner wall of the pipe mold in real time (10 times per second), calculates the real-time curvature radius R by the triangulation method, and the system dynamically adjusts the welding current and the moving speed of the welding torch according to the formula I=I0·(1+0.2 / R), V=V0·(1-0.15 / R), and at the same time, the mounting frame's screw slide mechanism fine-tunes the angle of the welding torch to ensure that the normal angle between the wire and the surface of the pipe mold always remains 85°±2° (to avoid a thickness difference of more than 0.3mm in the surfacing layer);

[0068] The infrared thermometer 3 collects 20 pool and interlayer temperature data per second, if the temperature exceeds 270°C, it immediately sends a command to the power supply to "reduce the current by 5-10A" or "increase the roller frame speed by 10%"; if the temperature is lower than 240°C, it sends a command to "increase the current by 5-10A" or "decrease the roller frame speed by 10%", to maintain stable temperature, the pool monitoring device 9 works synchronously: the high-definition camera takes 30 frames of pool images per second, the image processing system identifies the pool size by edge detection algorithm, if the pool length is greater than 15mm (judging that the heat input is too large), the current is reduced by 5A; if the pool brightness is abnormal (too bright / dark, judging that the arc is unstable), the wire feeding speed is fine-tuned by ±0.5m / min; the voltage sensor monitors the arc voltage in real time, if the fluctuation exceeds ±1V (such as insufficient flux supply), the flux delivery compensation is triggered (increased by 5%);

[0069] The alloy powder supply runs synchronously: according to the welding speed (8mm / min) and the wire consumption (about 1.2kg / h), the system calculates the powder demand per unit time (about 60g / h), the screw of the powder delivery module 15 delivers the powder quantitatively at a speed of 100r / min, at the same time, 0.15MPa argon gas is introduced into the powder feeding pipe 14 to push the powder to the pool accurately, mix with the melted Cr-W-Ni series wire, and realize the composition control of the surfacing layer (such as TiC particles uniformly dispersed to improve wear resistance);

[0070] At the same time of the start of the surfacing, the high-pressure centrifugal fan 11 starts to generate -60 kPa negative pressure, forming an airflow channel of "molten pool area -> high-temperature wear-resistant hose 12 -> cyclone separator 10 -> fan" inside the pipe mold;

[0071] The slag (temperature 300-500℃) formed by the cooling of the molten pool is sucked into the high-temperature wear-resistant hose 12 under the action of negative pressure, which can withstand ≤600℃, and the hose moves synchronously with the mounting frame through the support (always located 50-100mm behind the welding torch), ensuring that the slag is captured immediately after its generation;

[0072] The airflow containing the slag enters the cyclone separator 10 in a tangential direction, forming a high-speed rotating airflow of 1500r / min inside, and using "centrifugal force difference" (the density of the slag is 3-5g / cm 3 > the density of the gas) to throw the slag to the inner wall of the separator, and the slag slides down along the inner wall to the slag collection box 9, and the purified gas (containing a small amount of dust) is discharged from the top of the separator, and then discharged to the dust filter outside the workshop after the fan, the observation window on the side wall of the slag collection box 9 monitors the accumulation in real time, and when it reaches 2 / 3 of the volume, the fan is stopped after the current welding pass is completed, and the bottom sealing valve is opened to discharge the slag (to avoid affecting the continuity of surfacing during cleaning);

[0073] When the welding torch 6 moves to the other end of the pipe mold 7 (completes the surfacing of all the areas to be welded), the system automatically reduces the welding current (to 100A) and the wire feeding speed (to 2m / min), and turns off the power after maintaining the arc for 5 seconds, completes the end of the surfacing (to avoid shrinkage holes at the end of the welding pass), the molten pool monitoring device 9 automatically saves the whole process molten pool image and voltage fluctuation data, the laser scanner 5 performs full-size scanning on the inner wall of the pipe mold after surfacing, generates a thickness deviation report (requiring ≤±0.3mm), the alloy powder supply stops powder feeding, the vibration device is closed, and the slag automatic cleaning device 7 continues to operate for 5 minutes to ensure that all the residual slag in the pipe mold is sucked into the collection box 9, then the fan is turned off, the residual slag in the inner wall of the cyclone separator 10 is cleaned, and at this time the stepless speed automatic roller frame 1 is lowered to a low speed of 0.5r / min, and the pipe mold 7 is closed after the temperature drops below 200℃, the water cooling ring 8 continues to operate for 1 hour until the temperature of the end of the pipe mold 7 drops below 100℃, then the cooling water is turned off, the pipe mold 7 is removed from the water cooling ring 8, and the mounting frame and the high-frequency induction heating module 2 are moved to the standby position, the nozzle of the welding torch 6 is cleaned, the remaining powder in the powder feeding pipe 14 is recovered, the pipe mold after surfacing is lifted off the roller frame 1 by the travelling crane, and is transported to the subsequent heat treatment process, and the surface slag of the roller frame is cleaned, completing the reset of the whole system process.

[0074] Example 1

[0075] This example is aimed at DN1200 ductile cast iron pipe mold 7 (original inner diameter 1200 mm, length 6000 mm, wall thickness 80 mm, after use, there are heat fatigue cracks and wear of 3-5 mm in depth on the inner wall), focusing on verifying the heat fatigue performance, hardening of the surfacing layer and crack control effect.

[0076] (I) Pretreatment stage

[0077] Defect removal operation

[0078] CK61200 CNC lathe (spindle speed 50-200 r / min, feed speed 80-150 mm / min) is selected, CBN cubic boron nitride turning tool (tool tip arc radius 0.8 mm) is installed, and the inner wall of pipe mold 7 is turned as a whole. The cutting depth is set to 5.8-6.2 mm (cutting in three times: 3 mm for the first time, 2 mm for the second time, and 1 mm for the third time), and finally the inner wall surface roughness reaches Ra=5.8 μm (≤6.3 μm) detected by TR200 roughness meter, ensuring that the bottom layer of heat fatigue cracks, cracks and high-temperature oxidation layer (original oxidation layer thickness about 2 mm) are completely removed;

[0079] Crack detection and repair

[0080] CDX-III magnetic particle detector (magnetization current 1500 A, wet spray magnetic suspension, concentration 1.2 g / L) is used, every 500 mm along the axial direction of pipe mold 7 is a detection section, and the circumferential direction is divided into 8 detection areas. The inner wall is scanned section by section, and it is found that there are 2 radial cracks with lengths of 8 mm and 10 mm respectively at 1200 mm from one end of pipe mold 7. Local boring is carried out on this area using a boring machine (TX6213 type), and the boring depth is increased by 0.5 mm (total removal depth 6.3 mm), and no cracks are found again after detection.

[0081] Inner wall cleaning

[0082] 5% sodium hydroxide solution (temperature 60°C) is configured, and the inner wall is sprayed for 15 min by high-pressure spraying device (pressure 0.8 MPa, nozzle diameter 1.5 mm) to remove cutting oil stains; then deionized water (temperature 40°C) is sprayed for 20 min to rinse the residual lye; finally, hot air drying machine (wind temperature 80°C, wind speed 5 m / s) is used to dry along the axial direction of pipe mold 7 until the water content of the inner wall is ≤0.1% (detected by moisture meter).

[0083] (II) Low temperature preheating stage

[0084] Pipe mold 7 installation

[0085] The pretreated pipe mold 7 is hoisted to the stepless speed regulation automatic roller stand 1 (ZJ100 type, bearing capacity 100 t, roller diameter 500 mm), the roller spacing is adjusted to make the pipe mold 7 axis horizontal, the coaxiality of the pipe mold 7 is ensured to be ≤0.1 mm / m through the laser centering instrument, the roller stand is started to rotate at a low speed of 5 r / min, and the pipe mold 7 is stopped after the check that there is no shaking;

[0086] Induction heating control

[0087] The GP-300 high-frequency induction heating module 2 (working frequency 30 kHz, output power 300 kW) is selected, the induction coil (inner diameter 1220 mm, width 200 mm, number of turns 15 turns) is sleeved on the outer wall of the pipe mold 7, and the pipe mold 7 is preheated in three sections along the axial direction (each section length 2000 mm). A K-type thermocouple (accuracy ±1℃) is adhered to four point positions (0°, 90°, 180°, 270°) on the inner wall of the pipe mold 7 corresponding to the heating section to monitor the temperature in real time.

[0088] The heating process is divided into three stages: room temperature→150℃ (heating rate 50℃ / h), 150℃→250℃ (heating rate 30℃ / h), and 250℃ for 5h (meeting the requirements of 240-270℃ and 4.0-5.5h). The temperature is recorded every 30 minutes during the holding period to ensure that the temperature difference of the four point positions is ≤5℃;

[0089] (Three) submerged arc welding stage

[0090] Material preparation

[0091] Welding wire: Φ4.0mm Cr-W-Ni system solid core welding wire is selected, the composition is detected by a direct-reading spectrometer: Cr14.3%, W3.1%, Ni9.4%; QM-3SP4 planetary ball mill is used for mechanical alloying and pre-dispersion of nano Al□O3 (particle size 70 nm) and TiC (particle size 1 μm) (ball-to-material ratio 10:1, rotation speed 300 r / min, time 2h), and the welding wire base is mixed with 5wt% Al□O□+3wt% TiC and is formed by a wire drawing machine;

[0092] Flux: modified SJ101 flux (meeting GB / T5293), adding 10wt% CaF2 (fluxing) and 2wt% TiO2 (arc stabilizing), the slag basicity BIIW=2.0 is detected by an X-ray fluorescence spectrometer, and the weight ratio of the welding wire to the flux is set to 1.0;

[0093] Protective gas: 80% Ar+20% CO2 mixed gas (purity 99.99%), accurately proportioned by a gas mixer, the flow rate is set to 15 L / min, and is stably output by a flowmeter;

[0094] Equipment debugging and parameter setting

[0095] Overlaying system: MZ-1250 intelligent submerged arc welding machine was selected, and the welding parameters of DN800-DN2000 pipe mold 7 were pre-stored in the expert database. The reference parameters of DN1200 pipe mold 7 were set as follows: I□=650A, V□=32V, and wire feeding speed 1200mm / min;

[0096] Melt pool monitoring 4: a high-definition industrial camera (Hikvision MV-CA050-10GM, resolution 2448×2048, frame rate 30fps) was installed on the side of the welding torch 6, the lens axis was at an angle of 45° with the center of the molten pool, and a high-temperature resistant protective cover (temperature resistance 800℃) was provided. The infrared thermometer 3 (FLIRA655sc, temperature measurement range -40-1500℃, accuracy ±2%) was aligned 5mm behind the molten pool, and the interlayer temperature was collected in real time;

[0097] Curved surface self-adaptation: the laser scanner 5 (Keyence LK-G80, scanning accuracy 0.05mm, sampling frequency 100Hz) was fixed on the welding torch 6 support, the scanning range covered the area of 100mm×100mm on the inner wall of the pipe mold 7, and the curvature radius R=0.6m (DN1200 pipe mold 7 inner wall radius) was fed back in real time. The welding parameters were automatically adjusted according to the formula I=650×(1+0.2 / 0.6)=867A, V=1200×(1-0.15 / 0.6)=850mm / min;

[0098] Overlaying operation process

[0099] Start the roller stand (rotation speed 8r / min) to make the pipe mold 7 rotate at a constant speed. Turn on the shielding gas, start the intelligent power supply after 3min, and start the overlaying after the arc is successfully ignited.

[0100] Temperature control closed loop: if the molten pool temperature detected by the infrared thermometer 3 exceeds 270℃ (such as 275℃), the intelligent power supply automatically reduces the current to 850A and increases the speed to 870mm / min. If it is lower than 240℃ (such as 235℃), the current is increased to 880A and the speed is decreased to 830mm / min. At the same time, the air cooling device (SF-50 industrial air cooler, air volume 500m3 / h) is started, the air outlet is 100mm behind the welding torch 6, the air speed is 3m / s, and the temperature of the heat affected zone is reduced.

[0101] Stress release and slag treatment: a pneumatic dotting gun (ST-30, needle diameter 3 mm) was used to dot along the 7-axis of the pipe mold at a depth of 3.5 mm every 100 mm; multi-layer and multi-pass welding was used (each pass width 15 mm, each layer of overlay thickness 3.0 mm), a total of 8 layers of overlay, the total overlay thickness 24 mm; an automatic powder feeding device delivered Ni-Cr alloy powder to the molten pool (delivery amount 2 g / min), and a slag automatic cleaning device (negative pressure slag suction port is a flat square, size 50 mm x 20 mm; high pressure centrifugal fan 11 wind pressure 13 kPa, air volume 1200 m3 / h; cyclone separator 10 separation efficiency 96%) real-time suction of slag, the un-melted flux recovery rate was 75%.

[0102] (Four) Post-weld treatment stage

[0103] Zoned induction tempering

[0104] The GH-500 zoned induction tempering device (output power 500 kW, induction coil segmented design, each segment length 1000 mm) was selected to divide the pipe mold 7 into 6 tempering zones, heat each zone, set the tempering temperature to 550℃, the heating rate to 40℃ / h, and the holding time to 5h. During the holding period, the temperature of each zone was monitored by a thermocouple, and the temperature difference was ≤8℃. After the holding period ended, the heating was turned off, and the natural air cooling was performed to room temperature (cooling rate ≤20℃ / h to avoid excessive temperature difference and stress).

[0105] Quenching treatment

[0106] The medium-frequency quenching machine tool (GP-600, frequency 2.5 kHz, power 600 kW) was used for surface quenching of the overlay layer: heating temperature 880℃, holding time 15 min, followed by high-pressure water mist cooling (water pressure 1.2 MPa, water temperature 25℃), cooling time 3 min, so that the hardness of the overlay layer reaches HRC53-54 detected by a Rockwell hardness tester (HR-150A).

[0107] (Five) Finishing and detection stage

[0108] Finishing

[0109] The TK6920 numerical control floor boring and milling machine (spindle speed 100-500 r / min, feed speed 50-200 mm / min) was used to control the final inner diameter size of the pipe mold 7 to be 1200 mm±0.05 mm, the cylindricality to be ≤0.03 mm, and the surface roughness Ra to be 1.6 μm, which meets the precision requirements of the pipe mold 7.

[0110] Performance detection

[0111] Non-destructive testing: 100% scanning of the inner wall by ultrasonic scanner (CTS-9006 type, equipped with 5 MHz straight probe), no internal defects were found; X-ray diffractometer (D8 ADVANCE type, sin 2 Ψ method) to detect residual stress, the result is -80 MPa (compressive stress, which is beneficial to crack propagation).

[0112] Production test: remanufactured pipe mold 7 was installed on the cast pipe production line, and 300 DN1200 ductile iron pipes (each weighing about 2.5 tons, pouring temperature 1380℃) were continuously produced. After the production was completed, it was disassembled and tested, the maximum crack length of the surfacing layer was 0.6mm, and the wear amount was 0.3mm, which was much better than the traditional remanufactured pipe mold 7 (usually crack length ≥1.5mm, wear amount ≥0.8mm).

[0113] III. System implementation details

[0114] (I) Selection and connection of system units and equipment

[0115] Preprocessing unit

[0116] The numerical control lathe (CK61200) and the boring machine (TX6213) are connected through the guide rail type conveying table, and the pipe mold 7 can be transferred between the equipment by the electric hoist; the spray pipeline of the cleaning device is arranged along the direction of the main shaft of the lathe, and is connected in series with the hot air pipeline of the drying machine, realizing continuous operation of "cutting-cleaning-drying".

[0117] Support and drive unit

[0118] The stepless speed regulation automatic roller stand 1 (ZJ100) is equipped with a variable frequency motor (YVP225M-4 type, power 45kW), which is linked through PLC (Siemens S7-1200) with the control system of the surfacing execution unit, to ensure that the roller speed matches the welding speed (speed = welding speed / (π×pipe mold 7 inner diameter)).

[0119] Surfacing execution unit

[0120] The welding gun 6 unit (MZ-1250 matched with welding gun 6) is installed on the numerical control sliding table (stroke 6000mm, positioning accuracy ±0.02mm), which can move axially along the pipe mold 7; the laser scanner 5 (LK-G80) is fixed on the welding gun 6 100mm above through the support, and the scanning data is transmitted to the intelligent power supply through the RS485 interface.

[0121] The intelligent power supply (MZ-1250) is connected with the molten pool monitoring 4 camera (MV-CA050-10GM) and the infrared temperature instrument 3 (A655sc) through Ethernet, which can receive image and temperature signals in real time, and the response delay is ≤100ms.

[0122] Finally, it should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art will appreciate that the technical solutions described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalent features, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for remanufacturing pipe molds using submerged arc welding to improve thermal fatigue performance, characterized in that, Includes the following steps: Step 1, Pretreatment: The thermal fatigue cracks, crazing, wear scratches and high temperature oxidation fatigue layer of the inner wall of the tube mold (7) are removed by turning or boring process, with a thickness of 5.8 to 6.2 mm, so that the surface roughness Ra of the inner wall of the tube mold (7) is Ra≤6.3μm. Magnetic particle testing, dye penetrant testing or eddy current testing are used to detect cracks in the inner wall of the pretreated tube mold (7). Step 2, Low-temperature preheating: The pretreated pipe mold (7) is preheated by the high-frequency induction heating module (2) to the welding part of the pipe mold (7). The preheating temperature is controlled at 240-270℃ and the preheating holding time is 4.0-5.5 hours. Step 3, Submerged Arc Welding: Cr-W-Ni series welding wire is used. The base composition of the welding wire meets the following requirements: Cr 14.2±0.5%, W 3.0±0.3%, Ni 9.5±0.5%. Nano Al2O3 particles are added to the welding wire to reduce the sensitivity to hot cracking, and TiC particles are added to improve the wear resistance and corrosion resistance of the weld metal. The system employs an intelligent power supply and wire feeding system. The intelligent power supply is equipped with an expert database. It uses the molten pool image and voltage fluctuation signal obtained by the molten pool monitoring (4) to finely adjust the welding current, voltage and wire feeding speed in real time to maintain stable heat input. An infrared thermometer (3) and an intelligent power supply are used to form a closed-loop temperature control system; Adaptive surface welding is adopted: the integrated laser scanner (5) provides real-time feedback on the posture of the welding torch (6), and adjusts the welding current I and welding speed V in real time based on the curvature radius R of the tube mold (7). The adjustment formula is: I = I0·(1+0.2 / R), V = V0·(1-0.15 / R), where I0 is the reference current and V0 is the reference speed. Step 4: Perform zoned induction tempering on the weld overlay mold (7). The tempering temperature is 530-580℃ and the holding time is 4.0-5.5 hours. After tempering, air cool to room temperature and then quench the tempered mold (7) to make the hardness of the weld overlay reach HRC52-55. Perform precision machining on the weld overlay mold (7) to make the dimensions and accuracy of the mold (7) meet the specified requirements. Perform non-destructive testing and residual stress testing by ultrasonic scanning and X-ray diffraction respectively.

2. The method for remanufacturing pipe molds by submerged arc welding to improve thermal fatigue performance according to claim 1, characterized in that: In step three, the nano-Al2O3 particles have a particle size of 50-100nm and an addition amount of 4-7wt%, and the nano-Al2O3 particles are mixed into the welding wire after being pre-dispersed by mechanical alloying.

3. The method for remanufacturing pipe molds by submerged arc welding to improve thermal fatigue performance according to claim 1, characterized in that: In step three, the amount of TiC particles added is 2-5 wt%, and the TiC particles are pre-dispersed by mechanical alloying and then mixed with nano-Al2O3 particles into the welding wire.

4. The method for remanufacturing pipe molds by submerged arc welding to improve thermal fatigue performance according to claim 1, characterized in that: In step three, the flux used is modified SJ101 flux, which contains 10wt% CaF2 and 2wt% TiO2, has a slag basicity BIIW of 1.8-2.2, and has a weight ratio of welding wire to flux of 0.85-1.

05.

5. The method for remanufacturing pipe molds by submerged arc welding to improve thermal fatigue performance according to claim 1, characterized in that: In step three, the inner wall of the tube mold (7) is marked with dots during the welding process to release thermal stress; a multi-layer, multi-pass welding process is adopted to control the thickness of each layer of welding to reduce heat input; at the same time, alloy powder is delivered to the molten pool through an automatic powder feeding device, and welding slag is cleaned in real time through an automatic slag cleaning device.

6. A pipe mold submerged arc welding remanufacturing system for improving thermal fatigue performance, which can be used to implement the pipe mold submerged arc welding remanufacturing method for improving thermal fatigue performance as described in any one of claims 1-5, characterized in that, The device includes the following: a continuously variable speed automatic roller frame (1) and a welding torch (6). The tube mold (7) is placed on the continuously variable speed automatic roller frame (1). The front end of the continuously variable speed automatic roller frame (1) is provided with a water-cooling ring (8) and one end of the tube mold (7) is inserted into the water-cooling ring (8). The high-frequency induction heating module (2) is also located at the front end of the continuously variable speed automatic roller frame (1).

7. A pipe mold submerged arc welding remanufacturing system for improving thermal fatigue performance according to claim 6, characterized in that: The automatic slag cleaning device includes a slag collection box (9), which is connected to the front end of the stepless speed-regulating automatic roller frame (1). The surface of the slag collection box (9) is provided with a cyclone separator (10), and one end of the cyclone separator (10) is connected to a high-pressure centrifugal fan (11) through a pipe. One end of the high-pressure centrifugal fan (11) is connected to a high-temperature wear-resistant hose (12), and one end of the high-temperature wear-resistant hose (12) extends into the pipe mold (7).

8. A pipe mold submerged arc welding remanufacturing system for improving thermal fatigue performance according to claim 7, characterized in that: The welding torch (6) is connected to a mounting bracket at its bottom and is located at one end of a high-temperature wear-resistant hose (12). The infrared thermometer (3) is mounted on the mounting bracket, and the laser scanner (5) is located on the top of the mounting bracket.

9. A pipe mold submerged arc welding remanufacturing system for improving thermal fatigue performance according to claim 8, characterized in that: The molten pool monitor (4) is installed on the mounting bracket.

10. A pipe mold submerged arc welding remanufacturing system for improving thermal fatigue performance according to claim 7, characterized in that: The welding slag collection box (9) is connected to a powder hopper (13). One end of the bottom of the powder hopper (13) is connected to a powder feeding pipe (14), and a powder feeding and conveying module (15) is provided at the connection between the powder feeding pipe (14) and the powder hopper (13). One end of the powder feeding pipe (14) extends into the tube mold (7).

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