CN113579417A - Defect welding and heat treatment method for heat-resistant steel casting - Google Patents

Defect welding and heat treatment method for heat-resistant steel casting Download PDF

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Publication number
CN113579417A
CN113579417A CN202110834802.2A CN202110834802A CN113579417A CN 113579417 A CN113579417 A CN 113579417A CN 202110834802 A CN202110834802 A CN 202110834802A CN 113579417 A CN113579417 A CN 113579417A
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welding
casting
defect
heat
less
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冯周荣
陈得润
马文治
田定琪
郭宁
王龙虎
李成志
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Kocel Steel Foundry Co Ltd
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Kocel Steel Foundry Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K9/00—Arc welding or cutting
    • B23K9/04—Welding for other purposes than joining, e.g. built-up welding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24—Selection of soldering or welding materials proper
    • B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550 degrees C
    • B23K35/3053—Fe as the principal constituent
    • B23K35/308—Fe as the principal constituent with Cr as next major constituent
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K9/00—Arc welding or cutting
    • B23K9/013—Arc cutting, gouging, scarfing or desurfacing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K9/00—Arc welding or cutting
    • B23K9/235—Preliminary treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D11/00—Process control or regulation for heat treatments
    • C21D11/005—Process control or regulation for heat treatments for cooling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
    • C21D3/02—Extraction of non-metals
    • C21D3/06—Extraction of hydrogen
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
    • C21D9/505—Cooling thereof
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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  • Arc Welding In General (AREA)

Abstract

The invention belongs to the technical field of casting welding, and mainly relates to a defect welding and heat treatment method for a 9Cr-3W-3Co steel casting material resistant to high temperature of 630-650 ℃, wherein a preheating step is added before the defects are excavated, so that carbon migration caused by carbon deposition on a carbide layer on the surface of a gouging plane in a welding line can be reduced; the method selects proper welding materials and proper process parameters, reduces the generation of a weakening zone caused by coarse grain structure of a near seam zone to the maximum extent, and is matched with a heat treatment process, so that the good comprehensive mechanical property of a 9Cr-3W-3Co steel casting welding repair area is effectively ensured, the quality of a welding joint is ensured, the cracking risk of a casting is effectively reduced, the welding repair quality of the casting is improved, and the period is shortened. The welding and heat treatment method provided by the invention can solve the problems of cracking of a welding seam fusion area, local softening of base metal of a heat affected zone, poor impact toughness and the like caused by the welding method and the heat treatment method in the prior art.

Description

Defect welding and heat treatment method for heat-resistant steel casting
Technical Field
The invention belongs to the technical field of casting welding, and relates to a welding and heat treatment method for a novel heat-resistant steel casting.
Background
The upper limit of the use temperature of the martensite heat-resistant steel material widely used in the thermal power plant is 600-620 ℃, 650 ℃ is the limit use temperature of the martensite heat-resistant steel, and expensive alloy material or austenite steel can only be adopted at higher temperature. Therefore, the development of the martensite heat-resistant steel at 650 ℃ is not only the key point for improving the operating parameters of the thermal power station, but also the difficulty in the development process. In order to develop 650 ℃ martensitic heat-resistant steel better and faster, international research on the aspect must be known, and existing research experience and results are referred to. With the progress of science and technology, a G115 martensite heat-resistant steel material suitable for 630-650 ℃ is trial-produced and developed in a reheating inlet forged pipe of a steam turbine, and the like, the commercial brand has G115 steel developed in China, and the same grade of material for cylinder bodies and valve body castings of core parts of thermal power generation equipment which are matched with the G115 steel and have more difficult structure is still in the research and development stage in various countries at present.
The invention relates to 630-650 ℃ heat-resistant steel material 9Cr-3W-3Co steel, which is different from G115 steel in grade, and aiming at the comparison of the two materials, the 9Cr-3W-3Co steel is suitable for casting steel, and G115 is mainly used for pipeline steel. At present, related data mainly comprise G115 for a martensite material suitable for a high temperature of 630-650 ℃, groove welding is carried out in a structural butt joint mode, a welding method is limited to argon arc welding backing welding and other welding methods, and the combined process scheme is matched with a high post-welding stress relief force, but almost does not exist for 9Cr-3W-3Co steel. Referring to the welding repair process of the same heat-resistant steel martensite material, the common treatment scheme in the industry is to weld the casting defect and then perform stress relief on a welding repair area through postweld heat treatment, but the following problems still exist in the welding joint part after the execution of the scheme: cracking of a welding seam fusion area, local softening of parent metal of a heat affected zone, poor impact toughness and the like.
Disclosure of Invention
The invention aims to provide a defect welding and heat treatment method for a heat-resistant steel casting, which mainly relates to a casting made of a 630-650 ℃ high-temperature-resistant 9Cr-3W-3Co steel casting material, and solves the problems of cracking of a welding seam fusion area, local softening of a heat-affected zone base metal, poor impact toughness and the like caused by the welding method and the heat treatment method in the prior art.
A defect welding and heat treatment method for a heat-resistant steel casting comprises the following steps:
and (3) defect detection: and detecting the surface defects of the casting by adopting a magnetic powder flaw detection and ultrasonic flaw detection mode, and marking the overproof defects by using a proper method.
Heating the defect part: heating the defect part of the casting and the part around the defect to 150-200 ℃ by adopting a heating device. As the 9Cr-3W-3Co material contains more alloy elements and high content of metal elements, preheating is needed before the defects are excavated.
Digging out defects: and excavating the defects of the casting by adopting a carbon arc gouging mode, and polishing the surface of the excavated part of the defects of the casting under the condition that the peripheral temperature of the excavated part of the defects of the casting is more than 150 ℃.
Heating the defect excavated part of the casting: heating the defect excavated part of the casting to 300-400 ℃, preserving heat for 2-3h, and slowly cooling to room temperature.
Welding: because the difference of chemical components and welding process can directly cause the welded joint structure to present obvious nonuniformity, in order to reduce the welded joint structure difference and reduce the plasticity of a weakened area and the joint strength reduction caused by the growth of the grain structure of a heat affected zone, welding is carried out by adopting small-specification welding materials and a multilayer multi-pass filling mode; meanwhile, due to the existence of Cr and B elements in the materials, an oxide film is formed on the surface of the welding line at a high preheating temperature, and then inclusions with higher melting points are generated, so that the welding quality is influenced.
Carrying out dehydrogenation treatment;
and (3) heat treatment: heating the casting to 740-760 ℃ at a heating rate of less than 50 ℃/h, keeping the temperature for 6-10 h, then cooling the casting to less than 200 ℃ at a cooling rate of less than 40 ℃/h, discharging and air cooling, wherein the cooling rate needs to be slow enough to avoid the generation of stress cracks.
Further, before the welding step, heating the defect excavated part of the casting to 180-220 ℃, and keeping the temperature for more than 30 min. As the 9Cr-3W-3Co material contains more alloy elements and extremely high contents of W elements and Co elements, the welding crack tendency is very serious, and a higher preheating temperature is needed before welding in order to reduce the generation of cracks.
Further, in the welding step, the welding material is an E9015-G material which comprises the following components in percentage by mass: c: 0.09% or less, Si: less than or equal to 0.6 percent, Mn: less than or equal to 0.6 percent, P: less than or equal to 0.01 percent, S: < 0.01%, Cr: 8.5-9.5%, W: 2.5-3.2%, Co: 2.5-3.2%, V: < 0.18%, Cu: < 0.01%, N: less than or equal to 0.06%, Nb: less than or equal to 0.03%, B: less than or equal to 0.08 percent, Ni: less than or equal to 0.8 percent, and the balance of Fe and inevitable impurities. Because the welding of 9Cr-3W-3Co material in the prior art is still in the scientific research stage, and the G115 material for high-temperature pipeline contains Cu element which is close to 1%, the element is easy to generate hot brittleness phenomenon in the welding process, especially, the plasticity is obviously reduced after the percentage content of the Cu element exceeds 0.5%, the melting point of the Cu element is low, the thermal expansion coefficient is large, and the melting point of the Co element and the W element is high, and the expansion coefficient is small, therefore, in order to facilitate repair welding and repair in the production process, the casting industry is more inclined to replace the Cu element into Nb element which has higher temperature resistance for the material of a casting, the Nb element has the advantages of grain refining, reducing the overheating sensitivity and tempering brittleness of steel, improving the strength, improving the welding performance, and simultaneously increasing the content of Ni element to improve the plastic toughness of the material and achieve the purpose of improving the strength. In view of the above reasons, the welding material for repair welding and repair of the casting material 9Cr-3W-3Co is improved by tissue-related welding material suppliers, and finally an E9015-G (9Cr-3W-3Co) welding material is selected for process experimental verification, wherein the actual measured values of the components of the E9015-G (9Cr-3W-3Co) welding material in percentage by mass are as follows: the actual measured values of the specific chemical components are as follows: c: 0.09% or less, Si: less than or equal to 0.6 percent, Mn: less than or equal to 0.6 percent, P: less than or equal to 0.01 percent, S: < 0.01%, Cr: 8.5-9.5%, W: 2.5-3.2%, Co: 2.5-3.2%, V: < 0.18%, Cu: < 0.01%, N: less than or equal to 0.06%, Nb: less than or equal to 0.03%, B: less than or equal to 0.08 percent, Ni: less than or equal to 0.8 percent, and the balance of Fe and inevitable impurities. The performance of the welding material after the corresponding welding and heat treatment combined process test meets the standard requirement.
Further, in the step of dehydrogenation treatment, the range of 500mm around the welding line is covered by heat-insulating cotton, the temperature around the welding line is heated to 350-400 ℃, and the heat is preserved for 2-3h, so that hydrogen can be fully released.
Further, after the dehydrogenation treatment step, slowly cooling the casting to 80-120 ℃, and preserving heat for 2-3 h. Thus, the martensite structure can be completely transformed, and then the stress relief heat treatment after high-temperature welding is carried out, so as to achieve the purpose of obtaining the tempered martensite.
Further, in the welding step, after filling welding is finished, two layers of cover surfaces are welded, the welding range of the cover surface of the second layer is smaller than that of the cover surface of the first layer and is controlled within a range which is 3mm away from the boundary of the cover surface of the first layer, and meanwhile, the welding heat input is 8% -20% larger than that of the first layer until welding is finished. After filling welding is finished, in order to reduce the probability of producing hardened structures on the surface of a welding seam cover surface layer, two layers of cover surfaces are welded, and the rear layer is tempered to be the front layer by utilizing high temperature produced by welding, so that the structure transformation is ensured, and the stress is reduced.
Further, after the step of heating the excavated part of the defect, an alloy rotary file is adopted to polish the surface of the excavated part of the defect of the casting to remove an oxide layer. Therefore, in order to reduce the surface oxide layer of the welding metal and prevent the phenomenon that the hardening tendency is sharply increased due to the carburization of an improper tool at high temperature in the grinding process.
Furthermore, in the welding process, welding rods with the diameter phi of 3.2 are adopted for backing welding, and welding rods with the diameter phi of 4.0 are adopted for filling and covering welding; the control parameters of the welding process are as follows: welding by adopting a welding rod with the diameter phi of 3.2, controlling the current to be 80-120A, controlling the arc voltage to be 15-20V, and controlling the welding heat input to be 5 KJ/cm; welding by adopting a welding rod with the diameter phi of 4.0, controlling the current to be 130A to 160A, controlling the arc voltage to be 18V to 22V, and controlling the welding heat input to be not more than 12 KJ/cm; meanwhile, the thickness of the welding bead is less than or equal to 3mm, and the interlayer temperature is less than or equal to 260 ℃. Therefore, the welding quality can be met, the requirements of reducing heat input and welding cooling speed and reducing the generation of hardened tissues are met, and the cracking risk is prevented.
The invention mainly relates to a defect welding and heat treatment method of a 630-temperature and 650-temperature resistant 9Cr-3W-3Co steel casting material, which is characterized in that the Cu element content is lower than 0.02 percent in mass percentage compared with the chemical components of a G115 martensite heat-resistant steel material; and 0.045-0.055% of Nb element, and the G115 martensite heat-resistant steel material contains almost no Nb element. And (3) selecting and improving a welding material raw material with chemical components similar to those of the base material to carry out welding repair, and carrying out long-time stress relief heat treatment after welding to ensure that the comprehensive mechanical property of a welding repair area reaches the same requirement as that of the base material.
According to the defect welding and heat treatment method for the heat-resistant steel casting, provided by the invention, the preheating step is added before the defects are excavated, so that carbon migration caused by carbon deposition on a carbide layer on the surface of the gouging plane in a welding seam can be reduced; the method selects proper welding materials and proper process parameters, reduces the generation of a weakening zone caused by coarse grain structure of a near seam zone to the maximum extent, and is matched with a heat treatment process, so that the good comprehensive mechanical property of a 9Cr-3W-3Co steel casting welding repair area is effectively ensured, the quality of a welding joint is ensured, the cracking risk of a casting is effectively reduced, the welding repair quality of the casting is improved, and the period is shortened.
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Detailed Description
In order that the invention may be more fully understood, reference will now be made to the following description. Preferred embodiments of the present invention are given. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
The embodiment provides a defect welding and heat treatment method for a casting of a 630-650 ℃ high-temperature-resistant 9Cr-3W-3Co steel casting material, which comprises the following steps:
s01, defect detection: and detecting the surface defects of the casting by adopting a magnetic powder flaw detection and ultrasonic flaw detection mode, and marking the overproof defects by using a proper method.
S02, heating the defect part: heating the defect part of the casting and the part around the defect to 150-200 ℃ by adopting a heating device. As the 9Cr-3W-3Co material contains more alloy elements and high content of metal elements, preheating is needed before the defects are excavated.
Specifically, after the step of heating the excavated part of the defect, an alloy rotary file is adopted to polish the surface of the excavated part of the defect of the casting to remove an oxide layer. Therefore, in order to reduce the surface oxide layer of the welding metal and prevent the phenomenon that the hardening tendency is sharply increased due to the carburization of an improper tool at high temperature in the grinding process.
S03, digging out defects: and excavating the defects of the casting by adopting a carbon arc gouging mode, and polishing the surface of the excavated part of the defects of the casting under the condition that the peripheral temperature of the excavated part of the defects of the casting is more than 150 ℃.
S04, heating the defect digging part: heating the defect excavated part of the casting to 300-400 ℃, preserving heat for 2-3h, and slowly cooling to room temperature.
S05, welding: in the welding step, the welding material is E9015-G material, and comprises the following components in percentage by mass: c: 0.09% or less, Si: less than or equal to 0.6 percent, Mn: less than or equal to 0.6 percent, P: less than or equal to 0.01 percent, S: < 0.01%, Cr: 8.5-9.5%, W: 2.5-3.2%, Co: 2.5-3.2%, V: < 0.18%, Cu: < 0.01%, N: less than or equal to 0.06%, Nb: less than or equal to 0.03%, B: less than or equal to 0.08 percent, Ni: less than or equal to 0.8 percent, and the balance of Fe and inevitable impurities. During welding, welding is carried out by adopting a small-specification welding material and a multi-layer and multi-channel filling mode; and before welding the next welding seam in the welding process, polishing the surface of the welding seam by adopting a non-carbon-based material.
Specifically, before the welding step, the defect excavated part of the casting is heated to 180-220 ℃, and the heat preservation time is more than 30 min. As the 9Cr-3W-3Co material contains more alloy elements and extremely high contents of W elements and Co elements, the welding crack tendency is very serious, and a higher preheating temperature is needed before welding in order to reduce the generation of cracks.
Specifically, in the welding step, welding rods with the diameter phi of 3.2 are adopted for backing welding, and welding rods with the diameter phi of 4.0 are adopted for filling and cover surface welding; the control parameters of the welding process are as follows: welding by adopting a welding rod with the diameter phi of 3.2, controlling the current to be 80-120A, controlling the arc voltage to be 15-20V, and controlling the welding heat input to be 5 KJ/cm; welding by adopting a welding rod with the diameter phi of 4.0, controlling the current to be 130A to 160A, controlling the arc voltage to be 18V to 22V, and controlling the welding heat input to be not more than 12 KJ/cm; meanwhile, the thickness of the welding bead is less than or equal to 3mm, and the interlayer temperature is less than or equal to 260 ℃. Therefore, the welding quality can be met, the requirements of reducing heat input and welding cooling speed and reducing the generation of hardened tissues are met, and the cracking risk is prevented. And after the filling welding is finished, welding the two layers of cover surfaces, wherein the welding range of the cover surface of the second layer is smaller than that of the cover surface of the first layer, the welding range of the cover surface of the second layer is controlled within 3mm from the boundary of the cover surface of the first layer, and meanwhile, the welding heat input is 8% -20% larger than that of the first layer until the welding is finished. After filling welding is finished, in order to reduce the probability of producing hardened structures on the surface of a welding seam cover surface layer, two layers of cover surfaces are welded, and the rear layer is tempered to be the front layer by utilizing high temperature produced by welding, so that the structure transformation is ensured, and the stress is reduced.
It should be noted that, in the prior art, the welding of 9Cr-3W-3Co material is still in the scientific research stage, and the G115 material for high-temperature pipeline contains Cu element close to 1%, which is easy to generate hot brittleness during welding, especially when the percentage content of Cu element exceeds 0.5%, the plasticity is obviously reduced, and the melting point of Cu element is low, the thermal expansion coefficient is large, and on the contrary, the melting point of Co element and W element is high, and the expansion coefficient is small, so that in order to facilitate repair welding and repair in the production process, the casting industry tends to replace Cu element with Nb element which is more resistant to high temperature for the material of casting, which has the functions of grain refinement, reduction of steel overheating sensitivity and tempering brittleness, improvement of strength, improvement of welding performance, and increase of Ni element content, so as to improve the plastic toughness of material, and achieve the purpose of strength improvement. In view of the above reasons, the welding material for repair welding and repair of the casting material 9Cr-3W-3Co is improved by tissue-related welding material suppliers, and finally an E9015-G (9Cr-3W-3Co) welding material is selected for process experimental verification, wherein the actual measured values of the components of the E9015-G (9Cr-3W-3Co) welding material in percentage by mass are as follows: the actual measured values of the specific chemical components are as follows: c: 0.09% or less, Si: less than or equal to 0.6 percent, Mn: less than or equal to 0.6 percent, P: less than or equal to 0.01 percent, S: < 0.01%, Cr: 8.5-9.5%, W: 2.5-3.2%, Co: 2.5-3.2%, V: < 0.18%, Cu: < 0.01%, N: less than or equal to 0.06%, Nb: less than or equal to 0.03%, B: less than or equal to 0.08 percent, Ni: less than or equal to 0.8 percent, and the balance of Fe and inevitable impurities. The performance of the welding material after the corresponding welding and heat treatment combined process test meets the standard requirement. Moreover, the welding joint structure presents obvious nonuniformity directly due to different chemical components and welding processes, and small-specification welding materials and a multilayer and multi-pass filling mode are adopted for welding in order to reduce the welding joint structure difference and reduce the plasticity of a weakening area and joint strength reduction caused by the growth of a heat affected zone grain structure; meanwhile, due to the existence of Cr and B elements in the materials, an oxide film is formed on the surface of the welding line at a high preheating temperature, and then inclusions with higher melting points are generated, so that the welding quality is influenced.
S06, dehydrogenation treatment: covering the welding seam with heat insulation cotton within 500mm, heating the welding seam to 350-400 ℃, preserving heat for 2-3h to allow hydrogen to escape sufficiently, then slowly cooling to 80-120 ℃, and preserving heat for 2-3 h. Thus, the martensite structure can be completely transformed, and then the stress relief heat treatment after high-temperature welding is carried out, so as to achieve the purpose of obtaining the tempered martensite.
The main function of the post-welding dehydrogenation treatment is to accelerate the escape of hydrogen in a weld joint and a heat affected zone, and the effect of preventing the occurrence of welding cracks during the welding of alloy steel is very obvious. The conventional material is that a welding seam is heated to above 250 ℃ and is kept for 2-3h, then the temperature is directly raised to the post-welding stress relief heat treatment temperature, the welding seam is heated to 350-400 aiming at similar martensite structures, the heat is kept for 2-3h, then heat insulation cotton is covered, the welding seam is slowly cooled to below the material transformation temperature, the structure is completely transformed into the post-welding martensite structure, and then the post-welding stress relief heat treatment is carried out again, so that the tempered martensite structure is obtained.
S07, heat treatment: heating the casting to 740-760 ℃ at a heating rate of less than 50 ℃/h, keeping the temperature for 6-10 h, then cooling the casting to less than 200 ℃ at a cooling rate of less than 40 ℃/h, discharging and air cooling, wherein the cooling rate needs to be slow enough to avoid the generation of stress cracks.
The above-mentioned embodiments only express the specific embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (10)

1. A defect welding and heat treatment method for a heat-resistant steel casting is characterized by comprising the following steps:
heating the defect part: heating the defect part of the casting and the part around the defect to 150-200 ℃ by adopting a heating device;
digging out defects: excavating the defects of the casting by adopting a carbon arc gouging mode, and polishing the surface of the excavated part of the defects of the casting under the condition that the peripheral temperature of the excavated part of the defects of the casting is more than 150 ℃;
heating the defect excavated part of the casting: heating the defect excavated part of the casting to 300-400 ℃, preserving heat for 2-3h, and slowly cooling to room temperature;
welding: welding by adopting small-specification welding materials and a multi-layer and multi-channel filling mode; before welding each welding seam in the welding process, polishing the surface of the welding seam by adopting a non-carbon-based material;
carrying out dehydrogenation treatment;
post-weld stress relief heat treatment: heating the casting to 740-760 ℃ at a heating rate of less than 50 ℃/h, preserving heat, then cooling the casting to less than 200 ℃ at a cooling rate of less than 40 ℃/h, discharging and air cooling.
2. The method for defect welding and heat treating a heat resistant steel casting according to claim 1, wherein the excavated portion of the defect of the casting is heated to 180 ℃ to 220 ℃ for a holding time of more than 30min before the welding step.
3. The method for defect welding and heat treatment of the heat-resistant steel casting according to claim 1, wherein in the welding step, the welding material is an E9015-G material which comprises the following components in percentage by mass: c: 0.09% or less, Si: less than or equal to 0.6 percent, Mn: less than or equal to 0.6 percent, P: less than or equal to 0.01 percent, S: < 0.01%, Cr: 8.5-9.5%, W: 2.5-3.2%, Co: 2.5-3.2%, V: < 0.18%, Cu: < 0.01%, N: less than or equal to 0.06%, Nb: less than or equal to 0.03%, B: less than or equal to 0.08 percent, Ni: less than or equal to 0.8 percent, and the balance of Fe and inevitable impurities.
4. A method of defect welding and heat treatment of heat resistant steel castings according to claim 1, characterized in that in the dehydrogenation step, the weld periphery is heated to 350 ℃ to 400 ℃.
5. A method for defect welding and heat treating of heat resistant steel castings according to claim 1, characterized in that after the dehydrogenation step, the castings are slowly cooled to 80 ℃ to 120 ℃.
6. The method for defect welding and heat treatment of heat resistant steel castings according to claim 1, characterized in that in the welding step, after completion of the filling welding, two-layer facing welding is performed, the second layer facing welding range being smaller than the first layer facing welding range.
7. The method for defect welding and heat treatment of heat resistant steel castings according to claim 1, wherein after the step of heating the excavated portion of defects, the surface of the excavated portion of defects of the castings is ground using an alloy rotary file to remove the oxide layer.
8. A method for defect welding and heat treatment of heat resistant steel castings according to claim 1, characterized in that in the welding process, a welding rod with a diameter of phi 3.2 is used for the backing weld and a welding rod with a diameter of phi 4.0 is used for the fill cap weld.
9. The method for defect welding and heat treatment of heat resistant steel castings according to claim 8, characterized in that the welding process control parameters are: welding by adopting a welding rod with the diameter phi of 3.2, controlling the current to be 80-120A, controlling the arc voltage to be 15-20V, and controlling the welding heat input to be 5 KJ/cm; the welding is carried out by adopting an electrode with the diameter phi of 4.0, the current is controlled to be 130A to 160A, the arc voltage is controlled to be 18V to 22V, and the welding heat input is controlled to be not more than 12 KJ/cm.
10. A method of defect welding and heat treatment of heat resistant steel castings according to claim 1, characterized in that during welding, the bead thickness is 3mm or less and the interlaminar temperature is 260 ℃ or less.
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Application publication date: 20211102