Manufacturing process of super duplex stainless steel embedded part casting for circulating water pump of nuclear power plant

Abstract

The application relates to a manufacturing process of a super duplex stainless steel embedded part casting of a circulating water pump for a nuclear power plant, which comprises sand mold preparation, sand mold core assembling, material smelting, casting pouring, box lifting and sand cleaning, cutting pouring and riser and heat treatment processes; the application enables the application of super duplex stainless steel material ZERON25 to the embedded part casting with complex structure, uneven wall thickness, difficult core assembling of large size, strict internal quality requirement, improves the high precision of the casting size, internal quality, corrosion resistance and wear resistance, enables the stable working state of the casting, and prolongs the service life.

Description

Technical Field

[0001] This invention relates to a casting manufacturing process, and more particularly to a casting manufacturing process for a super duplex stainless steel embedded part for a circulating water pump used in a nuclear power plant. Background Technology

[0002] Embedded components for circulating water pumps are a crucial part of nuclear power plants, serving to secure and support the equipment underground. Due to the working environment, these components require high corrosion resistance and wear resistance, and the new material ZERON25 super duplex stainless steel can meet these performance requirements. In recent years, with the rapid development of my country's economic construction, the number of nuclear power units under construction has been continuously increasing, leading to a growing demand for these products.

[0003] However, due to the complex structure, uneven wall thickness, and large size of the embedded parts, making core assembly difficult, and the relatively strict internal quality requirements, the casting difficulty is increased. Super duplex stainless steel ZERON25, with its carbon content ≤0.06%, chromium content 24-26%, molybdenum content 2-3%, PREN greater than 35, and high ferrite content that easily leads to brittle cracking, is more difficult to process in melting and heat treatment compared to general products. This often results in numerous defects such as non-compliant casting dimensions, non-compliant casting composition, non-compliant casting performance, and casting-induced cracks. Summary of the Invention

[0004] This invention addresses the problems existing in the actual production process by providing a manufacturing process for super duplex stainless steel embedded parts castings for nuclear power plant circulating water pumps. This process yields super duplex stainless steel embedded parts castings for nuclear power plant circulating water pumps with high dimensional accuracy, good internal quality, corrosion and wear resistance, stable operation, and long service life. It solves the problems of low yield rates and unsuitable product performance for the special working environment of nuclear power plants in existing super duplex stainless steel embedded parts castings.

[0005] The technical solution of the present invention is as follows:

[0006] The manufacturing process of super duplex stainless steel embedded parts for circulating water pumps in nuclear power plants includes sand mold preparation, sand mold core assembly, material melting, casting pouring, mold removal and sand cleaning, cutting of risers and gating points, and heat treatment. The specific steps of each process are as follows:

[0007] 1) Sand mold preparation: The face sand is 50-70 mesh quartz furan resin sand, and the back sand is recycled quartz furan resin sand, forming an integral sand mold. The surface of the sand mold face sand is coated with alcohol-based zircon powder coating.

[0008] 2) Sand mold core assembly: The integral sand mold is cored according to the core assembly sequence of the process, and the core assembly dimensions of the casting are verified;

[0009] 3) Material smelting: super duplex stainless steel material ZERON25 smelting, chemical composition meets C≤0.06%, Si 0.15-0.55%, Mn 0.35-1.50%, P≤0.03%, S≤0.025%, Cr 24-26%, Ni 6.0-8.0%, Mo 2.0-3.0%, N 0.1-0.2%, ferrite content 35-60%, PREN≥35;

[0010] 4) Casting pouring: adopting a bottom return type pouring system leakage package pouring, the sprue, the runner and the ingate are all ceramic tubes, cold iron is uniformly laid on the bottom surface of the lower box except the position of the ingate, the thickness of the cold iron is 0.8 times the wall thickness of the casting, multiple risers are uniformly distributed on the upper box, the pouring temperature is 1560-1580 DEG C, and after pouring is completed, a heat preservation covering agent is scattered in the riser;

[0011] 5) Box opening and sand cleaning: after the casting is cooled for 48 hours, the temperature of the casting is 350-450 DEG C when sand is cleaned, and the box is opened and sand is cleaned;

[0012] 6) Cutting of the pouring and riser: after the casting is placed stably, the pouring and the riser are cut by using oxygen-acetylene cutting, and a 5mm excess amount is left for the riser cutting;

[0013] 7) Heat treatment: the embedded part is put into the furnace at a temperature of 100-200 DEG C, the heating rate is controlled to be 80-100 DEG C / h, when the temperature is heated to 980 DEG C, the temperature is kept for 1 hour, then the temperature is heated to 1080±10 DEG C, the temperature is kept for 6 hours, then the furnace is taken out and water quenched, the temperature from the furnace to the water is controlled to be within 5 minutes, the temperature of the circulating water is controlled to be 50 DEG C, and the temperature of the casting after water quenching is controlled to be 90-100 DEG C.

[0014] The advantages and effects of the present application are as follows:

[0015] The casting manufacturing process of the super duplex stainless steel embedded part for the circulating water pump of the nuclear power station disclosed in the present application enables the super duplex stainless steel material ZERON25 to be applied to the embedded part casting with complex structure, uneven wall thickness, difficult core assembly, and strict internal quality requirements, improves the precision, internal quality, corrosion resistance and wear resistance of the casting size, makes the working state of the casting stable, and improves the service life. PREFERRED EMBODIMENT

[0016] The casting manufacturing process of the super duplex stainless steel embedded part for the circulating water pump of the nuclear power station disclosed in the present application will be described in detail below in combination with specific implementation cases, so that the skilled person can more thoroughly understand the present application.

[0017] The embodiment is a pre-embedded part for a nuclear power plant circulating water pump, the casting has a geometry of 3684x3684x566mm, a wall thickness ranging from 45-117mm, uneven wall thickness, and a complex structure, and is made of super duplex stainless steel material ZERON25, and the manufacturing process is as follows:

[0018] The process includes sand mold preparation, sand mold core assembly, material melting, casting pouring, box lifting and sand cleaning, cutting pouring and riser, and heat treatment, and the specific requirements and implementation process are as follows:

[0019] 1) Sand mold preparation: the casting process difficulty of the pre-embedded part lies in the difficulty of assembling the core of the large-size casting sand mold, the difficulty of meeting the requirements of the casting surface quality and internal quality, and the difficulty of high casting size precision and non-deformation. In order to overcome the casting difficulty, the sand mold is divided into 1# sand mold and 2# sand mold, the 1# sand mold is an inner ring sand mold with 16 pieces, and the 16 pieces of 1# sand mold can form a complete inner ring structure after core assembly, the 2# sand mold is an outer ring sand mold with 16 pieces, and the 16 pieces of 2# sand mold can form a complete outer ring structure after core assembly, the surface sand of the pre-embedded part casting sand mold is 50-70 mesh quartz furan resin sand, and the back sand is regenerated quartz furan resin sand, which is filled after the thickness of 50-70 mesh quartz furan resin sand is 40mm, and then the regenerated quartz furan resin sand is filled, and the integral sand mold is obtained after demolding, wherein the mass ratio of furan resin to sulfonic acid curing agent is 3:1. The integral sand mold is brushed with alcohol-based zirconium powder paint on the surface of the sand mold, and the paint must be mixed uniformly before brushing, and the paint is brushed for 3 layers, and ignited for self-drying after brushing each layer, and baked with a baking gun, and the next layer is brushed after standing for 5-10 minutes. Through this step, the sand mold has fast curing speed, good sand mold collapse, high surface density, high sand mold strength, and can withstand the erosion of molten steel without slagging and sanding.

[0020] 2) Sand mold core assembly: the sand mold of the pre-embedded part casting has a total of 32 pieces, the flatness of the core bottom surface is checked using the closing inspection tooling of the pre-embedded part casting for nuclear circulating water pump, and after the inspection is qualified, the 1# sand mold is assembled first, and after the 16 pieces of 1# sand mold core assembly are completed, the 2# sand mold is assembled, and the 2# sand mold core assembly is assembled with the core assembly sample plate of the closing inspection tooling of the pre-embedded part casting for nuclear circulating water pump. Through this step, the sand mold core assembly is convenient, the core assembly precision is high, and the size precision of the casting is better guaranteed.

[0021] 3) Material smelting: The super duplex stainless steel material ZERON25 is smelted by the medium frequency induction furnace and the VOD furnace, and the chemical composition (percentage) of the molten steel is detected to meet C≤0.06%, Si 0.15-0.55%, Mn 0.35-1.50%, P≤0.03%, S≤0.025%, Cr 24-26%, Ni 6.0-8.0%, Mo 2.0-3.0%, N 0.1-0.2%, the ferrite content is 35-60%, and the pitting resistance equivalent PREN≥35. By controlling the percentage of the element composition, the molten steel meeting the performance and composition requirements is obtained.

[0022] 4) Casting pouring: The casting is poured by the bottom return type pouring system leakage package, the sprue, the runner and the ingate are all ceramic tubes, the sprue adopts the ceramic tube with the cross section of φ100mm, the runner adopts the ceramic tube with the cross section of φ70mm, and the four runners are adopted. The cold iron is uniformly laid on the bottom surface of the lower box except the position of the ingate, the thickness of the cold iron is 0.8 times of the wall thickness of the casting, and the solidification sequence of the casting from bottom to top is controlled. The 16 heat preservation and heating risers of the upper box are uniformly distributed, the diameter of the riser is 300mm, and due to the solidification sequence from bottom to top, the molten steel is finally solidified in the riser, so that the defects are finally retained in the riser. The pouring temperature is 1560-1580℃, so that the molten steel is smoothly filled, after the filling is completed, the heat preservation and heating covering agent is scattered in the riser, the heat preservation and heating covering agent can be selected from the positive Yang brand steel casting heat preservation and heating covering agent. The molten steel is smoothly filled, the solidification is in sequence, the shrinkage cavity and shrinkage porosity of the casting are avoided, the feeding rate of the riser and the yield of the casting are increased.

[0023] 5) Box opening and sand cleaning: after the casting is poured and cooled for 48 hours, the box is opened and the sand is cleaned, the temperature of the casting is 350-450℃ during the sand cleaning, and the casting body should not be hit during the sand cleaning, so as not to scratch the casting. Then it is hoisted to the shot blasting machine for shot blasting, so as to remove the surface sand sticking in the blind hole, the deep hole and the individual dead angle of the casting. The sand sticking on the surface and the dead angle of the casting is removed without damaging the casting, and the sand cleaning efficiency is high.

[0024] 6) Cutting of the pouring and riser: after the casting is placed stably, the pouring and the riser are cut by the oxygen acetylene cutting, the casting should not be cut during the cutting, and a 5mm allowance should be left during the cutting of the riser. The riser is cut by the gas cutting, and the residual stress between the casting and the riser is eliminated.

[0025] 7) Heat treatment: after the pouring and the riser are cut, the embedded part casting is put into the furnace at the temperature of 100-200℃, the heating rate is controlled to be 80-100℃ / h, the temperature is heated to 980℃, the temperature is kept for 1 hour, then the temperature is heated to 1080±10℃, the temperature is kept for 6 hours, then the embedded part casting is taken out and water quenched. Before the embedded part casting is put into the water, the circulating water temperature should be controlled to be within 50℃, the time from the embedded part casting being taken out of the furnace to being put into the water should be controlled to be within 2 minutes, and the temperature of the embedded part casting taken out of the water should be controlled to be 90℃. The internal quality of the casting is improved, and the required mechanical properties, physical properties and chemical properties are obtained.

[0026] The super duplex stainless steel embedded part castings for circulating water pump of nuclear power plant prepared by the above manufacturing process have good surface quality, compact internal structure, strong corrosion resistance and wear resistance, high dimensional accuracy, no cracks and other defects that can affect the use of the embedded part castings, stable working state and long service life. The sample for chemical composition analysis of the circulating water pump embedded part castings is prepared according to the provisions of GB / T20066, the chemical composition analysis is carried out according to GB / T223 and applicable parts of GB / T11170, the carbon content is ≤0.06%, the chromium content is 24-26%, the molybdenum content is 2-3%, which meets the composition requirements, the ferrite content is detected according to GB / T13305 standard, the ferrite content meets 35-60%, and the pitting resistance equivalent PREN is ≥35.

[0027] The above shows and describes the basic principles, main features and advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only preferred examples of the present application and are not intended to limit the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A manufacturing process of super duplex stainless steel castings for circulating water pump embedded parts of nuclear power plants, characterized in that The sand mold preparation, sand mold core assembly, material smelting, casting pouring, box lifting and sand cleaning, cutting pouring and heat treatment process are included, and the specific steps are as follows: Step 1, sand mold preparation: the surface sand is 50-70 mesh quartz furan resin sand, and the back sand is regenerated quartz furan resin sand, which is assembled into an integral sand mold, and the surface of the sand mold surface sand is brushed with alcohol-based zirconium powder paint; Step 2, sand mold core assembly: the integral sand mold is cored according to the process core sequence, and the core size of the casting is verified; Step 3, material smelting: super duplex stainless steel material ZERON25 is smelted, and the chemical composition meets C≤0.06%, Si 0.15-0.55%, Mn 0.35-1.50%, P≤0.03%, S≤0.025%, Cr 24-26%, Ni 6.0-8.0%, Mo 2.0-3.0%, N 0.1-0.2%, ferrite content 35-60%, and PREN≥35; Step 4, casting pouring: using a bottom return type pouring system, the casting is poured by a leakage package, the sprue, the runner and the ingate are all ceramic pipes, cold iron is uniformly laid on the lower box bottom surface except the inner gate position, the cold iron thickness is 0.8 times the casting wall thickness, multiple risers are uniformly distributed on the upper box, the pouring temperature is 1560-1580℃, and after pouring, a heat preservation covering agent is scattered into the riser; Step 5, box lifting and sand cleaning: after the casting is cooled for 48 hours, the casting temperature is 350-450℃ when the sand is cleaned, and the box is opened and the sand is cleaned; Step 6, cutting pouring and riser: after the casting is placed stably, the pouring gate and the riser are cut by using oxygen-acetylene cutting, and a 5mm excess amount is left for the riser cutting; Step 7, heat treatment: the embedded part is put into the furnace at a temperature of 100-200℃, the heating rate is controlled at 80-100℃ / h, when the temperature reaches 980℃, the temperature is kept for 1 hour, then the temperature is increased to 1080±10℃, and kept for 6 hours, then the furnace is taken out and water quenched, the temperature from taking out to entering water is controlled within 5 minutes, the circulating water temperature is controlled at 50℃, and the casting water temperature is controlled at 90-100℃, to obtain the finished product; In step 1, the sand mold is divided into 1# sand mold and 2# sand mold, the 1# sand mold is an inner ring sand mold with 16 blocks, and the 16 blocks of 1# sand mold form a complete inner ring structure after core assembly, and the 2# sand mold is an outer ring sand mold with 16 blocks, and the 16 blocks of 2# sand mold form a complete outer ring structure after core assembly; In step 1, 50-70 mesh quartz furan resin sand is filled to a thickness of 40mm, and then regenerated quartz furan resin sand is filled; In step 1, the mass ratio of furan resin to sulfonic acid curing agent used is 3:1; In step 1, the alcohol-based zirconium powder paint is brushed for 3 layers, each layer is ignited to dry after brushing, and then the next layer is brushed after baking with an oven gun for 5-10 minutes; In step 4, the straight runner adopts a ceramic pipe with a cross section of φ100mm, and the cross runner adopts a ceramic pipe with a cross section of φ70mm.