CN109518087B

CN109518087B - Low-temperature low-alloy high-strength corrosion-resistant oil field valve body and forging process thereof

Info

Publication number: CN109518087B
Application number: CN201811545504.6A
Authority: CN
Inventors: 苟建华
Original assignee: Suzhou Fujie Machinery Co ltd
Current assignee: Jiangsu Fujie high end equipment manufacturing (Group) Co.,Ltd.
Priority date: 2018-12-17
Filing date: 2018-12-17
Publication date: 2021-06-25
Anticipated expiration: 2038-12-17
Also published as: CN109518087A

Abstract

The invention relates to a low-temperature low-alloy high-strength corrosion-resistant oil field valve body and a forging process thereof, wherein the oil field valve body comprises the following raw materials in percentage by weight: C. 0.01-0.03 wt%; n, 0.01-0.03 wt%; 0.01-0.50 wt% of Si; 0.30-0.60 wt% of Mn; p, 0.01-0.25 wt%; s, 0.01-0.25 wt%; 12.0-14.0 wt% of Cr; 0.50-0.60 wt% of Mo; 3.55 to 4.50 wt% of Ni; 0.01-0.20 wt% of Cu; v, 0.01-0.07 wt%; nb, 0.010-0.045 wt%; the remainder being Fe. On one hand, the mechanical property and the corrosion resistance of the valve body are effectively improved, and the problems of good acid resistance, low strength, high strength and poor acid resistance of common materials are solved; on the other hand, the addition of the vanadium V element enhances the hardenability and the carbide of the material, can resist high temperature, has strong secondary hardening effect and has obvious effect on improving the hardness.

Description

Low-temperature low-alloy high-strength corrosion-resistant oil field valve body and forging process thereof

Technical Field

The invention belongs to the field of oil field valve body products, and particularly relates to a low-temperature low-alloy high-strength corrosion-resistant oil field valve body and a forging process for the low-temperature low-alloy high-strength corrosion-resistant oil field valve body.

Background

In the application, Cu element can improve the corrosion resistance of steel materials in the atmospheric environment and prolong the service life of the steel materials, and the formal research and development and production of Cu-containing steel are promoted by scholars in developed countries such as Europe, America and the like at the beginning of 20 th century. 1910, it was found that steel sheets manufactured by american steel company and having a copper content of 0.07% exhibited corrosion resistance 1.5 times better than plain carbon steel when exposed to three environments of different corrosivity (rural, industrial, and marine atmospheres). In 1911, steel companies in the united states began to push steel sheets containing a certain amount of copper into the market, and since such superiority of copper-containing steel was found, low alloy steel having both high strength and high corrosion resistance was produced. Around 1916, in the iron and steel association and the american society for testing and materials in the united kingdom, in order to study the corrosion law of steel, systematic atmospheric exposure test studies on the atmospheric corrosion resistance of steel were started, and as a result, it was found that when Cu element, Cr element, and P element were compositely added to steel, the corrosion resistance of steel in the atmospheric environment was significantly improved. In 1933, U.S. steel company successfully prepared corrosion-resistant low alloy steel containing Cu, i.e. Cor-Ten steel series, by adding a certain amount of Cu element into steel, and the mechanical properties of the steel are improved by 30% compared with that of the traditional plain carbon steel, so that the thickness and the corresponding weight of the steel plate are reduced while the steel is ensured to have the same mechanical properties. Then, Nishimura T, a scientist in Japan, controls the generation cost, ensures the corrosion resistance of the steel in the marine atmospheric environment, and simultaneously prepares alloy steel by using Al and Si alloy elements as main elements in the steel, so the developed steel not only reduces the cost, but also has high corrosion resistance, and the steel types are respectively ultrafine crystal high-strength weather-resistant steel in 780MPa grade and 760MPa grade.

Through years of research, the weathering steel sheet is successfully developed in 1963 in China, and the development of the weathering steel in China is started from this time. A great deal of experiments prove that the corrosion resistance of the weathering steel containing P, Cu element in the application is more than twice of that of low-carbon steel. With the development of the times, the design and development of materials with high strength and high corrosion resistance are very important and urgent.

According to the current development level and the current situation, the future development direction is as follows:

(1) the practical requirements are used as guidance, and key breakthroughs are made for common problems. Setting different research directions and targets for material requirements under different working conditions, and developing a new variety by combining service requirements of wear-resistant parts;

(2) in the technical aspect of equipment, the level of China is relatively lagged behind in the aspects of pressurized vacuum smelting, on-line heat treatment of medium and thick plates and section steel, shape control of high-strength steel parts and the like, and the equipment strength and intelligence are required to be continuously improved in exploration practice, so that the continuous integrated production of high-performance low-alloy wear-resistant steel is met;

(3) the economic and technical benefits are emphasized. The selection of material components, the reasonable distribution of process working hours and the reduction of rejection rate in the production operation process are performed, and the related work is completed by lean refinement. Research and production supplement each other, seamless butt joint from technical research make internal disorder or usurp to product development is realized, and technical benefit is maximized;

(4) the novel microalloying technology is an effective way for improving the strength level of steel, can increase the strength of common carbon steel and low alloy steel by multiple times, and is the development trend of alloy steel in the future. The Chinese microalloy technology is primarily applied to part of steel enterprises, but has obvious gap with the world advanced level, has huge development space and prospect, and is the inevitable direction for further research of low alloy steel.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a brand-new oil field valve body for low-temperature low-alloy high-strength corrosion resistance.

In order to achieve the aim, the invention provides a low-temperature low-alloy high-strength corrosion-resistant oil field valve body, which comprises the following raw materials in percentage by weight:

C、0.01～0.03wt％；

N、0.01～0.03wt％；

Si、0.01～0.50wt％；

Mn、0.30～0.60wt％；

P、0.01～0.25wt％；

S、0.01～0.25wt％；

Cr、12.0～14.0wt％；

Mo、0.50～0.60wt％；

Ni、3.55～4.50wt％；

Cu、0.01～0.20wt％；

V、0.01～0.07wt％；

Nb、0.010～0.045wt％；

the remainder being Fe.

Preferably, the sum of the weight percentages of C and N in the component is 0.02-0.05 wt%.

In the application, the alloy steel is prepared by using the Si alloy element as a main element in the steel, so that the developed steel not only reduces the cost, but also has high corrosion resistance. The Cu element can improve the corrosion resistance of the steel material in the atmospheric environment and prolong the service life of the steel material. When Cu element, Cr element and P element are added into steel in a compounding way, the corrosion resistance of the steel in the atmospheric environment is obviously improved. Compared with common valve body materials, the weight percentage of chemical elements Si, Cu, Mn and Ni in the Fe base of the low-alloy high-strength corrosion-resistant oil field valve body material is obviously increased, the weight percentage of chemical elements S, P is reduced, and the cost is reduced by increasing the Si content; the mechanical properties (fracture toughness and yield strength) of the product are increased by increasing the Mn content; the welding performance is improved by reducing the contents of S and P; the corrosion resistance under the atmospheric environment is improved by increasing the content of Ni; corrosion resistance is improved by increasing the content of Cu; as for the element V, the function of the element V in the steel is to enhance hardenability and carbides, and the element V can resist high temperature, has strong secondary hardening function and has obvious effect of improving hardness.

The invention also adopts the technical scheme that: a forging process for a low-temperature low-alloy high-strength corrosion-resistant oil field valve body comprises the following steps: s1, casting the raw materials according to the weight percentage of the raw materials of claim 1 or 2 into round steel blanks, and blanking according to the volume of the valve body;

s2, heating the blanked round steel blank in the step S1 to 1150 +/-30 ℃, knocking the surface of the round steel blank to enable an oxide layer adhered to the surface of the round steel blank to naturally fall off, then putting the heated round steel blank into a primary blank die cavity, and then clamping and pressing the die to form a primary blank;

s3, after S2, the primary blank is firstly placed into a pre-forging die cavity for pre-forging to enable the shape of the round steel blank to be the same as the shape required by the design, and then the round steel blank is placed into a finish-forging die cavity for further forging processing to enable the shape and the size to meet the design requirements;

s4, trimming and cooling the blank forged and formed in the step S3 to complete the forming of the valve body, wherein the temperature of the blank is less than or equal to 850 +/-50 ℃ in the trimming process;

s5, performing shot blasting, polishing and magnetic powder detection on the valve body blank in the S4, and then performing cutting processing to form a semi-finished valve body;

s6, carrying out heat treatment on the semi-finished valve body in the S5, specifically normalizing → quenching → tempering;

s7, performing performance test → hardness test → re-shot blasting → re-magnetic powder test → ultrasonic test of surface flaw detection type → marking and packaging on the semi-finished valve body after heat treatment in S6, and finishing the processing of the finished valve body.

Preferably, in the process of forming the round steel blank in S1, the oxygen content in the molten steel solution is less than or equal to 35 ppm; the hydrogen content is less than or equal to 1.6ppm, and the radioactivity level detection reading of the round steel blank is less than or equal to 0.4 Bp/g.

Furthermore, the hardness of the round steel blank is less than or equal to 241 HBW; the forging ratio is more than or equal to 5: 1; detecting the austenite grain size according to the ASTM E112-2013 standard, wherein the austenite grain size is more than or equal to grade 5; the high-temperature ferrite content is less than or equal to 5 percent.

Furthermore, the impact energy of the round steel blank at minus 46 ℃ (minus 46 ℃) is more than or equal to 27J. Thus, the valve body forged from the round steel billet can be used in some low-temperature environments.

According to a specific implementation and preferable aspect of the invention, the tensile strength of the finished valve body is more than or equal to 655MPa, the yield strength is more than or equal to 517MPa, the elongation is more than or equal to 18%, the reduction of area is more than or equal to 35%, and the Brinell hardness is more than or equal to 207-237 HB.

Preferably, in the heat treatment process of S6, the temperature is set to 871-927 ℃ during the normalizing, and the time T is selected according to the size of the maximum wall thickness of the semi-finished valve body, wherein each inch needs 0.5-1 hour.

Further, after the normalizing is finished and before the quenching is carried out, statically air-cooling the semi-finished valve body to be below 204 ℃ for austenitizing; meanwhile, during quenching, the temperature of the semi-finished valve body is 890 ℃, the temperature of the quenching liquid before quenching is less than 38 ℃, and the temperature of the quenching liquid after quenching is less than or equal to 49 ℃.

In addition, in the tempering in S6, two tempering treatments are carried out, wherein the temperature is controlled to be 649-732 ℃ under the mixed gas of air and nitrogen, and the time T is selected according to the size of the maximum wall thickness of the semi-finished valve body, wherein 0.75-2 hours is needed per inch.

Compared with the prior art, the invention has the following advantages:

the method mainly starts from two aspects of material components and process of valve body production, and fully utilizes the modern novel micro-alloying technology to research the strength and corrosion resistance of the valve body under the acidic working condition.

(1) Through the implementation of the valve body, the tensile strength of the valve body is larger than or equal to 655Mpa, the yield strength is larger than or equal to 517Mpa, the elongation is larger than or equal to 18%, the reduction of area is larger than or equal to 35%, and the Brinell hardness is larger than or equal to 207-237 HB. The mechanical property and the corrosion resistance of the valve body are effectively improved, and the problems of good acid resistance, low strength, high strength and poor acid resistance of common materials are solved. Meanwhile, an effective low-alloy high-strength corrosion-resistant valve body is provided for meeting special environment and high-pressure conveying requirements, and the practical application problem is solved.

(2) Through the implementation of the application, the application and the development of a novel microalloying technology are promoted. Microalloying is a process in which small amounts (generally not more than 0.2%, usually less than 0.1%) of specific alloying elements (such as niobium, vanadium, titanium, boron, etc.) are added to steel to improve properties. The addition of vanadium V element in the valve body material developed by the inventor enhances the hardenability and carbide of the material, and the material can resist high temperature, has strong secondary hardening effect and has obvious effect of improving the hardness.

(3) Through the implementation of the method and the device, seamless butt joint from technical research to product development is realized, and the technical benefit is maximized. From material component selection to reasonable distribution of process working hours, the production period of the low-alloy high-strength corrosion-resistant valve body can be effectively reduced, the material loss is reduced, meanwhile, secondary heating is not needed, the cost is saved, the efficiency is improved, the valve body has a good market application prospect, and good economic benefits are created.

Drawings

FIG. 1 is a sampling diagram of the mechanical properties of a round steel blank;

FIG. 2 is a schematic diagram of a selected position point for measuring hardness of a valve body;

FIG. 3 is a graph showing the results of the average grain size of the valve body (1);

FIG. 4 is a graph (2) showing the results of the average grain size of the valve body;

FIG. 5 is a graph showing the results of a macroscopic etching test of a valve body.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present application more comprehensible, embodiments accompanying the present application are described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. This application is capable of embodiments in many different forms than those described herein and that modifications may be made by one skilled in the art without departing from the spirit and scope of the application and it is therefore not intended to be limited to the specific embodiments disclosed below.

In the description of the present application, it is to be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the present application and for simplicity in description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the present application.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present application, "plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

In this application, unless expressly stated or limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can include, for example, fixed connections, removable connections, or integral parts; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.

In this application, unless expressly stated or limited otherwise, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through intervening media. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature. It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and the like as used herein are for illustrative purposes only and do not denote a unique embodiment.

Example 1

According to the oil field valve body for the low-temperature low-alloy high-strength corrosion-resistant oil field, the raw materials of the oil field valve body comprise the following components in percentage by weight, as shown in table 1:

TABLE 1

The steel-making process mainly uses pig iron or scrap steel as raw materials, the raw materials are re-melted for the second time through a smelting furnace, ores or ferroalloys of the required elements are added in the smelting process to meet the content requirements of the elements to form molten steel, and then the molten steel is poured into a casting mold through a ladle to be solidified to form steel ingots after smelting in the steel-making furnace. And (4) forging the steel ingot into a round steel blank by reheating the steel ingot.

In this example, the oxygen content in the molten steel solution was 30 ppm; the hydrogen content was 1.5ppm and the radioactivity level of the round steel billet measured 0.4 Bp/g.

The forging ratio of the round steel blank is 5: 1.

meanwhile, the austenite grain size is detected according to the ASTM E112-2013 standard, wherein the austenite grain size is 5 grades; the high temperature ferrite content was 5%.

Meanwhile, the round steel blank also meets the following requirements:

1. mechanical properties of the round steel billet:

in the embodiment, one round steel in each smelting furnace is randomly selected, a section of bar with the length of 200mm is taken at the dead head end, heated to 1010-1038 ℃ and insulated, air or oil or polymer is cooled to room temperature, the first tempering temperature is 677-691 ℃, air is cooled to room temperature after insulation, the second tempering temperature is 607-621 ℃ and air is cooled to room temperature, and the hardness is less than or equal to 241 HBW. After heat treatment, a sample is taken at a position 25mm away from the outer circle (a sampling graph is shown in figure 1), and the sample is processed into a standard sample according to ASTM 370, and the mechanical properties are tested according to ASTM E8 and ASTM E23, which are in accordance with the specification in Table 2:

TABLE 2

2. Macrostructure:

randomly drawing a round steel from each smelting furnace number, sampling at a dead head end, detecting according to GB/T226 and GB/T1979 standards, and preventing the cross section of the steel from being subjected to acid leaching on the macrostructure test piece to form visible shrinkage cavities, bubbles, cracks, inclusions, peeling, white spots and intergranular cracks. The acid-leached macrostructure grade should comply with the specifications of table 3.

TABLE 3

3. Non-metallic inclusions:

randomly selecting one round steel from each smelting furnace number, sampling at a feeder head end diameter 1/4, detecting according to a rating picture of an ASTM E45 standard, and according to the following table 4:

TABLE 4

4. Ultrasonic flaw detection:

the ultrasonic detection method is executed according to JB/T5000.15-2007 standard: the single defect is less than phi 3.2 mm; the continuity defect is less than phi 1.6mm, the continuity defect length is not more than 30mm, and the existence of dense defects is not allowed. The distance between two defects must not be less than 1 meter. The internal must not have hazardous defects that affect the problems of product quality, such as: foreign metal inclusions, slag inclusions, bubbles, cracks, shrinkage cavities, turning, white spots and intergranular cracks. Sampling quantity: root by root; sampling part: and (6) finishing the root.

5. Surface quality:

the surface has no defects such as cracks, folds and the like, and the surface roughness has to meet the requirement of ultrasonic flaw detection.

The defects on the surface of the steel must be removed, the maximum removal depth should not exceed 2% of the diameter of the steel, the cleaning process should be smooth and have no sharp edges and corners, and the removal width is not less than 5 times of the depth.

In the embodiment, the forging process for the low-temperature low-alloy high-strength corrosion-resistant oil field valve body comprises the following steps:

s1, according to the volume of the valve body, adopting round steel material blanks (material rods) meeting the requirements, and carrying out sawing blanking;

s2, heating the blanked round steel blank in the step S1 to 1150 ℃, knocking the surface of the round steel blank to enable an oxide layer adhered to the surface of the round steel blank to naturally fall off, then putting the heated round steel blank into a primary blank die cavity, and then clamping and pressing the die to form a primary blank;

s4, trimming and cooling the blank forged and formed in the step S3 to complete the forming of the valve body, wherein the temperature of the blank is 850 ℃ in the trimming process;

In this example, the heat treatment steps used were: normalizing (including austenitizing), quenching, tempering, and re-tempering. Specifically, the media and temperature conditions in each step are as follows:

TABLE 5 Heat treatment Process Medium and temperature conditions

Finally, the completed valve body performance test results are as follows:

1. tensile test

2. Impact test

3. Hardness test

The test position is shown in the attached figure 2, and the specific information is as follows:

4. average grain size assessment

Serial number	Average grain size grade	Picture frame
			1	5	FIG. 3
2	5	FIG. 4

5. Evaluation of non-metallic inclusions

Remarking: in the table, "-" indicates that no such inclusion is found, and the non-metallic inclusion of class D in number 1 is oversized, and the maximum diameter is 17 microns; the non-metallic inclusions of class D in number 2 were oversized and had a maximum diameter of 15 μm.

6. Macroscopic erosion test

Test results	Picture frame
		No obvious defect is found	FIG. 5

In summary, compared with the prior art, the invention has the following advantages:

Comparative example 1

The specific implementation of the oilfield valve body according to the present embodiment is the same as that of embodiment 1, except that:

aiming at the casting process of the round steel blank, the contents of various elements are as follows:

meanwhile, the forging process comprises the following steps: heating → free forging → knockout → reheating → die forging → trimming to finish the processing of the valve body blank, that is, in the process of re-forging, the first forging is free forging; the second forging is die forging and the two operations are independent of each other, so that two heats are required for blank forging.

Then, the same heat treatment as in the above step is performed, but in the heat treatment, tempering treatment is performed only once.

Therefore, the performance detection result of the valve body finished product is as follows:

1. tensile test

2. Impact test

3. Hardness test

The tested positions are the same as those detected in example 1, and the specific information is as follows:

therefore, from the comparative analysis of the tensile test, the impact test and the hardness test, the embodiment of example 1 is characterized and innovative in that:

(1) the alloy has improved high acid resistance, high temperature strength and high temperature compression strength, is suitable for valves applied to acid occasions, has long service life and high qualification rate, greatly improves the quality of products, and is suitable for wide popularization;

(2) the one-step forming process in the re-forging process can effectively reduce the production period and the material loss, and meanwhile, secondary heating is not needed, so that the cost is saved, and the efficiency is improved; and then combining the heat treatment processes of two times of tempering to ensure the excellent mechanical properties (tensile strength is more than 655Mpa, yield strength is more than 517Mpa, elongation after fracture is more than 17%, shrinkage rate is more than 35%, impact energy at minus 46 ℃ is more than 27J, Brinell hardness is more than or equal to 207-237 HBW) of the finished valve body, meanwhile, comparing the data in the embodiment 1 and the comparative example 1, the embodiment 1 has obvious advantages in the aspects of convenient processing and final mechanical properties, and is particularly suitable for application in low-temperature, high-acid resistance, high-temperature strength, high-temperature compression strength and acid occasions.

Example 2

This example is the same as example 1 except for the following forging process:

1. the oil field valve body comprises the following raw materials in percentage by weight, as shown in Table 6:

TABLE 6

2. Tensile test

3. Impact test

4. Hardness test

The test sites were the same as in example 1, and the specific results are as follows:

comparative example 2

The specific implementation of the oilfield valve body related to the embodiment is the same as that of the oilfield valve body of the comparative example 1, except that:

meanwhile, the forging process is also as follows: heating → free forging → knockout → reheating → die forging → trimming to finish the processing of the valve body blank, that is, in the process of re-forging, the first forging is free forging; the second forging is die forging and the two operations are independent of each other, so that two heats are required for blank forging.

1. tensile test

2. Impact test

3. Hardness test

(2) the one-step forming process in the re-forging process can effectively reduce the production period and the material loss, and meanwhile, secondary heating is not needed, so that the cost is saved, and the efficiency is improved; and then combining the heat treatment processes of two times of tempering to ensure the excellent mechanical properties (tensile strength is more than 655Mpa, yield strength is more than 517Mpa, elongation after fracture is more than 17%, shrinkage rate is more than 35%, impact energy at minus 46 ℃ is more than 27J, Brinell hardness is more than or equal to 207-237 HBW) of the finished valve body, meanwhile, comparing the data in the embodiment 2 with the data in the comparative example 2, the embodiment 2 has obvious advantages in the aspects of convenient processing and final mechanical properties, and is particularly suitable for application in low-temperature, high-acid resistance, high-temperature strength, high-temperature compression strength and acid occasions.

The above embodiments are merely illustrative of the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the content of the present invention and implement the invention, and not to limit the scope of the invention, and all equivalent changes or modifications made according to the spirit of the present invention should be covered by the scope of the present invention.

Claims

1. A forging process for a low-temperature low-alloy high-strength corrosion-resistant oil field valve body comprises the following steps:

s1, taking pig iron or scrap steel as a raw material, carrying out secondary remelting on the raw material through a smelting furnace, and adding ores or ferroalloys in the smelting process so that the molten steel contains the following elements in percentage by weight: C. 0.01-0.03 wt%; n, 0.01-0.03 wt%; 0.01-0.50 wt% of Si; 0.30-0.60 wt% of Mn;

P、0.01~0.25wt%；S、0.01~0.25wt%；Cr、12.0~14.0 wt%；Mo、0.50~0.60 wt%；

3.55 to 4.50 wt% of Ni; 0.01-0.20 wt% of Cu; v, 0.01-0.07 wt%; nb, 0.010-0.045 wt%; the balance is Fe, then molten steel is smelted in a steelmaking furnace, the molten steel is poured into a casting mold through a ladle to be solidified to form a steel ingot, the steel ingot is forged into a round steel blank by reheating after the steel ingot is finished, and blanking is carried out according to the volume of a valve body, wherein in the forming process of the round steel blank, the oxygen content in the molten steel solution is less than or equal to 35 ppm; the hydrogen content is less than or equal to 1.6ppm, the radioactivity level detection reading of the round steel blank is less than or equal to 0.4Bq/g, and the round steel blank simultaneously meets the following requirements: 1. the mechanical property of the round steel blank is processed into a standard sample according to ASTM 370, the mechanical property is tested by referring to ASTM E8 and ASTM E23, Rm (tensile strength) is more than or equal to 655MPa, Rp0.2 (yield strength) is more than or equal to 517MPa, and A (elongation) is more than or equal to 17 percent; z (shrinkage) is more than or equal to 35 percent; the impact energy is more than or equal to 27J at the temperature of minus 46 ℃, and the hardness is less than or equal to 241 HBW; 2. the macrostructure is detected according to GB/T226 and GB/T1979 standards, and the cross section acid leaching macrostructure test piece of the steel material cannot have visual shrinkage cavities, bubbles, cracks, inclusions, peeling, white spots and intergranular cracks; 3. non-metallic inclusions, as measured by the ASTM E45 standard rating picture; 4. ultrasonic flaw detection is carried out according to JB/T5000.15-2007 standard, a single flaw is smaller than phi 3.2mm, a continuous flaw is smaller than phi 1.6mm, the length of the continuous flaw is not larger than 30mm, and the distance between the two flaws is not smaller than 1 meter; 5. the method comprises the following steps that (1) cracks cannot exist on the surface, folding defects cannot exist, the surface roughness must meet the requirement of ultrasonic flaw detection, the defects on the surface of steel must be removed, the maximum depth of the removal should not exceed 2% of the diameter of the steel, the removal process should be smooth and have no sharp edges, the removal width is not less than 5 times of the depth, S2, the round steel blank after being fed in S1 is heated to 1150 +/-30 ℃, the temperature of the round steel blank is 1150 +/-30 ℃, the surface of the round steel blank is knocked to enable an oxide layer adhered to the surface of the round steel blank to naturally fall off, then the heated round steel blank is placed into a primary blank die cavity, and then the die is subjected to clamping and pressing treatment to form a;

s6, performing heat treatment on the semi-finished valve body in the S5, specifically, performing normalizing → quenching → tempering, wherein in the tempering in the S6, performing tempering treatment twice, wherein in the mixed gas of air and nitrogen, the temperature is controlled to be 649-732 ℃, the time T is selected according to the maximum wall thickness of the semi-finished valve body, and each inch needs 0.75-2 hours;

2. The forging process for the low-temperature low-alloy high-strength corrosion-resistant oilfield valve body according to claim 1, wherein the forging process comprises the following steps: the sum of the weight percentage of C and N in the components is 0.02-0.05 wt%.

3. The forging process for the low-temperature low-alloy high-strength corrosion-resistant oilfield valve body according to claim 1 or 2, wherein the forging process comprises the following steps: in S1, the hardness of the round steel billet is less than or equal to 241 HBW; the forging ratio is more than or equal to 5: 1; detecting the austenite grain size according to the ASTM E112-2013 standard, wherein the austenite grain size is more than or equal to grade 5; the high-temperature ferrite content is less than or equal to 5 percent.

4. The forging process for the low-temperature low-alloy high-strength corrosion-resistant oilfield valve body according to claim 1, wherein the forging process comprises the following steps: the impact energy at-46 ℃ is more than or equal to 27J.

5. The forging process for the low-temperature low-alloy high-strength corrosion-resistant oilfield valve body according to claim 1, wherein the forging process comprises the following steps: the tensile strength of the finished valve body is more than or equal to 655MPa, the yield strength is more than or equal to 517MPa, the elongation is more than or equal to 18%, the reduction of area is more than or equal to 35%, and the Brinell hardness is more than or equal to 207-237 HB.

6. The forging process for the low-temperature low-alloy high-strength corrosion-resistant oilfield valve body according to claim 1, wherein the forging process comprises the following steps: in the heat treatment process of S6, the temperature is set to 871-927 ℃ during normalizing, and the time T is selected according to the size of the maximum wall thickness of the semi-finished valve body, wherein each inch needs 0.5-1 hour.

7. The forging process for the low-temperature low-alloy high-strength corrosion-resistant oilfield valve body according to claim 6, wherein the forging process comprises the following steps: after the normalizing is finished and before quenching, statically air-cooling the semi-finished valve body to below 204 ℃ for austenitizing; meanwhile, during quenching, the temperature of the semi-finished valve body is 890 ℃, the temperature of the quenching liquid before quenching is less than 38 ℃, and the temperature of the quenching liquid after quenching is less than or equal to 49 ℃.