Forging process of a 4330V alloy

Abstract

The present invention discloses a forging process for 4330V alloy. The technical solution includes the following steps: Step S1, prepare an ingot; Step S2, heat treatment of the ingot, including the following working steps: (1) The first heat treatment stage: heat up to 500 ± 20 °C and hold for heat preservation; (2) The second heat treatment stage: heat up to 930 ± 15 °C and hold for heat preservation; (3) The third heat treatment stage: heat up to 1230 ± 15 °C and hold for heat preservation; Step S3, heat treatment of the ingot, including: (1) The first heat treatment stage: heat up to 650 ± 10 °C and hold for heat preservation; (2) The second heat treatment stage: heat up to 850 ± 10 °C and hold for heat preservation; (3) The third heat treatment stage: heat up to 1200 ± 10 °C and hold for heat preservation; Step S4, machining; Step S5, the second heat treatment, including (4) quenching stage: heat up the ingot to 860 ± 10 °C and hold for heat preservation; (5) tempering stage: heat up the ingot to 560 ± 10 °C and hold for heat preservation. The advantages of the present invention are to improve the internal tissue grains, eliminate forging defects, refine the grains, and improve the alloy properties.

Description

Technical Field

[0001] The present invention relates to the technical field of special alloy manufacturing, and particularly to a forging process for 4330V alloy. Background Art

[0002] At present, with the in-depth exploration and development of domestic natural gas, the shallow-layer oil has basically been nearly developed, and deeper crude oil needs to be gradually exploited. As the depth and development difficulty of oil and gas wells continue to increase, both the total construction volume and the construction scale are gradually increasing every year, and the operating pressure and displacement of fracturing construction are getting larger and larger. At present, the multi-stage fracturing technology for horizontal wells in China has moved from experimental development to the stage of large-scale implementation. The large-scale fracturing construction is expanding both in terms of total volume and scale, and the development of fracturing equipment should also keep up with the requirements of construction operations. From the current development of fracturing equipment, the research and development of fracturing equipment are also moving towards the large and extra-large directions. The oil equipment is developing towards large fracturing equipment with high strength, high wear resistance, and long service life. Therefore, the demand and requirements for alloy 4330V are getting higher and higher.

[0003] However, the products made of 4330V currently have the following problems:

[0004] 1. The conventional heat treatment method for 4330V alloy is high-temperature tempering at 500°C - 600°C. The main structure of 4330V alloy is tempered sorbite, which is a composite structure with cementite distributed in the matrix ferrite. For the deeper underground working environment, the products made of 4330V alloy need to collide with hard rock formations, and the strength and toughness of tempered sorbite are slightly insufficient, affecting the service life of 4330V alloy.

[0005] 2. For the 4330V alloy treated by high-temperature tempering, the grains of its tempered sorbite are relatively coarse, and there is segregation phenomenon inside the grains, resulting in low grain uniformity, which is likely to cause forging defects such as cracking and porosity during the forging process. Summary of the Invention

[0006] Aiming at the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a forging process for 4330V alloy, the advantage of which is to improve the internal tissue grains, eliminate forging defects, and adopt special quenching and tempering heat treatment to refine the grains and improve the comprehensive performance of the alloy by re-designing the alloy formula and combining corresponding forging process technologies.

[0007] The above technical purpose of the present invention is achieved through the following technical solutions:

[0008] A forging process for 4330V alloy includes the following steps:

[0009] Step S1, preparing 4330V ingot: putting each elemental raw material into a vacuum furnace for melting, and obtaining an ingot blank after cooling;

[0010] Step S2, heat treatment of the ingot, including the following working steps:

[0011] (1) The first heat treatment stage: The ingot is heated to 500 ± 20 °C and held for heat preservation;

[0012] (2) The second heat treatment stage: The ingot is heated to 930 ± 15 °C and held for heat preservation;

[0013] (3) The third heat treatment stage: The ingot is heated to 1230 ± 15 °C and held for heat preservation, and then the ingot is naturally cooled to below 800 °C;

[0014] Step S3, forging of the ingot, including the following working steps:

[0015] The first heat treatment: The surface of the ingot is treated, then the ingot is put into the furnace and heated to the forging temperature of 850 - 1250 °C, and then the ingot is sent to the press for forging;

[0016] The second heat treatment: The ingot is put into the furnace and heated to the forging temperature of 850 - 1250 °C, then the ingot is sent to the press for forging, and finally the forging is air-cooled to room temperature;

[0017] Step S4, machining of the ingot;

[0018] Step S5, the second heat treatment, including the following working steps:

[0019] (4) Quenching stage: The ingot is heated to 860 ± 10 °C and held for heat preservation;

[0020] (5) Tempering stage: The ingot is heated to 560 ± 10 °C and held for heat preservation, then the ingot is cooled in the furnace to below 500 °C and taken out of the furnace and cooled to room temperature, and then the ingot is heated to 560 ± 10 °C and held for heat preservation, and the ingot is cooled to room temperature.

[0021] Furthermore, in step S3, the forging ratio of the first heat treatment and the second heat treatment > 3.0.

[0022] Furthermore, in the first heat treatment stage of step S2, the heating rate is 1.33 °C / min (80 °C / h), and the heat preservation time range is 3 - 6 h.

[0023] Furthermore, in the first heat treatment stage of step S3, the charging temperature of the ingot ≤ 400 °C.

[0024] Furthermore, in the second heat treatment stage of step S3, the heating rate is 1.33 °C / min (80 °C / h), and the heat preservation time range is 2.5 - 3 h.

[0025] Furthermore, in the third heat treatment stage of step S3, the heating rate is 0.833 °C / min (50 °C / h), and the heat preservation time range is 3 - 4 h.

[0026] Further, in the quenching stage of step S5, the heating rate is 1.33 °C / min (80 °C / h), and the holding time ranges from 8 to 12 h.

[0027] Further, in the tempering stage of step S5, the heating rate is 1.33 °C / min (80 °C / h), and the holding time ranges from 5 to 12 h.

[0028] Further, in the tempering stage of step S5, the ingot is cooled to room temperature with water whose temperature is not higher than 60 °C.

[0029] Further, in step S1, the 4330V steel ingot comprises elements by mass percentage: C: 0.28 - 0.32%; Si: 0.05 - 0.25%; Mn: 0.50 - 0.80%; P ≤ 0.015%; S ≤ 0.010%; Cr: 1.20 - 1.50%; Mo: 0.52 - 0.60%; Ni: 3.00 - 3.50%; Cu ≤ 0.20; V: 0.10 - 0.20%; impurity elements in the alloy: O ≤ 30 ppm; N ≤ 130 ppm; H ≤ 2.00 ppm.

[0030] In summary, the present invention has the following beneficial effects:

[0031] 1. By appropriately increasing the lower or upper limit content of elements such as C, Mn, Cr, Ni, Mo, N, Nb, V, etc., and combining with the corresponding forging process and heat treatment process, the internal tissue grains are improved, enabling the tissue grains to undergo large deformation, breaking the coarse mixed crystal structure, increasing the forging density of the forging, better controlling the streamline distribution of the metal fiber structure, further improving the uniformity and fineness of the grain structure, and thus improving the performance of the forging.

[0032] 2. In the heat treatment, a three-stage heat treatment sequence is adopted. The first stage and the second stage are mainly for preheating the ingot, gradually raising the temperature by 200 °C and holding the temperature. In order to eliminate the temperature gradient inside and outside the ingot to the greatest extent, during this process, the structure of the alloy is sorbite, strip or massive ferrite. Finally, solution strengthening is carried out at 1200 °C, which is beneficial to the diffusion of Cr, Mo, and Ni atoms mainly formed by ferrite, promotes the austenitization of sorbite, and the austenite structure and ferrite are in a suitable equilibrium state. Along with the diffusion of relevant atoms such as Cr and Ni that form ferrite, the strip or massive ferrite gradually disperses and transforms into a uniform and fine ferrite structure. Some ferrite also undergoes austenitization transformation to form a supersaturated solid solution, and the grain structure becomes more uniform, maximizing the effect of fine grain strengthening; strictly limit the solution temperature to avoid the solution temperature exceeding 1300 °C. The reason is that during the solution strengthening process, ferrite will undergo a dynamic recrystallization process. When the temperature is too high, a large proportion of coarse ferrite recrystallized structure will appear, destroying the equilibrium state between austenite and ferrite, and also resulting in coarse grains, leading to a decrease in material properties.

[0033] 3. Due to the strong tissue heredity of 4330V itself, the structure after forging becomes larger and uneven. During the quenching treatment, part of the eutectoid ferrite transforms into austenite, and the austenite forms fine and uniform austenite grains. The austenite transforms into a low-temperature metastable phase martensite during the cooling process. The hardness of martensite is much higher than that of austenite, strengthening the strength and hardness of the alloy.

[0034] 4. In the tempering treatment, under the same quenching temperature, the strength and hardness of the material during actual application will decrease with the increase of the tempering temperature, and the decrease amplitude will become larger and larger. Because when the temperature is lower than 500 °C, alloying elements cannot diffuse quickly, so 560 ± 10 °C is selected as the temperature window, and all C atoms in the material will be precipitated. In this case, strong carbides in the material will form Mo and V alloy carbides, and avoid excessive decrease in the material properties, achieving the best balance point. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the steps of the forging process of 4330V alloy.

[0036] Figure 2 It is a schematic diagram of the macro flaw detection of the sample in Example 1.

[0037] Figure 3 It is a schematic diagram of the metallographic examination of the sample in Example 1.

[0038] Figure 4 It is a schematic diagram of the macro flaw detection of the sample in Example 2.

[0039] Figure 5 It is a schematic diagram of the metallographic examination of the sample in Example 2.

[0040] Figure 6 It is a schematic diagram of the low-magnification flaw detection of the sample in Example 3.

[0041] Figure 7 It is a schematic diagram of the metallographic inspection of the sample in Example 3. Specific implementation manners

[0042] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the solutions proposed by the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners. According to the following description, the advantages and features of the present invention will be clearer.

[0043] Example 1:

[0044] A forging process of 4330V alloy, as Figure 1 shown, includes the following steps:

[0045] Step S1, prepare a 4330V steel ingot: Put the raw materials of each element into a vacuum furnace for melting, and obtain a steel ingot blank after cooling. The 4330V steel ingot includes elements counted by mass percentage:

[0046] Step S2, heat treatment of the steel ingot, including the following working steps:

[0047] (1), the first heat treatment stage: The steel ingot is charged into the furnace for heating at a temperature condition of ≤400 °C, the steel ingot is heated to 480 °C and held, the heating rate is 1.33 °C / min (80 °C / h), and the holding time range is 3 - 6 h.

[0048] (2), the second heat treatment stage: The steel ingot is heated to 915 °C and held, the heating rate is 1.33 °C / min (80 °C / h), and the holding time range is 2.5 - 3 h.

[0049] (3), the third heat treatment stage: The steel ingot is heated to 1215 °C and held, and then the steel ingot is naturally cooled to below 800 °C, the heating rate is 0.833 °C / min (50 °C / h), and the holding time range is 3 - 4 h.

[0050] Step S3, forging the steel ingot, including the following working steps:

[0051] The first heat treatment: The steel ingot is surface-treated to remove defects such as burrs on the surface of the steel ingot. Then the steel ingot is sent to be heated to the forging temperature of 850 °C. During the heating process of the steel ingot, the mold is preheated at the same time, and the preheating temperature range of the mold is 700 - 800 °C. In order to reduce the temperature difference between the steel ingot and the mold and avoid the rapid cooling of the surface of the steel ingot. Then the steel ingot is loaded into the mold and sent to the press for forging, and the forging ratio > 3.0.

[0052] The second heating: The ingot is heated in the furnace to the forging temperature of 850 °C, then the ingot is sent to the press for forging, and finally the forging is air-cooled to room temperature, with a forging ratio > 3.0.

[0053] Step S4: Machining of the ingot: The staff stamps the ingot and inspects the ingot blank, and then performs external machining means such as cutting on the ingot according to the design drawing of the product.

[0054] Step S5: The second heat treatment, including the following working steps:

[0055] (4) Quenching stage: The ingot is heated to 850 °C and held, with a heating rate of 1.33 °C / min (80 °C / h), and the holding time ranges from 8 to 12 h.

[0056] (5) Tempering stage: The ingot is heated to 550 °C and held, then the ingot is cooled in the furnace to below 500 °C and taken out of the furnace and cooled to room temperature, with a heating rate of 1.33 °C / min (80 °C / h), the holding time ranges from 5 to 12 h, and then the ingot is heated to 550 °C and held, and the ingot is cooled to room temperature to complete the secondary tempering.

[0057] Step S6: Detect the hardness of the product.

[0058] Step S7: Machining of the product.

[0059] Step S8: Non-destructive testing of the product.

[0060] Step S9: Comprehensive performance testing of the product: The product is made into a sample, a sample is taken, and mechanical property tests and microscopic structure tests are carried out using the sample. If the sample passes the test, the product is degreased, and then the product is marked and stored in the warehouse.

[0061] Example 2:

[0062] The steps different from Example 1 are as follows:

[0063] The first heating: The surface of the ingot is treated to remove defects such as burrs on the surface of the ingot. Then the ingot is sent into a furnace heated to the forging temperature of 1150 °C.

[0064] The second heating: The ingot is heated in the furnace to the forging temperature of 1150 °C, then the ingot is sent to the press for forging, and finally the forging is air-cooled to room temperature.

[0065] Step S2: Heat treatment of the ingot, including the following working steps:

[0066] (1) The first heat treatment stage: The ingot is charged into the furnace and heated under the temperature condition of ≤ 400 °C, the ingot is heated to 500 °C and held, with a heating rate of 1.33 °C / min (80 °C / h), and the holding time ranges from 3 to 6 h.

[0067] (2) The second heat treatment stage: The ingot is heated to 930 °C and held, with a heating rate of 1.33 °C / min (80 °C / h), and the holding time ranges from 2.5 to 3 h.

[0068] (3) The third heat treatment stage: The ingot is heated to 1230 °C and held, then the ingot is naturally cooled to below 800 °C, with a heating rate of 0.833 °C / min (50 °C / h), and the holding time ranges from 3 to 4 h.

[0069] Step S3: Ingot forging, including the following operations:

[0070] The first heat: The ingot is surface-treated to remove defects such as burrs on the ingot surface. Then the ingot is sent into a furnace heated to the forging temperature of 1040 °C. During the heating of the ingot, the die is preheated simultaneously, and the preheating temperature range of the die is 700 - 800 °C to reduce the temperature difference between the ingot and the die and avoid the rapid cooling of the ingot surface. Then the ingot is loaded into the die and sent into a press for forging, with a forging ratio > 3.0.

[0071] The second heat: The ingot is heated in the furnace to the forging temperature of 1040 °C, then the ingot is sent into a press for forging, and finally the forging is air-cooled to room temperature, with a forging ratio > 3.0.

[0072] Step S5: The second heat treatment, including the following operations:

[0073] (4) Quenching stage: The ingot is heated to 860 °C and held, with a heating rate of 1.33 °C / min (80 °C / h), and the holding time ranges from 8 to 12 h.

[0074] (5) Tempering stage: The ingot is heated to 560 °C and held, then the ingot is cooled in the furnace to below 500 °C and taken out of the furnace and cooled to room temperature, with a heating rate of 1.33 °C / min (80 °C / h), and the holding time ranges from 5 - 12 h. Then the ingot is heated to 560 °C and held, and the ingot is cooled to room temperature to complete the secondary tempering.

[0075] Example 3:

[0076] The steps different from Example 1 are as follows:

[0077] The first heat: The ingot is surface-treated to remove defects such as burrs on the ingot surface. Then the ingot is sent into a furnace heated to the forging temperature of 1250 °C.

[0078] The second heat: The ingot is heated in the furnace to the forging temperature of 1250 °C, then the ingot is sent into a press for forging, and finally the forging is air-cooled to room temperature.

[0079] Step S2: Ingot heat treatment, including the following operations:

[0080] (1) First heat treatment stage: The ingot is charged into the furnace and heated at a temperature of ≤400°C. The ingot is heated to 520°C and held for heat preservation. The heating rate is 1.33°C / min (80°C / h), and the heat preservation time ranges from 3 to 6 hours.

[0081] (2) Second heat treatment stage: The ingot is heated to 945°C and held for heat preservation. The heating rate is 1.33°C / min (80°C / h), and the heat preservation time ranges from 2.5 to 3 hours.

[0082] (3) Third heat treatment stage: The ingot is heated to 1245°C and held for heat preservation. Then the ingot is naturally cooled to below 800°C. The cooling rate is 0.833°C / min (50°C / h), and the heat preservation time ranges from 3 to 4 hours.

[0083] First forging pass: The ingot is surface-treated to remove defects such as burrs on the surface of the ingot. Then the ingot is sent into a furnace heated to the forging temperature of 1240°C. During the heating process of the ingot, the die is preheated simultaneously. The preheating temperature range of the die is 700 - 800°C to reduce the temperature difference between the ingot and the die and avoid the rapid cooling of the surface of the ingot. Then the ingot is loaded into the die and sent into the press for forging, and the forging ratio > 3.0.

[0084] Second forging pass: The ingot is heated in the furnace to the forging temperature of 1240°C, then the ingot is sent into the press for forging, and finally the forging is air-cooled to room temperature, and the forging ratio > 3.0.

[0085] Step S5. Second heat treatment, including the following steps:

[0086] (4) Quenching stage: The ingot is heated to 870°C and held for heat preservation. The heating rate is 1.33°C / min (80°C / h), and the heat preservation time ranges from 8 to 12 hours.

[0087] (5) Tempering stage: The ingot is heated to 570°C and held for heat preservation. Then the ingot is cooled in the furnace to below 500°C and taken out of the furnace and cooled to room temperature. The cooling rate is 1.33°C / min (80°C / h), and the heat preservation time ranges from 5 to 12 hours. Then the ingot is heated to 570°C and held for heat preservation, and the ingot is cooled to room temperature to complete the second tempering.

[0088] Alloy microstructure detection:

[0089] Experimental preparation: The samples taken in Example 1 are denoted as Specimen 1; the samples taken in Example 2 are denoted as Specimen 2; the samples taken in Example 3 are denoted as Specimen 3.

[0090] Low-power appearance detection of specimens:

[0091] Specimen 1: As Figure 2 shown, the specimen has no defects such as bubbles, cracks, inclusions, white spots, skin turning, residual shrinkage cavities, general porosity, central porosity, and general segregation.

[0092] Specimen 2: As Figure 4 shown, there are no bubbles, cracks, inclusions, white spots, skin turning, residual shrinkage cavities, general porosity, central porosity, and general segregation defects in the specimen.

[0093] Specimen 3: As Figure 6 shown, there are no bubbles, cracks, inclusions, white spots, skin turning, residual shrinkage cavities, general porosity, central porosity, and general segregation defects in the specimen.

[0094] Metallographic inspection of the specimen:

[0095] Specimen 1: As Figure 3 shown, the magnification specification is 100μm, the grain size is 6.5 - 8.0 grades, and there is no phenomenon of uneven grain size.

[0096] Specimen 2: As Figure 5 shown, the magnification specification is 100μm, the grain size is 6.0 - 7.0 grades, and there is no phenomenon of uneven grain size.

[0097] Specimen 3: As Figure 7 shown, the magnification specification is 100μm, the grain size is 6.5 - 7.5 grades, and there is no phenomenon of uneven grain size.

[0098] Mechanical tests: The results are shown in Table 1.

[0099]

[0100] Table 1

[0101] The technical features of the above - described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above - described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0102] The above - described embodiments only represent several implementation manners of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. A forging process for a 4330V alloy, characterized in that, It includes the following steps: Step S1, preparing a 4330V ingot: putting raw materials of each element into a vacuum furnace for melting, and obtaining an ingot blank after cooling; Step S2, heat treatment of the ingot, including the following working steps: (1), the first heat treatment stage: heating the ingot to 500±20°C and holding the temperature; (2), the second heat treatment stage: heating the ingot to 930±15°C and holding the temperature; (3), the third heat treatment stage: heating the ingot to 1230±15°C and holding the temperature, and then the ingot is naturally cooled to below 800°C; Step S3, forging the ingot, including the following working steps: The first heat treatment: performing surface treatment on the ingot, then heating the ingot in a furnace to the forging temperature of 850 - 1250°C, and then sending the ingot into a press for forging; The second heat treatment: heating the ingot in a furnace to the forging temperature of 850 - 1250°C, then sending the ingot into a press for forging, and finally the forging is air-cooled to room temperature; Step S4, machining the ingot; Step S5, the second heat treatment, including the following working steps: (4) Quenching stage: heating the ingot to 860±10°C and holding the temperature; (5) Tempering stage: heating the ingot to 560±10°C and holding the temperature, then cooling the ingot in the furnace to below 500°C and taking it out of the furnace to cool to room temperature, then heating the ingot to 560±10°C and holding the temperature, and finally cooling the ingot to room temperature; In step S3, the forging ratio of the first heat treatment and the second heat treatment > 3.0; In the first heat treatment stage of step S2, the heating rate is 1.33°C / min (80°C / h), and the holding time range is 3 - 6h; In the first heat treatment stage of step S2, the charging temperature of the ingot ≤ 400°C; In the second heat treatment stage of step S2, the heating rate is 1.33°C / min (80°C / h), and the holding time range is 2.5 - 3h; In the third heat treatment stage of step S2, the heating rate is 0.833°C / min (50°C / h), and the holding time range is 3 - 4h; In step S1, the 4330V ingot includes elements by mass percentage: C: 0.28 - 0.32%; Si: 0.05 - 0.25%; Mn: 0.50 - 0.80%; P ≤ 0.015%; S ≤ 0.010%; Cr: 1.20 - 1.50%; Mo: 0.52 - 0.60%; Ni: 3.00 - 3.50%; Cu ≤ 0.20; V: 0.10 - 0.20%; impurity elements in the alloy: O ≤ 30PPm; N ≤ 130PPm; H ≤ 2.00PPm; In the quenching stage of step S5, the heating rate is 1.33°C / min (80°C / h), and the holding time range is 8 - 12h; In the tempering stage of step S5, the heating rate is 1.33°C / min (80°C / h), and the holding time range is 5 - 12h.

2. The forging process of a 4330V alloy according to claim 1, characterized in that: In the tempering stage of step S5, the ingot is cooled to room temperature by water with a water temperature not higher than 60°C.

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