Steel for deep hole reamer and method for manufacturing the same

Abstract

The application provides a steel for deep well reamer and a manufacturing method thereof, and belongs to the technical field of steel materials. The manufacturing method of the steel for deep well reamer adopts a new smelting method, adopts refining and slag replacement, and feeds a silicon-calcium wire after vacuum to perform inclusion modification treatment, effectively controls the morphology, quantity and size of inclusions, obviously reduces the inclusion index of the steel material, reduces the generation of large-particle inclusions, improves the internal purity of the steel material, and is beneficial to the improvement of the impact toughness of the steel material; meanwhile, a new heat treatment mode is adopted to further improve the impact toughness of the steel material. The steel for deep well reamer prepared by the above preparation method has a large specification, the size of the internal inclusions of the steel material is within 10 microns, the inclusion index is less than or equal to 4.3, the purity requirement is met, the normal temperature impact energy at the position of 70mm under the skin of the steel material is more than 81J, and the steel material has good impact toughness.

Description

Technical Field

[0001] This invention relates to the field of steel technology, and in particular to a steel for deep well reamers and its manufacturing method. Background Technology

[0002] Currently, most steel used in deep well reamers is 4330V quenched and tempered round steel. Due to the requirements of its application, it needs to have high strength, specifically a tensile strength of 150KSI to 180KSI within 70mm of the surface, an inclusion index ≤4.3, and no inclusions larger than 10μm allowed. It also needs high toughness within 70mm of the surface to prevent fracture during use, an impact energy of at least 81J at room temperature within 70mm of the surface, and a microstructure of tempered martensite at 70mm. Existing manufacturing methods can produce round steel that meets these performance requirements, but its diameter is typically within 300mm.

[0003] For large-size 4330V quenched and tempered round steel (diameter ≥ 300mm), due to the large differences between the beginning and end of the ingot, using existing manufacturing methods, inclusions are often strip-shaped, easily exceeding 10μm in size, and even larger than 20μm. Furthermore, the large number and large shape of these inclusions lead to unstable impact toughness in the steel. Moreover, the larger the size, the worse the hardenability of the steel, making it prone to bainite formation at the 70mm depth, further contributing to lower impact toughness at this depth. In other words, there are currently no large-size 4330V quenched and tempered round steels on the market that meet the requirements for steel used in deep well reamers.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a steel for deep well reamers and a method for manufacturing the same. This method, by employing a new smelting method and a new heat treatment method, enables the steel for deep well reamers to have large dimensions while also possessing good purity and strength properties.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a steel for deep well reamers. The steel for deep well reamers is a large-size 4330V quenched and tempered round steel with a diameter of 300-450mm, a tensile strength of 150-180KSI within 70mm of the surface, an impact energy of ≥81J at room temperature within 70mm of the surface, and a microstructure of tempered sorbite at 70mm of the surface.

[0008] Furthermore, based on the above-mentioned technical solution of the present invention, the steel for the deep well reamer comprises the following chemical composition by mass fraction: C 0.28-0.33%, Si 0.15-0.35%, Mn 0.75-1.00%, P≤0.015%, S≤0.010%, Cr 0.75-1.10%, Ni 1.65-2.00%, Mo 0.35-0.50%, V 0.05-0.10%, with the balance being Fe and unavoidable impurities.

[0009] The present invention also provides a method for manufacturing the steel used in the above-mentioned deep well reamer, comprising the following steps:

[0010] (a) Smelting: The smelting raw materials are subjected to primary smelting, ladle refining, vacuum degassing and feeding into the silicon-calcium wire to obtain molten steel; wherein, at least one refining slag replacement is carried out during the ladle refining process;

[0011] (b) Casting: Molten steel is cast into ingots to obtain steel ingots;

[0012] (c) Forging: Forging steel ingots into round bars;

[0013] (d) Heat treatment: The round steel is subjected to annealing, normalizing, quenching and tempering in sequence to obtain steel for deep well reamers.

[0014] Furthermore, based on the above technical solution of the present invention, in step (a), refining slag replacement is performed at least once during the refining process;

[0015] Preferably, the refining slag comprises the following components in the following mass fractions: 38%–43% silicon dioxide, 13.5%–18.5% calcium oxide, 10%–15% aluminum oxide, 3%–7% magnesium oxide, 3%–8% ferric oxide, 1%–6% sodium oxide and potassium oxide, and 3%–8% fluoride ions;

[0016] Preferably, the amount of refining slag used is 10-15 kg per ton of molten steel.

[0017] Furthermore, based on the above technical solution of the present invention, in step (a), a silicon-calcium wire is fed into the molten steel through a wire feeder, and the length of the silicon-calcium wire is 1.0-1.5m / ton of molten steel.

[0018] Furthermore, based on the above-mentioned technical solution of the present invention, in step (a), an electric furnace is used for primary refining. By adding scrap steel and molten iron, the steel is then melted, dephosphorized, decarburized and alloyed in an electric furnace under an oxidizing atmosphere. The carbon content at the end of the electric furnace is ≥0.08%, the phosphorus content is controlled to be ≤0.010%, and the tapping temperature is 1650-1680℃.

[0019] And / or, after ladle refining, control the sulfur content to ≤0.005% and the tapping temperature to 1615-1635℃;

[0020] And / or, vacuum degassing, with a vacuum degree ≤0.5 Torr and a total vacuum time of 25-40 min, while using argon soft blowing for 20-35 min.

[0021] Furthermore, based on the above-mentioned technical solution of the present invention, in step (b), the molten steel is poured into the central column tube at a certain speed using the pouring method. The molten steel rises slowly from the bottom of the ingot through the slurry system, and the pouring temperature of the ladle is 1535-1545℃.

[0022] Furthermore, based on the above-mentioned technical solution of the present invention, in step (c), the steel ingot is heated to 1180-1220°C and fully heated, and then a fast forging machine is used for billet preparation and forging, and the final shape is round steel, with a final forging temperature of not less than 800°C.

[0023] Furthermore, based on the above technical solution of the present invention, in step (d), the quenching temperature is 840-870℃, and the quenching holding time is t. 淬 The range is (3H / 100mm*D+1H)~(3H / 100mm*D+4H), where H represents the hour and D represents the diameter of the round steel in mm;

[0024] And / or, the cooling method for quenching is water cooling; preferably, the round steel bars after being taken out of the furnace are suspended into the water by a chain, and the time from taking out of the furnace to just before entering the water is controlled within 3 minutes. After entering the water, the round steel bars swing up and down and always remain below the water surface for quenching.

[0025] Furthermore, based on the above technical solution of the present invention, in step (d), the annealing temperature is 660-680℃;

[0026] And / or, the normalizing temperature is 880-900℃, and the normalizing holding time is t. 正 The diameter is (2H / 100mm*D) to (2H / 100mm*D+3H), where H represents the hour and D represents the diameter in mm; the cooling method is air cooling.

[0027] And / or, the tempering temperature is 580–600℃, and the tempering holding time is t. 回 The range is (4H / 100mm*D+1H) to (4H / 100mm*D+6H), where H represents the hour and D represents the diameter in mm; the cooling method is air cooling.

[0028] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0029] (1) The present invention provides a steel for deep well reamers, which has large dimensions, good purity and strength properties.

[0030] (2) The present invention provides a method for manufacturing steel for deep well reamers. By adopting a new smelting method, using an external refining process for slag replacement and vacuum feeding of silicon-calcium wire for inclusion modification treatment, the morphology, quantity and size of inclusions are effectively controlled, resulting in a significant reduction in the inclusion index of the steel, reducing the generation of large particle inclusions, and improving the internal purity of the steel, which is conducive to improving the impact toughness of the steel. At the same time, a new heat treatment method can further improve the impact toughness of the steel.

[0031] The steel for deep well reamers prepared by this method has large dimensions, and the size of the inclusions inside the steel is within 10 micrometers, with a low inclusion index, preferably ≤4.3, which meets the purity requirements. Moreover, the area within 70mm of the steel surface is completely hardened, transforming into martensite, and after tempering, it obtains tempered sorbite, thus ensuring that the room temperature impact energy at 70mm below the surface meets more than 81J, exhibiting good impact toughness. Attached Figure Description

[0032] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0033] Figure 1 The metallographic diagrams of the steel used for deep well reamers provided in Embodiment 1 of the present invention are shown, wherein (a) is a metallographic diagram at a distance of 25.4 mm from the surface, and (b) is a metallographic diagram at a distance of 70 mm from the surface.

[0034] Figure 2 The metallographic diagrams of the steel used for deep well reamers provided in Embodiment 5 of the present invention are shown, wherein (a) is a metallographic diagram at a distance of 25.4 mm from the surface, and (b) is a metallographic diagram at a distance of 70 mm from the surface. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0036] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0037] According to a first aspect of the present invention, a steel for a deep well reamer is provided, which is a large-size 4330V quenched and tempered round steel with a diameter of 300-450mm, a tensile strength of 150-180KSI within 70mm below the surface, a microstructure of tempered martensite at 70mm below the surface, and an impact energy of ≥81J at room temperature within 70mm below the surface.

[0038] In this invention, "large-size 4330V quenched and tempered round steel" refers to 4330V quenched and tempered round steel with a diameter of 300-450mm, typically but not limitingly, to 300mm, 320mm, 340mm, 350mm, 360mm, 380mm, 400mm, 420mm, 440mm or 450mm, and any numerical range between any two points.

[0039] The large-size 4330V quenched and tempered round steel provided by this invention has excellent strength properties, namely, a tensile strength of 150-180 KSI within 70 mm of the subsurface, with typical non-limiting tensile strengths being 150 KSI, 155 KSI, 160 KSI, 165 KSI, 170 KSI, 175 KSI, or 180 KSI. The microstructure of this large-size 4330V quenched and tempered round steel at 70 mm of the subsurface is tempered sorbite, thus ensuring high room temperature impact energy, namely ≥81J within 70 mm of the subsurface, for example, 82J, 84J, 85J, 86J, 88J, or 90J.

[0040] As an optional embodiment of the present invention, the steel for deep well reamers comprises the following chemical composition by mass fraction: C 0.28-0.33%, Si 0.15-0.35%, Mn 0.75-1.00%, P≤0.015%, S≤0.010%, Cr 0.75-1.10%, Ni 1.65-2.00%, Mo 0.35-0.50%, V 0.05-0.10%, with the balance being Fe and unavoidable impurities.

[0041] The typical but non-limiting mass fractions of C are 0.28%, 0.29%, 0.30%, 0.31%, 0.32%, or 0.33%; the typical but non-limiting mass fractions of Si are 0.15%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, 0.29%, 0.30%, 0.31%, 0.32%, 0.33%, or 0.35%; the typical but non-limiting mass fractions of Mn are 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, or 1.00%; the typical but non-limiting mass fractions of P are 0.015%, 0.012%, 0.010%, 0.008%, or 0.006%, etc.; and the typical but non-limiting mass fractions of S are 0.010%, 0.009%, etc. Typical but non-limiting mass fractions of Cr are 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1.00%, 1.05%, or 1.10%; typical but non-limiting mass fractions of Ni are 1.65%, 1.70%, 1.75%, 1.80%, 1.85%, 1.90%, 1.95%, or 2.00%; typical but non-limiting mass fractions of Mo are 0.35%, 0.38%, 0.40%, 0.42%, 0.45%, 0.48%, or 0.50%; typical but non-limiting mass fractions of V are 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, or 0.10%.

[0042] According to a second aspect of the present invention, a method for manufacturing the steel for deep well reamers described above is also provided, comprising the following steps:

[0043] (a) Smelting: The smelting raw materials are subjected to primary smelting, ladle refining, vacuum degassing and feeding into the silicon-calcium wire to obtain molten steel; wherein, at least one refining slag replacement is carried out during the ladle refining process;

[0044] (b) Casting: Molten steel is cast into ingots to obtain steel ingots;

[0045] (c) Forging: Forging steel ingots into round bars;

[0046] (d) Heat treatment: The round steel is subjected to annealing, normalizing, quenching and tempering in sequence to obtain steel for deep well reamers.

[0047] In step (a), the primary refining mainly utilizes a heat source to provide heat to the smelting raw materials. Its main functions are to molten steel, dephosphorize, desulfurize, and alloy the steel. Ladle refining, also known as secondary steelmaking, involves degassing, deoxidizing, and desulfurizing the molten steel from the primary refining in a container with inert gas, removing inclusions, and fine-tuning the composition.

[0048] In conventional manufacturing methods, molten steel refined outside the ladle is directly degassed under vacuum, and then directly cast. The manufacturing method of this invention differs from this, adding a slag replacement step during the refining process and a process of feeding a silicon-calcium wire after vacuum degassed.

[0049] Refining slag replacement refers to replacing the refining slag at least once during the refining process. The purpose of refining slag replacement is to further adsorb inclusions in the molten steel, making the molten steel purer and ensuring that the inclusion content B (fine series) of the steel is ≤1 grade (refer to the national standard "GB / T10561-2023 Determination of Non-metallic Inclusion Content in Steel - Standard Rating Chart Microscopic Examination Method"), thereby reducing the adverse effects of oxide inclusions on the impact toughness of the steel.

[0050] After refining and slag replacement, vacuum degassing is performed. The purpose of vacuum degassing is to remove hydrogen and oxygen, control nitrogen within a suitable range, remove non-metallic inclusions, and improve the purity of the molten steel. After vacuum degassing, a silicon-calcium wire is fed in to perform non-metallic inclusion modification treatment, changing the morphology and quantity of inclusions, which is beneficial to improving the impact toughness of the steel.

[0051] Step (b) casting involves casting the molten steel obtained in step (a) into shape, and step (c) involves further forging the shaped steel ingot.

[0052] The heat treatment process in step (d) includes annealing, normalizing, quenching, and tempering. Annealing, performed on the forged round steel, primarily removes hydrogen and prevents white spots from forming. Normalizing mainly improves the internal microstructure of the steel, refining the grains to obtain a balanced pearlite structure. Quenching primarily produces a martensitic structure; after quenching, timely tempering is necessary to prevent cracking and to obtain a tempered sorbite structure.

[0053] The manufacturing method of steel for deep well reamers provided by this invention employs a new smelting method, using refining and slag replacement, as well as vacuum feeding with a silicon-calcium wire to modify inclusions. This effectively controls the morphology, quantity, and size of inclusions, resulting in a significant reduction in the steel inclusion index and a decrease in the generation of large-particle inclusions. This improves the internal purity of the steel and thus enhances its impact toughness. Furthermore, the new heat treatment method further improves the impact toughness of the steel.

[0054] The steel for deep well reamers prepared by this method has large dimensions, and the size of the inclusions inside the steel is within 10 micrometers, with a low inclusion index, preferably ≤4.3, which meets the purity requirements. Moreover, the area within 70mm of the steel surface is completely hardened, transforming into martensite, and after tempering, it obtains tempered sorbite, thus ensuring that the room temperature impact energy at 70mm below the surface meets more than 81J, exhibiting good impact toughness.

[0055] As an optional embodiment of the present invention, in step (a), an electric furnace is used for primary refining. By adding scrap steel and molten iron, the steel is then melted, dephosphorized, decarburized, and primarily alloyed in a furnace under an oxidizing atmosphere. The carbon content at the end of the electric furnace is ≥0.08%, and the phosphorus (P) content is controlled to be ≤0.010% (e.g., 0.010%, 0.009%, 0.008%, 0.006%, 0.005%, 0.004%, etc.). The tapping temperature is then 1650-1680℃ (typically but not limitingly 1650℃, 1652℃, 1655℃, 1658℃, 1660℃, 1662℃, 1665℃, 1668℃, 1670℃, 1672℃, 1675℃, 1678℃, or 1680℃).

[0056] In one optional embodiment of the present invention, in step (a), the molten steel that has been pre-refined in the electric furnace is transferred to an LF refining furnace for refining. The pre-refined molten steel is degassed, deoxidized, and desulfurized in a container under vacuum, inert gas, or reducing atmosphere to remove inclusions and fine-tune the composition, controlling the sulfur content to be ≤0.005% (e.g., 0.005%, 0.004%, 0.003%, 0.002%, 0.001%, etc.). After ladle refining, the tapping temperature is 1615-1635℃ (typically but not limitingly 1615℃, 1618℃, 1620℃, 1622℃, 1625℃, 1628℃, 1630℃, 1632℃, 1634℃, or 1635℃).

[0057] As an optional embodiment of the present invention, in step (a), in the later stage of the LF refining furnace, the refining slag on the surface of the molten steel is poured off and replaced with new refining slag (10-15 kg of refining slag is added per ton of molten steel, such as 10 kg, 12 kg, 14 kg or 15 kg, etc.), which is then melted and covered on the surface of the molten steel.

[0058] In a preferred embodiment of the present invention, the refining slag comprises the following components in the indicated mass fractions: 38%–43% silicon dioxide, 13.5%–18.5% calcium oxide, 10%–15% aluminum oxide, 3%–7% magnesium oxide, 3%–8% ferric oxide, 1%–6% sodium oxide and potassium oxide, and 3%–8% fluoride ions. Typical but not limited mass fractions of silicon dioxide are 38%, 39%, 40%, 42%, or 43%, etc.; typical but not limited mass fractions of calcium oxide are 13.5%, 14%, 15%, 16%, 17%, 18%, or 18.5%, etc.; typical but not limited mass fractions of aluminum oxide are 10%, 11%, 12%, 13%, 14%, or 15%, etc.; typical but not limited mass fractions of magnesium oxide are 3%, 4%, 5%, 6%, or 7%, etc.; typical but not limited mass fractions of ferric oxide are 3%, 4%, 5%, 6%, or 8%, etc.; typical but not limited mass fractions of sodium oxide and potassium oxide are 1%, 2%, 3%, 4%, 5%, or 6%, etc.; typical but not limited mass fractions of fluoride ions are 3%, 4%, 5%, 6%, or 8%, etc.

[0059] As an optional embodiment of the present invention, in step (a), vacuum degassing is performed using an RH or VD furnace, argon gas is used for soft blowing, the vacuum pump is started to evacuate the gas until the pressure in the chamber reaches the required vacuum level, the ultimate vacuum level is ≤0.5 Torr, and it is maintained for a period of time. The total vacuum time is 25-40 min (e.g., 25 min, 28 min, 30 min, 32 min, 35 min, 38 min or 40 min), and the soft blowing time is 20-35 min (e.g., 20 min, 22 min, 25 min, 28 min, 30 min, 32 min or 35 min).

[0060] In an optional embodiment of the present invention, in step (a), after the molten steel is vacuum degassed in an RH or VD furnace, a silicon-calcium wire is fed into the molten steel through a wire feeder. The length of the silicon-calcium wire is 1.0-1.5 m / ton of molten steel (e.g., 1.0 m / ton, 1.1 m / ton, 1.2 m / ton, 1.3 m / ton, 1.4 m / ton, or 1.5 m / ton). If the length of the silicon-calcium wire is less than 1.0 m / ton of molten steel, it may lead to an increase in the inclusion index, thereby causing a decrease in the room temperature impact energy.

[0061] As an optional embodiment of the present invention, in step (b), the molten steel is poured into the central column tube at a certain speed using the bottom pouring method. The molten steel rises slowly from the bottom of the ingot through the slurry system. The pouring temperature of the ladle is 1535-1545℃ (e.g., 1535℃, 1536℃, 1538℃, 1540℃, 1542℃, 1544℃ or 1545℃, etc.).

[0062] As an optional embodiment of the present invention, in step (c), the steel ingot is heated to 1180-1220°C (e.g., 1180°C, 1185°C, 1190°C, 1195°C, 1200°C, 1205°C, 1210°C, 1215°C, or 1220°C, etc.) and fully heated. Then, it is forged and shaped using a high-speed forging machine, and the final shape is round steel. The final forging temperature is not lower than 800°C (e.g., 800°C, 805°C, 810°C, 815°C, 820°C, 825°C, or 830°C, etc.).

[0063] As an optional embodiment of the present invention, in step (d), the annealing temperature is 660-680°C, and typical but non-limiting annealing temperatures are 660°C, 662°C, 665°C, 668°C, 670°C, 672°C, 675°C, 678°C or 680°C, etc.

[0064] As an optional embodiment of the present invention, in step (d), after annealing, high and low magnification inspections are performed (inclusions, low magnification, composition and gas, austenite grain size), the steel is straightened to prevent bending from affecting subsequent heat treatment, and then the steel surface is peeled and magnetic particle testing is performed to ensure that there are no defects on the surface before quenching, and ultrasonic testing is performed on the inside of the steel to check whether the internal quality of the steel meets the standards.

[0065] In an optional embodiment of the present invention, in step (d), the normalizing temperature is 880–900°C (e.g., 880°C, 882°C, 884°C, 885°C, 886°C, 888°C, 890°C, 892°C, 894°C, 895°C, 896°C, 898°C, or 900°C), and the normalizing holding time is t. 正 The formula is (2H / 100mm*Dmm) to (2H / 100mm*Dmm+3H), where H represents the hour and D represents the diameter (mm), and the cooling method is air cooling. For example, when the diameter of the round steel is 450mm, according to the above formula, the normalizing holding time t 正 The normalizing holding time is 9–12 hours, and when the diameter of the round steel is 400 mm, the holding time is t. 正 It takes 8 to 11 hours, and so on.

[0066] In an optional embodiment of the present invention, in step (d), the quenching temperature is 840–870℃ (e.g., 840℃, 842℃, 844℃, 845℃, 846℃, 848℃, 850℃, 852℃, 854℃, 855℃, 856℃, 858℃, 860℃, 862℃, 864℃, 865℃, 868℃, or 870℃), and the quenching holding time is t. 淬The quenching holding time is (3H / 100mm*Dmm+1H) to (3H / 100mm*Dmm+4H), where H represents the hour and D represents the diameter (mm); the cooling method is water cooling. For example, when the diameter of the round steel is 450mm, according to the above formula, the quenching holding time t... 淬 The quenching holding time is 14.5–17.5 hours, and when the diameter of the round steel is 400 mm, the quenching holding time is t. 淬 It takes 13 to 16 hours, and so on.

[0067] In a preferred embodiment of the present invention, in step (d), the steel after being taken out of the furnace is lowered into the water by a chain. The time from taking out of the furnace to just before being put into the water is controlled within 3 minutes (e.g., 1 minute, 1.5 minutes, 2 minutes, 2.5 minutes or 3 minutes). After the steel is put into the water, it swings up and down and always stays below the water surface for quenching.

[0068] The steel is lowered into the water using a chain and swung up and down below the surface to break the air film on the steel surface and accelerate cooling. The cooling time is determined according to the specifications. After the steel is removed from the water, its surface temperature is controlled below 90℃ to ensure that the surface microstructure fully transforms into martensite.

[0069] The immersion time should be controlled within 3 minutes to ensure that the surface temperature of the steel is not too low. If the immersion temperature is too low, the cooling effect of the steel will be poor and the depth of the quenched layer will be shallow.

[0070] In an optional embodiment of the present invention, in step (d), the tempering temperature is 580–600°C, and the tempering holding time is t. 回 The range is (4H / 100mm*Dmm+1H) to (4H / 100mm*Dmm+6H), where H represents the hour and D represents the diameter (mm), and the cooling method is air cooling. For example, when the diameter of the round steel is 450mm, according to the above formula, the tempering holding time t 回 The tempering holding time is 19–24 hours, and when the diameter of the round steel is 400 mm, the tempering holding time is t. 回 It takes 17 to 22 hours, and so on.

[0071] After tempering, steel needs to be straightened and stress-relieved to ensure that the internal stress of the steel is reduced to a minimum and to prevent deformation in subsequent processing.

[0072] Meanwhile, after the steel passes the tensile and impact mechanical property tests, internal ultrasonic testing and external magnetic particle testing are performed to ensure that the steel is defect-free before packaging and warehousing. The ultrasonic testing grade is GB / T4162 Class B, and the magnetic particle testing accuracy is controlled to a defect rate of 0.3mm.

[0073] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0074] Example 1

[0075] This embodiment provides a method for manufacturing steel for deep well reamers, including the following steps:

[0076] (a) Smelting

[0077] Primary refining: The smelting raw materials are primary refined in an electric furnace by adding scrap steel and molten iron, and then melting, dephosphorizing, decarburizing and main alloying are carried out in an oxidizing atmosphere. The carbon content at the end of the electric furnace is 0.12%, the phosphorus content is controlled at 0.005%, and the tapping temperature is 1650℃.

[0078] Ladle refining: The molten steel, initially refined in the electric arc furnace, is transferred to the LF refining furnace for further refining. The initially refined molten steel undergoes degassing, deoxidation, desulfurization, inclusion removal, and composition fine-tuning in a reducing atmosphere, controlling the sulfur content to 0.002%. The tapping temperature is 1620℃.

[0079] Meanwhile, in the later stages of the LF refining furnace, the refining slag on the surface of the molten steel is discarded and replaced with new refining slag, which, after melting, covers the surface of the molten steel. The refining slag includes the following components by mass fraction: silicon dioxide 41%–43%, calcium oxide 13.5%–15%, aluminum oxide 13%–15%, magnesium oxide 5%–7%, ferric oxide 6%–8%, sodium oxide and potassium oxide 5%–6%, and fluoride ions 6%–8%. The amount of refining slag used is 10 kg per ton of molten steel.

[0080] Vacuum degassing: Vacuum degassing is performed using an RH or VD furnace, with argon gas soft blowing. The vacuum pump is started to evacuate the air until the pressure in the chamber reaches the required vacuum level, with an ultimate vacuum level ≤ 0.5 Torr, and is maintained for a period of time. The total vacuum time is 30 minutes, and the argon gas soft blowing time is 25 minutes.

[0081] Feeding silicon-calcium wire: After the molten steel is degassed in a vacuum furnace using an RH or VD furnace, silicon-calcium wire is fed into the molten steel through a wire feeder. A length of 20m of silicon-calcium wire corresponds to 20 tons of molten steel, that is, 1.0m / ton of molten steel, to obtain molten steel.

[0082] (b) Casting

[0083] The molten steel is poured into the central column tube at a certain speed using the bottom pouring method. The molten steel rises slowly from the bottom of the ingot through the slurry system, and the pouring temperature in the ladle is 1540℃.

[0084] (c) Forging

[0085] The steel ingot is heated to 1200℃ and fully heated. Then, it is forged and shaped using a high-speed forging machine. The final shape is round steel with a diameter of 450mm. The final forging temperature is not lower than 800℃.

[0086] (d) Heat treatment

[0087] The round steel bars are subjected to annealing, normalizing, quenching and tempering in sequence.

[0088] The annealing temperature is 670℃;

[0089] The normalizing temperature is 890℃, and the normalizing holding time is t. 正 The duration is 10 hours, and the normalizing cooling method is air cooling;

[0090] The quenching temperature is 860℃, and the quenching holding time is t. 淬 The quenching time is 16 hours, and the quenching cooling method is water cooling. Specifically, the normalized round steel is suspended into the water by a chain. The time from when it comes out of the furnace to when it is about to enter the water is controlled within 2 minutes. After the round steel enters the water, it swings up and down and always keeps the round steel below the water surface for quenching.

[0091] The tempering temperature is 595℃, and the tempering holding time is t. 回 It lasts for 20 hours.

[0092] After tempering, steel needs to be straightened and stress-relieved to ensure that the internal stress of the steel is reduced to a minimum and to prevent deformation in subsequent processing.

[0093] Meanwhile, after the steel passes the mechanical performance tests such as tensile and impact tests, internal ultrasonic testing (ultrasonic testing grade GB / T4162 B) and external magnetic particle testing (magnetic particle testing accuracy is controlled at 0.3mm defects) are carried out to ensure that the steel is free of defects before it is packaged and put into storage, and finally the steel for deep well reamers is obtained.

[0094] The steel used for this deep well reamer has the following chemical composition by mass fraction: C 0.30%, Si 0.25%, Mn 0.92%, P 0.006%, S 0.002%, Cr 1.05%, Ni 1.97%, Mo 0.45%, V 0.08%, with the balance being Fe and unavoidable impurities.

[0095] Example 2

[0096] This embodiment provides a method for manufacturing steel for deep well reamers. Except for step (a), where the length of the silicon-calcium wire fed in is 30m corresponding to 20 tons of molten steel, i.e., 1.5m / ton of molten steel, the other steps are the same as in embodiment 1.

[0097] The steel used for this deep well reamer has the following chemical composition by mass fraction: C 0.31%, Si 0.24%, Mn 0.93%, P 0.007%, S 0.003%, Cr 1.06%, Ni 1.98%, Mo 0.46%, V 0.079%, with the balance being Fe and unavoidable impurities.

[0098] Example 3

[0099] This embodiment provides a method for manufacturing steel for deep well reamers. Except for step (a), where the length of the silicon-calcium wire fed in is 16m corresponding to 20 tons of molten steel, i.e., 0.8m / ton of molten steel, the other steps are the same as in embodiment 1.

[0100] The steel used for this deep well reamer has the following chemical composition by mass fraction: C 0.30%, Si 0.26%, Mn 0.94%, P 0.006%, S 0.002%, Cr 1.03%, Ni 1.96%, Mo 0.45%, V 0.081%, with the balance being Fe and unavoidable impurities.

[0101] Example 4

[0102] This embodiment provides a method for manufacturing steel for deep well reamers. Except for step (d) quenching, in which the normalized round steel is suspended into water by a chain and the time from taking it out of the furnace to just before it is about to enter the water is controlled at 3.5 minutes, the round steel swings up and down after entering the water and always stays below the water surface for quenching, the rest of the steps are the same as in embodiment 1.

[0103] The steel used for this deep well reamer has the following chemical composition by mass fraction: C 0.31%, Si 0.25%, Mn 0.95%, P 0.008%, S 0.0025%, Cr 1.04%, Ni 1.97%, Mo 0.46%, V 0.082%, with the balance being Fe and unavoidable impurities.

[0104] Example 5

[0105] This embodiment provides a method for manufacturing steel for deep well reamers. Except for step (d), which uses a conventional quenching method, that is, the normalized round steel is suspended into water by a chain and the time from taking it out of the furnace to just before it is about to enter the water is controlled within 2 minutes. After the round steel enters the water, it remains stationary and always stays below the water surface for quenching. The remaining steps are the same as in embodiment 1.

[0106] The steel used for this deep well reamer has the following chemical composition by mass fraction: C 0.30%, Si 0.24%, Mn 0.92%, P 0.006%, S 0.002%, Cr 1.06%, Ni 1.98%, Mo 0.45%, V 0.079%, with the balance being Fe and unavoidable impurities.

[0107] Example 6

[0108] This embodiment provides a method for manufacturing steel for deep well reamers, including the following steps:

[0109] (a) Smelting

[0110] Primary refining: The raw materials are primary refined in an electric furnace by adding scrap steel and molten iron, and then melting, dephosphorizing, decarburizing and main alloying are carried out in an oxidizing atmosphere. The carbon content at the end of the electric furnace is 0.08%, the phosphorus content is controlled at 0.010%, and the tapping temperature is 1680℃.

[0111] Ladle refining: The molten steel that has been initially refined in the electric furnace is transferred to the LF refining furnace for further refining. The initially refined molten steel is degassed, deoxidized, desulfurized, and has inclusions removed and composition fine-tuned in a reducing atmosphere container, with the sulfur content controlled at 0.005% and the tapping temperature at 1635℃.

[0112] Refining and slag replacement: In the later stages of LF refining furnace, the refining slag on the surface of the molten steel is discarded and replaced with new refining slag, which, after melting, covers the surface of the molten steel. The refining slag includes the following components by mass fraction: silicon dioxide 41%–43%, calcium oxide 13.5%–15%, aluminum oxide 13%–15%, magnesium oxide 5%–7%, ferric oxide 6%–8%, sodium oxide and potassium oxide 5%–6%, and fluoride ions 6%–8%. The amount of refining slag added is 10 kg per ton of molten steel.

[0113] Vacuum degassing: Vacuum degassing is performed using an RH or VD furnace, with argon gas soft blowing. The vacuum pump is started to evacuate the air until the pressure in the chamber reaches the required vacuum level, with an ultimate vacuum level ≤ 0.5 Torr, and is maintained for a period of time. The total vacuum time is 25 minutes, and the argon gas soft blowing time is 20 minutes.

[0114] Feeding silicon-calcium wire: After the molten steel is degassed in a vacuum furnace by RH or VD furnace, silicon-calcium wire is fed into the molten steel through a wire feeder. The length of the silicon-calcium wire is 60m, which corresponds to 50 tons of molten steel, that is, 1.2m / ton of molten steel, to obtain molten steel.

[0115] (b) Casting

[0116] The molten steel is poured into the central column tube at a certain speed using the bottom pouring method. The molten steel rises slowly from the bottom of the ingot through the slurry system, and the pouring temperature in the ladle is 1545℃.

[0117] (c) Forging

[0118] The steel ingot is heated to 1220℃ and fully heated. Then, it is forged and shaped using a high-speed forging machine. The final shape is round steel with a diameter of 440mm. The final forging temperature is not lower than 800℃.

[0119] (d) Heat treatment

[0120] The round steel bars are subjected to annealing, normalizing, quenching and tempering in sequence.

[0121] The annealing temperature is 680℃;

[0122] The normalizing temperature is 900℃, and the normalizing holding time is t. 正 The duration is 9 hours, and the normalizing cooling method is air cooling;

[0123] The quenching temperature is 870℃, and the quenching holding time is t. 淬 The quenching time is 15 hours, and the quenching cooling method is water cooling. Specifically, the normalized round steel is suspended into the water by a chain. The time from when it comes out of the furnace to when it is about to enter the water is controlled within 3 minutes. After the round steel enters the water, it swings up and down and always keeps the round steel below the water surface for quenching.

[0124] The tempering temperature is 600℃, and the tempering holding time is t. 回 It takes 19 hours.

[0125] After tempering, steel needs to be straightened and stress-relieved to ensure that the internal stress of the steel is reduced to a minimum and to prevent deformation in subsequent processing.

[0126] Meanwhile, after the steel passes the mechanical performance tests such as tensile and impact tests, internal ultrasonic testing (ultrasonic testing grade GB / T4162 B) and external magnetic particle testing (magnetic particle testing accuracy is controlled at 0.3mm defects) are carried out to ensure that the steel is free of defects before it is packaged and put into storage, and finally the steel for deep well reamers is obtained.

[0127] The steel used for this deep well reamer has the following chemical composition by mass fraction: C 0.31%, Si 0.26%, Mn 0.93%, P 0.007%, S 0.003%, Cr 1.05%, Ni 1.96%, Mo 0.46%, V 0.081%, with the balance being Fe and unavoidable impurities.

[0128] Comparative Example 1

[0129] This comparative example provides a method for manufacturing steel for deep well expanders. Except for the absence of a refining and slag-changing step in the ladle refining process, the other steps are the same as in Example 1.

[0130] The steel used for this deep well reamer has the following chemical composition by mass fraction: C 0.30%, Si 0.23%, Mn 0.94%, P 0.005%, S 0.002%, Cr 1.04%, Ni 1.97%, Mo 0.45%, V 0.082%, with the balance being Fe and unavoidable impurities.

[0131] Comparative Example 2

[0132] This comparative example provides a method for manufacturing steel for deep well reamers. Except that the silicon-calcium wire is not fed in after vacuum degassing, i.e., the casting is carried out directly after vacuum degassing, the other steps are the same as in Example 1.

[0133] The steel used for this deep well reamer has the following chemical composition by mass fraction: C 0.31%, Si 0.25%, Mn 0.95%, P 0.006%, S 0.0025%, Cr 1.03%, Ni 1.98%, Mo 0.46%, V 0.08%, with the balance being Fe and unavoidable impurities.

[0134] To further verify the technical effects of the above embodiments and comparative examples, the following experimental examples are provided.

[0135] Experimental Example 1

[0136] Taking Examples 1 and 5 as examples, metallographic samples were taken from the steel used for the deep well reamers provided in Examples 1 and 5, respectively. The samples were ground and polished to a smooth surface according to the national standard GB / T 13298-2015 "Metallic Microstructure Examination Method". Subsequently, the sample surface was etched with 4% nitric acid alcohol (10s), and the metallographic structure was examined using a German Scope.A1 metallographic microscope. Specifically, as follows... Figure 1 and Figure 2 As shown. Figure 1 The metallographic images are of the metallographic specimens in Example 1, where (a) is the metallographic image at a distance of 25.4 mm from the surface and (b) is the metallographic image at a distance of 70 mm from the surface. Figure 2 The metallographic images are of the metallographic specimens in Example 5, where (a) is the metallographic image at a distance of 25.4 mm from the surface and (b) is the metallographic image at a distance of 70 mm from the surface.

[0137] As can be seen from the figure, the microstructure at a distance of 25.4 mm from the surface in Example 1 is tempered sorbite. Figure 1 (a) The tissue at the same location as in Example 5 is consistent, see [example]. Figure 2 (a). In Example 1, the microstructure at a distance of 70 mm from the surface is tempered sorbite, see... Figure 1 (b) In Example 5, the microstructure of the same area was tempered sorbite with a large amount of bainite, see Figure 2 (b) The significant difference between the two indicates that the quenching method of the present invention has a better cooling effect and a deeper hardened layer in the steel than the conventional quenching method.

[0138] Experiment Example 2

[0139] The steel used for deep well reamers provided in each embodiment and comparative example was subjected to inclusion detection. The samples were ground and polished to a smooth surface in accordance with the national standard GB / T 30834-2014 Evaluation and Statistical Scanning Electron Microscopy Method for Non-metallic Inclusions in Steel. The inclusions were then detected using an explorer 4 metal quality analyzer. The specific results are shown in Table 1.

[0140] Table 1

[0141]

[0142]

[0143] As can be seen from the data in Table 1, by comparing different silicon-calcium wire feeding methods in the examples, when the silicon-calcium wire length is controlled at 1.0-1.5 m / ton of molten steel, the inclusion index is ≤4.3. When the silicon-calcium wire length is reduced to 0.8 m / ton of molten steel, the inclusion index exceeds 4.3, and the total number of inclusions with a size >5 μm increases. In addition, by comparing the two cases of no refining slag replacement and no silicon-calcium wire feeding, the inclusion index exceeds 10 in both cases, and the total number of inclusions with a size >5 μm increases significantly.

[0144] The mechanical properties of the steel used in the deep well reamers provided in each embodiment and comparative example were tested after quenching and tempering. Yield strength and tensile strength tests were conducted according to ASTM E8 standards, and the 21°C longitudinal impact KV8 test was conducted according to ASTM E23 standards. Specific results are shown in Table 2. It should be noted that the three sets of data for the 21°C longitudinal impact KV8 in Table 2 represent test values ​​from three consecutive tests. To determine whether the impact energy meets the relevant requirements (≥81J), the average of the three sets of data can be calculated and compared with the relevant requirements (≥81J).

[0145] Table 2

[0146]

[0147]

[0148] As can be seen from the data in Table 2, by comparing the feeding of different silicon-calcium wires in Examples 1, 2, and 6, when the length of the silicon-calcium wire was controlled at 1.0-1.5 m / ton of molten steel, the room temperature impact energy was ≥81 J. When the silicon-calcium wire was reduced to 0.8 m / ton of molten steel in Example 3, the room temperature impact energy decreased to 68 J to 80 J. In addition, by comparing the two cases of no refining slag replacement and no silicon-calcium wire feeding in Examples 1 and 2, the room temperature impact energy decreased significantly due to the large number of inclusions, both ranging from 40 J to 70 J. At the same time, by using the conventional quenching method in Example 5, due to the poor cooling effect, the room temperature impact energy at 70 mm from the surface also decreased, falling below 81 J.

[0149] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A type of steel for deep well reamers, characterized in that, The steel used in the deep well reamer is a large-size 4330V quenched and tempered round steel with a diameter of 300-450mm. The tensile strength within 70mm of the subcutaneous layer is 150-180KSI, the room temperature impact energy within 70mm of the subcutaneous layer is ≥81J, and the microstructure at 70mm of the subcutaneous layer is tempered sorbite. The steel used for the deep well reamer has the following chemical composition by mass fraction: C 0.28-0.33%, Si 0.15-0.35%, Mn 0.75-1.00%, P≤0.015%, S≤0.010%, Cr 0.75-1.10%, Ni 1.65-2.00%, Mo 0.35-0.50%, V 0.05-0.10%, with the balance being Fe and unavoidable impurities; The method for manufacturing the steel used in the deep well reamer includes the following steps: (a) Smelting: The smelting raw materials are subjected to primary smelting, ladle refining, vacuum degassing and feeding into the silicon-calcium wire to obtain molten steel; wherein, at least one refining slag replacement is carried out during the ladle refining process, and the amount of refining slag used is 10-15 kg of refining slag per ton of molten steel. After vacuum degassing, silicon-calcium wire is fed into the molten steel through a wire feeder, with the amount of silicon-calcium wire added being 1.0-1.5 meters per ton of molten steel; (b) Casting: Molten steel is cast into ingots to obtain steel ingots; (c) Forging: Forging steel ingots into round bars; (d) Heat treatment: The round steel is subjected to annealing, normalizing, quenching and tempering in sequence to obtain steel for deep well reamers; The cooling method for quenching is as follows: the round steel bars after being taken out of the furnace are suspended into the water by a chain, and the time from taking out of the furnace to just before entering the water is controlled within 3 minutes. After entering the water, the round steel bars swing up and down and always remain below the water surface.

2. The steel for deep well reamers according to claim 1, characterized in that, In step (a), the refining slag comprises the following components in the following mass fractions: silicon dioxide 38-43%, calcium oxide 13.5-18.5%, aluminum oxide 10-15%, magnesium oxide 3-7%, ferric oxide 3-8%, sodium oxide and potassium oxide 1-6%, and fluoride ions 3-8%.

3. The steel for deep well reamers according to claim 1, characterized in that, In step (a), an electric furnace is used for primary refining. By adding scrap steel and molten iron, the steel is then melted, dephosphorized, decarburized, and primarily alloyed in an oxidizing atmosphere in the electric furnace. The carbon content at the end of the electric furnace is ≥0.08%, the phosphorus content is controlled to be ≤0.010%, and the tapping temperature is 1650-1680℃. And / or, after ladle refining, control the sulfur content to ≤0.005% and the tapping temperature to 1615-1635℃; And / or, vacuum degassing, with a vacuum degree ≤0.5 Torr and a total vacuum time of 25-40 min, while using argon soft blowing for 20-35 min.

4. The steel for deep well reamers according to claim 1, characterized in that, In step (b), the molten steel is poured into the central column tube at a certain speed using the bottom pouring method. The molten steel rises slowly from the bottom of the ingot through the slurry system, and the pouring temperature in the ladle is 1535-1545℃.

5. The steel for deep well reamers according to claim 1, characterized in that, In step (c), the steel ingot is heated to 1180-1220℃ and fully heated. Then, it is forged and shaped using a high-speed forging machine, and the final shape is round steel. The final forging temperature is not lower than 800℃.

6. The steel for deep well reamers according to claim 1, characterized in that, In step (d), the quenching temperature is 840–870℃, and the quenching holding time is t. 淬 The range is (3H / 100mm*D+1H) to (3H / 100mm*D+4H), where H represents the hour and D represents the diameter of the round steel in mm.

7. The steel for deep well reamers according to claim 1, characterized in that, In step (d), the annealing temperature is 660-680℃; And / or, the normalizing temperature is 880-900℃, and the normalizing holding time is t. 正 The diameter is (2H / 100mm*D) to (2H / 100mm*D+3H), where H represents the hour and D represents the diameter in mm; the cooling method is air cooling. And / or, the tempering temperature is 580–600℃, and the tempering holding time is t. 回 The range is (4H / 100mm*D+1H) to (4H / 100mm*D+6H), where H represents the hour and D represents the diameter in mm; the cooling method is air cooling.

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