Bar for deep well in desert and preparation method thereof

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a bar for a desert deep well and a preparation method of the bar, the bar for the desert deep well comprises the following chemical components in percentage by weight: 0.19-0.22% of C, 0.15-0.35% of Si, 0.45-0.55% of Mn, less than or equal to 0.010% of P, less than or equal to 0.001% of S, 0.45-0.55% of Cr, 0.70-0.80% of Mo, 0.02-0.05% of Nb, 0.09-0.11% of V, 0.01-0.025% of Al, 0.01-0.025% of Ti, 0.0015-0.0025% of B, less than or equal to 0.15% of Cu, less than or equal to 0.15% of Ni, less than or equal to 0.020% of Sn, less than or equal to 0.020% of As, less than According to the invention, reasonable component design is carried out on the bar material, so that the bar material has better corrosion resistance and hydrogen induced cracking resistance, and the bar material is suitable for extreme weather in desert areas, and is especially suitable for oil wells with the depth of more than 5000 meters.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a rod for desert deep wells and a preparation method thereof. Background Art

[0002] Steel is an important basic consumable in the process of oil development and production. Some oil wells mined in the desert can reach a depth of more than 10,000 meters. These oil wells are called desert deep wells. Rods for desert deep wells need to work in high temperature, high pressure, and corrosive environments, that is, their use conditions are harsh. Therefore, high requirements are placed on the performance of steel. They must have high strength, high toughness, high temperature resistance, corrosion resistance, strong resistance to hydrogen-induced cracking (HIC) and resistance to sulfur stress corrosion cracking (SSC).

[0003] Corrosion can seriously affect the service life of steel. The steel used in some oil fields has serious corrosion problems two or three years after being put into production. Some are scrapped after five or six years of use due to severe corrosion. The problems caused by steel corrosion will not only reduce the transportation efficiency of the pipeline, but also increase the difficulty of pipeline operation and maintenance. Therefore, the development of steel with corrosion-resistant properties has great promotion and application value for harsh application environments such as deep wells in deserts. Summary of the invention

[0004] The purpose of the present invention is to provide a rod for desert deep wells and a preparation method thereof, which specifically adopts the following technical scheme:

[0005] The invention discloses a rod for desert deep wells, which comprises the following chemical components by weight percentage: C: 0.19-0.22%, Si: 0.15-0.35%, Mn: 0.45-0.55%, P: ≤0.010%, S: ≤0.001%, Cr: 0.45-0.55%, Mo: 0.70-0.80%, Nb: 0.02-0.05%, V: 0.09-0.11%, A l: 0.01~0.025%, Ti: 0.01~0.025%, B: 0.0015~0.0025%, Cu: ≤0.15%, Ni: ≤0.15%, Sn: ≤0.020%, As: ≤0.020%, Pb: ≤0.020%, Sb: ≤0.020%, Bi: ≤0.020%, Ca: 0.001~0.005%, the balance is Fe and unavoidable impurities.

[0006] The present invention also provides a method for preparing a rod for a desert deep well, which is characterized by comprising the following steps:

[0007] 1) Production preparation: The composition of molten iron is measured by weight percentage, P is controlled at ≤0.150%, preferably P is controlled at ≤0.140%; Si is controlled at 0.25-0.80%, preferably Si is controlled at 0.25-0.40%; S is controlled at 0.001-0.040%, preferably S is controlled at 0.001-0.030%; the molten iron temperature is controlled at 1300-1380°C, preferably the molten iron temperature is controlled at 1320-1380°C, the ladle baking temperature is ≥800°C, and it is not allowed to use new ladles, new slag line ladles, repaired ladles, etc. to avoid inclusions entering the molten steel.

[0008] 2) KR desulfurization: add desulfurizer (lime), stir for 8 to 30 minutes, S control target ≤ 0.007%, preferably S control target ≤ 0.005%.

[0009] 3) Converter smelting: The pre-desulfurized molten iron in step 2) is loaded into the converter, and the raw materials into the converter are molten iron and scrap steel, and the final slag basicity is controlled at 2.8-3.4, and the preferred final slag basicity is controlled at 3.0. The end point C is controlled at 0.07-0.12%, and the preferred end point C is controlled at 0.08%, and the end point P is controlled at 0.003-0.008%, and the preferred end point P is controlled ≤0.005%. The residual element content meets the technical requirements, and the tapping temperature is 1600-1640°C. Lime and low-titanium slag are added to the converter when discharging steel, and slag is strictly prohibited during the discharging process.

[0010] 4) LF furnace refining: The molten steel smelted in the converter in step 3) is subjected to LF furnace refining, the slag basicity is controlled to be greater than 3.0, and the desulfurization operation is strengthened. White slag is produced throughout the process, the white slag retention time is ≥30 minutes, the refining cycle is ≥50 minutes, and the refined steel S control target is ≤0.001%.

[0011] 5) VD furnace vacuum refining: the molten steel after LF furnace refining in step 4) is subjected to slag treatment, and the slag thickness after slag removal is 50-60 mm. The molten steel is vacuum degassed, and the vacuum degree is less than 67 Pa and the time is maintained for ≥20 minutes, and soft argon is blown for ≥20 minutes. After VD is broken, a covering agent is added, and hydrogen is set to [H]≤2PPM, preferably [H]≤1.5PPM, and pure calcium cored wire 1.0-1.3m / ton steel is fed for calcium treatment. The present invention controls the VD slag system: CaO: 53-59%, Al2O3: 27-37%, SiO2≤13%, MgO≤10%, TFe+MnO≤0.6%, and the basicity is controlled within the range of 4.60-7.31. The present invention can effectively regulate the basicity of the VD slag system by setting the TFe+MnO of the VD slag system to ≤0.6%, thereby further reducing the S content in the steel, thereby achieving the control of the S content in the steel within an extremely low range of ≤0.001%.

[0012] The desert deep well rod material of the present invention requires a small number of inclusions and a small size, so calcium treatment is used to modify the inclusions in the steel. The principle is that by increasing the effective calcium content in the steel, on the one hand, large-grained Al2O3 inclusions can be modified into low-melting-point and low-density calcium-aluminate composite inclusions (such as 12CaO·7Al2O3), which promotes the floating of inclusions, purifies the molten steel, and improves the quality of the steel; on the other hand, high-melting-point CaS particles are formed in advance during the solidification process of the molten steel, which can inhibit the total amount and aggregation degree of MnS generated by the molten steel in this process, and partially or completely modify the MnS into CaS, and modify the long strip-shaped MnS inclusions into spherical CaS or CaO-Al2O3-CaS composite inclusions, thereby improving the hydrogen-induced cracking resistance.

[0013] 6) Continuous casting: After the treatment in step 5), the molten steel is continuously cast in an integral tundish, and argon is blown in advance during the pouring. During the production process, argon is blown in the tundish throughout the entire process, and full protection casting is adopted. Low-carbon peritectic steel protective slag is used, and the principle of adding is "frequent addition, small addition, and uniform addition". The slag surface should not be red when viewed visually, and it is best to cover the slag surface with a blue flame to prevent secondary oxidation of the molten steel. The crystallizer liquid level fluctuation is ≤±3mm; low superheat casting is adopted, and the superheat of the molten steel in the tundish is controlled at 15-35℃. Electromagnetic stirring is used in the crystallizer and the end of solidification to reduce organizational defects such as segregation and improve the quality of the casting. The casting adopts the three constant operations of "constant liquid level, constant temperature, and constant pulling speed" to obtain a large round billet of 650-800mm. In order to reduce the content of inclusions, the billet head and tail are cut off for more than 6 meters (the billet head and tail of general steel grades are cut off for 2-3 meters).

[0014] 7) Rolling: The large round billet in step 6) is hot-rolled to reduce carbon consumption. The control parameters during rolling are: the temperature of the heating furnace soaking section is 1170-1240°C, the total heating time is ≥7.0 hours, so that the billet is evenly burned through, and the allowable temperature difference is ≤30°C, which is necessary to ensure that the billet is heated evenly and prevent decarburization and furnace sticking. The starting rolling temperature is 1110-1170°C, and the control of the rolling rhythm is strengthened to ensure the final rolling temperature is 920-1020°C. Before rolling, the rollers, guides, rollers, etc. should be carefully checked to avoid damaging the surface of the steel. This type of steel is prone to surface cracks. After rolling, it needs to be collected in time to the insulation pit. The hot steel in the insulation pit is paved and covered with an insulation cover. The surface temperature of the steel can reach ≥500°C, and the slow cooling time is ≥48 hours to obtain the desert deep well bar with the specification of Φ200-350mm.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The present invention makes the rod material adaptable to the extreme weather in desert areas by rationally designing its composition, and is particularly suitable for oil wells with a depth of more than 5,000 meters. Specifically:

[0017] The present invention controls the C content in the steel to 0.19-0.22%, the P content to ≤0.010%, and in particular, the S content to 0.001%, so that the corrosion resistance of the steel meets the strict use requirements;

[0018] Cr and Mo are elements that improve strength and hardenability. The present invention can further improve the corrosion resistance of the bar by regulating the Cr and Mo contents.

[0019] V and Nb are effective grain-refining elements. Grain refinement is beneficial to improving the strength, toughness and hydrogen sulfide stress corrosion resistance of steel.

[0020] Ti is an active metal element. By regulating the Ti content, the present invention can significantly refine the grains, reduce dendrite segregation, and improve the strength and toughness of the steel.

[0021] A trace amount of boron can significantly improve the hardenability of steel. The composite addition of Nb-B and Mo-B makes the grain boundary precipitates dispersed on the matrix, promotes the occurrence of bainite phase transformation, and improves the hardenability of steel. When the boron element is excessive, a structure that is not conducive to toughness is formed, resulting in deterioration of impact toughness. Therefore, the present invention controls the B content to 0.0015-0.0025%;

[0022] Since Ti is easy to combine with oxygen, it can protect the B element from being oxidized. In the present invention, the Ti content is controlled at 0.01-0.025%. While improving the hardenability, it can also combine with the B element to generate TiB2, thereby improving the impact toughness. The synergistic effect of Ti and B significantly improves the impact toughness.

[0023] The present invention controls the oxygen content and hydrogen content in the steel to be as low as possible, and strictly controls the contents of harmful elements such as Si, As, Zn, Pb, Bi, Sb, Cu and the like in the steel.

[0024] 2. The macrostructure of the steel of the present invention has a general porosity of 0.5, a central porosity of 1.0, and a segregation of 0.

[0025] 3. The inclusion levels of the rods for desert deep wells of the present invention are: A fine: 1.0 level, A coarse: 0 level, B fine: 0-0.5 level, B coarse: 0-1.0 level, C fine: 0 level, C coarse: 0 level, D fine: 0.5 level, D coarse: 0 level, DS: 0 level, the total of various inclusions is 2.0-2.5 levels, and non-metallic inclusions are well controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the EBSD of the desert deep well rod obtained in Example 1 of the present invention, and the obtained phase is bainite + a small amount of ferrite and pearlite.

[0027] Figure 2The metallographic structure of the rod for desert deep wells obtained in Example 1 of the present invention, 200X, is bainite + a small amount of pearlite and ferrite.

[0028] Figure 3 The inclusions in the desert deep well rod obtained in Comparative Example 1 of the present invention are Class B coarse inclusions of level 1.5.

[0029] Figure 4 This is the energy spectrum of inclusions in the desert deep well rod obtained in Comparative Example 1 of the present invention.

[0030] Figure 5 This is a photo of the desert deep well pipe obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings.

[0032] The technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention belong to the scope of protection of the present invention. The embodiments of the present invention adopt KR desulfurization, converter smelting, LF furnace refining, VD vacuum degassing treatment process smelting, continuous casting pouring continuous casting billet, and rolling into products to produce steel. The present invention is further described below in conjunction with specific embodiments.

[0033] Example 1

[0034] A method for preparing a rod for a desert deep well comprises the following steps:

[0035] 1) Production preparation: In this embodiment, the composition of molten iron is P: 0.140%, Si: 0.39%, S: 0.024%, and the temperature of molten iron is 1378° C. The ladle baking temperature is 950° C. It is not a brand new ladle, a new slag line ladle, a repaired ladle, etc.

[0036] 2) KR desulfurization: add desulfurizer and stir for 26 minutes. The S control target after KR treatment is ≤0.007%. In this embodiment, the S is actually controlled at 0.002%.

[0037] 3) Converter smelting: The pre-desulfurized molten iron in step 2) is loaded into the converter. The raw materials are molten iron and scrap steel. The weight of scrap steel is 22 tons. The final slag basicity is 2.85. The end point C is controlled at 0.07-0.12%, and the tapping carbon [C] is controlled to be ≥ 0.05% to prevent the molten steel from being overoxidized. The molten steel has a decarburization amount of more than 0.2% to promote the escape of nitrogen in the steel. The end point P is controlled at 0.003-0.008%. In this example, the end point C is controlled at 0.08%, and the end point P is controlled at 0.004%. The residual element content meets the standard requirements, and the tapping temperature is 1620°C. Aluminum, alloy, primary active lime and synthetic slag are added to the converter when discharging steel. Slag is strictly prohibited during the discharging process.

[0038] 4) LF furnace refining: The molten steel smelted in the converter in step 3) is subjected to LF furnace refining, and the slag basicity is controlled to be greater than 3.0. In this example, the slag basicity is 7.24. The desulfurization operation is strengthened, and a large amount of slag is used for desulfurization. White slag is produced throughout the process, and the white slag retention time is ≥30 minutes. The refining cycle is ≥50 minutes. In this example, the white slag retention time is 56 minutes, and the refining cycle is 66 minutes. Argon is blown throughout the refining process to promote the floating of inclusions. The refined steel S control target is ≤0.001%, and the actual refined steel S in this example is controlled at 0.0006%.

[0039] 5) VD furnace vacuum refining: The molten steel after LF furnace refining in step 4) is subjected to slag treatment. The slag thickness after slag removal is 50-60mm, and the actual slag thickness in this example is 59mm. The molten steel is vacuum degassed, and the vacuum degree is less than 67Pa, and the holding time is ≥20 minutes, and the soft argon blowing is ≥20 minutes. The actual vacuum degree in this example is the lowest 62Pa, the holding time is 27 minutes, and the soft argon blowing is 36 minutes. After VD is broken, a covering agent is added, and hydrogen is set, [H] ≤ 2PPM, and the hydrogen is set to 1.0PPM in this example. 1.0-1.3m / ton of pure calcium cored wire is fed for calcium treatment to increase the effective calcium content in the steel. In this example, 1.2m / ton of pure calcium cored wire is fed.

[0040] 6) Continuous casting: After the molten steel is treated in step 5), the steel flow from the large ladle to the middle ladle is protected by long nozzle + sealing pad + argon seal for pouring, and argon is blown in advance during pouring. During the production process, argon is blown in the middle ladle throughout the process, and full protection pouring is adopted. Low-carbon peritectic steel protective slag is adopted, and low-phosphorus and low-sulfur covering agents are used. The adding principle is "add frequently, add less, and add evenly". The slag surface should not be red when viewed visually, and it is best to cover the slag surface with a blue flame to prevent secondary oxidation of the molten steel. The crystallizer liquid level fluctuation is ≤±3mm; low superheat pouring is adopted, and the superheat of the molten steel in the middle ladle is controlled at 15-35℃. In this embodiment, the superheat of the ladle molten steel is controlled at 20℃, and electromagnetic stirring is adopted at the crystallizer and the end of solidification. Under the action of electromagnetic force, the inclusions gather toward the center of the liquid phase and float to the meniscus to be absorbed by the slag, thereby reducing the content of inclusions, reducing segregation and other organizational defects, and improving the quality of the ingot.

[0041] The casting adopts the three constant operations of "constant liquid level, constant temperature, and constant pulling speed" to obtain a 650mm large round billet. In this example, in order to reduce the inclusion content, the amount of cutting off the billet head and tail is more than 6 meters.

[0042] 7) Rolling: The 650mm round billet in step 6) is hot-rolled to reduce carbon consumption. The control parameters during rolling are: the temperature of the heating furnace soaking section is 1170-1240°C, the total heating time is ≥7.0 hours, the billet is evenly burned through, and the allowable temperature difference is ≤30°C. It is necessary to ensure that the billet is heated evenly and to prevent decarburization and furnace sticking. In this example, the temperature of the heating furnace soaking section is 1219°C, and the total heating time is 7.5 hours. The starting rolling temperature is 1110-1170°C, and the control of the rolling rhythm is strengthened to ensure that the final rolling temperature is 920-1020°C. In this example, the starting rolling temperature is 1149°C and the final rolling temperature is 972°C. Before rolling, carefully check the rollers, guides, rollers, etc. to avoid damaging the steel surface. After rolling, the steel is promptly collected to the insulation pit, the hot steel is laid on the floor of the insulation pit, and an insulation cover is placed on it. The surface temperature of the steel can reach ≥500°C, and the slow cooling time is ≥48 hours. In this example, the surface temperature of the steel can reach 530°C, and the slow cooling time is 60 hours, and a rod for desert deep wells with a specification of Φ300mm is obtained.

[0043] Embodiment 2-10

[0044] Example 2 provides a method for preparing rods for desert deep wells, which differs from Example 1 in that:

[0045] Step 1) Molten iron composition P: 0.150%, Si: 0.38%, S: 0.024%; Molten iron temperature 1370°C; Ladle baking temperature 950°C;

[0046] Step 2) see Table 1;

[0047] Step 3) Final slag basicity 2.90, C controlled at 0.08%, end point P controlled at 0.004%; tapping temperature 1620°C;

[0048] Step 4) slag basicity 7.24, white slag retention time 56 minutes, refining cycle 66 minutes; refined steel S0.0006%;

[0049] Step 5) After slagging, the slag thickness is 57mm; vacuum degree (Pa) is 65Pa, vacuum time is 26 minutes, and soft argon blowing is 36 minutes; hydrogen determination is shown in Table 6; the amount of pure calcium cored wire fed is 1.3m / ton of steel;

[0050] Step 6) The superheat of molten steel is controlled at 25°C; the amount of billet head and billet tail removed is 7 meters;

[0051] Step 7) The temperature of the soaking section of the heating furnace is 1219°C, and the total heating time is 7.5 hours; the starting rolling temperature is 1149°C, the final rolling temperature is 972°C; the steel surface temperature is 530°C; and the slow cooling time is 60 hours.

[0052] Example 3 provides a method for preparing rods for desert deep wells, which differs from Example 1 in that:

[0053] Step 1) molten iron composition P: 0.140%, Si: 0.39%, S: 0.020%; molten iron temperature 1368°C; ladle baking temperature 940°C;

[0054] Step 2) see Table 1;

[0055] Step 3) Final slag basicity 2.85, C controlled at 0.07%, end point P controlled at 0.003%; steel tapping temperature 1630°C;

[0056] Step 4) slag basicity 7.14, white slag retention time 52 minutes, refining cycle 68 minutes; refined steel S0.0007%;

[0057] Step 5) After slagging, the slag thickness is 55mm; vacuum degree (Pa) is 63Pa, vacuum time is 25 minutes, and soft argon blowing is 30 minutes; hydrogen determination is shown in Table 6; the amount of pure calcium cored wire fed is 1.3m / ton of steel;

[0058] Step 6) The superheat of molten steel is controlled at 20°C; the billet head and tail are cut off by 6 meters;

[0059] Step 7) The temperature of the soaking section of the heating furnace is 1222°C, and the total heating time is 7.5 hours; the starting rolling temperature is 1130°C, the final rolling temperature is 972°C; the steel surface temperature is 530°C; and the slow cooling time is 50 hours.

[0060] Example 4 provides a method for preparing rods for desert deep wells, which differs from Example 1 in that:

[0061] Step 1) molten iron composition P: 0.130%, Si: 0.35%, S: 0.020%; molten iron temperature 1354°C; ladle baking temperature 940°C;

[0062] Step 2) see Table 1;

[0063] Step 3) Final slag basicity 2.90, C controlled at 0.07%, end point P controlled at 0.004%; steel tapping temperature 1630°C;

[0064] Step 4) slag basicity 7.24, white slag retention time 52 minutes, refining cycle 66 minutes; refined steel S0.0008%;

[0065] Step 5) After slagging, the slag thickness is 58mm; vacuum degree (Pa) is 62Pa, vacuum time is 25 minutes, and soft argon blowing is 35 minutes; hydrogen determination is shown in Table 6; the amount of pure calcium cored wire fed is 1.1m / ton of steel;

[0066] Step 6) The superheat of molten steel is controlled at 15°C; the billet head and tail are cut off by 7 meters;

[0067] Step 7) The temperature of the soaking section of the heating furnace is 1203°C, and the total heating time is 7.5 hours; the starting rolling temperature is 1129°C, the final rolling temperature is 970°C; the steel surface temperature is 530°C; and the slow cooling time is 55 hours.

[0068] Example 5 provides a method for preparing rods for desert deep wells, which differs from Example 1 in that:

[0069] Step 1) Molten iron composition P: 0.135%, Si: 0.37%, S: 0.025%; Molten iron temperature 1350°C; Ladle baking temperature 940°C;

[0070] Step 2) see Table 1;

[0071] Step 3) final slag basicity 3.00, C controlled at 0.07%, end point P controlled at 0.004%; tapping temperature 1625°C;

[0072] Step 4) slag basicity 7.24, white slag retention time 55 minutes, refining cycle 66 minutes; refined steel S0.0008%;

[0073] Step 5) After slagging, the slag thickness is 54mm; vacuum degree (Pa) is 62Pa, vacuum time is 27 minutes, and soft argon blowing is 35 minutes; hydrogen determination is shown in Table 6; the amount of pure calcium cored wire fed is 1.2m / ton of steel;

[0074] Step 6) The superheat of molten steel is controlled at 28°C; the amount of billet head and billet tail removed is 6 meters;

[0075] Step 7) The temperature of the soaking section of the heating furnace is 1188°C, and the total heating time is 8.0 hours; the starting rolling temperature is 1158°C, the final rolling temperature is 920°C; the steel surface temperature is 535°C; and the slow cooling time is 58 hours.

[0076] Example 6 provides a method for preparing rods for desert deep wells, which differs from Example 1 in that:

[0077] Step 1) Molten iron composition P: 0.140%, Si: 0.35%, S: 0.018%; Molten iron temperature 1350°C; Ladle baking temperature 950°C;

[0078] Step 2) see Table 1;

[0079] Step 3) Final slag basicity 3.10, C controlled at 0.08%, end point P controlled at 0.005%; tapping temperature 1620°C;

[0080] Step 4) slag basicity 7.14, white slag retention time 52 minutes, refining cycle 70 minutes; refined steel S0.0006%;

[0081] Step 5) After slagging, the slag thickness is 55mm; vacuum degree (Pa) is 65Pa, vacuum time is 28 minutes, and soft argon blowing is 38 minutes; hydrogen determination is shown in Table 6; the amount of pure calcium cored wire fed is 1.1m / ton of steel;

[0082] Step 6) The superheat of molten steel is controlled at 28°C; the amount of billet head and billet tail removed is 6 meters;

[0083] Step 7) The temperature of the soaking section of the heating furnace is 1175°C, and the total heating time is 7.5 hours; the starting rolling temperature is 1168°C, the final rolling temperature is 950°C; the steel surface temperature is 530°C; and the slow cooling time is 56 hours.

[0084] Example 7 provides a method for preparing rods for desert deep wells, which differs from Example 1 in that:

[0085] Step 1) molten iron composition P: 0.140%, Si: 0.37%, S: 0.025%; molten iron temperature 1378°C; ladle baking temperature 935°C;

[0086] Step 2) see Table 1;

[0087] Step 3) final slag basicity 3.00, C controlled at 0.10%, end point P controlled at 0.004%; tapping temperature 1625°C;

[0088] Step 4) slag basicity 7.24, white slag retention time 56 minutes, refining cycle 66 minutes; refined steel S0.0006%;

[0089] Step 5) After slagging, the slag thickness is 59mm; vacuum degree (Pa) is 62Pa, vacuum time is 27 minutes, and soft argon blowing is 28 minutes; hydrogen determination is shown in Table 6; the amount of pure calcium cored wire fed is 1.2m / ton of steel;

[0090] Step 6) The superheat of molten steel is controlled at 27°C; the amount of billet head and billet tail removed is 6 meters;

[0091] Step 7) The temperature of the soaking section of the heating furnace is 1230°C, and the total heating time is 8.5 hours; the starting rolling temperature is 1170°C, the final rolling temperature is 992°C; the steel surface temperature is 530°C; and the slow cooling time is 60 hours.

[0092] Example 8 provides a method for preparing rods for desert deep wells, which differs from Example 1 in that:

[0093] Step 1) molten iron composition P: 0.145%, Si: 0.35%, S: 0.030%; molten iron temperature 1368°C; ladle baking temperature 945°C;

[0094] Step 2) see Table 1;

[0095] Step 3) Final slag basicity 3.10, C controlled at 0.09%, end point P controlled at 0.005%; steel tapping temperature 1620°C;

[0096] Step 4) slag basicity 7.22, white slag retention time 57 minutes, refining cycle 69 minutes; refined steel S0.0005%;

[0097] Step 5) After slagging, the slag thickness is 55mm; vacuum degree (Pa) is 61Pa, vacuum time is 28 minutes, and soft argon blowing is 26 minutes; hydrogen determination is shown in Table 6; the amount of pure calcium cored wire fed is 1.1m / ton of steel;

[0098] Step 6) The superheat of molten steel is controlled at 30°C; the amount of billet head and billet tail removed is 6 meters;

[0099] Step 7) The temperature of the soaking section of the heating furnace is 1235°C, and the total heating time is 7.5 hours; the starting rolling temperature is 1110°C, the final rolling temperature is 1020°C; the steel surface temperature is 535°C; and the slow cooling time is 62 hours.

[0100] Example 9 provides a method for preparing rods for desert deep wells, which differs from Example 1 in that:

[0101] Step 1) molten iron composition P: 0.150%, Si: 0.35%, S: 0.030%; molten iron temperature 1378°C; ladle baking temperature 930°C;

[0102] Step 2) see Table 1;

[0103] Step 3) Final slag basicity 2.85, C controlled at 0.11%, end point P controlled at 0.004%; tapping temperature 1630°C;

[0104] Step 4) slag basicity 7.24, white slag retention time 56 minutes, refining cycle 66 minutes; refined steel S0.0006%;

[0105] Step 5) After slagging, the slag thickness is 60 mm; vacuum degree (Pa) is 62 Pa, vacuum time is 27 minutes, and soft argon blowing is 33 minutes; hydrogen determination is shown in Table 6; the amount of pure calcium cored wire fed is 1.3 m / ton of steel;

[0106] Step 6) The superheat of molten steel is controlled at 20°C; the amount of billet head and billet tail removed is 8 meters;

[0107] Step 7) The temperature of the soaking section of the heating furnace is 1209°C, and the total heating time is 7.5 hours; the starting rolling temperature is 1149°C, the final rolling temperature is 1000°C; the steel surface temperature is 520°C; and the slow cooling time is 60 hours.

[0108] Example 10 provides a method for preparing rods for desert deep wells, which differs from Example 1 in that:

[0109] Step 1) molten iron composition P: 0.130%, Si: 0.30%, S: 0.024%; molten iron temperature 1378°C; ladle baking temperature 930°C;

[0110] Step 2) see Table 1;

[0111] Step 3) Final slag basicity 2.85, C controlled at 0.08%, end point P controlled at 0.004%; tapping temperature 1640°C;

[0112] Step 4) slag basicity 7.20, white slag retention time 58 minutes, refining cycle 70 minutes; refined steel S0.0006%;

[0113] Step 5) After slagging, the slag thickness is 59mm; vacuum degree (Pa) is 62Pa, vacuum time is 28 minutes, and soft argon blowing is 36 minutes; hydrogen determination is shown in Table 6; the amount of pure calcium cored wire fed is 1.2m / ton of steel;

[0114] Step 6) The superheat of molten steel is controlled at 20°C; the billet head and tail are cut off by 6 meters;

[0115] Step 7) The temperature of the soaking section of the heating furnace is 1219°C, and the total heating time is 7.5 hours; the starting rolling temperature is 1149°C, the final rolling temperature is 972°C; the steel surface temperature is 530°C; and the slow cooling time is 68 hours.

[0116] Table 1 KR desulfurization situation

[0117]

[0118] The chemical composition of the desert deep well rods of Examples 1-10 is shown in Table 2.

[0119] Table 2 Chemical composition of Examples 1-10

[0120]

[0121] The residual element contents of the desert deep well rods of Examples 1-10 are shown in Table 3.

[0122] Table 3 Residual elements in Examples 1-10 (%)

[0123]

[0124]

[0125] The macrostructures of the desert deep well rods of Examples 1-10 are shown in Table 4. The general porosity is 0.5, the central porosity is 1.0, and the segregation is 0.

[0126] Table 4 Macrostructure (grade) of Examples 1-10

[0127]

[0128] The non-metallic inclusion control indicators of the desert deep well rods of Examples 1-10 are shown in Table 5, A fine: 1.0 level, A coarse: 0 level, B fine: 0-0.5 level, B coarse: 0-1.0 level, C fine: 0 level, C coarse: 0 level, D fine: 0.5 level, D coarse: 0 level, DS: 0 level, the total of various inclusions is 2.0-2.5 levels, and the non-metallic inclusions are well controlled.

[0129] Table 5 Non-metallic inclusions (grade) in Examples 1-10

[0130]

[0131]

[0132] The gas content of the steel of the desert deep well rods of Examples 1-10 is shown in Table 6.

[0133] Table 6 Gases of Examples 1-10

[0134]

[0135] The steel sample obtained in Example 1 was sampled and subjected to EBSD, and the obtained phase was bainite + a small amount of ferrite and pearlite, as shown in Table 7 and Figure 1 .

[0136] Table 7 EBSD of Example 1

[0137]

[0138]

[0139] , Figure 2 The metallographic structure of the rod for desert deep wells obtained in Example 1 of the present invention, 200X, is bainite + a small amount of pearlite and ferrite. Figure 5 This is a photo of the desert deep well pipe obtained in Example 1 of the present invention.

[0140] Table 8 SSC test for sulfur stress corrosion cracking

[0141]

[0142] Table 9 Mechanical properties test

[0143]

[0144]

[0145] It can be seen from the above test results that the rod material for desert deep wells prepared by the present invention has good control of non-metallic inclusions, and has excellent corrosion resistance and mechanical properties.

[0146] Comparative Example 1

[0147] This comparative example provides a method for preparing rods for desert deep wells, which differs from Example 1 in that:

[0148] The process of step 2) was not performed;

[0149] In step 4), desulfurization is not carried out by using a large amount of slag;

[0150] Step 5) RH is used for vacuum treatment; when feeding pure calcium cored wire, the feeding amount is 0.5m / ton steel;

[0151] In step 6), the amount of cutting off the billet head and tail is 2 meters.

[0152] This comparative example discloses the main method for preparing desert deep well rods in the prior art, that is, the technical solution before optimization of the present invention.

[0153] Before the process optimization (ie, comparative example 1), the inclusions in the desert deep well rods were mainly composed of Ti and Nb carbonitrides, grade 1.5, which exceeded the standard requirement of 1.0 grade.

[0154] Table 10 Composition of rod inclusions before process optimization %

[0155]

[0156] Figure 3 The inclusions in the desert deep well rods obtained before optimization are Class B coarse inclusions, level 1.5. Figure 4 This is the energy spectrum of inclusions in desert deep well rods before optimization.

[0157] In summary, the inclusion content in the existing desert deep well rods obviously exceeds the standard. The desert deep well rods prepared by the preparation method of the present invention have all inclusions in the rods that meet the standard requirements, and the corrosion resistance and mechanical properties of the rods are also better, which is more suitable for the use environment of desert deep wells.

[0158] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A rod for desert deep wells, characterized in that: The chemical components are as follows: C: 0.19~0.22%, Si: 0.15~0.35%, Mn: 0.45~0.55%, P: ≤0.010%, S: ≤0.001%, Cr: 0.4 5~0.55%, Mo: 0.70~0.80%, Nb: 0.02~0.05%, V: 0.09~0.11%, Al: 0.01~0.025%, Ti: 0.01~0.025%, B: 0.0015~0.0025%, Cu: ≤0.15%, Ni: ≤0.15%, Sn: ≤0.020%, As: ≤0.020%, Pb: ≤0.020%, Sb: ≤0.020%, Bi: ≤0.020%, Ca: 0.001~0.005%, the balance is Fe and unavoidable impurities.

2. A method for preparing the rod for desert deep wells according to claim 1, characterized in that: The steps include: 1) Production preparation: The composition of molten iron is calculated by weight percentage, P is controlled at ≤0.150%, Si is controlled at 0.25-0.80%, and S is controlled at 0.001-0.040%; The molten iron temperature is controlled at 1300-1380℃, and the ladle baking temperature is ≥800℃; 2) KR desulfurization: add desulfurizer, S control target ≤ 0.007%; 3) Converter smelting: the molten iron pre-desulfurized in step 2) is charged into the converter, and the end point C is controlled at 0.07-0.12%, and the end point P is controlled at 0.003-0.008%; 4) LF furnace refining: the molten steel obtained in step 3) through converter smelting is subjected to LF furnace refining, and the refined steel S control target is ≤0.001%; 5) VD furnace vacuum refining: the molten steel after LF furnace refining in step 4) is subjected to slag removal treatment, vacuum degassing treatment, hydrogen fixation treatment and calcium treatment in sequence; 6) Continuous casting; 7) Rolling.

3. The preparation method according to claim 2, characterized in that: In step 3), the raw materials entering the furnace are molten iron and scrap steel, the final slag basicity is controlled at 2.8-3.4, and the steel tapping temperature is controlled at 1600-1640°C.

4. The preparation method according to claim 2, characterized in that: In step 4), during LF furnace refining, the slag basicity is controlled to be greater than 3.0, white slag is produced throughout the process, the white slag retention time is ≥30 minutes, and the refining cycle is ≥50 minutes.

5. The preparation method according to claim 2, characterized in that: In step 5), the molten steel after LF furnace refining in step 4) is subjected to slag treatment, and the slag thickness after slag removal is 50-60 mm; the molten steel is vacuum degassed, and the vacuum degree is less than 67 Pa and the time is maintained for ≥20 minutes, and soft argon is blown for ≥20 minutes; a covering agent is added after VD is broken, and hydrogen is determined, [H]≤2PPM; pure calcium cored wire 1.0-1.3m / ton steel is fed for calcium treatment.

6. The preparation method according to claim 2, characterized in that: In step 5), the VD slag system is controlled to be: CaO 53-59%, Al2O3 27-37%, SiO2≤13%, MgO≤10%, TFe+MnO≤0.6%, and the basicity is controlled at 4.60-7.

31.

7. The preparation method according to claim 2, characterized in that: In step 6), the molten steel after vacuum refining in the VD furnace in step 5) is continuously cast in an integral tundish, argon is pre-blown at the start of pouring, argon is blown in the tundish throughout the production process, and full-process protective casting is adopted; low-carbon peritectic steel protective slag is used, and the crystallizer liquid level fluctuation is ≤±3mm; low superheat casting is adopted, the superheat of the molten steel in the tundish is controlled at 15-35°C, and electromagnetic stirring is adopted at the crystallizer and the end of solidification to obtain a billet with a large round billet of 650-800mm.

8. The preparation method according to claim 2, characterized in that: In step 7), the large round billet obtained in step 6) is hot-rolled, and the control parameters during rolling are: the temperature of the soaking section of the heating furnace is 1170-1240°C, the total heating time is ≥7.0 hours, and the allowable temperature difference is ≤30°C; the starting rolling temperature is 1110-1170°C, and the final rolling temperature is 920-1020°C; after rolling, it is promptly collected to the insulation pit, the surface temperature of the steel reaches ≥500°C, and the slow cooling time is ≥48 hours, so as to obtain the desert deep well bar with a specification of Φ200-350mm.

9. The preparation method according to claim 2, characterized in that: In step 6), the amount of cutting off the billet head and tail is more than 6 meters.

10. The preparation method according to claim 2, characterized in that: In step 1), P is controlled at ≤ 0.140%, Si is controlled at 0.25-0.40%, and S is controlled at 0.001-0.030%.

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