Steel for improving stress corrosion resistance of non-magnetic drill collar and preparation method of steel

Abstract

The invention discloses non-magnetic drill collar steel capable of improving stress corrosion resistance and a preparation method of the non-magnetic drill collar steel. The preparation method of the non-magnetic drill collar steel for improving the stress corrosion resistance comprises the steps of electric furnace smelting, AOD smelting, LF refining, continuous casting, electroslag, cogging, solution treatment and low-temperature forging. The non-magnetic drill collar steel for improving stress corrosion resistance comprises the following chemical components in percentage by mass: 0.02%-0.06% of C, less than or equal to 0.45% of Si, 20.0%-22.5% of Mn, less than or equal to 0.03% of P, less than or equal to 0.01% of S, 17.0%-20.0% of Cr, 0.90%-3.50% of Ni, 0.6%-2.0% of Mo, 0.6%-0.8% of N, less than or equal to 0.01% of B, more than or equal to 31% of PREN (Cr + 3.3 Mo + 16N), and the balance of Fe and inevitable impurities. According to the method, a high-alkalinity slag system and Al are adopted for deep deoxidation, a 40F pre-melting slag system is adopted for electroslag, argon filling protection is conducted, so that the steel billet is low in oxygen and high in purity, the round steel with the uniform grain size is forged through fast forging cogging high-temperature solid solution and low-temperature forging strengthening, the conventional mechanical performance, the non-magnetic performance, the intergranular corrosion resistance and the like are improved, and meanwhile the long stress corrosion service life is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a non-magnetic drill collar steel with improved stress corrosion resistance and a preparation method thereof. Background Art

[0002] Non-magnetic drill collar steel is the most important material in the oil and gas production process. In the existing technology, non-magnetic materials can better meet the use of oil and gas production in conventional environments, but in high CI - When oil and gas extraction operations are carried out in marine environments, stress cracking and intergranular corrosion cracking often occur, which affects the oil and gas extraction operations, further increases costs, and affects production efficiency.

[0003] Therefore, in view of the above-mentioned characteristics of stress cracking and intergranular corrosion cracking, it is necessary to provide a non-magnetic drill collar steel with improved stress corrosion resistance and a preparation method thereof to solve the above-mentioned technical problems. Summary of the invention

[0004] In order to solve some or all of the technical problems existing in the above-mentioned prior art, the present invention provides a non-magnetic drill collar steel with improved stress corrosion resistance and a preparation method thereof.

[0005] The preparation method of the non-magnetic drill collar steel with improved stress corrosion resistance of the present invention comprises: electric furnace smelting-AOD smelting-LF refining-continuous casting-electroslag-coiling-solid solution treatment-low temperature forging, wherein the chemical composition of the non-magnetic drill collar steel with improved stress corrosion resistance is controlled by mass percentage as follows: C: 0.02%-0.06%, Si≤0.45%, Mn: 20.0%-22.5%, P≤0.03%, S≤0.01%, Cr: 17.0%-20.0%, Ni: 0.90%-3.50%, Mo: 0.6%-2.0%, N: 0.6%-0.8%, B: ≤0.01%, PREN (Cr+3.3Mo+16N): ≥31, and the balance is Fe and unavoidable impurities;

[0006] Electric furnace smelting: put the stainless steel into an electric furnace, add C: 2.5%, Cr: 22.5 and Mn ≤ 2.0%, smelt into molten steel, and remove the slag when tapping the steel. The thickness of the slag in the ladle is ≤ 50mm;

[0007] AOD smelting: transfer the molten steel after slag removal from electric furnace smelting into AOD furnace, add Mn for smelting in batches, and add 70kgAI for reduction. The pre-reduction slag removal is greater than 80%, and the slag is adjusted to make the S target ≤0.003. Slag removal is performed before steelmaking, and the composition is adjusted according to the reduction composition.

[0008] LF refining: the molten steel after AOD smelting slag removal is transferred to the LF refining furnace, the N target is adjusted to 0.65% using nitriding alloy, and the molten steel composition is adjusted according to the target chemical composition by mass percentage. The temperature is adjusted before tapping, and 200 meters of Ca-Si or Ca wire is fed per furnace. After feeding the wire, 10 kg of FeB is added per furnace, and the white slag is kept for 45 minutes before tapping;

[0009] Continuous casting: preparing steel ingots from molten steel after LF refining;

[0010] Electroslag: Weld the tail of the steel ingot with a dummy electrode, and fill the slag system with argon gas with a pressure of >0.2MPa before electroslag for a period of ≥10min. Use a lower voltage and a smaller current first, and then gradually increase the voltage and current to obtain a remelted steel ingot.

[0011] Billeting: Heat the remelted steel ingot to 1240℃ and keep it warm for more than 4 hours, and then perform rapid forging or radial forging to form a billet, so that the forging ratio is ≥6%;

[0012] Solution treatment: the billet is quickly returned to the furnace and heated to 1100℃ for 2 hours, then quickly cooled in water, cooled to 200℃ and air cooled;

[0013] Low temperature forging: Heat the solution treated steel ingot to 550°C and keep it warm for 4 hours, and perform two passes of low temperature forging with a forging ratio of 10% to form a forged circle, and cool it naturally after forging.

[0014] Furthermore, in the above-mentioned preparation method of non-magnetic drill collar steel with improved stress corrosion resistance, nitrogen is blown throughout the AOD smelting process, the reduction time is 6min-7min, and CaSi powder and 30kg / furnace AI powder are used for slag adjustment.

[0015] Furthermore, in the above-mentioned method for preparing non-magnetic drill collar steel with improved stress corrosion resistance, during the LF refining process, N 2 , and add lime at a rate of ≯50Kg / batch to maintain the basicity of lime-saturated refined slag, while ensuring that FeO≤0.5%, NiO≤0.05%, oxygen content in steel≤30ppm, MgO: 5%-10%, and binary basicity is controlled at 2.5%-3.0%.

[0016] Furthermore, in the above-mentioned method for preparing non-magnetic drill collar steel with improved stress corrosion resistance, during the LF refining process, the chemical composition of the white slag is controlled by mass percentage as follows: TFe: 0.48%, FeO ≤ 0.5%, SiO 2 : 22.58%, AI 2 O 3:3.44%, CaO: 58.16%, MgO: 5%-10%, P: 0.01%, S: 0.24%, Cr 2 O 3 : 0.12%, NiO≤0.05%.

[0017] Furthermore, in the above-mentioned method for preparing non-magnetic drill collar steel with improved stress corrosion resistance, a cleaning step is also included before the electroslag step to clean the oxide scale on the surface of the steel ingot and remove the head and tail caps of the steel ingot.

[0018] Furthermore, in the above-mentioned method for preparing non-magnetic drill collar steel with improved stress corrosion resistance, in the electroslag process, the slag system adopts 40F pre-melted slag system.

[0019] In a second aspect of the present invention, a non-magnetic drill collar steel with improved stress corrosion resistance is provided. The non-magnetic drill collar steel with improved stress corrosion resistance is produced using the above-mentioned method for preparing non-magnetic drill collar steel with high stress corrosion resistance.

[0020] The non-magnetic drill collar steel with improved stress corrosion resistance and the preparation method thereof of the present invention have the following advantages and beneficial effects:

[0021] The present invention adopts a slag system with relatively high basicity and Al deep deoxidation in the smelting process, and the electroslag adopts a 40F pre-melted slag system and argon protection, so as to prepare a steel billet with low oxygen and high purity. The forging adopts high-speed forging and high-temperature solid solution + appropriate low-temperature forging strengthening to forge into round steel with uniform grain size, so that the round steel has excellent conventional mechanical properties, non-magnetic properties, intergranular corrosion resistance, etc., and at the same time has a relatively high stress corrosion life. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings in the following descriptions are only used to further understand the embodiments of the present invention and constitute a part of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0023] Figure 1 It is the heating curve diagram in Example 1;

[0024] Figure 2 This is a schematic diagram of the grain structure of 25 mm below the skin of the application layer in Example 1;

[0025] Figure 3 Schematic diagram of non-metallic inclusions in Example 1. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] The level of inclusions is an important factor affecting the quality of the passivation film. The macro defects caused by inclusions will cause discontinuity of the passivation film or a potential difference between the inclusions and the metal matrix, thereby causing the generation of many micro galvanic cells. These micro galvanic cells can drive local electrochemical dissolution and eventually form pitting corrosion, which is one of the inducing factors of stress corrosion. Non-metallic inclusions cannot be completely removed, but should be reduced as much as possible. When the inclusion type A+B+C+D is ≤3.0, the non-magnetic steel is relatively pure, and the stress corrosion life has a correspondingly good performance.

[0028] The preparation method of the non-magnetic drill collar steel with improved stress corrosion resistance of the present invention comprises: electric furnace smelting-AOD smelting-LF refining-continuous casting-electroslag-coiling-solid solution treatment-low temperature forging, wherein the chemical composition of the non-magnetic drill collar steel with improved stress corrosion resistance is controlled by mass percentage as follows: C: 0.02%-0.06%, Si≤0.45%, Mn: 20.0%-22.5%, P≤0.03%, S≤0.01%, Cr: 17.0%-20.0%, Ni: 0.90%-3.50%, Mo: 0.6%-2.0%, N: 0.6%-0.8%, B: ≤0.01%, PREN (Cr+3.3Mo+16N): ≥31, and the balance is Fe and unavoidable impurities;

[0029] Electric furnace smelting: put the stainless steel into an electric furnace, add C: 2.5%, Cr: 22.5 and Mn ≤ 2.0%, smelt into molten steel, and remove the slag when tapping the steel. The thickness of the slag in the ladle is ≤ 50mm;

[0030] AOD smelting: transfer the molten steel after slag removal from electric furnace smelting into AOD furnace, add Mn for smelting in batches, and add 70kgAI for reduction. The pre-reduction slag removal is greater than 80%, and the slag is adjusted to make the S target ≤0.003. Slag removal is performed before steelmaking, and the composition is adjusted according to the reduction composition.

[0031] LF refining: the molten steel after AOD smelting slag removal is transferred to the LF refining furnace, the N target is adjusted to 0.65% using nitriding alloy, and the molten steel composition is adjusted according to the target chemical composition by mass percentage. The temperature is adjusted before tapping, and 200 meters of Ca-Si or Ca wire is fed per furnace. After feeding the wire, 10 kg of FeB is added per furnace, and the white slag is kept for 45 minutes before tapping;

[0032] Continuous casting: preparing steel ingots from molten steel after LF refining;

[0033] Electroslag: Weld the tail of the steel ingot with a dummy electrode, and fill the slag system with argon gas with a pressure of >0.2MPa before electroslag for a period of ≥10min. Use a lower voltage and a smaller current first, and then gradually increase the voltage and current to obtain a remelted steel ingot.

[0034] Billeting: Heat the remelted steel ingot to 1240℃ and keep it warm for more than 4 hours, and then perform rapid forging or radial forging to form a billet, so that the forging ratio is ≥6%;

[0035] Solution treatment: the billet is quickly returned to the furnace and heated to 1100℃ for 2 hours, then quickly cooled in water, cooled to 200℃ and air-cooled to adjust the grain uniformity;

[0036] Low temperature forging: Heat the solution treated steel billet to 550°C and keep it warm for 4 hours, and perform two passes of low temperature forging with a forging ratio of 10% to form a forged circle. After forging, cool it naturally to make the application layer have uniform grain size and grain size grade <3.

[0037] Furthermore, in the preparation method of non-magnetic drill collar steel with improved stress corrosion resistance of the present invention, nitrogen is blown throughout the AOD smelting process, the reduction time is 6min-7min, and CaSi powder and 30kg / furnace AI powder are used for slag adjustment.

[0038] Furthermore, in the method for preparing non-magnetic drill collar steel with improved stress corrosion resistance of the present invention, during the LF refining process, N 2 , and add lime at a rate of ≯50Kg / batch to maintain the basicity of lime-saturated refined slag, while ensuring that FeO≤0.5%, NiO≤0.05%, oxygen content in steel≤30ppm, MgO: 5%-10%, and binary basicity is controlled at 2.5%-3.0%.

[0039] Furthermore, in the above-mentioned method for preparing non-magnetic drill collar steel with improved stress corrosion resistance, during the LF refining process, the chemical composition of the white slag is controlled by mass percentage as follows: TFe: 0.48%, FeO ≤ 0.5%, SiO 2 : 22.58%, AI 2 O 3:3.44%, CaO: 58.16%, MgO: 5%-10%, P: 0.01%, S: 0.24%, Cr 2 O 3 : 0.12%, NiO≤0.05%.

[0040] Furthermore, in the method for preparing non-magnetic drill collar steel with improved stress corrosion resistance of the present invention, a cleaning step is also included before the electroslag step to clean the oxide scale on the surface of the steel ingot and remove the head and tail caps of the steel ingot.

[0041] Furthermore, in the preparation method of the non-magnetic drill collar steel with improved stress corrosion resistance of the present invention, in the electroslag process, the slag system adopts a 40F pre-melted slag system, thereby ensuring that the slag has good fluidity during the electroslag process. At the same time, the wetting angle between the slag system and the steel is large, which can ensure that the slag and the steel are well separated; the slag system and the oxides in the steel (such as Al 2 O 3 ) has a small wetting angle, which can achieve better adsorption of inclusions and effectively ensure the purity of the steel.

[0042] In a second aspect of the present invention, a non-magnetic drill collar steel with improved stress corrosion resistance is provided. The non-magnetic drill collar steel with improved stress corrosion resistance is produced using the above-mentioned method for preparing non-magnetic drill collar steel with high stress corrosion resistance.

[0043] Example 1

[0044] This embodiment manufactures a 220mm diameter, 0Cr18Mn22Ni2Mo2N non-magnetic drill collar steel

[0045] The preparation method includes: electric furnace smelting-AOD smelting-LF refining-continuous casting-electroslag-cogging-solid solution treatment-low temperature forging, wherein the chemical composition of the non-magnetic drill collar steel for improving stress corrosion resistance is controlled by mass percentage as shown in Table 1:

[0046] Table 1 Chemical composition percentage

[0047]

[0048] Electric furnace smelting:

[0049] Put the stainless steel into an electric furnace, add C: 2.5%, Cr: 22.5 and Mn ≤ 2.0%, smelt into molten steel, remove the slag when tapping, and the slag thickness in the bag is ≤ 50mm;

[0050] AOD smelting:

[0051] The molten steel after slag removal from electric furnace smelting is transferred to AOD furnace, and nitrogen blowing is carried out throughout the smelting process. Mn is added in batches, and 70kg AI is added for 6min-7min reduction. The pre-reduction slag removal is greater than 80%, and new slag is made and slag is adjusted with 30kg / furnace of CaSi powder and AI powder. The target S of the finished product is ≤0.003. Slag is removed before steelmaking, and the composition is adjusted according to the reducing components.

[0052] LF Refining:

[0053] The molten steel after AOD smelting is transferred to LF refining furnace for smelting with N blowing throughout the whole process. 2 , use nitriding alloy to adjust the N target to 0.65%, and adjust the molten steel composition according to the target chemical composition by mass percentage, adjust the temperature before tapping, and feed Ca-Si or Ca wire 200 meters / furnace, add FeB 10kg per furnace after feeding the wire, and add lime at ≯50Kg / batch to maintain the basicity of lime-saturated refined slag, while ensuring FeO≤0.5%, NiO≤0.05%, ensuring that the oxygen content in the steel is ≤30ppm, making MgO: 5%-10%, binary basicity controlled at 2.5%-3.0%, and keeping the white slag for 45 minutes, tapping;

[0054] The percentage of white slag components is shown in Table 2:

[0055] Table 2 White slag composition percentage

[0056] TFe FeO <![CDATA[SiO 2 ]]> <![CDATA[Al 2 THE 3 ]]> CaO MgO P S <![CDATA[Cr 2 THE 3 ]]> NiO 0.48 0.29 22.58 3.44 58.16 6.84 0.01 0.24 0.12 0.037

[0057] Continuous Casting:

[0058] The molten steel after LF refining was prepared into a steel ingot with a diameter of 550 mm and a weight of 5.6 tons, and the oxide scale was cleaned;

[0059] Electroslag:

[0060] The tail of the steel ingot is welded to the dummy electrode, and argon gas with a pressure of >0.2MPa is charged into the slag system before electroslag for a period of ≥10min. A lower voltage and a smaller current are first used during electroslag, and then the voltage and current are gradually increased to obtain a steel ingot with a diameter of 700mm after remelting;

[0061] Among them, the electroslag requirements are shown in Table 3, and the electroslag melting rate is shown in Table 4:

[0062] Table 3 Electroslag requirements

[0063]

[0064] Table 4 Electroslag melting rate

[0065]

[0066]

[0067] Opening:

[0068] Heat the remelted steel ingot to 1240±10℃. Figure 1 As shown, the total heating time is ≥14h, and the heat preservation is carried out for more than 4h, and the steel ingot with a diameter of 700mm is forged into a steel billet with a diameter of 250mm, and the forging ratio is 7.84%;

[0069] Solution treatment:

[0070] The billet is quickly returned to the furnace and heated to 1100°C for 2 hours, then quickly cooled in water, cooled to 200°C and air-cooled;

[0071] Low temperature forging:

[0072] The solution treated steel billet is heated to 550°C and kept at this temperature for 4 hours, and two passes of low temperature forging are performed to forge a 250 mm steel billet to form a forging circle with a diameter of 225 mm. After forging, the forging circle is allowed to cool naturally.

[0073] Inspection of forged rounds after low temperature forging:

[0074] The chemical composition percentage of the forged round after low temperature forging is shown in Table 5:

[0075] Table 5 Chemical composition percentage of forged round after low temperature forging

[0076]

[0077] The forged round was stretched at room temperature, and the tensile properties were shown in Table 6:

[0078] Table 6 Room temperature tensile properties

[0079]

[0080] The grain size of the forged round is tested, as shown in Table 7 and Figure 2 As shown:

[0081] Table 7 Grain size

[0082]

[0083] The forged round is tested for non-metallic inclusions, as shown in Table 8 and Figure 3 As shown:

[0084] Table 8 Non-metallic inclusions

[0085]

[0086] The stress corrosion life test of the forged circle is shown in Table 9:

[0087] Table 9 Stress corrosion life

[0088]

[0089] In summary, compared with the prior art, the non-magnetic drill collar steel with improved stress corrosion resistance and the preparation method thereof of the present invention have the following advantages and beneficial effects:

[0090] The present invention adopts a slag system with relatively high basicity and Al deep deoxidation in the smelting process, and the electroslag adopts a 40F pre-melted slag system and argon protection, so as to prepare a steel billet with low oxygen and high purity. The forging adopts high-speed forging and high-temperature solid solution + appropriate low-temperature forging strengthening to forge into round steel with uniform grain size, so that the round steel has excellent conventional mechanical properties, non-magnetic properties, intergranular corrosion resistance, etc., and at the same time has a relatively high stress corrosion life.

[0091] It should be noted that, in this article, unless otherwise clearly specified and limited, the term "connection" or its synonyms should be understood in a broad sense. For example, "connection" can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. Moreover, expressions such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. At the same time, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such a process, method, article or device. In addition, "front", "back", "left", "right", "upper" and "lower" in this article are all referenced to the placement state shown in the accompanying drawings.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing non-magnetic drill collar steel with improved stress corrosion resistance, characterized in that: The preparation method of the non-magnetic drill collar steel with improved stress corrosion resistance comprises: electric furnace smelting-AOD smelting-LF refining-continuous casting-electroslag-blading-solid solution treatment-low temperature forging, wherein the chemical composition of the non-magnetic drill collar steel with improved stress corrosion resistance is controlled by mass percentage as follows: C: 0.02% to 0.06%, Si≤0.45%, Mn: 20.0% to 22.5%, P≤0.03%, S≤0.01%, Cr: 17.0% to 20.0%, Ni: 0.90% to 3.50%, Mo: 0.6% to 2.0%, N: 0.6% to 0.8%, B: ≤0.01%, PREN (Cr+3.3Mo+16N): ≥31, and the balance is Fe and unavoidable impurities; Electric furnace smelting: put the stainless steel into an electric furnace, add C: 2.5%, Cr: 22.5 and Mn ≤ 2.0%, smelt into molten steel, and remove the slag when tapping the steel. The thickness of the slag in the ladle is ≤ 50mm; AOD smelting: transfer the molten steel after slag removal from electric furnace smelting into AOD furnace, add Mn for smelting in batches, and add 70kg AI for reduction. The pre-reduction slag removal is greater than 80%, and the slag is adjusted to make the S target ≤0.

003. Slag removal is performed before steelmaking, and the composition is adjusted according to the reduction composition. LF refining: the molten steel after AOD smelting slag removal is transferred to the LF refining furnace, the N target is adjusted to 0.65% using nitriding alloy, and the molten steel composition is adjusted according to the target chemical composition by mass percentage. The temperature is adjusted before tapping, and 200 meters of Ca-Si or Ca wire is fed per furnace. After feeding the wire, 10 kg of FeB is added per furnace, and the white slag is kept for 45 minutes before tapping; Continuous casting: preparing steel ingots from molten steel after LF refining; Electroslag: Weld the tail of the steel ingot with a dummy electrode, and fill the slag system with argon gas with a pressure of >0.2MPa before electroslag for a period of ≥10min. Use a lower voltage and a smaller current first, and then gradually increase the voltage and current to obtain a remelted steel ingot. Billeting: Heat the remelted steel ingot to 1240℃ and keep it warm for more than 4 hours, and perform rapid forging or radial forging to form a billet, so that the forging ratio is ≥6%; Solution treatment: the billet is quickly returned to the furnace and heated to 1100℃ for 2 hours, then quickly cooled in water, cooled to 200℃ and air cooled; Low temperature forging: Heat the solution treated steel billet to 550°C and keep it warm for 4 hours, and perform two passes of low temperature forging with a forging ratio of 10% to form a forged circle, and cool it naturally after forging.

2. The method for preparing non-magnetic drill collar steel with improved stress corrosion resistance according to claim 1, characterized in that: During the AOD smelting process, nitrogen is blown throughout the smelting process, the reduction time is 6min-7min, and CaSi powder and 30kg / furnace AI powder are used for slag adjustment.

3. The method for preparing non-magnetic drill collar steel with improved stress corrosion resistance according to claim 1, characterized in that: During the LF refining process, N2 is blown in throughout the process, and lime is added at a rate of ≯50Kg / batch to maintain the basicity of the lime-saturated refining slag, while ensuring that FeO≤0.5%, NiO≤0.05%, the oxygen content in the steel≤30ppm, MgO: 5%-10%, and the binary basicity is controlled at 2.5%-3.0%.

4. The method for preparing non-magnetic drill collar steel with improved stress corrosion resistance according to claim 1, characterized in that: During the LF refining process, the chemical composition of white slag is controlled by mass percentage as follows: TFe: 0.48%, FeO≤0.5%, SiO2: 22.58%, AI2O3: 3.44%, CaO: 58.16%, MgO: 5%-10%, P: 0.01%, S: 0.24%, Cr2O3: 0.12%, NiO≤0.05%.

5. The method for preparing non-magnetic drill collar steel with improved stress corrosion resistance according to claim 1, characterized in that: Before the electroslag step, a cleaning step is also included to clean the oxide scale on the surface of the steel ingot and remove the head and tail caps of the steel ingot.

6. The method for preparing non-magnetic drill collar steel with improved stress corrosion resistance according to claim 1, characterized in that: In the electroslag process, the slag system adopts 40F pre-melted slag system.

7. A non-magnetic drill collar steel with improved stress corrosion resistance, characterized in that: The non-magnetic drill collar steel with improved stress corrosion resistance is produced by the preparation method of the non-magnetic drill collar steel with improved stress corrosion resistance according to any one of claims 1 to 6.

Images