Refractory steel for 460MPa-grade well control emergency equipment and preparation method thereof

Abstract

The invention discloses fire-resistant steel for 460MPa-grade well control and emergency rescue equipment. The fire-resistant steel for the well control and emergency rescue equipment comprises the following chemical components in percentage by mass: 0.05%-0.1% of C, 0.08%-0.4% of Si, 2.0%-2.2% of Mn, 0.3%-0.6% of Cr, 0.2%-0.4% of Mo, 0.08%-0.15% of Nb, 0.04%-0.11% of V, 0.01%-0.12% of Ti and less than 0.5 of carbon equivalent. The invention further discloses a preparation method of the refractory steel, a two-stage rolling process combining rough rolling and finish rolling is adopted, the finish rolling temperature of rough rolling is controlled to be 960-1060 DEG C, and rolling is conducted for 3-5 passes; 3-5 passes of finish rolling are controlled, the single rolling reduction is 15-20 mm, the accumulated rolling reduction rate of the three passes after finish rolling is larger than 30%, and the finish rolling temperature is 750-780 DEG C. The method is simple and easy to control, and the prepared steel for well control emergency rescue is good in comprehensive performance.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas well control emergency rescue equipment manufacturing, relates to a 460MPa-level refractory steel for well control emergency rescue equipment, and also relates to a preparation method of the 460MPa-level refractory steel for well control emergency rescue equipment. Background Art

[0002] As exploration and development advances into new areas, ultra-deep layers, and unconventional areas, new and old risks of well control in drilling are intertwined and superimposed. The risks of "three highs and one super" wells, horizontal wells, factory-made wells, and shallow gas wells are prominent, which poses new challenges to well control safety. Well control emergency rescue equipment mainly includes wellhead demolition and reconstruction machines. Wellhead demolition and reconstruction machines need to operate near the wellhead, facing high temperature and flame environment, and the operation time is long. In the past, the carbon structural steel used in well control rescue machines had insufficient thermal strength. As the temperature increased, its yield strength dropped rapidly, especially when the temperature was higher than 350℃, and it did not have the load-bearing capacity at high temperatures. At present, "one wrap, two packs, and three sprays" are used to provide fire and temperature protection for operating machines. It is inconvenient to install and use on site, easy to damage, and costly. The 460MPa-level refractory steel for well control rescue equipment based on service temperature induced precipitation strengthening will become the preferred material for steel for well control emergency rescue equipment due to its simple manufacturing process, high thermal strength at service temperature, and good welding performance.

[0003] Since Mo is the most effective alloying element for improving high-temperature strength, a large amount of Mo is added to traditional heat-resistant steels to improve the static strength of the material at room temperature by solid solution strengthening, thereby improving the relative strength of the material at high temperature. However, Mo is expensive. Adding a large amount of Mo will increase the material cost on the one hand, and increase the carbon equivalent on the other hand, affecting weldability. In addition, the improvement of thermal strength is limited only through the solid solution strengthening effect, and the structural stability is lacking. Therefore, reducing the Mo content to reduce costs is the focus of research. Since the properties of Nb and Mo are similar, many scholars use Nb to replace the solid solution strengthening effect of Mo, and at the same time use V, Ti and other elements to enhance thermal strength by precipitating MC carbides. However, although the precipitated MC carbides have a certain stability during the heat treatment process, they will still aggregate and grow during long-term high-temperature service, thereby reducing the grain boundary strength. At the same time, research shows that granular bainite can significantly improve the high-temperature strength of refractory steel. On the one hand, the MA structure in granular bainite will decompose into a large number of fine alloy cementite particles under service conditions, generating a large number of dislocations on the ferrite matrix, and the strength of refractory steel will drop significantly under high temperature. On the other hand, the strip structure in the bainitic ferrite in granular bainite becomes an obstacle to crack propagation. Therefore, controlling the content of granular bainite in well control and rescue steel has become a technical difficulty. Summary of the invention

[0004] The purpose of the present invention is to provide a 460MPa grade refractory steel for well control and rescue equipment, which solves the problem that the existing well control and rescue steel has low thermal strength and cannot be used for a long time at high temperature.

[0005] The present invention also aims to provide a method for preparing 460MPa grade refractory steel for well control and rescue equipment.

[0006] The first technical solution adopted by the present invention is that the 460MPa grade refractory steel for well control rescue equipment includes the following components in mass percentage: C 0.05%-0.1%, Si 0.08%-0.4%, Mn2.0%-2.2%, Cr 0.3%-0.6%, Mo 0.2%-0.4%, Nb 0.08%-0.15%, V 0.04-0.11%, Ti 0.01-0.12%, carbon equivalent <0.5, and the balance is Fe and unavoidable impurities.

[0007] The present invention is also characterized in that:

[0008] The fire-resistant steel of the present invention has a granular bainite structure in a slow cooling state. At the service temperature, the Mo element enters into the carbides formed by Nb, V and Ti to refine the carbide grains, so that the material has a higher strength at high temperature.

[0009] The room temperature yield strength of refractory steel is ≥460MPa, and the high temperature yield strength at 600℃ does not drop by more than 1 / 3 of the room temperature yield strength.

[0010] In the above technical solution, C is the most economical strengthening element. Adding C can significantly improve the strength of steel, but for refractory steel, in order to ensure excellent toughness and welding performance, the C content is controlled at 0.05% to 0.1%. Si plays a role of solid solution strengthening in steel, thereby improving the strength of refractory steel, but too high Si content will affect the surface quality of steel and damage its performance, so the Si content needs to be controlled at 0.08% to 0.4% to meet the use requirements. Mn can improve the strength of steel through solid solution strengthening, but too high Mn elements will cause central segregation of the material, which is not conducive to the corrosion resistance of refractory steel. Therefore, the Mn content needs to be controlled at 2.0% to 2.2%; the addition of Cr elements will improve the atmospheric corrosion resistance of the material. In refractory steel, the addition of Cr elements with a mass percentage of >0.2% is usually beneficial, but when the Cr element content is >0.6%, the atmospheric corrosion resistance of the material is not significantly increased. It is mainly used to improve the hardenability of steel and thus improve the strength. Therefore, the Cr content needs to be controlled at 0.3% to 0.6%; Mo elements can play a role in solid solution strengthening, and can also promote the formation of bainite, thereby achieving the effect of bainite phase transformation strengthening. The addition of Mo elements within 5% can increase the bainite content and improve the high temperature yield strength of the material. When the content is greater than 5%, Mo elements usually begin to precipitate, so the Mo element content is controlled at 0.2% to 0.4%. Nb, V, and Ti elements mainly rely on the precipitation strengthening of MC-type carbides to increase the high-temperature yield strength of steel. Therefore, the Nb content is controlled at 0.08% to 0.15%, the V content is controlled at 0.04 to 0.11%, and the Ti content is controlled at 0.01 to 0.12% to meet the use requirements, and the carbon equivalent is <0.5 to meet the welding performance.

[0011] The second technical scheme adopted by the present invention is a method for preparing 460MPa grade refractory steel for well control rescue equipment, which includes molten steel converter smelting, continuous casting, heating, hot rolling and cooling processes; in the hot rolling process, a two-stage rolling process of rough rolling combined with fine rolling is adopted, the final rolling temperature of rough rolling is controlled to be 960-1060°C, the rough rolling is controlled to be 3-5 times, and the single reduction is 20-25mm; the fine rolling is controlled to be 3-5 times, and the single reduction is 15-20mm, the starting temperature of fine rolling is 850-880°C, the cumulative reduction rate of the three times after fine rolling is greater than 30%, the final rolling temperature is 750-780°C, water cooling is accelerated to 450°C, and slowly cooled to room temperature.

[0012] The present invention is also characterized in that:

[0013] The molten steel is composed of the following components in mass percentage: C 0.05%-0.1%, Si 0.08%-0.4%, Mn2.0%-2.2%, Cr 0.3%-0.6%, Mo 0.2%-0.4%, Nb 0.08%-0.15%, V0.04-0.11%, Ti 0.01-0.12%, carbon equivalent <0.5, and the balance is Fe and unavoidable impurities.

[0014] During the converter, argon is used for converter low blowing and ladle low blowing, and ferrosilicon, metallic manganese and low-carbon ferrochrome are used in the refining process to fine-tune the composition.

[0015] The above technical solution, in the rough rolling process, controls the rolling to be 3 to 5 times, the single reduction is 20 to 25 mm, and the rough rolling final rolling temperature is controlled to be 960 to 1060 ° C. The temperature range during rough rolling is the austenite recrystallization zone. This stage adopts multiple passes and large deformation. The austenite grains obtain sufficient driving force in this stage to produce critical strain and further recrystallize, thereby reducing the grain size; in the finishing rolling process, controls the rolling to be 3 to 5 times, the single reduction is 15 to 20 mm, the finishing rolling start temperature is 850 to 880 ° C, the cumulative reduction rate of the three passes after finishing rolling is greater than 30%, and the final rolling temperature is 750 to 780 ° C; in the cooling process, water cooling is accelerated to 450 ° C, and slowly cooled to room temperature. It is self-tempered to ensure the formation of granular bainite and to ensure that the heat-resistant MC precipitation phase has supersaturation and disperses and precipitates in the service temperature (> 600 ° C) range, providing the material with high temperature strength.

[0016] The beneficial effects of the present invention are:

[0017] 1) The well control and rescue steel provided by the present invention adopts a low-carbon design in terms of composition design, and adds Nb, V, and Ti microalloy strengthening elements. The carbide precipitation strengthening material formed by Nb, V, and Ti at the service temperature makes the material have higher strength at high temperature, and the carbon equivalent is less than 0.5 to meet good welding performance.

[0018] 2) The 460MPa grade well control emergency steel based on service temperature induced precipitation strengthening of the present invention refines the carbide grains at the service temperature through the entry of Mo element into the carbides formed by Nb, V and Ti, so that the material has higher strength at high temperature.

[0019] 3) A two-stage rolling process of rough rolling combined with finishing rolling is adopted, the final rolling temperature of rough rolling is controlled to be 960-1060℃, the rolling is controlled to be 3-5 times, and the single reduction is 20-25mm; the finishing rolling is controlled to be 3-5 times, and the single reduction is 15-20mm, the starting temperature of finishing rolling is 850-880℃, the cumulative reduction rate of the three passes after finishing rolling is greater than 30%, and the final rolling temperature is 750-780℃; water cooling is accelerated to 400-500℃, and slowly cooled to room temperature. It is self-tempered to ensure the formation of granular bainite and the heat-resistant MC precipitation phase has supersaturation, dispersed precipitation in the service temperature range (>600℃), and provide high temperature strength of the material.

[0020] 4) Through composition design and organization control, the steel grade obtains granular bainite organization. The MA organization in the granular bainite will decompose into a large number of fine alloy cementite particles under service conditions, and a large number of dislocations will be generated on the ferrite matrix. The strength of the refractory steel will drop significantly at high temperatures, and the strip structure in the bainitic ferrite will become an obstacle to crack propagation. The room temperature yield strength of the heat-resistant steel is ≥460MPa, and the high temperature yield strength at 600°C does not drop by more than 1 / 3 of the room temperature yield strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the following briefly introduces the drawings required for use in the embodiment:

[0022] Figure 1 This is the metallographic structure diagram of Example 1 of the present invention;

[0023] Figure 2 This is the metallographic structure diagram of Example 2 of the present invention. DETAILED DESCRIPTION

[0024] The following is a detailed description in conjunction with the accompanying drawings and embodiments of the present invention. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0025] Example 1

[0026] Rolling 30mm fire-resistant steel plate for well control and rescue equipment:

[0027] The steel billet is composed of the following components by mass percentage: C: 0.08%, Si: 0.1%, Mn: 2.0%, Cr: 0.3%, Mo: 0.4%, Nb: 0.09%, V: 0.04%, Ti: 0.014%, and the rest is Fe and inevitable impurities; the specific preparation steps are as follows:

[0028] (1) Argon is used for steel materials entering the furnace, low-pressure blowing in the converter and low-pressure blowing in the ladle. Ferrosilicon, metallic manganese and low-carbon ferrochrome are used for fine-tuning of the composition during the refining process. Ferrosilicon powder and aluminum particles are deoxidized, and the steel is tapped after the temperature and composition are appropriate.

[0029] (2) Continuous casting: The molten steel is cast into continuous casting billets with a thickness of 100 mm, ensuring that the compression ratio during the rolling process is not less than 3 times;

[0030] (3) Reheating of the cast slab: The continuous casting slab is heated to 1100°C and the furnace time is 9 min / cm;

[0031] (4) The final rolling temperature of the rough rolling is controlled to be 1060°C, and the rolling is controlled to be 5 passes with a single rolling reduction of 25 mm;

[0032] (5) Controlled finishing rolling: 5 passes, with a single reduction of 20 mm, a finishing starting temperature of 870 ° C, a cumulative reduction rate of more than 30% in the last three passes of finishing, and a final rolling temperature of 760 ° C.

[0033] (6) Accelerate cooling by water cooling to 480°C and then slowly cool to room temperature.

[0034] The structure of the above 30 mm fire-resistant steel plate is ferrite + granular bainite structure, and the bainite content is about 52%.

[0035] The mechanical properties of the above 30mm fire-resistant steel plate are as follows: Room temperature: Rm: 630MPa, R p0.2 528MPa, high temperature (600℃): Rm: 408MPa, R p0.2 365MPa.

[0036] Example 2

[0037] Rolling 20mm fire-resistant steel plate for well control and rescue equipment:

[0038] The steel billet is composed of the following components in mass percentage: C: 0.10%, Si: 0.2%, Mn: 2.2%, Cr: 0.5%, Mo: 0.5%, Nb: 0.04%, V: 0.043%, Ti: 0.016%, and the rest is Fe and unavoidable impurities; the preparation steps are as follows:

[0039] (1) Argon is used for steel materials entering the furnace, low-pressure blowing in the converter and low-pressure blowing in the ladle. Ferrosilicon, metallic manganese and low-carbon ferrochrome are used for fine-tuning of the composition during the refining process. Ferrosilicon powder and aluminum particles are deoxidized, and the steel is tapped after the temperature and composition are appropriate.

[0040] (2) Continuous casting: The molten steel is cast into continuous casting billets with a thickness of 80 mm, ensuring that the compression ratio during the rolling process is not less than 3 times;

[0041] (3) Reheating of the cast slab: The continuous casting slab is heated to 1100°C and the furnace time is 9 min / cm;

[0042] (4) The final rolling temperature of the rough rolling is controlled to be 1050°C, and the rolling is controlled to be 5 passes with a single rolling reduction of 20 mm;

[0043] (5) Controlled finishing rolling: 5 passes, single rolling reduction is 18 mm, finishing rolling start temperature is 870 ° C, the cumulative rolling reduction rate of the last three passes is greater than 30%, and the final rolling temperature is 760 ° C.

[0044] (6) Accelerate cooling by water cooling to 450°C and then slowly cool to room temperature.

[0045] The above-mentioned 20mm fire-resistant steel plate for well control rescue equipment has a ferrite + granular bainite structure, and the bainite content is about 87%.

[0046] The mechanical properties of the above 12.5mm fire-resistant steel plate for construction are as follows: Room temperature: Rm: 643MPa, R p0.2 531MPa, high temperature (600℃): Rm: 414MPa, R p0.2 374MPa.

[0047] Figure 1 is a metallographic structure photograph of Example 1, Figure 2 is a metallographic photograph of Example 2, and the test method refers to GB / T13298-2015; Table 1 is the room temperature and high temperature mechanical properties data of Example 1, Example 2, and the control example, and the test method refers to GB / T 228.1-2010;

[0048] Table 1

[0049]

[0050] It can be seen that the microstructures of all embodiments are bainite structures, and the bainite content is greater than 50%. The yield strength at a high temperature of 600° C. is much higher than 2 / 3 of the yield strength at room temperature.

[0051] Example 3

[0052] Rolling 25mm fire-resistant steel plate for well control rescue equipment:

[0053] The steel billet is composed of the following components by mass percentage: C: 0.06%, Si: 0.2%, Mn: 2.0%, Cr: 0.5%, Mo: 0.5%, Nb: 0.04%, V: 0.08%, Ti: 0.03%; the rest is Fe and inevitable impurities; the preparation steps are as follows:

[0054] (1) Argon is used for steel materials entering the furnace, low-pressure blowing in the converter and low-pressure blowing in the ladle. Ferrosilicon, metallic manganese and low-carbon ferrochrome are used for fine-tuning of the composition during the refining process. Ferrosilicon powder and aluminum particles are deoxidized, and the steel is tapped after the temperature and composition are appropriate.

[0055] (2) Continuous casting: The molten steel is cast into continuous casting billets with a thickness of 80 mm, ensuring that the compression ratio during the rolling process is not less than 3 times;

[0056] (3) Reheating of the cast slab: The continuous casting slab is heated to 1100°C and the furnace time is 9 min / cm;

[0057] (4) The final rolling temperature of the rough rolling is controlled to be 1050°C, and the rolling is controlled to be 5 passes with a single rolling reduction of 20 mm;

[0058] (5) Controlled finishing rolling: 5 passes, single rolling reduction is 18 mm, finishing rolling start temperature is 870 ° C, the cumulative rolling reduction rate of the last three passes is greater than 30%, and the final rolling temperature is 760 ° C.

[0059] (6) Accelerate cooling by water cooling to 450°C and then slowly cool to room temperature.

[0060] The above-mentioned 20mm fire-resistant steel plate for well control rescue equipment has a ferrite + granular bainite structure, and the bainite content is about 78%.

[0061] Although the embodiments of the present invention are described in conjunction with the accompanying drawings, the patent owner may make various variations or modifications within the scope of the appended claims. As long as they do not exceed the protection scope described in the claims of the present invention, they should be within the protection scope of the present invention.

Claims

1. 460MPa grade fire-resistant steel for well control and rescue equipment, characterized in that: The invention comprises the following components in mass percentage: C 0.05%-0.1%, Si 0.08%-0.4%, Mn 2.0%-2.2%, Cr 0.3%-0.6%, Mo 0.2%-0.4%, Nb 0.08%-0.15%, V 0.04-0.11%, Ti 0.01-0.12%, carbon equivalent <0.5, and the balance is Fe and unavoidable impurities.

2. The 460MPa grade refractory steel for well control and rescue equipment according to claim 1, characterized in that: The fire-resistant steel has a granular bainite structure in the slow cooling state.

3. The 460MPa grade refractory steel for well control and rescue equipment according to claim 1, characterized in that: The room temperature yield strength of the fire-resistant steel is ≥460MPa, and the high temperature yield strength at 600°C decreases by no more than 1 / 3 of the room temperature yield strength. The method for preparing 4.460MPa grade refractory steel for well control and rescue equipment is characterized in that: The invention comprises the steps of molten steel converter smelting, continuous casting, heating, hot rolling and cooling; in the hot rolling step, a two-stage rolling process of rough rolling combined with finish rolling is adopted, the final rolling temperature of the rough rolling is controlled to be 960-1060°C, the rough rolling is controlled to be 3-5 times, and the single reduction is 20-25mm; the finish rolling is controlled to be 3-5 times, and the single reduction is 15-20mm, the start temperature of the finish rolling is 850-880°C, the cumulative reduction rate of the three times after the finish rolling is greater than 30%, the final rolling temperature is 750-780°C, the water cooling is accelerated to 450°C, and the cooling is slowly cooled to room temperature.

5. The method for preparing 460MPa grade refractory steel for well control and rescue equipment according to claim 4, characterized in that: The molten steel is composed of the following components in mass percentage: C 0.05%-0.1%, Si 0.08%-0.4%, Mn 2.0%-2.2%, Cr 0.3%-0.6%, Mo 0.2%-0.4%, Nb 0.08%-0.15%, V 0.04%-0.11%, Ti 0.01%-0.12%, carbon equivalent <0.5, and the balance is Fe and unavoidable impurities.

6. The method for preparing 460MPa grade refractory steel for well control and rescue equipment according to claim 4, characterized in that: During the converter, argon is used for converter low blowing and ladle low blowing, and ferrosilicon, metallic manganese and low-carbon ferrochrome are used in the refining process to fine-tune the composition.

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