Low-alloy structural steel for preparing petroleum drilling tool and preparation method of low-alloy structural steel

Abstract

The invention discloses a low-alloy structural steel component for preparing a petroleum drilling tool, which comprises the following elements in percentage by mass: 0.32 to 0.41 percent of carbon, 0.12 to 0.38 percent of silicon, 0.65 to 1.20 percent of manganese, less than or equal to 0.010 percent of phosphorus, less than or equal to 0.008 percent of sulfur, 0.75 to 1.35 percent of chromium, 0.2 to 0.4 percent of molybdenum, less than or equal to 0.3 percent of nickel, 0.01 to 0.04 percent of niobium, 0.005 to 0.015 percent of titanium and the balance of iron. The alloy element ratio is improved and the technological process is optimized on the basis of the prior art, the problems that 4137MA alloy structural steel is insufficient in toughness, coarse and large in grain, limited in strength, poor in high-temperature stability and the like are successfully solved, no technical obstacle exists when the 4137MA alloy structural steel is implemented under the conditions of the prior art, and a petroleum drilling tool made of the 4137MA alloy structural steel is good in mechanical property and good in performance. Compared with the prior art, the material has the advantages of simple structure and high use safety, so that the probability of occurrence of accidents such as thread slipping or rod breakage of the petroleum drilling tool is remarkably reduced, the popularization and application of the material have greater economic benefits and social benefits, the mechanical property and the use reliability of the petroleum drilling tool material are remarkably improved, and a safer and more durable material solution is provided for petroleum drilling engineering.

Description

Technical Field

[0001] The invention relates to the technical field of metal material preparation, in particular to a low alloy structural steel for preparing oil drilling tools and a preparation method thereof. Background Art

[0002] Oil drilling is a complex and high-risk operation, and the drilling depth can usually reach several thousand meters. In this process, the supporting oil drilling tools not only have to bear the cumulative weight formed by multiple sections in series, but also have to cope with the huge torque applied by the drilling rig, so there are extremely high requirements for the mechanical properties of the drilling tool materials, such as strength, toughness, and wear resistance.

[0003] At present, the material of oil drilling tools generally uses the commercially available 4137MA alloy structural steel. This steel has long been widely used in drilling tool manufacturing because its mechanical properties are closer to the requirements of oil drilling tools. However, many years of application practice have shown that although 4137MA alloy structural steel can meet the basic requirements of oil drilling tools to a certain extent, it still has some shortcomings that cannot be ignored, especially under high load and complex stress conditions, its performance limitations gradually emerge. The main problems are as follows: 1. Lack of toughness During use, 4137MA alloy structural steel has poor toughness performance, especially in high-stress situations such as deep well drilling, and is prone to local brittle fracture. This fracture not only increases the frequency of drilling tool replacement, but may also lead to a series of problems such as project shutdown and equipment damage, thus causing huge economic losses.

[0004] 2. Grain size problem After the quenching and tempering treatment, the metal grain size of the traditional 4137MA steel is relatively coarse, resulting in the material's strength and toughness failing to reach the ideal state. The coarse grains reduce the material's fatigue resistance, making it easy for microcracks to expand under complex working conditions, which in turn causes the drill tool to break.

[0005] 3. Limited material strength The tensile strength and yield strength of steel are important indicators of oil drilling tool safety. However, 4137MA steel has limited strength performance in long-term operations and cannot meet the requirements of some more extreme drilling conditions. Especially in ultra-deep wells or ultra-high torque conditions, its strength is obviously insufficient, which makes the drilling tools prone to catastrophic accidents such as thread slippage and rod breakage.

[0006] 4. Poor stability under high temperature operation During the oil drilling process, drilling tools are often in a high temperature and high pressure environment. The existing 4137MA alloy steel has poor structural stability at high temperatures, and austenite grains tend to grow, resulting in unsatisfactory durability and stability at high temperatures, thus affecting the overall drilling efficiency and safety. Summary of the invention

[0007] The present invention mainly aims at the practical problems that the existing 4137MA alloy structural steel has insufficient toughness, coarse grains, limited material strength and poor high-temperature stability, and proposes a low-alloy structural steel for preparing oil drilling tools and a preparation method thereof. The component is based on the component of the grade 4137MA alloy structural steel, and some alloy elements that promote metal grain refinement are added to achieve the purpose of enhancing the mechanical properties of the material, so as to meet the use requirements of oil drilling tools under extreme working conditions.

[0008] In order to solve the above problems, the present invention provides a low alloy structural steel for preparing oil drilling tools, wherein the low alloy structural steel contains the following elements in percentage by mass: Carbon (C): 0.32-0.41%, Silicon (Si): 0.12-0.38%, Manganese (Mn): 0.65-1.20%, Phosphorus (P): ≤0.010%, Sulfur (S): ≤0.008%, Chromium (Cr): 0.75-1.35%, Molybdenum (Mo): 0.2-0.4%, Nickel (Ni): ≤0.3%, Niobium (Nb): 0.01-0.04%, Titanium (Ti): 0.005-0.015%, The balance is iron.

[0009] As a further improvement, the low-alloy structural steel contains the following elements in mass percentage: carbon: 0.32-0.41%, silicon: 0.12-0.38%, manganese: 0.65-1.20%, phosphorus: ≤0.010%, sulfur: ≤0.008%, chromium: 0.75-1.35%, molybdenum: 0.2-0.4%, nickel: ≤0.3%, niobium: 0.015-0.035%, titanium: 0.007-0.012%, and the balance is iron.

[0010] As a further improvement, the low-alloy structural steel contains the following elements in mass percentage: carbon: 0.32-0.41%, silicon: 0.12-0.38%, manganese: 0.65-1.20%, phosphorus: ≤0.010%, sulfur: ≤0.008%, chromium: 0.75-1.35%, molybdenum: 0.2-0.4%, nickel: ≤0.3%, niobium: 0.025-0.030%, titanium: 0.008-0.010%, and the balance is iron.

[0011] As a further improvement, the method for preparing low alloy structural steel comprises the following steps: S1. Raw materials composed of the chemical elements are arranged in proportion, wherein the raw materials include carbon, silicon, manganese, phosphorus, sulfur, chromium, molybdenum, nickel, niobium, titanium and the remainder iron; S2. Smelting the iron, carbon, silicon, manganese, phosphorus, sulfur, chromium, molybdenum and nickel in the raw materials, controlling the temperature in the furnace to ensure uniform dissolution of the chemical components; S3. During the smelting process, titanium is added to react with nitrogen to form TiN compounds. TiN plays a role in refining the grains and absorbs hydrogen in the molten steel, acting as a deoxidizer and degassing agent, playing a role in deoxidation and grain refinement. S4, then adding niobium element, the added niobium has a dragging effect in the molten steel, resulting in recrystallization of the austenite metallographic structure during the thermal deformation process, thereby achieving the purpose of grain refinement, and at the same time niobium combines with sulfur, nitrogen and carbon in the molten steel, and forms an alloy with elements such as chromium and nickel, refining the austenite grains, and niobium element is mixed with titanium element in the molten steel to form NbTi alloy, further improving the mechanical properties of low alloy structural steel; S5. The material is formed through rolling and heat treatment processes, and the required low-alloy structural steel product is obtained after quenching and tempering; S6. Finally test the mechanical properties of low alloy structural steel to ensure that it meets the tensile strength and yield strength requirements of oil drilling tools.

[0012] As a further improvement scheme, the smelting temperature is controlled at 1500-1600° C., and the molten steel is continuously stirred during the smelting process to ensure that all elements are evenly distributed in the molten steel to prevent element segregation.

[0013] As a further improvement plan, during the rolling process, by controlling the cooling rate and heating temperature, the excessive growth of austenite grains can be prevented and the recrystallization process in the hot deformation stage can be delayed, thereby improving the mechanical properties of the material.

[0014] As a further improvement, the heating temperature is controlled at 850-950°C to ensure that the material is fully austenitized and to avoid excessive grain growth.

[0015] As a further improvement plan, during the cooling process after rolling, the cooling rate is controlled at 10-30℃ / s to maintain grain refinement and prevent excessive internal stress in the material due to too fast cooling or grain coarsening due to too slow cooling.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: 1. Improve toughness and fracture resistance The present invention significantly refines the grain structure of the material and enhances toughness by adding appropriate amounts of niobium (Nb) and titanium (Ti) elements to 4137MA alloy structural steel. The added niobium directly produces compounds with sulfur, carbon and nitrogen in the air in high-temperature molten steel, and directly forms alloys with elements such as titanium, chromium, and nickel. Among them, the niobium-titanium alloy has the greatest impact on improving the mechanical properties of low-alloy structural steel. The alloy formed by niobium and titanium elements effectively prevents the growth of austenite grains and delays recrystallization during thermal deformation, so that the material exhibits better resistance to brittle fracture under high stress and complex stress conditions, especially in deep wells and high torque operations, thereby greatly reducing the risk of drill fracture. Therefore, adding niobium and titanium elements is the most correct choice.

[0017] 2. Enhance the strength and fatigue resistance of materials By introducing trace amounts of niobium and titanium, the present invention successfully refines austenite grains, and by adding niobium, promotes the recrystallization of austenite grains during thermal deformation, significantly improving the tensile strength and yield strength of the material. In addition, the refined grain structure improves the material's fatigue resistance, effectively reduces the tendency of microcracks to expand, greatly prolongs the service life of drilling tools in long-term operations, reduces the frequency of replacement, and improves operational safety and economic benefits.

[0018] 3. Improve high temperature stability The present invention significantly improves the stability of low alloy structural steel at high temperatures by reasonably controlling the temperature and cooling rate during smelting and heat treatment. The added titanium element and nitrogen generate TiN compounds, which not only refine the grains, but also the smaller the grains of the metal structure, the greater its strength. The refined grains can prevent the growth of austenite grains and delay the recrystallization of the thermal deformation process, thereby achieving the purpose of improving the mechanical properties of the material. It can also effectively absorb hydrogen in the molten steel and act as a deoxidizer, thereby reducing the damage caused by hydrogen embrittlement. This refinement and deoxidation process enhances the durability of the material under high temperature and high pressure environments, ensuring its long-term stable operation in oil drilling.

[0019] 4. Reduce the internal stress of the material By properly controlling the cooling rate, the present invention effectively avoids grain coarsening and excessive internal stress concentration. Accurate control of the cooling rate not only helps maintain the refined grain structure, but also effectively reduces the internal stress accumulation problem caused by excessive cooling, and prevents the drill from breaking due to internal stress imbalance during use, thereby further improving the safety of the material.

[0020] 5. Simple process and significant economic benefits Based on the existing 4137MA alloy structural steel, the present invention achieves a significant improvement in mechanical properties by optimizing the addition of trace elements without the need for complex process modifications. Although the addition of niobium and titanium elements will increase production costs to a certain extent, the performance improvement brought about by it far exceeds the increased costs, especially significantly extending the service life of the drilling tools, reducing the accident rate, and bringing great economic benefits.

[0021] In summary, the present invention successfully solves the problems of insufficient toughness, coarse grains, limited strength and poor high-temperature stability of 4137MA alloy structural steel by improving the alloy element ratio and optimizing the process flow on the basis of the existing technology, significantly improves the mechanical properties and reliability of oil drilling tool materials, and provides a safer and more durable material solution for oil drilling projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the metallographic structure diagram of the sample of the present invention.

[0023] Figure 2 This is the metallographic structure diagram of the 4137MA alloy structure sample.

[0024] Figure 3 The present invention shows the chemical composition and mechanical properties of low alloy structural steel used for the preparation of oil drilling tools. DETAILED DESCRIPTION

[0025] The present invention will be further explained below in conjunction with the accompanying drawings and embodiments.

[0026] The method for preparing low alloy structural steel of the present invention comprises the following steps: S1. Raw materials composed of the chemical elements are arranged in proportion, wherein the raw materials include carbon, silicon, manganese, phosphorus, sulfur, chromium, molybdenum, nickel, niobium, titanium and the remainder iron; S2. Smelting the iron, carbon, silicon, manganese, phosphorus, sulfur, chromium, molybdenum and nickel in the raw materials, controlling the temperature in the furnace to ensure uniform dissolution of the chemical components; S3. During the smelting process, titanium is added to react with nitrogen to form TiN compounds. TiN plays a role in refining the grains and absorbs hydrogen in the molten steel, acting as a deoxidizer and degassing agent, playing a role in deoxidation and grain refinement. S4, then adding niobium element, the added niobium has a dragging effect in the molten steel, resulting in recrystallization of the austenite metallographic structure during the thermal deformation process, thereby achieving the purpose of grain refinement, and at the same time niobium combines with sulfur, nitrogen and carbon in the molten steel, and forms an alloy with elements such as chromium and nickel, refining the austenite grains, and niobium element is mixed with titanium element in the molten steel to form NbTi alloy, further improving the mechanical properties of low alloy structural steel; S5. The material is formed through rolling and heat treatment processes, and the required low-alloy structural steel product is obtained after quenching and tempering; S6. Finally test the mechanical properties of low alloy structural steel to ensure that it meets the tensile strength and yield strength requirements of oil drilling tools.

[0027] During the rolling process, by controlling the cooling rate and heating temperature, the excessive growth of austenite grains is prevented, and the recrystallization process in the hot deformation stage is delayed, thereby improving the mechanical properties of the material. The heating temperature is controlled at 850-950°C to ensure that the material is fully austenitized and to avoid excessive grain growth. During the cooling process after rolling, the cooling rate is controlled at 10-30°C / s to maintain grain refinement and prevent excessive internal stress from being generated inside the material due to too fast cooling or grain coarsening caused by too slow cooling. By reasonably controlling the cooling rate, the present invention effectively avoids grain coarsening and excessive concentration of internal stress. Precise control of the cooling rate not only helps to maintain the refined grain structure, but also effectively reduces the problem of internal stress accumulation caused by too fast cooling, and prevents fracture accidents caused by internal stress imbalance during use of the drill bit, thereby further improving the safety of the material.

[0028] The low alloy structural steel component for preparing oil drilling tools described in the present invention contains the following element components measured by mass percentage, wherein carbon: 0.32-0.41, silicon: 0.12-0.38, manganese: 0.65-1.20, phosphorus: ≤0.010, sulfur: ≤0.008, chromium: 0.75-1.35, molybdenum: 0.2-0.4, nickel: ≤0.3, niobium: 0.01-0.04, titanium: 0.005-0.015, and the rest is iron. The principle of the above component configuration is based on the proportion of the commercially available grade 4137 alloy structural steel, and trace amounts of niobium and titanium are added to improve the mechanical properties of the target material. Professional and technical personnel are well aware that there are many factors that affect the mechanical properties of steel in nature, among which chemical elements have the greatest influence, such as niobium and titanium elements directly affect the grain size of the metal in the metallurgical process. As known from metallurgy, niobium is a metal element with high thermal stability and thermal conductivity. It is easy to directly combine with sulfur, nitrogen and carbon in molten steel, and form alloys with elements such as titanium, chromium and nickel. Among them, niobium and titanium alloys have the greatest impact on improving the mechanical properties of low-alloy structural steel. Titanium is a transition metal element. Titanium added to molten steel combines with nitrogen to form TiN. TiN has the ability to absorb hydrogen. Therefore, titanium will act as a deoxidizer and degasser in the steelmaking process. The most important thing is that titanium plays a role in refining grains during the smelting process. It is common sense that the smaller the grain size of the metal structure, the better the mechanical properties obtained. In addition, the refined grains can prevent the growth of austenite grains and delay the quenching and recrystallization in the hot deformation stage. The benefit brought by this effect is to improve the mechanical properties of the material. In order to verify the rationality of the components described in the present invention, the inventors fine-tune the proportion of niobium and titanium elements within the permitted range of component measurement, and after smelting and rolling into profiles, take samples for mechanical property testing to seek the best performance and economic ratio. The present invention has been verified by 9 examples in the qualitative verification stage. Figure 3 Table of chemical composition and mechanical properties of low alloy structural steel used for the preparation of oil drilling tools.

[0029] It can be seen from the above examples that the present invention achieves the purpose of material enhancement by reasonably adding a certain amount of niobium and titanium elements on the basis of the formula of grade 4137 alloy steel. This technical solution is simple and reasonable, and there is no technical obstacle to its implementation under existing technical conditions. Although the addition of trace niobium and titanium elements will increase the production cost a little, the later benefits brought by the increase in material performance are far greater than the increased production cost. From the above example verification data, it can be seen that for every 0.01% increase in the mass fraction of titanium element, its yield strength increases by 10-15Mpa and the tensile strength increases by 20-30Mpa. Despite this, the titanium element in the component cannot be too much, otherwise the hardness of the material made is too hard, resulting in poor toughness of the material. Therefore, the amount of titanium element added should be controlled within a certain range. In addition, the added niobium has a dragging effect in the molten steel, resulting in the recrystallization of the austenite metallographic structure during the hot deformation process, thereby achieving the purpose of grain refinement. In addition, the added niobium element is mixed with the titanium element in the molten steel to form a NbTi alloy, which can increase the mechanical properties of the material. The above positive effects are reflected in the examples to varying degrees. After comprehensive performance comparison, it is concluded that Example 9 is the best example of the present invention. The material made of this component has excellent mechanical properties and is particularly suitable for oil drilling tool manufacturing. The improvement has avoided the occurrence of slippage or rod breakage accidents during the operation of oil drilling tools from the material aspect, and its application has great economic and social benefits.

[0030] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features of the invention described herein.

Claims

1. A low alloy structural steel for preparing oil drilling tools, characterized in that: The low alloy structural steel contains the following elements in percentage by mass: Carbon (C): 0.32-0.41%, Silicon (Si): 0.12-0.38%, Manganese (Mn): 0.65-1.20%, Phosphorus (P): ≤0.010%, Sulfur (S): ≤0.008%, Chromium (Cr): 0.75-1.35%, Molybdenum (Mo): 0.2-0.4%, Nickel (Ni): ≤0.3%, Niobium (Nb): 0.01-0.04%, Titanium (Ti): 0.005-0.015%, The balance is iron.

2. The low alloy structural steel according to claim 1, characterized in that: The low alloy structural steel contains the following elements by mass percentage: carbon: 0.32-0.41%, silicon: 0.12-0.38%, manganese: 0.65-1.20%, phosphorus: ≤0.010%, sulfur: ≤0.008%, chromium: 0.75-1.35%, molybdenum: 0.2-0.4%, nickel: ≤0.3%, niobium: 0.015-0.035%, titanium: 0.007-0.012%, the balance is iron.

3. The low alloy structural steel according to claim 1, characterized in that: The low alloy structural steel contains the following elements in percentage by mass: carbon: 0.32-0.41%, silicon: 0.12-0.38%, manganese: 0.65-1.20%, phosphorus: ≤0.010%, sulfur: ≤0.008%, chromium: 0.75-1.35%, molybdenum: 0.2-0.4%, nickel: ≤0.3%, niobium: 0.025-0.030%, titanium: 0.008-0.010%, and the balance is iron.

4. The low alloy structural steel according to any one of claims 1 to 3, characterized in that: The method for preparing low alloy structural steel comprises the following steps: S1. Raw materials composed of the chemical elements are arranged in proportion, wherein the raw materials include carbon, silicon, manganese, phosphorus, sulfur, chromium, molybdenum, nickel, niobium, titanium and the remainder iron; S2. Smelting the iron, carbon, silicon, manganese, phosphorus, sulfur, chromium, molybdenum and nickel in the raw materials, controlling the temperature in the furnace to ensure uniform dissolution of the chemical components; S3. During the smelting process, titanium is added to react with nitrogen to form TiN compounds. TiN plays a role in refining the grains and absorbs hydrogen in the molten steel, acting as a deoxidizer and degassing agent, playing a role in deoxidation and grain refinement. S4, then adding niobium element, the added niobium has a dragging effect in the molten steel, resulting in recrystallization of the austenite metallographic structure during the thermal deformation process, thereby achieving the purpose of grain refinement, and at the same time niobium combines with sulfur, nitrogen and carbon in the molten steel, and forms an alloy with elements such as chromium and nickel, refining the austenite grains, and niobium element is mixed with titanium element in the molten steel to form NbTi alloy, further improving the mechanical properties of low alloy structural steel; S5. The material is formed through rolling and heat treatment processes, and the required low-alloy structural steel product is obtained after quenching and tempering; S6. Finally test the mechanical properties of low alloy structural steel to ensure that it meets the tensile strength and yield strength requirements of oil drilling tools.

5. The low alloy structural steel according to claim 4, characterized in that: The smelting temperature is controlled at 1500-1600° C., and the molten steel is continuously stirred during the smelting process to ensure that all elements are evenly distributed in the molten steel to prevent element segregation.

6. The low alloy structural steel according to claim 4, characterized in that: During the rolling process, by controlling the cooling rate and heating temperature, the excessive growth of austenite grains is prevented and the recrystallization process in the hot deformation stage is delayed, thereby improving the mechanical properties of the material.

7. The low alloy structural steel according to claim 6, characterized in that: The heating temperature is controlled at 850-950℃ to ensure that the material is fully austenitized and to avoid excessive grain growth.

8. The low alloy structural steel according to claim 6 or 7, characterized in that: During the cooling process after rolling, the cooling rate is controlled at 10-30℃ / s to maintain grain refinement and prevent excessive internal stress in the material due to too fast cooling or grain coarsening due to too slow cooling.

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