An H-class sucker rod steel and its heat treatment process

Abstract

The present invention relates to an H-class pumping steel and its heat treatment process, belonging to the special steel technology field. The main feature of the present invention is that on the basis of the conventional 30CrNiMo steel, the nickel and chromium are reduced, the amount of copper is increased, and a trace amount of vanadium is added. Through the matching heat treatment process, its mechanical properties reach the national standard of the original steel for H-class pumping rods, reducing the production cost of the steel. The present invention determines two heat treatment process conditions of normalizing + tempering and quenching and tempering, and the matrix structure is tempered sorbite. It has been proved that both meet the performance standards of H-class pumping rod steel and have good anti-hydrogen embrittlement performance.

Description

Technical Field

[0001] The present invention relates to an H-class sucker rod steel and its heat treatment process, belonging to the special steel technology field. Background Art

[0002] Looking at the world's oil and gas development situation, rod pumping is the most traditional and widely used oil production method. Approximately 75% of China's oil is extracted using sucker rod technology. With the increase in the number of deep wells and ultra-deep wells, the pump depth and rod load of sucker rods have also increased accordingly. The traditional C, D, and K grades can no longer meet the requirements for the exploitation of unconventional oilfields. Due to its high-strength characteristics, H-class sucker rod steel has gradually replaced other grades in oilfields with complex environments. However, in oilfields with complex environments, substances such as H2S can cause corrosion or hydrogen embrittlement effects on sucker rods, resulting in the failure of sucker rods, which has a significant impact on production safety and economic benefits. At the same time, with the soaring prices of various metal elements in the international market, relatively expensive alloy elements such as nickel in sucker rods have greatly increased the production cost.

[0003] Therefore, considering anti-hydrogen embrittlement and economic costs, it is particularly important to design a low-cost sucker rod steel with high anti-hydrogen embrittlement performance and its corresponding heat treatment process. In terms of alloy composition design, according to relevant literature, ~1% wt.% of nickel has good anti-H2S performance, and appropriate addition of copper helps to improve anti-hydrogen embrittlement performance. Finally, through experimental verification, normalizing + tempering and quenching and tempering heat treatment processes can obtain H-class sucker rod steel that meets mechanical and hydrogen embrittlement performance requirements.

[0004] Comparative Document 1, a super H-class sucker rod disclosed in the patent application with the application number CN200710188007.0, the chemical composition of the steel used for the sucker rod is as follows by weight percentage: carbon 0.07% - 0.13%, silicon 0.40% - 1.20%, manganese 1.60% - 2.2%, chromium 0.60% - 1.70%, molybdenum 0.20% -

[0005] 0.40%, nickel ≤ 0.3%, copper ≤ 0.20%, phosphorus ≤ 0.025%, sulfur ≤ 0.25%, and the balance is iron; the sucker rod undergoes quenching and tempering heat treatment in sequence, and the quenching temperature of the heat treatment of the sucker rod is 900°C -

[0006] At 950°C, hold for 1 hour, then carry out water cooling, followed by tempering treatment. The tempering temperature is 330°C to 370°C. After holding for 2 hours, air cool. The tensile strength of the present invention exceeds the highest level H of the current sucker rod strength, that is, it exceeds 1136 MPa, and the fatigue strength meets the petroleum industry standard. Its manufacturing process is simple and the performance is stable, and it can be used in oil wells with very high load requirements. However, the invention is only based on the basic requirements of the SY / T5029-2003 H-class sucker rod standard and the SY / T6272-1997 sucker rod fatigue strength standard for mechanical properties and fatigue strength, and does not consider the hydrogen embrittlement and corrosion effects caused by H2S, etc. in complex environment oilfields, which may lead to fractures. Comparative document 2, CN200410079237.X discloses a corrosion-resistant sucker rod and its manufacturing method. The material of the corrosion-resistant sucker rod of the present invention is alloy steel, and the alloy steel contains the following alloy elements (weight percentage): C: 0.40 - 0.45%, Mn: 0.65 - 1.10%, Si: 0.15 - 0.35%, Cr: 0.80 - 1.10%, Mo: 0.15 - 0.25%, P: 0.010 - 0.035%, S: 0.015 - 0.040%, Ni: 0.015 - 0.045%. After: smelting, rolling, forging; heat treatment, using the principle that the compression coefficient is less than the allowable maximum compression coefficient and no forging defects such as bending, folding, and cracking occur, the large rod diameter rod is increased in specifications, which increases the selection space for the matching of multi-stage sucker rods in deep wells. The produced sucker rods have good bearing capacity and corrosion resistance. Summary of the Invention

[0007] The purpose of the present invention is to propose an H-class sucker rod steel and its heat treatment process. Through composition design and related heat treatment processes, an H-class sucker rod steel with mechanical properties meeting the national standard requirements and having certain hydrogen embrittlement resistance is obtained.

[0008] For the above purpose, the specific technical solution of the present invention is as follows:

[0009] An H-class sucker rod steel, characterized in that the mass percentage of chemical components is:

[0010] C 0.26 - 0.32%, Si 0.15 - 0.30%, Mn 0.5 - 0.9%, Mo 0.2 - 0.5%, Cr 0.6 - 1.0%, Ni 0.9 - 1.4%, Cu 0.1 - 0.3%, V 0.06 - 0.10%, S < 0.01%, P < 0.01%, and the balance is Fe. For the heat treatment process of the H-class sucker rod steel as described above, it is characterized in that the heat treatment process is divided into two types: normalizing + tempering heat treatment process and quenching and tempering heat treatment process. Among them, the normalizing + tempering heat treatment process is divided into heat preservation,

[0011] cooling, tempering, and air cooling stages:

[0012] Step 1: Heat the original steel billet to the austenitizing temperature and hold for a certain time, then air cool to obtain granular bainite.

[0013] Step 2: Temper to eliminate internal stress, and at the same time precipitate and stabilize the carbides in the granular bainite, so as to obtain a good strength-ductility match. During tempering, tempered sorbite is formed, and the carbides precipitate at grain boundaries and within grains.

[0014] Furthermore, during the normalizing + tempering heat treatment process, the normalizing holding temperature is 860 - 900 °C, the time is 53 - 57 min, the tempering temperature is 580 - 620 °C, and the time is 65 - 69 min.

[0015] Furthermore, the matrix structure obtained by the normalizing + tempering heat treatment process is tempered sorbite, which is mainly composed of a ferrite matrix and precipitation phases.

[0016] Furthermore, the precipitation phases in the ferrite matrix are distributed in the orientation of the original MA component. The original MA at the ferrite grain boundaries decomposes into larger precipitates, while there are a small number of fine precipitates inside the matrix.

[0017] Furthermore, the quenching and tempering heat treatment process is divided into stages of holding, water cooling, tempering, and air cooling:

[0018] Step 1: Heat the original steel billet to the austenitizing temperature and hold for a certain time, then water cool to obtain martensite.

[0019] Step 2: Temper to eliminate internal stress, and at the same time transform martensite into stable states such as ferrite and carbides, so as to obtain a good strength-ductility match. During tempering, tempered sorbite is formed, and the carbides are evenly distributed on the martensite matrix.

[0020] Furthermore, during the quenching and tempering heat treatment process, the quenching holding temperature is 840 - 880 °C, the time is 53 - 57 min, the tempering temperature is 580 - 620 °C, and the time is 65 - 69 min.

[0021] Furthermore, the tempered sorbite obtained by the quenching and tempering heat treatment process is mainly composed of a ferrite matrix and precipitation phases.

[0022] Furthermore, the grain boundaries in the sorbite are no longer clearly visible. The precipitates in the ferrite matrix are mainly distributed in the orientation of the original quenched lath martensite, and the morphology of the precipitates is finer and more numerous than that of the normalizing + tempering treatment.

[0023] The technical creative point of the present invention lies in

[0024] 1. The differences from Comparative Document 1 are as follows: The invention in Document 1 is only based on the basic requirements for mechanical properties and fatigue strength in SY / T5029-2003 H-class sucker rod standard and SY / T6272-1997 sucker rod fatigue strength standard, without considering the hydrogen embrittlement and corrosion effects caused by H2S, etc. in complex environment oilfields, which may lead to fractures. In view of the actual situation of the sucker rod serving in the extreme environment of stress-H2S-corrosion coupling, vanadium is added to the alloying elements in the present invention to promote the precipitation of vanadium carbides. While having the precipitation strengthening effect, it firmly captures the hydrogen diffused into the steel (irreversible hydrogen trap effect), thus greatly improving the hydrogen embrittlement resistance of the material; adding copper to the steel can not only effectively improve the strength and impact toughness of the steel, but also enhance its corrosion resistance; considering the important role of improving hydrogen embrittlement resistance, low manganese content is adopted in this study to improve the intergranular fracture strength and reduce the generation of MnS inclusions. Compared with Comparative Document 1, the present invention is applied to the field of hydrogen embrittlement-resistant sucker rod steel and has innovation.

[0025] 2. The differences from Comparative Document 2 are as follows: The strength level of the sucker rod manufactured in the invention of Document 2 is only KD level (GB / T26075-2019, tensile strength 793-965 MPa), which does not reach the H-level standard (GB / T26075-2019, tensile strength 965-1195 MPa), showing a huge difference from this patent. This invention also does not consider the influence of hydrogen embrittlement of steel caused by the oil well environment. Research shows that when the carbon content in the steel is relatively high, its resistance to the damage of H2S medium is relatively low, especially when the carbon content is above 0.3%, this phenomenon is more obvious. Considering the hydrogen embrittlement resistance performance, the carbon content in the present invention is designed to be 0.26-0.32%. Nickel elements can refine the original austenite grains, increase the stacking fault energy of body-centered cubic iron, improve toughness, and improve the anti-hydrogen sulfide corrosion performance of the sucker rod steel. Compared with Comparative Document 2, the present invention is applied to the field of hydrogen embrittlement-resistant sucker rod steel and has innovation.

[0026] The beneficial effects of the above technical solutions of the present invention are as follows: The present invention reduces the manufacturing cost of H-class sucker rod steel through the overall composition design, obtains the mechanical properties meeting the requirements of H-class sucker rod through the supporting heat treatment process, and has good hydrogen embrittlement resistance, which has far-reaching significance for the production cost control and safety guarantee of sucker rod steel. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. The following drawings are only some embodiments of the present invention.

[0028] Figure 1 It is the microstructural diagram of normalizing + tempering (NT) and quenching + tempering (QT) specimens;

[0029] Figure 2are the slow strain rate tensile engineering stress-strain curves of normalized and tempered (NT) and quenched and tempered (QT) specimens in air and hydrogen-charged environments;

[0030] Figure 3 are the desorption peaks (TDS) and hydrogen concentration after hydrogen charging of normalized and tempered (NT) and quenched and tempered (QT) specimens. Detailed implementation manners

[0031] The present invention provides an H-class sucker rod steel and its heat treatment process. The following describes the embodiments of the present invention in detail with reference to the accompanying drawings.

[0032] Step (1): The chemical composition of the H-class sucker rod steel of the present invention is shown in Table 1. According to the designed chemical composition of the sucker rod steel, it is melted and processed into steel billets;

[0033] Table 1 Chemical composition of the H-class sucker rod steel of the present invention wt.%

[0034]

[0035] Step (2): Two heat treatment processes are adopted, namely normalized and tempered heat treatment process, and the process includes heat preservation, cooling, tempering, and air cooling stages; quenched and tempered heat treatment process is divided into heat preservation, water cooling, tempering, and air cooling stages. The specific implementation process parameters are shown in Table 2.

[0036] Table 2 Heat treatment scheme of H-class sucker rod steel

[0037]

[0038]

[0039] Step (3): Mechanical property tests and dynamic hydrogen charging slow strain rate tensile tests (SSRT) are carried out on the samples after two heat treatments. Electrochemical hydrogen charging is used in SSRT, the hydrogen charging current density is 2 mA / cm 2 , the hydrogen charging time is 24 h, the hydrogen charging solution is 0.2 mol / L NaOH + 0.25 g / L thiourea, the tensile rate is 1×10 -5 / s, and the preload is 400 N. The hydrogen embrittlement sensitivity is expressed by the percentage of elongation loss: I HE =(1 - δ0 / δ H )×100%. The mechanical properties and hydrogen embrittlement sensitivity of the test steel are shown in Table 3.

[0040] Table 3 Mechanical properties (room temperature) and hydrogen embrittlement sensitivity of H-class sucker rod steel

[0041]

[0042] The mechanical properties of the H-class sucker rod steel of the present invention meet the requirements for H-class in "GB / T 26075-201 - Round Steel for Sucker Rods", that is, the tensile strength is 965-1195 MPa, the minimum yield strength is greater than 795 MPa, the elongation is greater than 10%, and the impact energy at room temperature is greater than 60 J / cm 2 . In the set hydrogen charging environment, the hydrogen embrittlement sensitivities of the two heat treatment methods are similar, and this strength level steel has a certain hydrogen embrittlement resistance ability.

[0043] After heat treatment, the microstructure of the H-class sucker rod steel is as Figure 1 shown. After both heat treatments, it is tempered sorbite, which is composed of a ferrite matrix and precipitates. After normalizing + tempering, the matrix is massive ferrite, and carbides precipitate along the grain boundaries and in the grains along a certain orientation. After quenching + tempering, the matrix is also ferrite, and the precipitates mainly precipitate along the original martensite lath interfaces.

[0044] Through slow strain rate tensile (SSRT), the engineering stress-strain curve is as Figure 2 shown. The hydrogen embrittlement sensitivity of the normalized + tempered sample is 66.80%, and the hydrogen embrittlement sensitivity of the quenched + tempered sample is 54.64%, with a relatively low hydrogen embrittlement sensitivity. Figure 3 is the hydrogen desorption peak (TDS) and hydrogen concentration diagram, indicating that this steel is mainly a reversible hydrogen trap, and the hydrogen concentrations under the two processes are close.

[0045] The key point in the preparation method of the present invention lies in the design of low-cost alloy compositions and corresponding heat treatment process parameters, so that the final product meets the performance requirements of sucker rod steel.

Claims

1. A heat treatment process for H-class sucker rod steel, characterized in that The mass percentages of the chemical components of the H-class sucker rod steel are as follows: C 0.26 - 0.32%, Si 0.15 - 0.30%, Mn 0.5 - 0.9%, Mo 0.2 - 0.5%, Cr 0.6 - 1.0%, Ni 0.9 - 1.4%, Cu 0.1 - 0.3%, V 0.06 - 0.10%, S < 0.01%, P < 0.01%, and the balance is Fe; The heat treatment process of the H-class sucker rod steel is a normalizing + tempering heat treatment process, and the normalizing + tempering heat treatment process is divided into the stages of heat preservation, cooling, tempering, and air cooling; Step 1: Heat the original steel billet to the austenitizing temperature and hold for a period, and obtain granular bainite after air cooling; Step 2: Temper to eliminate internal stress, and at the same time make the carbides in the granular bainite precipitate and stabilize, so as to obtain a good strength and toughness match. During the tempering process, tempered sorbite is formed, and the carbides precipitate at grain boundaries and within grains; During the normalizing + tempering heat treatment process, the normalizing heat preservation temperature is 860 - 900 °C, the time is 53 - 57 min, the tempering temperature is 580 - 620 °C, and the time is 65 - 69 min; The matrix structure obtained by the normalizing + tempering heat treatment process is tempered sorbite, which is mainly composed of a ferrite matrix and precipitates.

2. The heat treatment process for H-class sucker rod steel according to claim 1, characterized in that The precipitates in the ferrite matrix are distributed in the orientation of the original MA component. The original MA at the ferrite grain boundaries decomposes into larger precipitates, while there are a small number of fine precipitates inside the matrix.

3. A heat treatment process for H-class sucker rod steel, characterized in that The mass percentages of the chemical components of the H-class sucker rod steel are as follows: C 0.26 - 0.32%, Si 0.15 - 0.30%, Mn 0.5 - 0.9%, Mo 0.2 - 0.5%, Cr 0.6 - 1.0%, Ni 0.9 - 1.4%, Cu 0.1 - 0.3%, V 0.06 - 0.10%, S < 0.01%, P < 0.01%, and the balance is Fe; The heat treatment process of the H-class sucker rod steel is a quenching and tempering heat treatment process, and the quenching and tempering heat treatment process is divided into the stages of heat preservation, water cooling, tempering, and air cooling: Step 1: Heat the original steel billet to the austenitizing temperature and hold for a period, and obtain martensite after water cooling; Step 2: Temper to eliminate internal stress, and at the same time make the martensite transform into a stable state of ferrite and carbides, obtain a good strength and toughness match. During the tempering process, tempered sorbite is formed, and the carbides are evenly distributed on the martensite matrix; During the quenching and tempering heat treatment process, the quenching heat preservation temperature is 840 - 880 °C, the time is 53 - 57 min, the tempering temperature is 580 - 620 °C, and the time is 65 - 69 min; The tempered sorbite obtained by the quenching and tempering heat treatment process is mainly composed of a ferrite matrix and precipitates.

4. The heat treatment process for H-class sucker rod steel according to claim 3, characterized in that The grain boundaries in the sorbite are no longer clearly visible. The precipitates in the ferrite matrix are mainly distributed in the orientation of the original quenched lath martensite, and the morphology of the precipitates is finer and more numerous than that of the normalizing + tempering treatment.

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