A high-strength steel part resistant to soil corrosion and a preparation method and application thereof

Abstract

This invention discloses a high-strength steel component resistant to soil corrosion, its preparation method, and its application, belonging to the field of metallic materials technology. The high-strength steel component resistant to soil corrosion has the following chemical composition by mass percentage: C: 0.10%–0.30%, Si: 0.10%–0.60%, Mn: 0.50%–1.50%, Cr: 3.0%–5.0%, Ni: ≤0.5%, Mo: 0.20–0.50%, V: ≤0.1%, Nb ≤0.1%, Ti: ≤0.1%, Cu: 0.30%–0.70%, P ≤0.02%, with the balance being Fe and unavoidable impurities. This invention, by controlling the distribution of Cr element during heat treatment and oxidation tempering, enables the component to achieve high strength while also possessing good resistance to hydrogen-induced delayed fracture and soil corrosion.

Description

Technical Field

[0001] This invention relates to a high-strength steel component resistant to soil corrosion, its preparation method, and its application, belonging to the field of metal materials technology. Background Technology

[0002] Due to Cl in the soil environment - SO4 2- HCO3 - Due to the presence of microorganisms and high moisture content, steel materials are highly susceptible to corrosion. Currently, corrosion-resistant steel plates for underground culverts, tunnels, oil pipelines, and other deeply buried structures have been widely adopted. However, research on matching soil corrosion-resistant bolts, supports, and other components is limited, especially for high-strength components such as 10.9-grade high-strength bolts, for which there is almost no research and development or production of dedicated soil corrosion-resistant materials.

[0003] High-strength components are being rapidly adopted due to their significant weight reduction and improved equipment safety. However, in soil environments, high-strength bolts, especially at their threads, are more prone to accumulating moisture and various ions, leading to highly complex corrosion behavior; attached microorganisms may even metabolize H+. + This leads to hydrogen-induced delayed fracture, and the higher the strength of the part, the more severe the delayed fracture. Patent ZL202010040639.8 discloses a high-strength bolt resistant to marine atmospheric corrosion, whose main alloying element is 3% Ni, exhibiting excellent resistance to Cl. - Corrosion resistance. However, soil has a higher water content than the ocean atmosphere, resulting in a greater quantity and more complex types of dissolved salt ions, and also leading to microbial corrosion. Ni can only be dissolved in solid form and cannot form carbides, thus failing to create sufficient hydrogen traps. Therefore, Ni-reinforced oxide layers and matrices are insufficient to resist soil corrosion and delayed fracture. A denser, more stable oxide layer and more fine carbides are needed to meet the requirements for soil corrosion resistance. While 304 stainless steel bolts containing more than 12% Cr can form a denser Cr-containing oxide layer, the austenitic structure has lower strength, failing to achieve a synergistic improvement in both high corrosion resistance and high strength. Furthermore, stainless steel is very expensive, limiting its widespread application.

[0004] In summary, common Cu-containing weathering steels and Ni-containing marine atmospheric corrosion-resistant steels cannot effectively prevent corrosion in soil; high-Cr stainless steels suffer from insufficient strength and high cost. Therefore, it is of great significance to develop low-cost, paint-free, and replacement-reduced or even replacement-free methods for preparing high-strength, soil-corrosion-resistant steel materials and components that combine high strength and soil corrosion resistance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to obtain a method for preparing high-strength steel parts resistant to soil corrosion without significantly increasing the cost of alloying elements. This method can improve the parts' resistance to hydrogen-induced delayed fracture and soil corrosion resistance.

[0006] Meanwhile, the present invention provides a high-strength steel component resistant to soil corrosion, which achieves a synergistic improvement in high corrosion resistance, resistance to hydrogen-induced delayed fracture, and high strength.

[0007] Meanwhile, this invention provides an application of high-strength steel parts resistant to soil corrosion.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A high-strength steel component resistant to soil corrosion has the following chemical composition by mass percentage: C: 0.10%–0.30%, Si: 0.10%–0.60%, Mn: 0.50%–1.50%, Cr: 3.0%–5.0%, Ni: ≤0.5%, Mo: 0.20–0.50%, V: ≤0.1%, Nb ≤0.1%, Ti: ≤0.1%, Cu: 0.30%–0.70%, P ≤0.02%, with the balance being Fe and unavoidable impurities.

[0010] Preferably, the mass percentage of Ti+Nb+V is 0.05% to 0.20%, the mass percentage of Cr is 3.50% to 4.50%, and the mass percentage of Cu is 0.40% to 0.60%.

[0011] High-strength steel components resistant to soil corrosion, including bolts.

[0012] The bolts have a longitudinal tensile strength of 1082-1206 MPa, a yield strength of 982-1093 MPa, an elongation after fracture of 14.9-18.2%, an impact energy (KV2) of 67-178 J at -20℃, a DFSR value of 0.84-0.88, and a weight loss of 2.7-3.5 g in accelerated testing in simulated soil environment.

[0013] A method for preparing high-strength steel parts resistant to soil corrosion includes the following steps:

[0014] S01, which is made by smelting raw materials, continuous casting, and hot rolling into bars or wires;

[0015] S02, bars or wires are kept at 1000℃-1100℃ for 0.5h-1.5h, then water-cooled or air-cooled to 700℃-750℃, and then naturally cooled to room temperature;

[0016] S03, bar or wire blanks are cold-formed into bolt component blanks;

[0017] S04. Heat the bolt component blank to 900℃-950℃, hold for 30min-60min, and then oil cool to room temperature.

[0018] S05, reheat to 500℃-600℃ and hold for 1-1.5 hours, then air cool to room temperature;

[0019] S06, then machined into finished bolts;

[0020] S07. The finished bolts are placed in an oxidizing atmosphere furnace for oxidation tempering. They are heated to 200℃-250℃ and held for 10-20 minutes, then air-cooled to room temperature to obtain high-strength steel parts resistant to soil corrosion.

[0021] In S03, cold turning includes cold heading or cold bending.

[0022] In S02, the surface cooling rate, whether water-cooled or air-cooled, is controlled at 50-100℃ / s.

[0023] If the bolt component blank obtained in S03 is hot forged, then S02 is moved to be completed after S03.

[0024] In S07, the oxygen volume fraction in the furnace during oxidation tempering is controlled at 30%-50%.

[0025] Application of a high-strength steel component resistant to soil corrosion in underground culverts, tunnels, and oil pipelines.

[0026] This invention has the following novel features:

[0027] (1) Based on the traditional medium-carbon alloy steel used for parts, the carbon (C) content is reduced and the chromium (Cr) content is increased. Solid-solution Cr is used to compensate for the insufficient strength caused by C and to increase the potential of the matrix, thereby improving corrosion resistance. The heat treatment process is controlled to allow some Cr to form a high-Cr martensitic tempered structure in the matrix, achieving high strength. During oxidation tempering, a high-Cr, defect-free, dense, and stable oxide film is formed, preventing corrosion during use, especially improving resistance to SO4 in soil environments. 2- HCO3 - Cl - H + Its corrosion resistance.

[0028] (2) Adding appropriate amounts of Mo and Cu elements further improves the compactness of the Cr-containing oxide film and increases the resistance to Cl with small diameters. - H + The ability to enter and improve resistance to Cl - Corrosion and hydrogen-induced delayed fracture capability.

[0029] (3) Control the heat treatment process so that some Cr elements form fine Cr-containing carbides during the tempering process. Cr elements have a stronger bonding ability with C, and the Cr-containing carbides formed during the tempering process are finer than cementite, enhancing the ability to capture hydrogen ions and further improving the resistance of parts to hydrogen-induced delayed fracture.

[0030] (4) After hot rolling into bars or wires, the raw materials are held at 1000℃-1100℃ for 1 hour to eliminate any large-sized Cr-containing carbides that may exist, improve the utilization efficiency of Cr element, and reduce the large-sized Cr-containing carbides from becoming the cathode in the galvanic cell, thus mitigating electrochemical corrosion. At the same time, the carbonitrides of Ti and Nb remain undissolved, preventing austenite grain growth, refining the microstructure, and improving plasticity and toughness. The cooling rate is controlled at 50-100℃ / s to cool to 750℃ to avoid the precipitation and growth of Cr-containing carbides in the high-temperature cooling section, which would then form alloy cementite during the subsequent air cooling process.

[0031] (5) During the heat treatment of the blank, heat it to 900℃-950℃ and hold it for 30min-60min to allow the Cr in the alloy cementite to fully dissolve. When oil-cooled, all the Cr will dissolve into the matrix. Hold it at 500℃-600℃ for 1h-1.5h. Some Cr will replace Fe and precipitate to form Cr-containing carbides, which will improve the strength and resistance to hydrogen-induced delayed fracture. The other part will dissolve in the matrix, which will improve the strength and form a dense Cr-containing oxide film, which will improve the resistance to soil corrosion.

[0032] (6) The oxidation tempering process of the finished product artificially increases the oxidation temperature and oxygen content to form an extremely thin, artificially produced Cr-containing oxide layer on the surface of the parts. Compared with the oxide layer formed in the natural environment, this layer is denser, has fewer defects, and significantly improves the ability to resist large amounts of SO4 in high-moisture soil environments. 2- HCO3 - Cl - H + Plasma penetrates through the oxide film to react with the substrate and cause corrosion. It also avoids the pollution and hydrogen embrittlement risks associated with surface treatments such as phosphating.

[0033] The roles and proportions of the elements in this invention are based on the following:

[0034] C: A fundamental strengthening element in steel. After heat treatment, it forms Cr-containing carbides, achieving dispersion strengthening and improving strength. Furthermore, Cr-containing carbides act as hydrogen traps, enhancing hydrogen ion capture and reducing hydrogen-induced delayed fracture during use. However, excessively high C content leads to the formation of more cementite, reducing corrosion resistance and ductility. Therefore, the C content in this invention is 0.10%–0.30%.

[0035] Si: A fundamental element for strengthening ferrite. Increasing the silicon content increases the strength of steel but decreases its plasticity. The Si content in this invention is 0.10%–0.60%.

[0036] Mn: Strengthens the matrix and improves strength and toughness; forms MnS, reducing the promoting effect of sulfur on hydrogen embrittlement. The Mn content in this invention is 0.50%–1.50%.

[0037] Cr: A common element in steel that improves hardenability, generally not exceeding 1.5%. This invention significantly increases the Cr content, allowing some to dissolve into the matrix after quenching and tempering, achieving both increased strength and improved corrosion resistance of the matrix. During use, it forms a dense oxide film on the surface of parts, achieving corrosion resistance. Compared to the oxide film of traditional weathering steel containing Cu and P, the Cr-containing oxide film is denser, more stable, and thicker, exhibiting better resistance to SO4 in soil. 2- HCO3 - Plasma corrosion resistance is stronger. Another portion forms Cr-containing carbides, which act as dispersion strengthening agents, increasing strength; simultaneously, the Cr-containing carbides precipitated during tempering are finer than cementite, making them more likely to become hydrogen traps, thus improving resistance to hydrogen-induced delayed fracture. The Cr element content of this invention is 3.0%–5.0%, preferably 3.50%–4.50% by mass.

[0038] Mo: Prevents brittleness from high-temperature tempering; improves the density of Cr-containing oxide films and enhances resistance to Cl in soil. - Corrosion resistance. The Mo element content in this invention is 0.20% to 0.50%.

[0039] Cu: A commonly used element in weathering steel, it forms a dense Cu-containing oxide film on the surface of steel parts, improving corrosion resistance and preventing H2 corrosion. + Hydrogen-induced delayed fracture occurs when it penetrates into the steel. However, the Cu-containing oxide film is resistant to SO4 in the soil. 2- HCO3 - It has poor resistance to plasma corrosion. In this invention, it works synergistically with a Cr-containing oxide film to improve resistance to H+ in the soil. + This improves the ability to penetrate and enhances resistance to hydrogen-induced delayed fracture. The Cu content in this invention is 0.30%–0.70%, preferably 0.40%–0.60%.

[0040] Ti, Nb, and V are commonly used microalloying elements in steel that refine grain size and promote precipitation strengthening. They form stable carbonitrides, refine austenite grains during hot working and heat treatment, thereby refining the room temperature microstructure and improving strength and toughness. However, they are costly, and excessive addition can lead to the formation of large-sized carbonitrides, resulting in significant galvanic cell reactions and accelerating corrosion of steel parts. Therefore, in this invention, the content of V, Nb, and Ti is ≤0.1%, and preferably, the mass percentage of Ti+Nb+V is 0.05% to 0.20%.

[0041] Ni: A commonly added element in steel to improve hardenability and toughness, it is relatively expensive and difficult to remove during smelting. This invention features a high Cr content, ensuring sufficient hardenability, and allows for the addition of small amounts of Ni or residual Ni from steelmaking. The Ni content in this invention is ≤0.5%.

[0042] This invention achieves a synergistic improvement in component strength and soil corrosion resistance without significantly increasing alloying costs, while also enhancing resistance to hydrogen-induced delayed fracture (DHFC). The finished bolts and other components exhibit a longitudinal tensile strength of 1082-1206 MPa, a yield strength of 982-1093 MPa, an elongation after fracture of 14.9-18.2%, and an impact energy (KV2) of 67-178 J at -20℃. They demonstrate excellent DHFC resistance and soil corrosion resistance, with a DFSR value of 0.84-0.88 and a weight loss of 2.7-3.5 g in simulated soil environment accelerated testing.

[0043] This invention controls the distribution of Cr element during the heat treatment process and the oxidation tempering treatment, so that the parts can obtain high strength level, good resistance to hydrogen-induced delayed fracture and soil corrosion resistance. Attached Figure Description

[0044] Figure 1 The solid solution precipitation equilibrium curves of large-size carbonitrides and alloy cementite obtained by computer simulation of the raw material composition in Example 1 are shown.

[0045] Figure 2 This is a metallographic photograph of the cross-section of the core of the finished bolt in Example 1;

[0046] Figure 3 The image shows the morphology of the Cr-containing oxide layer produced by oxidation and tempering on the surface of the finished bolt (near the tensile fracture) in Example 1.

[0047] Figure 4 The scanning electron microscope morphology and energy dispersive spectroscopy composition analysis of the finished bolt microstructure in Example 1 are presented. Detailed Implementation

[0048] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0049] A high-strength steel component resistant to soil corrosion, the chemical composition of which is shown in Table 1.

[0050] Table 1 Chemical composition (wt%) (the remainder is Fe and impurity elements)

[0051] Comparative Example 1 0.42 0.67 0.88 0.80 0.21 0.25 0.40 0.04 0.02 0.02 0.012 0.22 Comparative Example 2 0.21 0.43 0.70 4.84 0.33 0.65 0.007 0.02 0.01 0.02 0.010 0.05 Comparative Example 3 0.21 0.43 0.70 4.84 0.33 0.65 0.007 0.02 0.01 0.02 0.010 0.05 Comparative Example 4 0.30 0.43 0.70 0.04 0.33 0.35 3.22 0.03 0.06 0.06 0.008 0.05 Example 1 0.20 0.52 0.85 3.50 0.40 0.42 0.23 0.04 0.03 0.03 0.011 0.12 Example 2 0.17 0.55 1.02 3.87 0.36 0.48 0.30 0.08 0.02 0.02 0.013 0.09 Example 3 0.28 0.20 0.58 4.77 0.22 0.33 0.19 0.06 0.03 0.04 0.015 0.18 Example 4 0.12 0.60 1.45 3.20 0.47 0.58 0.02 0.07 0.06 0.05 0.012 0.06

[0052] According to the above comparative examples and embodiments, ingots or continuously cast billets obtained by conventional smelting processes were rolled into bars or wires after roughing and hot rolling. The bars (18mm in diameter) of Comparative Example 1 and Embodiment 1 were heated to 1050℃ and held for 1 hour, then water-cooled to a surface temperature of 750℃ at a cooling rate of approximately 90℃ / s. After cold heading into bolts, they were heated to 920℃ and held for 45 minutes, oil-cooled to room temperature, heated to 540℃ and held for 70 minutes, and then air-cooled. The surfaces were precision-machined and thread-rolled into finished bolts, which were then held in a furnace at 200℃ with an oxygen content of 35% for 15 minutes before being air-cooled to room temperature.

[0053] As attached Figure 1 The figure shows the solid solution precipitation equilibrium curves for large-sized carbonitrides and alloy cementite calculated according to the composition of Example 1. The complete dissolution temperature of large-sized carbonitrides is approximately 1021°C, and the complete dissolution temperature of alloy cementite is 810°C. Considering the influence of a small amount of V, the complete dissolution temperature of alloy cementite will be higher. Therefore, the hot-rolled bar is heated to 1050°C to ensure complete dissolution of large-sized carbonitrides, preventing them from re-nucleating and precipitating during cooling, and instead transforming them entirely into alloy cementite. After cold heading into bolts, the bolts are heated to 920°C and held for 45 minutes to ensure complete solid solution of Cr, followed by oil quenching. After heating to 540°C and holding for 70 minutes, they are air-cooled. Some Cr-containing carbides precipitate out, while some remain dissolved in the matrix. The metallographic structure of the bolt cross-section is shown in the figure. Figure 2 As shown, the alloy exhibits a tempered sorbitic structure, exhibiting strong corrosion resistance. After oxidation tempering, a dense Cr-containing oxide layer approximately 5 μm thick is formed on the surface of the finished product, as shown... Figure 3 As shown, it prevents corrosion from various ions in the soil. The matrix was observed using a scanning electron microscope, as shown... Figure 4 As shown, a small number of slightly larger Cr-containing carbides (indicated by the white arrow, with a diameter of about 0.3 μm) can be seen. Using energy dispersive spectroscopy analysis, in addition to the Fe element in the matrix, a large amount of Cr element can be seen in them. After local magnification, many fine Cr-containing carbides (with a diameter of about tens of nanometers) can also be seen distributed in the matrix.

[0054] Application of a high-strength steel component resistant to soil corrosion in underground culverts, tunnels, and oil pipelines.

[0055] Comparative Example 2: The processing technology of the bar stock (20mm in diameter) was as follows: the hot-rolled bar stock was directly cold-forged into bolts, then heated to 920℃ and held for 45 minutes, oil-cooled to room temperature, heated to 540℃ and held for 70 minutes, and then air-cooled; the surface was precision-machined and thread-rolled to form finished bolts. Afterwards, it was held in a furnace at 250℃ with an oxygen content of 40% for 15 minutes, and then air-cooled to room temperature.

[0056] Comparative Example 3 used the same bar stock as Comparative Example 2. The bar stock was heated to 1050℃ and held for 1.2 hours, then water-cooled to a surface temperature of 730℃ at a cooling rate of approximately 85℃ / s. After cold-forging into bolts, it was heated to 920℃ and held for 45 minutes, then oil-cooled to room temperature, and finally heated to 540℃ and held for 70 minutes before air-cooling. The surface was then precision-machined and thread-rolled to form finished bolts. Subsequently, it was stress-relief annealed in a furnace at 150℃ with an oxygen content of 20% for 15 minutes, and then air-cooled to room temperature.

[0057] Comparative Example 4 is a marine atmospheric corrosion resistant bolt steel containing 3% Ni. Referring to patent ZL202010040639.8, the bolts were hot-forged, heated to 1150℃ and held for 50 minutes, then cooled by air blowing, held at 980℃ for 45 minutes, then oil-quenched, tempered at 400℃ for 45 minutes, tempered at 600℃ for 75 minutes, and then surface-machined, thread-rolled, and phosphated to form the finished product.

[0058] Example 2: The processing technology for the bar stock (24mm in diameter) is as follows: The bar stock is heated to 1090℃ and held for 1 hour, then water-cooled to a surface temperature of 750℃ at a cooling rate of approximately 85℃ / s; after being cold-bent into a support rod, it is heated to 940℃ and held for 60 minutes, oil-cooled to room temperature, then heated to 520℃ and held for 75 minutes before air-cooling; the surface is shot-peened to obtain the finished support rod. Afterwards, it is held in a furnace at 200℃ with an oxygen content of 50% for 10 minutes, and then air-cooled to room temperature.

[0059] This embodiment describes the application of a high-strength steel component resistant to soil corrosion in underground culverts, tunnels, and oil pipelines.

[0060] Example 3: The processing technology for bar stock (40mm diameter) is as follows: After hot forging the bar stock into bolts, it is heated to 1090℃ and held for 1 hour, then water-cooled to a surface temperature of 750℃ at a cooling rate of approximately 65℃ / s; it is then heated to 900℃ and held for 60 minutes, oil-cooled to room temperature, and then heated to 550℃ and held for 85 minutes before air cooling; the surface is then precision-machined and thread-rolled to form finished bolts. Afterwards, it is held in a furnace at 250℃ with an oxygen content of 30% for 10 minutes, and then air-cooled to room temperature.

[0061] This embodiment describes the application of a high-strength steel component resistant to soil corrosion in underground culverts, tunnels, and oil pipelines.

[0062] Example 4: The wire (8mm diameter) processing technology is as follows: The wire is heated to 1020℃ and held for 1 hour, then air-cooled to a surface temperature of 750℃ at a cooling rate of approximately 55℃ / s; after straightening and cold-forging into bolts, it is heated to 950℃ and held for 30 minutes, then oil-cooled to room temperature, and then heated to 510℃ and held for 60 minutes before air-cooling; the surface is then precision-machined and thread-rolled to form finished bolts. Afterwards, it is held in a furnace at 220℃ with an oxygen content of 40% for 15 minutes, and then air-cooled to room temperature.

[0063] This embodiment describes the application of a high-strength steel component resistant to soil corrosion in underground culverts, tunnels, and oil pipelines.

[0064] To characterize the performance of the finished parts, standard tensile and impact test specimens were taken from the parts according to national standards to determine tensile properties and impact energy at -20℃. Notched tensile specimens were placed in Walpole corrosion inhibitor solution (hydrochloric acid, sodium acetate, deionized water) for constant load notched tensile testing, and the notched tensile delayed fracture strength (DFSR) ratio before and after hydrogen embrittlement was measured. A higher DFSR value indicates stronger resistance to hydrogen embrittlement. Finished parts were cut to the same length and subjected to accelerated corrosion testing for 200 hours in a weakly acidic mixed solution of 0.5% NaCl, 0.5% NaSO4, 0.5% NaHCO3, and 50% soil leachate (pH 6.5). The weight loss of the parts was measured; a smaller weight loss indicates better corrosion resistance.

[0065] Although Comparative Example 1 met the strength and -20℃ impact resistance requirements for 10.9 grade bolts, its resistance to hydrogen-induced delayed fracture (DFSR) and corrosion test weight loss were significantly greater than those of Example 1, indicating poor soil corrosion resistance. Comparative Example 2, while meeting the composition requirements of this invention, did not meet the processing requirements, resulting in significantly higher corrosion weight loss and strength not meeting the 10.9 grade bolt requirements. Comparative Example 3's bolts, including thread rolling, finishing, and prior processing, met the requirements of this invention. However, no oxidation tempering was performed; only stress-relief annealing at a lower temperature was conducted in a furnace with lower oxygen content, failing to form a Cr-containing oxide film on the bolt surface. Therefore, while its strength and impact resistance met the 10.9 grade bolt requirements, its resistance to hydrogen-induced delayed fracture was slightly lower, especially its soil corrosion resistance, which was significantly reduced. Comparative Example 4's bolts, although reaching the 10.9 grade strength level, exhibited significantly poor resistance to hydrogen-induced delayed fracture and soil corrosion resistance. This invention did not include a comparative example with a thicker Cr-containing oxide film (>5μm) because increasing the thickness of the Cr-containing oxide film would cause problems such as dimensional deviations and unsatisfactory surface quality of the finished parts. Specific mechanical property parameters are shown in Table 2 below.

[0066] Table 2. Ratio of mechanical properties to delayed fracture strength

[0067]

[0068]

[0069] Example 5

[0070] A high-strength steel component resistant to soil corrosion has the following chemical composition by mass percentage: C: 0.10%, Si: 0.10%, Mn: 0.50%, Cr: 3.0%, Ni: 0.5%, Mo: 0.20%, V: 0.1%, Nb: 0.1%, Ti: 0.1%, Cu: 0.30%, P: 0.02%, with the balance being Fe and unavoidable impurities.

[0071] The bolt has a longitudinal tensile strength of 1103 MPa, a yield strength of 995 MPa, an elongation after fracture of 17.5%, an impact energy (KV2) of 162 J at -20℃, a DFSR value of 0.84, and a weight loss of 3.3 g in the accelerated test under simulated soil conditions.

[0072] A method for preparing high-strength steel parts resistant to soil corrosion includes the following steps:

[0073] S01, raw materials are smelted, continuously cast, and hot-rolled into bars;

[0074] S02, the bar is kept at 1000℃ for 1.5h, then water-cooled to 720℃, and then naturally cooled to room temperature;

[0075] S03, bar stock blanking, cold deformation to form bolt component blanks;

[0076] S04, heat the bolt component blank to 900℃, hold for 30 minutes, and then oil cool to room temperature;

[0077] S05, reheat to 500℃ and hold for 1 hour, then air cool to room temperature;

[0078] S06, then machined into finished bolts;

[0079] S07, the finished bolts are placed in an oxidizing atmosphere furnace for oxidation tempering, heated to 200℃ and held for 10 minutes, and then air-cooled to room temperature to obtain high-strength steel parts resistant to soil corrosion.

[0080] In S03, cold is transformed into cold forging.

[0081] In S02, the surface cooling rate of water cooling is controlled at 50℃ / s, and the water cooling method is adjusted according to the diameter of the bar.

[0082] If the bolt component blank obtained in S03 is hot forged, then S02 is moved to be completed after S03.

[0083] In S07, the oxygen volume fraction in the furnace during oxidation tempering is controlled at 30%. This step can be omitted if the components are used in a dry alkaline soil environment.

[0084] Application of a high-strength steel component resistant to soil corrosion in underground culverts, tunnels, and oil pipelines.

[0085] Example 6

[0086] A high-strength steel component resistant to soil corrosion has the following chemical composition by mass percentage: C: 0.30%, Si: 0.60%, Mn: 1.50%, Cr: 5.0%, Ni: 0.4%, Mo: 0.50%, V: 0.1%, Nb: 0.05%, Ti: 0.05%, Cu: 0.70%, P: 0.01%, with the balance being Fe and unavoidable impurities.

[0087] The bolt has a longitudinal tensile strength of 1183 MPa, a yield strength of 1065 MPa, an elongation after fracture of 15.2%, an impact energy (KV2) of 75 J at -20℃, a DFSR value of 0.87, and a weight loss of 2.8 g in the accelerated test under simulated soil conditions.

[0088] A method for preparing high-strength steel parts resistant to soil corrosion includes the following steps:

[0089] S01, raw materials are smelted, continuously cast, and hot-rolled into wire rods;

[0090] S02, the wire is kept at 1100℃ for 0.5h, then air-cooled to 700℃, and then naturally cooled to room temperature;

[0091] S03, wire cutting, cold deformation to form bolt component blanks;

[0092] S04, heat the bolt component blank to 950℃, hold for 60 minutes, and then cool to room temperature with oil;

[0093] S05, reheat to 600℃ and hold for 1.5 hours, then air cool to room temperature;

[0094] S06, then machined into finished bolts;

[0095] S07, the finished bolts are placed in an oxidizing atmosphere furnace for oxidation tempering, heated to 250℃ and held for 20 minutes, and then air-cooled to room temperature to obtain high-strength steel parts resistant to soil corrosion.

[0096] In S03, cold bending is transformed into cold bending.

[0097] In S02, the surface cooling rate of air cooling is controlled at 100℃ / s.

[0098] If the bolt component blank obtained in S03 is hot forged, then S02 is moved to be completed after S03.

[0099] In S07, the oxygen volume fraction in the furnace during oxidation tempering is controlled at 50%.

[0100] Application of a high-strength steel component resistant to soil corrosion in underground culverts, tunnels, and oil pipelines.

[0101] Example 7

[0102] The only difference between this embodiment and embodiment 6 is that:

[0103] A high-strength steel component resistant to soil corrosion has the following chemical composition by mass percentage: C: 0.20%, Si: 0.30%, Mn: 1.00%, Cr: 3.5%, Ni: 0.3%, Mo: 0.25%, V: 0.01%, Nb: 0.02%, Ti: 0.02%, Cu: 0.40%, P: 0.02%, with the balance being Fe and unavoidable impurities.

[0104] Example 8

[0105] The only difference between this embodiment and embodiment 6 is that:

[0106] A high-strength steel component resistant to soil corrosion has the following chemical composition by mass percentage: C: 0.25%, Si: 0.45%, Mn: 1.20%, Cr: 4.5%, Ni: 0.2%, Mo: 0.35%, V: 0.05%, Nb: 0.05%, Ti: 0.05%, Cu: 0.60%, P: 0.01%, with the balance being Fe and unavoidable impurities.

[0107] It should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the above description of exemplary embodiments of the invention. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all the features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0108] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0109] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength steel parts resistant to soil corrosion, characterized in that, The chemical composition of the high-strength steel parts resistant to soil corrosion, by mass percentage, is as follows: C: 0.10%~0.30%, Si: 0.10%~0.60%, Mn: 0.50%~1.50%, Cr: 3.0%~5.0%, Ni: ≤0.5%, Mo: 0.20~0.50%, V: ≤0.1%, Nb≤0.1%, Ti: ≤0.1%, Cu: 0.30%~0.70%, P≤0.02%, with the balance being Fe and unavoidable impurities; Notched tensile specimens were placed in Walpole corrosion inhibitor solution for constant load notched tensile testing, and the notched tensile delayed fracture strength ratio (DFSR) before and after hydrogen purging was measured. Finished parts were cut to the same length and placed in a weakly acidic mixed solution of 0.5% NaCl, 0.5% NaSO4, 0.5% NaHCO3 and 50% soil leachate, pH=6.5 for accelerated corrosion testing for 200 hours, and the weight loss of the parts was measured. The impact energy (KV2) of the high-strength steel parts resistant to soil corrosion at -20℃ is 67-178J, the DFSR value is 0.84~0.88, and the weight loss in the accelerated test under simulated soil environment is 2.7~3.5g. After oxidation and tempering, a dense Cr-containing oxide layer with a thickness of 5μm is formed on the surface of the finished product; The preparation method includes the following steps: S01, which is made by smelting raw materials, continuous casting, and hot rolling into bars or wires; S02, bars or wires are kept at 1000℃-1100℃ for 0.5h-1.5h, then water-cooled or air-cooled to 700℃-750℃, and then naturally cooled to room temperature; S03, bar or wire blanks are cold-formed into bolt component blanks; S04. Heat the bolt component blank to 900℃-950℃, hold for 30min-60min, and then oil cool to room temperature. S05, reheat to 500℃-600℃ and hold for 1-1.5 hours, then air cool to room temperature; S06, then machined into finished bolts; S07. The finished bolts are placed in an oxidizing atmosphere furnace for oxidation tempering. They are heated to 200℃-250℃ and held for 10-20 minutes, then air-cooled to room temperature to obtain high-strength steel parts resistant to soil corrosion.

2. The method for preparing a high-strength steel component resistant to soil corrosion according to claim 1, characterized in that, The mass percentages of Ti+Nb+V are 0.05%~0.20%, Cr is 3.50%~4.50%, and Cu is 0.40%~0.60%.

3. The method for preparing a high-strength steel component resistant to soil corrosion according to claim 1, characterized in that, High-strength steel components resistant to soil corrosion, including bolts.

4. The method for preparing a high-strength steel component resistant to soil corrosion according to claim 3, characterized in that, The longitudinal tensile strength of the bolt is 1082-1206 MPa, the yield strength is 982-1093 MPa, and the elongation after fracture is 14.9-18.2%.

5. The preparation method according to claim 1, characterized in that, In S03, cold turning includes cold heading or cold bending.

6. The preparation method according to claim 1, characterized in that, In S02, the surface cooling rate, whether water-cooled or air-cooled, is controlled at 50-100℃ / s.

7. The preparation method according to claim 1, characterized in that, If the bolt component blank obtained in S03 is hot forged, then S02 is moved to be completed after S03.

8. The preparation method according to claim 1, characterized in that, In S07, the oxygen volume fraction in the furnace during oxidation tempering is controlled at 30%-50%.

9. The application of a high-strength steel component resistant to soil corrosion obtained by the preparation method according to any one of claims 1 to 8 in underground culverts, tunnels, and oil pipelines.

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