High-strength and high-toughness steel and preparation method and application thereof

Abstract

The invention provides high-toughness steel as well as a preparation method and application thereof, and belongs to the field of metal materials. The high-toughness steel provided by the invention is prepared from the following elements in percentage by mass: 0.18 to 0.39 percent of C, 0.09 to 0.40 percent of Si, 0.1 to 0.42 percent of Mn, less than or equal to 0.0128 percent of P, less than or equal to 0.0028 percent of S, 0.37 to 1.15 percent of Cr, 1.15 to 2.0 percent of Mo, 0.001 to 0.048 percent of Nb, 0.19 to 0.46 percent of V, less than or equal to 0.020 percent of Al, less than or equal to 0.0030 percent of B and the balance of Fe. According to the high-strength and high-toughness steel, the tensile strength is not smaller than 1260 Mpa, the longitudinal impact energy is not smaller than 100 J, and the transverse impact energy is not smaller than 70 J; the notched constant load critical fracture stress ratio n is not less than 0.8, and the alloy does not fracture after more than 100 hours, and has high strength and high toughness.

Description

Technical Field

[0001] The present invention relates to the field of metal materials, and in particular to high-strength and toughness steel and a preparation method and application thereof. Background Art

[0002] With the development of the world's oil industry, oil and gas wells are getting deeper and deeper. At present, there are wells more than 8,000 meters deep. The increase in well depth makes the drilling working conditions more and more complicated. Therefore, during the drilling process, the drill pipe will encounter problems with sediment and settlement, and the forces on the drill pipe are becoming more and more complex, such as tension, compression, bending, torsion, shear and their combination, alternating loads, etc., which significantly increase the probability of drill pipe failure. Drill pipe failure sometimes leads to the scrapping of the entire well, which will cause significant economic losses and even casualties. With the development of the national economy and the improvement of people's living standards, China's demand for oil and natural gas is increasing, and deep well operations in oil and gas wells are inevitable. With the advancement of drilling technology, drilling parameters are gradually strengthened, and the requirements for the service life and service performance of drill pipes are getting higher and higher.

[0003] In order to improve the service life and service performance of drill pipes, the related research "A preparation method for a complex-phase drill pipe material" adds Cr, Mo, V, Nb and other alloy elements that increase hardenability on the basis of the conventional elements of S135 steel grade drill pipes, adds rare earth lanthanum, and optimizes a complex-phase drill pipe material composed of lower bainite, tempered troostite and a small amount of residual austenite through graded quenching heat treatment, which improves the fatigue resistance of drill pipes and reduces the failure probability of drill pipes. However, the addition of rare earth components greatly increases the manufacturing cost of drill pipes, and the strength decreases to a certain extent. The related research "A high-grade sulfur-resistant drill pipe material and its preparation method" controls the lower carbon content (0.1-0.22%) and the appropriate Mo and V content (0.2-0.6%, 0.05-0.15%) to make it have good impact toughness (0℃ transverse Charpy impact energy ≥120J), but it also leads to insufficient tensile strength and yield strength of such steel, and does not meet the high strength requirements. The related study "A titanium alloy drill pipe material with a tensile strength of 860-1086MPa" improves the tensile strength of the drill pipe by adjusting the content of Al, Mo, and Ti, but the impact absorption energy is only ≥54J. The related study "An ultra-high strength oil drill pipe body and its heat treatment process" uses high-strength martensite as the matrix to introduce a composite structure composed of tough phases such as austenite, bainite or ferrite. The high strength and toughness of martensite are matched with each other to obtain good properties of high strength and high toughness, so that the steel has a higher toughness level than single martensite, but the material strength surplus is low and the impact performance (≤100J). Therefore, the existing drill pipe still has deficiencies in matching high strength and high toughness, and it is necessary to further improve the strength and toughness of the drill pipe material. Summary of the invention

[0004] The purpose of the present invention is to provide a high-strength and toughness steel and a preparation method and application thereof. The high-strength and toughness steel provided by the present invention has high strength and high toughness, and also has good resistance to hydrogen-induced delayed fracture.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a high-strength and tough steel, which is composed of the following elements by mass percentage: C0.18-0.39%, Si 0.09-0.40%, Mn 0.1-0.42%, P≤0.0128%, S≤0.0028%, Cr0.37-1.15%, Mo 1.15-2.0%, Nb 0.001-0.048%, V 0.19-0.46%, Al≤0.020%, B≤0.0030% and the balance of Fe.

[0007] Preferably, the high-strength and toughness steel is composed of the following elements: C 0.18-0.38%, Si 0.09-0.39%, Mn 0.1-0.40%, P≤0.0127%, S≤0.0027%, Cr 0.38-1.15%, Mo 1.17-2.0%, Nb 0.001-0.047%, V 0.20-0.46%, Al 0.005-0.020%, B 0.0010-0.0030% and the balance Fe.

[0008] Preferably, the high-strength and toughness steel is composed of the following elements: C 0.18-0.37%, Si 0.09-0.38%, Mn 0.10-0.39%, P≤0.0126%, S≤0.0026%, Cr 0.4-1.15%, Mo 1.18-2.0%, Nb 0.001-0.046%, V 0.21-0.46%, Al 0.005-0.010%, B 0.0010-0.0020% and the balance Fe.

[0009] The present invention provides a method for preparing the high-strength and toughness steel described in the above technical solution, comprising:

[0010] (1) melting the raw materials and then casting to obtain a steel ingot;

[0011] (2) The steel ingot obtained in step (1) is sequentially hot-rolled and subjected to quenching and tempering heat treatment to obtain high-strength and toughness steel.

[0012] Preferably, the starting temperature of the hot rolling is 1100-1190°C, and the finishing temperature of the hot rolling is 1020-1080°C.

[0013] Preferably, the steel ingot is subjected to insulation treatment before hot rolling; the temperature of the insulation treatment is 1200-1280° C., and the insulation treatment time is greater than 3 hours.

[0014] Preferably, the tempering heat treatment includes a quenching heat treatment and a tempering heat treatment performed sequentially.

[0015] Preferably, the quenching temperature of the quenching heat treatment is 880-920° C., and the holding time of the quenching heat treatment is 30-60 min.

[0016] Preferably, the temperature of the tempering heat treatment is 640-680° C., and the holding time of the tempering heat treatment is 75-120 min.

[0017] The present invention provides the application of the high-strength and toughness steel described in the above technical solution or the high-strength and toughness steel prepared by the preparation method described in the above technical solution in petroleum equipment.

[0018] The invention provides a high-strength and tough steel, which is composed of the following elements by mass percentage: C0.18-0.39%, Si 0.09-0.40%, Mn 0.1-0.42%, P≤0.0128%, S≤0.0028%, Cr0.37-1.15%, Mo 1.15-2.0%, Nb 0.001-0.048%, V 0.19-0.46%, Al≤0.020%, B≤0.0030% and the balance of Fe. The high-strength and toughness steel provided by the present invention utilizes the Mn element to improve the hardenability of the steel, enhance the strength, toughness and hardness, and at the same time forms MnS inclusions with the S element to reduce the influence of S and improve the hot processing performance of the steel. By limiting the Mn content, the steel has high strength and high toughness while having good resistance to hydrogen-induced delayed fracture; utilizes an appropriate amount of Mo element as an alloying element to effectively improve the high-temperature strength and toughness of the steel, and improve the corrosion resistance of the steel in an acidic solution; at the same time, the Mo element forms fine M2C carbides in the alloy, which plays a role of dispersion strengthening and improves the tempering resistance of the material; utilizes an appropriate amount of V element to refine the structure and grains, improve the strength and toughness of the alloy, and reduce the overheating sensitivity; and by adjusting the content of other elements to cooperate with the Mn, Mo and V elements, the strength and toughness of the steel are further improved. The results of the embodiments show that the tensile strength of the high-strength and toughness steel provided by the present invention is not less than 1260 MPa, the longitudinal impact energy is not less than 100 J, and the transverse impact energy is not less than 70 J. In a constant load notch delayed fracture test, the notch constant load critical fracture stress ratio n is not less than 0.8, and it does not break for more than 100 h, indicating high strength and high toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The microstructure diagram of the high-strength and toughness steel prepared in Example 1 of the present invention;

[0020] Figure 2 The microstructure diagram of the high-strength and toughness steel prepared in Example 2 of the present invention;

[0021] Figure 3 The microstructure diagram of the high-strength and toughness steel prepared in Comparative Example 1 of the present invention;

[0022] Figure 4 This is a microstructure diagram of the high-strength and toughness steel prepared in Comparative Example 2 of the present invention;

[0023] Figure 5 1 is a structural dimension diagram of a specimen for a constant load notch tensile test in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The invention provides a high-strength and tough steel, which is composed of the following elements by mass percentage: C0.18-0.39%, Si 0.09-0.40%, Mn 0.1-0.42%, P≤0.0128%, S≤0.0028%, Cr0.37-1.15%, Mo 1.15-2.0%, Nb 0.001-0.048%, V 0.19-0.46%, Al≤0.020%, B≤0.0030% and the balance of Fe.

[0025] By mass percentage, the high-strength and toughness steel provided by the present invention includes C 0.18-0.39%, preferably 0.18-0.38%, more preferably 0.18-0.37%, further preferably 0.19-0.36%, further preferably 0.2-0.35%, and most preferably 0.25-0.30%. In the present invention, C has a significant effect on improving the strength of steel through solid solution strengthening and precipitation strengthening. The present invention limits the C content within the above range to improve the strength, plasticity, toughness and other properties of the material, and avoids the negative impact of excessive C content on the plasticity and toughness of the steel.

[0026] In terms of mass percentage, the high-strength and tough steel provided by the present invention includes 0.09-0.40% Si, preferably 0.09-0.39%, more preferably 0.09-0.38%, further preferably 0.1-0.37%, further preferably 0.1-0.35%, and most preferably 0.25-0.30%. In the present invention, Si, as an important reducing agent and deoxidizing agent in the steelmaking process, can be dissolved in ferrite and austenite to improve the hardness and strength of steel. The present invention limits the content of Si within the above range, which can reduce the precipitation tendency of Fe3C and avoid excessive Si content, which reduces the plasticity and toughness of steel.

[0027] By mass percentage, the high-strength and tough steel provided by the present invention includes 0.1-0.42% Mn, preferably 0.1-0.40%, more preferably 0.10-0.39%, further preferably 0.12-0.38%, further preferably 0.15-0.35%, and most preferably 0.30-0.35%. In the present invention, Mn can improve the hardenability of steel, enhance strength, toughness and hardness, form MnS inclusions with S elements, reduce the influence of S, and improve the hot working properties of steel; excessive Mn content will cause segregation of continuous casting billets, increase the banded structure level of steel pipes, deteriorate the uniformity of the structure, reduce the low-temperature toughness, and reduce the corrosion resistance of the material. By limiting the content of Mn within the above range, the present invention can make the material have good resistance to hydrogen-induced delayed fracture while having high strength and high toughness.

[0028] In terms of mass percentage, the high-strength and tough steel provided by the present invention includes P≤0.0128%, preferably ≤0.0127%, more preferably ≤0.0126%, further preferably ≤0.0125%, further preferably ≤0.012%, and most preferably 0.005-0.010%. In the present invention, P is an impurity element, which can cause a significant decrease in plasticity and impact toughness, especially at low temperatures, making the steel material significantly brittle. The present invention limits the P content to the above range, which can reduce the influence of P on the performance of the steel material.

[0029] In terms of mass percentage, the high-strength and tough steel provided by the present invention includes S≤0.0028%, preferably ≤0.0027%, more preferably 0.0026%, further preferably ≤0.0025%, further preferably ≤0.002%, and most preferably 0.001-0.002%. In the present invention, S is an impurity element, which is detrimental to the ductility, toughness, weldability and corrosion resistance of steel; if S exists in the form of FeS in steel, it can also produce "hot brittleness" during hot working. The present invention limits the S content to the above range, which can reduce the influence of S on the properties of steel.

[0030] In terms of mass percentage, the high-strength and tough steel provided by the present invention includes 0.37-1.15% Cr, preferably 0.38-1.15%, more preferably 0.4-1.15%, further preferably 0.4-1.1%, further preferably 0.5-1.0%, and most preferably 0.7-0.9%. In the present invention, Cr can increase the hardenability of steel and has a secondary hardening effect, which can improve the strength, hardness and wear resistance of steel without making the steel brittle, but will reduce the elongation and cross-sectional shrinkage; the main role of Cr in the quenched and tempered structure is to improve the hardenability, so that the steel has better comprehensive mechanical properties after quenching and tempering. The present invention limits the content of Cr within the above range, avoiding the problem that excessive Cr addition leads to the precipitation and aggregation and growth of Cr-containing carbides at the original austenite grain boundaries during tempering, which seriously damages the low-temperature toughness of the steel, and cooperates with other components to make the steel have high strength and high toughness.

[0031] In terms of mass percentage, the high-strength and toughness steel provided by the present invention includes 1.15-2.0% Mo, preferably 1.17-2.0%, more preferably 1.18-2.0%, further preferably 1.18-1.9%, further preferably 1.2-1.8%, and most preferably 1.4-1.6%. In the present invention, the Mo element as an alloying element can effectively improve the strength of the steel, especially the high-temperature strength and toughness, and improve the corrosion resistance of the steel in acidic solutions; improve the wear resistance of the steel, improve the hardenability and weldability; the Mo element can greatly improve the creep resistance of the ferrite, effectively inhibit the aggregation of cementite at 450-600°C, promote the precipitation of special carbides, produce secondary hardening, and improve the hardness and strength of the material; the Mo element tends to form M2C carbides, and the size of the carbides is smaller, which can play a role in dispersion strengthening and improve the tempering resistance of the material. The present invention limits the content of Mo to the above range and combines it with other components to make the material have high strength and high toughness.

[0032] In terms of mass percentage, the high-strength and tough steel provided by the present invention includes 0.001-0.048% Nb, preferably 0.001-0.047%, more preferably 0.001-0.046%, further preferably 0.001-0.045%, further preferably 0.01-0.04%, and most preferably 0.02-0.03%. In the present invention, Nb partially dissolves into solid solution to play a solid solution strengthening role; when Nb element exists in the form of carbide, nitride and oxide particles, it can increase the tempering stability of steel and have a secondary hardening effect; trace Nb can increase the strength of steel without affecting the plasticity or toughness of steel; Nb element has the effect of refining grains, can improve the impact toughness of steel and reduce its brittle transition temperature; during the rolling process, the solid-solution Nb significantly increases the recrystallization temperature of the steel, which can complete the rolling process of the steel in a higher temperature range, thereby reducing the internal stress of the steel. The present invention limits the Nb content within the above range and combines it with other components to make the material have high strength and high toughness.

[0033] By mass percentage, the high-strength and tough steel provided by the present invention includes V 0.19-0.46%, preferably 0.20-0.46%, more preferably 0.21-0.46%, further preferably 0.23-0.46%, further preferably 0.26-0.45%, and most preferably 0.28-0.30%. In the present invention, V has the effects of refining the structure and grains, improving strength and toughness, and reducing overheating sensitivity; V is dissolved in austenite at high temperature, hindering the growth of austenite grains and improving the hardenability of the material; increasing the V content can increase the tempering stability of the steel, so that the steel maintains the shape of martensitic laths during tempering, or precipitates vanadium carbide during tempering to produce a secondary hardening effect, thereby improving the strength of the steel. The present invention limits the V content within the above range and can improve the strength of the material in combination with other components.

[0034] In terms of mass percentage, the high-strength and tough steel provided by the present invention includes Al≤0.020%, preferably ≤0.010%, and more preferably 0.005-0.010%. In the present invention, Al, as a deoxidizer or alloying element, can refine the grains and fix nitrogen in the steel, thereby significantly improving the impact toughness of the steel, reducing the cold brittleness tendency and aging tendency; aluminum can also improve the corrosion resistance of the steel. The present invention limits the content of Al to the above range and combines it with other components to improve the strength and toughness of the material.

[0035] In terms of mass percentage, the high-strength and tough steel provided by the present invention includes B≤0.0030%, preferably ≤0.0020%, and more preferably 0.0010-0.0020%. In the present invention, B is a surface active element with a very small atomic radius, and it is very easy to diffuse to the austenite grain boundary at high temperature. Boron gathers at the austenite grain boundary, the grain boundary energy is reduced, the austenite stability is increased, the austenite grain growth is inhibited, and the toughness is improved. The present invention limits the content of B within the above range and cooperates with other components to improve the toughness of the material.

[0036] The high-strength and toughness steel provided by the present invention utilizes the Mn element to improve the hardenability of the steel, enhance the strength, toughness and hardness, and at the same time forms MnS inclusions with the S element to reduce the influence of S and improve the hot processing performance of the steel. By limiting the Mn content, the steel has high strength and high toughness while having good resistance to hydrogen-induced delayed fracture; utilizes an appropriate amount of Mo element as an alloying element to effectively improve the high-temperature strength and toughness of the steel, and improve the corrosion resistance of the steel in an acidic solution; at the same time, the Mo element forms fine M2C carbides in the alloy, which plays a role of dispersion strengthening and improves the tempering resistance of the material; utilizes an appropriate amount of V element to refine the structure and grains, improve the strength and toughness of the alloy, and reduce the overheating sensitivity; and by adjusting the content of other elements to cooperate with the Mn, Mo and V elements, the strength and toughness of the steel are further improved.

[0037] The present invention provides a method for preparing the high-strength and toughness steel described in the above technical solution, comprising:

[0038] (1) melting the raw materials and then casting to obtain a steel ingot;

[0039] (2) The steel ingot obtained in step (1) is sequentially hot-rolled and subjected to quenching and tempering heat treatment to obtain high-strength and toughness steel.

[0040] The present invention melts the raw materials and then casts them to obtain steel ingots.

[0041] The present invention has no particular limitation on the sources of the raw materials, and the raw materials may be prepared by using commercially available products or well-known preparation methods known to those skilled in the art.

[0042] In the present invention, the smelting is preferably carried out in a vacuum furnace; the smelting preferably includes vacuum melting, vacuum refining and alloying carried out in sequence.

[0043] In the present invention, the vacuum degree of the vacuum melting is preferably 0.5 to 1.5 Pa. The present invention has no particular limitation on the temperature of the vacuum melting, as long as the alloy raw material can be melted.

[0044] In the present invention, the vacuum refining time is preferably 5 to 15 minutes. The present invention has no particular limitation on the temperature of the vacuum refining, as long as the molten steel is kept in a molten state. The present invention has no special requirements on the vacuum degree of the vacuum refining, and the vacuum degree commonly used by those skilled in the art can be used.

[0045] In the present invention, the alloying is preferably performed under argon protection.

[0046] The present invention has no special limitation on the casting method, and the casting method commonly used by those skilled in the art can be used. The present invention has no special limitation on the type of the steel ingot, and the type of steel ingot commonly used in the art can be used. In an embodiment of the present invention, the type of the steel ingot is a shell-shaped steel ingot.

[0047] After obtaining the steel ingot, the present invention performs hot rolling and quenching and tempering heat treatment on the steel ingot to obtain high-strength and toughness steel.

[0048] In the present invention, the steel ingot is preferably subjected to a heat preservation treatment before hot rolling.

[0049] In the present invention, the temperature of the heat preservation treatment is preferably 1200-1280°C, more preferably 1230-1250°C; the time of the heat preservation treatment is preferably >3h, more preferably 4-5h; the speed of heating to the heat preservation treatment temperature is preferably 9-11°C / s, more preferably 10°C / s. The present invention can transform the steel ingot into complete austenite by heat preservation treatment of the steel ingot before hot rolling.

[0050] In the present invention, the rolling direction of the hot rolling is preferably longitudinal rolling; the starting rolling temperature of the hot rolling is preferably 1100-1190°C, more preferably 1130-1170°C, and further preferably 1150°C; the final rolling temperature of the hot rolling is preferably 1020-1080°C, more preferably 1140-1160°C, and further preferably 1050°C. In the present invention, the starting rolling temperature and the final rolling temperature of the hot rolling are limited to the above ranges to ensure that the alloy has good mechanical properties.

[0051] As an embodiment of the present invention, the number of hot rolling passes can be 6 and the cumulative reduction of hot rolling can be 75%. The present invention limits the number of hot rolling passes and the cumulative reduction to the above ranges so that the alloy has good mechanical properties.

[0052] After the hot rolling is completed, the present invention preferably further cools the hot-rolled steel; the cooling is preferably water cooling to 750° C. and then air cooling to room temperature.

[0053] As an embodiment of the present invention, the thickness of the rolled steel may be 17 to 19 mm.

[0054] In the present invention, the tempering heat treatment preferably includes a quenching heat treatment and a tempering heat treatment performed sequentially.

[0055] As an embodiment of the present invention, the quenching temperature of the quenching heat treatment can be 880-920°C, 890-910°C, or 900°C; the holding time of the quenching heat treatment can be 30-60 minutes, 45-55 minutes, or 50 minutes. The present invention limits the quenching temperature and holding time of the quenching heat treatment to the above ranges, which can help improve the strength and toughness of the steel material.

[0056] As an embodiment of the present invention, the tempering temperature of the tempering heat treatment can be 640-680°C, 640-660°C, or 650°C; the holding time of the tempering heat treatment can be 75-120 minutes, 85-115 minutes, or 90-100 minutes. The present invention limits the quenching temperature and holding time of the tempering heat treatment to the above ranges, which can help improve the strength and toughness of the steel material.

[0057] The invention transforms the structure of the steel into troostite and a small amount of martensite through hot rolling and quenching and tempering heat treatment, makes the grains fine, and improves the tensile strength, yield strength and toughness of the material.

[0058] The present invention provides the application of the high-strength and toughness steel described in the above technical solution in petroleum equipment, preferably as steel for oil drill pipes.

[0059] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] Example 1

[0061] A high-strength and toughness steel is composed of the following elements, measured by mass percentage: C 0.23%, Si 0.15%, Mn 0.16%, P 0.006%, S 0.001%, Cr 0.80%, Mo 1.37%, Nb 0.02%, V 0.27%, Al 0.009%, B 0.002% and the balance Fe.

[0062] The preparation method of the high-strength and toughness steel comprises the following steps:

[0063] (1) Prepare the raw materials according to the above ingredients, load the raw materials into a vacuum furnace, evacuate to 1 Pa, heat until melted, refine the molten steel at high temperature and high vacuum for 10 minutes, fill with protective gas argon, and cast into a cannonball-shaped steel ingot after the alloy material is completely melted;

[0064] (2) The steel ingot obtained in step (1) is heated to 1250° C. at a rate of 10° C. / s, kept at this temperature for 4 hours, and longitudinally rolled, with the starting rolling temperature being 1150° C., the final rolling temperature being 1050° C., the number of hot rolling passes being 6, the cumulative reduction of hot rolling being 75%, and after the last hot rolling pass is completed, water is sprayed to 750° C. and then air-cooled to room temperature to obtain rolled steel (thickness being 18 mm); the rolled steel is quenched at 880° C. for 45 min, and then tempered at 660° C. for 100 min to obtain high-strength and toughness steel.

[0065] Example 2

[0066] A high-strength and toughness steel, composed of the following elements by mass percentage: C 0.26%, Si 0.29%, Mn 0.35%, P 0.009%, S 0.0015%, Cr 0.77%, Mo 1.46%, Nb 0.015%, V 0.29%, Al 0.01%, B 0.0030% and the balance Fe;

[0067] The preparation method of the high-strength and toughness steel is different from that of Example 1 only in that in step (2), the quenching heat treatment temperature is 890° C., and the quenching heat treatment time is 55 min; the tempering heat treatment temperature is 640° C., and the tempering heat treatment time is 85 min. The rest is the same as in Example 1.

[0068] Example 3

[0069] A high-strength and toughness steel, composed of the following elements by mass percentage: C 0.28%, Si 0.33%, Mn 0.40%, P 0.005%, S 0.002%, Cr 0.96%, Mo 1.66%, Nb 0.03%, V 0.30%, Al 0.02%, B 0.0030% and the balance Fe;

[0070] The preparation method of the high-strength and toughness steel is different from that of Example 1 only in that in step (2), the quenching heat treatment temperature is 910° C., and the quenching heat treatment time is 60 min; the tempering heat treatment temperature is 660° C., and the tempering heat treatment time is 115 min. The rest is the same as in Example 1.

[0071] Example 4

[0072] A high-strength and toughness steel, composed of the following elements by mass percentage: C 0.25%, Si 0.30%, Mn 0.30%, P 0.010%, S 0.001%, Cr 0.87%, Mo 1.55%, Nb 0.036%, V 0.32%, Al 0.006%, B 0.003% and the balance Fe;

[0073] The preparation method of the high-strength and toughness steel is different from that of Example 1 only in that in step (2), the quenching heat treatment temperature is 900° C. and the quenching heat treatment time is 30 min; the tempering heat treatment temperature is 660° C. and the tempering heat treatment time is 90 min. The rest is the same as in Example 1.

[0074] Comparative Example 1

[0075] A high-strength and toughness steel, composed of the following elements by mass percentage: C 0.22%, Si 0.24%, Mn 1.52%, P 0.013%, S 0.002%, Cr 1.60%, Mo 1.10%, Nb 0.01%, V 0.21%, Al 0.22% and the balance Fe;

[0076] The preparation method of the high-strength and toughness steel is different from that of Example 1 only in that in step (2), the quenching heat treatment temperature is 880° C., and the quenching heat treatment time is 30 min; the tempering heat treatment temperature is 660° C., and the tempering heat treatment time is 90 min. The rest is the same as in Example 1.

[0077] Comparative Example 2

[0078] A high-strength and toughness steel, composed of the following elements by mass percentage: C 0.39%, Si 0.21%, Mn 0.75%, P 0.015%, S 0.005%, Cr 1.51%, Mo 1.40%, Nb 0.025%, V 0.06%, Al 0.05% and the balance Fe;

[0079] The preparation method of the high-strength and toughness steel is different from that of Example 1 only in that in step (2), the quenching heat treatment temperature is 880° C., and the quenching heat treatment time is 60 min; the tempering heat treatment temperature is 640° C., and the tempering heat treatment time is 90 min. The rest is the same as in Example 1.

[0080] Comparative Example 3

[0081] A high-strength and tough steel, composed of the following elements by mass percentage: C 0.30%, Si 0.10%, Mn 1.00%, P 0.015%, S 0.003%, Cr 1.14%, Mo 1.50%, Nb 0.03%, V 0.01%, Al 0.06% and the balance Fe;

[0082] The preparation method of the high-strength and toughness steel is different from that of Example 1 only in that in step (2), the quenching heat treatment temperature is 900° C. and the quenching heat treatment time is 45 min; the tempering heat treatment temperature is 660° C. and the tempering heat treatment time is 90 min. The rest is the same as in Example 1.

[0083] Comparative Example 4

[0084] A high-strength and toughness steel, composed of the following elements by mass percentage: C 0.18%, Si 0.4%, Mn 0.8%, P 0.015%, S 0.003%, Mo 0.6%, Nb 0.035%, V 0.12%, Al 0.02%, B 0.0016% and the balance Fe;

[0085] The preparation method of the high-strength and toughness steel is different from that of Example 1 only in that in step (2), the quenching heat treatment temperature is 900° C. and the quenching heat treatment time is 60 min; the tempering heat treatment temperature is 640° C. and the tempering heat treatment time is 100 min. The rest is the same as in Example 1.

[0086] Comparative Example 5

[0087] The difference between Comparative Example 5 and Example 1 is that the high-strength and toughness steel is composed of the following elements by mass percentage: C 0.25%, Si 0.30%, Mn 0.52%, P 0.010%, S 0.001%, Cr 0.87%, Mo 1.55%, Nb 0.036%, V 0.32%, Al 0.006%, B 0.003% and the balance Fe;

[0088] The preparation method of the high-strength and toughness steel is the same as that of Example 4.

[0089] Comparative Example 6

[0090] The difference between Comparative Example 6 and Example 1 is that the high-strength and toughness steel is composed of the following elements by mass percentage: C 0.25%, Si 0.30%, Mn 0.52%, P 0.010%, S 0.001%, Cr 0.87%, Mo 1.30%, Nb 0.036%, V 0.32%, Al 0.006%, B 0.003% and the balance Fe;

[0091] The preparation method of the high-strength and toughness steel is the same as that of Example 4.

[0092] Comparative Example 7

[0093] The difference between Comparative Example 7 and Example 4 is that the high-strength and toughness steel is composed of the following elements by mass percentage: C 0.25%, Si 0.30%, Mn 0.52%, P 0.010%, S 0.001%, Cr 0.87%, Mo 1.55%, Nb 0.036%, V 0.15%, Al 0.006%, B 0.003% and the balance Fe;

[0094] The preparation method of the high-strength and toughness steel is the same as that of Example 4.

[0095] The microstructures of the high-strength and toughness steels prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were observed using an optical microscope. The microstructure of the high-strength and toughness steel prepared in Example 1 is shown in FIG. Figure 1 As shown, the microstructure of the high-strength and tough steel prepared in Example 2 is as shown in Figure 2 As shown, the microstructure of the high-strength and tough steel prepared in Example 3 is as shown in Figure 3 As shown, the microstructure of the high-strength and tough steel prepared in Example 4 is as shown in Figure 4 As shown. Figures 1 to 4 It can be seen that compared with Comparative Examples 1 and 2, the structures of Examples 1 and 2 are refined, and no obvious segregation bands appear, and the martensite laths are clearly visible, indicating that the proper matching of the contents of Mn, Mo and V can optimize the structure.

[0096] According to GB / T 228.1-2010 "Metallic Materials Tensile Test Part 1: Room Temperature Test Method" and GB / T 229-2007 "Metallic Materials Charpy Pendulum Impact Test Method" standards, the high-strength and tough steels prepared in Examples 1 to 4 and Comparative Examples 1 to 7 were tested for mechanical properties. The test data are shown in Table 1. The structural dimensions of the specimens for the constant load notch tensile test are shown in Table 1. Figure 5 shown.

[0097] Table 1 Mechanical properties test data of high strength and toughness steel obtained in Examples 1 to 4 and Comparative Examples 1 to 7

[0098]

[0099] It can be seen from the data in Table 1 that the yield strength of the high-strength and toughness steel provided by the present invention is greater than 1200MPa, the tensile strength is greater than 1260MPa, the longitudinal impact at 0°C is greater than 100J, and during the notch load test, the notch tensile specimen is subjected to constant load stretching in Walpole acetic acid corrosion inhibition solution, and its notch load critical fracture stress ratio n is not less than 0.8, and it does not break for more than 100h.

[0100] By comparing the data of Example 4 and Comparative Examples 5 to 7, it can be seen that the performance of the steel decreases to varying degrees by increasing the Mn content, decreasing the Mo content, or decreasing the V content, which indicates that the present invention optimizes the contents of Mn, Mo, and V and combines them with other ingredients to enable the material to have high strength and high toughness.

[0101] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A high-strength and tough steel, composed of the following elements by mass percentage: C 0.18~0.39%, Si 0.09~0.40%, Mn 0.1~0.42%, P≤0.0128%, S≤0.0028%, Cr 0.37~1.15%, Mo 1.15~2.0%, Nb 0.001~0.048%, V 0.19~0.46%, Al≤0.020%, B≤0.0030% and the balance Fe.

2. The high-strength and toughness steel according to claim 1, characterized in that: It is composed of the following elements: C 0.18-0.38%, Si 0.09-0.39%, Mn 0.1-0.40%, P≤0.0127%, S≤0.0027%, Cr 0.38-1.15%, Mo 1.17-2.0%, Nb 0.001-0.047%, V 0.20-0.46%, Al 0.005-0.020%, B 0.0010-0.0030% and the balance Fe.

3. The high-strength and toughness steel according to claim 2, characterized in that: It is composed of the following elements: C 0.18-0.37%, Si 0.09-0.38%, Mn 0.10-0.39%, P≤0.0126%, S≤0.0026%, Cr0.4-1.15%, Mo 1.18-2.0%, Nb 0.001-0.046%, V 0.21-0.46%, Al0.005-0.010%, B 0.0010-0.0020% and the balance Fe.

4. The method for preparing the high-strength and toughness steel according to any one of claims 1 to 3, comprising: (1) melting the raw materials and then casting to obtain a steel ingot; (2) The steel ingot obtained in step (1) is sequentially hot-rolled and subjected to quenching and tempering heat treatment to obtain high-strength and toughness steel.

5. The preparation method according to claim 4, characterized in that: In the step (2), the starting temperature of hot rolling is 1100-1190°C, and the finishing temperature of hot rolling is 1020-1080°C.

6. The preparation method according to claim 4 or 5, characterized in that: The steel ingot is subjected to insulation treatment before hot rolling; the temperature of the insulation treatment is 1200-1280°C, and the insulation treatment time is greater than 3h.

7. The preparation method according to claim 4, characterized in that: The tempering heat treatment in step (2) includes quenching heat treatment and tempering heat treatment performed sequentially.

8. The preparation method according to claim 7, characterized in that: The quenching temperature of the quenching heat treatment is 880-920° C., and the holding time of the quenching heat treatment is 30-60 minutes.

9. The preparation method according to claim 7, characterized in that: The temperature of the tempering heat treatment is 640-680° C., and the holding time of the tempering heat treatment is 75-120 minutes.

10. Use of the high-strength and toughness steel according to any one of claims 1 to 3 or the high-strength and toughness steel prepared by the preparation method according to any one of claims 4 to 9 in petroleum equipment.

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