CN112553525A - Medium-carbon low-alloy high-strength steel and preparation method thereof - Google Patents
Medium-carbon low-alloy high-strength steel and preparation method thereof Download PDFInfo
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Abstract
The invention discloses medium-carbon low-alloy high-strength steel and a preparation method thereof, belongs to the technical field of alloy materials, and solves the problems of low strength and toughness, low-temperature impact resistance and poor corrosion resistance of seabed wellhead and oil extraction equipment materials in the prior art. The high-strength steel comprises the following components in percentage by weight: 0.20-0.30% of C, 0.70-0.90% of Mn, 0.15-0.35% of Si, 0.70-1.00% of Cr, 0.30-0.50% of Mo, less than or equal to 0.01% of P, less than or equal to 0.01% of S, 0.50-0.70% of Ni, less than or equal to 0.05% of V, less than or equal to 0.15% of Cu, less than or equal to 0.015% of Nb, less than or equal to 0.015% of Ti and the balance of Fe and inevitable impurities. According to the preparation method, the ingot is obtained by smelting according to the composition of the medium-carbon low-alloy high-strength steel; carrying out hot processing on the cast ingot to obtain a blank; and carrying out heat treatment on the blank. The medium-carbon low-alloy high-strength steel and the preparation method thereof can be used for key components on seabed wellhead drilling and production equipment.
Description
Technical Field
The invention belongs to the technical field of alloy materials, and particularly relates to medium-carbon low-alloy high-strength steel and a preparation method thereof.
Background
Subsea wellheads and production equipment in marine engineering are important unit equipment in the development of marine oil and gas fields, and are also key equipment of subsea production systems. Under the severe working conditions of high pressure, low temperature, seawater and oil gas corrosion and the like on the seabed, the performance and the quality of seabed equipment play an important role in the safety of an oil well. At present, marine engineering equipment is developed from shallow sea equipment to deep sea large-scale equipment, which puts higher requirements on marine wellhead materials.
The requirements of seabed well heads and oil extraction equipment on various properties of materials are continuously improved, but the comprehensive properties of the materials are improved only by improving a heat treatment system, the effect is very limited, and the existing well head equipment materials are low in strength and toughness and poor in low-temperature impact resistance and corrosion resistance.
Disclosure of Invention
In view of the above analysis, the invention aims to provide medium-carbon low-alloy high-strength steel and a preparation method thereof, and solves the problems of low strength and toughness, low-temperature impact resistance and poor corrosion resistance of seabed wellhead and oil extraction equipment materials in the prior art.
The purpose of the invention is mainly realized by the following technical scheme:
the invention provides medium-carbon low-alloy high-strength steel which comprises the following components in percentage by weight: 0.20-0.30% of C, 0.70-0.90% of Mn, 0.15-0.35% of Si, 0.70-1.00% of Cr, 0.30-0.50% of Mo, less than or equal to 0.01% of P, less than or equal to 0.01% of S, 0.50-0.70% of Ni, less than or equal to 0.05% of V, less than or equal to 0.15% of Cu, less than or equal to 0.015% of Nb, less than or equal to 0.015% of Ti and the balance of Fe and inevitable impurities.
Further, the medium-carbon low-alloy high-strength steel comprises the following components in percentage by weight: 0.23 to 0.27 percent of C, 0.75 to 0.80 percent of Mn, 0.20 to 0.25 percent of Si, 0.80 to 0.95 percent of Cr, 0.35 to 0.45 percent of Mo, less than or equal to 0.01 percent of P, less than or equal to 0.01 percent of S, 0.55 to 0.60 percent of Ni, 0.03 to 0.04 percent of V, 0.01 to 0.1 percent of Cu, 0.001 to 0.010 percent of Nb, 0.001 to 0.010 percent of Ti, and the balance of Fe and inevitable impurities.
Furthermore, in the medium-carbon low-alloy high-strength steel, the final structure is tempered sorbite, the tensile strength is 880-900 MPa, the yield strength is 810-830 MPa, the elongation is 17-21%, the reduction of area is 73-74%, and the impact energy at-18 ℃ is 200-210J.
The invention also provides a preparation method of the medium-carbon low-alloy high-strength steel, which is used for preparing the medium-carbon low-alloy high-strength steel, and the preparation method comprises the following steps:
step S1: according to the composition of the medium-carbon low-alloy high-strength steel, obtaining an ingot by smelting;
step S2: carrying out hot processing on the cast ingot to obtain a blank;
step S3: and carrying out heat treatment on the blank to obtain the medium-carbon low-alloy high-strength steel.
Further, the step S2 includes the following steps:
step S21: heating the ingot to 1100-1250 ℃, preserving heat for 5-10 h, and carrying out homogenization heat treatment, and cooling to room temperature along with the furnace, wherein the heating mode can be heating the ingot along with the furnace or putting the ingot into the furnace heated to 1100-1250 ℃;
step S22: and heating and forging the ingot after the homogenization heat treatment, wherein the heating and heat preservation temperature is 1100-1180 ℃, the heating and heat preservation time is 2-5 hours, the forging ratio is not less than 3, and the forging starting temperature of the blank is not lower than 1100 ℃.
Further, the step S3 includes the following steps:
step S31: heating the blank to 850-900 deg.C(Ac3Above temperature) keeping the temperature for 2-8 h, carrying out isothermal transformation along with furnace cooling, and air-cooling to room temperature;
step S32: heating the blank after air cooling to 850-900 ℃ (Ac)3Above the temperature) keeping the temperature for 1 to 8 hours for quenching;
step S33: heating the quenched blank to 580-650 ℃ (Ac)1Below the temperature) and keeping the temperature for 2 to 24 hours for tempering.
Further, in the step S31, the temperature is raised in two stages, wherein the first stage is raising the temperature from room temperature to 750 ℃ at a temperature raising rate of 280 ℃/h to 330 ℃/h, and the second stage is raising the temperature from 750 ℃ to 850 ℃ to 900 ℃ at a temperature raising rate of 120 ℃/h to 230 ℃/h.
Further, in the step S32, the temperature is raised in two stages, wherein the first stage is raising the temperature from room temperature to 750 ℃ at a temperature raising rate of 280 ℃/h to 330 ℃/h, and the second stage is raising the temperature from 750 ℃ to 850 ℃ to 900 ℃ at a temperature raising rate of 120 ℃/h to 230 ℃/h.
Further, cooling to below 80-100 ℃ by adopting a water quenching and/or oil quenching mode.
Further, in the above step S33, the number of tempering is at least two.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
a) the medium-carbon low-alloy high-strength steel and the preparation method thereof provided by the invention can obtain excellent mechanical property and processing property and H resistance through multiple design, optimization and matching of the composition and the preparation method, such as components, microstructures, heat treatment process and the like2S corrosion performance medium carbon low alloy high strength steel.
b) The medium-carbon low-alloy high-strength steel provided by the invention has the characteristics of high strength, high toughness, low-temperature impact resistance, corrosion resistance and the like, the content of C is properly reduced, the content of Ni element is increased so as to increase the toughness of a matrix, less than 0.05% of V element is added, crystal grains are refined, and the toughness and the corrosion resistance are improved. The invention obtains good matching of strength, toughness and plasticity by properly reducing the content of C, improving the content of Ni element and adding a small amount of V element, and is suitable for key components on the submarine wellhead drilling and production equipment.
c) In the preparation method of the medium-carbon low-alloy high-strength steel, the segregation elements are fully diffused through high-temperature homogenization heat treatment, and the aim of dehydrogenation can be fulfilled; the purpose of refining grains can be achieved through forging, and therefore a good foundation is laid for improving the comprehensive performance of the medium-carbon low-alloy high-strength steel.
d) In the preparation method of the medium-carbon low-alloy high-strength steel, the blank can obtain finer and uniform crystal grains after normalizing (step S31); the quenching is controlled, so that the secondary refining effect of crystal grains can be achieved; the tempering temperature is controlled, the good matching of strength, plasticity and toughness can be promoted, the dispersion distribution of carbides in a microstructure is promoted, and the size is less than 50 nm.
e) According to the preparation method of the medium-carbon low-alloy high-strength steel, a tempered sorbite structure can be formed in the steel through normalizing (step S31), quenching (step S32), tempering (step S33) and controlling the tempering temperature to be 580-650 ℃, and the tempered sorbite is beneficial to the hydrogen sulfide corrosion resistance of the medium-carbon low-alloy high-strength steel.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating the particular invention and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout the figures.
FIG. 1 is a surface result of a sample of the medium-carbon low-alloy high-strength steel provided in example 1 of the present invention after hydrogen sulfide corrosion resistance;
FIG. 2 is the surface result of the sample after the medium-carbon low-alloy high-strength steel provided by the embodiment 2 of the invention resists the corrosion of hydrogen sulfide.
Detailed Description
The preferred invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and which together with the description serve to explain the principles of the invention.
The invention provides medium-carbon low-alloy high-strength steel which comprises the following components in percentage by weight: 0.20-0.30% of C, 0.70-0.90% of Mn, 0.15-0.35% of Si, 0.70-1.00% of Cr, 0.30-0.50% of Mo, less than or equal to 0.01% of P, less than or equal to 0.01% of S, 0.50-0.70% of Ni, less than or equal to 0.05% of V, less than or equal to 0.15% of Cu, less than or equal to 0.015% of Nb, less than or equal to 0.015% of Ti and the balance of Fe and inevitable impurities.
Compared with the prior art, the medium-carbon low-alloy high-strength steel provided by the invention has the characteristics of high strength, high toughness, low-temperature impact resistance, corrosion resistance and the like, the content of C is properly reduced, the content of Ni element is increased to improve the toughness of a matrix, less than 0.05% of V element is added, crystal grains are refined, and the toughness and the corrosion resistance are improved. The invention obtains good matching of strength, toughness and plasticity by properly reducing the content of C, improving the content of Ni element and adding a small amount of V element, and is suitable for key components on the submarine wellhead drilling and production equipment.
Specifically, in the medium-carbon low-alloy high-strength steel, the functions of the components are as follows:
c: the C content is reduced as much as possible within a reasonable range, the ductility and toughness and low-temperature impact toughness of the steel can be effectively improved, and the ductile-brittle transition temperature is reduced.
Mn: the hardenability of the material can be improved, the material has a solid solution strengthening effect, and the toughness of a matrix can be improved and the ductile-brittle transition temperature can be reduced by adding a proper amount of Mn; however, the MnS inclusions are a main factor causing wet hydrogen sulfide corrosion, and increase the susceptibility to stress corrosion cracking, and therefore, the influence of Mn on the mechanical properties and the corrosivity of steel is comprehensively considered, and the amount of Mn added is controlled within the range of 0.70 to 0.90.
Si: although Si has a solid-solution strengthening effect while improving the hardenability of the material, Si is likely to segregate at the grain boundaries and promote intergranular cracks in low-alloy high-strength steel, and therefore, the amount of Si added is controlled within a range of 0.15 to 0.35.
Cr: can effectively improve the hardenability, the heat resistance and the hydrogen sulfide stress corrosion resistance of the medium-carbon low-alloy high-strength steelAnd the steel has a solid solution strengthening effect, the Cr content has great influence on the sulfuration resistance of the medium-carbon low-alloy high-strength steel, and the steel is beneficial to reducing the relative corrosion of sulfide on the medium-carbon low-alloy high-strength steel. At high temperature H2In the corrosion medium of S, Cr in the medium-carbon low-alloy high-strength steel has the function of inhibiting mercaptan adsorption, so that the addition amount of Cr is controlled within the range of 0.70-1.00.
Mo: the passivation of the medium-carbon low-alloy high-strength steel can be promoted, and the corrosion resistance and the pitting resistance of the medium-carbon low-alloy high-strength steel in sulfuric acid, hydrochloric acid and partial organic acid are improved; during high-temperature tempering, Mo can inhibit brittleness caused by segregation of impurities such as phosphorus and the like in grain boundaries, thereby enhancing the H resistance of a matrix2S corrosion performance, and meanwhile, the addition of Mo can also effectively improve the hardenability and the heat strength of the medium-carbon low-alloy high-strength steel, and has a solid solution strengthening effect, so that the addition amount of Mo is controlled within the range of 0.30-0.50.
Ni: the main elements for promoting the medium-carbon low-alloy high-strength steel to form a stable austenite structure, but because the hydrogen evolution overpotential on the nickel-containing steel is the lowest, hydrogen ions are easy to discharge, and the hydrogen absorption process is strengthened, the sulfide fracture sensitivity in the steel is increased, therefore, in the design process of the medium-carbon low-alloy high-strength steel, the addition amount of Ni cannot approach or reach 1%, and the addition amount of Ni is controlled within the range of 0.50-0.70.
V: the strong carbon compound forming element can refine crystal grains and improve the sensitivity to Sulfide Stress Corrosion (SSC), but if the addition amount of V is too large, the VC is too hard and easily generates grinding cracks, which can cause poor grinding and welding performance of steel, therefore, the addition amount of V is controlled within the range of V less than or equal to 0.05.
Cu: can accelerate the recombination velocity of hydrogen atoms, further reduce the activity of hydrogen, improve the corrosion resistance and the pitting resistance of the medium-carbon low-alloy high-strength steel in an acid medium, and enhance the H resistance2S stress corrosion capability; however, since too large an amount of Cu causes low high-temperature strength and toughness of the steel and deterioration of weldability, the amount of Cu is controlled to be in the range of 0.10 or less.
Ti: can effectively improve the cracking sensitivity of sulfide, form elements for strong carbon compounds, reduce the amount of solid solution carbon, thereby reducing the formation of untempered martensite and reducing the hardness, therefore, the addition amount of Ti is controlled within the range of less than or equal to 0.015.
Nb: the unevenness of the medium-carbon low-alloy high-strength steel structure can be reduced, and the sulfide corrosion resistance of the medium-carbon low-alloy high-strength steel is improved; meanwhile, when Nb and Mo are added compositely, the crack resistance can be further improved, so that the adding amount of Nb is controlled within the range of less than or equal to 0.015.
P: as an accelerator for the hydrogen absorption process, the non-metallic inclusions easily cause lamellar tearing cracks and bead tail cracks, and the cracks can be accelerated to propagate after overlapping with stress corrosion cracks, so that the P content should be strictly controlled within 1%.
S: as one of hydrogen embrittlement sources of sulfide inclusions in steel, the sulfide inclusions are easy to crack along the boundary of the inclusions and are also factors causing Z-direction fracture; similar to the harm of P, the nonmetallic inclusion of the composite material can easily cause lamellar tearing crack and welding bead tail crack, and the crack can be accelerated to expand after being overlapped with the stress corrosion crack, and the content of S is strictly controlled within 0.01 percent.
In order to further optimize the performance of the medium-carbon low-alloy high-strength steel, the composition comprises the following components in percentage by weight: 0.23 to 0.27 percent of C, 0.75 to 0.80 percent of Mn, 0.20 to 0.25 percent of Si, 0.80 to 0.95 percent of Cr, 0.35 to 0.45 percent of Mo, less than or equal to 0.01 percent of P, less than or equal to 0.01 percent of S, 0.55 to 0.60 percent of Ni, 0.03 to 0.04 percent of V, 0.01 to 0.1 percent of Cu, 0.001 to 0.010 percent of Nb, 0.001 to 0.010 percent of Ti, and the balance of Fe and inevitable impurities.
The invention also provides a preparation method of the medium-carbon low-alloy high-strength steel, which is used for preparing the medium-carbon low-alloy high-strength steel, and the preparation method comprises the following steps:
step S1: according to the composition of the medium-carbon low-alloy high-strength steel, obtaining an ingot by smelting;
step S2: carrying out hot processing on the cast ingot to obtain a blank;
step S3: and carrying out heat treatment on the blank to obtain the medium-carbon low-alloy high-strength steel.
Compared with the prior art, the beneficial effects of the preparation method of the medium-carbon low-alloy high-strength steel provided by the invention are basically the same as those of the medium-carbon low-alloy high-strength steel, and are not repeated herein.
Specifically, the step S2 includes the following steps:
step S21: heating the ingot to 1100-1250 ℃, preserving heat for 5-10 h, and carrying out homogenization heat treatment, and cooling to room temperature along with the furnace, wherein the heating mode can be heating the ingot along with the furnace or putting the ingot into the furnace heated to 1100-1250 ℃;
step S22: and (3) heating and forging the ingot after the homogenization heat treatment, wherein the heating and heat preservation temperature is 1100-1180 ℃, the heating and heat preservation time is 2-5 hours, the forging ratio is not less than 3, the forging temperature of the blank is not less than 1100 ℃, it needs to be noted that after the forging is finished, the ingot can be subjected to stress relief annealing by returning to the furnace or can be directly subjected to air cooling, and the specific treatment mode can be flexibly treated according to the size of the sample piece and the field conditions and is not limited to the two treatment modes.
Step S2 is to fully diffuse the segregation elements through high-temperature homogenization heat treatment in the above way, and simultaneously achieve the aim of dehydrogenation; the purpose of refining grains can be achieved through forging, and therefore a good foundation is laid for improving the comprehensive performance of the medium-carbon low-alloy high-strength steel.
The step S3 includes the following steps:
step S31: heating the blank to 850-900 ℃ (Ac)3Above temperature) keeping the temperature for 2-8 h, carrying out isothermal transformation along with furnace cooling, and air-cooling to room temperature;
step S32: heating the blank after air cooling to 850-900 ℃ (Ac)3Above the temperature) keeping the temperature for 1 to 8 hours for quenching;
step S33: heating the quenched blank to 580-650 ℃ (Ac)1Below the temperature) and keeping the temperature for 2 to 24 hours for tempering.
According to the heat treatment method, after normalizing (step S31), the blank can obtain relatively fine and uniform grains; the quenching is controlled, so that the secondary refining effect of crystal grains can be achieved; the tempering temperature is controlled, the good matching of strength, plasticity and toughness can be promoted, the dispersion distribution of carbides in a microstructure is promoted, and the size is less than 50 nm.
Further, by normalizing (step S31), quenching (step S32), tempering (step S33) and controlling the tempering temperature at 580 to 650 ℃, a tempered sorbite structure can be formed in the steel, which contributes to the hydrogen sulfide corrosion resistance of the above-mentioned medium-carbon low-alloy high-strength steel.
Specifically, the medium-carbon low-alloy high-strength steel prepared by the composition and the preparation method of the medium-carbon low-alloy high-strength steel is basically all tempered sorbite in a microstructure, the tensile strength is 880-900 MPa, the yield strength is 810-830 MPa, the elongation is 17-21%, the reduction of area is 73-74%, and the impact energy at-18 ℃ is 200-210J.
In order to improve the heating efficiency of the normalizing on the basis of ensuring the temperature uniformity of the blank, in the step S31, two-stage heating is adopted, wherein the first stage heating is to heat from room temperature to 750 ℃ at a heating rate of 280 ℃/h-330 ℃/h, and the second stage heating is to heat from 750 ℃ to 850-900 ℃ at a heating rate of 120 ℃/h-230 ℃/h. The rapid heating is adopted in the first stage of temperature rise because the blank has a certain thickness, the microstructure transformation in the steel is basically not influenced in the temperature range of room temperature to 750 ℃, and the rapid heating can effectively improve the temperature rise efficiency; the reason why the second stage heating adopts slow heating is that the microstructure in the steel can generate austenite transformation at about 750 ℃, and the slow heating is beneficial to the temperature homogenization of the blank.
Similarly, in order to improve the heating efficiency of quenching while ensuring the temperature uniformity of the slab, in step S32, two-stage heating is employed, where the first stage heating is performed from room temperature to 750 ℃ at a heating rate of 280 ℃/h to 330 ℃/h, and the second stage heating is performed from 750 ℃ to 850 ℃ to 900 ℃ at a heating rate of 120 ℃/h to 230 ℃/h. The rapid heating is adopted in the first stage of temperature rise because the blank has a certain thickness, the microstructure transformation in the steel is basically not influenced in the temperature range of room temperature to 750 ℃, and the rapid heating can effectively improve the temperature rise efficiency; the reason why the second stage heating adopts slow heating is that the microstructure in the steel can generate austenite transformation at about 750 ℃, and the slow heating is beneficial to the temperature homogenization of the blank.
The quenching cooling method may be, specifically, water quenching and/or oil quenching to 80 to 100 ℃.
It should be noted that, in order to achieve better usability, in step S33, the number of tempering is at least two, and through multiple tempering, good matching of strength, plasticity and toughness can be further promoted, and dispersion distribution of carbides in the microstructure can be promoted.
In conclusion, the medium-carbon low-alloy high-strength steel and the preparation method thereof provided by the invention can obtain excellent mechanical property and processing property and H resistance through multiple design, optimization and matching of the composition and the preparation method, such as components, microstructures, heat treatment process and the like2S corrosion performance medium carbon low alloy high strength steel.
Example 1
The chemical components and ingredients of embodiment 1 of the invention comprise, in weight percent (%): 0.26 percent of C, 0.86 percent of Mn, 0.25 percent of Si, 0.93 percent of Cr, 0.40 percent of Mo, less than or equal to 0.005 percent of P, less than or equal to 0.0018 percent of S, 0.60 percent of Ni, 0.031 percent of V, 0.15 percent of Cu, less than 0.005 percent of Nb and less than or equal to 0.010 percent of Ti; the balance of Fe and inevitable impurities.
The steel ingot of example 1 was subjected to the following hot working process: heating the steel ingot to 1230 ℃, preserving the temperature for 10 hours, and carrying out homogenization heat treatment, and then furnace cooling to room temperature. And then carrying out hot working, keeping the temperature at 1160 ℃, keeping the temperature for 4 hours, discharging from the furnace and forging after the heating is finished, wherein the forging ratio is 5.6, and cooling in air after the forging is finished.
The following heat treatment process was used for example 1: heating the forging to 900 ℃, preserving heat for 2h, cooling to 700 ℃ along with the furnace, then air-cooling to room temperature, heating the forging to 870 ℃, preserving heat for 2h, then quenching by water cooling, finally heating to 650 ℃, preserving heat for 4h, and then tempering along with the furnace cooling.
Example 2
The chemical components and ingredients of embodiment 2 of the invention, in percentage by weight (%), comprise: 0.24 percent of C, 0.78 percent of Mn, 0.21 percent of Si, 0.84 percent of Cr, 0.38 percent of Mo, less than or equal to 0.005 percent of P, 0.0014 percent of S, 0.56 percent of Ni, 0.031 percent of V, 0.011 percent of Cu, less than 0.010 percent of Nb and less than or equal to 0.010 percent of Ti; the balance of Fe and inevitable impurities.
The steel ingot of example 2 was subjected to the following hot working process: heating the steel ingot to 1230 ℃, preserving the temperature for 10 hours, and carrying out homogenization heat treatment, and then furnace cooling to room temperature. And then carrying out hot working, keeping the temperature at 1160 ℃, keeping the temperature for 4 hours, discharging from the furnace and forging after the heating is finished, wherein the forging ratio is 5.6, and cooling in air after the forging is finished.
The following heat treatment process was used for example 2: heating the forging to 900 ℃, preserving heat for 2h, cooling to 700 ℃ along with the furnace, then air-cooling to room temperature, heating the forging to 890 ℃, preserving heat for 1h, water-cooling for quenching, finally heating to 650 ℃, preserving heat for 4h, then cooling along with the furnace for tempering.
Through the heat treatment, in 2 embodiments of the invention, the carbon low-alloy steel has very excellent comprehensive properties of strength, plasticity and toughness, especially low-temperature impact toughness at-18 ℃, and is greatly improved, and in addition, the tempered sorbite obtained after high-temperature tempering has very excellent corrosion resistance.
The specific chemical components of a certain company modified 8630 as a comparative example are shown in Table 1. After the material is smelted by an electric furnace, refining by Vacuum Degassing (VD), argon stirring degassing, Argon Oxygen Decarburization (AOD), electroslag remelting (ESR) or Vacuum Arc Remelting (VAR); the forging ratio during forging is not less than 3.0; normalizing 899-972 ℃; quenching 871-927 ℃; tempering 677-722 ℃.
Composition comparison of inventive example 1, example 2 and comparative example 1, see table 1; the properties of inventive example 1, example 2 and comparative example 1 were compared, see table 2.
Table 1 comparison of compositions of example 1, example 2 and comparative example 1
Table 2 comparison of the properties of example 1, example 2 and comparative example 1 according to the invention
As can be seen from Table 2, the performances of the examples 1 and 2 are more excellent, especially the low-temperature impact energy reaches 207J and 201J respectively at-18 ℃; the corrosion resistance is good according to NACE TM0177-2016, hydrogen sulfide corrosion resistance (SSC 2 area) is developed, and appearance after corrosion is good (10X pictures), see FIG. 1 and FIG. 2.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. The medium-carbon low-alloy high-strength steel is characterized by comprising the following components in percentage by weight: 0.20-0.30% of C, 0.70-0.90% of Mn, 0.15-0.35% of Si, 0.70-1.00% of Cr, 0.30-0.50% of Mo, less than or equal to 0.01% of P, less than or equal to 0.01% of S, 0.50-0.70% of Ni, less than or equal to 0.05% of V, less than or equal to 0.15% of Cu, less than or equal to 0.015% of Nb, less than or equal to 0.015% of Ti, and the balance of Fe and inevitable impurities.
2. A medium carbon low alloy high strength steel according to claim 1, characterized in that the composition comprises, in weight percent: 0.23 to 0.27 percent of C, 0.75 to 0.80 percent of Mn, 0.20 to 0.25 percent of Si, 0.80 to 0.95 percent of Cr, 0.35 to 0.45 percent of Mo, less than or equal to 0.01 percent of P, less than or equal to 0.01 percent of S, 0.55 to 0.60 percent of Ni, 0.03 to 0.04 percent of V, 0.01 to 0.1 percent of Cu, 0.001 to 0.010 percent of Nb, 0.001 to 0.010 percent of Ti, and the balance of Fe and inevitable impurities.
3. The medium carbon low alloy high strength steel according to claim 1 or 2, wherein the final structure is tempered sorbite.
4. The medium-carbon low-alloy high-strength steel as claimed in claim 1 or 2, wherein the tensile strength of the medium-carbon low-alloy high-strength steel is 880-900 MPa, the yield strength is 810-830 MPa, the elongation is 17-21%, the reduction of area is 73-74%, and the impact energy at-18 ℃ is 200-210J.
5. A method for producing a medium carbon low alloy high strength steel, characterized by producing a medium carbon low alloy high strength steel according to claims 1 to 4, said method comprising the steps of:
step S1: according to the composition of the medium-carbon low-alloy high-strength steel, obtaining an ingot by smelting;
step S2: carrying out hot processing on the cast ingot to obtain a blank;
step S3: and carrying out heat treatment on the blank to obtain the medium-carbon low-alloy high-strength steel.
6. The method for preparing medium carbon low alloy high strength steel according to claim 5, wherein the step S2 includes the steps of:
step S21: heating the cast ingot to 1100-1250 ℃, preserving heat for 5-10 h, carrying out homogenization heat treatment, and cooling to room temperature along with the furnace;
step S22: and heating and forging the ingot after the homogenization heat treatment, wherein the heating and heat preservation temperature is 1100-1180 ℃, the heating and heat preservation time is 2-5 hours, the forging ratio is not less than 3, and the forging starting temperature of the blank is not lower than 1100 ℃.
7. The method for preparing medium carbon low alloy high strength steel according to claim 5, wherein the step S3 includes the steps of:
step S31: heating the blank to 850-900 ℃, preserving heat for 2-8 h, carrying out isothermal transformation along with furnace cooling, and air cooling to room temperature;
step S32: heating the blank after air cooling to 850-900 ℃, and keeping the temperature for 1-8 h for quenching;
step S33: heating the quenched blank to 580-650 ℃, and keeping the temperature for 2-24 h for tempering.
8. The method of claim 7, wherein the step S31 includes two-stage heating, the first stage heating is from room temperature to 750 ℃ at a heating rate of V1, the second stage heating is from 750 ℃ to 850 ℃ -900 ℃ at a heating rate of V2, and V1> V2.
9. The method for preparing a medium-carbon low-alloy high-strength steel as claimed in claim 8, wherein in the step S31, V1 is 280 ℃/h to 330 ℃/h, and V2 is 120 ℃/h to 230 ℃/h.
10. The method for preparing the medium-carbon low-alloy high-strength steel as claimed in claim 7, wherein in the step S32, two-stage heating is adopted, the first stage heating is carried out from room temperature to 750 ℃ at a heating rate of 280 ℃/h-330 ℃/h, and the second stage heating is carried out from 750 ℃ to 850-900 ℃ at a heating rate of 120 ℃/h-230 ℃/h.
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