CN117904541A - Ageing-strengthening low-temperature container steel with yield strength not less than 345Mpa and production method - Google Patents
Ageing-strengthening low-temperature container steel with yield strength not less than 345Mpa and production method Download PDFInfo
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Abstract
An ageing-strengthening low-temperature container steel with yield strength not less than 345Mpa comprises the following components in percentage by weight: c:0.04 to 0.09 percent, si:0.11 to 0.22 percent, mn:0.6 to 1.20 percent, P is less than or equal to 0.005 percent, S is less than or equal to 0.003 percent, alt:0.03 to 0.025 percent, cu: 0.09-0.20%; the production method comprises the following steps: desulfurizing molten iron; smelting in a converter; continuous casting after vacuum treatment; heating a casting blank; cooling and rough rolling; finish rolling to the thickness of the product; cooling and coiling; cutting into sections; solution treatment; cooling; and (5) aging treatment. The invention ensures that the yield strength of the steel plate is more than 345MPa, the tensile strength is 430-640 MPa, the elongation is more than 21%, and the impact toughness of the steel plate can reach more than 60J at the temperature of minus 20 ℃.
Description
Technical Field
The invention relates to steel for a container and a production method thereof, in particular to ageing-strengthening low-temperature container steel with yield strength of more than or equal to 345Mpa and a production method thereof.
Background
At present, low alloy ultrahigh strength steel container steel applied to the fields of storage tanks, gas cylinders, LNG receiving station structural members and the like is mainly steel grade Q345R, 16MnDR, HP345 and the like with 345 Mpa-level yield strength. The series of steel mainly takes carbon, silicon and manganese as main materials, and combines a small amount of niobium, vanadium and titanium strength alloy elements; the normalizing or normalizing and tempering heat treatment process is adopted in the process, because the martensitic structure, the bainitic structure or the acicular ferrite structure can be obtained through different heat treatment processes, so that the proper toughness is obtained, and the required performance application requirements are met.
In the prior art, the technical field has the defects of high economic cost, resource saving, production cost reduction and environmental friendliness due to the addition of more alloy elements. The alloy components are simpler, but the mechanical properties of the alloy cannot meet the development requirement, and the requirements of simplifying chemical elements and reducing the production cost on the premise of meeting the market requirement on the mechanical properties of the alloy are not met, such as the requirement of preliminary search:
And (5) carrying out preliminary retrieval:
The document with the Chinese patent application number of CN202210257135.0 discloses an anti-aging micro carbon steel deep drawing strip steel and a production method thereof, and the strip steel is prepared from the following raw materials in percentage by mass: 0.010-0.025 percent of C, less than or equal to 0.05 percent of Si, 0.10-0.25 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.015 percent of S, and less than or equal to Al:0.020-0.060%, N is less than or equal to 0.0040%, and the balance is iron and unavoidable impurities. Although the literature has the characteristics of low production cost, good surface quality, good product performance, good aging resistance, good stamping forming and simple process, solid solution carbon is precipitated in crystal and grain boundary when a micro carbon steel component system is adopted for continuous annealing cooling, so that less solid solution carbon is caused, when the carbon content is low, solid solution carbon is only precipitated in the grain boundary in the cooling process, the content of non-precipitated solid solution carbon is far more than that of carbide precipitated in the grain boundary, the final solid solution carbon content of the material is high, the solid solution carbon is precipitated in the aging process, the yield strength is only 140-190 MPa, the tensile strength is only 310-360 MPa, and the literature has lower yield strength grade and cannot meet the requirements of good strength and toughness of steel for a low-temperature pressure container.
The document of Chinese patent application No. CN202310700416.3 discloses an S355-grade large-strain aging wind power steel and a manufacturing method thereof, wherein the steel comprises the following chemical components ：C：0.045～0.065％,Si:0.05～0.15％,Mn：1.48～1.58％,P≤0.01％、S≤0.0015％,Cu:0.15～0.25％,Ni：0.20～0.30％,Nb：0.016～0.024％,Ti：0.009～0.016％,Ca:0.001～0.003％,Al：0.025～0.050％, in percentage by mass, and the balance of Fe and unavoidable impurities, and satisfies the following relation: V+Nb+Ti is less than or equal to 0.15%; the method comprises the steps of smelting, casting, heating, rough rolling, finish rolling, cooling and the like of designed chemical components, so that the large-strain aging wind power steel with the thickness of 35-45 mm can be manufactured, and the microstructure of the wind power steel mainly comprises refined ferrite and bainite, has the mechanical property characteristics of high strength and high toughness, and has the low-temperature impact toughness of more than 100J at the temperature of minus 40 ℃ after 7% pre-strain and aging treatment for 1 hour at the temperature of 250 ℃. The steel of the literature has multiple types of chemical elements, the steel grade is characterized by strain aging, and the steel grade has good low-temperature toughness effect.
The invention discloses a heat treatment method of a high-strength and high-toughness light wear-resistant high-manganese steel casting, which relates to a heat treatment method of a high-strength and high-toughness light wear-resistant high-manganese steel casting, and comprises the following steps of: pretreatment: coating an anti-oxidation protective coating on the surface of the high manganese steel casting; and (3) water toughening treatment: heating the high manganese steel casting at a preset speed to reach a water toughness temperature, preserving heat and then quenching; and (3) deep cooling treatment: cooling the high manganese steel casting after water toughening to the cryogenic treatment temperature, and preserving heat; aging treatment: heating the high manganese steel casting subjected to the cryogenic treatment to an aging temperature for heat preservation, then air-cooling to room temperature, wherein the interval between the cryogenic treatment and the aging treatment is not more than 1h; shot blasting: and (5) performing shot blasting on the surface of the high manganese steel casting subjected to ageing treatment. The invention utilizes the combination of water toughness, deep cooling and aging treatment to obtain a single austenite structure, obtains the effective dispersed nano-scale carbide structure, and effectively improves the grain refinement and solid solution strengthening effects of the high-strength and high-toughness light-weight high-manganese steel. The patent of the document mainly realizes the improvement of the strength of the single-phase austenitic high manganese steel by combining different heat treatment means. The effect of the heat treatment process is fully exerted. The invention adopts the component design concept of low carbon, low manganese and a small amount of austenite forming element Cu, and combines the solid solution and aging heat treatment processes to realize the improvement of the strength and toughness of the steel grade.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides the ageing-strengthening low-temperature container steel which ensures that the yield strength of a steel plate is more than 345MPa, the tensile strength is 430-640 MPa, the elongation is more than 21 percent, and the impact toughness of the steel plate reaches more than 60J at the temperature of minus 20 ℃ and the yield strength is more than or equal to 345MPa, and the production method.
Measures for achieving the above object:
An ageing-strengthening low-temperature container steel with yield strength not less than 345Mpa comprises the following components in percentage by weight: c:0.04 to 0.09 percent, si:0.11 to 0.22 percent, mn:0.6 to 1.20 percent, P is less than or equal to 0.005 percent, S is less than or equal to 0.003 percent, alt:0.03 to 0.025 percent, cu: 0.09-0.20%, and the balance of iron and unavoidable impurities.
Preferably: the weight percentage content of Cu is 0.12-0.20%.
A method for producing ageing-strengthening low-temperature container steel with yield strength not less than 345Mpa comprises the following steps:
1) Desulfurizing molten iron, and desulfurizing target: s is less than or equal to 0.005 percent, and the temperature of molten iron before entering a converter is controlled to be not lower than 1250 ℃;
2) Smelting in a converter, and controlling the tapping temperature to be not lower than 1680 ℃; during the tapping process, the method is to carry out tapping pre-refining after adding lime with granularity not more than 30mm and fluorite with granularity not more than 50mm according to the set values, and then pre-deoxidizing by adopting the amount of aluminum added at one time, wherein the addition amount of the aluminum reaches the deoxidizing set value;
Adding ferromanganese to carry out secondary deoxidation when tapping is carried out to 1/3; adding until tapping reaches 2/3; the tapping time is controlled to be 2.5-6 min;
3) Continuous casting is carried out after vacuum treatment, and the period is as follows: controlling the vacuum degree not lower than 15Pa; the straightening temperature of the casting blank is not lower than 950 ℃;
4) Heating the casting blank, and controlling the temperature of the casting blank entering a furnace to be not lower than 400 ℃; the tapping temperature is 1200-1240 ℃, and the heating rate is 9-15 min/cm;
5) After cooling, rough rolling is carried out, the initial rolling temperature of the rough rolling is controlled to be 1060-1180 ℃, the reduction rate of the first pass of the rough rolling is not lower than 15%, and the thickness of the outlet of the steel plate after the rough rolling is 3.5-10.5 times of the thickness of the finished product;
6) Finish rolling to the thickness of the product, controlling the finish rolling temperature at 850-880 ℃, and controlling the accumulated rolling reduction to be not lower than 70% and the final pass rolling reduction to be not lower than 40%;
7) Coiling after cooling, and controlling the coiling temperature to be 560-600 ℃;
8) Cutting, naturally cooling to room temperature, straightening, uncoiling according to the requirement,
9) Performing solid solution treatment, controlling the solid solution temperature to be between 830 and 870 ℃, and controlling the solid solution heat preservation time to be (plate thickness +30) min
Proceeding;
Wherein: the thickness unit of the steel plate is mm;
10 Cooling to room temperature at a cooling rate of 50-80 ℃/s;
11 Carrying out aging treatment, adopting a heat preservation pit to preserve heat, wherein the heat preservation temperature is 80-100 ℃, and the heat preservation time is 8-24 hours; and then air-cooling to room temperature.
Preferably: the solid solution temperature is 836-863 ℃.
Preferably: the heat preservation temperature of the aging treatment is 87-95 ℃ and the heat preservation time is 9-16 hours.
The action and mechanism of each raw material and main process in the invention
The setting range of C is not more than 0.09%, preferably 0.05 to 0.09%. The carbon element is one of the indispensable elements in the steel material, and its content in the steel largely determines the properties of the material. In the solid solution stage, part of carbon element in the steel can be fused into a matrix of the steel to play a role of solid solution strengthening; some of the carbon may form carbides with other alloying elements in the steel. During aging, the matrix of martensite can disperse out carbides, and the increase of carbide content can cause secondary hardening of the material. When the carbon content exceeds a certain range, the aging effect is rather reduced.
Si is set in a range of 0.22% or less, preferably 0.12 to 0.22%. Not the alloying elements which are intentionally added, but are carried in from scrap steel and pig iron raw materials during smelting. The silicon content in the steel is increased, so that the strength can be improved, si element can be dissolved in epsilon carbide in a solid manner, the conversion of epsilon carbide into theta carbide is delayed, the formation of carbide is promoted, and the stability is improved. Meanwhile, the plasticity and toughness are reduced, so that the content of silicon element in the steel is controlled as much as possible.
Mn is set in a range of not more than 1.20%, preferably 0.60 to 1.20%. The solid solution strengthening effect can improve the hardness and strength of the steel with little influence on the ductility of the steel. Mn is also an austenite forming element, and after a large amount of Mn is added, a residual austenite structure can be obtained, so that the quenching temperature and hardness of the steel are reduced, and the quenching deformation is reduced. However, the higher the manganese content, the more severe the steel is susceptible to overheating and temper embrittlement.
Cu: the setting range is not more than 0.20%, preferably 0.12 to 0.20%. According to the invention, on the premise of not affecting the service performance of the steel plate, the original strength alloy elements are removed by optimizing and simplifying the original chemical components, and a small amount of Cu is added to make up for the performance deficiency caused by component reduction. The Cu element is one of the austenite forming elements in the invention, and researches show that after the Cu element is added, the content of the rotary austenite in the steel is greatly increased compared with that in the copper-free steel, and the content of the rotary austenite in the steel is also increased along with the increase of the content of the Cu element, but when the content of the Cu element is higher, the stability of the rotary austenite in the steel is reduced, the yield strength and the tensile strength of the steel are slightly increased after the Cu element is added by adopting solution treatment and aging treatment, and the low-temperature impact toughness is obviously improved.
Alt: the setting range is less than or equal to 0.025 percent, preferably 0.015 to 0.025 percent. The common deoxidizer in steel fixes free nitrogen in the steel, has the maximum solubility of about 0.6% in austenite, only weakly increases hardenability after being dissolved into austenite, can improve the grain coarsening temperature of the steel, reduces the brittle transition temperature of the steel, prevents strain and temperature aging, and improves the impact toughness of the steel.
P, S and other impurity elements: p, S is a harmful impurity element in steel, and although P can greatly improve the strength, segregation is easy to form in the steel, the toughness and the welding performance of the steel are reduced, S is easy to form plastic sulfide, the anisotropy of the steel is serious, and the impact toughness and the processing performance of the steel are deteriorated. Therefore, the contents of P, S and other impurity elements in the steel should be strictly controlled.
In the tapping process, the invention is controlled to perform tapping pre-refining after lime with granularity not more than 30mm and fluorite with granularity not more than 50mm are added according to the preset conditions, and then the primary aluminum adding quantity is adopted for pre-deoxidization, wherein the adding quantity reaches the deoxidization set value; adding ferromanganese to carry out secondary deoxidation when tapping is carried out to 1/3; adding until tapping reaches 2/3; the tapping time is controlled to be 2.5-6 min, and the lime and fluorite with smaller granularity can shorten the heat preservation time, improve the fluidity of slag, and ensure the stability of the absorption rate of the alloy due to the proper tapping time control, so that the added alloy can be fully melted and distributed more uniformly.
The invention controls the temperature of casting blank entering into the furnace to be not lower than 400 ℃; the tapping temperature is 1200-1240 ℃, and the heating rate is 9-15 min/cm, so that the self heat of the casting blank is utilized, the hot charging and hot feeding are adopted, the self heat of the continuous casting blank is effectively utilized, the energy consumption of a heating furnace is reduced, the casting blank is insulated and soaked in the heating furnace, the heat insulation time and the tapping temperature are ensured, and the head-tail temperature difference of the casting blank is reduced.
The invention controls the initial rolling temperature of rough rolling at 1060-1180 ℃, the first pass rolling reduction rate of rough rolling is not lower than 15%, and the thickness of the outlet of the steel plate after rough rolling is 3.5-10.5 times of the thickness of the finished product.
The final rolling temperature is controlled at 850-880 ℃, the accumulated rolling reduction is not lower than 70%, and the final pass rolling reduction is not lower than 40%, so that the proper final rolling temperature and pass rolling reduction can fully refine the austenite grain size and plate type precision, and the target size and good comprehensive performance are obtained.
The solid solution temperature is controlled between 830 and 870 ℃, and the solid solution heat preservation time is carried out according to (plate thickness +30) min, because the proper solid solution temperature can lead the rolled ferrite and pearlite structure to reach the austenite solid solution phase region again, and the heat preservation is carried out for proper time, so that the precipitated phase in the original structure is dissolved into the solid solution, thus preparing for the subsequent aging treatment. Solution treatment processes are currently commonly used for alloys or stainless steel. The low-carbon alloy steel is generally subjected to heat treatment such as normalizing. The solution treatment principle is to heat the steel or alloy with solid solubility increased with temperature to a proper temperature in the single solid solution phase zone and keep the temperature for a proper time to dissolve the precipitated phase in the original structure into solid solution. By the solution treatment, the obtained tissue is a supersaturated solid solution. Because the supersaturated solid solution is in an unstable state, the aim of tissue homogenization is fulfilled by combining the subsequent aging treatment.
The invention adopts a heat preservation pit for heat preservation, the heat preservation temperature is 80-100 ℃, and the heat preservation time is 8-24 hours, because the tissue is in an unbalanced state after solution treatment, and the solute element tends to be spontaneously separated out. Under a certain temperature condition, a metastable phase epsilon carbide and a copper-containing phase are separated out from the heterogeneous solid solution, the separated metastable phase and a mother phase solid solution keep a coherent relation, and meanwhile, the dislocation movement is blocked, so that the purpose of precipitation strengthening is realized.
Compared with the prior art, the invention ensures that the yield strength of the steel plate is more than 345MPa, the tensile strength is 430-640 MPa, the elongation is more than 21 percent, and the impact toughness of the steel plate can reach more than 60J at the temperature of minus 20 ℃.
Drawings
FIG. 1 is a metallographic structure diagram of the present invention.
Detailed Description
The present invention will be described in detail below:
table 1 is a listing of chemical components of each example and comparative example of the present invention;
table 2 is a list of the main process parameters for each example and comparative example of the present invention;
Table 3 shows a list of performance tests for each example and comparative example of the present invention.
The embodiments of the invention were produced according to the following steps
1) Desulfurizing molten iron, and desulfurizing target: s is less than or equal to 0.005 percent, and the temperature of molten iron before entering a converter is controlled to be not lower than 1250 ℃;
2) Smelting in a converter, and controlling the tapping temperature to be not lower than 1680 ℃; during the tapping process, the method is to carry out tapping pre-refining after adding lime with granularity not more than 30mm and fluorite with granularity not more than 50mm according to the set values, and then pre-deoxidizing by adopting the amount of aluminum added at one time, wherein the addition amount of the aluminum reaches the deoxidizing set value;
Adding ferromanganese to carry out secondary deoxidation when tapping is carried out to 1/3; adding until tapping reaches 2/3; the tapping time is controlled to be 2.5-6 min;
3) Continuous casting is carried out after vacuum treatment, and the period is as follows: controlling the vacuum degree not lower than 15Pa; the straightening temperature of the casting blank is not lower than 950 ℃;
4) Heating the casting blank, and controlling the temperature of the casting blank entering a furnace to be not lower than 400 ℃; the tapping temperature is 1200-1240 ℃, and the heating rate is 9-15 min/cm;
5) After cooling, rough rolling is carried out, the initial rolling temperature of the rough rolling is controlled to be 1060-1180 ℃, the reduction rate of the first pass of the rough rolling is not lower than 15%, and the thickness of the outlet of the steel plate after the rough rolling is 3.5-10.5 times of the thickness of the finished product;
6) Finish rolling to the thickness of the product, controlling the finish rolling temperature at 850-880 ℃, and controlling the accumulated rolling reduction to be not lower than 70% and the final pass rolling reduction to be not lower than 40%;
7) Coiling after cooling, and controlling the coiling temperature to be 560-600 ℃;
8) Cutting, naturally cooling to room temperature, straightening, uncoiling according to the requirement,
9) Performing solid solution treatment, controlling the solid solution temperature to be between 830 and 870 ℃, and controlling the solid solution heat preservation time to be (plate thickness +30) min
Proceeding;
Wherein: the thickness unit of the steel plate is mm;
10 Cooling to room temperature at a cooling rate of 50-80 ℃/s;
11 Carrying out aging treatment, adopting a heat preservation pit to preserve heat, wherein the heat preservation temperature is 80-100 ℃, and the heat preservation time is 8-24 hours;
And then air-cooling to room temperature.
TABLE 1 list of chemical Components (wt%) of examples and comparative examples of the present invention
TABLE 2 list of the main process parameters for each example and comparative example of the present invention
Continuous table 2
TABLE 3 mechanical property test results list for each example and comparative example of the present invention
Note that: (1) tensile Property test: transverse samples were taken at 1/4 of the thickness of the steel sheet at room temperature according to GB/T228.1 Metal materials tensile test section 1: the room temperature test method is used for measuring the yield strength ReL, the tensile strength Rm and the elongation A of the steel plate;
(2) Low temperature impact toughness test: and taking a transverse sample at the position of 1/4 of the thickness of the steel plate at the temperature of-20 ℃ under the condition of the ambient temperature, and carrying out a detection test according to GB/T229 Charpy pendulum impact test method for metal materials to obtain the KV 2 impact average value of the standard sample at the temperature of-20 ℃.
As can be seen from Table 3, the yield strength and the tensile strength of the low-carbon steel are higher than those of the common low-carbon alloy steel at room temperature through solution treatment and aging treatment, and meanwhile, the low-carbon steel still has a higher impact power value at-20 ℃, which shows that the low-carbon steel has good toughness matching and completely meets the use requirement of structural members. The steel provided by the invention adopts a chemical composition design of low carbon, low manganese and a small amount of copper element (about 61000 yuan/ton in the current market), and compared with the conventional method of adding higher carbon, manganese content and niobium (about 208000 yuan/ton in the current market), vanadium (about 86000 yuan/ton in the current market) and titanium (about 23000 yuan/ton in the current market) alloy elements, the production cost can be effectively reduced.
This embodiment is merely a best example and is not intended to limit the implementation of the technical solution of the present invention.
Claims (5)
1. An ageing-strengthening low-temperature container steel with yield strength not less than 345Mpa comprises the following components in percentage by weight: c:
0.04 to 0.09 percent, si:0.11 to 0.22 percent, mn:0.6 to 1.20 percent, P is less than or equal to 0.005 percent, S is less than or equal to 0.003 percent, alt:0.03 to 0.025 percent, cu: 0.09-0.20%, and the balance of iron and unavoidable impurities.
2. The age-strengthened low temperature container steel with yield strength not less than 345Mpa as claimed in claim 1, wherein: the weight percentage content of Cu is 0.12-0.20%.
3. A method for producing an age-strengthened low temperature container steel having a yield strength of greater than or equal to 345Mpa as claimed in claim 1, comprising the steps of:
1) Desulfurizing molten iron, and desulfurizing target: s is less than or equal to 0.005 percent, and the temperature of molten iron before entering a converter is controlled to be not lower than 1250 ℃;
2) Smelting in a converter, and controlling the tapping temperature to be not lower than 1680 ℃; during the tapping process, the method is to carry out tapping pre-refining after adding lime with granularity not more than 30mm and fluorite with granularity not more than 50mm according to the set values, and then pre-deoxidizing by adopting the amount of aluminum added at one time, wherein the addition amount of the aluminum reaches the deoxidizing set value;
Adding ferromanganese to carry out secondary deoxidation when tapping is carried out to 1/3; adding until tapping reaches 2/3; the tapping time is controlled to be 2.5-6 min;
3) Continuous casting is carried out after vacuum treatment, and the period is as follows: controlling the vacuum degree not lower than 15Pa; the straightening temperature of the casting blank is not lower than 950 ℃;
4) Heating the casting blank, and controlling the temperature of the casting blank entering a furnace to be not lower than 400 ℃; the tapping temperature is 1200-1240 ℃,
The heating rate is 9-15 min/cm;
5) After cooling, rough rolling is carried out, the initial rolling temperature of the rough rolling is controlled to be 1060-1180 ℃, the reduction rate of the first pass of the rough rolling is not lower than 15%, and the thickness of the outlet of the steel plate after the rough rolling is 3.5-10.5 times of the thickness of the finished product;
6) Finish rolling to the thickness of the product, controlling the finish rolling temperature at 850-880 ℃, and controlling the accumulated rolling reduction to be not lower than 70% and the final pass rolling reduction to be not lower than 40%;
7) Coiling after cooling, and controlling the coiling temperature to be 560-600 ℃;
8) Cutting, naturally cooling to room temperature, straightening, uncoiling according to the requirement,
9) Performing solid solution treatment, controlling the solid solution temperature to be between 830 and 870 ℃, and controlling the solid solution heat preservation time to be (plate thickness +30) min
Proceeding;
Wherein: the thickness unit of the steel plate is mm;
10 Cooling to room temperature at a cooling rate of 50-80 ℃/s;
11 Carrying out aging treatment, adopting a heat preservation pit to preserve heat, wherein the heat preservation temperature is 80-100 ℃, and the heat preservation time is 8-24 hours; and then air-cooling to room temperature.
4. The method for producing an age-strengthened low-temperature container steel with yield strength not less than 345Mpa according to claim 3, wherein: the solid solution temperature is 836-863 ℃.
5. The method for producing an age-strengthened low-temperature container steel with yield strength not less than 345Mpa according to claim 3, wherein: the heat preservation temperature of the aging treatment is 87-95 ℃ and the heat preservation time is 9-16 hours.
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