Production method of gas cylinder steel with ultrahigh toughness

Abstract

The invention discloses a production method of gas cylinder steel with ultrahigh toughness. The production method comprises the following steps: smelting pretreated molten iron by adopting an EBT electric furnace; reducing the weak carbide slag refined by an LF furnace, and adjusting the components of the molten steel according to the component requirements; vD (vacuum degassing) is adopted, and a silicon-calcium line is fed; performing die casting to obtain a steel ingot; uniformly heating the steel ingot and rolling into a steel billet with a specified size; the yield strength Rp0.2 of the high-toughness gas cylinder steel produced through the method is larger than or equal to 990MPa, the tensile strength Rm of the high-toughness gas cylinder steel is larger than or equal to 1130 MPa, the percentage elongation after fracture A of the high-toughness gas cylinder steel is larger than or equal to 14%, the low-temperature impact value Akv of the high-toughness gas cylinder steel at the temperature of-50 DEG C is larger than or equal to 60J / cm < 2 >, the use requirements of the 30MPa-grade ultrahigh-toughness gas cylinder steel are completely met, the material mechanical property index is improved, the surface quality is good, and the service life of the high-toughness gas cylinder steel is prolonged. And the technical blank of high-grade and high-performance gas cylinder steel in enterprise production is filled.

Description

Technical Field

[0001] The invention belongs to the technical field of gas cylinder steel, and in particular relates to a production method of ultra-high strength and toughness gas cylinder steel. Background Art

[0002] Ultra-high strength and toughness gas cylinders are used to fill compressed gases such as O2, N2, Ar, He, H2 and CNG. Their working pressure is 30MPa, and the wall thickness of ultra-high strength and toughness gas cylinders is smaller than that of ordinary gas cylinders, which can achieve lightweight ultra-high pressure gas cylinders, save costs, increase the gas loading capacity of a single gas cylinder, and provide favorable conditions for the use of gas. At the same time, the performance requirements of 30MPa ultra-high strength and toughness gas cylinder steel are relatively high, and the yield strength R p0.2 The requirement is not less than 990MPa, the tensile strength R m The requirements are not less than 1130MPa, the elongation after fracture A is not less than 14%, and the low-temperature lateral impact performance Akv at -50℃ is not less than 60J / cm 2 .

[0003] The working pressure of ordinary gas cylinders in the prior art is only 15-20MPa, and their tensile strength, elongation after fracture and low-temperature impact performance are low, the application range is small, the service life is short, and they cannot meet the requirements of ultra-high strength and toughness gas cylinder steel. Summary of the invention

[0004] In order to solve the technical problems existing in the above-mentioned prior art, the present invention provides a method for producing ultra-high strength and toughness gas cylinder steel, comprising the following steps:

[0005] (1) EBT electric furnace smelting

[0006] Add ≥50% pretreated molten iron into the EBT electric furnace, the mass percentage contents of P, S and C in the molten iron are controlled to be P: 0.04-0.07%, S: 0.04-0.08%, C: 3.7-4.2%, and the molten oxygen combined smelting process and foamed slag submerged arc operation are used for smelting. The mass percentage contents of P and C in the tapped steel are controlled to be P≤0.004%, C: 0.10-0.20%, and the tapping temperature is controlled at 1640-1685°C;

[0007] (2) LF refining

[0008] Before entering the LF furnace, 2.5±3m of aluminum wire is fed per ton of molten steel, the amount of refining slag lime added is controlled at 150±50Kg, the composition of LF slag is controlled by mass percentage as CaO: 53-57%, Al2O3: 27-32%, SiO2: 5-8%, MgO: 3-6%, and the LF tapping temperature is controlled at 1660-1680℃;

[0009] (3) VD vacuum degassing

[0010] The ladle is hoisted into the vacuum tank for VD vacuum degassing. The holding time under high vacuum is controlled to be 20±2min. After breaking the air, 1~1.5m of silicon calcium wire is fed into the tank per ton of molten steel. The feeding speed is controlled to be 120~150m / min. Then, hydrogen is determined online to control the hydrogen content to [H]≤1.5ppm. The VD tapping temperature is controlled to be 1573±5℃;

[0011] (4) Die Casting

[0012] Use argon seal protection pouring, cap mouth pouring height is controlled at 300-400mm, add 15Kg of carbon-free heating agent to each ingot when pouring to 2 / 3 of the cap mouth height, the ingot body pouring speed is controlled at 40-45Kg / s, and the pouring speed is gradually adjusted to 10-15Kg / s when pouring to the cap mouth position. After pouring, the ingot is naturally cooled in the mold, and the calming time after pouring is controlled to be ≥150min;

[0013] (5) Ingot uniform heating

[0014] After demoulding, the steel ingot is heated to 1270±20℃ in a heating furnace, and the holding time is controlled to be 4 to 6 hours;

[0015] (6) Rolling

[0016] The steel ingot is rolled into steel billet by a preliminary rolling mill, the preliminary rolling temperature is controlled at 1100±20℃, and the final rolling temperature is controlled at 900±20℃;

[0017] (7) Cooling

[0018] After the steel billet is rolled, it is naturally cooled to room temperature by slow cooling or pile cooling;

[0019] (8) Finishing

[0020] Use grinding wheel to clean the surface defects of steel billet.

[0021] Furthermore, in the production method of the above-mentioned ultra-high strength and toughness gas cylinder steel, in the LF refining step, sampling is performed for component analysis after reduction for 10 to 15 minutes, and ferrochromium, ferromolybdenum and ferrotitanium alloys are added to adjust the composition of the molten steel according to the analysis results and the chemical composition requirements of the finished product.

[0022] Furthermore, in the above-mentioned production method of ultra-high strength and toughness gas cylinder steel, in the VD vacuum degassing step, the bottom blowing argon flow rate is adjusted to 25-50L / mi after the VD feeding line, and the argon blowing sedation time is controlled to 16-18min.

[0023] Furthermore, in the above-mentioned production method of ultra-high strength and toughness gas cylinder steel, in the die casting step, after the ladle reaches the casting table, the temperature of the molten steel is controlled at 1560±5°C, and the temperature of the ingot mold is controlled at 50-100°C.

[0024] Furthermore, in the above-mentioned production method of ultra-high strength and toughness gas cylinder steel, in the rolling step, a 1000mm reversible initial rolling mill is used to roll the steel ingot into a square billet with a length of 9000±500mm, a width of 203±4mm, and a thickness of 203±4mm.

[0025] Furthermore, in the above-mentioned method for producing ultra-high strength and toughness gas cylinder steel, in the cooling step, the hydrogen content in the steel billet after cooling is controlled to [H]≤1.0ppm.

[0026] Furthermore, in the above-mentioned method for producing ultra-high strength and toughness gas cylinder steel, the yield strength R of the ultra-high strength and toughness gas cylinder steel is p0.2 ≥990MPa, tensile strength R m ≥1130MPa, elongation after fracture A≥14%, -50℃ low temperature impact value Akv≥60J / cm 2 .

[0027] The production method of the ultra-high strength and toughness gas cylinder steel of the present invention has the following advantages and beneficial effects: the present invention adopts the process of using EBT electric furnace to smelt pre-treatment of molten iron; adopts LF furnace to refine weak electric slag for reduction and adjusts the composition of molten steel according to the composition requirements; adopts VD vacuum degassing and feeds silicon calcium wire; mold casting into steel ingot; after the steel ingot is heated, it is rolled into a steel billet of specified size; after the steel billet is piled and cooled to room temperature, the steel billet is finely ground, and the yield strength R of the produced high strength and toughness gas cylinder steel is R p0.2 ≥990MPa, tensile strength R m ≥1130MPa, elongation after fracture A≥14%, -50℃ low temperature impact value Akv≥60J / cm 2 It fully meets the use requirements of 30MPa grade ultra-high strength and toughness gas cylinder steel, the material's mechanical properties are improved, and the surface quality is good, filling the technical gap in the production of high-grade and high-performance gas cylinder steel in enterprises. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0029] Aiming at the low tensile strength, elongation after fracture and low-temperature impact performance of existing common gas cylinder steel, the present invention successfully develops ultra-high strength and toughness gas cylinder steel by controlling the steelmaking, die casting and steel rolling processes. p0.2Reaching above 990MPa, the tensile strength R m Reaching above 1130MPa, -50℃ low temperature impact value Akv reaches 60J / cm 2 The above are fully suitable for the manufacture and use of ultra-high strength and toughness gas cylinders, meeting the ultra-high strength and toughness gas cylinder industry's high quality, long life, lightweight, ultra-high strength and toughness requirements, filling the technical gap in the production of high-grade and high-performance gas cylinder steel in enterprises.

[0030] Improving the strength and toughness of materials will make them more sensitive to surface defects, including cracks, inclusions, and surface processing defects. In order to reduce this sensitivity, improve the performance of materials, and improve safety and reliability in industrial applications, it is necessary to adopt high-purity smelting processes, reduce the content of harmful elements and gas inclusions, use special hot molds, control the appropriate pouring temperature and pouring speed, strictly control the surface cleaning of the steel billet, and strictly control the heating system, starting rolling temperature, and final rolling temperature of the steel rolling process. These measures will help improve the quality of steel, enhance its toughness and strength, and improve its application effect. To this end, based on the characteristics of ultra-high strength and toughness gas cylinder steel, the control of impurity elements in its steelmaking process and the rolling process are deeply analyzed and studied, and a production method for ultra-high strength and toughness gas cylinder steel is proposed, including the following steps:

[0031] (1) EBT electric furnace smelting

[0032] In the EBT electric furnace, pretreated molten iron with a proportion of ≥50% is added, and the mass percentage contents of P, S and C components in the molten iron are controlled to be P: 0.04-0.07%, S: 0.04-0.08%, C: 3.7-4.2%. The molten oxygen combined smelting process and foamed slag submerged arc operation are adopted for smelting to reduce air absorption of molten steel. The mass percentage contents of P and C components in the tapping molten steel are controlled to be P≤0.004%, C: 0.10-0.20%, and the tapping temperature is controlled at 1640-1685℃. When tapping, the electric furnace requires to retain steel and slag to ensure that the molten steel in the ladle does not carry oxidized slag.

[0033] (2) LF refining

[0034] Before entering the LF furnace, 2.5±3m of aluminum wire is fed per ton of molten steel; the amount of refining slag-making lime added is controlled at 150±50Kg, and the slag is adjusted in place as early as possible to ensure the slag retention time. The composition of LF slag is controlled in mass percentage as CaO: 53~57%, Al2O3: 27~32%, SiO2: 5~8%, MgO: 3~6%; after 10~15min of reduction, samples are taken for component analysis, and ferrochrome, ferromolybdenum, and ferrotitanium alloy are added according to the analysis results and the chemical composition requirements of the finished product to adjust the composition of the molten steel; the molten steel temperature reaches 1660~1680℃, and the LF refining process is completed.

[0035] (3) VD vacuum degassing

[0036] After the LF process, the ladle is hoisted into the vacuum tank for VD vacuum degassing, and the high vacuum is maintained for 20±2min. After breaking the air, 1~1.5m of silicon-calcium wire is fed into the tank for every ton of molten steel, and the wire feeding speed is controlled to 120~150m / min. Then the temperature is measured, sampling is performed, and hydrogen is determined online to control the hydrogen content to [H]≤1.5ppm; after VD wire feeding, the bottom blowing argon flow rate is adjusted, and the stirring flow rate is adjusted to 25~50L / min, based on the slight fluctuation of the slag surface, to prevent the argon flow rate from being too large to break the slag surface and expose the molten steel. The argon blowing calming time is controlled to 16~18min to promote the full floating of inclusions; the VD steelmaking temperature is controlled to 1573±5℃.

[0037] (4) Die Casting

[0038] The ladle is lifted to the casting station. After arriving at the casting table, the temperature of the molten steel is controlled at 1560±5℃, and the temperature of the ingot mold is controlled at 50-100℃. Argon sealing protection is used for pouring. The argon sealing ring is required to be tightly connected without leakage and the vent is unobstructed and stable. The cap mouth pouring height is controlled at 300-400mm. When pouring to 2 / 3 of the cap mouth height, 15Kg of carbon-free heat-generating agent is added to each ingot. The ingot body pouring speed is controlled at 40-45Kg / s, and the pouring speed is gradually adjusted to 10-15Kg / s when pouring to the cap mouth position. After pouring, the ingot is naturally cooled in the mold, and the calming time after pouring is controlled to be ≥150min.

[0039] (5) Ingot uniform heating

[0040] After the steel ingot is demoulded, the temperature is raised to 1270±20℃ in the heating furnace, and the holding time is controlled to be 4 to 6 hours. During the equalization process, overheating and overburning defects are prevented.

[0041] (6) Rolling

[0042] The rolling adopts a 1000mm reversible initial rolling mill, the initial rolling temperature is controlled at 1100±20℃, the final rolling temperature is controlled at 900±20℃, and the square steel billet with a length of 9000±500mm, a width of 203±4mm, and a thickness of 203±4mm is rolled to avoid problems such as steel billet de-squareness, twisting, and bending during the rolling process.

[0043] (7) Cooling

[0044] After the billet is rolled, it is cooled to room temperature naturally by slow cooling or stack cooling as soon as possible to avoid thermal stress. After cooling, the billet [H] is controlled to ≤1.0ppm.

[0045] (8) Finishing

[0046] Use grinding wheel to clean the surface defects of the steel billet to ensure that there are no crack defects on the surface of the steel billet.

[0047] The actual test proves that the surface quality and flaw detection of the finished steel billet are good. Samples are cut from the finished steel billet and subjected to quenching and tempering heat treatment. After being processed into tensile and impact samples, mechanical properties are tested. According to the test, the ultra-high-pressure yield strength of the gas cylinder steel prepared by the production method of the ultra-high-strength and toughness gas cylinder steel of the present invention reaches above 990MPa, the tensile strength reaches above 1130MPa, and the low-temperature impact value at -50°C reaches 60J / cm 2 above.

[0048] The production method of the ultra-high strength and toughness gas cylinder steel of the present invention is described in detail below in conjunction with specific embodiments.

[0049] Example 1

[0050] The specific implementation process of the production method of the ultra-high strength and toughness gas cylinder steel of Example 1 of the present invention is as follows:

[0051] (1) EBT electric furnace smelting

[0052] Into an EBT electric furnace with a nominal capacity of 80 tons, 68.68 tons of pretreated molten iron were added. The mass percentage contents of P, S and C components in the molten iron were P: 0.06%, S: 0.06%, C: 3.9%. The molten oxygen combined smelting process and foamed slag submerged arc operation were adopted. The mass percentage contents of P and C components in the tapped steel were P: 0.003%, C: 0.125%, and the tapping temperature was controlled at 1645°C.

[0053] (2) LF refining

[0054] Before entering the LF furnace, 3m of aluminum wire is fed per ton of molten steel; the amount of refining slag-making lime added is 200Kg, and the composition of LF slag is CaO: 55.3%, Al2O3: 28.3%, SiO2: 6.9%, MgO: 4.8%; sampling is carried out for component analysis after 10 minutes of reduction, and ferrochrome, ferromolybdenum and ferrotitanium alloy are added according to the analysis results and the chemical composition requirements of the finished gas cylinder steel to adjust the composition of the molten steel. The composition of the LF molten steel is C: 0.33%, Si: 0.29%, Mn: 0.74%, P: 0.006%, S: 0.001%, Cr: 1.03%, Mo: 0.27%, A1: 0.066%, Nb: 0.016%, Ti: 0.01%, Ni: 0.19%, Cu: 0.01%, and the remainder is Fe and unavoidable impurities; the LF tapping temperature is 1677℃.

[0055] (3) VD vacuum degassing

[0056] The ladle is hoisted into the vacuum tank for vacuum degassing and maintained at high vacuum for 20 minutes. After breaking the air, 1.5m of silicon calcium wire is fed into the steel liquid per ton, and the wire feeding speed is 120m / min. Then the temperature is measured and sampled, and hydrogen is determined online, and [H] is 0.59ppm; after VD wire feeding, the bottom blowing argon flow rate is adjusted, and the stirring flow rate is adjusted to 35L / min, based on the slight fluctuation of the slag surface, to prevent the argon flow from being too large to blow the slag surface and expose the molten steel. The argon blowing calming time 17min; the composition of VD molten steel is C: 0.33%, Si: 0.29%, Mn: 0.71%, P: 0.006%, S: 0.001%, Cr: 1.01%, Mo: 0.27%, A1: 0.031%, Nb: 0.016%, Ti: 0.02%, Ni: 0.19%, Cu: 0.01%, and the balance is Fe and unavoidable impurities; the VD tapping temperature is 1578℃.

[0057] (4) Die Casting

[0058] The ladle is lifted to the casting station. After arriving at the casting table, the temperature of the molten steel is 1564℃, the temperature of the ingot mold is 53℃, and argon sealing is used for pouring. When pouring to 2 / 3 of the cap height, 15Kg of carbon-free heating agent is added to each ingot. The pouring speed of the ingot body is maintained at 43Kg / s, and the pouring speed is adjusted to 14Kg / s when pouring to the cap position. After pouring, the ingot is naturally cooled in the mold, and the calming time after pouring is 270min. The size of the ingot is: length 2010mm, head 806mm×806mm, tail 673mm×673mm.

[0059] (5) Ingot uniform heating

[0060] After the steel ingot is demoulded, the temperature is raised to 1290°C in a heating furnace and the holding time is 6 hours.

[0061] (6) Rolling

[0062] The rolling adopts a 1000mm reversible initial rolling mill, the initial rolling temperature is 1100℃, the final rolling temperature is 900℃, and the rolled steel billet is 9000mm long, 203mm wide and 203mm thick.

[0063] (7) Cooling

[0064] After the billet is rolled, it is naturally cooled to room temperature by pile cooling. After cooling, the billet [H] is 0.59ppm.

[0065] (8) Finishing

[0066] Use grinding wheel to clean the surface defects of the steel billet to ensure that there are no crack defects on the surface of the steel billet.

[0067] (9) Mechanical properties test

[0068] Samples are cut from the finished steel billet and subjected to quenching and tempering heat treatment, and then processed into tensile and impact specimens for mechanical property testing. After actual testing, the mechanical properties of the high-strength and toughness gas cylinder steel produced by Example 1 of the present invention are as follows: yield strength R p0.2 The tensile strength is 1072MPa, m The tensile strength is 1144MPa, the elongation after fracture A is 14%, and the low-temperature lateral impact value Akv at -50℃ reaches 66.2J / cm 2 .

[0069] In summary, the present invention aims at the problems of low tensile strength, elongation after fracture and low-temperature impact performance of existing common gas cylinder steel. The invention adopts EBT electric furnace to smelt and pretreat molten iron; adopts LF furnace to refine weak electric slag for reduction and adjusts the composition of molten steel according to the composition requirements; adopts VD vacuum degassing and feeds silicon calcium wire; mold casting into steel ingot; after the steel ingot is heated, it is rolled into a steel billet of specified size; after the steel billet is piled and cooled to room temperature, the steel billet is finely ground to produce a high-strength and toughness gas cylinder steel with a yield strength R p0.2 ≥990MPa, tensile strength R m ≥1130MPa, elongation after fracture A≥14%, -50℃ low temperature impact value Akv≥60J / cm 2 It fully meets the use requirements of 30MPa grade ultra-high strength and toughness gas cylinder steel, the material's mechanical properties are improved, and the surface quality is good, filling the technical gap in the production of high-grade and high-performance gas cylinder steel in enterprises.

[0070] It should be noted that, in this article, the term "comprise" or any other variation thereof is intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such article or device.

[0071] It should also be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A method for producing ultra-high strength and toughness gas cylinder steel, characterized in that: The following steps are involved: (1) EBT electric furnace smelting Add ≥50% pretreated molten iron into the EBT electric furnace, the mass percentage contents of P, S and C in the molten iron are controlled to be P: 0.04-0.07%, S: 0.04-0.08%, C: 3.7-4.2%, and the molten oxygen combined smelting process and foamed slag submerged arc operation are used for smelting. The mass percentage contents of P and C in the tapped steel are controlled to be P≤0.004%, C: 0.10-0.20%, and the tapping temperature is controlled at 1640-1685°C; (2) LF refining Before entering the LF furnace, 2.5±3m of aluminum wire is fed per ton of molten steel, the amount of refining slag lime added is controlled at 150±50Kg, the composition of LF slag is controlled by mass percentage as CaO: 53-57%, Al2O3: 27-32%, SiO2: 5-8%, MgO: 3-6%, and the LF tapping temperature is controlled at 1660-1680℃; (3) VD vacuum degassing The ladle is hoisted into the vacuum tank for VD vacuum degassing. The holding time under high vacuum is controlled to be 20±2min. After breaking the air, 1~1.5m of silicon calcium wire is fed into the tank per ton of molten steel. The feeding speed is controlled to be 120~150m / min. Then, hydrogen is determined online to control the hydrogen content to [H]≤1.5ppm. The VD tapping temperature is controlled to be 1573±5℃; (4) Die Casting Use argon seal protection pouring, cap mouth pouring height is controlled at 300-400mm, add 15Kg of carbon-free heating agent to each ingot when pouring to 2 / 3 of the cap mouth height, the ingot body pouring speed is controlled at 40-45Kg / s, and the pouring speed is gradually adjusted to 10-15Kg / s when pouring to the cap mouth position. After pouring, the ingot is naturally cooled in the mold, and the calming time after pouring is controlled to be ≥150min; (5) Ingot uniform heating After demoulding, the steel ingot is heated to 1270±20℃ in a heating furnace, and the holding time is controlled to be 4 to 6 hours; (6) Rolling The steel ingot is rolled into steel billet by a preliminary rolling mill, the preliminary rolling temperature is controlled at 1100±20℃, and the final rolling temperature is controlled at 900±20℃; (7) Cooling After the steel billet is rolled, it is naturally cooled to room temperature by slow cooling or pile cooling; (8) Finishing Use grinding wheel to clean the surface defects of steel billet.

2. The method for producing ultra-high strength and toughness gas cylinder steel according to claim 1, characterized in that: In the LF refining step, samples are taken for component analysis after reduction for 10 to 15 minutes, and ferrochrome, ferromolybdenum and ferrotitanium alloys are added to adjust the composition of the molten steel according to the analysis results and the chemical composition requirements of the finished product.

3. The method for producing ultra-high strength and toughness gas cylinder steel according to claim 1, characterized in that: In the VD vacuum degassing step, the bottom blowing argon flow rate is adjusted to 25-50 L / mi after the VD line is fed, and the argon blowing sedation time is controlled to 16-18 min.

4. The method for producing ultra-high strength and toughness gas cylinder steel according to claim 1, characterized in that: In the mold casting step, after the ladle reaches the casting table, the temperature of the molten steel is controlled at 1560±5℃, and the temperature of the ingot mold is controlled at 50-100℃.

5. The method for producing ultra-high strength and toughness gas cylinder steel according to claim 1, characterized in that: In the rolling step, a 1000 mm reversible primary rolling mill is used to roll the steel ingot into a square billet with a length of 9000 ± 500 mm, a width of 203 ± 4 mm, and a thickness of 203 ± 4 mm.

6. The method for producing ultra-high strength and toughness gas cylinder steel according to claim 1, characterized in that: In the cooling step, the hydrogen content in the cooled steel slab is controlled to [H]≤1.0 ppm.

7. The method for producing ultra-high strength and toughness gas cylinder steel according to any one of claims 1 to 6, characterized in that: The yield strength R of the ultra-high strength and toughness gas cylinder steel p0.2 ≥990MPa, tensile strength R m ≥1130MPa, elongation after fracture A≥14%, -50℃ low temperature impact value Akv≥60J / cm 2 .