Low-cost, low-yield-ratio and high-toughness steel for welding bottle and production method of low-cost, low-yield-ratio and high-toughness steel

Abstract

The invention provides a production method of low-cost, low-yield-ratio and high-toughness steel for a welding bottle, which comprises the following steps: carrying out steelmaking according to chemical components and contents of the steel for the welding bottle, and then respectively carrying out molten iron desulfurization, converter blowing, continuous casting, hot direct charging, soaking, rough rolling, finish rolling, laminar cooling and coiling processes, and alloy is added in the deslagging process of converter blowing for microalloying. According to the invention, carbon, silicon and manganese are properly proportioned, crack sensitivity influence of peritectic reaction points is avoided, quality design of medium carbon, low manganese, properly proportioned silicon and other low-price alloys, narrow composition control, controlled rolling, controlled cooling and other means is adopted, the cost is reduced by more than 20%, and the product is good in stamping forming and welding performance, high in yield and high in product quality. According to performance detection of a welding area of a finished product formed through stamping, the tensile strength reaches 460-520 MPa, the ductility reaches 28% or above, the yield ratio is smaller than 0.77, and the yield ratio is larger than 50 J through low-temperature impact test detection at the temperature of-20 DEG C.

Description

Technical Field

[0001] The invention relates to the technical field of production of steel for pressure vessel welding, and in particular to low-cost, low-yield ratio, high-toughness steel for pressure vessel welding and a production method thereof. Background Art

[0002] Steel materials for welding bottles are mainly used for the production and manufacturing of steel products for mobile pressure vessels that can be repeatedly filled with liquefied petroleum gas or dissolved gas. The domestically produced steel products for welding bottles mainly include HP235, HP265, HP295, HP325, HP345, etc. Among them, the national standard mechanical properties of HP295 require yield strength ≥295MPa, tensile strength of 440-560MPa, elongation ≥26%, yield strength ratio ≤0.8, -20° low temperature impact ≥23J. Most of the existing technologies can produce HP295 steel that meets the above national standards, but due to differences in components and content and inaccurate process control, the steel materials for pressure vessel welding bottles have shortcomings such as poor stamping formability, high yield strength ratio within the national standard range, high cost, poor welding performance, and low low temperature stamping performance. Summary of the invention

[0003] The problem to be solved by the present invention is that the steel material for pressure vessel welding bottle has shortcomings such as poor stamping formability, high yield strength ratio within the national standard range, high cost, poor welding performance, and low low-temperature stamping performance.

[0004] In order to solve at least one aspect of the above problems, the present invention provides a method for producing low-cost, low-yield ratio, high-toughness steel for welding bottles, comprising: steelmaking according to the chemical composition and content of the steel for welding bottles, and then respectively carrying out molten iron desulfurization, converter blowing, continuous casting, hot direct charging furnace, soaking, rough rolling, finishing rolling, laminar cooling and coiling processes, and adding alloys for micro-alloying during the slag discharge process of the converter blowing;

[0005] The chemical composition of the steel for welding bottles is as follows by weight percentage: C: 0.14-0.17%, Si: 0.05-0.10%, Mn: 0.82-92%, P: ≤0.015%, S: <0.005%, Als: 0.02-0.04%, and the rest is iron and unavoidable impurities.

[0006] Preferably, the converter blowing adopts a bottom blowing converter, and the bottom blowing gas includes nitrogen and argon. During the bottom blowing process, the nitrogen and the argon are switched for use.

[0007] Preferably, after the converter blowing is completed, the slag is blocked and the steel is tapped, and an alloy containing Si and Mn and a carburizer are added during the tapping process.

[0008] Preferably, during the continuous casting process, the liquidus temperature of the molten steel is 1518°C, the target temperature of the molten steel in the tundish is 1538°C, and the mold protection slag adopts a special medium-carbon protection slag.

[0009] Preferably, when the hot direct charging furnace is carried out, the minimum charging temperature of the slab is ≥200°C.

[0010] Preferably, during the hot direct charging furnace process, for slabs with a thickness of 2.0-3.6 mm, the furnace temperature is 1210±30°C, and the heating time is 180 min; for slabs with a thickness of 3.61-5.0 mm, the furnace temperature is 1200±30°C, and the heating time is 180 min.

[0011] Preferably, the soaking treatment time is more than 22 minutes.

[0012] Preferably, for slabs with a thickness of 2.0-3.0 mm, the entrance reference temperature of the finishing rolling is 1040±30°C, the final rolling temperature is 860±20°C, and the coiling temperature is 630±20°C; for slabs with a thickness of 3.1-6.0 mm, the entrance reference temperature of the finishing rolling is 1060±30°C, the final rolling temperature is 850±20°C, and the coiling temperature is 620±20°C.

[0013] Preferably, in the laminar cooling process, a front-stage cooling method is adopted, and cooling is performed in the second, third and fifth cooling stages.

[0014] The advantages of the production method of the present invention over the prior art are:

[0015] The present invention designs the carbon content to be 0.14-0.17%. At the same time, in order to avoid the influence of the carbon content on the crack sensitivity of the peritectic reaction point, the ratio of silicon and manganese is designed, and the manganese content is controlled to be 0.82-92%, so that the product performance is more uniform and the slab quality is good. The cold inspection process before entering the furnace can be reduced, and direct hot charging treatment can be performed, thereby reducing costs and increasing efficiency. In addition, by performing alloying treatment during the steel tapping process of the converter blowing, the refining furnace is eliminated, thereby reducing costs. The invention adopts low-cost alloys such as medium carbon, low manganese, silicon in appropriate proportion, and quality design by means of narrow component control, controlled rolling, controlled cooling, etc., so as to reduce the cost by more than 20%, and the stamping forming and welding performance of the product are good. After stamping forming, the tensile strength of the welding zone of the finished product reaches 460-520MPa, the elongation reaches more than 28%, the product has good toughness, the yield strength ratio is less than 0.77, and the -20°C low-temperature impact test is greater than 50J, avoiding the problems of low carbon and high manganese design in the prior art, uneven ports that are prone to affect welding, high yield strength ratio, and substandard performance detection of the welding zone, etc.

[0016] The present invention also provides a low-cost, low-yield-strength ratio, high-toughness steel for welding bottles, which is produced by the production method of the low-cost, low-yield-strength ratio, high-toughness steel for welding bottles as described above.

[0017] The advantages of the steel for welding bottles produced by the present invention over the prior art are the same as the advantages of its production method over the prior art, which will not be repeated here. DETAILED DESCRIPTION

[0019] A method for producing low-cost, low-yield ratio, high-toughness welding bottle steel according to an embodiment of the present invention comprises: steelmaking according to the chemical composition and content of the welding bottle steel, and then respectively carrying out molten iron desulfurization, converter blowing, continuous casting, hot direct charging furnace, soaking, rough rolling, finishing rolling, laminar cooling and coiling processes, and adding alloys for micro-alloying during the slag discharge process of the converter blowing;

[0020] The chemical composition of the steel for welding bottles is as follows by weight percentage: C: 0.14-0.17%, Si: 0.05-0.10%, Mn: 0.82-92%, P: ≤0.015%, S: <0.005%, Als: 0.02-0.04%, and the rest is iron and unavoidable impurities.

[0021] The production method of this embodiment first adopts a design of medium carbon with low manganese in terms of composition and content. The manganese content is reduced by 0.05% compared with the existing medium manganese content, and the manganese content is within a narrower range than the existing technology design, which reduces the composition difference between large production furnaces and makes the product performance more uniform. However, in the prior art, the performance difference between each furnace is large, which makes the performance difference of the produced steel large, which is not conducive to the forming of the product. For example, for steel products with too high strength, it is more difficult to control its formability, thereby increasing the forming cost, etc. For example, if the yield strength ratio is too low, the formability is relatively soft, it is easy to deform after forming, the weld is not easy to align, and the product is easy to produce harshness after stamping. This embodiment also avoids the crack sensitivity of the peritectic reaction point through the ratio of C, Si, and Mn. This embodiment designs the C content to be 0.14-0.17%. In this range, the steel product is prone to slab crack defects and casting leakage. However, this embodiment reasonably avoids the influence of the carbon range on the crack sensitivity of the peritectic reaction point through the design of Si, Mn, etc., and the slab quality is good. The strength and performance of the steel for welding bottles are leanly controlled. The HP295 grade steel produced in this embodiment has a yield strength of 320-380MPa, an elongation of 28-36.5%, and an impact energy of 50-78J at -20°C. In terms of technology, this embodiment cancels the LF furnace (i.e., ladle refining furnace) process, and directly performs alloying operation during the steel tapping process after the converter blowing is completed, and directly performs continuous casting process after steel tapping. The continuous casting slab is directly hot-charged to the furnace, and hot rolling is performed after the heat treatment to eliminate the internal stress. This embodiment avoids the peritectic range through the aforementioned component quality control, so that the quality of the slab is effectively guaranteed, thereby reducing the cold inspection process, changing the method of putting the slab into the furnace after cold inspection in the prior art, and not cold inspecting the slab before entering the furnace, and all using hot direct charging furnace production, reducing heat loss, reducing carbon emissions, reducing costs, improving efficiency, and achieving the purpose of reducing costs and increasing efficiency. This embodiment controls the steel composition within a narrow range, and strictly controls the content of impurities such as S and P, and adds alloys for micro-alloying during the blowing process, and cancels the LF furnace to achieve cost reduction. The steel products produced have a low yield ratio and are controlled within a narrow range, with the yield ratio being 0.68-0.77. The narrow range of yield ratio control is conducive to improving toughness and other properties, and solves the problems of harsh ports that are prone to occur during the stamping process and affect welding, so that the produced welding bottle steel has good welding performance, low temperature stamping performance, etc.

[0022] According to the present invention, first, the molten iron is pre-desulfurized before being sent to the steelmaking furnace for smelting. Since the S element has a great influence on the formability and fatigue performance of steel and is a harmful element in steel, it is generally recommended that its content is as low as possible, and at the same time, the desulfurization cost will also increase. However, since the LF furnace process is eliminated in the production process of the steel for welding bottles in this embodiment, and in general, the cost of the LF furnace process is about 70 yuan / ton, while the desulfurization cost is only about 20 yuan / ton, it can be seen that the desulfurization cost is much lower than the cost of the LF furnace process, so the requirements for molten iron desulfurization can be appropriately increased. For example, in this embodiment, the sulfur content can be removed to below 0.005%, that is, the molten iron is desulfurized to S < 0.005%. In this way, the cost is controlled, and the content of harmful elements that affect the performance of steel is also controlled, so that the content of the S element is controlled at a lower level under the requirement of low cost control.

[0023] Secondly, further impurities are removed through converter blowing. In this embodiment, a bottom-blown converter is used for converter blowing, and nitrogen and argon are used as bottom-blowing gases. Nitrogen and argon are switched. Since the cost of argon is higher than that of nitrogen, this embodiment adopts the method of switching between argon and nitrogen, which also achieves the purpose of reducing costs and increasing efficiency. After the converter blowing is completed, slag is blocked for steel tapping, and the amount of slag under the converter is strictly controlled. At the same time, alloys containing Si and Mn and carburizers are added during the steel tapping process to carry out alloying treatment. Preferably, the alloy is added when 1 / 2-2 / 3 of the steel is tapped so that the alloy can be completely melted. Compared with the prior art, this embodiment does not add ferrotitanium alloy, which reduces the cost of titanium alloy and reduces the LF furnace process. Therefore, the alloy can be added during the converter tapping process. In addition, this embodiment uses a low-priced silicon-manganese alloy instead of medium-carbon ferromanganese, cancels the addition of ferrotitanium, and achieves the effect of reducing the cost of the alloy.

[0024] After the converter blowing is completed, the embodiment does not perform ladle refining, and the blown molten steel is directly transported to the continuous casting machine for protective casting. In the continuous steel casting process, the liquidus temperature of the molten steel is 1518°C, the target temperature of the molten steel in the middle ladle is 1538°C, and the mold protective slag uses a special medium carbon protective slag.

[0025] The molten steel is blown to obtain a slab through continuous protective pouring, and then the slab is directly charged into the heating furnace in a hot state. The slab enters the heating furnace for heating in a hot state, which can make full use of the residual temperature of the slab, reduce heat loss, shorten the heating time of the heating furnace, and reduce the energy consumption of the heating furnace. In this embodiment, the slab that is not hot-charged into the furnace is stacked and slowly cooled so that the minimum charging temperature of the slab is ≥200°C. Among them, the temperature of the slab after being heated out of the furnace is related to the thickness of the slab. For slabs with a thickness of 2.0-3.6mm, the furnace temperature is 1210±30°C, and the heating time in the heating furnace is 180min. For slabs with a thickness of 3.61-5.0mm, the furnace temperature is 1200±30°C, and the heating time in the heating furnace is 180min.

[0026] After the slab is taken out of the furnace, it is subjected to uniform heat treatment. The uniform heating time is more than 22 minutes. The uniform heat treatment is used to eliminate the internal stress of the slab.

[0027] The continuous casting slab is heated in a heating furnace and then soaked for hot rolling. Hot rolling includes rough rolling and finishing rolling. The soaked slab enters the rough rolling mill. The rough rolling material enters the finishing mill after cutting the head and tail. After the final rolling, it is cooled and coiled. Among them, the finishing inlet reference temperature, final rolling temperature and coiling temperature of the continuous casting slab in different thickness ranges are shown in Table 1:

[0028] Table 1:

[0029]

[0030] After rolling, the slab is subjected to laminar cooling treatment, and a front-stage and sparse cooling method is adopted. The so-called sparse cooling means that only some sections are selected for cooling in multiple cooling sections. Exemplarily, the sections for cooling the slab include 18 sections, and the rolled slab is cooled in the second, third and fifth sections. By omitting the cooling of the fourth section, the slab can be buffered, thereby reducing mixed crystals, improving performance stability and organizational uniformity.

[0031] This embodiment uses low-cost, narrow composition, stable performance medium carbon, low manganese and a small amount of micro-alloyed steel through controlled rolling and controlled cooling, and obtains significant strengthening effect through the interaction of micro-alloy carbonitride dispersion precipitation and dislocation, so as to meet the testing indicators such as meeting the performance standards of the welding heat affected zone, good stamping formability, and pressure burst test meeting the standard requirements.

[0032] Compared with the prior art, the production method of the embodiment of the present invention has the following advantages:

[0033] ①Compared with the existing design, the LF furnace process is reduced, and the LF furnace process cost and auxiliary material cost are reduced;

[0034] ② Subtracting the addition of alloy titanium, the titanium alloy is reduced by 0.015%, which reduces the cost of titanium alloy;

[0035] ③ The alloy ratio was optimized, and part of the low-cost silicon manganese was used to replace the high-priced medium-carbon ferromanganese;

[0036] ④ Reduce the amount of manganese alloy added, and reduce the manganese content by 0.05% compared with the domestic advanced technology;

[0037] ⑤ Optimize the hot rolling process, change the two-stage cooling to the front-stage interval cooling to ensure stable performance and uniform structure;

[0038] ⑥ Reasonably avoid the influence of manganese and carbon content ratio on the crack sensitivity of peritectic reaction point, the slab quality is good, change the previous slab cold inspection and furnace entry path, the slab is not cold inspected, and all are produced by direct hot charging;

[0039] ⑦ Solved the problem of thin-gauge medium and high carbon steel being easy to flatten and roll;

[0040] ⑧The yield-to-strength ratio was effectively reduced from the previous 0.85 to below 0.77, achieving the expected goal.

[0041] The thermomechanical properties of the steel for welding bottles produced in this embodiment are shown in Table 2 (Test results of mechanical properties of HP295 hot-rolled coil).

[0042] Table 2

[0043]

[0044] The following is a detailed description through examples

[0045] Example 1

[0046] This embodiment provides a method for producing low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles, comprising the steps of:

[0047] Steel is made according to the following chemical composition and contents, by weight percentage: C: 0.14-0.17%, Si: 0.05-0.10%, Mn: 0.82-92%, P: ≤0.015%, S: <0.005%, Als: 0.02-0.04%, the rest being iron and unavoidable impurities;

[0048] The molten iron is pre-desulfurized, and the desulfurized molten iron is sent to the converter, and air is blown from the bottom. After refining, the slag is blocked and the steel is tapped. Silicon manganese alloy and carburizer are added when 1 / 2-2 / 3 of the steel is tapped. The molten steel after blowing is sent to the continuous casting machine for protective pouring. During the pouring process, the liquidus temperature of the molten steel is 1518℃, and the target temperature of the molten steel in the middle package is 1538℃. The crystallizer protective slag uses a special medium-carbon protective slag. The slab is directly loaded into the heating furnace for heating in a hot state. The heating temperature and time are shown in Table 3:

[0049] Table 3:

[0050] Thickness range(mm) Oven temperature (℃) Heating time (min) 2.0-3.6 1210±30 180 3.61-5.0 1200±30 180

[0051] After the slab is taken out of the furnace, it is subjected to a uniform heat treatment. The uniform heating time is more than 22 minutes. The uniformly heated slab enters the rough rolling mill. After the rough rolling material is cut, it enters the finishing mill. After the final rolling, it is cooled and coiled. Among them, the reference temperature of the finishing rolling entrance, the final rolling temperature and the coiling temperature of the continuous casting billet of different thickness ranges are shown in Table 4:

[0052] Table 4:

[0053]

[0054] After rolling, the slab is subjected to laminar cooling treatment, with front-stage cooling being adopted, and the rolled slab is cooled in the second, third and fifth stages, and is coiled after cooling to obtain the low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles.

[0055] The sampled steel for welding bottles prepared in this embodiment was tested, and the results are shown in Table 5:

[0056] Table 5:

[0057]

[0058] The steel obtained in this embodiment was processed into a pipe to obtain a finished product, and the finished product was tested. The mechanical property test results are shown in Table 6:

[0059] Table 6:

[0060]

[0061] The HP295 grade steel produced in this embodiment has high strength, high toughness and excellent welding performance. After striping, stamping forming, welding area performance testing, and pressure blasting inspection, it is found that there is no cracking, performance substandard, etc., and the stamping forming and welding performance are good. After stamping forming, the tensile strength of the finished product welding area performance test reaches 460-520MPa, the elongation is more than 28%, the yield ratio is less than 0.77, and the -20°C low-temperature impact test is greater than 50J, which meets the standard requirements of HP295 steel for low yield ratio, high strength and high toughness welding steel, avoids the problems of strip distortion in low-carbon and high-manganese design, harsh and uneven ports that are prone to occur during stamping and affecting welding, high yield ratio, and substandard performance testing of the welding area. The quality design adopts low-cost alloys such as medium carbon, low manganese, and appropriately proportioned silicon, narrow component control, and controlled rolling and controlled cooling, so as to reduce the cost by more than 20%.

[0062] Although the disclosure is disclosed as above, the protection scope of the disclosure is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for producing low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles, characterized in that: include: Steel is made according to the chemical composition and content of the steel for welding bottles, and then hot metal desulfurization, converter blowing, continuous casting, hot direct charging furnace, soaking, rough rolling, finishing rolling, laminar cooling and coiling are respectively carried out, and alloy is added in the slag discharge process of the converter blowing for micro-alloying; The chemical composition of the steel for welding bottles is as follows by weight percentage: C: 0.14-0.17%, Si: 0.05-0.10%, Mn: 0.82-92%, P: ≤0.015%, S: <0.005%, Als: 0.02-0.04%, and the rest is iron and unavoidable impurities.

2. The method for producing low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles according to claim 1, characterized in that: The converter blowing adopts a bottom blowing converter, and the bottom blowing gas includes nitrogen and argon. During the bottom blowing process, the nitrogen and the argon are switched for use.

3. The method for producing low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles according to claim 1, characterized in that: After the converter blowing is completed, the slag is blocked and the steel is tapped, and an alloy containing Si and Mn and a carburizer are added during the tapping process.

4. The method for producing low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles according to claim 1, characterized in that: During the continuous casting process, the liquidus temperature of the molten steel is 1518°C, the target temperature of the molten steel in the tundish is 1538°C, and the mold protection slag adopts a special medium-carbon protection slag.

5. The method for producing low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles according to claim 1, characterized in that: When the hot direct charging furnace is carried out, the minimum charging temperature of the slab is ≥200°C.

6. The method for producing low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles according to claim 1, characterized in that: During the hot direct charging furnace process, for slabs with a thickness of 2.0-3.6 mm, the furnace temperature is 1210±30°C and the heating time is 180 min. For slabs with a thickness of 3.61-5.0 mm, the furnace temperature is 1200±30°C and the heating time is 180 min.

7. The method for producing low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles according to claim 1, characterized in that: The time of the soaking treatment is more than 22 minutes.

8. The method for producing low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles according to claim 1, characterized in that: For slabs with a thickness of 2.0-3.0 mm, the entrance reference temperature of the finishing rolling is 1040±30°C, the final rolling temperature is 860±20°C, and the coiling temperature is 630±20°C; for slabs with a thickness of 3.1-6.0 mm, the entrance reference temperature of the finishing rolling is 1060±30°C, the final rolling temperature is 850±20°C, and the coiling temperature is 620±20°C.

9. The method for producing low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles according to claim 1, characterized in that: In the laminar cooling process, a front-stage cooling method is adopted, and cooling is performed in the second, third and fifth cooling stages.

10. A low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles, characterized in that: The steel is produced by the production method of low-cost, low-yield-to-strength ratio, high-toughness steel for welding bottles as described in any one of claims 1 to 9.

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