Die casting production method of 12Cr2Mo1VR steel

Abstract

The invention discloses a die casting production method of 12Cr2Mo1VR steel, which realizes the control of low nitrogen content and low cost, and adopts a converter-LF furnace-slag salvaging-LF furnace-RH furnace-LF furnace-VD furnace-die casting production process, the converter molten iron ratio is 0.85-0.90, the tapping oxygen content is more than or equal to 0.05%, the phosphorus content is less than or equal to 0.008%, lime is firstly added in the tapping process, no alloy is added, and the molten iron content is less than or equal to 0.008%. In the first LF entering process, lime is added, steel ladle bottom blowing strong argon is combined for stirring and dephosphorization till the dephosphorization degree is smaller than or equal to 0.003%, a proper amount of low-carbon ferrochrome is added, dephosphorization slag is completely fished out, second LF entering is carried out, micro-positive pressure operation is kept on a furnace opening of the LF in the whole process, ferrovanadium is not added, all other elements except V, B and Al need to be within the required range, calcium treatment is not carried out before the LF leaves a station, and an RH furnace is vacuumized till the vacuum degree is smaller than 67 Pa; keeping vacuum for 12-15 minutes, adding ferrovanadium alloy to a required range after about 3 minutes before vacuum breaking, entering the LF furnace for three times, blowing argon from the bottom in the whole process and stirring weakly, adjusting boron and aluminum to the required range before leaving the station, and feeding a pure calcium wire.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a die casting production method of 12Cr2Mo1VR steel, which realizes the control of low nitrogen content and low cost. Background Art

[0002] 12Cr2Mo1VR steel has high strength and good plasticity, which can meet the use requirements of various parts of high-temperature and high-pressure containers and boilers. In addition, it has good processing performance and welding performance, which is convenient for processing and maintenance. It belongs to the national standard special steel plate for medium and high-temperature boilers and pressure vessels. It is widely used in the petroleum, chemical, electric power and other industries to make various equipment and components, such as reactors, heat exchangers, separators, spherical tanks, oil and gas tanks, etc. With the issuance of the new implementation standard GB / T 713-2023, it requires the nitrogen content of the finished product to be ≤0.0070%. For steel plates with a rolling thickness of ≥120mm, die casting is required. When all low-carbon ferrochrome is used, the nitrogen content of molten steel before casting is high, and the die casting protection casting effect is relatively poor. The nitrogen increase during the casting process is generally above 10ppm, and some even exceed 20ppm. 12Cr2Mo1VR steel contains a high V content, which will cause nitrogen increase in molten steel and aggravate the nitrogen fixation effect. Therefore, the nitrogen content of the finished product is easy to exceed the standard requirements. The use of metallic chromium will increase production costs. How to achieve low nitrogen content and low cost control in die-cast 12Cr2Mo1VR steel has become a difficult problem that plagues many steel mills. Summary of the invention

[0003] 1. Technical issues to be resolved The invention aims to provide a die casting production method of 12Cr2Mo1VR steel, which can realize low nitrogen content and low cost control of molten steel.

[0004] (II) Technical solution To achieve the above object, the present invention provides the following technical solution: a die casting production method of 12Cr2Mo1VR steel, comprising the following process steps: A) Converter: Select molten iron, whose chemical composition weight percentage is: P≤0.012, S≤0.040, As≤0.006, Sn≤0.005; molten iron ratio is 0.85~0.90, all special scrap steel with low residual elements is used, 14.0~15.0 kg / t (steel) of ferromolybdenum is added, argon is blown at the bottom of the converter throughout the whole process, oxygen level of steel tapping is ≥0.05%, phosphorus ≤0.008%, steel tapping temperature is 1590~1620℃, and final slag basicity is 3.5~5.0; infrared slag detection and slide plate are used in combination for slag blocking, and lime 4.0~5.0 kg / t (steel) is added in the process of steel tapping; B) LF furnace (dephosphorization): Raise the temperature of molten steel to above 1560℃, add active lime 5.0~7.0 kg / t (steel) in batches, and melt the lime to avoid agglomeration. Use ladle bottom blowing and strong stirring to provide, when the molten steel P≤0.003, add low carbon ferrochrome 15.0~20.0 kg / t (steel); C) Slag removal: Use a slag removal machine to remove slag, and the exposed surface of molten steel must be ≥80%; D) LF furnace: After slag removal, enter the LF furnace, add 2.0~4.0 kg / t (steel) of low silicon and low titanium refined slag to cover the molten steel surface, raise the temperature of the molten steel to above 1560 ℃, feed aluminum wire for deoxidation, and require the LF furnace to maintain a slight positive pressure operation throughout the process. Lime and low silicon and low titanium pre-melted slag are used to make slag, and deoxidation is carried out by feeding Al wire combined with adding aluminum shots. The total slag volume is 12.0~15.0 kg / t (steel). Low nitrogen graphite recarburizer and low carbon and low nitrogen ferrochrome, ferroniobium, ferromolybdenum and other low phosphorus and low nitrogen alloys are added to adjust the composition. Ferrovanadium shall not be added. The LF station time is ≥70min, and the white slag retention time is ≥25min. Except for V, B, and Al elements, all other elements must meet the requirements; E) RH furnace: evacuate to a vacuum degree of 67Pa, add vanadium-iron alloy 6.0~7.0 kg / t (steel) to the required range about 3 minutes before breaking the vacuum, and maintain the vacuum for 12~15 minutes; F) LF furnace: The bottom blowing argon flow rate is 100~200L / min for weak stirring throughout the process. The boron and aluminum are adjusted to the required range before leaving the station. The pure calcium line is fed at 0.25~0.35 kg / t (steel). The molten steel outlet temperature is 1630~1650℃; G) VD furnace: The VD furnace is evacuated to a vacuum degree of <67 Pa, the vacuum maintenance time is ≥18 min, the soft blowing time after vacuum must be ≥15 min, and pure calcium line 0.15~0.25 g / t (steel) is fed before leaving the station; H) Mold casting: The whole process is protected. The ladle water inlet to the center pouring nozzle is protected by a steel cover. At the same time, 0.2~0.3Mpa argon gas is used for sealing. The casting superheat is 45~47 ℃. The ingot casting adopts uniform speed casting to ensure the steady rise of the liquid level. Preferably, A) no deoxidizing and alloying alloy is added during the converter steel tapping process, and the converter steel tapping weight needs to ensure that the ladle clearance meets the conditions for simultaneous VD furnace and RH furnace processing.

[0005] Preferably, B) the lime content before the LF furnace (dephosphorization) leaves the station is 2.0-4.0 kg / t (steel) thick slag, and the outlet temperature is 1550-1570 °C.

[0006] Preferably, the D) LF furnace: no calcium treatment is performed before leaving the station, and the leaving station temperature is 1650-1670°C.

[0007] (III) Beneficial effects Compared with the prior art, the present invention provides a die casting production method of 12Cr2Mo1VR steel, which has the following beneficial effects: 1) The die casting production method of 12Cr2Mo1VR steel uses low-carbon ferrochrome in its entirety, thereby reducing costs and alloy costs; 2) Adding part of the low-carbon ferrochrome to the LF furnace without deoxidation can oxidize Si and P therein into the slag, effectively reducing the Si content of the finished product by 0.02%~0.03% and the P content by 0.0005%~0.0006%; 3) No ferrovanadium is added to the LF furnace, reducing the amount of nitrogen added to the molten steel; ferrovanadium is added to the RH furnace in the later stage of the vacuum process, reducing the nitrogen addition and nitrogen fixation of ferrovanadium; weak stirring is used throughout the entire process of entering the LF furnace again, and less nitrogen addition is achieved; VD vacuum treatment can control the nitrogen content of the outlet to below 50ppm, and the nitrogen content of the die-cast finished product to below 65ppm. DETAILED DESCRIPTION

[0008] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the 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.

[0009] Example 1 A die casting production method for 12Cr2Mo1VR steel comprises the following production steps: converter→LF furnace→slag removal→LF furnace→RH furnace→LF furnace→VD furnace→die casting; A) Converter: Iron-metal ratio 0.86, iron-metal composition: P=0.112%, S=0.031%, As =0.004%, Sn=0.002%, tapping oxygen 0.0612%, tapping P=0.0071%, tapping temperature 1615°C, final slag basicity CaO / SiO2=4.1, N=0.0018%, lime 4.6kg / t (steel) was added during tapping.

[0010] B) LF furnace (dephosphorization): raise the temperature of molten steel to 1565 ℃, add 6.5 kg / t (steel) of active lime and 17.2 kg / t (steel) of low-carbon ferrochrome in batches, add 3.0 kg / t (steel) of lime to thick slag before leaving the station, the leaving station temperature is 15558 ℃, and the leaving station molten steel P=0.0025%.

[0011] C) Remove the residue cleanly.

[0012] D) LF furnace: When the molten steel enters the station, 3.0 kg / t (steel) of low-silicon and low-titanium refined slag is added to cover the molten steel surface. After the temperature reaches 1562℃, deoxidation and alloying are carried out. Lime and low-silicon and low-titanium refined slag are added during the process. The total slag amount is 14.2 kg / t (steel). The LF station time is 85min. The outgoing V=0.003%, B=0.0003%, Al=0.0025%, P=0.0047%, N=0.0095%, and the remaining elements are within the required range. The outgoing temperature is 1652℃.

[0013] E) RH furnace: evacuate to vacuum degree <67Pa, ultimate vacuum degree 29Pa, maintain vacuum for 15 minutes, add 6.5 kg / t (steel) of vanadium-iron alloy when maintaining vacuum for 12 minutes, exit V=0.324%, N=0.0065%.

[0014] F) LF furnace: The bottom blowing argon flow rate is 150L / min for weak stirring throughout the whole process, the outlet B=0.0015%, Al=0.041%, N=0.0071%, and the other elements are within the required range. The pure calcium wire is fed at 0.29 kg / t (steel), and the outlet temperature is 1638℃.

[0015] G) VD furnace: evacuate to vacuum degree <67 Pa, ultimate vacuum degree 40Pa, vacuum maintenance time 20min, feed pure calcium line 0.18 kg / t (steel); soft blowing time 20min; exit H=0.00011%, N=0.0046%, Al=0.022%.

[0016] H) Mold casting: The whole process is protected. The ladle water inlet to the center pouring nozzle is protected by a steel cover, and 0.25Mpa argon is used for sealing. The casting superheat is 45°C. The ingot casting adopts a uniform speed of pouring steel, and the liquid level rises steadily. Samples are taken from the head and tail of the rolled steel plate. The head: N = 0.0058%, the tail: N = 0.0057%. Example 2 A die casting production method for 12Cr2Mo1VR steel comprises the following production steps: converter→LF furnace→slag removal→LF furnace→RH furnace→LF furnace→VD furnace→die casting; A) Converter: Iron-metal ratio 0.87, iron-metal composition: P=0.115%, S=0.029%, As =0.003%, Sn=0.003%, tapping oxygen 0.0586%, tapping P=0.0074%, tapping temperature 1599°C, final slag basicity CaO / SiO2=4.2, N=0.0020%, lime 4.5kg / t (steel) during tapping.

[0017] B) LF furnace (dephosphorization): raise the temperature of molten steel to 1567℃, add 6.2 kg / t (steel) of active lime and 17.1 kg / t (steel) of low-carbon ferrochrome in batches, add 2.8 kg / t (steel) of lime thick slag before leaving the station, the leaving station temperature is 1560℃, and the leaving station molten steel P=0.0028%.

[0018] C) Remove the residue cleanly.

[0019] D) LF furnace: When the molten steel enters the station, 3.2 kg / t (steel) of low-silicon and low-titanium refined slag is added to cover the molten steel surface. After the temperature reaches 1568℃, deoxidation and alloying are carried out. Lime and low-silicon and low-titanium refined slag are added during the process. The total slag amount is 14.2 kg / t (steel). The LF station time is 80min. The outgoing V=0.004%, B=0.0003%, Al=0.0028%, P=0.0052%, N=0.0089%, and the remaining elements are within the required range. The outgoing temperature is 1655℃.

[0020] E) RH furnace: evacuate to vacuum degree <67Pa, ultimate vacuum degree 30Pa, maintain vacuum for 15 minutes, add 6.5 kg / t (steel) of vanadium-iron alloy when maintaining vacuum for 12 minutes, exit V=0.327%, N=0.0062%.

[0021] F) LF furnace: The bottom blowing argon flow rate is 150L / min for weak stirring, the outlet B=0.0015%, Al=0.047%, N=0.0070%, and the other elements are within the required range. The pure calcium wire is fed at 0.29 kg / t (steel), and the outlet temperature is 1641℃.

[0022] G) VD furnace: evacuate to vacuum degree <67 Pa, ultimate vacuum degree 39Pa, vacuum maintenance time 20min, feed pure calcium line 0.18 kg / t (steel); soft blowing time 25min; exit H=0.00012%, N=0.0043%, Al=0.024%.

[0023] H) Die casting: full protection casting, steel cover is used to protect the ladle water inlet to the center injection nozzle, 0.25Mpa argon gas is used for sealing, casting superheat is 46 ℃, ingot casting adopts uniform speed steel pouring, and the liquid level rises steadily. Samples are taken from the head and tail of the rolled steel plate, head: N=0.0056%, tail: N=0.0055%.

[0024] Table 1 Chemical composition of example steel (wt, %) Chemical Elements C Si Mn P≤ S Mo Cr Ni V Cu Example 1 0.14 0.08 0.49 0.005 0.002 0.95 2.35 0.11 0.325 0.03 Example 2 0.13 0.08 0.52 0.005 0.002 0.96 2.38 0.10 3.33 0.03 Chemical Elements Nb Ti AT B Sn As Ca [O] [H] [N] Example 1 0.028 0.011 0.015 0.0014 0.004 0.005 0.0009 0.0017 0.0011 0.0058 Example 2 0.027 0.010 0.019 0.0014 0.003 0.005 0.0010 0.0015 0.0012 0.0056 Comparative Example 1 A die casting production method for 12Cr2Mo1VR steel, comprising the following production steps: converter → LF furnace → slag removal → LF furnace → RH furnace → die casting; A) Converter: Iron-metal ratio 0.86, iron-metal composition: P=0.114%, S=0.032%, As =0.003%, Sn=0.003%, tapping oxygen 0.0649%, tapping P=0.0065%, tapping temperature 1602°C, final slag basicity CaO / SiO2=4.5, N=0.0022%, lime 4.4kg / t (steel) was added during tapping.

[0025] B) LF furnace (dephosphorization): raise the temperature of molten steel to 1564℃, add 6.2 kg / t (steel) of active lime and 17.6 kg / t (steel) of low-carbon ferrochrome in batches, add 2.8 kg / t (steel) of lime thick slag before leaving the station, the leaving station temperature is 1561℃, and the leaving station molten steel P=0.0024%.

[0026] C) Remove the residue cleanly.

[0027] D) LF furnace: When the molten steel enters the station, 3.5 kg / t (steel) of low-silicon and low-titanium refined slag is added to cover the molten steel surface. After the temperature of the molten steel reaches 1570℃, lime and low-silicon and low-titanium refined slag are added during the process. The total slag amount is 14.3 kg / t (steel). The LF station time is 90 minutes. The steel output V=0.320%, B=0.0016%, P=0.0044%, Al=0.0038%, N=0.0118%, and the remaining elements are within the required range. The outlet temperature is 1652℃.

[0028] E) RH furnace: evacuate to vacuum degree <67Pa, ultimate vacuum degree 30Pa, maintain vacuum twice, the first vacuum maintenance time is 15min, the second vacuum maintenance time is 21min according to the temperature measurement result, break the vacuum and feed pure calcium wire 0.18 kg / t (steel); soft blowing time is 17min. Outgoing N=0.0073%, and the other elements are within the required range.

[0029] F) Die casting: full protection casting, steel cover is used to protect the ladle water inlet to the center injection nozzle, 0.25Mpa argon gas is used for sealing, casting superheat is 46 ℃, ingot casting adopts uniform speed steel pouring, and the liquid level rises steadily. Samples are taken from the head and tail of the rolled steel plate, head: N=0.0085%, tail: N=0.0083%.

[0030] Comparative Example 2 A die casting production method for 12Cr2Mo1VR steel, comprising the following production steps: converter → LF furnace → slag removal → LF furnace → RH furnace → die casting; A) Converter: Iron-metal ratio 0.87, iron-metal composition: P=0.109%, S=0.027%, As =0.004%, Sn=0.003%, tapping oxygen 0.0652%, tapping P=0.0075%, tapping temperature 1610°C, final slag basicity CaO / SiO2=4.6, N=0.0021%, lime 4.6kg / t (steel) was added during tapping.

[0031] B) LF furnace (dephosphorization): raise the temperature of molten steel to 1569℃, add 6.0 kg / t (steel) of active lime and 17.4 kg / t (steel) of low-carbon ferrochrome in batches, add 2.8 kg / t (steel) of lime thick slag before leaving the station, the leaving station temperature is 1559℃, and the leaving station molten steel P=0.0025%.

[0032] C) Remove the residue cleanly.

[0033] D) LF furnace: When the molten steel enters the station, 3.4 kg / t (steel) of low-silicon and low-titanium refined slag is added to cover the molten steel surface. After the temperature of the molten steel reaches 1570℃, lime and low-silicon and low-titanium refined slag are added during the process. The total slag amount is 14.3 kg / t (steel). The LF station time is 85 min. The steel output V=0.309%, B=0.0014%, P=0.0045%, Al=0.0072%, N=0.00125%, and the remaining elements are within the required range. The outlet temperature is 1680℃.

[0034] E) VD furnace: evacuate to vacuum degree 67Pa, ultimate vacuum degree 30Pa, maintain vacuum twice, the first vacuum time is 15min, the second vacuum time is 20min according to the temperature measurement result, feed pure calcium wire 0.18 kg / t (steel) through air; soft blowing time is 22min. Outgoing N=0.0061%, other elements are within the required range.

[0035] F) Die casting: full protection casting, steel cover is used to protect the ladle water inlet to the center injection nozzle, 0.25Mpa argon is used for sealing, casting superheat is 46 ℃, ingot casting adopts uniform speed steel pouring, and the liquid level rises steadily. The head and tail of the rolled steel plate are sampled, head: N=0.0075%, tail: N=0.0073%. Although the embodiments of the present invention have been shown and described, it can be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the attached claims and their equivalents.

Claims

1. A die casting production method for 12Cr2Mo1VR steel, characterized in that: The process steps include: A) Converter: Select molten iron, whose chemical composition weight percentage is: P≤0.012, S≤0.040, As≤0.006, Sn≤0.005; molten iron ratio is 0.85~0.90, all special scrap steel with low residual elements is used, 14.0~15.0 kg / t (steel) of ferromolybdenum is added, argon is blown at the bottom of the converter throughout the whole process, oxygen level of steel tapping is ≥0.05%, phosphorus ≤0.008%, steel tapping temperature is 1590~1620℃, and final slag basicity is 3.5~5.0; infrared slag detection and slide plate are used in combination for slag blocking, and lime 4.0~5.0 kg / t (steel) is added in the process of steel tapping; B) LF furnace (dephosphorization): Raise the temperature of molten steel to above 1560℃, add active lime 5.0~7.0 kg / t (steel) in batches, and melt the lime to avoid agglomeration. Use ladle bottom blowing and strong stirring to provide. When the molten steel P≤0.003, add low-carbon ferrochrome 15.0~20.0 kg / t (steel); C) Slag removal: Use a slag removal machine to remove slag, and the exposed surface of molten steel must be ≥80%; D) LF furnace: After slag removal, enter the LF furnace, add 2.0~4.0 kg / t (steel) of low silicon and low titanium refined slag to cover the molten steel surface, raise the temperature of the molten steel to above 1560 ℃, feed aluminum wire for deoxidation, and require the LF furnace to maintain a slight positive pressure operation throughout the process. Lime and low silicon and low titanium pre-melted slag are used to make slag, and deoxidation is carried out by feeding Al wire combined with adding aluminum shots. The total slag volume is 12.0~15.0 kg / t (steel). Low nitrogen graphite recarburizer and low carbon and low nitrogen ferrochrome, ferroniobium, ferromolybdenum and other low phosphorus and low nitrogen alloys are added to adjust the composition. Ferrovanadium shall not be added. The LF station time is ≥70min, and the white slag retention time is ≥25min. Except for V, B, and Al elements, all other elements must meet the requirements; E) RH furnace: evacuate to a vacuum degree of 67Pa, add vanadium-iron alloy 6.0~7.0 kg / t (steel) to the required range about 3 minutes before breaking the vacuum, and maintain the vacuum for 12~15 minutes; F) LF furnace: The bottom blowing argon flow rate is 100~200L / min for weak stirring throughout the process. The boron and aluminum are adjusted to the required range before leaving the station. The pure calcium line is fed at 0.25~0.35 kg / t (steel). The molten steel outlet temperature is 1630~1650℃; G) VD furnace: VD furnace is evacuated to a vacuum degree of <67 Pa, the vacuum maintenance time is ≥18 min, the soft blowing time after vacuum must be ≥15 min, and pure calcium line 0.15~0.25 g / t (steel) is fed before leaving the station; H) Mold casting: The whole process is protected. The ladle water inlet to the center pouring nozzle is protected by a steel cover. At the same time, 0.2~0.3Mpa argon gas is used for sealing. The casting superheat is 45~47 ℃. The ingot body is cast with uniform speed to ensure that the liquid level rises steadily.

2. The die casting production method of 12Cr2Mo1VR steel according to claim 1, characterized in that: A) No deoxidizing and alloying alloy is added during the converter steel tapping process, and the converter steel tapping weight must ensure that the ladle clearance meets the conditions for simultaneous VD furnace and RH furnace processing.

3. The die casting production method of 12Cr2Mo1VR steel according to claim 1, characterized in that: The B) LF furnace (dephosphorization) lime before leaving the station is 2.0~4.0 kg / t (steel) thick slag, and the exit temperature is 1550~1570 ℃.

4. The die casting production method of 12Cr2Mo1VR steel according to claim 1, characterized in that: The D) LF furnace: no calcium treatment is performed before leaving the station, and the exit temperature is 1650~1670℃.