Smelting and casting process of blade steel

Abstract

The invention relates to a blade steel smelting and casting process adopting EBT electric arc furnace smelting, LF furnace refining, VOD / VD vacuum treatment and electrode blank pouring. The tapping temperature of an electric arc furnace is controlled to be 1620-1660 DEG C; the method comprises the following steps: carrying out LF furnace alloying treatment, considering blowing loss, ensuring that components after VD meet a set target, controlling the carbon content to be 0.5-0.55% and the temperature to be greater than or equal to 1580 DEG C, carrying out VOD / VD vacuum treatment, ending VD, adding 2-5Kg / t of ferrosilicon alloy, 1.5-3Kg / t of aluminum blocks and 2-3Kg / t of fluorite, adjusting slag system reduction, maintaining the temperature by using chemical heat of carbon-oxygen reaction in a VOD stage, and stirring for 35 minutes to meet the requirement of a crane ladle at 1545-1560 DEG C; the method comprises the following steps: directly transferring to a pouring station, standing for more than or equal to 15 minutes, carrying out pouring molding by adopting a bottom pouring method, carrying out argon protection pouring in the pouring process, carrying out annealing, cap cutting and inspection on an electrode blank, transferring to an electroslag process, and carrying out electroslag remelting, so that the material cost can be reduced, and the purity of molten steel can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking, and relates to a smelting and casting process for blade steel using EBT electric arc furnace smelting + LF furnace refining + VOD / VD vacuum treatment + electrode blank casting (electroslag remelting of parent material). Background Art

[0002] Blade steel is a special material specially used for manufacturing turbine blades. Due to its complex working environment, it must have ultra-high performance guarantees for durability, safety, stability, etc. of operation. Blade steel is a martensitic steel, which requires pure molten steel and uniform composition, and δ ferrite ≤5%. Blade steel is widely used in important fields such as power generation, shipbuilding, and aviation.

[0003] At present, the more common smelting processes are "IF+EBT electric arc furnace smelting+LF furnace refining+VD degassing+ingot pouring (forging parent material)" and "EBT electric arc furnace smelting+LF furnace refining+VD vacuum treatment+ingot pouring (forging parent material)". Although "IF+EBT electric arc furnace smelting+LF furnace refining+VD degassing+ingot pouring (forging parent material)" can use some of the raw materials to reduce costs, the IF melting furnace cannot remove P, and the P component in the smelting process is not easy to control. High carbon alloys cannot be used in the process route of "EBT electric arc furnace smelting+LF furnace refining+VD degassing+ingot pouring (forging parent material)", and low carbon and micro carbon alloys are mainly used, which has high costs. In addition, the ingots are directly forged, and the grain structure and mechanical properties are less stable. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and to provide a blade steel smelting and casting process for electroslag remelting of parent material to improve the comprehensive performance of the material, which can reduce costs.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows: A smelting and casting process for blade steel adopts the process route of "EBT arc furnace smelting + LF furnace refining + VOD / VD vacuum treatment + electrode blank casting". The mass percentage of the smelted blade steel elements is: [C]=0.2%~0.25%, [Cr]=11.0%~12.50%, [Ni]=0.70~1.00%, [Mo]=0.90~1.25%, [P]≤0.025%, [S]≤0.005%, [V]=0.2~0.3%, [W]=0.8~1.20%, [Si]≤0.60%, [Mn]≤1.00%, the remainder is iron, and delta ferrite is ≤5%; the specific smelting process steps are as follows: Step 1), add 750-800kg / t of chromium-molybdenum scrap steel, 150-200kg / t of pig iron, 80-100kg / t of carbon chips, and 50kg / t of lime into the EBT electric furnace, melt and evenly temperature, take samples at a temperature of 1580-1630°C, and control the tapping temperature at 1620-1660°C; ensure that [P]≤0.003%, [C]≤0.05%; add 2.0-3.5Kg / t of aluminum blocks, 2.0-3.0Kg / t of medium carbon ferromanganese alloy, and 4.0-6.0Kg / t of lime during the tapping process; Step 2), turn to the LF furnace station, feed 3.0-5.0 m / t of aluminum wire, add 10.0-20.0 kg / t of lime and 2.0-5.0 kg / t of silicon calcium powder in batches, adjust the alloy in batches, add 6.3 kg / t of ferrosilicon alloy, 9.9 kg / t of manganese metal, 60 kg / t of high carbon ferrochrome alloy (containing 8% carbon), and 150 kg / t of low carbon ferrochrome alloy (containing 0.15% carbon). , add 40Kg / t of micro-carbon ferrochromium alloy (containing 0.03% carbon), 9Kg / t of electrolytic nickel, 17Kg / t of ferromolybdenum alloy, 5.5Kg / t of ferrovanadium alloy, 16Kg / t of ferrotungsten alloy, take samples at a temperature between 1560 and 1620℃, control the temperature at 1580 to 1600℃, control the carbon content between 0.5 and 0.55%, the net space of the ladle ≥800mm, and switch to VOD / VD station; Step 3) Position the VOD / VD station, turn on the vacuum pump, and when the vacuum reaches 180mbar, start blowing oxygen from the gun. After blowing slowly for 2 to 3 minutes, gradually adjust the oxygen flow rate to 900 to 1200Nm 3 / h, set to 600m 3 After the total amount of oxygen is blown away, the oxygen concentration difference is close to zero and no longer rebounds, that is, the gun is lifted and the oxygen is stopped. During this period, the flue temperature is observed not to exceed 300℃. After stopping the oxygen, the VCD stage is entered, and the argon flow rate is set to 80-100NL / min. The excess oxygen content is used for deep decarburization. At the same time, the vacuum degree is gradually reduced. It is maintained at ≤0.7mbar for ≥20 minutes before breaking the air. After temperature measurement and sampling, the vacuum cover is dropped and covered tightly. [C]≤0.22%, stirring time≥35 minutes, online setting [H]≤1.5ppm, [O]≤6ppm, online temperature measurement between 1545 and 1560℃, and the hanging bag is transferred to the pouring station; Step 4), transfer to the pouring station, measure the temperature after the calming time ≥15 minutes, when the temperature is ≤1550℃, use the pouring method to pour into the electrode blank, use argon protection pouring during the pouring process, clean the mold wall before pouring steel, the mold temperature is ≥60℃, the pouring system and its materials are kept clean and dry, 1-1.5kg / t of low-carbon mold casting protective slag is hoisted into the mold before pouring, the ingot body pouring speed is 15Kg / s, the weight of the molten steel in the cap mouth accounts for 13% of the total weight of the steel ingot, the cap mouth pouring speed is 9Kg / s, when the cap mouth pouring height exceeds one-third, add 1.0-1.5kg / t of heating agent, add 1.0-2.0kg / t of carbonized rice husk to the cap mouth after pouring, anneal after demoulding the electrode blank, saw the cap mouth after annealing, and transfer to the electroslag process for electroslag remelting after the surface is inspected.

[0006] The positive effects of the technical solution of the present invention are as follows: the raw materials of the present invention include pig iron, chromium-molybdenum scrap steel, carbon steel chips, high-carbon ferrochrome (containing 8% carbon), low-carbon ferrochrome (containing 0.15% carbon), micro-carbon ferrochrome (containing 0.03% carbon), metallic manganese, electrolytic nickel, ferromolybdenum alloy, ferrotungsten alloy, and ferrovanadium alloy.

[0007] (1) Use part of high carbon ferrochrome to replace low carbon ferrochrome to reduce material cost; (2) Vacuum oxygen decarburization, divided into two stages: VOD (oxygen decarburization) and VCD (carbon deoxidation). Moderate stirring is performed under the action of argon gas stirring, so that inclusions float fully and the purity of the molten steel is improved; (3) Use vacuum oxygen blowing to generate heat from carbon-oxygen reaction to keep the temperature of molten steel above 1650 degrees, ensure that the temperature after VD is between 1545 and 1560 degrees, and meet the conditions for direct ladle pouring; (4) The electrode blank with uniform composition and internal purity provides guarantee for the production of high-quality electroslag remelting ingots. DETAILED DESCRIPTION

[0008] Embodiment: The present invention adopts the process route of "60tEBT arc furnace smelting + 60tLF furnace refining + VOD / VD vacuum treatment + electrode blank casting" for smelting. The mass fraction of the smelted blade steel elements is: [C] = 0.2% ~ 0.25%, [Cr] = 11.0% ~ 12.50%, [Ni] = 0.70 ~ 1.00%, [Mo] = 0.90 ~ 1.25%, [P] ≤ 0.025%, [S] ≤ 0.005%, [V] = 0.2 ~ 0.3%, [W] = 0.8 ~ 1.20%, [Si] ≤ 0.60%, [Mn] ≤ 1.00%, the remainder is Fe, and delta ferrite ≤ 5%. The specific smelting process steps are as follows: Step 1), add 750-800kg / t of CrMo scrap steel, 150-200kg / t of pig iron, 80-100kg / t of carbon chips, and 50kg / t of lime into the EBT electric furnace, melt and evenly temperature, take samples at a temperature of 1580-1630°C, and control the tapping temperature at 1620-1660°C; ensure that [P]≤0.003%, [C]≤0.05%; add 2.0-3.5Kg / t of Al blocks, 2.0-3.0Kg / t of medium carbon ferromanganese alloy, and 4.0-6.0Kg / t of lime during the tapping process; Step 2), turn to the LF furnace station, feed 3.0-5.0 m / t of aluminum wire, add 10.0-20.0 kg / t of lime and 2.0-5.0 kg / t of calcium silicon powder in batches, adjust the alloy in batches, add 6.3 kg / t of ferrosilicon, 9.9 kg / t of metallic manganese, 60 kg / t of high carbon ferrochrome alloy (containing 8% carbon), and 150 kg / t of low carbon ferrochrome alloy (containing 0.15% carbon). Add 40Kg / t of micro-carbon ferrochromium alloy (containing 0.03% carbon), 9Kg / t of electrolytic nickel, 17Kg / t of ferromolybdenum alloy, 5.5Kg / t of ferrovanadium alloy, and 16Kg / t of ferrotungsten alloy. Take samples at a temperature between 1560 and 1620°C, control the temperature at 1580 and 1600°C, control the carbon content between 0.5 and 0.55%, and make the net space of the ladle ≥800mm. Switch to VOD / VD station. Step 3) Position the VOD / VD station, turn on the vacuum pump, and when the vacuum reaches 180mbar, start blowing oxygen from the gun. After blowing slowly for 2 to 3 minutes, gradually adjust the oxygen flow rate to 900 to 1200Nm 3 / h, set to 600m 3 After the total amount of oxygen is blown away, the oxygen concentration difference is close to zero and no longer rebounds, that is, the gun is lifted and the oxygen is stopped. During this period, the flue temperature is observed not to exceed 300℃. After stopping the oxygen, the VCD stage is entered, and the argon flow rate is set to 80-100NL / min. The excess oxygen content is used for deep decarburization. At the same time, the vacuum degree is gradually reduced. It is maintained at ≤0.7mbar for ≥20 minutes before breaking the air. After temperature measurement and sampling, the vacuum cover is dropped and covered tightly. [C]≤0.22%, stirring time≥35 minutes, online setting [H]≤1.5ppm, [O]≤6ppm, online temperature measurement between 1545 and 1560℃, and the hanging bag is transferred to the pouring station; Step 4), transfer to the pouring station, measure the temperature after the calming time ≥15 minutes, when the temperature is ≤1550℃, use the pouring method to pour into the electrode blank, use argon protection pouring during the pouring process, clean the mold wall before pouring steel, the mold temperature is ≥60℃, the pouring system and its materials are kept clean and dry, 1-1.5kg / t of low-carbon mold casting protective slag is hoisted into the mold before pouring, the ingot body pouring speed is 15Kg / s, the weight of the molten steel in the cap mouth accounts for 13% of the total weight of the steel ingot, the cap mouth pouring speed is 9Kg / s, when the cap mouth pouring height exceeds one-third, add 1.0-1.5kg / t of heating agent, add 1.0-2.0kg / t of carbonized rice husk to the cap mouth after pouring, anneal after demoulding the electrode blank, saw the cap mouth after annealing, and transfer to the electroslag process for electroslag remelting after the surface is inspected.

[0009] According to the smelting process of this embodiment, two groups of smelting were carried out. The chemical compositions of the products obtained by the two groups of smelting are shown in the attached table, and both meet the target requirements: Appendix Chemical Composition (mass fraction) % element Target ingredients This embodiment 1 This embodiment 2 C 0.2～0.25 0.22 0.23 Si ≤0.6 0.50 0.45 Mn ≤1.00 0.68 0.70 P ≤0.025 0.020 0.018 S ≤0.005 0.004 0.005 Cr 11.0～12.50 11.9 12.0 Ni 0.70～1.00 0.85 0.9 Mo 0.90～1.25 1.0 1.05 V 0.20～0.30 0.23 0.25 W 0.80～1.20 0.98 1.02 Delta Ferrite ≤5% ≤3% ≤1% This smelting process is only applicable to the smelting of blade steel using 60tEBT electric arc furnace + 60tLF furnace + VOD / VD.

Claims

1. A smelting and casting process for blade steel, adopting the process route of "EBT arc furnace smelting + LF furnace refining + VOD / VD vacuum treatment + electrode blank casting", the mass percentage of the smelted blade steel elements is: [C] = 0.2% ~ 0.25%, [chromium] = 11.0% ~ 12.50%, [Ni] = 0.70 ~ 1.00%, [Mo] = 0.90 ~ 1.25%, [P] ≤ 0.025%, [S] ≤ 0.005%, [V] = 0.2 ~ 0.3%, [W] = 0.8 ~ 1.20%, [Si] ≤ 0.60%, [Mn] ≤ 1.00%, the balance is iron, delta ferrite ≤ 5%; the specific smelting process steps are as follows: Step 1), add 750-800kg / t of chromium-molybdenum scrap steel, 150-200kg / t of pig iron, 80-100kg / t of carbon chips, and 50kg / t of lime into the EBT electric furnace, melt and evenly temperature, take samples at a temperature of 1580-1630°C, and control the tapping temperature at 1620-1660°C; ensure that [P]≤0.003%, [C]≤0.05%; add 2.0-3.5Kg / t of aluminum blocks, 2.0-3.0Kg / t of medium carbon ferromanganese alloy, and 4.0-6.0Kg / t of lime during the tapping process; Step 2), turn to the LF furnace station, feed 3.0-5.0 m / t of aluminum wire, add 10.0-20.0 kg / t of lime and 2.0-5.0 kg / t of silicon calcium powder in batches, adjust the alloy in batches, add 6.3 kg / t of ferrosilicon, 9.9 kg / t of manganese metal, 60 kg / t of high carbon ferrochrome alloy containing 8% carbon, 150 kg / t of low carbon ferrochrome alloy containing 0.15% carbon, Add 40Kg / t of micro-carbon ferrochromium alloy with carbon 0.03%, 9Kg / t of electrolytic nickel, 17Kg / t of ferromolybdenum alloy, 5.5Kg / t of ferrovanadium alloy, and 16Kg / t of ferrotungsten alloy. Take samples at 1560-1620℃, control the temperature at 1580-1600℃, control carbon at 0.5-0.55%, and make the net space of the ladle ≥800mm. Switch to VOD / VD station. Step 3) Position the VOD / VD station, turn on the vacuum pump, and when the vacuum reaches 180mbar, start blowing oxygen from the gun. After blowing slowly for 2 to 3 minutes, gradually adjust the oxygen flow rate to 900 to 1200Nm 3 / h, set to 600m 3 After the total amount of oxygen is blown away, the oxygen concentration difference is close to zero and no longer rebounds, that is, the gun is lifted and the oxygen is stopped. During this period, the flue temperature is observed not to exceed 300℃. After stopping the oxygen, the VCD stage is entered, and the argon flow rate is set to 80-100NL / min. The excess oxygen content is used for deep decarburization. At the same time, the vacuum degree is gradually reduced. It is maintained at ≤0.7mbar for ≥20 minutes before breaking the air. After temperature measurement and sampling, the vacuum cover is dropped and covered tightly. [C]≤0.22%, stirring time≥35 minutes, online setting [H]≤1.5ppm, [O]≤6ppm, online temperature measurement between 1545 and 1560℃, and the hanging bag is transferred to the pouring station; Step 4), transfer to the pouring station, measure the temperature after the calming time ≥15 minutes, when the temperature is ≤1550℃, use the pouring method to pour into the electrode blank, use argon protection pouring during the pouring process, clean the mold wall before pouring steel, the mold temperature is ≥60℃, the pouring system and its materials are kept clean and dry, 1-1.5kg / t of low-carbon mold casting protective slag is hoisted into the mold before pouring, the ingot body pouring speed is 15Kg / s, the weight of the molten steel in the cap mouth accounts for 13% of the total weight of the steel ingot, the cap mouth pouring speed is 9Kg / s, when the cap mouth pouring height exceeds one-third, add 1.0-1.5kg / t of heating agent, add 1.0-2.0kg / t of carbonized rice husk to the cap mouth after pouring, anneal after demoulding the electrode blank, saw the cap mouth after annealing, and transfer to the electroslag process for electroslag remelting after the surface is inspected.