Smelting and continuous casting process for high-aluminum steel

Abstract

The invention relates to a high-aluminum steel smelting and continuous casting process adopting EBT electric arc furnace smelting, LF furnace refining, VD vacuum treatment and CC continuous casting, raw materials comprise pig iron, CrMo steel cuttings, carbon cuttings, high manganese, high chromium, ferromolybdenum, ferrosilicon and aluminum blocks, tapping is carried out after C and P in an electric arc furnace are removed to target values, the aluminum blocks are added into a steel ladle before tapping, the Al content is adjusted in advance, LF furnace deoxidation and alloying treatment are carried out, and the high-aluminum steel is obtained. The temperature is measured after vacuum breaking, sampling is conducted, the weak stirring time is larger than or equal to 15 min after calcium lines are fed, the VD station is switched to the CC station, a water gap of a large ladle is sealed through a long water gap, an overall submersed water gap is adopted for a tundish, molten steel in the tundish is subjected to heat preservation through a carbon-free covering agent and double-layer rice hulls, and an argon blowing stopper rod is adopted for the tundish; annealing treatment is carried out after a continuous casting billet is discharged, the method is suitable for smelting high-aluminum steel through a 60t EBT electric arc furnace, a 60t LF furnace and VOD / VD, and the problem that the Al content is unqualified after VD is solved; ca treatment prevents continuous casting flocculation flow; the molten steel utilization rate is improved through continuous casting production.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking technology and relates to a smelting and continuous casting process for high-alumina steel using EBT electric arc furnace smelting + LF furnace refining + VD vacuum treatment + CC continuous casting. Background Technology

[0002] High-aluminum steel, as a nitriding steel, is widely used in the manufacture of high-precision components such as molds, cylinder liners, gears, and high-pressure valves. Aluminum enhances the strength and toughness of the material by refining the grain size.

[0003] High-alumina steel has a relatively high aluminum content (0.85%-1.05%). Al is an easily oxidized element, which can easily lead to the following problems during smelting: the aluminum content is not up to standard after VD, and the LF needs to be returned to continue adjusting the aluminum content; a large amount of Al2O3 is generated during smelting, which can cause the molten steel to turbulently flow, which is not conducive to continuous casting production, etc.

[0004] Due to the control of Al content and the problem of turbulent flow in molten steel, the most common smelting process for high-alumina steel is currently "EBT electric arc furnace smelting + LF furnace refining + VD degassing + IC die casting". This smelting process involves single-furnace casting, but the yield is low and the labor intensity is high. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of incompatible composition and turbulent flow of molten steel after VD (Volume Deposition) of high-alumina steel, and to provide a smelting and continuous casting process for high-alumina steel that enables continuous casting production and improves the yield of high-alumina steel.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A continuous casting process for smelting high-alumina steel adopts the process route of "EBT electric arc furnace smelting + LF furnace refining + VD vacuum treatment + CC continuous casting". The mass percentage of the main elements in the smelted high-alumina steel is as follows: [C]=0.36~0.41%, [Si]=0.20~0.40%, [Mn]=0.30~0.60%, [Cr]=1.40~1.65%, [Mo]=0.18~0.25%, [Al]=0.85~1.05%, [P]≤0.015%, [S]≤0.005%, with the remainder being Fe. The specific smelting process steps are as follows: Step 1) In the EBT electric furnace, add 750-800 kg / t of CrMo steel scrap, 150-200 kg / t of pig iron, 80-100 kg / t of carbon scrap, and 40 kg / t of lime. Melt at a uniform temperature of 1580-1620℃ and take samples. Control the tapping temperature at 1630-1660℃, ensuring [P] ≤ 0.008% and [C] ≤ 0.20%. Before tapping, add 12.0-15.0 kg / t of aluminum blocks to the ladle. During tapping, add 15.0-20.0 kg / t of high-chromium, 3.0-4.0 kg / t of high-manganese, and 3.0-5.0 kg / t of lime to the ladle along with the steel flow, then transfer to the LF station. Step 2) Position the furnace at the LF furnace station, connect argon gas, add 3.0-5.0 kg / t of lime to form slag, and add calcium carbide 1-3 kg / t, carbon powder 1-3 kg / t, and aluminum powder 1-2 kg / t in batches for deoxidation; take samples at a temperature ≥1620℃, and add high chromium 13 kg / t, high manganese 2 kg / t, ferromolybdenum 1.4 kg / t, ferrosilicon 3.5 kg / t, and Al wire 3-5 m / t according to the sampling results; control the temperature at 1660-1680℃, [Al] at 1.00-1.05%, and other components meet the requirements, then transfer to the VD station; Step 3) Position the VD station, connect the argon gas, turn on the vacuum pump, control the argon gas flow rate to 40-60 NL / min, maintain at ≤0.7mbar for ≥20 minutes, then break the vacuum, measure the temperature, and take samples to confirm the composition; feed 1.5m / t of calcium wire into the molten steel at a feeding speed of 120m / min; control the argon gas flow rate to 10 NL / min, weakly stir for ≥15min, and switch to the CC station at a temperature of 1570~1580℃; Step 4) Position the tundish at the CC station. The tundish baking time is 4.5 to 6.0 hours. The ladle nozzle is sealed with a long nozzle. The tundish nozzle is an integral submerged type. The molten steel in the tundish is insulated with a carbon-free covering agent and double-layer rice husks. The tundish stopper rod has an argon blowing function. The argon flow rate is set to 0.3-0.5 NL / min. The superheat of the continuous casting tundish is 25-40℃. For φ600mm specifications, the casting speed is set to 0.22m / min. The crystallizer water flow rate is 2600L / min. The secondary cooling water flow rate is 21NL / min in zone 1, 34NL / min in zone 2, and 20NL / min in zone 3. The continuous casting billet is annealed after exiting the tundish.

[0007] The positive effects of the technical solution of the present invention are as follows: (1) The problem of unqualified Al content after VD was solved; (2) Ca treatment to prevent flocculation in continuous casting; (3) Continuous casting production improves the utilization rate of molten steel. Detailed Implementation

[0008] Example: This invention employs a process route of "60t EBT electric arc furnace smelting + 60t LF furnace refining + VD vacuum treatment + CC continuous casting" for smelting. The main element mass percentages of the smelted high-alumina steel are: [C]=0.36~0.41%, [Si]=0.20~0.40%, [Mn]=0.30~0.60%, [Cr]=1.40~1.65%, [Mo]=0.18~0.25%, [Al]=0.85~1.05%, [P]≤0.015%, [S]≤0.005%, with the remainder being Fe. The specific smelting process steps are as follows: Step 1) In the EBT electric furnace, add 750-800 kg / t of CrMo steel scrap, 150-200 kg / t of pig iron, 80-100 kg / t of carbon scrap, and 40 kg / t of lime. Melt at a homogenous temperature of 1580-1620℃ and take samples. Control the tapping temperature at 1630-1660℃. Ensure [P] ≤ 0.008% and [C] ≤ 0.20%. Before tapping, add 12.0-15.0 kg / t of aluminum blocks to the ladle. During tapping, add 15.0-20.0 kg / t of high-chromium, 3.0-4.0 kg / t of high-manganese, and 3.0-5.0 kg / t of lime to the ladle along with the steel flow, then transfer to the LF station.

[0009] Step 2) Position the furnace at the LF station, connect argon gas, add 3.0-5.0 kg / t of lime to form slag, and add 1-3 kg / t of calcium carbide, 1-3 kg / t of carbon powder, and 1-2 kg / t of aluminum powder in batches for deoxidation; take samples at a temperature ≥1620℃, and add 13 kg / t of high chromium, 2 kg / t of high manganese, 1.4 kg / t of ferromolybdenum, 3.5 kg / t of ferrosilicon, and 3-5 m / t of Al wire according to the sampling results; control the temperature at 1660-1680℃, control [Al] at 1.00-1.05%, and ensure that other components meet the requirements, then transfer to the VD station.

[0010] Step 3) Position the VD station, connect the argon gas, turn on the vacuum pump, control the argon gas flow rate to 40-60 Nl / min, maintain at ≤0.7 mbar for ≥20 minutes, then break the vacuum, measure the temperature, and take samples to confirm the composition; feed 1.5 m / t of calcium wire into the molten steel at a feeding speed of 120 m / min; control the argon gas flow rate to 10 NL / min, weak stirring time for ≥15 min, and temperature at 1570~1580℃, then switch to the CC station.

[0011] Step 4) Position the tundish at the CC station. The tundish baking time is 4.5 to 6.0 hours. The ladle nozzle is sealed with a long nozzle. The tundish nozzle is an integral submerged type. The molten steel in the tundish is insulated with a carbon-free covering agent and double-layer rice husks. The tundish stopper rod has an argon blowing function. The argon flow rate is set to 0.3-0.5 NL / min. The superheat of the continuous casting tundish is 25-40℃. For φ600mm specifications, the casting speed is set to 0.22m / min. The crystallizer water flow rate is 2600L / min. The secondary cooling water flow rate is 21NL / min in zone 1, 34NL / min in zone 2, and 20NL / min in zone 3. The continuous casting billet is annealed after exiting the tundish.

[0012] According to the smelting process of this embodiment, four groups of smelting were carried out for φ600mm high-aluminum steel. The chemical composition of the products obtained from the four groups of smelting is shown in the attached table, and all of them meet the target requirements. Appendix: Chemical composition (mass fraction) % element Target ingredient Example 1 Example 2 Example 3 Example 4 C 0.36～0.41 0.39 0.38 0.37 0.38 Si 0.20～0.40 0.35 0.33 0.34 0.36 Mn 0.30～0.60 0.47 0.46 0.44 0.45 P ≤0.015 0.010 0.009 0.009 0.010 S ≤0.005 0.002 0.002 0.002 0.002 Cr 1.40～1.65 1.56 1.52 1.54 1.58 Mo 0.18～0.25 0.22 0.21 0.21 0.22 Al 0.85～1.05 0.98 0.95 0.96 0.97 This smelting process is only applicable to smelting high-alumina steel using a 60t EBT electric arc furnace + 60t LF furnace + VOD / VD.

Claims

1. A smelting continuous casting process of high aluminum steel, adopting a process route of "EBT electric arc furnace smelting + LF furnace refining + VD vacuum treatment + CC continuous casting", the mass percentage of main elements of the smelted high aluminum steel is: [C]=0.36-0.41%, [Si]=0.20-0.40%, [Mn]=0.30-0.60%, [Cr]=1.40-1.65%, [Mo]=0.18-0.25%, [Al]=0.85-1.05%, [P]≤0.015%, [S]≤0.005%, and the rest is Fe; the specific smelting process steps are as follows: Step 1), in the EBT electric furnace, CrMo type steel scrap 750-800 kg / t, pig iron 150-200 kg / t, carbon scrap 80-100 kg / t, lime 40 kg / t are added, and the temperature is uniformly melted, and the sample is taken at 1580-1620 ℃; the tapping temperature is controlled at 1630-1660 ℃, and the [P] is ensured to be ≤0.008%, and the [C] is ensured to be ≤0.20%; before tapping, aluminum blocks 12.0-15.0 Kg / t are added into the ladle, and during the tapping process, high chromium 15.0-20.0 Kg / t, high manganese 3.0-4.0 Kg / t, and lime 3.0-5.0 Kg / t are added into the ladle along with the steel flow, and the LF station is transferred; Step 2), the LF station is positioned, argon is connected, lime 3.0-5.0 Kg / t is added for slagging, and calcium carbide 1-3 kg / t, carbon powder 1-3 kg / t, and aluminum powder 1-2 kg / t are added in batches for deoxidization; the temperature is ≥1620 ℃, the sample is taken, high chromium 13 Kg / t, high manganese 2 Kg / t, ferromolybdenum 1.4 Kg / t, ferrosilicon 3.5 Kg / t, and Al wire 3-5 m / t are added according to the sampling results; the temperature is controlled at 1660-1680 ℃, the [Al] is controlled at 1.00-1.05%, and other components meet the requirements, and the VD station is transferred; Step 3), the VD station is positioned, argon is connected, the vacuum pump is started, the argon flow is controlled at 40-60 NL / min, the pressure is kept at ≤0.7 mbar for ≥20 minutes, then the vacuum is broken, the temperature is measured, the sample is taken to confirm the components; calcium wire 1.5 m / t is fed into the molten steel, the wire feeding speed is 120 m / min, the argon flow is controlled at 10 NL / min, the weak stirring time is ≥15 min, the temperature is 1570-1580 ℃, and the CC station is transferred; Step 4), the CC station is positioned, the tundish is baked for 4.5-6.0 hours, the long nozzle seal is used for the ladle, the whole submerged nozzle is used for the tundish, the carbon-free covering agent and double-layer rice husk are used for the molten steel in the tundish, the tundish stopper has argon blowing function, the argon flow is set at 0.3-0.5 NL / min, the tundish superheat is 25-40 ℃, the φ600 mm specification is set at the drawing speed of 0.22 m / min, the crystallizer water quantity is 2600 L / min, the secondary cooling water quantity is 21 NL / min in the first zone, 34 NL / min in the second zone, and 20 NL / min in the third zone, and the continuous casting billet is annealed after being discharged. ​ ​ ​ ​