A smelting method for low-phosphorus, low-sulfur and high-nickel alloy structural steel

Abstract

The invention relates to a smelting method for low-phosphorus, low-sulfur, high-nickel alloy structural steel, which meets the production requirements of low-phosphorus, low-sulfur, high-nickel alloy structural steel and solves the technical problems of low production efficiency and high cost. The invention adopts a smelting method of selected raw materials + electric arc furnace smelting + vacuum refining + vacuum degassing + vacuum casting + electroslag remelting to control P≤0.005%; S≤0.003%, gas content [O]≤10ppm, [H]≤1.0ppm, [N]≤50ppm. The invention controls P≤0.005%; S≤0.003%, gas content [O]≤10ppm, [H]≤1.0ppm, [N]≤50ppm through the smelting methods of selected ingredients, selected lime, selected alloys, controlling phosphorus content of residual molten steel, electric arc furnace smelting, vacuum refining, vacuum degassing, vacuum casting, and electroslag remelting to meet the production requirements of low-phosphorus, low-sulfur, high-nickel alloy structural steel.

Description

Technical Field

[0001] The present invention belongs to the field of smelting technology, and in particular relates to a smelting method of low-phosphorus, low-sulfur and high-nickel alloy structural steel which meets the production requirements of low-phosphorus, low-sulfur and high-nickel alloy structural steel and solves the technical problems of low production efficiency and high cost. Background Art

[0002] At present, the domestic high nickel alloy structural steel with high requirements for low phosphorus and low sulfur is smelted by vacuum induction + vacuum consumables. Due to the small tonnage and low production efficiency of the vacuum induction furnace, the material production cycle is long and the cost is high. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a smelting method for low-phosphorus, low-sulfur, high-nickel alloy structural steel, which meets the production of low-phosphorus, low-sulfur, high-nickel alloy structural steel through electric arc furnace smelting + vacuum refining + vacuum degassing + vacuum casting + electroslag remelting, thereby achieving the purposes of high production efficiency and low cost.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A smelting method of low-phosphorus, low-sulfur, high-nickel alloy structural steel, adopting a smelting method of selecting raw materials + arc furnace smelting + vacuum refining + vacuum degassing + casting electrode blanks + electroslag remelting, controlling P≤0.005%; S≤0.003%, gas content [O]≤10ppm, [H]≤1.0ppm, [N]≤50ppm; the smelting process steps are as follows:

[0006] Step 1), select the ingredients and control the content of five harmful elements: select high-purity pig iron + high-quality scrap steel with a weight percentage of 20-80%, and the ratio of high-purity pig iron to high-quality scrap steel is 3:2; control the As≤0.006%, Sn≤0.004%, Pb≤0.003%, Sb≤0.002%, Bi≤0.002%, As+Sn+Pb+Sb+Bi≤0.02% in the raw materials according to the weight percentage to improve the purity of the molten steel; calculate the amount of molybdenum iron according to the lower and middle limits of the weight percentage of molybdenum in the composition and put it into the electric furnace together with the ingredients to remove harmful phosphorus elements as soon as possible;

[0007] Step 2), select lime to control phosphorus content in arc furnace smelting and refining process: select first-grade lime, with P≤0.008% in lime; first-grade lime is used in the whole smelting process; the usage of first-grade lime is 50~150kg / t;

[0008] Step 3), select alloys and control phosphorus content during the refining process: select metal manganese, metal chromium or low-phosphorus ferrochrome, with P ≤ 0.005% in the alloy;

[0009] Step 4), preparation before smelting, control the phosphorus content of the remaining molten steel: before smelting low-phosphorus, low-sulfur and high-nickel alloy structural steel in a basic eccentric bottom electric arc furnace, first smelt a furnace of low-phosphorus steel;

[0010] Step 5), use alkaline eccentric bottom electric arc furnace for smelting, dephosphorization, decarburization, degassing and inclusion removal, [P] ≤ 0.003% for steel tapping, and slag is strictly prohibited during the steel tapping process to prevent rephosphorization;

[0011] Step 6), vacuum refining in ladle furnace, adding 1.0-6.0 kg / t of carbon powder, calcium silicon powder and aluminum powder for deoxidation and maintaining reducing atmosphere, white slag holding time ≥ 20 minutes, temperature measurement and sampling after slag whitening, composition reaches target composition P≤0.005%, S≤0.003%;

[0012] Step 7), perform VD vacuum degassing, maintain the time at ≤0.7mbar for ≥20 minutes, and determine hydrogen and oxygen online after VD to control [H]≤0.8ppm and [O]≤5.0ppm; take a glass tube sample to analyze the nitrogen content and control [N]≤45ppm;

[0013] Step 8), casting into electrode blank;

[0014] Step 9), use gas-protected electric slag furnace for electric slag remelting, blow argon gas for protection during the remelting process, control the gas content [O] ≤ 10ppm, [H] ≤ 1.0ppm, [N] ≤ 50ppm; the slag system adopts full pre-melted slag, and the remelting process is controlled by controlling the current 8000 ~ 12500A, the voltage 40-60V to achieve the purpose of controlling the melting rate, so as to remove inclusions and gas and control the segregation of the electroslag ingot composition.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] The present invention controls P≤0.005%; S≤0.003%, gas content [O]≤10ppm, [H]≤1.0ppm, [N]≤50ppm through the smelting methods of selecting ingredients, selecting lime, selecting alloys, controlling the phosphorus content of residual molten steel, electric arc furnace smelting, vacuum refining, vacuum degassing, vacuum casting, and electroslag remelting, so as to meet the production of low-phosphorus, low-sulfur and high-nickel alloy structural steel. DETAILED DESCRIPTION

[0017] The following examples are detailed descriptions of the present invention. The examples are merely descriptions of the best mode for carrying out the present invention and do not limit the scope of the present invention in any way.

[0018] Example 1: A low-phosphorus and low-sulfur 25CrNi4MoVA smelting method, using selected raw materials + arc furnace smelting + vacuum refining + vacuum degassing + vacuum casting + electroslag remelting smelting method, controlling P≤0.005%; S≤0.003%, gas content [O]≤10ppm, [H]≤1.0ppm, [N]≤50ppm; the process steps are as follows:

[0019] Step 1), select the ingredients and control the content of five harmful elements: select high-purity pig iron + high-quality scrap steel with a weight percentage of 20-80%, and the ratio of high-purity pig iron to high-quality scrap steel is 3:2; control the As≤0.006%, Sn≤0.004%, Pb≤0.003%, Sb≤0.002%, Bi≤0.002%, As+Sn+Pb+Sb+Bi≤0.02% in the raw materials according to the weight percentage to improve the purity of the molten steel; calculate the amount of molybdenum iron according to the lower and middle limits of the weight percentage of molybdenum in the composition and put it into the electric furnace together with the ingredients to remove harmful phosphorus elements as soon as possible;

[0020] Step 2), select lime to control phosphorus content in arc furnace smelting and refining process: select first-grade lime, with P≤0.008% in lime; first-grade lime is used in the whole smelting process; the usage of first-grade lime is 50~150kg / t;

[0021] Step 3), select alloys and control phosphorus content during the refining process: select metal manganese, metal chromium or low-phosphorus ferrochrome, with P ≤ 0.005% in the alloy;

[0022] Step 4), preparation before smelting, control the phosphorus content of the remaining molten steel: before smelting low-phosphorus, low-sulfur and high-nickel alloy structural steel in a basic eccentric bottom electric arc furnace, first smelt a furnace of low-phosphorus steel;

[0023] Step 5), use alkaline eccentric bottom electric arc furnace for smelting, dephosphorization, decarburization, degassing and inclusion removal, [P] ≤ 0.003% for steel tapping, and slag is strictly prohibited during the steel tapping process to prevent rephosphorization;

[0024] Step 6), vacuum refining in ladle furnace, adding 1.0-6.0 kg / t of carbon powder, calcium silicon powder and aluminum powder for deoxidation and maintaining reducing atmosphere, white slag holding time ≥ 20 minutes, temperature measurement and sampling after slag whitening, composition reaches target composition P≤0.005%, S≤0.003%;

[0025] Step 7), perform VD vacuum degassing, maintain the time at ≤0.7mbar for ≥20 minutes, and determine hydrogen and oxygen online after VD to control [H]≤0.8ppm and [O]≤5.0ppm; take a glass tube sample to analyze the nitrogen content and control [N]≤45ppm;

[0026] Step 8), casting into electrode blank;

[0027] Step 9), use gas-protected electric slag furnace for electric slag remelting, blow argon gas for protection during the remelting process, control the gas content [O] ≤ 10ppm, [H] ≤ 1.0ppm, [N] ≤ 50ppm; the slag system adopts full pre-melted slag, and the remelting process is controlled by controlling the current 8000 ~ 12500A, the voltage 40-60V to achieve the purpose of controlling the melting rate, so as to remove inclusions and gas and control the segregation of the electroslag ingot composition.

Claims

1. A method for smelting low-phosphorus, low-sulfur, high-nickel alloy structural steel, characterized in that: The smelting method is selected raw materials + electric arc furnace smelting + vacuum refining + vacuum degassing + casting electrode blank + electroslag remelting, and P is controlled to be ≤ 0.005%; S is ≤ 0.003%, and the gas content [O] is ≤ 10ppm, [H] is ≤ 1.0ppm, and [N] is ≤ 50ppm. The smelting process steps are as follows: Step 1), select the ingredients and control the content of five harmful elements: select high-purity pig iron + high-quality scrap steel with a weight percentage of 20-80%, and the ratio of high-purity pig iron to high-quality scrap steel is 3:2; control the As≤0.006%, Sn≤0.004%, Pb≤0.003%, Sb≤0.002%, Bi≤0.002%, As+Sn+Pb+Sb+Bi≤0.02% in the raw materials according to the weight percentage to improve the purity of the molten steel; calculate the amount of molybdenum iron according to the lower and middle limits of the weight percentage of molybdenum in the composition and put it into the electric furnace together with the ingredients to remove harmful phosphorus elements as soon as possible; Step 2), select lime to control phosphorus content in arc furnace smelting and refining process: select first-grade lime, with P≤0.008% in lime; first-grade lime is used in the whole smelting process; the usage of first-grade lime is 50~150kg / t; Step 3), select alloys and control phosphorus content during the refining process: select metal manganese, metal chromium or low-phosphorus ferrochrome, with P ≤ 0.005% in the alloy; Step 4), preparation before smelting, control the phosphorus content of the remaining molten steel: before smelting low-phosphorus, low-sulfur and high-nickel alloy structural steel in a basic eccentric bottom electric arc furnace, first smelt a furnace of low-phosphorus steel; Step 5), use alkaline eccentric bottom electric arc furnace for smelting, dephosphorization, decarburization, degassing and inclusion removal, [P] ≤ 0.003% for steel tapping, and slag is strictly prohibited during the steel tapping process to prevent rephosphorization; Step 6), vacuum refining in ladle furnace, adding 1.0-6.0 kg / t of carbon powder, calcium silicon powder and aluminum powder for deoxidation and maintaining reducing atmosphere, white slag holding time ≥ 20 minutes, temperature measurement and sampling after slag whitening, composition reaches target composition P≤0.005%, S≤0.003%; Step 7), perform VD vacuum degassing, maintain the time at ≤0.7mbar for ≥20 minutes, and determine hydrogen and oxygen online after VD to control [H]≤0.8ppm and [O]≤5.0ppm; take a glass tube sample to analyze the nitrogen content and control [N]≤45ppm; Step 8), casting into electrode blank; Step 9), use gas-protected electric slag furnace for electric slag remelting, blow argon gas for protection during the remelting process, control the gas content [O] ≤ 10ppm, [H] ≤ 1.0ppm, [N] ≤ 50ppm; the slag system adopts full pre-melted slag, and the remelting process is controlled by controlling the current 8000 ~ 12500A, the voltage 40-60V to achieve the purpose of controlling the melting rate, so as to remove inclusions and gas and control the segregation of the electroslag ingot composition.