High-nickel ultralow-phosphorus special welding steel and production process thereof

Abstract

The invention belongs to the technical field of steel and iron smelting, and particularly relates to high-nickel ultralow-phosphorus special welding steel and a production process thereof, the process comprises the steps of molten iron pretreatment, converter smelting, furnace rear slagging-off, LF refining, continuous casting and the like, the phosphorus content is directly reduced to 0.003% or below, the step of LF refining and temperature increasing in a traditional process is omitted, and the production period is shortened; and meanwhile, the components are controlled through the low-phosphorus alloy and the low-aluminum low-nitrogen titanium wire, and accurate control over the content of Ni being 2.35%-2.50%, the content of P being smaller than or equal to 0.005% and the content of N being smaller than or equal to 60 ppm is achieved. The prepared high-nickel ultralow-phosphorus special welding steel is stable in component, meets user requirements, can be used in the high-end fields of aerospace, ocean engineering and the like, and solves the problem that high-end welding material import depends on the high-end welding material import.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of steel smelting, and particularly relates to a high-nickel ultra-low-phosphorus special welding steel and a production process thereof. BACKGROUND

[0002] In the current rapid development of high-end manufacturing, the performance requirements for welding steel are increasingly stringent. Conventional welding steels generally have problems of high phosphorus content (usually higher than 0.010%) and low nickel content (generally lower than 1.0%), which leads to poor low-temperature toughness and insufficient corrosion resistance of the material, and a large amount of smoke and spatter is easily generated during the welding process, and the purity of the weld metal is difficult to meet the use requirements in extreme environments.

[0003] At present, the high-nickel ultra-low-phosphorus special welding steel required in high-end fields has long relied on imports, and the existing production process in China has the following core problems: first, it is difficult to control the ultra-low phosphorus (P≤0.005%), and the traditional process needs multiple refining and temperature raising, and if the temperature control is not proper and the slag on the surface of the molten steel is not cleaned, the phosphorus element is easily returned; second, it is difficult to achieve the coordination of high-nickel composition and ultra-low phosphorus requirements, and impurities are easily introduced during the alloy adding process; third, the production cycle is long, and the conventional process needs converter smelting→LF refining and temperature raising→slag cleaning→secondary refining, which is complicated and high in energy consumption. SUMMARY

[0004] The present application proposes a special welding steel production process capable of stably controlling the ultra-low phosphorus content and ensuring the uniformity of high-nickel composition to solve the problem of dependence on imports of high-end welding materials in China, aiming at the technical problems of difficult control of ultra-low phosphorus and long production cycle of the existing production process for high-nickel ultra-low-phosphorus special welding steel in China.

[0005] To achieve the above-mentioned purposes, the technical solution adopted by the present application is as follows: A high-nickel ultra-low-phosphorus special welding steel, the chemical composition of which is as follows in terms of mass percentage: C 0.05%-0.08%, Si 0.55%-0.70%, Mn 1.35%-1.50%, P≤0.005%, S≤0.010%, Ni 2.35%-2.50%, Cr≤0.05%, Ti 0.04%-0.07%, Mo 0.06%-0.09%, N≤60ppm, and the rest is Fe and inevitable impurities.

[0006] As a preferred option, the chemical composition is as follows in terms of mass percentage: C 0.058%-0.062%, Si 0.60%-0.65%, Mn 1.40%-1.42%, P≤0.004%, S≤0.005%, Ni 2.40%-2.45%, Cr≤0.02%, Ti 0.060%-0.065%, Mo 0.07%-0.082%, N≤40ppm, and the rest is Fe and inevitable impurities.

[0007] The application also provides a production process of the high-nickel ultra-low-phosphorus special welding steel. (1) Pretreatment of molten iron: KR desulfurization process is adopted, and the sulfur content of the treated molten iron is less than or equal to 0.005%; (2) Converter smelting: the phosphorus content at the end point of the converter is less than or equal to 0.012%, and the end point temperature is greater than or equal to 1610 DEG C; the tapping is performed by using a stopper and a slide plate, and when the tapping amount reaches 30 tons, 800 kg of lime and 800 kg of oxidizing slag dephosphorization agent are added; after the tapping, the ladle is stirred by bottom blowing argon at 400-500 NL / min for 1-2 minutes, and then 100 kg of lime thick slag is added; (3) Post-furnace slagging: the ladle car is opened to the ladle position, and the floating slag on the surface of the molten iron is mechanically removed to ensure that the surface of the molten iron has no obvious floating slag; (4) LF refining: after the slagging treatment, the molten iron is lifted to the LF furnace for refining, 800-900 kg of lime and 200-300 kg of fluorite are added to form slag, so that the refining slag has a certain fluidity and the ability to absorb inclusions, the first power supply is performed for 15 minutes, the phosphorus content in the primary refined molten iron is detected, and low-phosphorus primary refined molten iron is obtained; when the phosphorus content is less than or equal to 0.003%, a low-phosphorus alloy is added to adjust the composition, and at the end of the refining, a low-aluminum and low-nitrogen titanium wire is fed, and soft blowing is performed for 10-15 minutes, so that the low-phosphorus molten iron is finally obtained; (5) Continuous casting: the molten iron is lifted to the continuous casting machine for casting, and the overheat degree during casting is 15-25 DEG C, and the pulling speed is 0.8-1.0 m / min.

[0008] Preferably, the oxidizing slag dephosphorization agent in step (2) is composed of CaO and FeO in a mass ratio of 3.8:1, wherein CaO provides a high alkalinity environment, FeO acts as an oxidizing agent, and the ratio of 3.8:1 can maximize the improvement of the dephosphorization reaction kinetics; if the phosphorus content at the end point of the converter is higher than 0.012%, the ratio of lime to oxidizing slag dephosphorization agent is adjusted to 1.2:1 to further enhance the ability of the slag phase to absorb phosphorus and avoid the return of phosphorus.

[0009] Preferably, the phosphorus content of the low-phosphorus alloy in step (4) is less than or equal to 0.003%, the titanium content of the low-aluminum and low-nitrogen titanium wire is greater than or equal to 65%, and the nitrogen content is less than or equal to 200 ppm.

[0010] Preferably, the low-phosphorus alloy in step (4) is micro-aluminum ferrosilicon, metal manganese, nickel plate and molybdenum iron.

[0011] Compared with the prior art, the application has the advantages and positive effects that: (1) The production process of the high-nickel ultra-low-phosphorus special welding steel is through the synergistic process of "converter endpoint phosphorus control + dephosphorizing agent added during tapping + bottom argon blowing stirring", dephosphorizing agent is added during tapping, and the phosphorus content is reduced to below 0.003% during the tapping stage of the converter by using the stirring dephosphorizing technology under the tapping kinetic condition, so that the problem of phosphorus return in the traditional process is solved.

[0012] (2) The step of "first LF refining and temperature raising after converter tapping and then slagging" is omitted, and the production cycle is shortened, and the energy consumption and alloy loss are reduced; low-phosphorus alloy and low-aluminum low-nitrogen titanium wire are used, combined with KR desulfurization and double-slagging operation, to realize accurate control of S≤0.010%, N≤60ppm, and Ni 2.35%-2.50%, and to ensure the stability of high-nickel and ultra-low-phosphorus composition. The production process provides reliable process guarantee for realizing ultra-low-phosphorus steel smelting and improving the continuous casting production furnace number, and effectively solves the industry problem of difficult smelting of such steel. DETAILED DESCRIPTION

[0013] In order to better understand the present application, the following will be specifically described in combination with examples. Example 1

[0014] A production process of a high-nickel ultra-low-phosphorus special welding steel, comprising the following steps: (1) Hot metal pretreatment: KR stirring desulfurization is used, and the final sulfur content of the hot metal after treatment is 0.0009%, and there is no floating slag on the surface after slagging; (2) Converter smelting: through converter smelting, the final phosphorus content is controlled to be 0.0102%, and the final temperature is 1622℃; 800kg of lime and 800kg of dephosphorizing agent of oxidizing slag are added when 30 tons of molten steel is tapped; after tapping, argon blowing is performed at 450NL / min, and after stirring for 1.5 minutes, 100kg of lime thick slag is added; the phosphorus content is detected to be 0.0026% by sampling at the argon blowing station; (3) Post-converter slagging: the ladle car is opened to the ladle position for slagging operation, and there is no floating slag on the surface of the molten steel after mechanical slagging; (4) LF refining: after slagging treatment, the ladle is lifted to the LF refining, 800kg of lime and 230kg of fluorite are added for slagging, and power is supplied for 15 minutes, and the phosphorus content is detected by sampling to obtain low-phosphorus primary refined molten steel with a phosphorus content of 0.0028%; Adding micro-aluminum silicon iron (1.04t), metal manganese (1.64t), molybdenum iron (0.16t), nickel plate (2.81t); after refining, feeding titanium wire 0.17t, soft blowing for 12 minutes; taking the molten steel and detecting the composition, the results are: C 0.059%, Si 0.61%, Mn 1.40%, P 0.0037%, S 0.0043%, Ni 2.42%, Ti 0.065%, Cr 0.015%, Mo 0.082%, N 0.0037%; (5) Continuous casting: after the soft blowing of the LF refining furnace is finished, the continuous casting machine is hoisted for casting, and the stopper is stable during the continuous casting and pouring process. The overheat degree of casting is 20℃, the casting speed is 0.9m / min, and the casting blank is defect-free. Example 2

[0015] A production process of a high-nickel ultra-low-phosphorus special welding steel, comprising the following steps: (1) Hot metal pretreatment: KR stirring desulfurization is adopted, and the sulfur content of the final hot metal after treatment is 0.0010%, and there is no scum on the surface after slagging; (2) Converter smelting: through converter smelting, the end point phosphorus content is controlled to be 0.0098%, and the end point temperature is 1617℃; 800kg of lime and 800kg of oxidizing slag dephosphorizing agent are added when 30 tons of molten steel is tapped; after tapping, argon blowing is performed at 480NL / min for 1.5 minutes, and then 100kg of lime thick slag is added; sampling at the argon blowing station detects that the phosphorus content is 0.0028%; (3) Post-furnace slagging: the ladle car is opened to the ladle position for slagging operation, and there is no scum on the surface of the molten steel after mechanical slagging; (4) LF refining: after the slagging treatment, the ladle is hoisted to the LF refining, 800kg of lime and 230kg of fluorite are added, and power is supplied for 15 minutes; adding micro-aluminum silicon iron (1.0t), metal manganese (1.65t), molybdenum iron (0.16t), nickel plate (2.82t); feeding titanium wire 0.165t; soft blowing for 13 minutes; taking the molten steel and detecting the composition, the results are: C 0.061%, Si 0.60%, Mn 1.41%, P 0.0039%, S 0.0041%, Ni 2.43%, Ti 0.060%, Cr 0.018%, Mo 0.080%, N 0.0035%; (5) Continuous casting: after the soft blowing of the LF refining furnace is finished, the continuous casting machine is hoisted for casting, and the stopper is stable during the continuous casting and pouring process. The overheat degree of casting is 22℃, the casting speed is 0.85m / min, and the casting blank is defect-free.

[0016] The above merely describes preferred embodiments of the present application, but is not intended to limit the present application to other forms, any person skilled in the art can make changes or modifications to the above disclosed technical contents into equivalent embodiments with equivalent changes, and apply to other fields, but any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application without departing from the technical solution content of the present application still belongs to the protection scope of the present application technical solution.

Claims

1. A high nickel ultra-low phosphorus specialty welding steel, characterized in that: The chemical composition in terms of mass percentage is: C 0.05%-0.08%, Si 0.55%-0.70%, Mn 1.35%-1.50%, P≤0.005%, S≤0.010%, Ni 2.35%-2.50%, Cr≤0.05%, Ti 0.04%-0.07%, Mo 0.06%-0.09%, N≤60ppm, and the rest is Fe and inevitable impurities.

2. The high nickel ultra-low phosphorus specialty welding steel according to claim 1, characterized in that: The chemical composition in terms of mass percentage is: C 0.058%-0.062%, Si 0.60%-0.65%, Mn 1.40%-1.42%, P≤0.004%, S≤0.005%, Ni 2.40%-2.45%, Cr≤0.02%, Ti 0.060%-0.065%, Mo 0.07%-0.082%, N≤40ppm, and the rest is Fe and inevitable impurities.

3. A production process of high nickel ultra-low phosphorus special welding steel, characterized in that, The method comprises the following steps: (1) Hot metal pretreatment: KR desulfurization process is adopted, and the sulfur content of the treated hot metal is ≤0.005%; (2) Converter smelting: the phosphorus content at the end point of the converter is ≤0.012%, and the end point temperature is ≥1610℃; the tapping is performed by using a stopper and a slide plate, 800kg of lime and 800kg of oxidizing slag dephosphorization agent are added when the tapping amount reaches 30 tons; after the tapping, the ladle is stirred by bottom blowing argon gas at 400-500NL / min for 1-2 minutes, and then 100kg of lime thick slag is added; (3) Post-converter slagging: the ladle car is opened to the ladle position, and the mechanical slagging is performed on the surface of the molten steel to ensure that the surface of the molten steel has no obvious floating slag; (4) LF refining: after the slagging treatment, the molten steel is lifted to the LF furnace for refining, 800-900kg of lime and 200-300kg of fluorite are added for slagging, the first power feeding is performed for 15 minutes, the phosphorus content in the primary refined molten steel is detected, the low-phosphorus alloy is added for adjusting the composition when the phosphorus content is ≤0.003%, and the low-aluminum and low-nitrogen titanium wire is fed at the end of the refining, and soft blowing is performed for 10-15 minutes; (5) Continuous casting: the molten steel is lifted to the continuous casting machine for casting, the overheat degree is 15-25℃, and the casting speed is 0.8-1.0m / min.

4. The process for producing high nickel ultra-low phosphorus special welding steel according to claim 3, characterized in that: The oxidizing slag dephosphorization agent in step (2) is composed of CaO and FeO in a mass ratio of 3.8:1; if the phosphorus content at the end point of the converter is higher than 0.012%, the ratio of lime to oxidizing slag dephosphorization agent is adjusted to 1.2:

1.

5. The process for producing high nickel ultra-low phosphorus special welding steel according to claim 4, characterized in that: The low-phosphorus alloy in step (4) has a phosphorus content of ≤0.003%, the low-aluminum and low-nitrogen titanium wire has a titanium content of ≥65% and a nitrogen content of ≤200ppm.

6. The process for producing high nickel ultra-low phosphorus special welding steel according to claim 5, characterized in that: The low-phosphorus alloy in step (4) is micro-aluminum ferrosilicon, metal manganese, nickel plate and molybdenum iron.