Preparation method of high-oxygen low-nitrogen welding wire steel

Abstract

The invention provides a preparation method of high-oxygen low-nitrogen welding wire steel. The preparation method comprises the following steps: S1) mixing a steel raw material and a graphite carbon block, and smelting in an electric arc furnace; refining in a ladle refining furnace; smelting in an argon-oxygen refining furnace; s2) pouring the molten steel obtained in the step S1), and processing to obtain high-oxygen pure iron; s3) mixing the high-oxygen pure iron, the nickel raw material, the molybdenum raw material and the graphite carbon block, and smelting in a vacuum induction furnace; s4) performing a carbon deoxidation process on the molten steel obtained in the step S3); and (S5) the molten steel obtained in the step (S4) is alloyed and poured, and the high-oxygen low-nitrogen welding wire steel is obtained. According to the preparation method of the high-oxygen low-nitrogen welding wire steel, high-oxygen low-impurity-content pure iron is firstly prepared through smelting of an EBT electric arc furnace, an LF refining furnace and a VOD argon oxygen refining furnace, then the nitrogen content is reduced by the level smaller than or equal to 0.001% through a vacuum induction furnace carbon deoxidation technology, and application of the high-oxygen pure iron in the new field is expanded.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgical production, and in particular to a method for preparing high-oxygen and low-nitrogen welding wire steel. Background Art

[0002] In the process of preparing the evaporator of the fourth-generation advanced nuclear energy system, in order to ensure its safety level and quality requirements, special welding wires are needed for welding, so that after welding, both the performance of the cladding metal and the smooth progress of the welding process are guaranteed. However, this type of special welding wire is blank in China and cannot be imported. The relevant imported or domestic substitutes cannot meet the welding process requirements and the performance requirements of the cladding metal. Therefore, how to obtain a special welding wire that meets the welding process requirements and the performance requirements of the cladding metal of the evaporator of the fourth-generation advanced nuclear energy system mentioned above, and fill the gaps in related fields, has become one of the problems that many front-line researchers in the industry need to solve urgently.

[0003] The main elements of special welding wire steel are shown in Table 1; it can be seen from the table that the oxygen content in special welding wire steel is 0.002-0.006%, the nitrogen content is ≤0.002%, and the content requirements of residual elements Pb, Sn, AS, Sb, Bi, V, and Nb are also very strict; that is, the chemical composition requirements of special welding wire steel are high oxygen, low nitrogen and low impurity elements. The existing smelting methods, such as ordinary pure iron as the charge, arc furnace and vacuum induction furnace cannot meet the special requirements of high oxygen, low nitrogen and low impurity elements at the same time.

[0004] Table 1 Main element range of special welding wire steel wt%

[0005]

[0006]

[0007] Therefore, it is of great significance to provide a method for preparing high-oxygen and low-nitrogen welding wire steel. Summary of the invention

[0008] The technical problem solved by the present invention is to provide a method for preparing high-oxygen and low-nitrogen welding wire steel. The welding wire steel prepared in the present application can meet the requirements of high oxygen content and low nitrogen content.

[0009] In view of this, the present application provides a method for preparing high-oxygen and low-nitrogen welding wire steel, comprising the following steps:

[0010] S1) mixing the steel raw material and the graphite carbon block and then melting them in an electric arc furnace, and the steel tapping conditions are: steel end point [C] ≥ 0.05wt%, [P] ≤ 0.002wt%, [N] ≤ 0.0035wt%;

[0011] The obtained molten steel is refined in a ladle refining furnace, and the ladle hanging conditions are: [S]≤0.005wt%, [N]≤0.005wt%, [C]: 0.20~0.70wt%;

[0012] The obtained molten steel is melted in an argon oxygen refining furnace, and the ladle conditions are: [N]≤0.003wt%, [C]≤0.03wt%, [S]≤0.002wt%, [O]: 0.06-0.10wt%, [Al]≤0.01wt%;

[0013] S2) pouring the molten steel obtained in step S1) to obtain high-oxygen pure iron after processing;

[0014] S3) mixing the high oxygen pure iron, manganese raw material, silicon raw material, molybdenum raw material, chromium raw material and graphite carbon block and then smelting them in a vacuum induction furnace;

[0015] S4) subjecting the molten steel obtained in step S3) to a carbon deoxidation process, wherein [C]: 0.02-0.05%, [O]: 0.003-0.005%, [N] ≤ 0.0015%;

[0016] S5) alloying the molten steel obtained in step S4), adding graphite carbon blocks, manganese raw materials, molybdenum raw materials, and silicon raw materials until the composition of the high-oxygen and low-nitrogen welding wire steel is met, and pouring to obtain the high-oxygen and low-nitrogen welding wire steel;

[0017] The components of the high-oxygen and low-nitrogen welding wire steel include: Cr: 2.0-5.0wt%, C: 0.05-0.3wt%, Si: 0.01-0.65wt%, Ni≤0.02%, Mo: 0.5-2.0wt%, Mn: 0.5-1.0wt%, N≤0.005wt%, P≤0.01wt%, S≤0.01wt%, O: 0.001-0.01wt%, Al≤0.01wt%, Ti≤0.005wt%, Cu≤0.05wt%, B≤0.005wt%, V≤0.05wt%, Nb≤0.005wt%, Co≤0.05wt%, Sb≤0.005wt%, Pb≤0.005wt%, Sn≤0.005wt%, Bi≤0.005wt%, As≤0.005wt%, and the balance is Fe.

[0018] Preferably, in step S1), the steel raw material comprises Anshan pure iron and selected steel grades, and the composition of the Anshan pure iron comprises: P≤0.05wt%, S≤0.003wt%, Al≤0.01wt%, Sb≤0.005wt%, Pb≤0.005wt%, Sn≤0.005wt%, Bi≤0.005wt%, As≤0.005wt%, C≤0.05wt%, Si≤0.01wt%, Mn≤0.10wt%, Fe balance; the composition of the selected steel grades comprises: Sb≤0.005wt %, Pb≤0.005wt%, Sn≤0.005wt%, Bi≤0.005wt%, As≤0.005wt%, Fe balance; the mass ratio of Anshan pure iron and selected steel grades is (1-15):1, and the carbon content is 0.2-1.5wt%, so that the composition of the mixed steel satisfies: P≤0.01wt%, S≤0.005wt%, Sb≤0.005wt%, Pb≤0.005wt%, Sn≤0.005wt%, Bi≤0.005wt%, As≤0.005wt%, Fe balance.

[0019] Preferably, during the electric arc furnace smelting process, the steel raw materials are dephosphorized after being fully melted, and the oxidation decarburization amount is ≥0.40wt%; the tapping temperature is 1600-1700°C; refined slag, lime and dolomite are added to the ladle, and then Al blocks are added with the steel flow, and a carburizer is added after tapping.

[0020] Preferably, during the refining process of the ladle refining furnace, 100-150 m of Al wire is fed / furnace, the inlet temperature is ≥1540°C, the argon flow rate is 20-60 NL / min, steel slag, refining slag and lime are added; and the ladle temperature is 1500-1600°C.

[0021] Preferably, during the argon oxygen refining furnace smelting process, when the vacuum degree is ≤200 torr, oxygen blowing is started, the oxygen pressure is 1-2 MPa, and the oxygen flow rate is 500-700 m 3 / h; when the vacuum degree drops to ≤300Pa, stop blowing oxygen; blow argon at the bottom for stirring at 10-20NL / min, stir with argon for 5-10min, break the air; add fluorite and lime to slag; evacuate the air to slag for 15-20min.

[0022] Preferably, in step S3), the carbon content is 0.02-0.05wt%, the vacuum degree is ≤2Pa when melting begins, and the melting power is 400-1000kW.

[0023] Preferably, in step S4), in the carbon deoxidation process, the decarbonization amount is ≥ 0.20wt%, the temperature of the carbon deoxidation process is ≥ 1600°C, and the time is ≥ 20min.

[0024] Preferably, in step S4), if [O] in the molten steel is ≥ 0.05wt%, the carbon deoxidation amount is recalculated and carbon deoxidation is performed again; if [O] is ≤ 0.003wt%, high-oxygen pure iron is added according to the calculated amount to make [O] in the steel 0.004-0.005wt%.

[0025] Preferably, in step S5), the alloying is started at: filling with argon gas at 2000-4000 Pa, cooling to 1550-1570°C; and the tapping temperature is 1580-1600°C.

[0026] Preferably, in step S5), the pouring is filled with argon to 3000-4000Pa.

[0027] The present application provides a method for preparing high-oxygen and low-nitrogen welding wire steel, which first prepares high-oxygen pure iron with high oxygen and low impurity content through the smelting processes of electric arc furnace melting, ladle refining furnace refining and argon oxygen refining furnace refining, and then uses the high-oxygen pure iron and other raw materials to reduce the dissolution of nitrogen and other impurities through a vacuum induction furnace, and at the same time quantitatively controls the carbon-oxygen reaction to fully denitrify it, with a nitrogen content of ≤0.001wt%, and finally prepares high-oxygen and low-nitrogen welding wire steel. DETAILED DESCRIPTION

[0028] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0029] In view of the demand for high oxygen and low nitrogen in special welding wire steel, the present application provides a high oxygen and low nitrogen welding wire steel, which first prepares high oxygen pure iron, and then uses high oxygen pure iron as raw material to ensure that its oxygen content is high and nitrogen content is low, and then the vacuum induction furnace smelting environment helps to reduce the dissolution of nitrogen and other impurities, and at the same time quantitatively controls the carbon oxygen reaction to fully denitrify it and retain a certain content, so that the prepared welding wire steel finally meets the high oxygen and low nitrogen requirements. Specifically, the present application provides a method for preparing high oxygen and low nitrogen welding wire steel, comprising the following steps:

[0030] S1) mixing the steel raw material and the graphite carbon block and then melting them in an electric arc furnace, and the steel tapping conditions are: steel end point [C] ≥ 0.05wt%, [P] ≤ 0.002wt%, [N] ≤ 0.0035wt%;

[0031] The obtained molten steel is refined in a ladle refining furnace, and the ladle hanging conditions are: [S]≤0.005wt%, [N]≤0.005wt%, [C]: 0.20~0.70wt%;

[0032] The obtained molten steel is melted in an argon oxygen refining furnace, and the ladle conditions are: [N]≤0.003wt%, [C]≤0.03wt%, [S]≤0.002wt%, [O]: 0.06-0.10wt%, [Al]≤0.01wt%;

[0033] S2) pouring the molten steel obtained in step S1) to obtain high-oxygen pure iron after processing;

[0034] S3) mixing the high oxygen pure iron, nickel raw material, molybdenum raw material and graphite carbon block and smelting them in a vacuum induction furnace;

[0035] S4) subjecting the molten steel obtained in step S3) to a carbon deoxidation process, wherein [C]: 0.02-0.05%, [O]: 0.003-0.005%, [N] ≤ 0.0015%;

[0036] S5) alloying the molten steel obtained in step S4), adding graphite carbon blocks, manganese raw materials, nickel raw materials, and molybdenum raw materials until the composition of high-oxygen and low-nitrogen welding wire steel is met, and casting to obtain high-oxygen and low-nitrogen welding wire steel; the composition of the high-oxygen and low-nitrogen welding wire steel includes: Cr: 2.0-5.0wt%, C: 0.05-0.3wt%, Si: 0.01-0.65wt%, Ni≤0.02%, Mo: 0.5-2.0wt%, Mn: 0.5-1.0wt%, N≤0.005wt%, P≤0 .01wt%, S≤0.01wt%, O:0.001~0.01wt%, Al≤0.01wt%, Ti≤0.005wt%, Cu≤0.05wt%, B≤0.005wt%, V≤0.05wt%, Nb≤0.005wt%, Co≤0.05wt%, Sb≤0.005wt%, Pb≤0.005wt%, Sn≤0.005wt%, Bi≤0.005wt%, As≤0.005wt%, and the balance is Fe.

[0037] In the preparation process of the high-oxygen and low-nitrogen welding wire steel provided in the present application, the present application first prepares high-oxygen pure iron, whose S content is ≤20ppm and O content is 0.06-0.10wt%; the high-oxygen pure iron is prepared by the EBT+LF+VOD process; in the electric arc furnace smelting (EBT), the steel raw materials and graphite carbon blocks are first mixed, melted by electricity, blown with oxygen, and dephosphorized after full melting, the temperature is ≥1540°C, the oxidation decarburization amount is ≥0.40%, and sampling is performed after the oxidation is completed. , and then tapping, the tapping conditions are: steel end point [C] ≥ 0.05%, [P] ≤ 0.002%, [N] ≤ 0.0035%, tapping temperature 1600 ~ 1700 ℃; then add refined slag, lime and dolomite into the ladle, and after a certain amount of molten steel is added into the ladle, add Al blocks along with the steel flow; after tapping, increase the Ar flow rate, and gradually add the recarburizer into the molten steel, the recarburizer is added according to [C] 0.20 ~ 0.70wt%, and then enter the LF furnace station. In this process, the steel raw materials include Anshan pure iron and selected steel grades, and the components of the Anshan pure iron include: P≤0.05wt%, S≤0.003wt%, Al≤0.01wt%, Sb≤0.005wt%, Pb≤0.005wt%, Sn≤0.005wt%, Bi≤0.005wt%, As≤0.005wt%, C≤0.05wt%, Si≤0.01wt%, Mn≤0.10wt%, and Fe balance; the components of the selected steel grades include: Sb≤0.005wt%, Pb≤0.005wt%, Sn≤0.005wt%, Bi≤0.005wt%, As≤0.005wt%, and Fe balance. The mass ratio of Anshan pure iron and selected steel is (1-15):1, and the carbon content is 0.2-1.5wt%, so that the composition of the mixed steel meets: P≤0.01wt%, S≤0.005wt%, Sb≤0.005wt%, Pb≤0.005wt%, Sn≤0.005wt%, Bi≤0.005wt%, As≤0.005wt%, Fe balance; more specifically, the carbon content is 1.1-1.3%, and an appropriate carbon content helps to maintain FeO in the slag, ensure the fluidity of the slag and effective dephosphorization. If the carbon content is too low, the chemical reaction effect is not good, and if the carbon content is too high, the molten steel will be overheated; the mass ratio of Anshan pure iron and the selected steel is (3-12):1, and more specifically, the mass ratio of Anshan pure iron and the selected steel is (5-9):1. The mass ratio of the refined slag, lime and dolomite added is 400:300:100.

[0038] According to the present invention, the steel is then put into a ladle refining furnace (IF) for refining, and the ladle hanging conditions are: [S]≤0.005wt%, [N]≤0.005wt%, [C]: 0.20-0.70wt%; specifically, in this process, the argon gas is required to be normal, 100-150m / furnace of Al wire is fed, the inlet temperature is ≥1540°C, the argon gas flow rate is 20-60NL / min, steel slag, refining slag and lime are added, electricity is supplied to raise the temperature to 1500-1600°C, the amount of desulfurizer added is 100-200kg, the refining time is >45min, and the carbon powder and white slag are reduced; the ladle hanging temperature is 1500-1600°C. Specifically, the Al wire is fed at 100-120 m / furnace, the inlet temperature is 1550-1600°C, and the argon flow rate is 30-40 NL / min; the addition ratio of the steel slag, refined slag and lime is 1:3:1, the power supply temperature is raised to 1560-1580°C, and the hanging bag temperature is 1550-1600°C.

[0039] The present invention then enters the argon oxygen refining furnace for smelting (VOD), and the bag hanging conditions are: [N]≤0.003wt%, [C]≤0.03wt%, [S]≤0.002wt%, [O]: 0.06~0.10wt%, [Al]≤0.01wt%; in this process, the carbon oxygen reaction under vacuum conditions is used to form CO bubbles for denitrification; when the vacuum degree is ≤200torr, oxygen blowing is started, the oxygen pressure is 1~2MPa, and the oxygen flow rate is 500~700m 3 / h; when the vacuum degree drops to ≤300Pa, stop blowing oxygen; bottom blowing argon stirring 10-20NL / min, argon stirring 5-10min, breaking the air; slag adding fluorite and lime; vacuuming slag, slag 15-20min. The decarburization amount of this process is 0.20-0.70%. Specifically, the oxygen flow rate is 550-650m 3 / h; the mass ratio of the fluorite to the lime is 1:10. The hanging bag temperature is 1600-1700°C, specifically, the hanging bag temperature is 1600-1640°C.

[0040] The present application then pours the obtained molten steel and obtains high-oxygen pure iron after machining; the machining can be specifically carried out by rolling or other methods, and the present application does not impose any special restrictions on this.

[0041] According to the above steel raw materials and the above smelting process, high oxygen pure iron is prepared, which has a high oxygen content, a low nitrogen content and a low impurity content; specifically, in the high oxygen pure iron, C: 0.02-0.03wt%, Cr 0.01-0.03wt%, Si0.005-0.006wt%, Mn0.02-0.03wt%, S≤0.005wt%, P≤0.002wt%, Al≤0.01wt%, V≤0.005wt%, Sb≤0.001wt%, Pb≤0.001wt%, Sn≤0.001wt%, Bi≤0.001wt%, As≤0.004wt%, Cu≤0.02wt%, O 0.06-0.10wt%, N≤0.003wt%, Nb≤0.001wt%, Co≤0.03wt%, and the balance is Fe.

[0042] In order to ensure that there is enough oxygen content for carbon-oxygen reaction denitrification, the oxygen content of high-oxygen pure iron is ≥0.06%, and the nitrogen content is ≤0.005%; because it contains 0.12-0.15% C in the smelting process of special welding wire steel, there are sufficient carbon-oxygen reaction conditions for denitrification during the VIM vacuum smelting process. When the nitrogen reaches the standard requirement of ≤0.001%, the nitrogen content of Mn and Cr added to the alloy elements subsequently must be strictly limited to avoid excessive nitrogen after addition, resulting in smelting failure. Therefore, this application first prepares high-oxygen pure iron that meets the residual element requirements to provide qualified raw materials for the preparation of special welding wire steel, and then uses a VIM vacuum induction furnace to control oxygen and nitrogen to prepare special high-oxygen and low-nitrogen welding wire steel.

[0043] The present application then mixes the above-mentioned high-oxygen pure iron, manganese raw material, molybdenum raw material, silicon raw material, chromium raw material and graphite carbon block and then performs vacuum induction furnace smelting; specifically, the manganese raw material is electrolytic manganese, wherein N≤0.002%, the molybdenum raw material is metallic molybdenum, the chromium raw material is metallic chromium, and the silicon raw material is single crystal silicon; wherein, the ultra-pure graphite carbon block is such that the carbon content is 0.02-0.05%. During the smelting process in the vacuum induction furnace, the vacuum degree is ≤2Pa when the melting starts, specifically, the vacuum degree is 1-2Pa when the melting starts; the melting power is 400-1000kW, specifically, the melting power is 600-800kW. Afterwards, sampling and analysis are performed. If [O] in the molten steel is ≥0.05wt%, the carbon deoxidation amount is recalculated and carbon deoxidation is performed again. If [O]≤0.003wt%, high-oxygen pure iron is added according to the calculated amount so that [O] in the steel is 0.004-0.005wt%.

[0044] According to the present invention, the obtained molten steel is then subjected to a carbon deoxidation process, the total oxygen content is calculated according to the [O] content in the molten steel, the carbon content required to remove 90% of the oxygen is calculated according to the reaction formula of O+C=CO, the decarbonization amount is ≥0.20%, otherwise [N] cannot meet the content requirements; the carbon deoxidation temperature is ≥1600°C, and the high-temperature stirring time is >20min; sampling analysis: when [C]: 0.02-0.05%, [O]: 0.003-0.005%, [N] ≤0.0015%, alloying is then performed. In the above process, the decarbonization amount is ≥0.05%, and the carbon deoxidation temperature is 1600-1640°C.

[0045] The nitrogen content in high-oxygen pure iron is still very high and does not meet the requirements of welding wire steel. It must be further denitrified in the vacuum induction furnace smelting. In the vacuum smelting process, the CO partial pressure denitrification formed by carbon deoxidation is a very effective denitrification method, which can significantly reduce the nitrogen content. At the same time, the oxygen content will also be greatly reduced. The speed of this process is related to the carbon-oxygen reaction time and the stirring effect. Because welding wire steel requires a certain amount of oxygen, in order to prevent oxygen and nitrogen from dropping very low at the same time, the oxygen content in the charge must be much higher than the nitrogen content to meet the necessary content of carbon deoxidation. The residual oxygen after deoxidation must be guaranteed to be within the required range of composition. This process can be accurately controlled by the oxygen content in pure iron, the carbon content (carbon deoxidation amount and residual carbon), temperature and pressure (vacuum degree) during vacuum smelting, combined with the sampling and analysis of oxygen and nitrogen in the furnace. The control of nitrogen is passive relative to oxygen, but the oxygen-nitrogen ratio (mass fraction) in pure iron is not less than 20 times, and the goal can be stably achieved through this process. As for the principle of CO partial pressure denitrification, in a vacuum induction furnace, by reducing the pressure in the furnace, that is, reducing the partial pressure of CO, the release of nitrogen from the molten metal can be promoted. This is because under vacuum conditions, the solubility of the gas is reduced, thereby reducing the solubility of nitrogen in the metal, making it easier for nitrogen to escape from the molten metal and achieve the purpose of denitrification. The prerequisite is to have CO, which is obtained by carbon-oxygen reaction.

[0046] The present application then alloys the molten steel obtained above, and then adds graphite carbon blocks, manganese raw materials, and molybdenum raw materials to the composition of the composite high-oxygen and low-nitrogen welding wire steel, and casts it to obtain high-oxygen and low-nitrogen welding wire steel; during this process, fill with argon gas at 2000-4000Pa, cool to 1550-1570℃ to stop the carbon-oxygen reaction, and then add graphite carbon blocks, electrolytic manganese, metallic molybdenum and single crystal silicon, stir and take samples for analysis, and adjust the temperature to 1580-1600℃ to tap steel after the composition meets the high-oxygen and low-nitrogen welding wire steel composition. In the above process, the argon pressure is not less than 3000Pa, otherwise it will cause a violent carbon-oxygen reaction, resulting in the loss of carbon and oxygen. During the pouring process, the pouring vacuum chamber is filled with argon at the same pressure as the alloying, 3000-4000Pa, and the flow trough is baked at a high temperature of ≥1250°C; specifically, the argon is filled to 3200-3700Pa, which must not be lower than the smelting pressure, otherwise it will cause a carbon-oxygen reaction and cause the loss of carbon and oxygen; the flow trough is baked at a high temperature of 1300-1400°C.

[0047] The preparation method of high-oxygen and low-nitrogen wire steel provided by the present invention can meet the demand for special welding wire for welding of fourth-generation advanced nuclear energy systems. High-oxygen pure iron is used as a basic raw material, and the vacuum degree, temperature and amount of carbon blocks are controlled in a vacuum induction furnace to control the carbon deoxidation reaction, thereby retaining part of the oxygen and rapidly denitrifying the wire. Finally, special welding wire steel that meets the demand for welding of fourth-generation advanced nuclear energy systems is prepared. High-oxygen pure iron can be used as a raw material for smelting ultra-low nitrogen in a vacuum induction furnace, and can make full use of the carbon deoxidation reaction to reduce nitrogen to an extremely low level, thereby expanding the application of high-oxygen pure iron in new fields, and has great advantages in the field of smelting ultra-pure secondary hardening steel and ultra-pure martensitic steel. The method provided in this application can be used to prepare high-oxygen and low-nitrogen welding wire steel by vacuum induction furnace smelting. The implementation effect is the only high-oxygen and low-nitrogen welding wire steel that has passed the welding wire steel assessment of the China Institute of Atomic Energy, meets the welding process requirements and quality requirements of GYHR-CFR-SG-S-0008 "Overall Technical Plan for the Assessment of Steam Generator Structural Materials", and meets the requirements of ASME Boiler and Pressure Vessel Code International Code II.

[0048] In order to further understand the present invention, the preparation method of the high-oxygen and low-nitrogen welding wire steel provided by the present invention is described in detail below in combination with examples. The protection scope of the present invention is not limited by the following examples.

[0049] The technical solution adopted by the present invention to solve the technical problem is: a high-oxygen and low-nitrogen welding wire steel, whose components are as follows: Cr: 2.0-5.0%, C: 0.05-0.3%, Si: 0.01-0.65%, Ni≤0.02%, Mo: 0.5-2.0%, Mn: 0.5-1.0%, N≤0.005%, P≤0.01%, S≤0.01%, O: 0.001-0.01%, Al≤0.01%, Ti≤0.005%, Cu≤0.05%, B≤0.005%, V≤0.05%, Nb≤0.005%, Co≤0.05%, Sb≤0.005%, Pb≤0.005%, Sn≤0.005%, Bi≤0.005%, As≤0.005%, and the balance is Fe and unavoidable impurities.

[0050] The steps of its preparation method are specifically as follows:

[0051] A) Preparation of high oxygen pure iron:

[0052] High oxygen pure iron is prepared by using Anshan pure iron and selected steel by EBT+LF+VOD process; wherein the components of selected Anshan pure iron DYCT~2 include: P≤0.05wt%, S≤0.003%, Al≤0.01%, Sb≤0.005%, Pb≤0.005%, Sn≤0.005%, Bi≤0.005%, As≤0.005%, C≤0.05%, Si≤0.01%, Mn≤0.10%, balance Fe; the components of selected steel include: Sb≤0.005%, Pb≤0.005%, Sn≤0.005%, Bi≤0.005%, As≤0.005%, balance Fe; the mass ratio of DYCT~2 pure iron and selected steel is 5:5, the total weight is 45 tons, and the carbon content is 1.2%;

[0053] 1) Electric arc furnace (EBT) smelting: Before charging the steel material mixed with the selected Anshan pure iron and selected steel grades, 800 kg of lime is placed on the furnace bottom, 25 tons of steel material is melted by electricity, oxygen is blown, and when more than 80% of the steel material is melted, another 20 tons of steel material is added; after the whole steel material is melted, dephosphorization is carried out at a temperature of 1550°C, and the amount of oxidative decarburization is 0.50%. After the oxidation is completed, samples are taken for analysis of C and P. The tapping conditions are as follows: the steel end point [C] ≥ 0.05%, [P] ≤ 0.002%, [N] ≤ 0.0035%, and the tapping temperature is 1660°C; Add 400kg / furnace of refined slag, 300kg / furnace of lime and 100kg / furnace of dolomite to the ladle; after a certain amount of molten steel is in the ladle, add Al blocks along with the steel flow (add 100kg / furnace of Al blocks when the steel tapping [C] is ≥ 0.06%, and add 120kg / furnace of Al blocks when the steel tapping [C] is < 0.06%); after the steel is tapped, open the flat car to the appropriate position, increase the Ar flow rate, and gradually add the recarburizer to the molten steel at the Ar gas stirring position, and add the recarburizer according to [C]: 0.50%, and then transfer to the LF furnace station;

[0054] 2) Ladle refining furnace (LF) refining: check whether Ar is normal, feed Al wire 100m / furnace, measure temperature, and require the inlet temperature to be 1600℃; add 100Kg of steel slag, 300Kg of refined slag, and 300Kg of lime, send power to raise the temperature to 1570℃, add 180Kg of desulfurizer, refine for 50min, and reduce carbon powder and white slag; hanging ladle conditions: [S]≤0.002%, [N]≤0.005%, [C]: 0.60%, hanging ladle temperature 1580℃, and then transfer to VOD station;

[0055] 3) Argon oxygen refining furnace (VOD) smelting: using carbon oxygen reaction under vacuum conditions to form CO bubbles for deoxidation, the decarburization amount is 0.50%, the furnace is evacuated, and oxygen blowing is started when the vacuum degree is ≤200torr, the oxygen pressure is 1MP, and the oxygen flow rate is 600m 3 / h, when the vacuum degree drops to ≤300Pa, the oxygen concentration difference potential E→0, stop blowing oxygen, the oxygen blowing process time is 18 minutes, bottom blowing argon stirring 15NL / min, argon stirring for 5 minutes, breaking the air, adding fluorite 80Kg and lime 800Kg for slagging, evacuating the air to slag, the slagging time is 18 minutes; breaking the air to take samples; hanging bag conditions: [N]≤0.003%, [C]: ≤0.03%, [S]≤0.002%, [O]: 0.08%, [Al]≤0.01%, temperature 1620℃;

[0056] 4) Pouring: The molten steel is poured into 3-ton ingots and sent to the 825 rolling mill for rolling. The round steel was sampled and analyzed for all components; 5 batches of high oxygen pure iron were produced according to the above method, and the specific composition of the high oxygen pure iron is shown in Table 2:

[0057] Table 2 Composition and content of high oxygen pure iron in No. 1 to 5 (wt%)

[0058] C Cr And min S P Al IT V Fe 1 0.03 0.02 0.005 0.02 0.001 0.002 0.005 0.002 0.005 Ball. 2 0.02 0.03 0.005 0.02 0.001 0.002 0.005 0.002 0.005 Ball. 3 0.03 0.01 0.005 0.03 0.001 0.0019 0.005 0.002 0.005 Ball. 4 0.02 0.01 0.005 0.02 0.001 0.0018 0.005 0.002 0.005 Ball. 5 0.02 0.02 0.005 0.02 0.001 0.002 0.005 0.002 0.005 Ball. Sat Pb Sn Bi Ace With O N Nb Co. 1 0.0005 0.0005 0.0005 0.0005 0.002 0.015 0.07 0.002 0.0005 0.01 2 0.0005 0.0005 0.0005 0.0005 0.002 0.013 0.08 0.002 0.0005 0.01 3 0.0005 0.0005 0.0005 0.0005 0.002 0.013 0.06 0.002 0.0005 0.01 4 0.0005 0.0005 0.0005 0.0005 0.002 0.016 0.09 0.002 0.0005 0.01 5 0.0005 0.0005 0.0005 0.0005 0.002 0.015 0.07 0.002 0.0005 0.01

[0059] As can be seen from Table 2, the S, Si, Mn, Al and P contents of the high oxygen pure iron prepared by the EBT+LF+VOD process are reduced, which further reduces the impurity elements of pure iron; the oxygen content of the high oxygen pure iron No. 1 to 5 meets the use requirements, creating conditions for sufficient carbon deoxidation in the subsequent vacuum induction furnace, and the contents of other elements meet the technical requirements for the preparation of high oxygen and low nitrogen welding wire steel.

[0060] B) Preparation of high oxygen and low nitrogen welding wire steel by melting in 6-ton vacuum induction furnace

[0061] The high oxygen and low nitrogen welding wire steel grade prepared in this embodiment is: SFA-5.28M ER90S-B3; it is smelted in a 6-ton Consac vacuum induction furnace; the raw materials charged into the furnace are: 5730 kg of high oxygen pure iron No. 1 prepared in step A), 7 kg of high purity graphite carbon block, 11 kg of electrolytic manganese, 60 kg of metal molybdenum, 36 kg of industrial silicon, and 156 kg of metal chromium; the specific preparation method comprises the following steps:

[0062] 5) Vacuum induction furnace smelting: 100% high oxygen pure iron, 95% metal molybdenum, 50% single crystal silicon, 95% metal chromium and 40% ultra-pure graphite carbon blocks are loaded into the furnace, with a carbon content of 0.04%. The vacuum degree is required to be ≤2Pa when melting begins, and the melting power is 600kw. The full melt sampling analysis shows: [C] 0.03%, [O] 0.0710%, [N] 0.002%;

[0063] 6) Carbon deoxidation process: According to the [O] content, the total oxygen content is calculated, and the carbon content required to remove 90% of the oxygen is calculated according to the O+C=CO reaction formula. The decarbonization amount is ≥0.05%, 3kg of carbon blocks are added, the carbon deoxidation temperature is 1620℃, and the high-temperature stirring time is greater than 20 minutes; sampling analysis: [C]: 0.03%, [O]: 0.0045%, [N]: ≤0.0011%; then the alloying process is switched;

[0064] 7) Alloying: fill with argon gas 2800Pa, cool to 1560℃ to stop carbon-oxygen reaction, add the remaining raw materials high-purity graphite carbon block, electrolytic manganese, metal molybdenum, single crystal silicon, and metal chromium to the composition control range; composition control points: [C]: 0.11%, [Mn]: 0.65%, [Si] 0.61%: [Cr] 2.62%, [Mo] 1.02%, stir for 10 minutes, take samples for full analysis; when all the components are within the specification range of Table 5, adjust the temperature to 1580-1600℃ and tap;

[0065] 8) Casting: injection molding The pouring process of steel ingot requires that the argon filling pressure of the pouring vacuum chamber be consistent with that of the melting chamber, and the argon filling pressure is 3200Pa, which cannot be lower than the melting pressure. The steel flow trough is baked at a high temperature of 1300℃ to obtain high-oxygen and low-nitrogen welding wire steel;

[0066] The specific composition of the high oxygen and low nitrogen welding wire steel prepared according to the above method is shown in Table 3;

[0067] Table 3 Specific composition of high oxygen and low nitrogen welding wire steel (wt%)

[0068]

[0069]

[0070] As can be seen from Table 3, the high oxygen and low nitrogen welding wire steel smelted by high oxygen pure iron + vacuum induction process has small fluctuation in composition, the oxygen content fully meets the material design, and the batch composition stability is high. It is currently a relatively economical and reliable method for producing high oxygen and low nitrogen welding wire steel for fourth-generation nuclear energy.

[0071] The method provided in this application can be used to prepare high-oxygen and low-nitrogen welding wire steel by vacuum induction furnace smelting. It is currently the only high-oxygen and low-nitrogen welding wire steel that has passed the evaluation of the China Institute of Atomic Energy, meets the welding process requirements and quality requirements of GYHR~CFR~SG~S~0008 "Overall Technical Plan for the Evaluation of Steam Generator Structural Materials", and meets the requirements of ASME Boiler and Pressure Vessel Code International Code II.

[0072] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0073] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing high oxygen and low nitrogen welding wire steel, comprising the following steps: S1) mixing the steel raw material and the graphite carbon block and then melting them in an electric arc furnace, and the steel tapping conditions are: steel end point [C] ≥ 0.05wt%, [P] ≤ 0.002wt%, [N] ≤ 0.0035wt%; The obtained molten steel is refined in a ladle refining furnace, and the ladle hanging conditions are: [S]≤0.005wt%, [N]≤0.005wt%, [C]: 0.20~0.70wt%; The obtained molten steel is melted in an argon oxygen refining furnace, and the ladle conditions are: [N]≤0.003wt%, [C]≤0.03wt%, [S]≤0.002wt%, [O]: 0.06-0.10wt%, [Al]≤0.01wt%; S2) pouring the molten steel obtained in step S1) to obtain high-oxygen pure iron after processing; S3) mixing the high oxygen pure iron, manganese raw material, silicon raw material, molybdenum raw material, chromium raw material and graphite carbon block and then smelting them in a vacuum induction furnace; S4) subjecting the molten steel obtained in step S3) to a carbon deoxidation process, wherein [C]: 0.02-0.05%, [O]: 0.003-0.005%, [N] ≤ 0.0015%; S5) alloying the molten steel obtained in step S4), adding graphite carbon blocks, manganese raw materials, molybdenum raw materials, and silicon raw materials until the composition of the high-oxygen and low-nitrogen welding wire steel is met, and pouring to obtain the high-oxygen and low-nitrogen welding wire steel; The components of the high-oxygen and low-nitrogen welding wire steel include: Cr: 2.0-5.0wt%, C: 0.05-0.3wt%, Si: 0.01-0.65wt%, Ni≤0.02%, Mo: 0.5-2.0wt%, Mn: 0.5-1.0wt%, N≤0.005wt%, P≤0.01wt%, S≤0.01wt%, O: 0.001-0.01wt%, Al≤0.01wt%, Ti≤0.005wt%, Cu≤0.05wt%, B≤0.005wt%, V≤0.05wt%, Nb≤0.005wt%, Co≤0.05wt%, Sb≤0.005wt%, Pb≤0.005wt%, Sn≤0.005wt%, Bi≤0.005wt%, As≤0.005wt%, and the balance is Fe.

2. The preparation method according to claim 1, characterized in that: In step S1), the steel raw material includes Anshan pure iron and selected steel grades, the composition of Anshan pure iron includes: P≤0.05wt%, S≤0.003wt%, Al≤0.01wt%, Sb≤0.005wt%, Pb≤0.005wt%, Sn≤0.005wt%, Bi≤0.005wt%, As≤0.005wt%, C≤0.05wt%, Si≤0.01wt%, Mn≤0.10wt%, Fe balance; the composition of the selected steel grades includes: Sb≤0.005wt%, Pb≤0.005wt%, Sn≤0.005wt%, Bi≤0.005wt%, As≤0.005wt%, Fe balance; the mass ratio of Anshan pure iron and selected steel grades is (1-15):1, and the carbon content is 0.2-1.5wt%, so that the composition of the mixed steel satisfies: P≤0.01wt%, S≤0.005wt%, Sb≤0.005wt%, Pb≤0.005wt%, Sn≤0.005wt%, Bi≤0.005wt%, As≤0.005wt%, Fe balance.

3. The preparation method according to claim 1, characterized in that: During the arc furnace smelting process, the steel raw materials are dephosphorized after being fully melted, and the oxidation decarburization amount is ≥0.40wt%; the tapping temperature is 1600-1700°C; refined slag, lime and dolomite are added to the ladle, and then Al blocks are added with the steel flow, and a carburizer is added after tapping.

4. The preparation method according to claim 1, characterized in that: During the refining process of the ladle refining furnace, 100-150 m of Al wire is fed into the furnace, the inlet temperature is ≥1540°C, the argon flow rate is 20-60 NL / min, and steel slag, refining slag and lime are added; the ladle temperature is 1500-1600°C.

5. The preparation method according to claim 1, characterized in that: During the argon oxygen refining furnace smelting process, when the vacuum degree is ≤200torr, oxygen blowing is started, the oxygen pressure is 1-2MPa, and the oxygen flow rate is 500-700m 3 / h; when the vacuum degree drops to ≤300Pa, stop blowing oxygen; blow argon at the bottom for stirring at 10-20NL / min, stir with argon for 5-10min, break the air; add fluorite and lime to slag; evacuate the air to slag for 15-20min.

6. The preparation method according to claim 1, characterized in that: In step S3), the carbon content is 0.02-0.05wt%, the vacuum degree is ≤2Pa when melting begins, and the melting power is 400-1000kW.

7. The preparation method according to claim 1, characterized in that: In step S4), in the carbon deoxidation process, the decarbonization amount is ≥ 0.20wt%, the temperature of the carbon deoxidation process is ≥ 1600°C, and the time is ≥ 20min.

8. The preparation method according to claim 1, characterized in that: In step S4), if [O] in the molten steel is ≥ 0.05wt%, the carbon deoxidation amount is recalculated and carbon deoxidation is performed again. If [O] is ≤ 0.003wt%, high-oxygen pure iron is added according to the calculated amount to make [O] in the steel 0.004-0.005wt%.

9. The preparation method according to claim 1, characterized in that: In step S5), the alloying is started at the following times: filling with argon gas at 2000-4000 Pa, cooling to 1550-1570°C; and the tapping temperature is 1580-1600°C.

10. The preparation method according to claim 1, characterized in that: In step S5), the pouring is filled with argon gas to 3000-4000Pa.

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