Production method of 600MPa-grade low-splashing rare earth welding wire steel

Abstract

The invention discloses a production method of 600MPa-grade low-splashing rare earth welding wire steel, which is characterized by comprising the steps of molten iron desulfurization, converter smelting, external refining and vacuum treatment of an RH-continuous casting machine, and rare earth alloy is added at an RH vacuum treatment station. The 600MPa-grade low-splashing rare earth welding wire steel steelmaking production technology is developed for splashing generated in the welding process of welding wires, the splashing rate in the welding process is reduced, and the product quality is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and particularly relates to a production method of a 600 MPa grade rare earth welding wire steel with low spatter. Background Art

[0002] Welding spatter refers to the situation where, during the welding process, the molten droplets do not normally transfer into the molten pool and fall outside the molten pool. Welding spatter seriously affects the welding quality. It not only consumes a large amount of manpower and material resources to remove the spatter particles, but also affects the welding efficiency and the properties of the steel. There are many factors affecting welding spatter, such as welding parameters (welding current, voltage, dry elongation), shielding gas, surrounding environment, base material, etc.

[0003] The amount of welding spatter decreases with the increase of the contents of Si, Ti, and Mn and the decrease of the contents of C and Al, which is related to the short-circuit frequency.

[0004] In the initial stage of molten droplet formation, when it falls into a special liquid and is rapidly cooled, analysis of the molten droplet shows that there is a large amount of oxygen element on the surface of the molten droplet. Since the radius of the oxygen ion is larger than that of the positive ion, when forming the melt, the surface is mainly occupied by oxygen ions. The more oxygen ions on the surface of the melt, the greater the surface tension of the melt. The thermal conductivity of ions such as K and Na is much lower than that of CO2 gas, and the thermal conductivity of the arc column and the surrounding gas is much lower. Therefore, the heat exchange conditions between the arc column and the surrounding gas are changed, greatly reducing the radial heat dissipation, promoting the expansion of the arc column. So, in terms of the arc shape, it shows a larger arc range, arc root expansion, uniform heat distribution, refined molten droplets, easy detachment from the welding wire, increased molten droplet transfer frequency, reduced spatter, and also reduced large particle spatter. Elements such as K and Na are surface-active elements that can effectively reduce the surface tension of the molten droplet, while basic oxides such as CaO, MgO, and BaO will increase the surface tension. Therefore, to reduce large particle welding spatter, it is necessary to reduce the inclusion content in the steel. Summary of the Invention

[0005] The purpose of the present invention is to provide a production method of a 600 MPa grade rare earth welding wire steel with low spatter, reducing the spatter rate during the welding process and improving the product quality.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A production method of a 600 MPa grade rare earth welding wire steel of the present invention includes: hot metal desulfurization KR - converter smelting LD - ladle furnace refining LF - vacuum treatment RH - continuous caster CC, and the rare earth alloy is added at the RH vacuum treatment station; wherein:

[0008] Hot metal desulfurization, after hot metal desulfurization, the sulfur content is controlled below 0.005%, and at the same time, for the scrap steel used in converter smelting, in-plant recycled scrap steel is adopted to control the sulfur element input from the raw materials;

[0009] The carbon content at the end of converter smelting is controlled at 0.03% ≤ C ≤ 0.05%, and the end temperature is controlled at T ≥ 1620°C;

[0010] In the LF process, aluminum-containing slag formers are not applicable. Calcium carbide and silicon carbide are used for deoxidation, and ferrosilicon powder is added to assist in deoxidation. The refining basicity R ≤ 2.0 is ensured. At the same time, the Al content in the refining slag is controlled at ≤ 6%. The refining white slag time T ≥ 8 min is required, and the off-position carbon in refining is controlled between 0.05% - 0.06%. The temperature supplied by LF to RH is T ≥ 1610°C;

[0011] During the RH vacuum treatment process, the vacuum treatment time T ≥ 20 min, and stepped vacuum degree control is adopted; After RH is in place, the first-stage treatment starts. All rare earth alloys are added according to the required rare earth content. After addition, vacuum circulation is carried out. After the heat treatment time node, the second-stage treatment starts, with vacuum circulation. After the time node, the vacuum-breaking negative pressure soft blowing operation is carried out; The soft blowing operation starts. After the soft blowing ends, continuous casting is carried out for pouring;

[0012] During the continuous casting process, oxygen burning operation in the tundish is prohibited to ensure self-opening. A tundish covering agent is used in the tundish, and full protection is carried out from the tundish to the mold to reduce the secondary oxidation of molten steel.

[0013] Furthermore, for hot metal desulfurization, the stirring head speed is controlled at 90 - 110 revolutions per minute, the desulfurizing agent is 5 ± 0.5 Kg / t, and the stirring time is greater than 15 min.

[0014] Furthermore, during the converter smelting process, supplementary blowing operation is prohibited. Argon blowing is carried out throughout the bottom blowing of the converter. The argon blowing volume from the start of oxygen supply to 8 minutes of oxygen supply is 0.05 - 0.08 Nm 3 / min·t, and the argon blowing volume from 8 minutes of oxygen supply to tapping is 0.08 - 0.10 Nm 3 / min·t.

[0015] Furthermore, during tapping, SiMn alloy deoxidation alloying operation is adopted, and lime is added to the top slag, with the lime addition amount being 3.0 - 3.5 kg / t.

[0016] Furthermore, the component content of the off-position furnace slag in terms of mass percentage is required: Ca: 45 - 50%, Si: 25 - 35%, MgO: 8.0 - 15.0%, Al 2 O 3 ≤ 6.0%, TFe + MnO ≤ 1.5%.

[0017] Furthermore, during the RH vacuum treatment process: A rare earth alloy with a Ce content of 30% is added, with an addition amount of 17 kg. After addition, the vacuum degree is 8 - 12 KPa, and the circulating gas flow rate is 120 - 160 Nm 3 / h, the cycle time T = 10 min. After the heat treatment time node, the second-stage treatment starts. The vacuum degree is 0.25 - 0.30 KPa, and the circulating gas flow rate is 120 - 140 Nm 3 / h, the cycle time T ≥ 10 min. After the time node, a vacuum-breaking negative pressure soft blowing operation is carried out.

[0018] Furthermore, the soft blowing argon gas flow rate is 25 NL / min, and the soft blowing time T ≥ 15 min.

[0019] Furthermore, during the continuous casting process, the tundish superheat is controlled at 35°C ± 5°C; the immersion nozzle insertion depth is 70 - 90 mm, and the steel passing amount in the mold ≤ 5000 tons.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are:

[0021] By using the method of the present invention to produce low-spatter rare earth gas shielded welding wire steel, the contents of Ca and Al in the steel are significantly reduced, the quantity and size statistics of inclusions are significantly reduced, and the welding spatter rate of the product is reduced. Specific embodiments

[0022] The composition of the low-spatter rare earth welding wire steel produced by the inventive method is shown in Table 1. The main purpose is not to add elements such as Ti to control welding spatter, reduce the production alloy cost. Through vacuum treatment and addition of rare earth elements, the rare earth and Ca-Al inclusions in the steel form composite rare earth calcium aluminate inclusions, which float and are removed through the vacuum process, controlling the formation and retention of Ca and Al inclusions in the steel, effectively reducing the contents of Ca and Al in the steel, and reducing the spatter rate.

[0023] Table 1 Composition of rare earth gas shielded welding wire steel

[0024]

[0025] Production process route plan:

[0026] Hot metal desulfurization (KR) - converter smelting (LD) - secondary refining (LF) - vacuum treatment (RH) - continuous caster (CC). The rare earth alloy is added at the RH vacuum treatment station.

[0027] Production process parameter plan:

[0028] Hot metal desulfurization. After hot metal desulfurization, the sulfur content is controlled below 0.005%. At the same time, for the scrap steel used in converter smelting, in-plant recycled scrap steel is adopted to control the sulfur element input from raw materials.

[0029] The end-point control of converter smelting: the carbon content is 0.03% ≤ C ≤ 0.05%, and the end-point temperature control T ≥ 1620°C.

[0030] The LF process does not use aluminum-containing slag formers. Calcium carbide and silicon carbide are used for deoxidation, and ferrosilicon powder is added to assist in deoxidation. Ensure that the refining basicity R ≤ 2.0. At the same time, control the Al content in the refining slag ≤ 6%. It is required that the refining white slag time T ≥ 8 min, and the off-position carbon in refining is controlled between 0.05% - 0.06%. The LF supply temperature for RH is T ≥ 1610 °C.

[0031] During the RH vacuum treatment process, the vacuum treatment time T ≥ 20 min, and stepped vacuum degree control is adopted. After RH is in place, the first-stage heat treatment starts. All rare earth alloys are added according to the required rare earth content. After addition, vacuum circulation is carried out. After the heat treatment time node, the second-stage treatment starts, with vacuum circulation. After the time node, the operation of breaking vacuum and soft blowing under negative pressure is carried out. Start the soft blowing operation. After the soft blowing ends, connect to the continuous casting for pouring.

[0032] Oxygen burning operation is prohibited in the tundish of the continuous casting process to ensure self-opening. The tundish is covered with a tundish covering agent, and the whole process from the tundish to the mold is protected to reduce the secondary oxidation of the molten steel.

[0033] In order to more clearly understand the above aspects, features, and advantages of the present invention, the present invention will be further described in detail below in conjunction with specific embodiments.

[0034] This embodiment uses the KR-LD-LF-RH-CC (vacuum treatment) process route to produce low-spatter rare earth welding wire steel.

[0035] For hot metal desulfurization, control the stirring head speed at 90 - 110 revolutions per minute, the desulfurizer is about 5 Kg / t, the stirring time is greater than 15 min, and the sulfur content after hot metal desulfurization is controlled below 0.005%.

[0036] At the end of converter smelting, control the carbon content at 0.03% ≤ C ≤ 0.05%, and the end point temperature is controlled at T ≥ 1620 °C. During the converter smelting process, it is required to prohibit re-blowing operations. The bottom blowing of the converter adopts full-process argon blowing. From the start of oxygen supply to 8 minutes of oxygen supply, the argon blowing volume is 0.05 - 0.08 Nm 3 / min·t. From 8 minutes of oxygen supply to tapping, the argon blowing volume is 0.08 - 0.10 Nm 3 / min·t. For tapping, SiMn alloy deoxidation alloying operation is adopted, and lime top slag is added. The lime addition amount is 3.0 - 3.5 kg / t.

[0037] The LF process does not use aluminum-containing slag formers. Calcium carbide and silicon carbide are used for deoxidation, and ferrosilicon powder is added to assist in deoxidation. Ensure that the refining basicity R ≤ 2.0. At the same time, control the Al content in the refining slag ≤ 6%. It is required that the refining white slag time T ≥ 8 min, and the off-position carbon in refining is controlled between 0.05% - 0.06%. The LF supply temperature for RH is T ≥ 1610 °C. It is required that the component content of the off-position furnace slag is Ca: 45 - 50%, Si: 25 - 35%, MgO: 8.0 - 15.0%, Al2 O 3 ≤6.0%, TFe + MnO ≤ 1.5%.

[0038] During the RH vacuum treatment process, the vacuum treatment time T ≥ 20 min, and stepped vacuum degree control is adopted. After the RH is in place, the first-stage heat treatment is started. All rare earth alloys are added according to the required rare earth content. A rare earth alloy with a Ce content of 30% is added, and the addition amount is 17 kg. After the addition, the vacuum degree is 10 KPa, and the circulating gas flow rate is 120 - 160 Nm 3 / h, the circulation time T = 10 min. After the heat treatment time node, the second-stage treatment is started. The vacuum degree is 0.25 - 0.30 KPa, and the circulating gas flow rate is 120 - 140 Nm 3 / h, the circulation time T ≥ 10 min. After the time node, a vacuum-breaking negative pressure soft blowing operation is adopted. The soft blowing argon gas flow rate is 25 NL / min, the soft blowing time T ≥ 15 min. After the soft blowing is completed, continuous casting is carried out for pouring.

[0039] During the continuous casting process, oxygen burning operation in the tundish is prohibited to ensure self-opening. In the tundish, tundish covering agents are used, high-quality refractories and three major continuous casting parts (nozzle, seat brick, stopper rod) are used. During the continuous casting process, protective casting is carried out to avoid secondary oxidation of the molten steel, and the superheat of the tundish during continuous casting is controlled at 35°C ± 5°C. The immersion depth of the submerged nozzle is 70 - 90 mm, and the molten steel throughput of the mold ≤ 5000 tons.

[0040] Comparing the production data of the converter - LF refining - continuous casting (without vacuum treatment) using the original production process with the production data of the low - splash rare earth gas - shielded welding wire steel produced by the method of the present invention, the Ca and Al contents in the steel are significantly reduced, the statistics of the number and size of inclusions are significantly reduced, and the welding spatter rate of the product is reduced.

[0041] Table 2 Comparison of Ca and Al content test values

[0042]

[0043] Table 3 Comparison of inclusion data

[0044]

[0045] Table 4 Spatter rate

[0046]

[0047]

[0048] For the low - splash rare earth welding wire steel produced by the method of the present invention, the content of calcium, the main element causing spatter in the steel, is significantly reduced, the comparison of the number and size of inclusions is significantly improved, and at the same time, the spatter rate is significantly reduced. The production effect of the method of the present invention is obvious.

[0049] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the spirit of the present invention's design, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing 600MPa grade low spatter rare earth welding wire steel, characterized in that: include: Hot metal desulfurization - converter smelting - refining outside the furnace - vacuum treatment RH - continuous casting machine, the rare earth alloy is added at the RH vacuum treatment station; among them: Hot metal desulfurization: the sulfur content of hot metal after desulfurization is controlled to below 0.005%. At the same time, the scrap steel for converter smelting is recycled within the factory to control the amount of sulfur brought into the raw materials. The end point of converter smelting is controlled at carbon content 0.03%≤C≤0.05%, and the end point temperature is controlled at T≥1620℃; The LF process is not suitable for aluminum-containing slag-making agents. Calcium carbide and silicon carbide are used for deoxidation, and ferrosilicon powder is added to assist deoxidation to ensure that the refining basicity R≤2.0, and the Al content in the refining slag is controlled to be ≤6%. The refining white slag time T≥8min, the refining off-site carbon is controlled between 0.05%-0.06%, and the LF supply RH temperature T≥1610℃; During the RH vacuum treatment process, the vacuum treatment time T≥20min, and the step-by-step vacuum degree control is adopted; after the RH is in place, the first stage of treatment begins, and all rare earth alloys are added according to the required rare earth content, and vacuum circulation is carried out after the addition. After the heat treatment time node, the second stage of treatment begins, vacuum circulation is carried out, and the vacuum breaking negative pressure soft blowing operation is carried out after the time node; the soft blowing operation begins, and after the soft blowing is completed, continuous casting is carried out for pouring; In the continuous casting process, oxygen burning operation is prohibited in the ladle to ensure self-opening. A covering agent is used in the tundish to protect the entire process from the tundish to the crystallizer to reduce the secondary oxidation of the molten steel.

2. The method for producing 600MPa grade low-spatter rare earth welding wire steel according to claim 1, characterized in that: For molten iron desulfurization, the stirring head speed is controlled at 90-110 rpm, the desulfurizer is 5±0.5Kg / t, and the stirring time is greater than 15min.

3. The method for producing 600MPa level low spatter rare earth welding wire steel according to claim 1, characterized in that: The converter smelting process requires that supplementary blowing is prohibited. The converter bottom blowing adopts argon blowing throughout the whole process. The argon blowing amount is 0.05-0.08Nm from the start of oxygen supply to 8 minutes of oxygen supply. 3 / min·t, oxygen supply for 8min until carbon pulling, argon blowing volume 0.08-0.10Nm 3 / min·t.

4. The method for producing 600MPa grade low-spatter rare earth welding wire steel according to claim 1, characterized in that: The steelmaking process adopts SiMn alloy deoxidation and alloying operation, and lime is added to the top slag. The amount of lime added is 3.0-3.5kg / t.

5. The method for producing 600MPa grade low-spatter rare earth welding wire steel according to claim 1, characterized in that: The components required for the refined ex-situ slag in percentage by mass are: Ca: 45-50%, Si: 25-35%, MgO: 8.0-15.0%, Al2O3≤6.0%, TFe+MnO≤1.5%.

6. The method for producing 600MPa grade low-spatter rare earth welding wire steel according to claim 1, characterized in that: During the RH vacuum treatment, a rare earth alloy with a Ce content of 30% was added in an amount of 17 kg. After the addition, the vacuum degree was 8-12 KPa and the circulating gas flow rate was 120-160 Nm 3 / h, cycle time T = 10min, after the heat treatment time node, start the second stage of treatment, vacuum degree 0.25-0.30KPa, circulation gas flow 120-140Nm 3 / h, cycle time T≥10min, after the time node, vacuum breaking negative pressure soft blowing operation is adopted.

7. The method for producing 600MPa grade low spatter rare earth welding wire steel according to claim 1 or 6, characterized in that: The soft blowing argon flow rate is 25NL / min, and the soft blowing time T≥15min.

8. The method for producing 600MPa low-spatter rare earth welding wire steel according to claim 1 or 6, characterized in that: During the continuous casting process, the superheat is controlled at 35℃±5℃; the insertion depth of the invasive nozzle is 70~90mm, and the amount of steel passed through the crystallizer is ≤5000 tons.

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