A low-sulphur and phosphorus high manganese submerged arc welding wire steel and a method for producing the same

Abstract

The application provides a low-sulfur and low-phosphorus high-manganese submerged arc welding wire steel and a preparation method thereof, and the chemical components of the steel are as follows in terms of percentage by weight: C 0.07%-0.11%, Si≤0.10%, Mn 1.30%-1.50%, P≤0.012%, S≤0.008%, Mo 0.50%-0.65%, Ni 0.15%-0.25%, Cu≤0.10%, Al≤0.008%, O≤0.0040%, N≤0.0050%, and the rest is iron and inevitable impurities. The application adopts a production mode of '120t converter+LF furnace refining+small billet continuous casting+heating furnace heating+controlled rolling and controlled cooling rolling+heat preservation channel', and solves the problem of difficult oxygen control in the process of the low-silicon variety of the low-sulfur and low-phosphorus high-manganese submerged arc welding wire steel. The application not only guarantees the mechanical property requirements of the low-sulfur and low-phosphorus high-manganese submerged arc welding wire steel rod, but also has good drawing performance and welding performance.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a low-sulfur, high-phosphorus steel for submerged arc welding wire and its preparation method. Background Technology

[0002] A steel mill has developed and produced a low-sulfur, high-phosphorus submerged arc welding wire made of steel primarily used for welding structures requiring high toughness. It is an ideal welding material for bridges, ships, pressure vessels, engineering machinery, and steel structures in cold regions. The weld formation is aesthetically pleasing, and slag removal is excellent.

[0003] The surface quality requirements for the steel used in this low-sulfur, high-phosphorus submerged arc welding wire are as follows: the un-water-penetrated portions and defective portions of the wire rod should be removed. The surface of the wire rod must be free of scabs, folds, burrs, scratches, and visible cracks; indentations and localized bumps, scratches, and pitting are permissible, but their depth or height (measured from the actual dimensions) should not exceed 0.10 mm.

[0004] Currently, there are the following technical challenges to be solved in the production of high-manganese submerged arc welding wire with low sulfur and phosphorus: 1) It is difficult to control the strength properties of the wire rod; 2) It is difficult to control oxygen during the smelting process. Summary of the Invention

[0005] The purpose of this invention is to provide a low-sulfur, high-phosphorus steel for submerged arc welding wire and its preparation method. This invention employs a production mode of "120t converter + LF furnace refining + 150mm×150mm small billet continuous casting + heating furnace heating + controlled rolling and controlled cooling rolling + heat preservation channel" to solve the process oxygen control problem for low-silicon varieties of low-sulfur, high-phosphorus submerged arc welding wire steel. Furthermore, this invention ensures the mechanical properties of the low-sulfur, high-phosphorus high-manganese submerged arc welding wire steel wire rod while also possessing good drawability and weldability.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A low-sulfur, high-phosphorus steel for submerged arc welding wire, wherein the chemical composition of the steel by weight percentage is: C 0.07%–0.11%, Si ≤0.10%, Mn 1.30%–1.50%, P ≤0.012%, S ≤0.008%, Mo 0.50%–0.65%, Ni 0.15%–0.25%, Cu ≤0.10%, Al ≤0.008%, O ≤0.0040%, N ≤0.0050%, with the remainder being iron and unavoidable impurities.

[0008] The tensile strength of the steel wire rod for welding is 520-580 MPa, the elongation after fracture is 21%-25%, and the reduction of area is 70%-75%; the non-metallic inclusions A+C≤1.5; B+D≤1.5.

[0009] The rationale for the design of the components in this invention is as follows:

[0010] Carbon (C) is the most important strengthening element. Its content significantly affects the strength, toughness, plasticity, and microstructure of the weld, and should not be too high or too low. Excessive C content will rapidly decrease the weld's toughness and plasticity, and may even cause cracking. Insufficient C content will affect the weld's strength. A minimum C content of 0.07–0.11% should be strictly controlled.

[0011] Si has a strong solid solution strengthening effect and greatly increases the work hardening rate. However, excessive Si content leads to increased deformation resistance during cold drawing and tends to reduce ductility and toughness. Furthermore, Si oxidation forming inclusions will seriously damage the weld. Therefore, the Si content should be controlled to ≤0.10%.

[0012] Manganese (Mn) possesses solid solution strengthening and grain refinement strengthening properties, thus improving the strength of steel. It is an effective element for strengthening and toughening welds. Mn can refine grains, improve the low-temperature impact toughness of welds, and has deoxidizing and desulfurizing effects. Simultaneously, the addition of Mn ensures the strength lost due to carbon reduction. Considering the basic strength of steel, the Mn content should be controlled at 1.30–1.50%.

[0013] Sulfide (S) is a serious segregating element in steel. Sulfides can deteriorate the properties of steel, leading to decreased toughness and worsened drawing performance. P (P) affects the plasticity and weldability of steel. It is important to minimize the content of P and S to reduce the harmful effects of inclusions and ensure drawing elongation performance. The P content should be ≤0.012% and the S content should be ≤0.008%.

[0014] The presence of a certain amount of Mo in the weld is beneficial for increasing the content of acicular ferrite, reducing proeutectoid ferrite, and refining ferrite grains, thereby improving the strength and toughness of the weld. The Mo content in this invention is 0.50–0.65%.

[0015] Ni helps improve the toughness of weld metal and lower the ductile-brittle transition temperature. The Ni content in this invention is 0.15–0.25%.

[0016] A method for preparing low-sulfur, high-manganese submerged arc welding wire steel involves controlling the surface quality of the cast billet and reducing internal cracks and central defects by effectively controlling the superheat of the molten steel, the casting speed, electromagnetic stirring in the continuous casting crystallizer, and electromagnetic stirring at the end of solidification to ensure the quality of the cast billet. The process includes the following steps: blast furnace hot metal → hot metal pretreatment → combined blowing converter smelting → LF furnace refining → continuous casting of 150mm×150mm small square billets (electromagnetic stirring in the crystallizer and electromagnetic stirring at the end of solidification) → walking beam furnace heating → high-speed wire rod rolling → controlled cooling → sampling, inspection, and judgment → packaging and warehousing. Specific steps include the following:

[0017] 1) Converter smelting: Scrap steel accounts for 10%–15%, molten iron accounts for 85%–90%; 280–320 kg / furnace of nickel-iron is added to the oxygen top-and-bottom blown converter along with the scrap steel. The tapping temperature is 1600–1630℃, and the final carbon content at tapping is 0.045%–0.050%. Double-slag smelting is used in the converter, with a target P ≤ 0.008% after a single tapping; slag addition is strictly prohibited. Auxiliary materials added per ton of steel: 52–62 kg of active lime, 32.5–40.5 kg of dolomite, and additionally 14.8–16.8 kg of low-carbon ferromanganese, 0.95–1.05 kg of low-calcium ferrosilicon, and 9.5–10.5 kg of ferromolybdenum for alloying. Argon blowing time at tapping: ≥ 5 min.

[0018] 2) Static argon blowing: Static argon blowing time ≥ 8 min, pretreatment temperature 1600~1625℃, posttreatment temperature 1584~1594℃, after static argon blowing, feed pure calcium cored wire 1~1.2kg / t·steel, wire feeding speed 2.8~3.2m / s;

[0019] 3) LF furnace refining: White slag operation is required. While ensuring slag fluidity, the slag basicity and oxygen potential must be controlled. The molten steel is constantly monitored, and alloying is fine-tuned to ensure the steel composition meets standard requirements. LF refining time is 60–90 min, and the full analysis temperature is 1570–1615℃. Auxiliary material addition per ton of steel: 9.5–10.2 kg of active lime, 17–1.9 kg of ferrosilicon, and 1.2–1.4 kg of ferrosilicon. Aluminum granules are added in batches of 19–21 kg / furnace, and aluminum wire is added 19–21 m / furnace before leaving the furnace to fine-tune oxygen levels, effectively controlling the oxygen content in the steel and preventing silicon reversion. Additionally, 380–410 m / furnace of calcium-iron wire is added, and the molten steel is constantly monitored, with alloying adjustments to ensure the steel composition meets standard requirements. Soft blowing time is ≥12 min. Aluminum granules and aluminum wire act as deoxidizers, while calcium-iron wire alters the morphology of inclusions, facilitating their flotation and removal.

[0020] 4) Continuous casting: The electromagnetic stirring current in the crystallizer is 220-260A, frequency 4-6Hz, rotating in both directions; the electromagnetic stirring current at the end is 230-270A, frequency 4-8Hz, rotating continuously. The platform temperature is 1610-1620℃, the tundish temperature is 1565-1580℃, the superheat is maintained at 25-35℃, and the casting speed is 2.2-2.4m / min; the entire process is protected during casting, and low-carbon steel billet protective slag is used for the crystallizer; billet cutting is carried out using a combination of automatic and manual methods.

[0021] 5) Heating process: The heating process is carried out in a walking beam furnace with a “one-space-one-empty” heating mode, that is, there is an empty space between two adjacent billets. The preheating temperature is 860-900℃, the heating temperature is 1080-1120℃, the soaking temperature is 1120-1160℃, and the heating time is ≤2.5h.

[0022] 6) Rolling process: Roughing temperature 980~1020℃; Finishing inlet temperature 900~940℃; Wire drawing temperature 780~820℃; Air-cooled roller speed: Head roller 0.09~0.12m / s; Roller speed increase setting 2%~5%; All heat insulation covers are used.

[0023] Thermal insulation channels: The effective use of thermal insulation channels ensures the effective release of structural stress and internal stress, thereby guaranteeing the product's performance and meeting the requirements for good flowability.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1) Because this invention is a low-silicon variety, oxygen control throughout the process is quite difficult. During the refining process in the FL furnace, aluminum granules are added in batches of 19-21 kg / furnace, and aluminum wire is added in batches of 19-21 m / furnace before leaving the station to fine-tune the oxygen content, thereby effectively controlling the oxygen content in the steel and preventing silicon reversion.

[0026] 2) Electromagnetic stirring and end-point electromagnetic stirring are used in the continuous casting crystallizer to improve the surface quality of the billet and reduce defects such as central porosity.

[0027] 3) When heating in a walking beam furnace, a "one-interval-one-empty" heating mode is adopted to shorten the heating time, ensure more uniform heating of the billet, and avoid the formation of difficult-to-remove FeSiO4.

[0028] 4) By using the Stellmore controlled rolling and cooling process for steel rolling, combined with a slow cooling process, a metallographic structure composed of ferrite and pearlite is obtained.

[0029] 5) The iron oxide scale thickness of the wire rod of the present invention is 10-14μm, which is suitable for mechanical descaling. Attached Figure Description

[0030] Figure 1 This is a metallographic diagram of the product from Example 1.

[0031] Figure 2 The thickness of the iron oxide scale in Example 1 is shown. Detailed Implementation

[0032] The specific embodiments of the present invention will be further described below with reference to examples.

[0033] The chemical composition of the embodiments of the present invention is shown in Table 1; the manufacturing process parameters of the embodiments of the present invention are shown in Table 2; the amount of smelting auxiliary materials added in the embodiments of the present invention is shown in Table 3; the low magnification defects of the billet in the embodiments of the present invention are shown in Table 4; the mechanical properties of the products in the embodiments of the present invention are shown in Table 5; the microstructure and non-metallic inclusions in the embodiments of the present invention are shown in Table 6.

[0034] Table 1 Chemical composition of the examples

[0035] Example C Si Mn P S Mo Ni Cu Al O N 1 0.084 0.086 1.38 0.008 0.007 0.55 0.17 0.0148 0.0048 0.0032 0.0045 2 0.080 0.092 1.37 0.008 0.008 0.56 0.17 0.012 0.0060 0.0036 0.0043 3 0.10 0.090 1.40 0.007 0.007. 0.51 0.06 0.011 0.0050 0.0033 0.0045 4 0.99 0.078 1.45 0.008 0.008 0.52 0.23 0.012 0.0061 0.0032 0.0042 5 0.95 0.085 1.48 0.006 0.006 0.56 0.21 0.013 0.0052 0.0034 0.0041 6 0.93 0.079 1.46 0.008 0.007 0.61 0.24 0.014 0.0049 0.0033 0.0044 7 0.89 0.083 1.44 0.007 0.008 0.59 0.25 0.012 0.0045 0.0036 0.0041 8 0.78 0.082 1.42 0.006 0.006 0.62 0.22 0.013 0.0052 0.0035 0.0039 9 0.85 0.080 1.43 0.007 0.005 0.58 0.20 0.014 0.0056 0.0029 0.0040 10 0.81 0.071 1.41 0.008 0.007 0.64 0.19 0.012 0.0060 0.0030 0.0038

[0036] Table 2 Manufacturing process parameters for the first embodiment

[0037]

[0038]

[0039] Table 2 Manufacturing process parameters for Example (II)

[0040]

[0041] Table 3. Amount of smelting auxiliary materials added in the examples.

[0042]

[0043] Table 4: Results of low-magnification defect inspection of cast billets in the examples:

[0044]

[0045] Table 5 Mechanical properties of the products in the examples

[0046] Example Tensile strength / MPa Elongation after fracture / % Reduction of area / % 1 560 21.5 73 2 557 23 73 3 555 24.5 70 4 545 23 71 5 570 22 74 6 578 23 75 7 575 24 72 8 576 22.5 73 9 565 23.5 75 10 545 24 74

[0047] Table 6. Microstructure and Non-metallic Inclusions of Products from Examples

[0048]

[0049]

Claims

1. A low-sulfur, high-phosphorus steel for submerged arc welding wire, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C 0.07%~0.11%, Si≤0.10%, Mn 1.30%~1.50%, P≤0.012%, S≤0.008%, Mo 0.50%~0.65%, Ni 0.15%~0.25%, Cu≤0.10%, Al≤0.008%, O≤0.0040%, N≤0.0050%, with the remainder being iron and unavoidable impurities; The preparation method of low-sulfur, high-phosphorus steel for submerged arc welding wire includes the following steps: 1) Converter smelting: Nickel-iron is added to an oxygen top-and-bottom blown converter along with scrap steel. The tapping temperature is 1600-1630℃, and the final carbon content at tapping is 0.045%-0.050%. The converter uses double slag smelting, and the target is P≤0.008% after one-time furnace turnover. 2) Static argon blowing: Static argon blowing time ≥ 6 min, pretreatment temperature 1600~1625℃, posttreatment temperature 1584~1594℃; 3) LF furnace refining: LF refining time is 60-90 min, the total analysis temperature is 1570-1615℃, aluminum granules are added in batches of 19-21 kg / furnace, and aluminum wire is added 19-21 m / furnace for micro-oxygen adjustment before leaving the station; calcium iron wire is added 380-410 m / furnace. 4) Continuous casting: Platform temperature 1610~1620℃, tundish temperature 1565~1580℃, superheat maintained at 25~35℃, casting speed 2.2~2.4m / min; 5) Heating process: The heating process is carried out by a walking beam furnace with a "one-interval-one-empty" heating mode. The preheating section is 860-900℃, the heating section is 1080-1120℃, the soaking section is 1120-1160℃, and the heating time is ≤2.5h. 6) Rolling process: Roughing temperature 980~1020℃; Finishing inlet temperature 900~940℃; Wire drawing temperature 780~820℃; Air-cooled roller speed: Head roller 0.09~0.12m / s; Roller speed increase setting 2%~5%; All heat insulation covers are used.

2. The low-sulfur, high-phosphorus steel for submerged arc welding wire according to claim 1, characterized in that, The steel wire rods used for welding have a tensile strength of 520–580 MPa, an elongation after fracture of 21%–25%, and a reduction of area of ​​70%–75%; the non-metallic inclusions A+C≤1.5 and B+D≤1.

5.

3. A method for preparing low-sulfur, high-phosphorus steel for submerged arc welding wire as described in claim 1 or 2, characterized in that, The methods and steps include the following: 1) Converter smelting: Nickel-iron is added to an oxygen top-and-bottom blown converter along with scrap steel. The tapping temperature is 1600-1630℃, and the final carbon content at tapping is 0.045%-0.050%. The converter uses double slag smelting, and the target is P≤0.008% after one-time furnace turnover. 2) Static argon blowing: Static argon blowing time ≥ 6 min, pretreatment temperature 1600~1625℃, posttreatment temperature 1584~1594℃; 3) LF furnace refining: LF refining time is 60-90 min, the total analysis temperature is 1570-1615℃, aluminum granules are added in batches of 19-21 kg / furnace, and aluminum wire is added 19-21 m / furnace for micro-oxygen adjustment before leaving the station; calcium iron wire is added 380-410 m / furnace. 4) Continuous casting: Platform temperature 1610~1620℃, tundish temperature 1565~1580℃, superheat maintained at 25~35℃, casting speed 2.2~2.4m / min; 5) Heating process: The heating process is carried out by a walking beam furnace with a "one-interval-one-empty" heating mode. The preheating section is 860-900℃, the heating section is 1080-1120℃, the soaking section is 1120-1160℃, and the heating time is ≤2.5h. 6) Rolling process: Roughing temperature 980~1020℃; Finishing inlet temperature 900~940℃; Wire drawing temperature 780~820℃; Air-cooled roller speed: Head roller 0.09~0.12m / s; Roller speed increase setting 2%~5%; All heat insulation covers are used.

4. The method for preparing a low-sulfur, high-phosphorus steel for submerged arc welding wire according to claim 3, characterized in that, In step 1) above, the scrap steel in the converter smelting accounts for 10% to 15%, and the molten iron accounts for 85% to 90%.

5. The method for preparing a low-sulfur, high-phosphorus steel for submerged arc welding wire according to claim 3, characterized in that, In the converter smelting of step 1) above, the amount of auxiliary materials added per ton of steel is as follows: 52-62 kg of active lime and 32.5-40.5 kg of dolomite; in addition, low-carbon ferromanganese, low-calcium ferrosilicon and ferromolybdenum are added for alloying, and the argon blowing time during tapping is ≥5 min.

6. The method for preparing a low-sulfur, high-phosphorus steel for submerged arc welding wire according to claim 3, characterized in that, In the LF furnace refining process of step 3) above, the amount of auxiliary materials added per ton of steel is: 9.5-10.2 kg / t steel of active lime, and the soft blowing time is ≥12 min.

7. The method for preparing a low-sulfur, high-phosphorus steel for submerged arc welding wire according to claim 3, characterized in that, In step 4) above, the electromagnetic stirring current of the crystallizer is 220-260A, the frequency is 4-6Hz, and it rotates in both directions; the electromagnetic stirring current at the end is 230-270A, the frequency is 4-8Hz, and it rotates continuously.

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