Steel H08Mn2CrMo for Gas Shielded Welding Wire and Its Preparation Method

Abstract

The present invention provides a steel H08Mn2CrMo for gas shielded welding wire and a manufacturing method thereof. The chemical components in the steel are as follows by weight percentage: C 0.07% - 0.10%, Si 0.50% - 0.70%, Mn 1.65% - 1.90%, P ≤ 0.017%, S ≤ 0.010%, Ni 0.50% - 0.70%, Cr 0.25% - 0.40%, Mo 0.30% - 0.45%, Ti 0.080% - 0.120%, and the balance is iron and inevitable impurities. Combining with reasonable chemical composition design, the present invention adopts the manufacturing process of "120t converter + LF refining + small billet continuous casting + heating furnace heating + controlled rolling and controlled cold rolling + heat preservation channel" to produce the steel H08Mn2CrMo for gas shielded welding wire, which can meet the requirements of low strength and high toughness of the steel H08Mn2CrMo for gas shielded welding wire and has good drawing performance. The manufacturing method of the present invention can effectively reduce internal cracks and central defects in the steel, reduce slag inclusions and subcutaneous bubbles.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and particularly to a steel H08Mn2CrMo for gas shielded welding wire and a preparation method thereof. Background Art

[0002] The H08Mn2CrMo wire rod is the main raw material for high-toughness low-alloy steel gas shielded welding wires, which are mainly used for welding high-strength steel structures, such as the welding of structures in construction machinery, lifting machinery, ships, bridges, pipelines, and pressure vessels. The H08Mn2CrMo wire rod should not only ensure the drawing performance but also meet the requirements of weld quality and mechanical properties, and no bubbles should be generated, so strict requirements are imposed on the chemical composition of the steel. At the same time, to ensure the metallurgical quality of the steel and the uniformity of the performance of the gas shielded welding wire.

[0003] For the H08Mn2CrMo wire rod for gas shielded welding wire, the head and tail should be cut off cleanly. The surface quality requirements are that the surface should be smooth and should not have defects such as folds, ears, scabs, delamination, and cracks and slag inclusions visible to the naked eye. Local indentations, bumps, scratches, and pitted surfaces are allowed, and their depth or height (calculated from the actual size) should not be greater than 0.10 mm. The performance and quality requirements for the H08Mn2CrMo steel for gas shielded welding wire are high mechanical properties, high toughness, and good drawing performance, and there should be no excessive internal cracks and central defects in the steel, as well as subcutaneous bubbles.

[0004] The patent document with the application publication number CN 102528318 A discloses "a gas shielded welding wire for nuclear power". The chemical composition of the welding wire by weight percentage is: C 0.06 - 0.12, Mn 1.60 - 2.10, Si 0.50 - 0.80, Ni 1.40 - 1.80, Ti 0.1 - 0.3, S ≤ 0.025, P ≤ 0.025, Mo 0.15 - 0.5, B 0.001 - 0.006, and the balance is Fe and other inevitable impurities. The welding spatter is small and the process is good; the mechanical properties are stable, the tensile strength of the weld metal is 620 - 735 MPa, the yield strength ≥ 415 MPa, and Akv8 at - 29 °C ≥ 47; after annealing treatment at 593 °C - 620 °C for not less than 10 hours, its strength and toughness can still meet the same requirements as those in the welded state. This patent document only discloses the alloy composition of the welding wire and does not disclose the manufacturing process of the welding wire, nor the technical content related to how to control slag inclusions, bubbles, and visible cracks in the steel. Summary of the Invention

[0005] The object of the present invention is to provide a steel H08Mn2CrMo for gas shielded welding wire and its preparation method. Combining reasonable chemical composition design, the present invention adopts the manufacturing process of "120t converter + LF refining + continuous casting of 150mm×150mm small square billets + heating furnace heating + controlled rolling and controlled cold rolling + heat preservation channel" to produce the steel H08Mn2CrMo for gas shielded welding wire, which can meet the higher mechanical properties of the steel H08Mn2CrMo for gas shielded welding wire, has high toughness requirements and good drawing performance at the same time. The preparation method of the present invention can effectively reduce internal cracks and central defects in the steel, reduce slag inclusions and subcutaneous bubbles.

[0006] In order to achieve the above object, the present invention is realized by adopting the following technical solutions:

[0007] A steel H08Mn2CrMo for gas shielded welding wire, the chemical composition in the steel is calculated by weight percentage as follows: C 0.07% - 0.10%, Si 0.50% - 0.70%, Mn 1.65% - 1.90%, P≤0.017%, S≤0.010%, Ni 0.50% - 0.70%, Cr 0.25% - 0.40%, Mo 0.30% - 0.45%, Ti 0.080% - 0.120%, and the rest is iron and inevitable impurities.

[0008] The wire rod of the steel H08Mn2CrMo for gas shielded welding wire has a tensile strength of 805 - 890 MPa, an elongation rate of 16% - 25%, a reduction of area of 62% - 72%, and non-metallic inclusions A + C≤1.5, B + D≤1.5.

[0009] The wire rod metallographic structure of the steel H08Mn2CrMo for gas shielded welding wire is ferrite + pearlite.

[0010] The center segregation of the steel is ≤1.5 grade, the center porosity is ≤1.5 grade, and the center shrinkage cavity is ≤1.0 grade.

[0011] The reasons for the composition design of the present invention are as follows:

[0012] C: The C content has a great influence on the strength, toughness, plasticity and structure of the weld. It should not be too high or too low. If the C content is too high, the toughness and plasticity of the weld will rapidly decline, and even cause weld cracking. If the C content is too low, the weld strength will be affected. The C content of the present invention is controlled at 0.07% - 0.10%.

[0013] Si: Adding a certain amount of Si can make the weld metal calm, accelerate the deoxidation process of the molten pool metal, ensure the density of the weld, and at the same time can also improve the strength of the weld. However, excessive Si content is easy to form silicate inclusions and is also prone to silicon cracking. The Si content of the present invention is controlled at 0.50% - 0.70%.

[0014] Mn: An effective element for weld toughness and strength improvement. Mn can refine grains, enhance the low-temperature impact toughness of the weld, and has the functions of deoxidation and desulfurization. Meanwhile, the addition of Mn compensates for the strength loss caused by carbon reduction. In the present invention, the Mn content is controlled at 1.65% - 1.90%.

[0015] Ni: Contributes to improving the toughness of the weld metal and reducing the ductile-brittle transition temperature. In the present invention, the Ni content is controlled at 0.50% - 0.70%.

[0016] Cr: Increasing the content of Cr element is beneficial to improving the toughness of the weld. At the same time, it can form carbide with dispersed distribution with carbon and improve the weld strength; Cr element is conducive to increasing the content of acicular ferrite, reducing proeutectoid ferrite, and has the effect of refining ferrite grains, improving the strength and toughness of the weld. Cr also helps to maintain the performance of the weld at a relatively high level after heat treatment. In the present invention, the Cr content is controlled at 0.25% - 0.40%.

[0017] Mo: Is the main element to obtain high-strength weld metal; as a high melting point substance, it refines grains and improves the strength of steel at the same time. In the present invention, the Mo content is controlled at 0.30% - 0.45%.

[0018] Ti: During welding, Ti can combine with N and O to form TiN and TiO particles as crystal nuclei, preventing the growth of austenite grains during the welding heating process and refining the austenite grains of the weld. At the same time, it can also serve as a phase transformation core during the welding cooling process to form acicular ferrite with intragranular nucleation, improving the toughness of the weld. However, if Ti is excessive, a large number of TiC and TiN particles will reduce the toughness. In the present invention, the Ti content is 0.080% - 0.120%.

[0019] P, S: P and S are harmful elements. Controlling their content can improve the purity, so it is required to reach a relatively low level. Among them, P ≤ 0.017% and S ≤ 0.010%.

[0020] In order to ensure the quality of the continuous casting billet of the gas shielded welding wire steel H08Mn2CrMo, the present invention provides a preparation method for the gas shielded welding wire steel H08Mn2CrMo. By effectively controlling measures such as the superheat of molten steel, casting speed, electromagnetic stirring in the continuous casting mold, and electromagnetic stirring at the solidification end, the surface quality of the continuous casting billet is improved, and internal cracks and central defects are reduced. It includes the following technological processes: "blast furnace hot metal → hot metal pretreatment → combined blowing converter smelting → LF refining → continuous casting of 150mm × 150mm small square billets (electromagnetic stirring in the mold and electromagnetic stirring at the solidification end) → heating in a walking beam reheating furnace → high-speed wire rolling → controlled cooling → sampling, inspection, determination → packaging, warehousing", and the specific methods include:

[0021] 1) Converter smelting: Scrap steel accounts for 11% - 15%, hot metal accounts for 85% - 89%; Top and bottom combined blowing with oxygen, tapping temperature 1650 - 1680°C, tapping end point C is 0.04% - 0.05%, double slag smelting in the converter, target primary tapping P ≤ 0.008%, slagging is strictly prohibited; Auxiliary materials addition per ton of steel: 50 - 56 kg of active lime, 32 - 36 kg of dolomite, 0.9 - 1.3 kg of limestone. Ladle alloying: Add lime, pre-deoxidizer and ferroalloys for deoxidation alloying when 1 / 4 - 1 / 3 of the steel is tapped, argon blowing time ≥ 5 min; Target alloy addition per ton of steel: 5.0 - 5.2 kg of low-carbon ferrochrome, 6.5 - 6.7 kg of low-carbon ferromanganese, 19.1 - 19.4 kg of low-calcium ferrosilicon, 5.5 - 5.7 kg of nickel plate, 6.5 - 6.7 kg of ferromolybdenum.

[0022] 2) Stationary argon blowing: Stationary argon blowing time ≥ 8 min, temperature before treatment 1590 - 1610°C, temperature after treatment 1570 - 1590°C, feed 1 - 1.2 kg / t·steel of pure calcium cored wire after stationary argon blowing, wire feeding speed 3 m / s, change the morphology of inclusions, make inclusions float to the slag quickly, reduce inclusions in the steel.

[0023] 3) LF furnace refining: White slag operation is required, control the slag basicity and oxygen potential in the slag under the condition of ensuring slag fluidity; Continuously detect the molten steel, adjust the alloy slightly, ensure that the composition of the molten steel meets the standard requirements; LF refining time 60 - 80 min, full analysis temperature 1560 - 1600°C, auxiliary materials addition per ton of steel: 8.2 - 8.6 kg of active lime, 40 - 45 kg / ladle of fluorite, 4.0 - 4.2 kg of medium-carbon ferromanganese, 0.65 - 0.67 kg of low-carbon ferrochrome, 2.2 - 2.4 kg of ferrotitanium, 300 - 320 kg / ladle of ferrosilicon powder, and continuously detect the molten steel, adjust the alloy slightly, ensure that the composition of the molten steel meets the standard requirements, soft argon blowing time ≥ 12 min. [[ID=⑧]]

[0024] 4) Continuous casting: Mould electromagnetic stirring current 220 - 260 A, frequency 4 - 6 Hz, forward and reverse rotation; End electromagnetic stirring current 230 - 270 A, frequency 4 - 8 Hz, continuous rotation. Platform temperature 1615 - 1625°C, tundish temperature 1545 - 1580°C, superheat maintained at 25 - 35°C, casting speed 2.0 - 2.2 m / min; Protect the whole process during casting, use bloom low-carbon steel casting powder for the mould; The billet cutting adopts the combination of automatic and manual methods.

[0025] 5) Heating process: Step-type heating furnace heating, preheating section 860 - 900°C, heating section 1080 - 1120°C, soaking section 1120 - 1160°C, heating furnace heating time ≤ 2.5 h.

[0026] 6) Rolling process: rough rolling temperature is 1000 - 1040 °C; finish rolling entry temperature is 840 - 880 °C; wire laying temperature is 780 - 820 °C; air-cooling roller table speed at the head roller table is 0.07 - 0.09 m / s; all are covered with heat preservation covers.

[0027] 7) Heat preservation channel: The heat preservation channel ensures a temperature ≥ 60 °C, and the heat preservation channel is effectively utilized to ensure the effective release of tissue stress and internal stress, thereby also ensuring the product performance and the requirements for the difference in product performance along the whole bar.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] The present invention adopts the production mode of "controlled rolling and controlled cooling process + slow cooling process in heat preservation channel", which can effectively improve the quality of the wire rod H08Mn2CrMo for gas shielded welding wire. Through composition design, it ensures that the composition is close to that of the welded matrix of weathering steel and also ensures the weld quality. It guarantees the steel purity and the castability of molten steel, and prevents nozzle coking; continuous casting adopts mold electromagnetic stirring to improve the surface quality of the billet, reduce internal cracks and central defects; through the controlled rolling and controlled cooling process of the steel rolling Stelmor process, combined with the slow cooling process, a metallographic structure composed of ferrite and pearlite is obtained to ensure the strength and toughness of the wire rod.

[0030] For the wire rod H08Mn2CrMo for gas shielded welding wire of the present invention, the tensile strength is 805 - 890 MPa, the elongation is 16% - 25%, the reduction of area is 62% - 72%, and the non-metallic inclusions (A + C ≤ 1.5; B + D ≤ 1.5). Description of the drawings

[0031] Figure 1 It is the metallographic structure diagram of the product in Example 1. Detailed implementation manners

[0032] The following further illustrates the detailed implementation manners of the present invention in combination with the embodiments.

[0033] The chemical compositions of the embodiments of the present invention are shown in Table 1; the manufacturing process parameters of the embodiments of the present invention are shown in Table 2; the addition amounts of smelting auxiliary materials of the embodiments of the present invention are shown in Table 3; the macro-defects of the billets 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 microstructures and non-metallic inclusions in the embodiments of the present invention are shown in Table 6.

[0034] Table 1 Chemical compositions of the embodiments

[0035]

[0036]

[0037] Table 2 Manufacturing process parameters of the embodiments (I)

[0038]

[0039] Table 2 Manufacturing Process Parameters of Examples (II)

[0040]

[0041] Table 3 Additive Amounts of Smelting Auxiliary Materials in Examples

[0042]

[0043] Table 4 Inspection Results of Macro-Defects of Continuous Casting Billets in Examples:

[0044] Embodiment Central porosity Central segregation Shrinkage cavity Corner crack Edge crack Intermediate crack Center crack Subsurface blowhole Non-metallic inclusion 1 0.5 0.5 1.0 0.5 0.5 0.5 0.5 0.5 0.5 2 0.5 0.5 0.5 0.5 0.5 0.5 1.0 0.5 0.5 3 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 4 0.5 0.5 1.0 0.5 0.5 0.5 0.5 0.5 0.5 5 0.5 0.5 0.5 0.5 0.5 0.5 1.0 0.5 0.5 6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 7 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 8 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 9 0.5 0.5 1.0 0.5 0.5 0.5 0.5 0.5 0.5 10 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5

[0045] Table 5 Mechanical Properties of Products in Examples

[0046]

[0047]

[0048] Table 6 Microstructure and Non-Metallic Inclusions of Products in Examples

[0049]

Claims

1. A steel H08Mn2CrMo for gas shielded welding wire, characterized in that, The chemical components in the steel are by weight percentage: C 0.07% - 0.10%, Si 0.50% - 0.70%, Mn 1.83% - 1.90%, P ≤ 0.017%, S ≤ 0.010%, Ni 0.50% - 0.70%, Cr 0.31% - 0.40%, Mo 0.41% - 0.45%, Ti 0.080% - 0.120%, and the rest are iron and inevitable impurities; For the steel H08Mn2CrMo used for gas shielded welding wire, the tensile strength of its wire rod is 805 - 890 MPa, the elongation is 16% - 25%, the reduction of area is 62% - 72%, and the non-metallic inclusions A + C ≤ 1.5, B + D ≤ 1.5; For the steel H08Mn2CrMo used for gas shielded welding wire, the metallographic structure of its wire rod is ferrite + pearlite; The preparation method of the steel H08Mn2CrMo used for gas shielded welding wire includes the following method steps: 1) Converter smelting: Oxygen top and bottom combined blowing, tapping temperature 1650 - 1680 °C, tapping end point C is 0.04% - 0.05%, converter double slag smelting, target primary tapping P ≤ 0.008%; 2) Static argon blowing: Static argon blowing time ≥ 8 min, temperature before treatment 1590 - 1610 °C, temperature after treatment 1570 - 1590 °C; After static argon blowing, feed pure calcium cored wire 1 - 1.2 kg / t·steel, wire feeding speed 3 m / s, change the morphology of inclusions, make inclusions float to the slag quickly, and reduce inclusions in the steel; 3) LF furnace refining: White slag operation is required, LF refining time 60 - 80 min, full analysis temperature 1560 - 1600 °C, soft argon blowing time ≥ 12 min; 4) Continuous casting: Platform temperature 1615 - 1625 °C, tundish temperature 1545 - 1580 °C, superheat maintained at 25 - 35 °C, casting speed 2.0 - 2.2 m / min; Mould electromagnetic stirring current 220 - 260 A, frequency 4 - 6 Hz, forward and reverse rotation; End electromagnetic stirring current 230 - 270 A, frequency 4 - 8 Hz, continuous rotation; 5) Heating process: Step-type heating furnace heating, preheating section 860 - 900 °C, heating section 1080 - 1120 °C, soaking section 1120 - 1160 °C, heating furnace heating time ≤ 2.5 h; 6) Rolling process: Rough rolling temperature 1000 - 1040 °C; Finish rolling entry temperature 840 - 880 °C; Spinning temperature 780 - 820 °C; Air-cooling roller table speed at the head roller table 0.07 - 0.09 m / s; All are covered with heat preservation covers; 7) Heat preservation channel: The heat preservation channel ensures a temperature ≥ 60 °C.

2. The steel H08Mn2CrMo for gas shielded welding wire according to claim 1, characterized in that, The center segregation of the steel ≤ 1.5 grades, center porosity ≤ 1.5 grades, center shrinkage cavity ≤ 1.0 grade.

3. A preparation method of steel H08Mn2CrMo for gas shielded welding wire as described in claim 1 or 2, characterized in that, Including the following method steps: 1) Converter smelting: Oxygen top and bottom combined blowing, tapping temperature 1650 - 1680 °C, tapping end point C is 0.04% - 0.05%, converter double slag smelting, target primary tapping P ≤ 0.008%; 2) Stationary argon blowing: The stationary argon blowing time is ≥ 8 min, the temperature before treatment is 1590 - 1610 °C, and the temperature after treatment is 1570 - 1590 °C; After stationary argon blowing, 1 - 1.2 kg / t·steel of pure calcium cored wire is fed, the wire feeding speed is 3 m / s, the morphology of inclusions is changed, so that the inclusions quickly float up to the slag, reducing the inclusions in the steel; 3) LF furnace refining: White slag operation is required, the LF refining time is 60 - 80 min, the full analysis temperature is 1560 - 1600 °C, and the soft argon blowing time is ≥ 12 min; 4) Continuous casting: The platform temperature is 1615 - 1625 °C, the tundish temperature is 1545 - 1580 °C, the superheat is maintained at 25 - 35 °C, and the casting speed is 2.0 - 2.2 m / min; 5) Heating process: Step - type heating furnace heating, the preheating section is 860 - 900 °C, the heating section is 1080 - 1120 °C, the soaking section is 1120 - 1160 °C, and the heating time of the heating furnace is ≤ 2.5 h; 6) Rolling process: The rough rolling temperature is 1000 - 1040 °C; The entry temperature of finish rolling is 840 - 880 °C; The laying - head temperature is 780 - 820 °C; The speed of the air - cooled roller table at the head roller table is 0.07 - 0.09 m / s; All are covered with heat - insulating covers; 7) Heat - insulating channel: The heat - insulating channel ensures that the temperature is ≥ 60 °C.

4. The preparation method of steel H08Mn2CrMo for gas shielded welding wire according to claim 3, characterized in that, In the converter smelting of step 1) above, the scrap steel accounts for 11% - 15%, and the hot metal accounts for 85% - 89%.

5. The preparation method of steel H08Mn2CrMo for gas shielded welding wire according to claim 3, characterized in that, In the converter smelting of step 1) above, the addition amount of auxiliary materials per ton of steel is: 50 - 56 kg of active lime, 32 - 36 kg of dolomite, and 0.9 - 1.3 kg of limestone.

6. The preparation method of the steel H08Mn2CrMo for gas shielded welding wire according to claim 3, characterized in that, In the converter smelting of step 1) above: Deoxidation alloying is carried out when 1 / 4 - 1 / 3 of the steel is tapped, and the argon blowing time is ≥ 5 min.

7. The preparation method of steel H08Mn2CrMo for gas shielded welding wire according to claim 3, characterized in that, In the LF furnace refining of step 3) above, the addition amount of auxiliary materials: 8.2 - 8.6 kg / t·steel of active lime, and 40 - 45 kg / furnace of fluorite.

8. The preparation method of steel H08Mn2CrMo for gas shielded welding wire according to claim 3, characterized in that, In step 4) above, the current of the mold electromagnetic stirrer is 220 - 260 A, the frequency is 4 - 6 Hz, with forward and reverse rotation; The current of the final electromagnetic stirrer is 230 - 270 A, the frequency is 4 - 8 Hz, with continuous rotation.

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