Preparation method of H08MnMo wire rod for submerged arc welding wire and wire rod

Abstract

According to the preparation method of the H08MnMo wire rod for the submerged arc welding wire and the wire rod, the content of impurities such as sulfur and phosphorus in molten steel is effectively reduced through measures of carefully selecting raw materials, adding a slagging constituent with a specific proportion into a converter, deoxidizing and desulfurizing by adopting a silicon-calcium-barium alloy in the LF refining process, stirring by blowing argon from the bottom and the like; the number and size of inclusions are reduced, and the purity of molten steel is improved. A whole-course protection casting technology and appropriate crystallizer casting powder are adopted, the pulling speed and the secondary cooling specific water flow are accurately controlled, the quality of a casting blank is guaranteed, and internal defects are reduced. Through controlled rolling and controlled cooling, the steel wire rod is uniform in structure transformation in the rolling process, grains are refined, the structure of the steel wire rod is optimized, and the steel wire rod has good comprehensive mechanical properties. The H08MnMo steel wire rod prepared through the method is uniform in structure, small in grain size and uniform in grain distribution, the strength and toughness are well matched, and the performance requirement of the high-end welding field for submerged arc welding wires is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material preparation, and in particular relates to a preparation method of H08MnMo wire rod for submerged arc welding wire and the wire rod. Background Art

[0002] Submerged arc welding is a highly efficient welding method that is widely used in industrial production. The quality of submerged arc welding wire directly affects the performance of welded joints. H08MnMo steel wire rod is a commonly used material for preparing submerged arc welding wire due to its good welding process performance and weld mechanical properties. However, existing methods for preparing H08MnMo steel wire rod have some problems. For example, the purity of the molten steel is not high, resulting in a large number of inclusions inside the wire rod, which affects the arc stability and weld quality during welding; during the rolling process, the control of temperature and deformation is not precise enough, resulting in poor uniformity of the wire rod structure, and it is difficult to achieve an ideal matching state between strength and toughness, which cannot meet the high-quality and high-performance requirements of some high-end welding fields for submerged arc welding wire. Therefore, it is of great practical significance to develop a preparation method that can improve the quality of H08MnMo steel wire rod. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing H08MnMo wire rod for submerged arc welding wire and the wire rod, so as to solve the problems of low purity of molten steel and poor uniformity of wire rod structure in the existing preparation method, improve the quality of H08MnMo steel wire rod, and meet the needs of high-end welding field.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for preparing H08MnMo wire rod for submerged arc welding wire includes converter smelting, molten steel refining, continuous casting, heating and rolling, and Stelmor cooling, specifically comprising:

[0006] The converter smelting process uses high-quality scrap steel and pig iron as basic raw materials, wherein the sulfur content of the scrap steel is no more than 0.015% and the phosphorus content is less than 0.02%; the silicon content of the pig iron is between 0.8% and 1.2%, and the manganese content is between 0.6% and 1.0%. The scrap steel and pig iron are charged into the converter for smelting in proportion, and an appropriate amount of slag-forming agent is added. The slag-forming agent is composed of lime, fluorite, and bauxite in a mass ratio of (4.5-5.5): (1.8-2.2): (0.9-1.1). The amount of the slag-forming agent added is 2% to 3% of the total mass of the charge to promote slag formation and effectively remove impurities.

[0007] The molten steel refining process involves transferring the molten steel from the converter to an LF refining furnace for refining. During the LF refining process, a silicon-calcium-barium alloy is added to the molten steel for deoxidation and desulfurization. The amount of silicon-calcium-barium alloy added is 0.8-1.2 kg / t of molten steel. Simultaneously, bottom-blown argon is used for stirring, with the argon flow rate controlled at 80-120 L / min and the stirring time at 15-20 minutes, to homogenize the molten steel composition and further remove inclusions. After refining, the molten steel temperature is controlled at 1580-1620°C in preparation for continuous casting.

[0008] The continuous casting process utilizes a fully protected casting process to prevent secondary oxidation of the molten steel. The crystallizer utilizes a mold slag specifically formulated for high-carbon steel, with a melting temperature of 1050-1100°C and a viscosity of 1.0-1.5 Pa·s to ensure surface quality of the ingot. The continuous casting speed is controlled at 1.0-1.2 m / min. A weak cooling system is employed in the secondary cooling zone, with a water content controlled at 0.4-0.6 L / kg to ensure uniform cooling of the ingot and minimize internal cracking. The ingot's cross-sectional dimensions are 150 mm x 150 mm.

[0009] The heating and rolling process: The continuous casting slab is heated to 1080-1120°C and soaked in the heating furnace for 1.5-3.0 hours to make the temperature of the slab uniform. A high-speed wire rod mill is used for rolling. In the rough rolling stage, large reduction rolling is adopted, and the total reduction rate is controlled at 60%-65%. The slab is rolled into an intermediate slab of φ52-φ60mm. In the intermediate rolling stage, the intermediate slab is rolled into a billet of φ25-φ35mm, and the elongation coefficient of each intermediate rolling pass is controlled at 1.3-1.5. In the finishing rolling stage, micro-tension rolling is adopted, and the tension is set at 3-5N / mm. 2 The billet is rolled into φ4.5~φ12mm wire rod, and the finishing rolling outlet speed is controlled at 80~115m / s. During the rolling process, the temperature of the rolled piece is monitored in real time by an online temperature monitoring system. The rough rolling outlet temperature is controlled at 980~1030℃, the intermediate rolling outlet temperature is controlled at 930~990℃, the finishing rolling inlet temperature is controlled at 900~930℃, and the spinning temperature is 850~890℃.

[0010] The Stelmor cooling: the rolled wire rod passes through the spinning machine at high speed, and the spinning machine spits the wire rod into a uniform coil, which falls on the Stelmor cooling line. The wire rod enters the Stelmor cooling line for cooling, and adopts a combination of primary air cooling, slow cooling, and secondary air cooling. First, it enters the primary air cooling section. The purpose of the primary air cooling is to cool the wire rod from the high-temperature austenite state to a temperature range close to Ar3 (the temperature at which austenite begins to transform into ferrite). By adjusting the air volume of the fan, 1 to 2 fans are turned on in the primary air cooling section to cool the wire rod to 710 to 820°C at a cooling rate of 2 to 3°C / s; then it enters the slow cooling section and runs in the insulation cover for slow cooling. The function of the insulation cover is to reduce the heat exchange between the wire rod and the external environment, so that the wire rod can be kept at a relatively stable temperature for a period of time, so that the internal structure can be fully homogenized and prepared for the subsequent cooling process. Two to four insulation hoods are activated, and the cooling roller speed is 0.5 to 1.1 m / s. The wire rod runs inside the insulation hood for 7.5 to 8.2 minutes, with a cooling rate of 0.25 to 0.45°C / s. After exiting the insulation hood, the temperature drops to 510 to 600°C. This slows the cooling rate, allowing sufficient time for stress release within the wire rod, thus reducing internal stress levels. This helps reduce deformation, cracking, and other defects caused by internal stress during subsequent processing or use, improving the product's dimensional stability and reliability. Depending on product performance requirements, secondary air cooling is then activated at a cooling rate of 2 to 3°C / s to a temperature of 480 to 570°C. This allows the wire rod to undergo a transformation from austenite to pearlite and bainite at a specific cooling rate, achieving the desired microstructure and properties, such as strength, toughness, and hardness. Finally, air cooling is performed to 350 to 450°C before coiling. During the high-speed wire rolling process, strict process regulations are adhered to to ensure that the final product's grain size, metallographic structure, and oxide scale meet standard requirements.

[0011] The chemical composition of the wire rod steel prepared by the above preparation method is as follows by weight: C: 0.06%~0.10%, Si: 0.12%~0.18%, Mn: 1.35%~1.45%, P≤0.015%, S≤0.005%, Mo: 0.35%~0.45%, Ti: 0.05%~0.08%, and the rest is Fe and unavoidable impurities.

[0012] The tensile strength of the wire rod is 541-640 MPa, the cross-sectional shrinkage is 73%-79%, and the elongation is 30%-40%.

[0013] The cross section of the wire rod is an equiaxed grain structure with uniform grain size, grain size of 5 to 12μ, grain size of 8.0 to 8.5, and the metallographic structure is mainly ferrite (F), with a small amount of pearlite (P) or a small amount of pearlite (P) and bainite (B).

[0014] The crystallizer protection slag used in the present invention has a melting temperature of 1050-1100°C and a viscosity of 1.0-1.5 Pa·s. It can form a continuous liquid slag film between the crystallizer wall and the ingot, which plays a good lubricating role, effectively reduces the resistance to billet drawing, reduces the friction between the ingot and the crystallizer wall, prevents defects such as scratches and adhesion on the surface of the ingot, and improves the surface quality of the ingot. In addition, the protection slag can also regulate the heat transfer in the crystallizer, make the surface temperature of the ingot uniform, slow down the cooling rate of the ingot, and avoid cracks on the surface of the ingot caused by local overheating or overcooling. It ensures the temperature of the molten steel in the crystallizer is stable, which is conducive to the smooth solidification process of the ingot. The crystallizer protection slag of the present invention has a good inclusion adsorption function, and can well adsorb inclusions that float to the liquid surface in the molten steel, prevent inclusions from adhering to the surface of the ingot or entering the interior of the ingot, thereby improving the purity of the ingot and reducing inclusion defects.

[0015] The present invention accurately controls the continuous casting pulling speed to be: 1.0~1.2m / min. The continuous casting pulling speed directly affects the solidification time and solidification speed of the billet in the crystallizer. If the pulling speed is too fast, the solidification time of the billet in the crystallizer is shortened, and the billet shell thickness is insufficient, which can easily lead to defects such as bulging and steel leakage in the billet after it leaves the crystallizer; if the pulling speed is too slow, it will reduce production efficiency and may cause excessive iron oxide scale on the surface of the billet, affecting the quality of the billet. In addition, a suitable pulling speed helps the floating of inclusions in the molten steel. When the pulling speed is too slow, the molten steel stays in the crystallizer for too long, and the inclusions are likely to gather and grow and float to the surface of the molten steel and be adsorbed by the protective slag; if the pulling speed is too fast, the inclusions will not have time to float up and will be wrapped in the inside of the billet by the solidified molten steel, increasing the inclusion content of the billet and reducing the quality of the billet. The present invention precisely controls the continuous casting speed to 1.0-1.2 m / min, ensuring the appropriate solidification time for the strand in the mold, ensuring uniform growth of the strand shell, forming a good solidification structure, and improving the internal and surface quality of the strand. It also optimizes the conditions for inclusion floating and improves the purity of the strand.

[0016] The secondary cooling zone is the further cooling area after the billet exits the crystallizer. The secondary cooling water ratio directly affects the surface temperature and cooling rate of the billet. If the secondary cooling water ratio is too large, the billet surface will cool too quickly, which will generate large thermal stress and cause cracks on the billet surface; if the secondary cooling water ratio is too small, the billet surface temperature will be too high, which will cause the iron oxide scale on the billet surface to thicken, affecting the surface quality of the billet. In addition, the secondary cooling water ratio also has an important impact on the solidification structure and defects such as shrinkage cavities and porosity inside the billet. The present invention controls the water ratio to 0.4 to 0.6 L / kg, which can uniformly reduce the surface temperature of the billet, avoid excessive thermal stress, and thus improve the surface quality of the billet. It can also make the solidification structure inside the billet uniform and fine, reduce the columnar crystal area, expand the equiaxed crystal area, improve the density of the billet, and reduce the probability of forming defects such as shrinkage cavities and porosity, thereby improving the internal quality of the billet.

[0017] The selection of the crystallizer protective slag of the present application and the design of the accurate control of the withdrawal speed and the water quantity of the secondary cooling mutually cooperate and influence each other and jointly act on the casting billet quality in the production process of the high-speed wire rod casting billet. Only the three factors are accurately controlled and optimized, the high-quality high-speed wire rod casting billet can be produced.

[0018] The lower rolling temperature adopted in the present application is beneficial to the grain refinement. When rolling in the austenite zone, the lower temperature can increase the dislocation density in the austenite grain, and form a large number of deformation bands and substructures. These defects provide more nucleation sites for recrystallization, and promote the recrystallization of austenite in the subsequent cooling process, thereby refining the grains. When the rolling temperature is too low, the work hardening of the steel may be serious, the rolling force is increased, and even cracks and other defects may occur. Therefore, it is necessary to select a suitable low-temperature rolling range to obtain the effect of grain refinement, and to ensure the quality of the steel and the smooth progress of the rolling process. Therefore, the continuous casting billet is heated to 1080-1120℃ for rolling, the rough rolling outlet temperature is controlled at 980-1030℃, the medium rolling outlet temperature is controlled at 930-990℃, the fine rolling inlet temperature is controlled at 900-930℃, and the wire drawing temperature is 850-890℃.

[0019] In the rough rolling stage of the present application, large reduction is adopted, and the total reduction rate is controlled at 60%-65%, so as to roll the casting billet into a φ52-φ60mm intermediate billet; in the medium rolling stage, the intermediate billet is rolled into a φ25-φ35mm billet, and the elongation coefficient of each pass in the medium rolling stage is controlled at 1.3-1.5; in the fine rolling stage, micro-tension rolling is adopted, and the tension is set at 3-5N / mm 2 The billet is rolled into a φ4.5-φ12mm wire rod, and the fine rolling outlet speed is controlled at 80-115m / s. Increasing the deformation amount can elongate and flatten the austenite grains, increase the grain boundary area, and significantly improve the dislocation density, so as to form more subgrain boundaries and deformation bands. According to the grain boundary bowing nucleation mechanism, the increase of the grain boundary area provides more nucleation sites for recrystallization, so that the number of grains after recrystallization is increased, thereby realizing grain refinement. From the dislocation theory, a large number of dislocations are intertwined and intersected, forming dislocation cells and substructures. In the subsequent cooling process, these dislocation cells and substructures can act as the core of recrystallization, promote the occurrence of recrystallization, and refine the grains. At the same time, the increase of the deformation amount can also make the second phase particles more uniformly distributed in the matrix, which can hinder the growth of the austenite grains in the cooling process, and further refine the grains.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] 1. Improve the purity of molten steel: by carefully selecting raw materials, adding specific ratio of slag forming agent in the converter, and using silicon calcium barium alloy deoxidation and desulfurization and bottom blowing argon stirring in the LF refining process, etc. measures, effectively reduce the content of sulfur, phosphorus and other impurities in the molten steel, reduce the number and size of inclusions, improve the purity of molten steel, lay the foundation for subsequent preparation of high quality steel wire rod. Through detection, the sulfur content of the molten steel prepared by the method of the application can be reduced to below 0.005%, the phosphorus content is reduced to below 0.015%, the inclusion rating is significantly better than the traditional method, and the inclusion rating is not more than 1.0 level, while the inclusion rating of the traditional method is more than 1.5 level.

[0022] 2. Improve the uniformity of wire rod structure: In the continuous casting process, the whole process of protective casting technology, suitable crystallizer protective slag, precise control of pulling speed and two cold water volume are adopted to ensure the quality of the casting blank and reduce internal defects. In the heating and rolling stage, the heating temperature, soaking time, reduction rate, extension coefficient and rolling speed of each rolling stage are accurately controlled, and the rolling piece temperature is real-time regulated through the online temperature monitoring system, so that the wire rod has uniform structure transformation and grain refinement in the rolling process. The Stelmor cooling line adopts the combination of primary air cooling, slow cooling and secondary air cooling to accurately control the cooling speed and further optimize the structure of the wire rod, so that it has good comprehensive mechanical properties. Through metallographic analysis, the H08MnMo steel wire rod prepared by the application has uniform structure, small and uniform grain size, and good matching of strength and toughness, which meets the performance requirements of submerged arc welding wire for high-end welding field. In the petroleum, chemical, power and other industries, it is used to manufacture various high-pressure and super-high-pressure pressure vessels. These vessels usually need to withstand high temperature, high pressure and various corrosive media, and have very high requirements for the strength, toughness and crack resistance of the welded joints. The H08MnMo wire rod of the application can meet these requirements to ensure the safety and reliability of the pressure vessel. H08MnMo submerged arc welding wire can also be used for welding the main truss, box girder and other key structural components of the bridge, which can provide high-strength welded joints to withstand various loads during the use of the bridge, while having good fatigue resistance to ensure the stability of the bridge structure. Large cranes, excavators, mining machinery and other heavy machinery equipment, such as the key stressed components of the crane, the frame, the bucket, etc. usually use high-strength steel plates to manufacture, which need high-strength welding materials to ensure the welding quality, and also apply to H08MnMo submerged arc welding wire, which can meet the requirements of the application.

[0023] 3. The wire rod is sampled in the same circle, polished and etched with 4% nitric acid ethanol solution, and microstructure is observed and analyzed under a metallurgical microscope. The crack defects are greatly controlled, and there is only a little non-metallic slag. There is a slight crack in individual position of the wire rod, and the crack size is 50-175 μm. The cross section of each wire rod is equiaxed grain structure, and the grain size is uniform. Through quantitative analysis, it is determined that the grain size of each wire rod is 8.0-8.5 grade, and the microstructure is mainly ferrite (F) and a little pearlite (P) or a little pearlite (P) and bainite (B).

[0024] 4. The wire rod produced by the present application has a tensile strength of 541-640 MPa, a reduction of area of 73%-79%, and an elongation of 30%-40%. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a high-speed wire rod production process flow chart.

[0026] Figure 2 It is a wire rod steel grain size micrograph of example 1 of the present application.

[0027] Figure 3 It is a microstructure diagram of wire rod steel of example 1 of the present application.

[0028] Figure 4 It is a wire rod coil type and surface quality diagram of wire rod steel of example 1 of the present application. DETAILED DESCRIPTION

[0029] The specific implementation of the present application is further described below in combination with examples.

[0030] 1. The process flow of the present application is as follows:

[0031] hot metal pretreatment → converter → refining LF → continuous casting (crystallizer electromagnetic stirring, protective casting, end electromagnetic stirring) → heating furnace heating → high-pressure water descaling → controlled rolling and controlled cooling → air cooling transport line slow cooling, tail cutting → collecting and coiling → uncoiling → PF line transportation.

[0032] 2. The chemical composition is shown in Table 1:

[0033] Table 1: Chemical composition of H08MnMo wire rod steel product of example

[0034]

[0035] 3. Billet heating and descaling:

[0036] The billet is tested in high-speed wire rod rolling Figure 1, the size of continuous casting billet is 150mm*150mm*12000mm. Billet heating is a key process in steel production, which directly affects the subsequent rolling quality, steel performance and surface quality (see Figure 4 ). Billet heating is mainly to improve the plasticity of steel and reduce the deformation resistance. The internal and surface temperature of billet needs to be consistent to avoid large temperature difference, which will lead to uneven deformation in rolling process and then produce internal stress, affecting the quality of steel. Billet heating strictly implements the trial rolling scheme requirements, and the specific parameters are shown in Table 2. During the heating process, the heating temperature of each section in the furnace and the overall time of billet in the furnace are reasonably controlled to ensure that the temperature of the heated billet is uniform and the grain structure meets the rolling standard. The billet time in the furnace is 1.5-3.0 hours, which meets the requirements of the rolling scheme.

[0037] Table 2 Buried arc welding wire H08MnMo billet heating system

[0038]

[0039] During the heating process of billet, a layer of iron oxide scale (scale) will form on the surface. If these oxides are not removed, they will be pressed into the surface of the steel during rolling, resulting in a decrease in the surface quality of the finished product, and even affecting the performance. Using high-pressure water flow (usually 20-30 MPa pressure) to impact the surface of the billet can strip the iron oxide scale.

[0040] 4. Wire rod controlled rolling and controlled cooling:

[0041] The total length of the Stelmor air cooling line is 115m. Controlled rolling and controlled cooling is to control the microstructure of steel by precisely controlling the deformation temperature, deformation amount and subsequent cooling speed of steel during hot rolling, so as to adjust the mechanical properties of steel. During the process of controlled rolling and controlled cooling, the key parameters such as temperature, deformation amount and cooling speed need to be monitored and adjusted in real time to ensure the accuracy and consistency of the process parameters, and finally to ensure the stability of the size and performance of the finished product.

[0042] Example 1:

[0043] 1. Raw material preparation: 70t of scrap steel with sulfur content of 0.012% and phosphorus content of 0.018%, 30t of pig iron with silicon content of 1.0% and manganese content of 0.8%, are put into a 100t electric furnace. Add 3t of slagging agent (lime 1.88t, fluorite 0.76t, bauxite 0.38t) for smelting.

[0044] 2. Molten steel refining: After the converter, the molten steel is transferred to the LF refining furnace, and 100kg of silicon-calcium-barium alloy (1kg / t of molten steel) is added for deoxidation and desulfurization treatment. The argon flow rate is controlled at 100L / min, and the stirring time is 18min. After refining, the temperature of the molten steel is 1600℃.

[0045] 3. Continuous Casting: Fully protected casting is used, with a mold containing mold slag with a melting temperature of 1080°C and a viscosity of 1.2 Pa·s. The continuous casting speed is 1.1 m / min, the water content in the secondary cooling zone is 0.5 L / kg, and the cross-sectional dimensions of the ingot are 150 mm × 150 mm.

[0046] 4. Heating and Rolling: The continuous casting slab is heated to 1100°C and soaked in a heating furnace for 1.8 hours. Rough rolling is performed with a total reduction of 62%, and the slab is rolled into a φ60mm intermediate bar. Intermediate rolling is performed with an average elongation coefficient of 1.4 per pass, and the intermediate bar is rolled into a φ28mm billet. Finishing rolling is performed using a slight tension rolling process with an exit speed of 100 m / s, and the billet is rolled into φ6.5mm wire rod. The exit temperature of the roughing rolling process is 1000°C, the exit temperature of the intermediate rolling process is 970°C, the entrance temperature of the finishing rolling process is 910°C, and the wire laying temperature is 870°C.

[0047] 5. Stelmor cooling: In the primary air cooling section, a fan is turned on, and the wire rod is cooled to 790°C at a cooling rate of 2°C / s; then it enters the insulation cover for slow cooling, with a cooling rate of 0.35°C / s, and the temperature out of the insulation cover is 592°C; according to the product performance requirements, a fan is turned on for secondary air cooling, with a cooling rate of 2°C / s, the cooling temperature is cooled to 503°C, and then air-cooled to 445°C for coiling.

[0048] After testing, the H08MnMo steel wire rod prepared in this embodiment has an inclusion rating of 1.0. The metallographic structure is uniform, the grain size is small, about 6μ, the tensile strength is 622MPa, the elongation after fracture is 31%, the cross-sectional reduction rate is 75%, and the metallographic structure is mainly ferrite (F), with a small amount of pearlite (P) and bainite (B), meeting the high quality requirements of submerged arc welding wire. The finished wire rod steel grain size is shown in FIG. Figure 2 , the metallographic structure of wire rod steel is shown in Figure 3 .

[0049] Example 2:

[0050] 1. Raw Material Preparation: 65 tons of scrap steel with a sulfur content of 0.010% and a phosphorus content of 0.015%, and 35 tons of pig iron with a silicon content of 0.9% and a manganese content of 0.7% were placed in a 100-ton electric furnace. 2.5 tons of slagging agents (1.56 tons of lime, 0.62 tons of fluorite, and 0.31 tons of bauxite) were added for smelting.

[0051] 2. Molten Steel Refining: Molten steel from the converter is transferred to the LF refining furnace, where 80 kg of silicon-calcium-barium alloy (0.8 kg / t of molten steel) is added for deoxidation and desulfurization. The bottom-blown argon flow rate is controlled at 80 L / min, and the stirring time is 15 minutes. After refining, the molten steel temperature is 1590°C.

[0052] 3. Continuous Casting: Fully protected casting is used, with a mold containing mold slag with a melting temperature of 1060°C and a viscosity of 1.1 Pa·s. The continuous casting speed is 1.0 m / min, the water content in the secondary cooling zone is 0.4 L / kg, and the cross-sectional dimensions of the ingot are 150 mm × 150 mm.

[0053] 4. Heating and Rolling: The continuous casting slab is heated to 1110°C and soaked in a heating furnace for 1.6 hours. The rough rolling process uses a total reduction of 60%, and the slab is rolled into a 60mm φ intermediate bar. The intermediate rolling process uses a low-tension rolling process with an exit speed of 110 m / s, and the slab is rolled into a φ10mm wire rod. The rough rolling exit temperature is 1030°C, the intermediate rolling exit temperature is 982°C, the finishing entry temperature is 925°C, and the wire drawing temperature is 882°C.

[0054] 5. Stelmor cooling: In the primary air cooling section, a fan is turned on, and the wire rod is cooled to 780℃ at a cooling rate of 2.5℃ / s; then it enters the insulation cover for slow cooling, and two sets of insulation covers are dropped, with a cooling rate of 0.30℃ / s and a temperature out of the insulation cover of 530℃; then the secondary air cooling is turned on, with a cooling rate of 2.5℃ / s, and the cooling temperature is reduced to 512℃, and finally air-cooled to 450℃ for coiling.

[0055] Testing revealed that the H08MnMo steel wire rod produced in this example had an inclusion rating of 0.8. It also exhibited a uniform metallographic structure, fine grain size of approximately 7.5μ, a tensile strength of 553 MPa, an elongation of 37%, and a reduction of area of ​​77%. The metallographic structure was primarily ferrite (F) with a small amount of pearlite (P), meeting the high-quality requirements for submerged arc welding wire.

[0056] Example 3:

[0057] 1. Raw Material Preparation: 65 tons of scrap steel with a sulfur content of 0.015% and a phosphorus content of 0.012%, and 35 tons of pig iron with a silicon content of 1.2% and a manganese content of 1.0%, were placed in a 100-ton electric furnace. 3 tons of slagging agents (1.8 tons of lime, 0.76 tons of fluorite, and 0.37 tons of bauxite) were added for smelting.

[0058] 2. Molten Steel Refining: Molten steel from the converter is transferred to the LF refining furnace, where 100 kg of silicon-calcium-barium alloy (1 kg / t of molten steel) is added for deoxidation and desulfurization. The bottom-blown argon flow rate is controlled at 120 L / min, and the stirring time is 19 minutes. After refining, the molten steel temperature is 1580°C.

[0059] 3. Continuous casting process: full protection casting was adopted, and the protective slag with a melting temperature of 1100 °C and a viscosity of 1.5 Pa-s was used in the crystallizer. The continuous casting speed was 1.2 m / min, the specific water consumption in the secondary cooling zone was 0.6 L / kg, and the cross-sectional size of the casting blank was 150 mm x 150 mm.

[0060] 4. Heating and rolling: the continuous casting blank was heated to 1120 °C and soaked in the heating furnace for 3.0 h. The total reduction rate of rough rolling was 65%, and the blank was rolled into a φ 52 mm intermediate blank. The average elongation coefficient of each pass in the intermediate rolling was 1.4, and the intermediate blank was rolled into a φ 25 mm blank. The fine rolling adopted micro-tension rolling, the exit speed of fine rolling was 90 m / s, and the blank was rolled into a φ 4.5 mm rod. The rough rolling exit temperature was 986 °C, the intermediate rolling exit temperature was 938 °C, the fine rolling entry temperature was 909 °C, and the wire laying temperature was 875 °C.

[0061] 5. Stelmor cooling: two fans were opened in the primary air cooling section, and the rod was cooled to 760 °C at a cooling speed of 3 °C / s; then it entered the holding cover for slow cooling, fell into two holding covers, the cooling rate was 0.26 °C / s, and the exit temperature of the holding cover was 536 °C; then the secondary air cooling was opened, the cooling speed was 3 °C / s, and the cooling temperature was cooled to 515 °C, and finally air-cooled to 450 °C for collecting.

[0062] After detection, the H08MnMo steel rod prepared in this example had a sulfur content of 0.003%, a phosphorus content of 0.010%, and an inclusion rating of 1.0 grade. The metallographic structure was uniform, the grain size was small, about 6.2 μ, the tensile strength was 560 MPa, the elongation after fracture was 35%, the reduction of area was 79%, the metallographic structure was mainly ferrite (F) and a small amount of pearlite (P), which met the high quality requirements of submerged arc welding wire.

[0063] Example 4:

[0064] 1. Raw material preparation: 60 t of scrap steel with a sulfur content of 0.011% and a phosphorus content of 0.014%, and 40 t of pig iron with a silicon content of 0.92% and a manganese content of 0.75% were selected and put into a 100 t electric furnace. 2.4 t of slagging agent (1.46 t of lime, 0.65 t of fluorite, and 0.34 t of bauxite) was added for smelting.

[0065] 2. Molten steel refining: the molten steel after the converter was transferred to the LF refining furnace, and 80 kg (0.8 kg / t of molten steel) of silicon-calcium-barium alloy was added for deoxidation and desulfurization treatment. The argon flow rate of bottom blowing was controlled at 80 L / min, and the stirring time was 17 min. After the refining was completed, the molten steel temperature was 1597 °C.

[0066] 3. Continuous Casting: Fully protected casting is used, with a mold containing mold slag with a melting temperature of 1060°C and a viscosity of 1.1 Pa·s. The continuous casting speed is 1.1 m / min, the water content in the secondary cooling zone is 0.4 L / kg, and the cross-sectional dimensions of the ingot are 150 mm × 150 mm.

[0067] 4. Heating and Rolling: The continuous casting slab is heated to 1120°C and soaked in a heating furnace for 1.5 hours. The rough rolling process uses a total reduction of 60%, and the slab is rolled into a 60mm φ intermediate bar. The intermediate rolling process uses an average elongation coefficient of 1.35 for each pass, and the intermediate bar is rolled into a 30mm φ billet. Finishing rolling uses micro-tension rolling at an exit speed of 110 m / s, and the billet is rolled into a 12mm φ wire rod. The rough rolling exit temperature is 1024°C, the intermediate rolling exit temperature is 972°C, the finishing rolling inlet temperature is 922°C, and the wire drawing temperature is 886°C.

[0068] 5. Stelmor cooling: two fans are turned on in the primary air cooling section, and the wire rod is cooled to 760℃ at a cooling rate of 3℃ / s; then it enters the insulation cover for slow cooling, and four sets of insulation covers are dropped. The cooling rate is 0.30℃ / s, and the temperature out of the insulation cover is 540℃. Slow cooling can avoid the formation of a large amount of hard and brittle structures such as martensite due to too fast cooling rate, and prevent problems such as poor drawing performance and easy wire breakage; then the secondary air cooling is turned on, the cooling rate is 3℃ / s, the cooling temperature is cooled to 522℃, and finally air-cooled to 435℃ for coiling.

[0069] Testing revealed that the H08MnMo steel wire rod produced in this example had an inclusion rating of 0.7. It also exhibited a uniform metallographic structure, fine grain size of approximately 9.5μ, a tensile strength of 541 MPa, an elongation of 39%, and a reduction of area of ​​79%. The metallographic structure was primarily ferrite (F) with a small amount of pearlite (P), meeting the high-quality requirements for submerged arc welding wire.

[0070] Example 5:

[0071] 1. Raw Material Preparation: 62 tons of scrap steel with a sulfur content of 0.015% and a phosphorus content of 0.012%, and 38 tons of pig iron with a silicon content of 1.12% and a manganese content of 0.8% were placed in a 100-ton electric furnace. 3.5 tons of slagging agents (1.85 tons of lime, 0.76 tons of fluorite, and 0.37 tons of bauxite) were added for smelting.

[0072] 2. Molten Steel Refining: Molten steel from the converter is transferred to the LF refining furnace, where 100 kg of silicon-calcium-barium alloy (1 kg / t of molten steel) is added for deoxidation and desulfurization. The bottom-blown argon flow rate is controlled at 120 L / min, and the stirring time is 20 minutes. After refining, the molten steel temperature is 1583°C.

[0073] 3. Continuous casting process: full protection casting is adopted, the protective slag with melting temperature of 1096℃ and viscosity of 1.4 Pa·s is used in the crystallizer. The continuous casting speed is 1.2 m / min, the specific water consumption of the secondary cooling zone is 0.6 L / kg, and the cross-sectional size of the casting blank is 150 mm x 150 mm.

[0074] 4. Heating and rolling: the continuous casting blank is heated to 1105℃, and is soaked for 2.0 h in the heating furnace. The total reduction rate of rough rolling is 65%, the casting blank is rolled into a φ52 mm intermediate blank; the average elongation coefficient of each pass of the intermediate rolling is 1.4, the intermediate blank is rolled into a φ25 mm blank; the fine rolling adopts micro-tension rolling, the exit speed of the fine rolling is 100 m / s, and the blank is rolled into a φ7.5 mm rod. The rough rolling exit temperature is 996℃, the intermediate rolling exit temperature is 949℃, the fine rolling inlet temperature is 912℃, and the laying wire temperature is 888℃.

[0075] 5. Stelmor cooling: two fans are opened in the primary air cooling section, the rod is cooled to 770℃ at a cooling speed of 3℃ / s; then the rod is slowly cooled in the heat preservation cover, two groups of heat preservation covers are fallen, the cooling rate is 0.22℃ / s, and the exit temperature of the heat preservation cover is 545℃; according to the product performance requirement, one group of fans is opened in the secondary air cooling, the cooling speed is 2℃ / s, the cooling temperature is 501℃, and finally the air cooling is performed to 442℃ for collecting.

[0076] Through detection, the H08MnMo steel rod prepared in the embodiment has an inclusion rating of 1.0 level. The metallographic structure is uniform, the grain size is small about 5.5 μ, the tensile strength is 566 MPa, the elongation after fracture is 34%, the reduction of area is 79%, the metallographic structure is mainly ferrite (F) and a small amount of pearlite (P), and the requirements of the submerged arc welding wire are met.

[0077] As can be seen from the above embodiment, the preparation method of the submerged arc welding wire H08MnMo steel rod can effectively improve the purity of the molten steel, improve the uniformity of the rod structure, and improve the comprehensive performance of the rod, and has a good application prospect.

[0078] Example 6:

[0079] 1. Raw material preparation: 67 t of scrap steel with sulfur content of 0.013% and phosphorus content of 0.013%, 33 t of pig iron with silicon content of 0.8% and manganese content of 0.75% are put into a 100 t electric furnace. 2.3 t of slagging agent (1.46 t of lime, 0.52 t of fluorite, and 0.31 t of bauxite) is added for smelting.

[0080] 2. Molten Steel Refining: Molten steel from the converter is transferred to the LF refining furnace, where 80 kg of silicon-calcium-barium alloy (0.8 kg / t of molten steel) is added for deoxidation and desulfurization. The bottom-blown argon flow rate is controlled at 80 L / min, and the stirring time is 16 minutes. After refining, the molten steel temperature is 1615°C.

[0081] 3. Continuous Casting: Fully protected casting is used, with a mold containing mold slag with a melting temperature of 1064°C and a viscosity of 1.1 Pa·s. The continuous casting speed is 1.0 m / min, the water content in the secondary cooling zone is 0.4 L / kg, and the cross-sectional dimensions of the ingot are 150 mm × 150 mm.

[0082] 4. Heating and Rolling: The continuous casting slab is heated to 1087°C and soaked in a heating furnace for 2.6 hours. The rough rolling process uses a total reduction of 60%, and the slab is rolled into a 60mm φ intermediate bar. The intermediate rolling process uses an average elongation coefficient of 1.33 for each pass, and the intermediate bar is rolled into a 30mm φ billet. Finishing rolling uses micro-tension rolling at an exit speed of 96 m / s, and the billet is rolled into 4.8mm φ wire rod. The rough rolling exit temperature is 986°C, the intermediate rolling exit temperature is 938°C, the finishing rolling inlet temperature is 907°C, and the wire drawing temperature is 867°C.

[0083] 5. Stelmor cooling: In the primary air cooling section, a fan is turned on, and the wire rod is cooled to 760°C at a cooling rate of 2.5°C / s; then it enters the insulation cover for slow cooling, and two sets of insulation covers are dropped, with a cooling rate of 0.30°C / s and a temperature out of the insulation cover of 537°C; then the secondary air cooling is turned on, with a cooling rate of 2.5°C / s, and the cooling temperature is reduced to 521°C. Finally, it is air-cooled to 442°C for coiling.

[0084] Testing revealed that the H08MnMo steel wire rod produced in this example had an inclusion rating of 0.8. It also exhibited a uniform metallographic structure, fine grain size of approximately 7.5μ, a tensile strength of 588 MPa, an elongation of 33%, and a reduction of area of ​​74%. The metallographic structure was primarily ferrite (F), with minor amounts of pearlite (P) and bainite (B), meeting the high-quality requirements for submerged arc welding wire.

[0085] Example 7:

[0086] 1. Raw Material Preparation: 65 tons of scrap steel with a sulfur content of 0.015% and a phosphorus content of 0.012%, and 35 tons of pig iron with a silicon content of 1.2% and a manganese content of 1.0%, were placed in a 100-ton electric furnace. 3 tons of slagging agents (1.8 tons of lime, 0.77 tons of fluorite, and 0.36 tons of bauxite) were added for smelting.

[0087] 2. Molten Steel Refining: Molten steel from the converter is transferred to the LF refining furnace, where 100 kg of silicon-calcium-barium alloy (1 kg / t of molten steel) is added for deoxidation and desulfurization. The bottom-blown argon flow rate is controlled at 120 L / min, and the stirring time is 19 minutes. After refining, the molten steel temperature is 1582°C.

[0088] 3. Continuous Casting: The process utilizes fully protected casting, using a mold slag with a melting temperature of 1100°C and a viscosity of 1.5 Pa·s. The continuous casting speed is 1.2 m / min, the water content in the secondary cooling zone is 0.6 L / kg, and the cross-sectional dimensions of the ingot are 150 mm × 150 mm.

[0089] 4. Heating and Rolling: The continuous casting slab is heated to 1084°C and soaked in a heating furnace for 3.0 hours. The rough rolling process is performed with a total reduction of 65%, and the slab is rolled into a φ52mm intermediate bar. The intermediate rolling process uses an average elongation coefficient of 1.4 for each pass, and the intermediate bar is rolled into a φ25mm billet. Finishing rolling is performed using a slight tension rolling process with an exit speed of 90 m / s, and the billet is rolled into φ5.5mm wire rod. The rough rolling exit temperature is 984°C, the intermediate rolling exit temperature is 938°C, the finishing rolling inlet temperature is 910°C, and the wire drawing temperature is 885°C.

[0090] 5. Stelmor Cooling: Two fans are activated in the primary air cooling section, and the wire rod is cooled to 755°C at a cooling rate of 3°C / s. It then enters the insulation hood for slow cooling, with three sets of insulation hoods lowered. The cooling rate is 0.26°C / s, and the temperature out of the insulation hood is 566°C. Based on product performance requirements, two fans are activated in the secondary air cooling section, and the wire rod is cooled to 480°C at a cooling rate of 3°C / s. Increasing the cooling rate can inhibit the growth of austenite grains. Rapid cooling reduces the atomic diffusion capacity within the austenite grains, reducing the driving force for grain growth, thereby inhibiting the growth of austenite grains at high temperatures and retaining a relatively large fine-grained structure. From the perspective of phase transformation dynamics, the cooling rate affects the transformation of austenite to phases such as ferrite and pearlite. A higher cooling rate lowers the phase transformation point and increases the degree of undercooling. According to the C curve (isothermal transformation curve for undercooled austenite), increased undercooling shortens the incubation period for austenite transformation and accelerates the transformation rate, resulting in the formation of fine ferrite grains and pearlite. Furthermore, rapid cooling may also promote the formation of high-strength phases such as bainite, further improving the strength and toughness of the steel. Finally, the steel is air-cooled to 448°C for coiling.

[0091] Testing revealed that the H08MnMo steel wire rod produced in this example had an inclusion rating of 1.0. It also exhibited a uniform metallographic structure, fine grain size of approximately 5μ, a tensile strength of 640 MPa, an elongation of 30%, and a reduction of area of ​​73%. The metallographic structure was primarily ferrite (F), with minor amounts of pearlite (P) and bainite (B), meeting the high-quality requirements for submerged arc welding wire.

Claims

1. A method for preparing H08MnMo wire rod for submerged arc welding wire, comprising converter smelting, molten steel refining, continuous casting, heating and rolling, and Stelmor cooling, characterized in that: Specifically include: The continuous casting process comprises the following steps: the melting temperature of the mold powder is 1050-1100°C, the viscosity is 1.0-1.5 Pa·s, the continuous casting speed is controlled at 1.0-1.2 m / min, and the water content in the secondary cooling zone is controlled at 0.4-0.6 L / kg; The heating and rolling process includes heating the continuous casting billet to 1080-1120°C, soaking time in the heating furnace for 1.5-3.0 hours, controlling the total reduction rate in the rough rolling stage at 60%-65%, and controlling the elongation coefficient of each intermediate rolling pass at 1.3-1.5; controlling the outlet speed of the finishing rolling at 80-115 m / s; controlling the outlet temperature of the rough rolling at 980-1030°C, the outlet temperature of the intermediate rolling at 930-990°C, the inlet temperature of the finishing rolling at 900-930°C, and the wire laying temperature at 850-890°C. The Stelmor cooling comprises the following steps: in the primary air cooling section, the wire rod is cooled to 710-820°C at a cooling rate of 2-3°C / s; then the wire rod enters the heat preservation cover for slow cooling, the outlet temperature of the wire rod at the heat preservation cover is 510-600°C, and the cooling rate is 0.25-0.45°C / s; then the secondary air cooling is turned on, the cooling rate is 2-3°C / s, the cooling temperature is reduced to 480-570°C, and finally the wire rod is air cooled to 350-450°C for coiling.

2. The method for preparing H08MnMo wire rod for submerged arc welding wire according to claim 1, characterized in that: The converter smelting uses scrap steel and pig iron as basic raw materials, wherein the sulfur content of the scrap steel is not more than 0.015%, and the phosphorus content is lower than 0.02%; the silicon content of the pig iron is 0.8%-1.2%, and the manganese content is 0.6%-1.0%.

3. The method for preparing H08MnMo wire rod for submerged arc welding wire according to claim 1 or 2, characterized in that: The converter slag-forming agent is composed of lime, fluorite and bauxite in a mass ratio of (4.5-5.5): (1.8-2.2): (0.9-1.1), and the added amount of the slag-forming agent is 2%-3% of the total mass of the furnace charge.

4. The method for preparing H08MnMo wire rod for submerged arc welding wire according to claim 1, characterized in that: The molten steel refining comprises the following steps: the molten steel from the converter is transferred to an LF refining furnace for refining; during the LF refining process, a silicon-calcium-barium alloy is added to the molten steel for deoxidation and desulfurization, with the addition amount of the silicon-calcium-barium alloy being 0.8-1.2 kg / t of molten steel; and bottom-blown argon is used for stirring, with the argon flow rate controlled at 80-120 L / min and the stirring time being 15-20 min.

5. The method for preparing H08MnMo wire rod for submerged arc welding wire according to claim 4, characterized in that: After refining, the continuous casting steel temperature is 1580~1620℃.

6. A H08MnMo wire rod for submerged arc welding wire, characterized in that: The wire rod is prepared by the preparation method of H08MnMo wire rod for submerged arc welding wire as described in any one of claims 1 to 5, and the chemical composition of the wire rod steel is as follows by weight percentage: C: 0.06% to 0.10%, Si: 0.12% to 0.18%, Mn: 1.35% to 1.45%, P≤0.015%, S≤0.005%, Mo: 0.35% to 0.45%, Ti: 0.05% to 0.08%, and the rest is Fe and unavoidable impurities.

7. The H08MnMo wire rod for submerged arc welding wire according to claim 6, characterized in that: The tensile strength of the wire rod is 541-640 MPa, the cross-sectional shrinkage is 73%-79%, and the elongation is 30%-40%.

8. The H08MnMo wire rod for submerged arc welding wire according to claim 6, characterized in that: The cross section of the wire rod is an equiaxed grain structure with uniform grain size, grain size of 5 to 12μ, grain size of 8.0 to 8.5, and the metallographic structure is mainly ferrite, with a small amount of pearlite or a small amount of pearlite and bainite.

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