Hot-rolled pickled steel sheet for precision welded pipe and method for manufacturing the same

Abstract

The present application provides a kind of hot-rolled pickling steel plate for precision welded pipe and its manufacturing method, the steel plate includes the component and its percentage by weight as follows: C:0.040%~0.070%, Si≤0.030%, Mn:0.40%~0.80%, P≤0.015%, S≤0.010%, Al:0.020%~0.060%, Ni:0.005%~0.025%, B:0.0010%~0.0030%, and the balance of Fe and inevitable impurities;Wherein, (10C+5Mn+3Al+2Ni+20B) / (Si+P+S+0.001)≥100.The hot-rolled pickling steel plate of the present application, the yield strength of mechanical property is 280~360Mpa, the tensile strength is 400~500Mpa, A 50 elongation is ≥40%, the surface roughness Ra value is ≤1.0 μm, with good surface quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal materials, and particularly relates to a hot-rolled pickled steel plate for precision welded pipe and a manufacturing method thereof. BACKGROUND

[0002] Precision welded pipes are widely used in many fields such as construction, machinery manufacturing and automobile industry. This puts strict requirements on the quality of the steel plate for precision welded pipe. When the traditional hot-rolled steel plate is used for welded pipe manufacturing, many problems are exposed, such as poor surface quality, and the surface scale is easy to produce inclusions during welding, which seriously affects the strength and compactness of the weld. At the same time, the chemical composition and microstructure of the existing part of the hot-rolled steel plate are unreasonable, which cannot guarantee high strength while taking into account good toughness and processing performance. Moreover, the production method of part of the steel plate for welded pipe on the market is complex and costly, which is difficult to meet the needs of large-scale industrial production.

[0003] For example, Chinese patent (CN104263901A) “Manufacturing method of low yield ratio pipeline steel for straight seam welded pipe” discloses a manufacturing method of low yield ratio pipeline steel for straight seam welded pipe, which comprises: smelting-continuous casting production process: hot metal pretreatment-converter-LF refining-RH refining-casting machine; the chemical composition of the molten steel for the casting machine is C: 0.13-0.15%, Si: 0.10-0.20%, Mn: 1.05-1.20%, P≤0.010%, S≤0.005%, Nb: 0.010-0.020%, Ti: 0.010-0.020%, the balance being Fe and other unavoidable impurities; hot rolling production process: billet heating-coarse rolling-precision rolling-coiling. The pipeline steel plate produced by the present application has excellent tensile and impact properties, and the yield ratio is <0.86. At the same time, the alloy cost of the present application is low, the preparation method is simple, and it is suitable for industrial production. However, the steel plate in the patent is a hot-rolled steel plate, the surface quality cannot meet the requirements, the toughness and processing performance cannot meet the requirements, and the drawing cannot meet the requirements, which is suitable for welded pipeline, but not suitable for precision welded pipe.

[0004] For example, Chinese patent (CN117758158A) "Steel for low strength welded pipe with cover and its production method" discloses a steel for low strength welded pipe with cover and its production method, relates to the field of steel rolling, and aims to meet the needs of excellent forming performance and low coil strength; the chemical composition of the steel is as follows: C≤0.0020%, Si≤0.020%, Mn: 0.10%-0.20%, P≤0.015%, S≤0.010%, Al: 0.030%-0.060%, Ti: 0.050%-0.070%, B: 0.0010%-0.0020%, N≤0.0025%, and the rest is Fe and inevitable impurities; the production method comprises the steps of hot rolling, pickling, five-stand full six-roll cold continuous rolling, cover annealing, and flattening; the cold-rolled steel plate produced by the method has a thickness of 0.40 mm-1.00 mm, a yield strength of 120 MPa-140 MPa, a tensile strength of 280 MPa-320 MPa, and an elongation after fracture of ≥40%, and the prepared steel for welded pipe can meet the needs of excellent forming performance and low coil strength. The patent is different from the hot-rolled pickled steel plate for precision welded pipe of the present application, and the steel for welded pipe has low strength and can only be used to make condenser pipes, and cannot be used in industries with high strength requirements such as shock absorbers.

[0005] Therefore, it is of great practical significance to develop a hot-rolled pickled steel plate for precision welded pipe with good surface quality, excellent welding performance and reasonable production cost, and a production method thereof. SUMMARY

[0006] The present application aims to provide a hot-rolled pickled steel plate for precision welded pipe and a manufacturing method thereof, so as to solve the problem that the existing hot-rolled pickled steel plate for precision welded pipe cannot have good surface quality, excellent welding performance and reasonable production cost.

[0007] To solve the above technical problems, the present application provides a hot-rolled pickled steel plate for precision welded pipe, which comprises the following components and their weight percentages: C: 0.040%-0.070%, Si≤0.030%, Mn: 0.40%-0.80%, P≤0.015%, S≤0.010%, Al: 0.020%-0.060%, Ni: 0.005%-0.025%, B: 0.0010%-0.0030%, and the rest is Fe and inevitable impurities; wherein (10C+5Mn+3Al+2Ni+20B) / (Si+P+S+0.001)≥100.

[0008] Optionally, the surface quality of the hot-rolled pickled steel plate for precision welded pipe is above FB, the yield strength is 280-360 MPa, the tensile strength is 400-500 MPa, the A50 elongation ≥ 40%, surface roughness Ra value ≤ 1.0 μm.

[0009] Optionally, it comprises continuous casting, heating, hot rolling, laminar cooling, pickling and temper rolling processes, characterized in that the temper rolling is wet temper rolling.

[0010] Optionally, a hydrochloric acid solution with a concentration of 15% to 17% is used as the pickling medium, the pickling temperature is controlled at 65 to 75℃, and the pickling time is 6 to 12 minutes.

[0011] Optionally, during laminar cooling, the cooling speed is stabilized at 15 to 25℃ / s through precise flow and pressure control, and the final cooling temperature is controlled at 630 to 650℃.

[0012] Optionally, the final rolling temperature of the hot rolling process is controlled at 880 to 920℃.

[0013] Optionally, it further comprises a molten iron pretreatment process, which performs deep desulfurization and dephosphorization treatment on the molten iron to reduce the sulfur content in the molten iron to below 0.015% and the phosphorus content to below 0.015%.

[0014] Optionally, it further comprises a converter steelmaking process, in which the oxygen flow is controlled at 24000 to 26000 m³ / h, the final tapping temperature is controlled at 1630 to 1650℃, and the carbon content is controlled at 0.04% to 0.07%.

[0015] Optionally, it further comprises a refining process, and the refining time is controlled at 35-45 minutes.

[0016] Optionally, the continuous casting slab is heated to 1180 to 1220℃ during hot rolling heating, and the heating time is controlled at 130 to 160 minutes.

[0017] The present application provides a kind of hot-rolled pickling steel plate for precision welded pipe and its manufacturing method, with the following beneficial effects:

[0018] By accurately controlling the composition of steel, and by hot rolling, pickling, wet temper rolling process produces hot-rolled pickling steel plate for precision welded pipe. According to the method produced hot-rolled pickling steel plate, the yield strength of mechanical properties is 280~360Mpa, the tensile strength is 400~500Mpa, A 50 elongation ≥ 40%, surface roughness Ra value ≤ 1.0 μm, with good surface quality. CN104263901A yield strength ≥ 345Mpa, tensile strength ≥ 490Mpa, A 50 elongation ≤ 25%, surface roughness Ra value ≥ 3.0 μm, hot-rolled plate surface is rough, insufficient extension, only suitable for welded pipeline. CN117758158A yield strength 120~140Mpa, tensile strength 280~320Mpa, A50 The elongation is greater than or equal to 40%, the surface roughness Ra value is less than or equal to 0.8 microns, the strength is insufficient, and the low-strength condenser pipe is only applicable.

[0019] The present application establishes an element coordination formula, reconstructs a strengthening mechanism by using ultra-low carbon + ultra-low silicon + B-Ni micro-alloying, develops a medium-temperature high-concentration pickling + wet leveling technology, and makes the surface quality of the hot-rolled pickling plate first comparable to that of the cold-rolled plate. The present application successfully develops the first steel plate for precision welded pipe in the world, which has the surface quality (Ra≤1.0 microns) of the cold-rolled plate + the formability (A 50 ≥40%) of the cold-rolled plate + the strength (TS≥400Mpa) of the hot-rolled plate. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a metallographic structure picture of Example 1 of the present application. DETAILED DESCRIPTION

[0021] The present embodiment provides a hot-rolled pickling steel plate for precision welded pipe, which comprises the following components and their weight percentages: C: 0.040%~0.070%, Si≤0.030%, Mn: 0.40%~0.80%, P≤0.015%, S≤0.010%, Al: 0.020%~0.060%, Ni: 0.005%~0.025%, B: 0.0010%~0.0030%, and the balance of Fe and inevitable impurities.

[0022] Among them, (10C+5Mn+3Al+2Ni+20B) / (Si+P+S+0.001)≥100.

[0023] The hot-rolled pickling steel plate for precision welded pipe in the present embodiment has the characteristics of good surface quality, excellent welding performance, and reasonable production cost.

[0024] The hot-rolled pickling steel plate for precision welded pipe in the present embodiment has good surface quality and excellent mechanical properties mainly based on the following principles:

[0025] 1) Carbon (C): C is the most economical and effective solid solution strengthening element for improving strength. With the increase of C content, the strength increases, but the plasticity and formability of the steel decrease. The influence on the welding performance is negative. With the increase of carbon content, the welding performance of the steel will become worse. Therefore, the C content in the present embodiment is controlled within 0.040%~0.070%. Compared with CN104263901A, the ultra-low carbon design reduces the carbon equivalent by more than 50%, and the welding crack sensitivity is significantly reduced.

[0026] 2) Silicon (Si): Too high Si content, the scale on the surface of the steel plate is not easy to remove, the surface is easy to form micro-cracks due to oxide pressing, which affects the surface quality of the steel plate and the surface smoothness in pipe drawing, therefore, the Si content in the present embodiment is controlled in the range of ≤0.030%. Compared with CN104263901A, the present application adopts ultra-low silicon to inhibit the adhesion of scale from the root.

[0027] 3) Manganese (Mn): Mn can reduce the phase transition temperature of austenite to ferrite, which is beneficial to the refinement of ferrite grains; but too high Mn content increases the Mn segregation degree during continuous casting, and the center part of the steel plate is easy to form bainite or banded structure, which is easy to cause delamination defects for high-strength steel; at the same time, it is also the crack source of fatigue failure, which is not conducive to plasticity, welding performance, fatigue performance and surface quality. After comprehensive consideration, the Mn content in the present embodiment is controlled in the range of 0.40%~0.80%. Compared with CN104263901A and CN117758158A, the present application adopts medium manganese route to balance strength and workability, and avoid banded structure caused by high manganese.

[0028] 4) Phosphorus (P): Phosphorus is easy to form segregation in welded pipe steel, which has an adverse effect on the forming performance, low temperature impact toughness and welding performance of the welded pipe. Therefore, the phosphorus content in the welded pipe steel in the present embodiment is controlled below 0.015% to ensure the comprehensive performance of the welded pipe.

[0029] 5) Sulfur (S): S is also a harmful element under normal circumstances, which causes hot brittleness of steel, reduces the ductility and toughness of steel, causes cracks during forging and rolling, affects the surface quality of the steel plate, increases the risk of welding cracks, and requires the S content to be as low as possible, therefore, the S content of the steel grade in the present embodiment is controlled below 0.010%.

[0030] 6) Aluminum (Al): Al as the main deoxidizer helps to remove oxygen and inclusions in the welded pipe steel, and improves the purity and quality of the steel. At the same time, aluminum can also refine the grains, improve the strength and toughness of the steel. However, too high aluminum content will affect the hot working performance and welding performance of the welded pipe steel. The Al content in the present embodiment is controlled in the range of 0.020%~0.060%.

[0031] 7) Nickel (Ni): Nickel can improve the corrosion resistance, plasticity, high temperature strength and endurance strength of austenitic steel, and also significantly improve the toughness of the steel. Appropriate addition of nickel is usually beneficial to the welding performance. The Ni content of the steel grade in the present embodiment is controlled within 0.005%~0.025%.

[0032] 8) Boron (B): The element can significantly promote the clarification of the grain boundary of the steel material, enhance the plasticity and toughness of the grain boundary, and is an effective component for improving the welding performance, but too high B content will increase the crack sensitivity of the casting blank. The B percentage content of the steel grade in the embodiment is controlled in the range of 0.0010% to 0.0030%.

[0033] The B-Ni in the application is synergistic, B improves the hardenability, and Ni inhibits the grain boundary segregation.

[0034] (10C+5Mn+3Al+2Ni+20B) / (Si+P+S+0.001)≥100 The formula is used to comprehensively consider the influence of each element on the performance of the steel plate. The numerator (strengthening factor): the basic strength skeleton is constructed by 10C+5Mn, 3Al promotes deoxidization and refines the grain, and Ni+20B synergistically improves the hardenability (Ni inhibits B segregation, and B improves the phase change driving force); the denominator (weakening factor): strictly suppress Si, P, S and other elements (Si≤0.030%, P≤0.015%, S≤0.010%) that damage the weldability and surface quality. Technical effect: the formula first realizes the dynamic balance control of the strengthening elements and the weakening elements, and ensures that under the condition of ultra-low carbon (0.04-0.07%), the strength-formability-weldability triple optimization is realized through micro-alloying.

[0035] The surface quality of the hot-rolled pickled steel plate for precision welded pipes in the embodiment is above FB, the yield strength is 280-360 MPa, the tensile strength is 400-500 MPa, the A 50 The elongation is ≥40%, and the surface roughness Ra value is ≤1.0 μm.

[0036] The hot-rolled pickled steel plate for precision welded pipes in the embodiment has uniform surface color and luster.

[0037] The embodiment also provides a manufacturing method of the hot-rolled pickled steel plate for precision welded pipes, comprising:

[0038] Pretreatment of molten iron: the molten iron is subjected to deep desulfurization and dephosphorization treatment, so that the sulfur content in the molten iron is reduced to below 0.015%, and the phosphorus content is reduced to below 0.015%;

[0039] Converter steelmaking: the carbon content is controlled in the range of 0.04% to 0.07%;

[0040] Refining treatment: the sulfur content in the molten steel is further reduced to below 0.010%;

[0041] Continuous casting;

[0042] Heating;

[0043] Hot rolling;

[0044] Laminar cooling;

[0045] coiling;

[0046] pickling; and

[0047] wet skin pass to make the surface roughness Ra of the steel plate ≤1.0 μm.

[0048] Preferably, the molten iron pretreatment adopts a blowing process, and the subsequent steelmaking process provides pure and high-quality raw materials.

[0049] Preferably, the converter steelmaking: the oxygen flow is controlled at 24000-26000 m³ / h, and the blowing time is 20-24 minutes to ensure that the carbon content and temperature of the molten steel accurately reach the target range. The end-point tapping temperature is controlled at 1630-1650 ℃. Among them, the top and bottom combined blowing converter is used for steelmaking, and the oxygen flow and blowing time are strictly controlled by means of a high-precision automatic control system during the blowing process.

[0050] Preferably, the refining treatment: the refining time is controlled at 35-45 minutes. The composition uniformity of the molten steel is ensured by means of electromagnetic stirring and the like. After tapping, the molten steel is quickly transferred to the LF (ladle furnace) for refining. During the refining process, the addition amount and type of the refining slag are adjusted in real time according to the composition of the molten steel, and precise slagging operation is performed.

[0051] Preferably, the casting speed is accurately controlled at 1.1-1.4 m / min during continuous casting. The molten steel after refining is cast into a slab by using a high-efficiency continuous casting process. During the continuous casting process, the cooling water flow of the mold is reasonably adjusted according to the accurate calculation of the cross section of the cast slab to ensure that the solidification quality of the cast slab is uniform and stable.

[0052] Preferably, heating: the continuous casting slab is heated to 1180-1220 ℃, and the heating time is controlled at 130-160 minutes to ensure uniform heating of the slab and full austenitization of the internal organization, thereby laying a good foundation for the subsequent rolling process. After the continuous casting slab is sent into the heating furnace, it is heated by using a precise temperature control system.

[0053] Preferably, hot rolling: in the rough rolling stage, the heated slab is subjected to multi-pass high-precision rolling to uniformly thin the slab to 32-38 mm; in the finishing rolling stage, the slab is further rolled to the target thickness by the finishing rolling mill group equipped with an advanced automatic control system, and the final rolling temperature is controlled at 880-920 ℃ to ensure that the deformation amount in the austenite non-recrystallization zone is >70%. Among them, during the hot rolling process, high-pressure, high-flow high-pressure water descaling technology is adopted to ensure that the iron oxide scale on the surface of the steel plate is effectively removed, and the surface quality of the steel plate is ensured to reach high standards.

[0054] Preferably, laminar cooling: the cooling speed is stabilized at 15~25℃ / s through precise flow and pressure control, to obtain fine ferrite (grain size≥12 grade) + uniform pearlite structure, and the final cooling temperature is controlled at 630~650℃, to promote uniform nucleation of ferrite, so that the steel plate obtains ideal microstructure and performance, meeting the requirements of the steel for welded pipe. The hot-rolled steel plate is subjected to rapid cooling through the carefully designed laminar cooling device.

[0055] Preferably, coiling: the coiling temperature is controlled at 580~620℃, to ensure that the coil shape of the steel coil is compact and regular, facilitating subsequent processing.

[0056] Preferably, pickling: a hydrochloric acid solution with a concentration of 15%~17% (high-concentration hydrochloric acid) is used as the pickling medium, the pickling temperature is controlled at 65~75℃ (medium-temperature pickling), the efficiency is improved by 50%, the residual iron oxide scale is reduced to 0, and the pickling time is generally 6~12 minutes. Through pickling, the iron oxide scale and impurities on the surface of the steel plate are completely removed, so that the surface of the steel plate presents a uniform silver-gray metallic luster, meeting the specified surface roughness and cleanliness requirements. Among them, the pickling time is dynamically adjusted by an automatic detection system according to the actual thickness of the iron oxide scale on the surface of the steel plate. The pickling temperature is controlled through a precise temperature control system.

[0057] Preferably, wet skin pass: the roughness Ra of the skin pass mill is controlled at 1.0~1.5μm, so that the final surface roughness Ra value of the steel plate is ≤1.0μm, reaching the mirror level standard.

[0058] The application will be described in detail below through examples. Example 1

[0059] The chemical composition of the molten steel is shown in Table 1, and the rest is Fe and inevitable impurity elements.

[0060] Table 1 Chemical composition of Example 1, wt%

[0061] C Si Mn P S Al Ni B Example 1 0.050 0.014 0.72 0.012 0.002 0.028 0.025 0.0012

[0062] After continuous casting of the molten steel, a hot-rolled pickled steel plate for precision welded pipe is produced through hot rolling, pickling and wet skin pass, and the main process parameters, final mechanical properties and surface quality determination are shown in Table 2.

[0063] Table 2 Production process and product mechanical properties of Example 1

[0064] Oxygen flow rate m3 / h Blowing time min Tapping temperature °C Continuous casting speed m / min Heating temperature °C Heating time min Finishing temperature °C Cooling speed °C / s Final cooling temperature °C Coiling temperature °C Pickling temperature °C Pickling concentration % Pickling time min Temper rolling roughness Ra μm Yield strength MPa Tensile strength MPa A 50 elongation Surface roughness Ra μm Example 1 26000 20 1630 1.1 1185 132 916 15 632 580 65 16 10 1.0 286 415 41.5 0.52

[0065] Reference Figure 1 , Figure 1 is the metallographic structure picture of Example 1 of the application. Among them, it is enlarged by 500 times. Example 2

[0066] The chemical composition of the molten steel is shown in Table 3, with the remainder being Fe and inevitable impurity elements.

[0067] Table 3 Chemical composition of Example 2, wt%

[0068] C Si Mn P S Al Ni B Example 2 0.070 0.007 0.58 0.007 0.005 0.036 0.02 0.0021

[0069] After continuous casting of the molten steel, hot-rolled pickled steel plates for precision welded pipes were produced by hot rolling, pickling and wet skin pass, with the main process parameters, final mechanical properties and surface quality determination shown in Table 4.

[0070] Table 4 Production process and product mechanical properties of Example 2

[0071] Oxygen flow rate m3 / h Blowing time min Tapping temperature °C Continuous casting speed m / min Heating temperature °C Heating time min Finishing temperature °C Cooling speed °C / s Final cooling temperature °C Coiling temperature °C Pickling concentration % Pickling temperature °C Pickling time min Temper rolling roughness Ra μm Yield strength MPa Tensile strength MPa A 50 elongation Surface roughness Ra μm Example 2 25000 22 1640 1.2 1201 146 907 20 640 600 17 70 8 1.2 300 425 41.0 0.85 Example 3

[0072] The chemical composition of the molten steel is shown in Table 5, with the remainder being Fe and inevitable impurity elements.

[0073] Table 5 Chemical composition of Example 3, wt%

[0074] C Si Mn P S Al Ni B Example 3 0.06 0.010 0.42. 0.005 0.007 0.057 0.010 0.0029

[0075] After continuous casting of the molten steel, hot-rolled pickled steel plates for precision welded pipes were produced by hot rolling, pickling and wet skin pass, with the main process parameters, final mechanical properties and surface quality determination shown in Table 6.

[0076] Table 6 Production process and product mechanical properties of Example 3

[0077] Oxygen flow rate m3 / h Blowing time min Tapping temperature °C Continuous casting speed m / min Heating temperature °C Heating time min Finishing temperature °C Cooling speed °C / s Final cooling temperature °C Coiling temperature °C Pickling concentration % Pickling temperature °C Pickling time min Temper rolling roughness Ra μm Yield strength MPa Tensile strength MPa A 50 elongation Surface roughness Ra μm Example 3 24000 24 1650 1.4 1218 159 886 25 649 620 15 75 6 1.5 323 437 40.5 0.94

[0078] Comparative Example 1

[0079] The chemical composition of the molten steel is shown in Table 7, with the remainder being Fe and inevitable impurity elements.

[0080] Table 7 Chemical composition of Comparative Example 1, wt%

[0081]

[0082] After continuous casting of the molten steel, hot-rolled pickled steel plates for precision welded pipes were produced by hot rolling, pickling and wet skin pass, with the main process parameters, final mechanical properties and surface quality determination shown in Table 8.

[0083] Table 8 Production process and product mechanical properties of Comparative Example 1

[0084] Oxygen flow rate m3 / h Blowing time min Tapping temperature °C Continuous casting speed m / min Heating temperature °C Heating time min Finishing temperature °C Cooling speed °C / s Final cooling temperature °C Coiling temperature °C Pickling concentration % Pickling temperature °C Pickling time min Temper rolling roughness Ra μm Yield strength MPa Tensile strength MPa A 50 elongation Surface roughness Ra μm Comparative Example 1 24000 20 1630 1.5 1230 180 930 12 700 660 13 70 7 2.5 269 392 42.0 1.63

[0085] Comparative Example 2

[0086] The chemical composition of the molten steel is shown in Table 9, with the remainder being Fe and inevitable impurity elements.

[0087] Table 9 Chemical composition of Comparative Example 2, wt%

[0088] C Si Mn P S Al Ni B Comparative Example 2 0.030 0.200 0.30 0.020 0.024 0.056 0.002 0.0002

[0089] After continuous casting of the molten steel, hot-rolled pickled steel plates for precision welded pipes were produced by hot rolling, pickling and wet skin pass, with the main process parameters, final mechanical properties and surface quality determination shown in Table 10.

[0090] Table 10 Production process and product mechanical properties of Comparative Example 2

[0091] Oxygen flow rate m3 / h Blowing time min Tapping temperature °C Continuous casting speed m / min Heating temperature °C Heating time min Finishing temperature °C Cooling speed °C / s Final cooling temperature °C Coiling temperature °C Pickling concentration % Pickling temperature °C Pickling time min Temper rolling roughness Ra μm Yield strength MPa Tensile strength MPa A 50 elongation Surface roughness Ra μm Comparative Example 2 23000 15 1650 1.2 1170 150 865 30 600 570 16 60 5 1.3 251 362 42.5 0.88

[0092] Comparative Example 3

[0093] The chemical composition of the molten steel is shown in Table 11, with the remainder being Fe and inevitable impurity elements.

[0094] Table 11 Chemical composition of Comparative Example 3, wt%

[0095] C Si Mn P S Al Ni B Comparative Example 3 0.040 0.040 0.40 0.020 0.025 0.020 0.005 0.0010

[0096] After continuous casting of the molten steel, hot-rolled pickled steel plates for precision welded pipes were produced by hot rolling, pickling and wet skin pass, with the main process parameters, final mechanical properties and surface quality determination shown in Table 12.

[0097] Table 12 Production process and product mechanical properties of Comparative Example 3

[0098] Oxygen flow rate m3 / h Blowing time min Tapping temperature °C Continuous casting speed m / min Heating temperature °C Heating time min Finishing temperature °C Cooling speed °C / s Final cooling temperature °C Coiling temperature °C Pickling concentration % Pickling temperature °C Pickling time min Temper rolling roughness Ra μm Yield strength MPa Tensile strength MPa A 50 elongation Surface roughness Ra μm Comparative Example 3 23000 20 1640 1.5 1250 140 925 13 680 650 20 60 5 2.0 273 389 39.5 1.33

[0099] As can be seen from the above examples, when the chemical composition or process does not meet the requirements, the mechanical properties or surface quality of the steel plate will not meet the requirements for making precision welded pipes. For example, Figure 1 Figure 1 Si Mn Ni Comparative Example 3 Oxygen flow rate m3 / h Blowing time min Tapping temperature °C Continuous casting speed m / min Heating temperature °C Heating time min Finishing temperature °C Cooling speed °C / s Final cooling temperature °C Coiling temperature °C Pickling concentration % Pickling temperature °C Pickling time min Temper rolling roughness Ra μm Yield strength MPa Tensile strength MPa Surface roughness Ra μm Comparative Example 3 Figure 1As shown, the hot-rolled and pickled steel plate for precision welded pipe has a structure mainly of ferrite + a small amount of pearlite, a pearlite proportion of 3% to 8%, and a grain size of 11.0 to 12.0 grade. The ferrite + a small amount of pearlite structure arrangement can provide a good strength and plasticity match. The diameter of the lamellar cementite in the pearlite is less than 5 μm, which does not cut the ferrite continuity, and can improve the strength while ensuring a higher elongation. Through the synergistic effect of fine-grain strengthening and dispersion strengthening, the yield strength (280 to 360 MPa) and high elongation (≥40%) performance requirements are matched, the forming and drawing of the welded pipe production are satisfied, and no fracture occurs. There is no coarse cementite in the structure, and the high carbon martensite in the heat-affected zone caused by carbon diffusion during welding does not occur, and no welding cracks are caused. The steel plate with a grain size of 11.0 to 12.0 grade can inhibit grain coarsening after the austenitization and cooling during welding, the surface of the welded pipe is smooth during drawing, and no orange peel and other defects are caused. The hot-rolled and pickled steel plate for precision welded pipe produced by the present application has a yield strength of 280 to 360 MPa, a tensile strength of 400 to 500 MPa, an elongation of ≥40%, and a surface roughness Ra value of ≤1.0 μm, and has good surface quality, and can satisfy the welding and drawing during the precision welded pipe production process. 50 The present application is not limited to the above-mentioned embodiments, and any modification made by a person skilled in the art according to the above-mentioned disclosure falls within the protection scope of the present application.

[0100] The above-mentioned description is only a description of the preferred embodiments of the present application, and is not any limitation on the scope of the present application. Any modification made by a person skilled in the art according to the above-mentioned disclosure falls within the protection scope of the present application.

Claims

1. A hot-rolled pickled steel sheet for precision welded pipes, characterized by, The steel plate contains the following components and their weight percentages: C: 0.040%~0.070%, Si≤0.030%, Mn: 0.40%~0.80%, P≤0.015%, S≤0.010%, Al: 0.020%~0.060%, Ni: 0.005%~0.025%, B: 0.0010%~0.0030%, and the balance of Fe and inevitable impurities; Wherein, (10C+5Mn+3Al+2Ni+20B) / (Si+P+S+0.001)≥100.

2. The hot-rolled pickled steel sheet for precision pipe welding as claimed in claim 1, characterized by, The precision welded pipe hot-rolled pickled steel plate has a surface quality of FB or more, a yield strength of 280-360 MPa, a tensile strength of 400-500 MPa, A 50 an elongation of 40% or more, and a surface roughness Ra value of 1.0 μm or less.

3. A method of manufacturing a hot-rolled pickled steel sheet for precision pipe welding as claimed in claim 1 or 2, comprising continuous casting, heating, hot-rolling, laminar cooling, coiling, pickling, and skin-passing steps, characterized in that, The leveling is wet leveling.

4. The method of producing a hot-rolled pickled steel sheet for precision welded pipes according to claim 3, characterized by A hydrochloric acid solution with a concentration of 15%~17% is used as the pickling medium, the pickling temperature is controlled at 65~75℃, and the pickling time is 6~12 minutes.

5. The method of producing a hot-rolled pickled steel sheet for precision welded pipes according to claim 3, characterized by The cooling speed is stabilized at 15~25℃ / s through precise flow and pressure control, and the final cooling temperature is controlled at 630~650℃.

6. The method of producing a hot-rolled pickled steel sheet for precision welded pipes according to claim 3, characterized by The final rolling temperature of the hot rolling process is controlled at 880~920℃.

7. The method of producing a hot-rolled pickled steel sheet for precision welded pipes according to claim 3, characterized by, The process also includes a molten iron pretreatment process, which deeply desulfurizes and dephosphorizes the molten iron, reduces the sulfur content in the molten iron to below 0.015%, and reduces the phosphorus content to below 0.015%.

8. The method of producing a hot-rolled pickled steel sheet for precision welded pipes according to claim 3, characterized by, The process also includes a converter steelmaking process, in which the oxygen flow is controlled at 24000~26000m³ / h, the final tapping temperature is controlled at 1630~1650℃, and the carbon content is controlled at 0.04%~0.07%.

9. The method of producing a hot-rolled pickled steel sheet for precision welded pipes according to claim 3, characterized by, The process also includes a refining process, and the refining time is controlled at 35~45 minutes.

10. The method of producing a hot-rolled pickled steel sheet for precision welded pipes according to claim 3 or 6, characterized in that, The continuous casting slab is heated to 1180~1220℃ during the hot rolling heating, and the heating time is controlled at 130~160 minutes.

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