Hot-rolled coil plate high-strength thick-specification pipeline steel and preparation method thereof

Abstract

The invention discloses hot-rolled coil plate high-strength thick-specification pipeline steel and a preparation method thereof, and belongs to the technical field of steel, and the pipeline steel comprises the following components in percentage by weight: 0.05-0.08% of C, 0.16-0.24% of Si, 1.50-1.59% of Mn, 0.12-0.20% of Cr, 0.057-0.067% of Nb, 0.04-0.08% of Mo, 0.012-0.020% of Ti, 0.02-0.05% of Alt, less than or equal to 0.018% of P, less than or equal to 0.005% of S, less than or equal to 0.15% of Ni, less than or equal to 0.1% of Cu, less than or equal to 0.03% of V, less than or equal to 0.005% of B and the balance of iron and inevitable impurity elements. The preparation method comprises the steps of molten iron pretreatment, converter smelting, external refining, continuous casting, slab heating, rolling, cooling, coiling and the like. The pipeline steel prepared by adopting an alloying production process meets the requirements on various properties.

Description

Technical Field

[0001] The present invention relates to the technical field of steel, and in particular to a hot-rolled coil high-strength thick-gauge pipeline steel and a preparation method thereof. Background Art

[0002] Pipeline transportation is the most economical way to transport oil and natural gas over long distances. With the increase in global demand for oil and natural gas, the transportation pressure of pipeline steel for trunk roads has gradually increased. In order to ensure the safety and stability of oil and gas pipeline transportation, the requirements for material thickness specifications and strength and toughness have gradually increased. Steel for branch lines such as urban pipelines often use thin-walled products, but as the thickness of the product decreases, the strength increases, which will lead to a larger yield ratio. An excessively high yield ratio reduces the deformation strengthening ability of the material, resulting in a decrease in the yield strength and bearing capacity of the steel pipe, which is very likely to fail during service. Therefore, international restrictions have been placed on the yield ratio of pipeline steel. In recent years, the construction of energy transmission pipelines has developed rapidly. In order to improve the transmission efficiency and operation safety, the strength and toughness requirements of the selected steel raw materials are getting higher and higher. At present, major domestic and foreign pipeline trunk lines basically use X70 (L485M), X80 (L555M) steel grades and higher-grade coils, and branch lines, urban pipelines, etc. mostly use X65 (L450M) steel grades, and the yield strength ratio is relaxed to 0.90 or even 0.93. The personalized demand for various properties of pipeline steel has put forward higher requirements on the composition and production process of pipeline steel. For example, for parameters such as the toughness of steel, the detection temperature of the drop hammer and the ductile-brittle transition temperature, and the impact energy, it is far from meeting the requirements to simply meet the conventional specifications of pipeline steel. Summary of the invention

[0003] Technical problems to be solved: In view of the technical problems existing in the production process of pipeline steel in the prior art, the present invention provides a hot-rolled coil with high strength and thick specifications for pipeline steel. By adopting the C-Mn-Nb-Mo alloying production process, continuous casting and rolling can be achieved to produce high-strength and thick specifications (10-19mm) L450M pipeline steel hot-rolled coil, meeting the requirements for various performances.

[0004] The invention provides a hot-rolled coil high-strength thick specification pipeline steel. The hot-rolled coil high-strength thick specification pipeline steel comprises the following components and weight percentages: C 0.05-0.08%, Si 0.16-0.24%, Mn 1.50-1.59%, Cr 0.12-0.20%, Nb 0.057-0.067%, Mo 0.04-0.08%, Ti 0.012-0.020%, Alt 0.02-0.05%, P≤0.018%, S≤0.005%, Ni≤0.15%, Cu≤0.1%, V≤0.03%, B≤0.005%, and the rest are iron and unavoidable impurity elements.

[0005] Preferably, the hot-rolled coil high-strength and thick-specification pipeline steel contains the following components and weight percentages: C 0.05%, Si 0.19%, Mn 1.55%, Cr 0.16%, Nb 0.06%, Mo 0.05%, Ti 0.015%, Alt 0.035%, P≤0.018%, S≤0.005%, Ni≤0.15%, Cu≤0.1%, V≤0.03%, B≤0.0050%, and the rest are iron and unavoidable impurity elements.

[0006] Preferably, the cold crack sensitivity coefficient of the hot-rolled coil high-strength thick specification pipeline steel is: Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B≤0.20.

[0007] Preferably, the yield strength of the hot-rolled coil high-strength thick specification pipeline steel is ≥470MPa, the tensile strength is ≥550MPa, the elongation is ≥25%, the yield strength ratio is ≤0.87, the impact energy at 0°C is ≥390J, the hardness HV10 is ≤225, and the average shear area SA of the drop hammer tear test at 0°C is ≥90.

[0008] The present invention also discloses a method for preparing hot-rolled coil high-strength and thick-specification pipeline steel, the preparation method comprising: molten iron pretreatment → converter smelting → refining outside the furnace → continuous casting → slab heating → rolling → cooling → coiling; The composition of the molten steel produced in the off-furnace refining stage meets the composition requirements of pipeline steel; In the slab continuous casting stage, non-oxidation protection casting is performed, and the thickness of the continuous casting slab is 200-220 mm; In the slab heating stage, the heating temperature is controlled at 1200-1220°C and the time in the furnace is ≥180min; In the rough rolling stage, the rough rolling start temperature is 1100-1200° C., and the billet is rolled to an intermediate billet state for waiting for temperature. The rough rolling thickness of the billet is 40-50 mm. The final rolling temperature of the finishing rolling stage is 790-850°C, and the thickness of the finished steel plate after final rolling is 10-19mm; In the cooling stage, the rolled pipeline steel is cooled by an ultra-fast cooling system and a roughing section laminar cooling system; The coiling temperature in the coiling stage is 450-550°C.

[0009] Preferably, when the thickness of the finished steel plate is 10.0 mm ≤ h < 15.0 mm, the rough rolling thickness of the ingot is 45 mm, the rough rolling outlet temperature is 1000-1040° C., and the final rolling temperature in the finishing rolling stage is 800-850° C.; When the thickness of the finished steel plate is 15.0mm≤h≤19.0mm, the rough rolling thickness of the ingot is 48mm, the rough rolling outlet temperature is 1000~1040℃, and the final rolling temperature in the finishing rolling stage is 790~830℃.

[0010] Compared with the prior art, the present invention has at least the following beneficial effects: 1. The present invention adopts the C-Mn-Nb-Mo alloying production process, which can realize continuous casting and rolling to produce high-strength thick specification (10-19mm) L450M pipeline steel hot-rolled coils, meet the requirements for various properties, and reduce the alloy cost; 2. Optimize the process flow of slab heating, rough rolling and finishing rolling, and adopt ultra-fast cooling + laminar cooling process to obtain ideal product structure and performance and reduce production difficulty; 3. The alloy composition of the hot-rolled coil high-strength thick-specification pipeline steel of the present invention is reasonably designed, and the optimized smelting continuous casting, controlled rolling and ultra-fast cooling + laminar cooling process are adopted. The yield strength of the produced pipeline steel is ≥470MPa, the tensile strength is ≥550MPa, the elongation is ≥25%, the yield strength ratio is ≤0.87, the impact energy at 0℃ is ≥390J, the hardness HV10 is ≤225, and the average shear area of ​​the drop hammer tear test at 0℃ is SA≥90. Its comprehensive mechanical properties are improved to meet customer needs, broaden the supply specifications of pipeline steel hot-rolled coils, and improve the competitiveness of pipeline steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a production process flow chart of pipeline steel according to an embodiment of the present invention; Figure 2 This is a drop hammer cross-sectional structure of the debugging roll according to an embodiment of the present invention. DETAILED DESCRIPTION

[0012] To make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the following will be combined with the attached Figure 1~2 The technical solutions of the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the described embodiments of the present invention belong to the scope of protection of the present invention.

[0013] The invention provides a hot-rolled coil high-strength thick specification pipeline steel. The hot-rolled coil high-strength thick specification pipeline steel comprises the following components and weight percentages: C 0.05-0.08%, Si 0.16-0.24%, Mn 1.50-1.59%, Cr 0.12-0.20%, Nb 0.057-0.067%, Mo 0.04-0.08%, Ti 0.012-0.020%, Alt 0.02-0.05%, P≤0.018%, S≤0.005%, Ni≤0.15%, Cu≤0.1%, V≤0.03%, B≤0.005%, and the rest are iron and unavoidable impurity elements, and the cold crack sensitivity coefficient Pcm of the hot-rolled coil high-strength thick specification pipeline steel is ≤0.20.

[0014] The present invention adopts C-Mn-Nb-Mo alloying production process, can realize continuous casting and rolling production of high-strength thick specification (10~19mm) L450M pipeline steel hot rolled coil, meet the requirements for various performances. Among them, the C element content is second only to the iron element content, which directly affects the strength, plasticity, toughness and welding performance of steel, etc. The contribution of the C element to tensile strength is higher than the yield strength, and the yield strength ratio has a tendency to decrease with the increase of the C element. As the C content increases, the toughness and weldability of the steel gradually deteriorate, so the C element content is controlled to 0.05~0.08%. The Si element is an important reducing agent and deoxidizer in the steelmaking process. The Si element can also be dissolved in ferrite and austenite to improve the strength of the steel, but it is not conducive to the improvement of plasticity and toughness, so the Si element content is controlled to 0.16~0.24%. Mn has a solid solution strengthening effect, and can also reduce the phase transition temperature, refine the ferrite grains, and compensate for the strength loss caused by the reduction of carbon content. Too high manganese content will lead to serious segregation, so the manganese content is controlled at 1.50~1.59%. Nb is a functional element that controls rolling. It has the effects of reducing the phase transition temperature, expanding the rolling process window in the recrystallization zone, and promoting the formation of acicular ferrite structure. The grain refinement effect of Nb is the most important strengthening element in pipeline steel, but grain refinement easily leads to an increase in the yield strength ratio, so the Nb content is controlled at 0.057~0.067%. Mo can promote the formation of acicular ferrite and form a certain number of Maho islands, increase the number of nucleation nodules, dislocation density and precipitation hardening ability, and easily lead to an increase in the yield strength ratio, so the Mo content is controlled at 0.04~0.08%.

[0015] Examples 1 to 3 are used to specifically illustrate the contents of various components of the hot-rolled coil high-strength thick specification pipeline steel of the present invention. Examples 1 to 3 only give process control indicators of pipeline steel components, see Table 1 for details.

[0016] Table 1 Chemical composition index of steel grade L450M (mass fraction, %):

[0017] .

[0018] Note: Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

[0019] like Figure 1 As shown, the present invention also discloses a preparation method of a hot-rolled coil with high strength and thick specifications for pipeline steel, the preparation method comprising: molten iron pretreatment → converter smelting → refining outside the furnace → continuous casting → slab heating → rolling → cooling → coiling; wherein, the composition of the molten steel produced in the refining outside the furnace meets the composition requirements of pipeline steel; non-oxidation protection casting is performed in the slab continuous casting stage, and the thickness of the continuous casting slab is 200~220mm; in the slab heating stage, the heating temperature is controlled at 1200~1220℃, and the furnace time is ≥180min; in the rough rolling stage, the rough rolling start temperature is 1100~1200℃, and the slab is rolled to the intermediate slab state for waiting for temperature, and the rough rolling thickness of the cast slab is 40~50mm; the final rolling in the finishing stage The temperature is 790~850℃, and the thickness of the finished steel plate after final rolling is 10~19mm; wherein, when the thickness of the finished steel plate is 10.0mm≤h<15.0mm, the rough rolling thickness of the ingot is 45mm, the rough rolling outlet temperature is 1000~1040℃, and the final rolling temperature of the finishing stage is 800~850℃; when the thickness of the finished steel plate is 15.0mm≤h≤19.0mm, the rough rolling thickness of the ingot is 48mm, and the rough rolling outlet temperature is 1000~1040℃; the final rolling temperature of the finishing stage is 790~830℃; in the cooling stage, the rolled pipeline steel is cooled by the ultra-fast cooling system and the rough adjustment section laminar cooling system; the coiling temperature of the coiling stage is 450~550℃. The process parameters for implementing the preparation method of the present invention are shown in Table 2.

[0020] Table 2 Process system of steel grade L450M (mass fraction, %):

[0021] .

[0022] The performance of the L450M pipeline steel prepared in Examples 4 to 9 of the present invention was tested. The mechanical properties are shown in Table 3. The cross-sectional structure of the drop hammer sample of the commissioning roll is shown in Table 3. Figure 2 shown.

[0023] Table 3 Mechanical properties of steel grade L450M:

[0024] .

[0025] The hot-rolled coil high-strength thick specification pipeline steel produced by the preparation method of the present invention has a yield strength of ≥470MPa, a tensile strength of ≥550MPa, an elongation of ≥25%, a yield strength ratio of ≤0.87, an impact energy of ≥390J at 0°C, a hardness of HV10≤225, and an average shear area of ​​SA of a drop hammer tear test at 0°C of ≥90, and its comprehensive mechanical properties are improved to meet customer needs, broaden the supply specifications of pipeline steel hot-rolled coils, and improve the competitiveness of pipeline steel.

[0026] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A hot-rolled coil high-strength thick specification pipeline steel, characterized in that: The hot-rolled coil high-strength thick specification pipeline steel contains the following components and weight percentages: C 0.05~0.08%, Si 0.16~0.24%, Mn 1.50~1.59%, Cr 0.12~0.20%, Nb 0.057~0.067%, Mo 0.04~0.08%, Ti 0.012~0.020%, Alt 0.02~0.05%, P≤0.018%, S≤0.005%, Ni≤0.15%, Cu≤0.1%, V≤0.03%, B≤0.005%, and the rest are iron and unavoidable impurity elements.

2. The hot-rolled coil high-strength thick specification pipeline steel according to claim 1, characterized in that: The hot-rolled coil high-strength and thick specification pipeline steel contains the following components and weight percentages: C 0.05%, Si 0.19%, Mn 1.55%, Cr 0.16%, Nb0.06%, Mo 0.05%, Ti 0.015%, Alt 0.035%, P≤0.018%, S≤0.005%, Ni≤0.15%, Cu≤0.1%, V≤0.03%, B≤0.0050%, and the rest are iron and unavoidable impurity elements.

3. The hot-rolled coil high-strength thick specification pipeline steel according to claim 1 or 2, characterized in that: The cold crack sensitivity coefficient of the hot rolled coil high strength thick specification pipeline steel is: Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B≤0.

20.

4. The hot-rolled coil high-strength thick specification pipeline steel according to claim 3, characterized in that: The hot-rolled coil high-strength thick specification pipeline steel has a yield strength of ≥470MPa, a tensile strength of ≥550MPa, an elongation of ≥25%, a yield strength ratio of ≤0.87, an impact energy of ≥390J at 0°C, a hardness of HV10≤225, and a shear area SA of ≥90 in a 0°C average drop hammer tear test.

5. A method for preparing a hot-rolled coil high-strength and thick specification pipeline steel according to claim 4, characterized in that: The preparation method comprises: molten iron pretreatment → converter smelting → refining outside the furnace → continuous casting → slab heating → rolling → cooling → coiling; The composition of the molten steel produced in the off-furnace refining stage meets the composition requirements of pipeline steel; In the slab continuous casting stage, non-oxidation protection casting is performed, and the thickness of the continuous casting slab is 200-220 mm; In the slab heating stage, the heating temperature is controlled at 1200-1220°C and the time in the furnace is ≥180min; In the rough rolling stage, the rough rolling start temperature is 1100-1200° C., and the billet is rolled to an intermediate billet state for waiting for temperature. The rough rolling thickness of the billet is 40-50 mm. The final rolling temperature of the finishing rolling stage is 790-850°C, and the thickness of the finished steel plate after final rolling is 10-19mm; In the cooling stage, the rolled pipeline steel is cooled by an ultra-fast cooling system and a roughing section laminar cooling system; The coiling temperature in the coiling stage is 450-550°C.

6. The hot-rolled coil high-strength thick specification pipeline steel and the preparation method thereof according to claim 5, characterized in that: When the thickness of the finished steel plate is 10.0mm≤h<15.0mm, the rough rolling thickness of the ingot is 45mm, the rough rolling outlet temperature is 1000~1040℃, and the final rolling temperature of the finishing rolling stage is 800~850℃; When the thickness of the finished steel plate is 15.0mm≤h≤19.0mm, the rough rolling thickness of the ingot is 48mm, the rough rolling outlet temperature is 1000~1040℃, and the final rolling temperature in the finishing rolling stage is 790~830℃.

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