CN109112402B - Steel plate for VC (polyvinyl chloride) nanoparticle reinforced X80 plastic pipe and manufacturing method thereof - Google Patents

Abstract

The invention provides a VC nano-particle reinforced X80 plastic pipe steel sheet and a manufacturing method thereof. The composition of the steel sheet is as follows in weight percentage: C 0.06%-0.12%, Si 0.10%-0.30%, Mn 0.60%-1.40%, V 0.07%～0.15%, N 0.001%～0.004%, Ti 0.01%～0.04%, Al 0.025%～0.045%, P≤0.010%, S≤0.005%, Cu≤0.30%, Mo≤0.30%, Cr 0.12 %～0.30%, Ni 0.12%～0.30%, the rest are Fe and inevitable impurity elements. The production method includes material preparation→converter or electric furnace smelting→out-of-furnace refining→casting→slab reheating→controlled rolling→controlled cooling. The steel sheet produced by the invention has a ferrite structure with high uniform elongation characteristics; VC nano-particles are used as a reinforcing phase to meet the needs of high-pressure transportation of natural gas, oil and the like.

Description

VC nanoparticle reinforced X80 steel plate for plastic pipe and its manufacturing method

technical field

The invention belongs to the field of metal materials, and in particular relates to a steel sheet for X80 grade oil and gas plastic pipes using VC nanoparticles as a reinforcing phase and a manufacturing method thereof.

Background technique

With the increasing demand for oil and gas resources, the investment and construction of new oil and gas fields are gradually increasing. Because the production and consumption areas of oil and gas often need to pass through areas with harsh geological conditions such as tundra, seismic zones, and deserts, long-distance oil and gas pipelines need to have good plastic deformation capabilities. Typical performance parameters that characterize the plastic deformation ability of pipes are low yield ratio (eg Rt0.5/Rm≤0.80) and high uniform elongation (eg uEL≥10%).

In order to obtain good plastic deformation ability, two methods are usually adopted: 1) increase the wall thickness of the pipe; 2) increase the volume fraction of the high plastic phase in the pipe. In practical applications, using these two methods alone or in combination has certain shortcomings. Increasing the wall thickness of the pipe will increase the investment in pipeline construction and reduce the cost performance; increasing the high-plastic phase in the pipe will limit the strength of the pipe (the high-plastic phase is usually the low-strength phase), which is related to the development of high-strength materials for high-pressure transportation of oil and gas resources. Trend does not match.

At present, most of the steel plates for plastic pipes are dual-phase steel plates, and there are two main production process routes. One is to supply the hot-rolled steel plate after controlled rolling and controlled cooling (TMCP), and the other is to heat-treat the steel plate after controlled rolling and controlled cooling before use. . Since the dual-phase structure strategy is adopted to ensure the plastic deformation ability, the structure with large difference in strength between the two phases is not conducive to improving the low-temperature toughness and HIC resistance of the material.

For example, CN201510830269.7 discloses a high-strength, low-yield ratio quenched and tempered steel sheet for low temperature environment, and its chemical composition weight percentages are: C: 0.045-0.068%; Si: 0.13-0.25%; Mn: 1.55-1.74%; P≤0.020%; S≤0.0015%; Cr: 0.25～0.33%; Cu: 0.14～0.21%; Ni: 0.18～0.25%; Nb: 0.035～0.044%; V: 0.033～0.049%; Ti: 0.010～0.016 %; others are Fe and inevitable impurities. In this patent, the single-phase bainite structure is obtained by the modulation process, which ensures the low-temperature toughness of the two-pass steel plate, but the excellent plastic deformation ability of the present invention is not obtained. CN201510419067.3 provides a new type of Cu-containing pipeline steel with excellent resistance to hydrogen sulfide corrosion while ensuring high strength and toughness. The alloy composition and weight percentage are: C: 0.015-0.035%; Si: 0.10-0.20%; Mn : 0.8-1.1%; Cu: 1.0-2.0%; Ni: 0.30-0.40%; Mo: 0.30-0.40%; Cr: 0.30-0.40%; Nb: 0.04-0.06%. The excellent HIC capability in this invention comes from the high content of Cu, which is fundamentally different from the anti-corrosion principle in this invention. Patents CN101456034A and WO2009125863 provide X70 and X80 pipeline steels based on strain design requirements and their preparation methods. Although high plastic deformation ability can be obtained, their microstructure is F-B type dual-phase structure, which has the same characteristics as the single-phase structure of the present invention. significant difference.

The invention adopts VC as the strengthening phase to produce the single-phase structure steel plate, and obtains better comprehensive performance than the dual-phase steel plate.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the above-mentioned problems and deficiencies and provide a kind of oil and gas transmission line pipe that can ensure the safety of laying in complex geological areas, meet the purposes of high-pressure transportation of natural gas, oil, etc., and has a VC nano-particle reinforced X80 plastic pipe with good plastic deformation ability. Steel sheet and method of making the same.

The object of the present invention is achieved in this way:

A VC nano-particle reinforced X80 plastic pipe steel plate, the composition of the steel plate is as follows in weight percentage: C 0.06%-0.12%, Si 0.10%-0.30%, Mn 0.60%-1.40%, V 0.07%-0.15%, N 0.001%～0.004%, Ti 0.01%～0.04%, Al 0.025%～0.045%, P≤0.010%, S≤0.005%, Cu≤0.30%, Mo≤0.30%, Cr 0.12%～0.30%, Ni 0.12 %～0.30%, the rest are Fe and inevitable impurity elements.

Further, the microstructure of the steel sheet is a ferrite structure, the ferrite phase interface is uniformly distributed with nano-sized VC particles, the size of the VC particles does not exceed 300nm, and the volume fraction of the VC particles is 0.05%～ 0.20%.

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

C: the most economical and basic strengthening element in steel, has obvious effect on improving the strength of steel through solid solution strengthening and precipitation strengthening, but increasing the C content has a negative impact on the plasticity, toughness and weldability of steel; in the present invention , the main role of C is to combine with V element to form nano-sized VC particles for strengthening materials. For this reason, the present invention sets the C content in the range of 0.06% to 0.12%.

Si: Si has the effect of deoxidizing steelmaking and improving the strength of the matrix. If Si is excessive, it will reduce the toughness of the base metal welding heat affected zone and affect the field welding construction; increasing the content of Si can purify the ferrite and reduce the content of pearlite, which is beneficial to reduce the Bauschinger effect of the matrix material. Therefore, the Si content is set to 0.10% to 0.30% in the present invention.

Mn: It increases the strength of steel through solid solution strengthening, and is the most important and most economical strengthening element in pipeline steel to compensate for the loss of strength caused by the reduction of C content. Mn helps to obtain fine low-temperature transformation products, which can improve the toughness of steel. Increasing the content of Mn will aggravate the segregation in the center of the continuous casting billet, which is not conducive to the improvement of the low temperature toughness and HIC resistance of the steel plate. Therefore, the Mn content range of the present invention is designed to be 0.60% to 1.40%.

V: V is one of the commonly used elements in modern micro-alloyed pipeline steel, which has a good precipitation strengthening effect; after VC is precipitated on the material matrix, its yield strength can be improved without significantly affecting the plastic deformation ability of the material; excessive The V will increase the difficulty of process control in the continuous casting process. The present invention selects the V content in the range of 0.07% to 0.15%.

Ti: It is a strong solid N element and exists in the form of TiN in continuous slab casting. The fine TiN particles can effectively inhibit the growth of austenite grains when the slab is reheated, help to increase the solid solubility of V in austenite, and improve the impact toughness of the welding heat-affected zone. When the addition amount of Ti exceeds a certain value, the TiN particles will be coarsened and the stress concentration level between the particle interface and the matrix will be increased. Therefore, the present invention selects the Ti content in the range of 0.01% to 0.04%.

N: In addition to the formation of fine TiN particles to refine the austenite grains, the N element in the steel has no other obvious beneficial effects in the X80 steel plate for plastic pipes, so it needs to be kept at a lower content level. The N content ranges from 0.001% to 0.004%.

Al: Usually used as a deoxidizer in steel, if AlN is formed, it can also refine the structure. When the Al content exceeds 0.045%, excessive alumina inclusions will reduce the cleanliness of the steel. If the Al content is too low, the deoxidation will be insufficient, and easily oxidizable elements such as Ti will form oxides. Therefore, the lower limit of the Al content is set to 0.025%.

Cr, Mo, Cu, Ni: Cr and Mo are the main elements that delay the formation of ferrite and promote the formation of acicular ferrite, and play an important role in controlling the phase transformation structure. The bainite structure can be obtained, which is beneficial to the reasonable matching of strength, plasticity and toughness. While Cu and Ni increase the strength of steel through solid solution strengthening, Cu can also improve the corrosion resistance of steel. The addition of Ni mainly improves low temperature toughness and reduces the hot embrittlement tendency caused by Cu in steel. For these four alloy elements, the present invention selects the content range of Cr and Ni to be 0.12% to 0.30%, and the content of Cu and Mo to be ≤0.30%.

P, S: are inevitable impurity elements in steel, the lower the better. Considering the cost of smelting, it cannot be unrestrictedly low. Therefore, the present invention sets the upper limit of the content of P and S to 0.010% and 0.005%.

The second technical solution of the present invention is to provide a manufacturing method of a VC nanoparticle-reinforced X80 plastic pipe steel plate, including material preparation→converter or electric furnace smelting→out-of-furnace refining→casting→slab reheating→controlled rolling→controlled cooling;

(1) Slab reheating: the billet is reheated after cleaning, and the billet discharge temperature Tso is 1150-1220 °C;

(2) Controlled rolling: the final rolling temperature of rough rolling is Trf ≥ 1000 °C; the thickness t' of the intermediate slab to be warmed is 2.5t ~ 4.0t, t is the thickness of the finished steel plate; the finishing rolling temperature Tfs is 800 ~ 900 °C, The final rolling temperature Tff is 720～820℃;

(3) Controlled cooling: the opening cooling temperature Tcs is 720-800°C, the final cooling temperature Tcf is 400-600°C, and the cooling rate Sc is 15-24°C/s, to obtain a fine and uniform bainite structure;

(4) heat treatment is carried out after the controlled cooling, water-cooled to room temperature, and the heat treatment is solution treatment and isothermal heat treatment;

Solution treatment: Put the steel plate after controlled cooling into a heating furnace for solution treatment. The temperature Ti before the steel plate is put into the furnace is room temperature ~ Tcf, the solution temperature Ts1 is 1180 ~ 1220℃, and the solution treatment time ts1 is 0.5 ~2.5h (h, hour); the purpose of solution treatment is to fully dissolve V in austenite to prepare for subsequent VC precipitation;

Isothermal heat treatment: After the solution treatment is completed, the isothermal heat treatment is carried out immediately. The isothermal temperature Ts2 is 670~710℃, and the isothermal time ts2 is 0.1~5.0h; the purpose of the isothermal heat treatment is to make the VC nanoparticles fully and uniformly. The precipitation on the ferrite phase interface;

After the isothermal heat treatment is completed, use water as a cooling medium to accelerate cooling to room temperature, and finally obtain a ferrite structure. Nano-sized VC particles are uniformly distributed on the phase interface, the particle size does not exceed 300nm, and the particle volume fraction is 0.05% to 0.20% .

In order to meet the required properties of the X80 steel plate for plastic pipes, the present invention adopts the composition design of low carbon and low manganese, V and Ti composite microalloying, selective addition of Mo, Cu, appropriate addition of Cr and Ni, and no addition of Nb; Casting billet production adopts pure steel smelting technology and high-quality slab production technology; in the process of steel plate production, two-stage controlled rolling technology, controlled cooling and heat treatment technology are adopted, and the obvious ferrite-based and VC nano-particle-enhanced technology is obtained. The microstructure has good strength and toughness matching and plastic deformation resistance.

By adopting the above components, controlled rolling, controlled cooling and heat treatment scheme, the defects existing in the prior art are overcome, and the production and application of the steel sheet for X80 plastic pipes are realized.

The beneficial effects of the present invention are:

(1) Using low C and low Mn, compound addition of Cu, Mo, V, Ti, no addition of Nb, and selective addition of Ni and Cr to the composition design of low carbon equivalent, which effectively reduces the production cost.

(2) The two-stage controlled rolling TMCP process is used to produce hot-rolled steel sheets with bainite as the main structure.

(3) After solution treatment and isothermal heat treatment of hot-rolled steel sheet, a ferrite structure with high uniform elongation characteristics is obtained; VC nanoparticles are used as reinforcing phase to make the steel sheet have high yield strength; the heat treatment state after water cooling to room temperature The steel plate meets the requirements of various mechanical properties of X80 steel plate for plastic pipes, and the low temperature toughness and HIC resistance are particularly good.

(4) The transverse mechanical properties of the steel plate can meet the following requirements: the yield strength Rt0.5 is 470～570MPa, the tensile strength Rm is 650～750MPa, the yield strength ratio Rt0.5/Rm≤0.85, the impact energy CVN≥200J at -30℃ , -20℃ DWTT shear area SA≥85%, HV10≤260; the longitudinal mechanical properties of steel plate can meet the following requirements: Rt0.5 is 460~560MPa, tensile strength Rm is 640~740MPa, yield ratio Rt0.5/ Rm≤0.80, uniform extension uEL≥10%.

(5) The cost-effective production of X80 plastic pipe steel plate with low temperature toughness and excellent HIC resistance is realized through reasonable composition design and process system matching. The steel pipe manufactured by using the steel plate produced by the invention can be used in areas with complex geological conditions and meets the safety requirements of oil and gas transportation.

Detailed ways

The present invention will be further illustrated by the following examples.

In the embodiment of the present invention, according to the component distribution ratio of the technical scheme, material preparation→converter or electric furnace smelting→out-of-furnace refining→casting→slab reheating→controlled rolling→controlled cooling→solid solution treatment→isothermal heat treatment→water cooling to room temperature ,

(1) Slab reheating: the billet is reheated after cleaning, and the billet discharge temperature Tso is 1150-1220 °C;

(2) Controlled rolling: the final rolling temperature of rough rolling is Trf ≥ 1000 °C; the thickness t' of the intermediate slab to be warmed is 2.5t ~ 4.0t, t is the thickness of the finished steel plate; the finishing rolling temperature Tfs is 800 ~ 900 °C, The final rolling temperature Tff is 720～820℃;

(3) Controlled cooling: the opening cooling temperature Tcs is 720-800°C, the final cooling temperature Tcf is 400-600°C, and the cooling rate Sc is 15-24°C/s;

(4) heat treatment is carried out after the controlled cooling, water-cooled to room temperature, and the heat treatment is solution treatment and isothermal heat treatment;

Solution treatment: Put the steel plate after controlled cooling into a heating furnace for solution treatment. The temperature Ti before the steel plate is put into the furnace is room temperature ~ Tcf, the solution temperature Ts1 is 1180 ~ 1220℃, and the solution treatment time ts1 is 0.5 ~2.5h;

Isothermal heat treatment: After the solution treatment is completed, the isothermal heat treatment is carried out immediately.

After the isothermal heat treatment is completed, use water as a cooling medium to accelerate cooling to room temperature, and finally obtain a ferrite structure. Nano-sized VC particles are uniformly distributed on the phase interface, the particle size does not exceed 300nm, and the particle volume fraction is 0.05% to 0.20% .

The composition of the steel in the embodiment of the present invention is shown in Table 1. The main process parameters of the steel of the embodiment of the present invention are shown in Table 2. Table 3 shows the transverse properties of the steel in the embodiment of the present invention. The longitudinal properties and HIC resistance results of the steel in the embodiment of the present invention are shown in Table 4. See Table 5 for the size and volume fraction of VC nanoparticles in the steel sheet of the embodiment of the present invention.

Table 1 Composition (wt%) of the steel according to the embodiment of the present invention

C^* Si Mn Cu Cr Mo Ni V N^* Ti^* Al^* P^* S^* 1 60 0.30 0.60 0 0.12 0 0.12 0.14 1 20 25 9 2 2 80 0.20 0.75 0.28 0.28 0.28 0.28 0.13 2 30 35 6 2 3 100 0.15 0.90 0 0.20 0.10 0.20 0.12 2 30 45 3 4 4 120 0.10 1.15 0.10 0.20 0 0.20 0.11 1 20 35 6 4 5 115 0.14 1.30 0.15 0.15 0.15 0.15 0.10 3 40 25 9 3 6 95 0.23 1.39 0 0.20 0.10 0.20 0.09 4 40 25 5 5 7 75 0.28 1.39 0.10 0.20 0 0.20 0.08 3 40 35 9 2 8 65 0.25 1.25 0.05 0.17 0.05 0.12 0.07 2 30 45 6 2 9 65 0.20 1.20 0.25 0.25 0.25 0.25 0.10 1 20 35 3 4 10 95 0.15 0.95 0.20 0.15 0.15 0.15 0.14 1 10 25 6 4 11 75 0.12 0.80 0.15 0.20 0.15 0.15 0.11 3 40 30 9 3 12 110 0.22 0.65 0.15 0.15 0.15 0.20 0.12 2 20 30 5 5

Note: ^* means the value needs to be multiplied by 10 ^{~ 3}

Table 2 Main process parameters of the steel of the embodiment of the present invention

Note: RT stands for room temperature.

Table 3 Transverse properties of steel in the embodiment of the present invention

Rt0.5, MPa Rm, MPa Rt0.5/Rm -30℃CVN, J -20°C DWTT, % HV10 1 507 680 0.75 240 90 220 2 490 675 0.73 264 90 230 3 508 685 0.74 268 90 215 4 482 680 0.71 256 90 220 5 516 710 0.73 276 95 215 6 520 705 0.74 280 95 230 7 508 690 0.74 257 95 235 8 514 700 0.73 284 95 220 9 508 685 0.74 237 90 215 10 513 685 0.75 231 95 225 11 502 685 0.73 291 90 227 12 483 675 0.72 270 95 223

Table 4 Longitudinal properties and anti-HIC results of steels according to embodiments of the present invention

Rt0.5, MPa Rm, MPa Rt0.5/Rm uEL, % CLR, % CTR, % CSR, % 1 510 710 0.72 10 0 0 0 2 498 695 0.72 11 0 0 0 3 504 705 0.71 11 0 0 0 4 498 690 0.72 10 0 0 0 5 503 705 0.71 12 0 0 0 6 492 680 0.72 10 0 0 0 7 473 665 0.71 11 0 0 0 8 497 685 0.73 11 0 0 0 9 480 660 0.73 10 0 0 0 10 498 700 0.71 12 0 0 0 11 471 660 0.71 10 0 0 0 12 506 700 0.72 11 0 0 0

Table 5 VC nanoparticle size and volume fraction in the steel plate of the embodiment of the present invention

Particle volume fraction, % Average particle size, nm 1 0.14 108 2 0.13 114 3 0.13 118 4 0.12 121 5 0.14 149 6 0.13 146 7 0.10 132 8 0.09 129 9 0.10 113 10 0.16 133 11 0.14 138 12 0.15 143

In order to express the present invention, the present invention has been properly and fully described above through the examples. The above embodiments are only used to illustrate the present invention, but not to limit the present invention. Under the circumstance of the spirit and scope of the invention, various changes and modifications can also be made, and any modifications, equivalent replacements, improvements, etc. made should be included within the protection scope of the present invention, and the patent protection scope of the present invention should be The claims are limited.

Claims (2)

1. A steel sheet for reinforced X80 plastic pipes by VC nano-particles, characterized in that the composition of the steel sheet is as follows by weight percentage: C 0.06%～0.12%, Si 0.10%～0.30%, Mn 0.60%～1.40%, V 0.07 %～0.15%, N 0.001%～0.004%, Ti 0.01%～0.04%, Al 0.025%～0.045%, P≤0.010%, S≤0.005%, Cu≤0.30%, Mo≤0.30%, Cr 0.12%～ 0.30%, Ni 0.12% to 0.30%, and the rest are Fe and inevitable impurity elements; the manufacturing method of a VC nanoparticle-strengthened X80 plastic pipe steel plate includes material preparation→converter or electric furnace smelting→out-of-furnace refining→casting → slab reheating → controlled rolling → controlled cooling, (1) Slab reheating: The billet is reheated after cleaning, and the temperature of the billet is 1150-1220℃; (2) Controlled rolling: the final rolling temperature of rough rolling is greater than or equal to 1000 ℃; the thickness of the intermediate billet to be warmed is 2.5t ~ 4.0t, t is the thickness of the finished steel plate; the starting temperature of finishing rolling is 800 ~ 900 ℃, the finishing rolling The temperature is 720～820℃; (3) Controlled cooling: the opening cooling temperature is 720-800°C, the final cooling temperature is 400-600°C, and the cooling rate is 15-24°C/s; (4) heat treatment after controlled cooling, water cooling to room temperature, and the heat treatment is solution treatment and isothermal heat treatment; Solution treatment: The steel plate after controlled cooling is subjected to solution treatment. The temperature of the steel plate before entering the furnace is from room temperature to the final cooling temperature, the solution temperature is 1180-1220°C, and the solution treatment time is 0.5-2.5h; Isothermal heat treatment: After the solution treatment is completed, the isothermal heat treatment is carried out immediately. The isothermal temperature is 670~710℃, and the isothermal time is 0.1~5.0h. 2. A kind of VC nano-particle reinforced X80 plastic pipe steel sheet according to claim 1, characterized in that, the microstructure of the steel sheet is a ferrite structure, and nanometer size is uniformly distributed on the ferrite phase interface VC particles, the size of the VC particles does not exceed 300nm, and the volume fraction of the VC particles is 0.05% to 0.20%.