CN109112394B - A kind of quenched and tempered low yield ratio X60Q pipeline steel and preparation method - Google Patents

Abstract

The invention discloses a quenched and tempered low-yield ratio X60Q pipeline steel and a preparation method thereof, wherein the pipeline steel comprises the following chemical components: 0.07-0.09 wt% of C, 0.20-0.30 wt% of Si, 1.30-1.50 wt% of Mn, 0.01-0.03 wt% of Alt, less than or equal to 0.015 wt% of P, less than or equal to 0.005 wt% of S, 0.015-0.035 wt% of Nb, 0.01-0.02 wt% of Ti, 0.20-0.30 wt% of Cr, less than or equal to 0.008 wt% of N, and the balance of Fe and unavoidable impurity elements. Solves the technical problems that the quenched and tempered X60Q pipeline steel in the prior art is required to have low stiffness ratio and high difficulty in low-temperature toughness stability. The hardened and tempered low-yield-ratio X60Q pipeline steel provided by the invention has good comprehensive performance, low yield ratio and good low-temperature toughness, and can be suitable for the construction of oil and gas transmission pipelines in some regions such as Africa and the middle east.

Description

A kind of quenched and tempered low yield ratio X60Q pipeline steel and preparation method

technical field

The invention relates to the technical field of pipeline steel, in particular to a quenched and tempered low yield ratio X60Q pipeline steel and a preparation method.

Background technique

Pipeline steel for oil and gas pipelines is usually delivered in the thermomechanical rolled (TMCP) state, but in some regions such as Africa and the Middle East, due to the different transportation environments and media, the owner will also adopt the partially quenched and tempered state (Q+T) delivery. Cargo pipeline steel.

From the perspective of market demand, the first phase of the Algeria pipeline project in Africa requires 1,708 tons of quenched and tempered X60Q pipeline steel. Judging from the technical conditions of the quenched and tempered X60Q pipeline steel used in the Algeria pipeline project, the owner has put forward strict technical requirements. The main technical requirements for the material of the quenched and tempered X60Q pipeline steel project are: 1. How to meet the low yield ratio of the steel plate Performance requirements, the maximum yield ratio Rt0.5/Rm does not exceed 0.85; 2. The shear area of the steel plate at -25℃ in the transverse direction is ≥85%, especially the stability of low temperature toughness at -25℃ during mass production; 3 , Vickers hardness value of steel plate HV10≤235.

The above requirements are mainly reflected in the low yield ratio and low temperature toughness, which are difficult, which requires reasonable composition design and heat treatment process design of the steel plate.

SUMMARY OF THE INVENTION

The invention provides a quenched and tempered low yield ratio X60Q pipeline steel and a preparation method, which are used to solve the technical problems in the prior art that the quenched and tempered X60Q pipeline steel requires low yield ratio and low temperature toughness stability.

In order to solve the above problems, in the first aspect, the embodiment of the present invention provides a quenched and tempered state low yield ratio X60Q pipeline steel, the chemical composition of the pipeline steel includes: the weight percentage of C is 0.07-0.09%, the weight of Si is 0.07-0.09% The percentage is 0.20～0.30%, the weight percentage of Mn is 1.30～1.50%, the weight percentage of Alt is 0.01～0.03%, the weight percentage of P is ≤0.015%, the weight percentage of S is ≤0.005%, and the weight percentage of Nb is 0.015-0.035%, Ti is 0.01-0.02% by weight, Cr is 0.20-0.30% by weight, N is ≤0.008% by weight, and the balance is Fe and inevitable impurity elements.

Preferably, the average value of the transverse impact energy of the pipeline steel at -25°C is greater than 405J.

Preferably, the transverse -25°C drop weight shear area of the pipeline steel is 95% to 100%, the yield strength ratio is less than or equal to 0.80, and the Vickers hardness HV10 is less than or equal to 215.

Preferably, the metallographic structure of the pipeline steel as-rolled steel sheet is a fine polygonal ferrite and a lath bainite structure.

Preferably, the metallographic structure of the pipeline steel after quenching and tempering is a tempered sorbite structure or a ferrite and tempered sorbite structure.

In the second aspect, an embodiment of the present invention provides a method for preparing a quenched and tempered low yield ratio X60Q pipeline steel, including the steps of smelting, continuous casting, reheating, rolling, cooling, and heat treatment. The method includes: steel plate separation Two-stage controlled rolling, the first stage rolling temperature is 950 ~ 1150 ℃, and then the waiting temperature is 2 ~ 4 times the thickness of the finished steel plate, the second stage rolling temperature is 860 ~ 880 ℃, and the final rolling temperature Control the temperature in the range of 800-820°C; perform accelerated cooling, the cooling temperature is 730-750°C, the final cooling temperature is 200-400°C, and the cooling rate is 25-30°C/s; the pipeline steel is heat-treated.

Preferably, the method includes: quenching the pipeline steel at 800-900°C, and then tempering at 500-650°C.

The above-mentioned one or more technical solutions in the embodiments of the present invention have at least one or more of the following technical effects:

1. A quenched and tempered low yield ratio X60Q pipeline steel provided in the embodiment of the present invention, the chemical composition of the pipeline steel includes: the weight percentage of C is 0.07-0.09%, and the weight percentage of Si is 0.20-0.30% , Mn is 1.30-1.50% by weight, Alt is 0.01-0.03% by weight, P is ≤0.015% by weight, S is ≤0.005% by weight, Nb is 0.015-0.035% by weight, Ti The weight percentage of N is 0.01-0.02%, the weight percentage of Cr is 0.20-0.30%, the weight percentage of N is ≤0.008%, and the balance is Fe and inevitable impurity elements. The technical problems in the prior art that the quenched and tempered X60Q pipeline steel is required to have low stubbornness ratio and low temperature toughness stability are solved, and the comprehensive performance of the quenched and tempered low yield ratio X60Q pipeline steel provided by the invention is achieved. It is suitable for the construction of oil and gas transmission pipelines in some regions such as Africa and the Middle East, and has the technical effect of low yield ratio and good low temperature toughness.

2. A method for preparing a quenched and tempered low yield ratio X60Q pipeline steel provided by the embodiment of the present invention includes the steps of smelting, continuous casting, reheating, rolling, cooling and heat treatment. The method includes: the steel plate is divided into two stages. Controlled rolling, in the first stage, the rolling temperature is 950-1150°C, and then the temperature is 2 to 4 times the thickness of the finished steel sheet. The second stage is 860-880°C, and the final rolling temperature is controlled at 800-820°C range; accelerated cooling is carried out, the cooling temperature is 730-750°C, the final cooling temperature is 200-400°C, and the cooling rate is 25-30°C/s; In the technology, it is difficult to meet the requirements of quenched and tempered X60Q pipeline steel, and the technical problems of the drop impact toughness and low yield ratio of pipeline steel at -25℃. A good dual-phase structure is achieved, and a suitable heat treatment process is obtained through combined experiments, so that the steel has excellent low temperature toughness and low yield ratio, which can achieve the technical effect of engineering application.

The above description is only an overview of the technical solutions of the present invention, in order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the description, and in order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand , the following specific embodiments of the present invention are given.

Description of drawings

1 is a schematic flowchart of a method for preparing a quenched and tempered low yield ratio X60Q pipeline steel according to an embodiment of the present invention;

Fig. 2 is the metallographic structure diagram of rolling state in the embodiment of the present invention;

FIG. 3 is a metallographic structure diagram of the quenched and tempered state after heat treatment in an embodiment of the present invention.

Detailed ways

The embodiments of the present invention provide a quenched and tempered low yield ratio X60Q pipeline steel and a preparation method, which solve the technical problems in the prior art that the quenched and tempered X60Q pipeline steel requires a low stubborn ratio and low temperature toughness.

The general idea of the technical method in the embodiment of the present invention is as follows: the weight percentage of C is 0.07-0.09%, the weight percentage of Si is 0.20-0.30%, the weight percentage of Mn is 1.30-1.50%, and the weight percentage of Alt is 0.01-0.01% 0.03%, the weight percentage of P is ≤0.015%, the weight percentage of S is ≤0.005%, the weight percentage of Nb is 0.015～0.035%, the weight percentage of Ti is 0.01～0.02%, and the weight percentage of Cr is 0.20～0.30% , the weight percent of N is ≤0.008%, and the balance is Fe and inevitable impurity elements. It is achieved that the quenched and tempered low yield ratio X60Q pipeline steel provided by the present invention has good comprehensive performance, is suitable for the construction of oil and gas transmission pipelines in some regions such as Africa and the Middle East, and has the technical effects of low yield ratio and good low temperature toughness.

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

The embodiment of the present invention provides a quenched and tempered low yield ratio X60Q pipeline steel, the chemical composition of the pipeline steel includes: the weight percentage of C is 0.07-0.09%, the weight percentage of Si is 0.20-0.30%, and the weight percentage of Mn is 0.20-0.30%. The percentage is 1.30～1.50%, the weight percentage of Alt is 0.01～0.03%, the weight percentage of P is ≤0.015%, the weight percentage of S is ≤0.005%, the weight percentage of Nb is 0.015～0.035%, and the weight percentage of Ti is 0.01 to 0.02%, the weight percentage of Cr is 0.20 to 0.30%, the weight percentage of N is ≤0.008%, and the balance is Fe and inevitable impurity elements.

Specifically, the chemical composition of the pipeline steel in this embodiment includes: the weight percent of C is 0.07-0.09%, C is one of the most economical strengthening elements in steel, if the C content is too high, the desired extension cannot be guaranteed If the carbon content is too low, it will affect the wear resistance of the matrix, so the low C content ensures its low temperature toughness; the weight percentage of Mn is 1.30-1.50%, Mn It is a solid solution strengthening element. When the Mn content is too high, a serious band-like structure will be formed, which will reduce the lateral elongation and affect the cold formability. Therefore, considering the strength and toughness of the material, the weight ratio of Mn is designed to be 1.30-1.50%; The weight percentage is 0.01 to 0.03%. Alt acts as a deoxidizer during steelmaking. Improper deoxidation will lead to a decrease in the cold forming properties of the material. However, if the Alt content is too high, it will lead to too many AlN inclusions in the steel, reducing the material According to the requirements of the pipeline steel, the weight percentage of Alt is set to 0.01-0.03%; the weight percentage of P is ≤0.015%, and the weight percentage of S is ≤0.005%. The lower the impurity elements in the steel, the higher the Well, in order to obtain good low temperature toughness, a large number of tests are carried out in the embodiment of the present invention, and it is found that the impurity elements are controlled at P: ≤ 0.015%, S: ≤ 0.005%, which is beneficial to the low temperature toughness of the product; the weight percentage of Nb is 0.015-0.035% , the weight percentage of Ti is 0.01-0.02%, and the main functions of Nb and Ti elements in the present invention are precipitation strengthening and improving the strength properties of the material. Through a large number of experiments, the present invention proves that the Nb content is controlled in the range of 0.015-0.035%, and the Ti content is controlled in the range of 0.01-0.020%, which can achieve better precipitation strengthening effect and obtain good comprehensive performance; the weight percentage of Cr is 0.20-0.20% 0.30%, Cr element is effective to improve the tensile strength of pipeline steel, which can significantly reduce the yield ratio of the material. A large number of tests have proved that the yield ratio of the product can be significantly reduced when the Cr content is controlled within the range of 0.20-0.30%; the weight percentage of N is ≤0.008%, and the balance is Fe and inevitable impurity elements. The problem of drop impact toughness and low yield strength ratio of pipeline steel at -25°C is solved, and the quenched and tempered low yield strength ratio X60Q pipeline steel provided by the present invention has good comprehensive performance and can be applied to oil and gas in some regions such as Africa and the Middle East. Construction of transmission pipeline, which has the technical effect of low yield ratio and low temperature toughness stability.

Further, the average value of the impact energy in the transverse direction of the pipeline steel at -25°C is greater than 405J.

Further, the transverse -25°C drop weight shear area of the pipeline steel is 95% to 100%, the yield strength ratio is less than or equal to 0.80, and the Vickers hardness HV10 is less than or equal to 215.

Further, the metallographic structure of the as-rolled steel sheet of the pipeline steel is a fine polygonal ferrite and a lath bainite structure.

Further, the metallographic structure of the pipeline steel after quenching and tempering is a tempered sorbite structure or a ferrite and tempered sorbite structure.

Specifically, the quenched and tempered low yield ratio X60Q pipeline steel can obtain a good dual-phase structure, and the metallographic structure of the rolled steel sheet of the pipeline steel is a fine polygonal ferrite and a lath bainite structure, Biphasic tissue can reduce the yield-to-strength ratio. The quenched and tempered metallographic structure is very important to the mechanical properties of the product, and the shape, composition and size of the quenched and tempered metallographic structure of the present invention directly determine the low-temperature impact toughness, strength properties and yield ratio of the product. The metallographic structure of the pipeline steel after quenching and tempering is a tempered sorbite structure or a ferrite and tempered sorbite structure. The steel has excellent low temperature toughness and low yield ratio, the average value of impact energy of the pipeline steel at -25 ℃ is greater than 405J, the shear area of the pipeline steel at -25 ℃ is 95% to 100%, and the yield The strength ratio is less than or equal to 0.80, and the Vickers hardness HV10 is less than or equal to 215. It can realize engineering applications and is suitable for the construction of oil and gas pipelines in Africa, the Middle East and other regions.

Embodiment 2

This embodiment provides a method for preparing a quenched and tempered low yield ratio X60Q pipeline steel, including the steps of smelting, continuous casting, reheating, rolling, cooling, and heat treatment, and the method includes:

Step 10: The steel plate is controlled rolling in two stages. The first stage is rolled at a temperature of 950 to 1150°C, and then it is warmed up. The thickness of the steel plate to be warmed is 2 to 4 times the thickness of the finished steel plate. ℃, the final rolling temperature is controlled in the range of 800 ~ 820 ℃;

Specifically, in the first stage, the rolling temperature is 950-1150°C, and then the temperature is kept warm. The thickness of the hot-rolled steel sheet is 2-4 times the thickness of the finished steel sheet. The rolling temperature in the second stage is 860-880°C, and the final rolling temperature is controlled In the range of 800～820℃, the process parameters of the two-stage rolling can ensure that the product structure is fine and uniform, which plays a vital role in the subsequent low temperature toughness.

Step 20: perform accelerated cooling, the cooling temperature is 730-750°C, the final cooling temperature is 200-400°C, and the cooling rate is 25-30°C/s;

Specifically, after the hot rolling of the steel sheet, accelerated cooling is performed, the cooling start temperature is 730 to 750°C, the final cooling temperature is 200 to 400°C, and the cooling rate is 25 to 30°C/s. The F+B microstructure was obtained at lower opening and final cooling temperatures. The main reason is that in the process of water cooling after rolling, the lower opening and cooling temperature entered the ferrite transformation zone and formed proeutectoid ferrite. , the lower final cooling temperature, the hard phase bainite structure can be obtained, and the dual-phase structure can reduce the yield ratio.

Step 30: Heat treatment of the pipeline steel.

Further, the method includes: quenching the pipeline steel at 800-900°C, and then tempering at 500-650°C.

Specifically, the pipeline steel is subjected to heat treatment, and the heat treatment process is to quench the pipeline steel at 800-900°C, and then perform tempering at 500-650°C. It should be understood that the quenching is to heat the steel above the critical temperature, keep it for a certain period of time, and then cool it at a rate greater than the critical cooling rate, so as to obtain an unbalanced structure dominated by martensite (also obtain bainite or keep it according to needs). A heat treatment process for single-phase austenite). Quenching is the most widely used process method in steel heat treatment process. The most common are water-cooled quenching, oil-cooled quenching, air-cooled quenching, etc. There are four basic processes for steel heat treatment: annealing, normalizing, quenching and tempering. Tempering is to reduce the brittleness of steel parts. The quenched steel parts are kept at an appropriate temperature higher than room temperature but lower than 710 ° C for a long time, and then cooled. This process is called tempering.

A good dual-phase structure is obtained through the preparation process of the steel plate in the embodiment of the present invention, and a suitable heat treatment process is obtained through a combination experiment, which solves the problems of the drop impact toughness and low yield ratio of the pipeline steel at -25°C. The mechanical properties of the quenched and tempered low yield ratio X60Q pipeline steel are: (1) The average value of impact energy of the steel plate at -25℃ in the transverse direction is greater than 405J; (2) The shear area of the steel plate at -25℃ in the transverse direction is 95% to 100%; (3) Yield strength ratio≤0.80; (4) Vickers hardness HV10≤215. It is achieved that the quenched and tempered low yield ratio X60Q pipeline steel provided by the present invention has good comprehensive performance, is suitable for the construction of oil and gas transmission pipelines in some regions such as Africa and the Middle East, and has the technical effects of low yield ratio and stable low temperature toughness.

Embodiment 3

A quenched and tempered low yield ratio X60Q pipeline steel and a preparation method according to the embodiment of the present invention are smelted in a 100-ton converter, controlled rolling and controlled cooling on a 4300 mm production line, and then quenching and tempering heat treatment processes are carried out. Examples will further describe the present invention. In the embodiment, the chemical composition of the steel plate is shown in Table 1, the preparation method of the quenched and tempered state low yield ratio X60Q pipeline steel of the embodiment is shown in Table 2, and the mechanical properties of the quenched and tempered state low yield ratio X60Q pipeline steel of the embodiment are shown in Table 3:

Table 1. Chemical composition (wt%) of the present invention's quenched and tempered low yield ratio X60Q pipeline steel examples

Example C Si Mn P S Alt N Nb Ti Cr 1 0.077 0.25 1.36 0.009 0.003 0.020 0.0011 0.026 0.018 0.27 2 0.087 0.20 1.41 0.007 0.002 0.023 0.003 0.017 0.012 0.23 3 0.079 0.23 1.33 0.010 0.002 0.021 0.002 0.028 0.010 0.28 4 0.085 0.30 1.47 0.008 0.003 0.020 0.0018 0.032 0.016 0.25 5 0.083 0.26 1.39 0.010 0.002 0.026 0.0027 0.025 0.019 0.21

Table 2. Example process system of quenched and tempered low yield ratio X60Q pipeline steel of the present invention

The quenched and tempered low yield ratio X60Q pipeline steel produced by the invention has a fine polygonal ferrite and a lath bainite dual-phase structure in the rolled state, and the quenched and tempered metallographic structure is a tempered sorbite structure Or ferrite and tempered sorbite structure; a large number of test results of the present invention show that the quenched and tempered state metallographic structure is very important to the mechanical properties of the product, and the quenched and tempered state metallographic structure shape, composition and size of the present invention directly determine the product. Low temperature impact toughness, strength properties and yield ratio.

Referring to the photo of the metallographic structure in the rolled state in FIG. 1 and the photo of the metallographic structure in the quenched and tempered state after heat treatment in FIG. 2 , the mechanical properties of the examples are shown in Table 3.

Table 3. Mechanical properties of low yield ratio X60Q pipeline steel in the quenched and tempered state

The invention obtains good metallographic structure by controlling the chemical composition of the steel plate and the rolling and heat treatment processes, so that the steel has excellent low temperature toughness and low yield ratio, and can realize engineering application.

The technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

1. A quenched and tempered low yield ratio X60Q pipeline steel provided in the embodiment of the present invention, the chemical composition of the pipeline steel includes: the weight percentage of C is 0.07-0.09%, and the weight percentage of Si is 0.20-0.30% , Mn is 1.30-1.50% by weight, Alt is 0.01-0.03% by weight, P is ≤0.015% by weight, S is ≤0.005% by weight, Nb is 0.015-0.035% by weight, Ti The weight percentage of N is 0.01-0.02%, the weight percentage of Cr is 0.20-0.30%, the weight percentage of N is ≤0.008%, and the balance is Fe and inevitable impurity elements. The technical problems in the prior art that the quenched and tempered X60Q pipeline steel is required to have low stubbornness ratio and low temperature toughness stability are solved. It is achieved that the quenched and tempered low yield ratio X60Q pipeline steel provided by the invention has good comprehensive performance, can be applied to the construction of oil and gas transmission pipelines in Africa, the Middle East and other regions, and has the technical effects of low yield ratio and good low temperature toughness.

2. A method for preparing a quenched and tempered low yield ratio X60Q pipeline steel provided by the embodiment of the present invention includes the steps of smelting, continuous casting, reheating, rolling, cooling and heat treatment. The method includes: the steel plate is divided into two stages. Controlled rolling, in the first stage, the rolling temperature is 950-1150°C, and then the temperature is 2 to 4 times the thickness of the finished steel sheet. The second stage is 860-880°C, and the final rolling temperature is controlled at 800-820°C range; accelerated cooling is carried out, the cooling temperature is 730-750°C, the final cooling temperature is 200-400°C, and the cooling rate is 25-30°C/s; the pipeline steel is heat treated. It solves the technical problems that the requirements of the quenched and tempered X60Q pipeline steel in the prior art are difficult to meet, and the drop hammer impact toughness and low yield ratio of the pipeline steel at -25°C are solved. A good dual-phase structure is achieved, and a suitable heat treatment process is obtained through combined experiments, so that the steel has excellent low temperature toughness and low yield ratio, which can achieve the technical effect of engineering application.

3. In the embodiment of the present application, the metallographic structure of the pipeline steel after quenching and tempering is a tempered sorbite structure or a ferrite and tempered sorbite structure. The technical problem that the quenched and tempered X60Q pipeline steel in the prior art is difficult to meet the requirements of low stubbornness ratio and low temperature toughness stability is solved, and the product obtained by the quenched and tempered metallographic structure, composition and size of the present invention is achieved. It has the technical effect of low temperature impact toughness, strength performance and yield ratio and other indicators to meet engineering needs.

Although the preferred embodiments of the present invention have been described, additional changes and modifications to these embodiments may occur to those skilled in the art once the basic inventive concepts are known. Therefore, the appended claims are intended to be construed to include the preferred embodiment and all changes and modifications that fall within the scope of the present invention.

Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present invention without departing from the spirit and scope of the embodiments of the present invention. Thus, provided that these modifications and variations of the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims (4)

1. A quenched and tempered low-yield-ratio X60Q pipeline steel is characterized in that: the chemical composition of the pipeline steel comprises: 0.07-0.09 wt% of C, 0.20-0.30 wt% of Si, 1.30-1.50 wt% of Mn, 0.01-0.03 wt% of Alt, less than or equal to 0.015 wt% of P, less than or equal to 0.005 wt% of S, 0.015-0.035 wt% of Nb, 0.01-0.02 wt% of Ti, 0.20-0.30 wt% of Cr, less than or equal to 0.008 wt% of N, and the balance of Fe and unavoidable impurity elements;

the metallographic structure of the rolled steel plate of the pipeline steel is a polygonal ferrite structure and a lath bainite structure;

the metallographic structure of the pipeline steel after quenching and tempering is a tempered sorbite structure or a ferrite and tempered sorbite structure.

2. A pipeline steel as claimed in claim 1, wherein the pipeline steel has an average value of impact work at transverse-25 ℃ of greater than 405J.

3. A pipeline steel as claimed in claim 1, wherein the pipeline steel has a drop-weight shear area at-25 ℃ in the transverse direction of 95-100%, a yield ratio of 0.80 or less, and a vickers hardness HV10 of 215 or less.

4. A preparation method of quenched and tempered low-yield-ratio X60Q pipeline steel comprises the working procedures of smelting, continuous casting, reheating, rolling, cooling and heat treatment, and is characterized in that,

the rolling procedure is carried out in two stages, wherein the initial rolling temperature of the first stage is 950-1150 ℃, then the temperature is kept, the thickness of the temperature is 2-4 times of the thickness of a finished steel plate, the initial rolling temperature of the second stage is 860-880 ℃, and the final rolling temperature is controlled at 800-820 ℃;

the starting cooling temperature of the cooling process is 730-750 ℃, the final cooling temperature is 200-400 ℃, and the cooling speed is 25-30 ℃/s;

the heat treatment process includes: quenching the pipeline steel at 800-900 ℃, and tempering at 500-650 ℃ to perform heat treatment on the pipeline steel.

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