CN109112394B - Quenched and tempered X60Q pipeline steel with low yield ratio and preparation method thereof - Google Patents
Quenched and tempered X60Q pipeline steel with low yield ratio and preparation method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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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
Technical Field
The invention relates to the technical field of pipeline steel, in particular to quenched and tempered low-yield-ratio X60Q pipeline steel and a preparation method thereof.
Background
Pipeline steel for oil and gas transmission pipelines is usually delivered in a thermo-mechanical rolling (TMCP) state, but in some regions of Africa, the middle east and the like, due to different transmission environments and mediums, the owners also adopt pipeline steel delivered in a partially hardened and tempered state (Q + T).
From the market demand, the first-stage project of African Allan and Liya pipelines requires 1708 tons of tempered X60Q pipeline steel. From the technical conditions of the quenched and tempered X60Q pipeline steel for the Algorian and Liya pipeline project, the owner puts forward the harsh technical requirements, and the main technical requirements of the quenched and tempered X60Q pipeline steel project on the materials are as follows: 1. how to meet the performance requirement of the steel plate on low yield ratio, wherein the maximum value of the yield ratio Rt0.5/Rm is not more than 0.85; 2. the transverse-25 ℃ drop hammer shear area of the steel plate is more than or equal to 85 percent, and particularly the stability of the-25 ℃ low-temperature toughness in the batch production process; 3. the Vickers hardness value HV10 of the steel plate is less than or equal to 235.
The above requirements are mainly reflected in low yield ratio and low temperature toughness, which is difficult, and thus, reasonable component design and heat treatment process design of the steel plate are required.
Disclosure of Invention
The invention provides a quenched and tempered X60Q pipeline steel with low yield ratio and a preparation method thereof, which are used for solving the technical problems that quenched and tempered X60Q pipeline steel in the prior art is required to have low yield ratio and high difficulty in low-temperature toughness stabilization.
In order to solve the above problem, in a first aspect, an embodiment of the present invention provides a quenched and tempered low yield ratio X60Q pipeline steel, which has a chemical composition including: 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.
Preferably, the average value of the impact energy of the pipeline steel at the transverse temperature of-25 ℃ is more than 405J.
Preferably, the pipeline steel has a transverse falling weight shearing area of 95-100% at-25 ℃, a yield ratio of less than or equal to 0.80 and Vickers hardness HV10 of less than or equal to 215.
Preferably, the metallographic structure of the rolled steel plate of the pipeline steel is a fine polygonal ferrite and lath bainite structure.
Preferably, the metallographic structure of the line steel after quenching and tempering is a tempered sorbite structure or a ferrite and tempered sorbite structure.
In a second aspect, the embodiment of the invention provides a method for preparing a quenched and tempered low-yield-ratio X60Q pipeline steel, which comprises the following steps of smelting, continuous casting, reheating, rolling, cooling and heat treatment, wherein the method comprises the following steps: controlling rolling of the steel plate in two stages, wherein the initial rolling temperature of the first stage is 950-1150 ℃, then, waiting for temperature, the thickness of the temperature is 2-4 times of the thickness of the finished steel plate, the initial rolling temperature of the second stage is 860-880 ℃, and the final rolling temperature is controlled within the range of 800-820 ℃; carrying out accelerated cooling, wherein the start cooling temperature is 730-750 ℃, the final cooling temperature is 200-400 ℃, and the cooling speed is 25-30 ℃/s; and carrying out heat treatment on the pipeline steel.
Preferably, the method comprises: quenching the pipeline steel at 800-900 ℃, and then tempering at 500-650 ℃.
One or more technical solutions in the embodiments of the present invention at least have one or more of the following technical effects:
1. the embodiment of the invention provides a quenched and tempered low-yield-ratio X60Q pipeline steel, which 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. The technical problems that the quenched and tempered X60Q pipeline steel is required to have a low stiffness ratio and high stability difficulty in low-temperature toughness in the prior art are solved, and the quenched and tempered X60Q pipeline steel provided by the invention is good in comprehensive performance, applicable to construction of oil and gas conveying pipelines in some areas such as Africa and the middle east and has the technical effects of low stiffness ratio and high low-temperature toughness.
2. The preparation method of the quenched and tempered low-yield-ratio X60Q pipeline steel provided by the embodiment of the invention comprises the working procedures of smelting, continuous casting, reheating, rolling, cooling and heat treatment, and the method comprises the following steps: controlling rolling of the steel plate in two stages, wherein the initial rolling temperature of the first stage is 950-1150 ℃, then, waiting for temperature, the thickness of the temperature is 2-4 times of the thickness of the finished steel plate, the initial rolling temperature of the second stage is 860-880 ℃, and the final rolling temperature is controlled within the range of 800-820 ℃; carrying out accelerated cooling, wherein the start cooling temperature is 730-750 ℃, the final cooling temperature is 200-400 ℃, and the cooling speed is 25-30 ℃/s; the pipeline steel is subjected to heat treatment, and the technical problems that the requirements of the quenched and tempered X60Q pipeline steel in the prior art are more and difficult to meet, and the pipeline steel has the drop hammer impact toughness of-25 ℃ and the low yield ratio are solved. The method achieves the technical effects of obtaining a good two-phase structure, obtaining a proper heat treatment process through a combined experiment, enabling the steel to have excellent low-temperature toughness and low yield ratio, and realizing engineering application.
The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.
Drawings
FIG. 1 is a schematic flow chart of a method for preparing a quenched and tempered low yield ratio X60Q pipeline steel according to an embodiment of the invention;
FIG. 2 is a rolled metallographic structure diagram according to an embodiment of the present invention;
FIG. 3 is a metallographic structure diagram of a quenched and tempered state after heat treatment in the example of the invention.
Detailed Description
The embodiment of the invention provides a quenched and tempered X60Q pipeline steel with low yield ratio and a preparation method thereof, and solves the technical problems that the quenched and tempered X60Q pipeline steel in the prior art is required to have low yield ratio and high low-temperature toughness difficulty.
The technical method in the embodiment of the invention has the following general idea: 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 hardened and tempered low-yield-ratio X60Q pipeline steel provided by the invention has good comprehensive performance, can be suitable for 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 objects, 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 drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example one
The embodiment of the invention provides quenched and tempered low-yield-ratio X60Q pipeline steel, which 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.
Specifically, the chemical compositions of the pipeline steel in the embodiment include: the weight percentage of C is 0.07-0.09%, C is one of the most economic strengthening elements in steel, if the content of C is too high, the desired elongation value cannot be ensured, the cold formability, the low-temperature toughness and the welding performance of the steel are also reduced, and if the content of C is too low, the wear resistance of a matrix is influenced, so that the low-temperature toughness is ensured due to the low content of C; the weight percentage of Mn is 1.30-1.50%, Mn is a solid solution strengthening element, and a serious banded structure can be formed when the content of Mn is too high, so that the transverse elongation is reduced, and the cold formability is influenced, therefore, the toughness of the material is comprehensively considered, and the weight ratio of Mn is designed to be 1.30-1.50%; the weight percentage of Alt is 0.01-0.03%, Alt plays the role of a deoxidizer during steel making, the cold forming performance of the material is reduced due to incomplete deoxidation, but the elongation of the material is reduced due to excessive AlN inclusions in the steel caused by excessive Alt content, and the weight percentage of Alt is set to be 0.01-0.03% by integrating the requirements of the pipeline steel; the weight percentage of P is less than or equal to 0.015 percent, the weight percentage of S is less than or equal to 0.005 percent, the lower the impurity element in the steel is, the better, in order to obtain good low-temperature toughness, a large number of experiments are carried out in the embodiment of the invention, and the impurity element is controlled to be P: less than or equal to 0.015 percent, S: less than or equal to 0.005 percent, 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 Nb and Ti elements mainly play a role in precipitation strengthening and improving the strength performance of the material. A large number of tests prove that the Nb content is controlled within the range of 0.015-0.035%, the Ti content is controlled within the range of 0.01-0.020%, a good precipitation strengthening effect can be achieved, and good comprehensive performance is obtained; the weight percentage of Cr is 0.20-0.30%, and the Cr element is effective for improving the tensile strength of the pipeline steel and can obviously reduce the yield ratio of the material. A large number of experiments prove that the yield ratio of the product can be obviously reduced by controlling the content of Cr within the range of 0.20-0.30%; the weight percentage of N is less than or equal to 0.008 percent, and the balance is Fe and inevitable impurity elements. The problems of-25 ℃ drop hammer impact toughness and low yield ratio of the pipeline steel are solved, and the quenched and tempered low-yield ratio X60Q pipeline steel provided by the invention is good in comprehensive performance, applicable to construction of oil and gas transmission pipelines in some regions such as Africa and the middle east and stable in low-yield ratio and low-temperature toughness.
Further, the average value of the impact energy of the pipeline steel at the transverse direction of-25 ℃ is more than 405J.
Furthermore, the drop hammer shear area of the pipeline steel at the transverse temperature of-25 ℃ is 95-100%, the yield ratio is less than or equal to 0.80, and the Vickers hardness HV10 is less than or equal to 215.
Furthermore, the metallographic structure of the rolled steel plate of the pipeline steel is fine polygonal ferrite and lath bainite structures.
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 two-phase structure, the metallographic structure of the rolled steel plate of the pipeline steel is a fine polygonal ferrite and lath bainite structure, and the yield ratio can be reduced by the two-phase structure. The microstructure of the quenched and tempered state is crucial to the mechanical property of the product, and the morphology, the composition and the size of the microstructure of the quenched and tempered state directly determine the low-temperature impact toughness, the strength property and the 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 the impact energy of the pipeline steel at the transverse temperature of-25 ℃ is more than 405J, the drop hammer shearing area of the pipeline steel at the transverse temperature of-25 ℃ is 95% -100%, the yield ratio is less than or equal to 0.80, the Vickers hardness HV10 is less than or equal to 215, the engineering application can be realized, and the pipeline steel is suitable for the requirements of oil and gas transmission pipeline construction in some regions of Africa, middle east and the like.
Example two
The embodiment provides a preparation method of quenched and tempered low-yield ratio X60Q pipeline steel, which comprises the following steps of smelting, continuous casting, reheating, rolling, cooling and heat treatment, and the method comprises the following steps:
step 10: controlling rolling of the steel plate in two stages, wherein the initial rolling temperature of the first stage is 950-1150 ℃, then, waiting for temperature, the thickness of the temperature is 2-4 times of the thickness of the finished steel plate, the initial rolling temperature of the second stage is 860-880 ℃, and the final rolling temperature is controlled within the range of 800-820 ℃;
specifically, 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 ℃, the final rolling temperature is controlled within the range of 800-820 ℃, and the technological parameters of the two-stage rolling can ensure that the product is fine and uniform in structure and plays a vital role in the subsequent low-temperature toughness.
Step 20: carrying out accelerated cooling, wherein the start cooling temperature is 730-750 ℃, the final cooling temperature is 200-400 ℃, and the cooling speed is 25-30 ℃/s;
specifically, the steel plate is subjected to accelerated cooling after hot rolling, wherein the start cooling temperature is 730-750 ℃, the end cooling temperature is 200-400 ℃, and the cooling speed is 25-30 ℃/s. The F + B structure was obtained at lower start and finish cooling temperatures, mainly due to: in the process of water cooling after rolling, the lower start cooling temperature enters a ferrite phase transformation area to generate proeutectoid ferrite, the lower final cooling temperature obtains a hard phase bainite structure, and the yield ratio of the two-phase structure can be reduced.
Step 30: and carrying out heat treatment on the pipeline steel.
Further, the method comprises: quenching the pipeline steel at 800-900 ℃, and then tempering at 500-650 ℃.
Specifically, the pipeline steel is subjected to heat treatment, and the heat treatment process comprises the steps of quenching the pipeline steel at 800-900 ℃ and tempering at 500-650 ℃. It is understood that quenching is a heat treatment process in which the steel is heated above the critical temperature, held for a certain period of time, and then cooled at a rate greater than the critical cooling rate to obtain an unbalanced structure with predominantly martensite (and also bainite or single phase austenite if desired). Quenching is the most widely applied work technology method in the steel heat treatment technology, the most common is water cooling quenching, oil cooling quenching, air cooling quenching and the like, and the steel heat treatment mainly comprises four basic technologies of annealing, normalizing, quenching and tempering. Tempering is to reduce the brittleness of the steel, and the quenched steel is kept warm for a long time at a suitable temperature higher than room temperature and lower than 710 ℃, and then cooled, and this process is called tempering.
The steel plate preparation process in the embodiment of the invention obtains a good two-phase structure, and a proper heat treatment process is obtained through a combined experiment, so that the problems of drop hammer impact toughness and low yield ratio of pipeline steel at-25 ℃ are solved, and the mechanical properties of the quenched and tempered low yield ratio X60Q pipeline steel are as follows: (1) the average value of the transverse-25 ℃ impact energy of the steel plate is more than 405J; (2) the horizontal-25 ℃ drop hammer shear area of the steel plate is 95-100 percent; (3) the yield ratio is less than or equal to 0.80; (4) the Vickers hardness HV10 is less than or equal to 215. The hardened and tempered low-yield-ratio X60Q pipeline steel provided by the invention has good comprehensive performance, can be suitable for 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.
EXAMPLE III
The invention discloses a quenched and tempered low-yield-ratio X60Q pipeline steel and a preparation method thereof, wherein the quenched and tempered low-yield-ratio X60Q pipeline steel is smelted on a 100-ton converter, controlled rolling and controlled cooling are carried out on a 4300mm production line, and then quenching and tempering heat treatment processes are carried out, and the invention is further described by the following embodiments. The chemical components of the steel plates in the examples are shown in Table 1, the process system of the preparation method of the quenched and tempered low-yield-ratio X60Q pipeline steel in the examples is shown in Table 2, and the mechanical properties of the quenched and tempered low-yield-ratio X60Q pipeline steel in the examples are shown in Table 3:
TABLE 1 quenched and tempered low yield ratio X60Q pipeline steel example chemical composition (wt%)
| Examples | 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. Process schedule for example of quenched and tempered low yield ratio X60Q pipeline steel
The rolled metallographic structure of the quenched and tempered low-yield-ratio X60Q pipeline steel produced by the method is a fine polygonal ferrite and lath bainite dual-phase structure, and the quenched and tempered metallographic structure is a tempered sorbite structure or a ferrite and tempered sorbite structure; a large number of test results show that the metallographic structure in a quenched and tempered state is critical to the mechanical property of the product, and the shape, the composition and the size of the metallographic structure in the quenched and tempered state directly determine the low-temperature impact toughness, the strength property and the yield ratio of the product.
Referring to the rolled metallographic structure photograph in FIG. 1 and the quenched and tempered metallographic structure photograph in FIG. 2, the mechanical properties of the examples are shown in Table 3.
TABLE 3 mechanical properties of the quenched and tempered low yield ratio X60Q pipeline steel
The invention obtains good metallographic structure by controlling the chemical components 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 scheme provided in the embodiment of the application at least has the following technical effects or advantages:
1. the embodiment of the invention provides a quenched and tempered low-yield-ratio X60Q pipeline steel, which 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, can be suitable for 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.
2. The preparation method of the quenched and tempered low-yield-ratio X60Q pipeline steel provided by the embodiment of the invention comprises the working procedures of smelting, continuous casting, reheating, rolling, cooling and heat treatment, and the method comprises the following steps: controlling rolling of the steel plate in two stages, wherein the initial rolling temperature of the first stage is 950-1150 ℃, then, waiting for temperature, the thickness of the temperature is 2-4 times of the thickness of the finished steel plate, the initial rolling temperature of the second stage is 860-880 ℃, and the final rolling temperature is controlled within the range of 800-820 ℃; carrying out accelerated cooling, wherein the start cooling temperature is 730-750 ℃, the final cooling temperature is 200-400 ℃, and the cooling speed is 25-30 ℃/s; and carrying out heat treatment on the pipeline steel. Solves the technical problems that the requirements of the quenched and tempered X60Q pipeline steel in the prior art are more difficult to meet, and the pipeline steel has the drop hammer impact toughness of-25 ℃ and the low yield ratio. The method achieves the technical effects of obtaining a good two-phase structure, obtaining a proper heat treatment process through a combined experiment, enabling the steel to have excellent low-temperature toughness and low yield ratio, and realizing engineering application.
3. In the embodiment of the application, the metallographic structure of the pipeline steel after being quenched and tempered 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 has high difficulty in meeting the requirements of low stiffness ratio and low-temperature toughness stability is solved, and the technical effect that the obtained product has low-temperature impact toughness, strength performance, yield ratio and other indexes to meet engineering requirements due to the quenched and tempered metallographic structure form, composition and size is achieved.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments of the present invention without departing from the spirit or scope of the embodiments of the invention. Thus, if such 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 encompass 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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