CN109161813B - Low-compression-ratio pipeline steel X70 steel plate and production method thereof - Google Patents
Low-compression-ratio pipeline steel X70 steel plate and production method thereof Download PDFInfo
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Abstract
The invention provides a low-compression-ratio pipeline steel X70 steel plate and a production method thereof. The low-compression-ratio pipeline steel X70 steel plate comprises the following components in percentage by weight: c: 0.030-0.080%, Mn: 1.55-1.75%, Si: 0.10-0.40%, S is less than or equal to 0.0050%, P: less than or equal to 0.015 percent, Nb: 0.035 to 0.060%, Ti: 0.008-0.025%, V is less than or equal to 0.10%, Alt: 0.020 to 0.060%, Cr: less than or equal to 0.30 percent, Mo: less than or equal to 0.20 percent, and the balance of Fe and inevitable impurities. The production method of the steel plate adopts a laminar flow sectional cooling process to produce the X70 pipeline steel with low compression ratio and thick specification in batches, and meets the requirements of engineering technology.
Description
Technical Field
The invention belongs to the technical field of steel material engineering, and relates to a low-compression-ratio pipeline steel X70 steel plate and a production process thereof, in particular to a low-compression-ratio, high-strength and high-toughness pipeline steel X70 steel plate produced by a laminar flow segmented cooling process on a steckel mill production line.
Background
The oil and gas transmission pipeline engineering needs a large amount of X70 pipeline steel, the high-grade pipeline steel needs higher comprehensive performance, and the compression ratio in the production process is generally more than 10. As the casting blank of the steckel mill is thinner, the qualified rate of the drop hammer performance is lower when thick high-grade pipeline steel is produced, and mass production cannot be carried out. In recent years, as the level of smelting increases and the capacity of rolling equipment increases, and then, strictly controlled rolling and controlled cooling processes are performed, the compression ratio can be reduced to about 7. The steckel mill can mass-produce X70 pipeline steel plates with the thickness of 21mm by using casting blanks with the thickness of 150mm, and when the specification of the thickness of more than 21mm is produced, the mass production cannot be carried out due to the low qualified rate of drop weight.
Chinese patent publication No. CN 103639198A discloses "a method for producing a pipeline steel sheet using a continuous casting slab under a small compression ratio condition". The method adopts a 300mm continuous casting billet to produce the ultra-thick pipeline steel with the width of 40-50 mm and the width of 3200-4000 mm. The steel comprises the following main components and processes (C: 0.05-0.10%, Si: 0.15-0.30%, Mn: 1.0-2.0%, Nb: 0.05% or less, V: 0.05% or less, Ti: 0.05% or less), a 300mm casting blank is reheated and rolled in two stages, and then cooled, wherein mechanical properties are (Rt0.5: 511-541 MPa, Rm: 603-623 MPa, KV2/J at-20 ℃ of 200-250J, DWTT: 50-60) and although pipeline steel with a wall thickness of 40-50 mm can be produced, the alloy addition amount is small, but the impact toughness is not high, is barely higher than 200J, and particularly, the DWTT property at-10 ℃ is only 50-60%, and engineering technical requirements cannot be met.
Disclosure of Invention
The invention aims to provide a low-compression-ratio pipeline steel X70 steel plate, which is produced by adopting a 150mm continuous casting billet, has a thickness of more than 21mm, has a low compression ratio and a high drop weight yield and completely meets engineering technical requirements.
Another object of the present invention is to provide a method for producing the low compression ratio pipeline steel X70 steel plate, wherein the laminar flow staged cooling process is used to produce low compression ratio thick X70 pipeline steel in batch.
In order to achieve the purpose, the invention adopts the technical scheme that:
a low-compression-ratio pipeline steel X70 steel plate comprises the following components in percentage by weight: c: 0.030-0.080%, Mn: 1.55-1.75%, Si: 0.10-0.40%, S is less than or equal to 0.0050%, P: less than or equal to 0.015 percent, Nb: 0.035 to 0.060%, Ti: 0.008-0.025%, V is less than or equal to 0.10%, Alt: 0.020 to 0.060%, Cr: less than or equal to 0.30 percent, Mo: less than or equal to 0.20 percent, and the balance of Fe and inevitable impurities.
The invention is preferably a low-compression-ratio pipeline steel X70 steel plate, which comprises the following components in percentage by weight: c: 0.040-0.070%, Mn: 1.60-1.70%, Si: 0.10-0.40%, S is less than or equal to 0.0050%, P: less than or equal to 0.015 percent, Nb: 0.045-0.055%, Ti: 0.010-0.020%, V is less than or equal to 0.10%, Alt: 0.020 to 0.060%, Cr: less than or equal to 0.30 percent, Mo: less than or equal to 0.20 percent, and the balance of Fe and inevitable impurities.
The low-compression-ratio pipeline steel X70 steel plate has the yield strength of 490-550 MPa, the tensile strength of 590-640 MPa, the yield ratio of less than 0.85 and the proportion of the drop-weight shear area of more than 85% at-15 ℃.
The total compression ratio of the low-compression-ratio pipeline steel X70 steel plate produced by the invention is less than 6.
A production method of the low-compression-ratio pipeline steel X70 steel plate comprises the following steps of adopting a laminar flow sectional cooling process after rolling, and specifically comprises the following steps:
(1) two-stage controlled rolling is adopted, the rolling temperature of a recrystallization zone is 1100-1080 ℃, and the total reduction rate of the recrystallization zone is more than 50%; the initial rolling temperature of the non-recrystallization zone is less than or equal to 920 ℃, the total reduction rate of the non-recrystallization zone is more than 60%, and the final rolling temperature is 760-810 ℃;
(2) and after rolling, carrying out laminar flow sectional cooling, cooling the first section of water cooling to 660-720 ℃ at the speed of 15-40 ℃/s, carrying out air cooling for 9-12 s, then cooling to 360-440 ℃ at the speed of 10-30 ℃/s through the second section of water cooling, and carrying out air cooling on a roller way and a cooling bed to room temperature.
Wherein the steel structure obtained in the step (2) is a ferrite and bainite complex phase structure, wherein the ferrite accounts for 60-70%, the bainite accounts for 30-40%, and the ferrite and the bainite are in volume ratio.
The production method is suitable for a steckel mill production line and is also suitable for a traditional middle plate mill production line with longer laminar cooling.
The production method of the invention also comprises other procedures before rolling, such as a refining procedure, and the procedures before rolling are the prior art in the process of producing the pipeline steel, and are not described in detail in the invention.
Compared with the prior art, the invention has the beneficial effects that:
in the field, the drop hammer performance is essentially a strong plasticity comprehensive index, the invention controls the phase change through the laminar flow sectional cooling process, and compared with an acicular ferrite structure, the obtained ferrite and bainite complex phase structure has the advantages that on the basis of meeting the strength requirement of X70, the yield ratio is controlled at a lower level, the plastic index of uniform elongation of the material can be obviously improved, and the drop hammer performance of the thick X70 steel plate is improved.
Drawings
FIG. 1 is a metallographic structure diagram of a low compression ratio pipeline steel X70 steel plate in example 1 of the present invention.
Detailed Description
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.
Example 1
The chemical composition (wt%) of the low compression ratio line pipe steel X70 hot rolled plate of this example is shown in Table 1.
TABLE 1 chemical composition (wt%) of Low compression ratio line Steel X70 Steel sheet
| Element(s) | C | Si | Mn | P | S | Nb | Ti | Alt |
| Content (wt.) | 0.07 | 0.20 | 1.70 | 0.009 | 0.003 | 0.050 | 0.012 | 0.035 |
Specific parameters of the rolling process and the laminar flow sectional cooling process in the production process of the low compression ratio pipeline steel X70 steel plate in the embodiment are shown in Table 2.
The production process of the low compression ratio pipeline steel X70 steel plate in the embodiment comprises the following steps: the reheating temperature is 1250 ℃ and the furnace time is 3 hours. Two-stage controlled rolling is adopted, wherein the rough rolling, namely 4-pass rolling in a recrystallization zone, is carried out at the initial rolling temperature of 1100 ℃ and the final rolling temperature of 1080 ℃; obtaining an intermediate blank with the thickness of 68mm, and carrying out finish rolling on the intermediate blank, namely rolling 7 times in a non-recrystallization area, wherein the initial rolling temperature is 880 ℃, and the final rolling temperature is 770 ℃. After rolling, the steel plate is cooled to 430 ℃ by adopting a laminar flow sectional cooling process, and then is cooled to room temperature on a roller way and a cooling bed, and other parameters are shown in table 2. The specific process of rolling: after rolling, the laminar flow sectional cooling is carried out, the first section of water cooling is carried out to cool the steel plate to 680 ℃ at the speed of 25 ℃/s, the steel plate is air-cooled for 10s, then the steel plate is cooled to 430 ℃ at the speed of 20 ℃/s by the second section of water cooling, and the steel plate is air-cooled to room temperature on a roller way and a cooling bed.
TABLE 2 concrete parameters of the rolling process and laminar flow staged cooling process in the production process of this example
The metallographic structure of the low compression ratio steel X70 sheet for pipeline of this example is shown in FIG. 1. it can be seen from FIG. 1 that this example produced a steel sheet having a complex phase structure of ferrite (65%) and bainite (35%).
The performance results of the low compression ratio pipeline steel X70 of this example are shown in Table 3.
TABLE 3 Properties (wt%) of the low compression ratio line pipe steel X70 steel sheet produced in this example
Example 2
The chemical composition (wt%) of the low compression ratio linepipe steel X70 hot rolled plate of this example is shown in Table 4.
TABLE 4 chemical composition (wt%) of Low compression ratio line Steel X70 Steel sheet
| Element(s) | C | Si | Mn | Cr | P | S | Nb | Ti | Alt |
| Content (wt.) | 0.05 | 0.22 | 1.60 | 0.20 | 0.010 | 0.002 | 0.052 | 0.014 | 0.038 |
The production process of the low compression ratio pipeline steel X70 steel plate in the embodiment comprises the following steps: the reheating temperature is 1250 ℃ and the furnace time is 3 hours. Two-stage controlled rolling is adopted, wherein rough rolling, namely rolling for 4 times in a recrystallization area, the initial rolling temperature is 1100 ℃, and the final rolling temperature is 1085 ℃; and (3) obtaining an intermediate blank with the thickness of 69mm, carrying out finish rolling, namely rolling 7 times in a non-recrystallization area, wherein the initial rolling temperature is 870 ℃, the final rolling temperature is 760 ℃, cooling to 420 ℃ by adopting a laminar flow sectional cooling process after rolling, and then cooling to room temperature on a roller way and a cooling bed, wherein other parameters are shown in Table 5. The specific process of rolling: after rolling, the laminar flow sectional cooling is carried out, the first section of water cooling is carried out to cool the steel plate to 690 ℃ at the speed of 25 ℃/s, the steel plate is air-cooled for 11s, then the steel plate is cooled to 420 ℃ at the speed of 20 ℃/s through the second section of water cooling, and the steel plate is air-cooled to room temperature on a roller way and a cooling bed.
TABLE 5 concrete parameters of the rolling process and laminar flow staged cooling process in the production process of this example
The metallographic structure of the low compression ratio pipeline steel X70 steel sheet of this example was a steel sheet having a complex phase structure of ferrite and bainite, in which ferrite accounted for 62% and bainite accounted for 38%.
The performance results of the low compression ratio pipeline steel X70 of this example are shown in Table 6.
TABLE 6 Properties (wt%) of the low compression ratio line pipe steel X70 steel sheet produced in this example
From the embodiment 1 and the embodiment 2, the invention obtains the thick X70 grade pipeline steel with good matching strength and toughness, especially the yield ratio and the low-temperature drop hammer performance, by adopting a low-carbon-Mn-Nb or low-carbon-Mn-Cr-Nb component system and adopting a two-stage controlled rolling process and a laminar flow segmented cooling process route through a 150mm continuous casting billet under the condition that the compression ratio is less than 6 (actually 5.9).
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (1)
1. A production method of a low-compression-ratio pipeline steel X70 steel plate with the thickness of 25.4mm is characterized in that the pipeline steel X70 steel plate comprises the following components in percentage by weight: c: 0.070%, Mn: 1.70%, Si: 0.20%%, S: 0.003%, P: 0.009%, Nb: 0.050%, Ti: 0.012%, Alt: 0.035%, the balance Fe and unavoidable impurities;
the yield strength of the low-compression-ratio pipeline steel X70 steel plate is 503MPa, the tensile strength is 610MPa, the elongation A is 49%, the yield ratio is 0.82, the impact energy at minus 20 ℃ is 250J, and the proportion of the drop-weight shear area at minus 15 ℃ is 88%; the compression ratio is 5.9;
the pipeline steel X70 steel plate is produced by a continuous casting billet with the thickness of 150mm, and the specific production method comprises the following steps of adopting a laminar flow sectional cooling process after rolling, and specifically comprises the following steps:
(1) the reheating temperature is 1250 ℃, the furnace time is 3 hours, two-stage rolling is adopted, the rough rolling, namely 4-pass rolling in a recrystallization zone, the initial rolling temperature is 1100 ℃, and the final rolling temperature is 1080 ℃; obtaining an intermediate blank with the thickness of 68mm, and performing finish rolling, namely rolling 7 times in a non-recrystallization area, wherein the initial rolling temperature is 880 ℃, and the final rolling temperature is 770 ℃;
(2) after rolling, the laminar flow sectional cooling is carried out, the first section of water cooling is carried out to cool to 680 ℃ at the speed of 25 ℃/s, the air cooling is carried out for 10s, then the laminar flow sectional cooling is carried out to cool to 430 ℃ at the speed of 20 ℃/s through the second section of water cooling, and the laminar flow sectional cooling is carried out to cool to room temperature on a roller way and a cooling bed;
the metallographic structure of the low-compression-ratio pipeline steel X70 steel plate is a steel plate with a complex phase structure of ferrite and bainite, wherein the ferrite accounts for 65% and the bainite accounts for 35%.
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