CN109252029B - Wedge-shaped weather-proof bridge steel with uniform performance at thin end and thick end and production method thereof - Google Patents
Wedge-shaped weather-proof bridge steel with uniform performance at thin end and thick end and production method thereof Download PDFInfo
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Abstract
The invention relates to a wedge-shaped weather-proof bridge steel plate with uniform thin and thick end performance, the thickness of the wedge-shaped steel plate is less than or equal to 80mm, and the wedge-shaped weather-proof bridge steel plate comprises the following chemical components in percentage by weight: c: 0.07% -0.09%, Si: 0.15% -0.35%, Mn: 1.15% -1.5%, P: less than or equal to 0.02 percent, S: less than or equal to 0.005 percent, Cu: 0.3% -0.42%, Ni: 0.3% -0.48%, Mo: 0.06% -0.10%, Cr: 0.38% -0.52%, Nb: 0.06% -0.08%, V: 0.01% -0.03%, Ti: 0.012% -0.025%, and the balance of Fe and inevitable impurities. According to the invention, the Nb element is utilized to inhibit austenite recrystallization, a larger deformation is applied to the steel plate, and the tissue distortion energy of the thin end and the thick end of the wedge-shaped steel plate is stored to an adjacent value, so that the thin end and the thick end have the same initial phase transformation state, and the wedge-shaped steel plate with uniform mechanical properties is obtained. The transverse yield strength of the wedge-shaped weather-proof bridge steel plate is 355 MPa-395 MPa, the transverse elongation is more than or equal to 23%, and the average value of longitudinal impact energy at minus 20 ℃ is more than or equal to 150J.
Description
Technical Field
The invention relates to the technical field of steel rolling, in particular to wedge-shaped weather-proof bridge steel with uniform properties of a thin end and a thick end and a production method thereof.
Background
The wedge-shaped steel plate (see attached figure 1), also known as longitudinal variable cross-section steel plate (L P plate for short), is a saving steel plate, is mainly used in shipbuilding and bridge engineering, can reduce the steel consumption and welding engineering amount by using the wedge-shaped steel plate, is helpful for reducing engineering cost and engineering period, accords with the concepts of 'green' and 'sustainable development', and in the last decade, the newly-built thick plate production line in China is basically equipped with the wedge rolling function, but the wedge-shaped steel plate supply capacity in batches is still limited, and the wedge-shaped steel plate has not been applied to domestic bridge engineering so far.
The thickness of the wedge-shaped steel plate is continuously changed along the longitudinal direction of the plate, the thickness directly influences the temperature change of the steel plate, so that the performance of the steel plate is influenced, and the condition that the thin end and the thick end of the wedge-shaped steel plate are qualified by adjusting components and process matching is one of production difficulties. After the wedge-shaped steel plate is rolled, the flatness of the wedge-shaped section is poor, and a straightening process is needed. The straightening of the wedge-shaped steel plate is the same as the principle of a common steel plate, namely positive and negative curvatures are given to the steel plate, and the residual curvatures of the steel plate gradually become smaller to zero. The flatness of wedge-shaped steel plates is qualified by straightening, which is another production difficulty. The two production difficulties are the key for restricting the supply of the wedge-shaped steel plates in steel mills in China.
The 345 MPa-grade weather-resistant bridge steel is weather-resistant bridge steel with the largest use amount at present due to good quality stability, although the initial investment cost of the weather-resistant steel is higher, the weather-resistant steel can obviously reduce the whole life cycle cost of a steel bridge, is the development direction of the bridge steel, and the application proportion of the weather-resistant bridge steel in bridge engineering is gradually improved. At present, the performance and the plate type of the steel for the wedge bridge are preliminarily researched:
patent 200910175208.6, a thickness control method for rolled wedge steel sheet. This patent discloses a method of rolling a wedge-shaped steel plate: the steel plate rolling process is that the rolling process is performed on a plurality of previous passes according to the conventional rectangular steel plate rolling technology, the oil column height change of a hydraulic cylinder of a rolling mill is controlled by a TDC controller at the last pass, the roll gap distance is continuously changed, and the continuous change of the longitudinal thickness of the steel plate is realized. The patent designs a control method for realizing wedge rolling mainly in an automatic control angle, but does not consider process factors influencing material performance.
Patent 201010282876.1, a method for producing longitudinally variable thickness steel sheet. The patent discloses a production method of a longitudinal variable-thickness steel plate, which controls and improves the plate shape, surface quality and mechanical property of the steel plate by controlling the temperature difference of the upper surface and the lower surface of a steel billet and the descaling pass of high-pressure water during discharging, controlling the diameter difference of an upper working roll and a lower working roll during roll matching, adjusting a zero self-adaptive numerical value of a mathematical model according to the actual thickness of the steel plate, controlling the rolling speed, the initial rolling temperature and the final rolling temperature of the steel plate, controlling the single-pass deformation of the last two passes, the cooling rate after rolling, the initial cooling temperature and the final cooling temperature and other technological measures, and producing the qualified longitudinal variable-thickness steel plate. Although the patent designs a production process of a longitudinally variable thickness steel plate, the influence of chemical components on process control and the influence of the process on the performance of the steel plate are not considered.
Patent 201110320517.5 discloses a method for producing a high-toughness steel sheet having a yield strength of 345 to 390 MPa. The patent comprises the following components: c: 0.08 to 0.20, Si: 0.03 to 0.55, Mn: 0.80-1.70, P is less than or equal to 0.015, S is less than or equal to 0.010, Nb: 0.01 to 0.07, V: 0.015 to 0.15, Ti: 0.005-0.035, N: 0.003-0.012, and the balance of Fe and inevitable impurities. The production process comprises the following steps: the method comprises the steps of molten iron desulphurization, converter, refining, heating, two-stage controlled rolling, ACC controlled cooling, normalizing and accelerated cooling. The method can be used for producing the high-toughness E-grade bridge steel with the yield strength of 345-390 MPa. The patent does not add Ni, Cr and Cu elements and has no weather resistance.
Patent 201710763956.0, a rare earth weather-resistant bridge steel plate with 345 MPa-level yield strength and a production method thereof. The chemical components of the patent are C: 0.04-0.06%, Si: 0.20 to 0.30%, Mn: 1.1-1.3%, P: less than or equal to 0.015%, S: less than or equal to 0.008 percent, Nb: 0.01-0.02%, Cu: 0.25 to 0.35%, Ni: 0.3-0.4%, Cr: 0.4-0.5%, Als: 0.024-0.034%, rare earth Ce: 0.0005-0.0030%, and the balance Fe and inevitable impurities. The production process mainly comprises two-stage rolling control and cooling control, and the produced bridge steel meets the national standard and has good weldability and weather resistance. This patent adds trace Ce, effectively improves the low temperature impact toughness of steel through the purification effect of tombarthite, but the price of tombarthite is more expensive, is unfavorable for cost control to need the control cooling, be unfavorable for the plate type control and the performance control of wedge-shaped steel sheet.
Patent 201710909081.0, TMCP type 345 MPa-level yield weather-proof bridge steel plate and a production method thereof. The chemical components of the patent are C: 0.04-0.07%, Si: 0.15 to 0.40%, Mn: 1.10-1.50%, P: 0.010-0.020%, S is less than or equal to 0.005%, Nb: 0.020-0.030%, Ni: 0.30-0.40%, Cr: 0.40-0.50%, Cu: 0.25-0.35%, Alt: 0.020-0.040%, and the balance of Fe and inevitable impurities. The rolling process comprises heating, two-stage controlled rolling and ACC controlled cooling. The content of C in the steel is low, a small amount of Nb is added into trace elements, and in order to obtain the weather-proof bridge steel with the yield strength of 450-600MPa, the cooling is required to be controlled, so that the plate type control and the performance control of the wedge-shaped steel plate are not facilitated.
The article: the authors' study of mechanical properties of longitudinally thickened steel plates [ J ]. Anhui Qing, Liuxian Ling, Liuming, Cold Pingyang, Hanxu. Steel structure, 2017, 32 (4): 16-21. the document shows that the mechanical properties of the steel plate are different along with the change of the thickness of the longitudinal variable thickness plate through experiments, and does not describe the manufacturing method of the longitudinal variable thickness steel plate.
The bridge weathering steel disclosed in the above documents needs controlled cooling, and the wedge-shaped steel plate has poor plate shape in the controlled cooling process, and the performance uniformity is difficult to ensure, so that the use requirements cannot be met.
Disclosure of Invention
The technical problem to be solved by the invention is to provide wedge-shaped weather-proof bridge steel with uniform thin and thick end performance and a production method thereof, the components are matched with the process, cooling is not required to be controlled, the thin and thick ends of the produced 345MP grade wedge-shaped weather-proof bridge steel are uniform in performance, and the plate shape is qualified.
In order to achieve the purpose, the invention adopts the following technical scheme:
the wedge-shaped weather-proof bridge steel plate with uniform thin and thick end performance is characterized in that the thickness of the wedge-shaped steel plate is less than or equal to 80mm, and the wedge-shaped weather-proof bridge steel plate comprises the following chemical components in percentage by weight: c: 0.07% -0.09%, Si: 0.15% -0.35%, Mn: 1.15% -1.5%, P: less than or equal to 0.02 percent, S: less than or equal to 0.005 percent, Cu: 0.3% -0.42%, Ni: 0.3% -0.48%, Mo: 0.06% -0.10%, Cr: 0.38% -0.52%, Nb: 0.06% -0.08%, V: 0.01% -0.03%, Ti: 0.012% -0.025%, and the balance of Fe and inevitable impurities.
A production method of a wedge-shaped weather-proof bridge steel plate with uniform thin and thick end performance comprises the following steps:
1) smelting process
Pretreating molten iron, smelting in a top-blowing or top-bottom combined blowing converter, refining, and carrying out electromagnetic stirring continuous casting;
2) heating process
Cleaning a plate blank, loading the plate blank into a furnace, and heating at the temperature of 1100-1250 ℃ for 3.5-5 h;
3) rolling process
A two-stage rolling mode is adopted, and wedge rolling is carried out at the last stage of rolling; the method specifically comprises the following steps:
a. the first-stage rolling temperature is more than or equal to 980 ℃;
b. the relationship between the two-stage rolling parameters and the thickness of the thick end of the wedge-shaped steel plate is as follows:
the thickness of the thick end of the wedge-shaped steel plate is less than or equal to 20mm, the thickness of the intermediate billet is more than or equal to 40mm, the initial rolling temperature is 920-980 ℃, and the final rolling temperature is 800-860 ℃;
the thickness of the thick end of the wedge-shaped steel plate is less than or equal to 40mm and more than 20 ℃, the thickness of the intermediate billet is more than or equal to 80mm, the initial rolling temperature is 880-980 ℃, and the final rolling temperature is 780-880 ℃;
the thickness of the thick end of the wedge-shaped steel plate is less than or equal to 60mm and more than 40 ℃, the thickness of the intermediate billet is more than or equal to 100mm, the initial rolling temperature is 860-960 ℃, and the final rolling temperature is 800-900 ℃;
the thickness of the thick end of the wedge-shaped steel plate is less than or equal to 80mm and more than 60 ℃, the thickness of the intermediate billet is more than or equal to 120mm, the initial rolling temperature is 840-960 ℃, and the final rolling temperature is 800-900 ℃;
c. when the thickness of the steel plate reaches the thickness requirement of the thick end of the wedge-shaped steel plate, starting wedge-shaped rolling until the rolling is finished, wherein the wedge-shaped rolling speed is 1-2m/s, and the relation between the total wedge-shaped rolling pass quantity and the wedge degree of the wedge-shaped steel plate and the thickness of the thick end is as follows:
the thickness of the wedge degree/thick end is less than or equal to 14 percent, and finally the wedge rolling is carried out for 1 to 3 passes;
the thickness of the wedge degree/thick end is more than 14 percent and less than or equal to 28 percent, and finally wedge rolling is carried out for 2 to 4 passes;
the thickness of the wedge degree/thick end is more than 28 percent and less than or equal to 42 percent, and finally wedge rolling is carried out for 3 to 5 passes;
the thickness of the wedge degree/thick end is more than 42% and less than or equal to 56%, and finally the wedge rolling is carried out for 4-6 passes;
the thickness of the wedge degree/thick end is more than 56 percent and less than or equal to 68 percent, and finally the wedge rolling is carried out for 5 to 7 passes;
4) cooling process
Cooling in an air cooling mode after rolling;
5) thermal straightening process
Straightening by a hot straightening machine, wherein the straightening temperature is more than 700 ℃, the straightening speed is 0.2-1.0m/s, the thick end of a wedge-shaped steel plate firstly enters the straightening machine, the gap between straightening rollers is reduced at a constant speed when the straightening enters a wedge-shaped section, the upper straightening roller is lowered in a linkage manner, and the calculation formula of the speed of the lowering roller is as follows:
roll down speed-wedge × straightening speed/wedge horizontal length
And after the wedge-shaped section is straightened, straightening the thin end of the wedge-shaped steel plate by keeping the roll gap and the straightening speed unchanged, and finishing the straightening.
The wedge degree of the steel plate is the thickness difference of the thin end and the thick end of the wedge-shaped steel plate.
The types and the contents of alloy elements of the wedge-shaped weather-proof bridge steel plate with uniform thin and thick end performance are selected as follows:
c: the steel is an essential element for ensuring the strength, the main participating strengthening modes are solid solution strengthening and precipitation strengthening, the weather-resistant steel needs to be added with more weather-resistant elements, so the content of C is not more than 0.09 percent in consideration of weldability, the steel is designed to be air-cooled, so the phase change strengthening cannot be obtained, the content of C is not too low, and the content of carbon is controlled to be 0.07-0.09 percent.
Si: is the main deoxidizing element in the steel-making process, and the welding property can be reduced when the content of the deoxidizing element is too high, and the range is controlled to be 0.15-0.35 percent.
Mn: is a main solid solution strengthening element, the content of which is too much and is easy to cause serious core segregation, and the range is controlled to be 1.15 to 1.5 percent
Ni, Cr, Cu: the main weather resistance adds elements and provides solid solution strengthening, the range controls Cu: 0.3% -0.42%, Ni: 0.3% -0.48%, Cr: 0.38% -0.52%.
Nb: the element is an element for inhibiting austenite recrystallization, the carbonitride of Nb can be precipitated at the austenite grain boundary at a high temperature to block the movement of the austenite grain boundary, the Nb has strong affinity to C, and the diffusion of C is inhibited by Nb in the austenite, so that the austenite recrystallization temperature is increased along with the increase of the Nb element in the steel type. The steel undergoes larger total amount of deformation in the non-recrystallization area, so that the tissue storage distortion energy in the thick end and the thin end of the wedge-shaped steel plate can reach a critical state, the purpose of doing so is to enable the tissue phase change initial states in the thin end and the thick end of the steel plate to be the same, and eliminate the performance unevenness caused by the thickness difference. Because the cost of the Nb element is higher, the selection meets the requirement of adding microalloy elements and Mo elements, the recrystallization inhibiting effect of Nb is improved, and the Nb range is controlled to be 0.06-0.08%.
V: can be precipitated in a ferrite matrix to improve the strength of the ferrite matrix, and the range is controlled to be 0.01-0.03%.
Ti: the Ti (C, N) precipitated phase has high-temperature precipitation characteristics, can be precipitated at an austenite grain boundary in the blank heating stage, effectively hinders the growth of austenite grains, and provides tissue preparation for subsequent tissue refinement. Considering the combined action of Ti and other microalloy elements, the Ti content is controlled to be 0.012-0.025 percent.
Mo: the element promotes the precipitation of Nb, V and Ti, improves the precipitation amount of the microalloy element carbonitride, reduces the size radius of the precipitate and has the effect of strengthening the action of the microalloy element.
P, S: is an inevitable impurity element in steel, and the range of P is controlled to be less than or equal to 0.020 percent and S is controlled to be less than or equal to 0.005 percent.
Compared with the prior art, the invention has the beneficial effects that:
(1) based on low C, Si and Mn, adding a proper amount of Ni, Cr and Cu to meet weather resistance, mainly utilizing Nb element to inhibit austenite recrystallization, applying a larger total deformation amount to the steel plate, and storing the tissue distortion energy of the thin end and the thick end of the wedge-shaped steel plate to the critical value to ensure that the thin end and the thick end have the same initial phase change state so as to obtain the wedge-shaped steel plate with uniform mechanical properties; the addition of Mo can enhance the effect of Nb, and in addition, proper amounts of V and Ti are added to make up for the insufficient strength caused by air cooling. By matching with a corresponding production process, the 345 MPa-grade wedge-shaped weather-resistant bridge steel plate with good plate shape and qualified and uniform mechanical properties is obtained.
(2) The design of high Nb and trace Mo components and the air cooling process after rolling are matched to effectively ensure the plate shape quality and the mechanical property uniformity.
(3) In order to ensure that the flatness of the wedge-shaped steel meets the requirement, the wedge-shaped section of the wedge-shaped steel plate is subjected to thermal straightening by adopting a continuous variable roll gap method, the roll gap is gradually reduced from a set value at the thick end of the wedge-shaped steel plate to a set value at the thin end by continuously reducing an upper straightening roll, and the straightening of the wedge-shaped section is completed in the process.
(4) The 345MPa wedge-shaped weather-proof bridge steel has the thickness of less than or equal to 80mm, the transverse yield strength of 355-395 MPa, the transverse elongation of more than or equal to 23 percent, the average value of longitudinal impact energy at minus 20 ℃ of more than or equal to 150J, the performance meeting the national standard, the plate shape is qualified, the yield strength difference of the thin and thick end of the same plate is less than 30MPa, the elongation difference is less than 6 percent, the average impact energy difference at minus 20 ℃ is less than 50J, and the performance uniformity is good.
Detailed Description
The invention is further illustrated by the following examples:
the following examples describe the invention in detail. These examples are merely illustrative of the best embodiments of the present invention and do not limit the scope of the invention.
The components of the wedge-shaped weather-proof bridge steel plate with uniform properties at the thin end and the thick end are shown in the table 1;
table 1 examples steel chemical composition (wt%)
The heating process and the one-stage rolling process of the wedge-shaped weather-proof bridge steel plate with uniform thin and thick ends are shown in the table 2;
TABLE 2 examples heating process and one-stage rolling process
The two-stage rolling process, the cooling process and the heat straightening process of the wedge-shaped weather-resistant bridge steel plate with uniform thin and thick end performance are shown in a table 3;
table 3 examples of the two-stage rolling process, cooling process and hot straightening process of wedge-shaped weather-resistant bridge steel
The hot rolling state mechanical properties of the wedge-shaped weather-proof bridge steel plate with uniform thin and thick end properties are shown in a table 4;
TABLE 4 examples of hot-rolled mechanical properties of wedge-shaped weather-resistant bridge steel
The 345MPa wedge-shaped weather-proof bridge steel has the thickness of less than or equal to 80mm, the transverse yield strength of 355-395 MPa, the transverse elongation of more than or equal to 23 percent, the average value of longitudinal impact energy at minus 20 ℃ of more than or equal to 150J, the plate shape is qualified, the performance meets the national standard, the yield strength difference of the thin end and the thick end of the same plate is less than 30MPa, the elongation difference is less than 6 percent, the average impact energy difference at minus 20 ℃ is less than 50J, and the performance uniformity is good.
Claims (2)
1. The production method of the wedge-shaped weather-proof bridge steel plate with uniform thin and thick end performance is characterized in that the thickness of the wedge-shaped steel plate is less than or equal to 80mm, and the wedge-shaped weather-proof bridge steel plate comprises the following chemical components in percentage by weight: c: 0.07% -0.09%, Si: 0.15% -0.35%, Mn: 1.15% -1.5%, P: less than or equal to 0.02 percent, S: less than or equal to 0.005 percent, Cu: 0.3% -0.42%, Ni: 0.3% -0.48%, Mo: 0.06% -0.10%, Cr: 0.38% -0.52%, Nb: 0.06% -0.08%, V: 0.01% -0.03%, Ti: 0.012% -0.025%, and the balance of Fe and inevitable impurities; the production method comprises a smelting process, a heating process, a rolling process, a cooling process and a hot straightening process; wherein:
1) rolling process
A two-stage rolling mode is adopted, and wedge rolling is carried out at the last stage of rolling; the method specifically comprises the following steps:
a. the first-stage rolling temperature is more than or equal to 980 ℃;
b. the relationship between the two-stage rolling parameters and the thickness of the thick end of the wedge-shaped steel plate is as follows:
the thickness of the thick end of the wedge-shaped steel plate is less than or equal to 20mm, the thickness of the intermediate billet is more than or equal to 40mm, the initial rolling temperature is 920-980 ℃, and the final rolling temperature is 800-860 ℃;
the thickness of the thick end of the wedge-shaped steel plate is less than or equal to 40mm and more than 20 ℃, the thickness of the intermediate billet is more than or equal to 80mm, the initial rolling temperature is 880-980 ℃, and the final rolling temperature is 780-880 ℃;
the thickness of the thick end of the wedge-shaped steel plate is less than or equal to 60mm and more than 40 ℃, the thickness of the intermediate billet is more than or equal to 100mm, the initial rolling temperature is 860-960 ℃, and the final rolling temperature is 800-900 ℃;
the thickness of the thick end of the wedge-shaped steel plate is less than or equal to 80mm and more than 60 ℃, the thickness of the intermediate billet is more than or equal to 120mm, the initial rolling temperature is 840-960 ℃, and the final rolling temperature is 800-900 ℃;
c. when the thickness of the steel plate reaches the thickness requirement of the thick end of the wedge-shaped steel plate, starting wedge-shaped rolling until the rolling is finished, wherein the wedge-shaped rolling speed is 1-2m/s, and the relation between the total wedge-shaped rolling pass quantity and the wedge degree of the wedge-shaped steel plate and the thickness of the thick end is as follows:
the thickness of the wedge degree/thick end is less than or equal to 14 percent, and finally the wedge rolling is carried out for 1 to 3 passes;
the thickness of the wedge degree/thick end is more than 14 percent and less than or equal to 28 percent, and finally wedge rolling is carried out for 2 to 4 passes;
the thickness of the wedge degree/thick end is more than 28 percent and less than or equal to 42 percent, and finally wedge rolling is carried out for 3 to 5 passes;
the thickness of the wedge degree/thick end is more than 42% and less than or equal to 56%, and finally the wedge rolling is carried out for 4-6 passes;
the thickness of the wedge degree/thick end is more than 56 percent and less than or equal to 68 percent, and finally the wedge rolling is carried out for 5 to 7 passes;
2) cooling process
Cooling in an air cooling mode after rolling;
3) thermal straightening process
Straightening by a hot straightening machine, wherein the straightening temperature is more than 700 ℃, the straightening speed is 0.2-1.0m/s, the thick end of a wedge-shaped steel plate firstly enters the straightening machine, the gap between straightening rollers is reduced at a constant speed when the straightening enters a wedge-shaped section, the upper straightening roller is lowered in a linkage manner, and the calculation formula of the speed of the lowering roller is as follows:
roll down speed-wedge × straightening speed/wedge horizontal length
And after the wedge-shaped section is straightened, straightening the thin end of the wedge-shaped steel plate by keeping the roll gap and the straightening speed unchanged, and finishing the straightening.
2. The method for producing the wedge-shaped weather-proof bridge steel plate with the uniform thin and thick end performance according to claim 1, wherein the wedge degree in the step 2) is the thickness difference of the thin and thick end of the wedge-shaped steel plate.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201811329589.4A CN109252029B (en) | 2018-11-09 | 2018-11-09 | Wedge-shaped weather-proof bridge steel with uniform performance at thin end and thick end and production method thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN201811329589.4A CN109252029B (en) | 2018-11-09 | 2018-11-09 | Wedge-shaped weather-proof bridge steel with uniform performance at thin end and thick end and production method thereof |
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| CN110863139B (en) * | 2019-10-31 | 2021-05-28 | 鞍钢股份有限公司 | Ultralow-temperature-impact-resistant 420 MPa-grade weather-resistant bridge steel and production method thereof |
| CN112126853B (en) * | 2020-09-07 | 2022-07-22 | 鞍钢股份有限公司 | Longitudinal variable-thickness high-strength ship board and production method thereof |
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