CN115852245B - Cold-rolled bainite type weathering steel and preparation method thereof - Google Patents
Cold-rolled bainite type weathering steel and preparation method thereof Download PDFInfo
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- 229910001563 bainite Inorganic materials 0.000 title claims abstract description 41
- 229910000870 Weathering steel Inorganic materials 0.000 title claims abstract description 32
- 238000002360 preparation method Methods 0.000 title claims abstract description 9
- 238000000034 method Methods 0.000 claims abstract description 28
- 230000008569 process Effects 0.000 claims abstract description 17
- 239000000126 substance Substances 0.000 claims abstract description 14
- 238000010438 heat treatment Methods 0.000 claims abstract description 10
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 9
- 238000001816 cooling Methods 0.000 claims description 23
- 238000004519 manufacturing process Methods 0.000 claims description 22
- 238000000137 annealing Methods 0.000 claims description 20
- 238000005096 rolling process Methods 0.000 claims description 16
- 239000012535 impurity Substances 0.000 claims description 12
- 238000005098 hot rolling Methods 0.000 claims description 11
- 238000002791 soaking Methods 0.000 claims description 11
- 238000005097 cold rolling Methods 0.000 claims description 9
- 238000009749 continuous casting Methods 0.000 claims description 6
- 238000004321 preservation Methods 0.000 claims description 6
- 230000009467 reduction Effects 0.000 claims description 6
- 238000003723 Smelting Methods 0.000 claims description 4
- 238000005554 pickling Methods 0.000 claims description 4
- 238000010583 slow cooling Methods 0.000 claims description 3
- 229910000831 Steel Inorganic materials 0.000 abstract description 60
- 239000010959 steel Substances 0.000 abstract description 60
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 30
- 239000010949 copper Substances 0.000 description 20
- 230000000052 comparative effect Effects 0.000 description 18
- 229910052802 copper Inorganic materials 0.000 description 15
- 229910052799 carbon Inorganic materials 0.000 description 14
- 239000011572 manganese Substances 0.000 description 13
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 13
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 12
- 229910052742 iron Inorganic materials 0.000 description 12
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 11
- 239000011651 chromium Substances 0.000 description 11
- 239000010955 niobium Substances 0.000 description 9
- 238000005728 strengthening Methods 0.000 description 9
- 239000010936 titanium Substances 0.000 description 9
- 229910052804 chromium Inorganic materials 0.000 description 7
- 230000007797 corrosion Effects 0.000 description 7
- 238000005260 corrosion Methods 0.000 description 7
- 229910052729 chemical element Inorganic materials 0.000 description 6
- 239000011159 matrix material Substances 0.000 description 6
- 229910052759 nickel Inorganic materials 0.000 description 6
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 229910052748 manganese Inorganic materials 0.000 description 5
- 229910000734 martensite Inorganic materials 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- 229910052758 niobium Inorganic materials 0.000 description 5
- 229910052760 oxygen Inorganic materials 0.000 description 5
- 239000001301 oxygen Substances 0.000 description 5
- 229910052698 phosphorus Inorganic materials 0.000 description 5
- 229910052719 titanium Inorganic materials 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 4
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 4
- 238000007670 refining Methods 0.000 description 4
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
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- 230000009286 beneficial effect Effects 0.000 description 3
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- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 239000011574 phosphorus Substances 0.000 description 3
- 229910052710 silicon Inorganic materials 0.000 description 3
- 239000006104 solid solution Substances 0.000 description 3
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- 150000001875 compounds Chemical class 0.000 description 2
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- 238000001556 precipitation Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 229910000797 Ultra-high-strength steel Inorganic materials 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
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- 238000007664 blowing Methods 0.000 description 1
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- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
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- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
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- -1 niobium carbide compound Chemical class 0.000 description 1
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- 239000002904 solvent Substances 0.000 description 1
- 229910052596 spinel Inorganic materials 0.000 description 1
- 239000011029 spinel Substances 0.000 description 1
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- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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Abstract
The invention discloses cold-rolled bainite type weathering steel, which is characterized by comprising chemical components ：C：0.13～0.16％;Mn：1.20～1.50％;Si：0.001～0.2％;P：0.008～0.025％;Alt：0.02～0.06％;Cu：0.25～0.40％;Cr：0.40～0.70％;Ni：0.10～0.30％;Ti：0.015～0.030％;Nb：0.008～0.020％;Fe≥90％; in percentage by mass, wherein the microstructure of the cold-rolled bainite type weathering steel comprises bainite and ferrite, and the volume fraction of the bainite is 40-80%; the yield strength of the steel is more than or equal to 700MPa, the tensile strength is more than or equal to 800MPa, and the elongation is more than or equal to 5%. By adopting the technical scheme, the content of chemical components in the steel can be controlled, the expected strength can be ensured under a certain heat treatment process, the finished product can obtain good weather resistance, and the cold-rolled bainite weather-resistant steel has good mechanical properties by combining the control of multiphase microstructure which takes bainite and ferrite as matrixes. The invention also discloses a preparation method of the cold-rolled bainite weathering steel.
Description
Technical Field
The invention relates to cold-rolled steel, in particular to cold-rolled bainite weather-resistant steel and a preparation method thereof.
Background
With the global warming and energy conservation and emission reduction requirements, actions are taken consistently across countries. In 9 months 2020, the government of China has promised to meet the peak of carbon before 2030 and strives to achieve carbon neutralization before 2060. Therefore, the high-strength weight reduction has important significance in the transportation industry, and the high-strength weight reduction of the sheet steel strip also becomes the development trend of the steel industry. The cold-rolled ultra-high strength weathering steel is mainly applied to the production and manufacture of container side plates and top plates, and mainly needs to meet the requirements of two aspects: weather resistance and yield strength.
Statistics of the related data show that about 1/6 of the steel materials in the world are consumed by corrosion every year. The weather-resistant steel is produced in such a background, and is characterized in that a small amount of Cu, P, cr, ni or other alloying elements are added to the steel. The effect of the method is that the iron and steel material forms a compact amorphous spinel type oxide layer with the thickness of about 50-100 mu m and good adhesion with the matrix metal between the rust layer and the matrix, and prevents water and oxygen in the atmosphere from penetrating into the iron and steel matrix, thereby improving the atmospheric corrosion resistance of the iron and steel material.
The main purpose of the steel with ultrahigh yield strength is to reduce the thickness by improving the strength of the strip steel, thereby improving the transportation efficiency and reducing the energy consumption and the carbon emission. In the first few decades of the twenty-first century, container panels were typically about 1.6mm thick, with a base yield strength of about 350 MPa. With the development of the production technology of cold-rolled ultra-high strength steel, the thickness of the panel is reduced to about 1.2mm, and the yield strength is correspondingly improved to 700MPa or more.
Related patents are also filed in China along with the development of the production technology of the ultra-high strength weathering steel. For example, chinese patent No. CN101376950a discloses an ultra-high strength cold rolled weather resistant steel sheet and a method for manufacturing the same, which uses chemical composition (wt％)：C：0.09～0.16、Si：0.20～0.60、Mn：1.00～2.00、P：≤0.030、S≤0.015、N≤0.008、Al：0.02～0.06、Cu：0.20～0.40、Cr：0.40～0.60、Mo：0.05～0.25、Nb+Ti：0.04～0.08、 other than Fe and unavoidable impurities. According to the method, the annealing soaking temperature is 680-790 ℃, and the preferable implementation case is 700-740 ℃, and the method belongs to the conventional production process of low-temperature annealing. The main disadvantages of this method are that the steel strength is not increased by phase transformation strengthening, and more noble alloys such as Mo, nb, ti, etc. need to be added, resulting in increased costs. Meanwhile, during continuous annealing low-temperature production, the internal stress of the strip steel is released unevenly, and the strip shape problem is likely to exist.
The invention patent CN103266274A discloses an ultra-high strength cold-rolled weather-resistant steel plate and a manufacturing method thereof, wherein the mass percentage of chemical elements is as follows: c:0.05 to 0.16 percent; mn:1.00 to 2.20 percent; al:0.02 to 0.06 percent; cu:0.20 to 0.40 percent; cr:0.40 to 0.60 percent; ti:0.015 to 0.035 weight percent; p is less than or equal to 0.03%; and satisfies 0.19% < C+Mn/16 < 0.23%; the balance being Fe and other unavoidable impurities. The matrix component of the patent is not added with Nb alloy, the microstructure is martensite, and in order to obtain martensite, a higher annealing soaking temperature, namely 850-880 ℃, and the cooling speed is more than 100 ℃/s are required. The annealing condition corresponding to the patent is more severe, and the requirement on the quick cooling capacity of an annealing unit is higher. According to the invention, the yield strength of the finished product is more than 700MPa, the tensile strength is more than 1000MPa, and the tensile strength given by the preferred embodiment is up to 1235MPa, so that the problem of strip steel cracking is easy to occur under certain use occasions due to the excessively high tensile strength.
Chinese patent CN107841689a discloses a weather-resistant steel sheet and a method for manufacturing the same, the composition of which contains C：0.04～0.10％、Si：0.18～0.35％、Mn：1.00～1.60％、P：0.008～0.015％、Cu：0.25～0.45％、Cr：0.40～0.60％、Ni：0.30～0.50％、Alt：0.02～0.05％、Nb：0.01～0.05％, by mass% of the balance iron and unavoidable impurities. The manufacturing method related to the patent comprises smelting, refining, continuous casting, heating and rolling, wherein the initial rolling temperature of the finish rolling stage is 850-970 ℃, the final rolling temperature is 780-860 ℃, and the residence time after finish rolling is 10-30 seconds, which is also the key process point of the patent. The corresponding product shape is a hot rolled product, not involving cold rolling of ultra-high strength and (5) producing and manufacturing weather-resistant steel.
The Chinese patent CN107829024A discloses a super-strength weather-resistant steel plate with the pressure of more than 700MPa and a hot continuous rolling production method thereof, wherein the chemical components are carbon: 0.06-0.08%, silicon: 0.15 to 0.25 percent of manganese: 1.25 to 1.35 percent of phosphorus: less than or equal to 0.018 percent, sulfur: less than or equal to 0.005 percent, all aluminum: 0.02 to 0.05 percent of niobium: 0.05 to 0.07 percent of titanium: 0.09-0.13%, chromium: 0.37 to 0.45 percent, copper: 0.20 to 0.28 percent, nickel: 0.10 to 0.15 percent, nitrogen: less than or equal to 0.0050 percent, and the balance of iron. The tapping temperature of the manufacturing process given by the patent is controlled to 1250-1280 ℃, and the coiling temperature is controlled to 570-610 ℃. The thickness of the finished product corresponding to the patent is 1.5-6.0 mm, and the corresponding product shape is a hot-rolled product, and the production and the manufacture of cold-rolled ultra-high-strength weathering steel are not involved.
Disclosure of Invention
In one aspect, the invention provides cold-rolled bainite type weathering steel, which is characterized in that a microstructure of the cold-rolled bainite type weathering steel comprises, in mass percent, ：C：0.13～0.16％;Mn：1.20～1.50％;Si：0.001～0.2％;P：0.008～0.025％;Alt：0.02～0.06％;Cu：0.25～0.40％;Cr：0.40～0.70％;Ni：0.10～0.30％;Ti：0.015～0.030％;Nb：0.008～0.020％;Fe≥90％; chemical components, bainite and ferrite, wherein the volume fraction of the bainite is 40-80%; the yield strength of the cold-rolled bainite weathering steel is more than or equal to 700MPa, the tensile strength is more than or equal to 800MPa, and the elongation is more than or equal to 5%.
By adopting the technical scheme of the application, the content of chemical components in the cold-rolled bainite weathering steel, for example, the content of C, mn elements is reasonably controlled, so that the expected strength can be ensured to be obtained under a certain heat treatment process; and the contents of Cu and Cr elements are controlled, so that the finished product can obtain good weather resistance. The cold-rolled bainite type weathering steel comprises a multiphase microstructure with bainite and ferrite as matrixes, so that the cold-rolled bainite type weathering steel has good mechanical properties: the yield strength is more than or equal to 700MPa, the tensile strength is more than or equal to 800MPa, the elongation percentage is more than or equal to 5 percent.
The design considerations of the individual chemical elements and their interactions with each other and the limitations of the chemical composition of the claimed alloy are briefly described below.
C: carbon is the most important matrix strengthening element in steel production, and the corresponding production cost is the lowest, so that the steel strength can be effectively improved, but excessive carbon has adverse effects on welding performance. The carbon content needs to be controlled within a reasonable range, and in the application, the mass percentage of C is controlled to be 0.13-0.16%.
Mn: manganese is a solid solution strengthening element in steel, and can also improve the hardenability of the steel, which is beneficial to improving the strength of the steel plate, but when the Mn content is too high, the welding performance of the steel is also deteriorated. Compared with carbon, manganese element can improve strength and maintain certain toughness. Therefore, in the present application, the mass percentage of Mn is controlled to be 1.20 to 1.50%.
Si: silicon is a solid solution strengthening element, can be dissolved in ferrite to improve the hardness and strength of steel, and simultaneously improve the plasticity; however, when excessive Si is added, the surface problems of hot rolling red iron sheet and other working procedures are brought about, and in the application, the mass percentage of Si is controlled to be 0.001-0.2%;
p: on one hand, phosphorus element can form a corrosion-resistant barrier layer with Cu, so that the atmospheric corrosion resistance of the steel plate is improved, and on the other hand, the welding performance and cold bending performance of the strip steel are also reduced. In the cold-rolled bainite weathering steel of the present application, the mass percentage of phosphorus is controlled to be 0.008 to 0.025%.
Al: the main purpose of adding aluminum element to steel is to deoxidize. Because the molten steel has certain free oxygen after the converter is finished, the free oxygen is removed by adding aluminum, so that the content of endogenous inclusions in the steel is reduced. Meanwhile, certain surplus aluminum is maintained, alN particles can be formed with N, so that grains are refined, and the yield strength of a finished product is improved. In the present application, the total Al content (Alt) is controlled to 0.02 to 0.06%.
Cu: copper element is a key control element of weathering steel, and can promote the surface of a steel plate to form stable and compact corrosion products, thereby achieving the aim of resisting atmospheric corrosion. To achieve this, the copper content is generally not less than 0.2%. On the other hand, copper has a relatively low melting point, and when the copper-rich phase on the surface layer of the slab reaches a certain level in the molten state during the heating process of the slab, the surface cracks, thereby causing a defect of copper embrittlement, so that the upper limit of copper also needs to be controlled. In the present application, the copper content is controlled to be 0.25 to 0.40%.
Cr: on the one hand, the chromium element is a solid solution strengthening element, so that the strength of the matrix can be improved; on the other hand, chromium and copper are added simultaneously to form a dense oxide film on the surface of the steel sheet, thereby improving weather resistance. However, when chromium is added too high, the weldability of the finished product is lowered. In the present application, the content of chromium is controlled to be 0.40 to 0.70%.
Ni: the nickel element can improve the corrosion resistance of the strip steel on one hand and can relieve the defect of copper embrittlement on the other hand; in addition, the nickel element can strengthen ferrite so as to improve the strength of the strip steel. In the present application, the content of nickel is controlled to be 0.10 to 0.30%.
Ti: titanium has extremely strong affinity with nitrogen, oxygen and carbon, and can generate corresponding compounds. The yield strength and the forming property of the finished product can be improved through precipitation strengthening and fine crystal strengthening. In the present application, the content of titanium is controlled to be 0.015 to 0.030%.
Nb: niobium has similar effect with titanium, can form niobium carbide compound with carbon, and has precipitation strengthening and fine crystal strengthening effects, thereby improving the yield strength of the strip steel. In addition, the niobium alloy has high unit price, and excessive addition causes production cost. In the present application, the content of niobium is controlled to be 0.008 to 0.020%.
Further, the balance of the chemical components in the cold-rolled bainite weathering steel is Fe and unavoidable impurities.
Further, among the above unavoidable impurities, the content of S is controlled: s is less than or equal to 0.01 percent.
S is an impurity element in steel, and in order to obtain cold rolled steel with better performance, the content of the impurity element in steel should be reduced as much as possible under the condition of allowing.
On the other hand, the invention also discloses a preparation method of the cold-rolled bainite weathering steel, which comprises the following steps: smelting, continuous casting, hot rolling, pickling, cold rolling, continuous annealing and flattening; wherein the cold-rolled bainite type weathering steel comprises the chemical components in percentage by mass ：C：0.13～0.16％;Si：0.001～0.2％;Mn：1.20～1.50％;P：0.008～0.025％;Alt：0.02～0.06％;Cu：0.25～0.40％;Cr：0.40～0.70％;Ni：0.10～0.30％;Nb：0.008～0.020％;Ti：0.015～0.030％;Fe≥90％;
The microstructure of the cold-rolled bainite weathering steel comprises bainite and ferrite, wherein the volume fraction of the bainite is 40-80%; the yield strength of the cold-rolled bainite weathering steel is more than or equal to 700MPa, the tensile strength is more than or equal to 800MPa, and the elongation is more than or equal to 5%.
By adopting the preparation method, after the steel with the chemical components is subjected to two rolling steps (hot rolling and cold rolling) and continuous annealing steps, the cold-rolled bainite type weathering steel can be obtained, comprises 40-80% by volume of bainite, and has good mechanical properties: the yield strength is more than or equal to 700MPa, the tensile strength is more than or equal to 800MPa, the elongation is more than or equal to 5%, and the requirements of steel reinforcement and weight reduction can be met.
Further, in the continuous annealing step, the soaking heat preservation temperature is controlled to be more than or equal to 820 ℃, the soaking heat preservation time is controlled to be 120-200 s, the slow cooling ending temperature is controlled to be 700-730 ℃, the rapid cooling ending temperature is controlled to be 340-360 ℃, and the rapid cooling speed is controlled to be 55-70 ℃/s.
In the application, the main purpose of controlling the annealing soaking heat preservation temperature to be above 820 ℃ and preserving heat for 120-200 s is to fully recrystallize and austenitize the rolling hard state tissue; firstly, slowly cooling to the end temperature of 700-730 ℃, and then cooling to the temperature of 340-360 ℃ of the bainite transformation zone at the fast cooling rate of 55-70 ℃ per second, namely the fast cooling end temperature. The rapid cooling rate of 55-70 ℃/s is adopted to cool to 340-360 ℃ so as to obtain the tissue with the target bainite volume fraction, thereby improving the yield strength of the finished product. Compared with the martensite high-hydrogen rapid cooling process (the rapid cooling rate is more than 100 ℃/s), the rapid cooling rate (55-70 ℃/s) provided by the technical scheme is lower, the rapid cooling capacity requirement of a continuous annealing unit can be reduced, and the cold-rolled bainite weathering steel performance can be obtained under the condition of limited rapid cooling capacity.
Further, in the hot rolling step, the heating temperature is controlled to 1150 to 1220 ℃, the finishing temperature is controlled to 850 to 910 ℃, and the coiling temperature is controlled to 480 to 540 ℃.
For the hot rolling process, the lower slab heating temperature is 1150-1220 ℃, so that the 'copper embrittlement' defect of the slab is reduced as much as possible on the premise of ensuring that C, N compounds are fully dissolved; when the hot coil is coiled, the coiling temperature is 480-540 ℃, and the coiling is mainly considered at a lower temperature, so that flat coils generated by the hot coil are avoided.
In addition, in the cold rolling step, the rolling mill reduction may be controlled to 55 to 70%. When the rolling reduction is low, the hot rolled grains are not fully rolled and crushed, the accumulated deformation energy is insufficient, the size of recrystallized grains is relatively large during annealing, and the yield strength of the finished product is reduced; and the increased deformation can cause larger roller loss, thereby bringing the problems of hard rolling plate shape and the like. But increasing the amount of deformation is beneficial in reducing the annealing soak temperature and increasing the yield strength of the strip. In the application, the rolling mill rolling reduction is controlled to be 55-70%.
The invention has the beneficial effects that:
1. In the chemical components, the content of carbon and manganese is moderate, so that the finished product can obtain certain strength; and then the weather resistance of the finished product is ensured by reasonably controlling the contents of Cu, cr and Ni elements, and the yield strength of the finished product can be improved by adding Nb and Ti to refine grains.
2. The long-flow manufacturing method provided by the invention comprises hot rolling and cold rolling steps, and can be used for producing the cold-rolled bainite weathering steel with higher yield ratio by adopting lower continuous annealing soaking temperature and lower rapid cooling speed. And in a general continuous annealing unit, the cold-rolled steel sheet manufactured through the bainite transformation process can be used for manufacturing a container panel. The container panel has excellent shape and surface quality, and the yield strength of the finished product can meet the standard requirement.
Drawings
FIG. 1 is a microstructure photograph of a cold rolled bainitic weathering steel of example 1;
FIG. 2 is a microstructure photograph of the cold rolled bainite weathering steel of comparative example 2.
Detailed Description
Further advantages and effects of the present invention will become apparent to those skilled in the art from the disclosure of the present specification, by describing the embodiments of the present invention with specific examples. While the description of the invention will be described in connection with the preferred embodiments, it is not intended to limit the inventive features to the implementation. Rather, the purpose of the invention described in connection with the embodiments is to cover other alternatives or modifications, which may be extended by the claims based on the invention. The following description contains many specific details for the purpose of providing a thorough understanding of the present invention. The invention may be practiced without these specific details. Furthermore, some specific details are omitted from the description in order to avoid obscuring the invention. It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
Examples 1 to 16 and comparative examples 1 to 4
The cold rolled bainitic weathering steels of examples 1-16 and comparative examples 1-4 of the present invention were prepared by the following steps:
And 1, smelting. In this step, the blast furnace molten iron is blown through a steelmaking converter unit and then refined by a vacuum circulation degassing method (RH).
Specifically, liquid iron is produced in a large-scale reaction vessel by using iron ore, coke and other solvents in a blast furnace, and is transported to a steelworks by a torpedo car, and is subjected to treatments such as desulfurization and desilication during transportation. The chemical element composition of the molten iron is controlled according to the conventional control requirement. In the converter process, top-bottom composite oxygen blowing is utilized to blow molten iron, and nonmetallic inclusion and various impurities in the molten iron are removed. The ladle molten steel is subjected to secondary refining by utilizing vacuum circulation degassing equipment during refining, and the main purposes are to degas and deoxidize, and alloy is added to adjust the chemical element components of the molten steel to be within a specified range, wherein the control requirements of the chemical elements are as described above, and the vacuum degassing time is controlled to be more than 15 min.
And 2, continuous casting. Pouring the molten steel subjected to secondary refining into a tundish, and controlling the superheat degree of the molten steel according to the temperature of 10-20 ℃; and (3) rapidly cooling and solidifying the steel billet into a solid state in continuous casting equipment, cutting the steel billet into a steel billet with a certain size by flame, and controlling the continuous casting speed according to 1.0-1.5 m/min, wherein the thickness of the steel billet is 230-250 mm.
And 3, hot rolling. In this step, the billet is reheated and rolled to a hot rolled coil of a certain thickness range according to certain process requirements, and the main process of hot rolling includes slab heating temperature: 1150-1220 ℃, the heat preservation time of the slab is more than 150min, the slab enters a 7-frame finishing mill after 5-pass rough rolling, and the finishing temperature of a finishing mill frame is 850-920 ℃; the coiling control temperature of the strip steel after laminar cooling is 480-540 ℃. The thickness of the hot rolled strip steel is only the middle thickness, and the range is 2.3-6.0 mm.
And 4, acid washing. Conventional pickling processes are employed. The main purpose of this step is to remove scale and dirt impurities on the surface of the hot rolled coil and to achieve a certain surface cleanliness, the thickness of the strip steel is not changed during this process.
And 5, cold rolling. The pickling coil is used as a raw material, and the main purpose is to further roll and thin strip steel and ensure certain plate shape, surface roughness and thickness precision. The key technology of this procedure is that the deformation, that is, rolling reduction, is generally controlled to be about 55-70%, and the product of this procedure is generally called as a rolled hard coil.
And 6, continuous annealing. The heat treatment is carried out by taking the rolled hard coil as a raw material, and the main purpose is to recrystallize the rolled hard structure through the heat treatment and obtain a desired metallographic structure with a certain proportion, thereby improving the plasticity of the steel and achieving a certain strength. In the step, the annealing soaking temperature is controlled to be more than or equal to 820 ℃, soaking and heat preserving time: 120-200 s; slow cooling end temperature: 700-730 ℃; rapid cooling end temperature: 340-360 ℃ and fast cooling rate: 55-70 ℃/s.
And 7, flattening.
The chemical composition of the cold rolled bainitic weathering steel and the process parameters of the preparation process in the above examples and comparative examples are specifically referred to the following tables.
Table 1 shows the mass percentages of the chemical elements of the cold rolled bainitic weathering steels of examples 1 to 16 and comparative examples 1 to 4.
Table 1 (balance Fe and unavoidable impurities other than S)
| Sequence number | C | Si | Mn | P | S | Alt | Nb | Ti | Cu | Ni | Cr |
| Comparative example 1 | 0.1231 | 0.041 | 1.22 | 0.0119 | 0.0017 | 0.0296 | 0.012 | 0.024 | 0.284 | 0.145 | 0.488 |
| Comparative example 2 | 0.1486 | 0.007 | 1.308 | 0.0094 | 0.0024 | 0.0321 | 0.003 | 0.0189 | 0.268 | 0.134 | 0.469 |
| Comparative example 3 | 0.1310 | 0.007 | 1.1 | 0.0094 | 0.0024 | 0.0321 | 0.003 | 0.0189 | 0.268 | 0.134 | 0.391 |
| Comparative example 4 | 0.1482 | 0.009 | 1.279 | 0.0096 | 0.0025 | 0.0255 | 0.0001 | 0.0187 | 0.252 | 0.140 | 0.472 |
| Example 1 | 0.1369 | 0.027 | 1.282 | 0.0095 | 0.0045 | 0.0325 | 0.009 | 0.0215 | 0.271 | 0.135 | 0.471 |
| Example 2 | 0.1414 | 0.002 | 1.29 | 0.0119 | 0.0029 | 0.0365 | 0.02 | 0.0185 | 0.267 | 0.149 | 0.455 |
| Example 3 | 0.1533 | 0.026 | 1.335 | 0.0080 | 0.0049 | 0.0496 | 0.012 | 0.0177 | 0.281 | 0.287 | 0.473 |
| Example 4 | 0.1482 | 0.009 | 1.279 | 0.0096 | 0.0025 | 0.0255 | 0.01 | 0.0187 | 0.252 | 0.140 | 0.472 |
| Example 5 | 0.1466 | 0.019 | 1.45 | 0.0122 | 0.0031 | 0.0306 | 0.008 | 0.0189 | 0.258 | 0.141 | 0.483 |
| Example 6 | 0.1591 | 0.016 | 1.336 | 0.0111 | 0.003 | 0.0348 | 0.01 | 0.0203 | 0.275 | 0.142 | 0.478 |
| Example 7 | 0.1435 | 0.016 | 1.355 | 0.0115 | 0.004 | 0.035 | 0.008 | 0.019 | 0.261 | 0.141 | 0.58 |
| Example 8 | 0.1523 | 0.04 | 1.31 | 0.0102 | 0.0031 | 0.029 | 0.011 | 0.0197 | 0.284 | 0.150 | 0.68 |
| Example 9 | 0.158 | 0.017 | 1.48 | 0.0207 | 0.0024 | 0.0305 | 0.009 | 0.02 | 0.304 | 0.140 | 0.468 |
| Example 10 | 0.1414 | 0.02 | 1.2 | 0.0119 | 0.0029 | 0.0365 | 0.019 | 0.0185 | 0.267 | 0.249 | 0.455 |
| Example 11 | 0.147 | 0.021 | 1.317 | 0.0171 | 0.0062 | 0.0548 | 0.008 | 0.0208 | 0.281 | 0.140 | 0.65 |
| Example 12 | 0.1322 | 0.017 | 1.22 | 0.0122 | 0.0031 | 0.0292 | 0.011 | 0.0191 | 0.275 | 0.142 | 0.489 |
| Example 13 | 0.1342 | 0.15 | 1.327 | 0.0249 | 0.0035 | 0.0201 | 0.014 | 0.0176 | 0.321 | 0.136 | 0.45 |
| Example 14 | 0.138 | 0.18 | 1.312 | 0.0118 | 0.0093 | 0.0286 | 0.011 | 0.0195 | 0.272 | 0.110 | 0.402 |
| Example 15 | 0.1469 | 0.017 | 1.274 | 0.0122 | 0.0031 | 0.06 | 0.01 | 0.0298 | 0.275 | 0.300 | 0.489 |
| Example 16 | 0.1533 | 0.026 | 1.335 | 0.0080 | 0.0049 | 0.0396 | 0.013 | 0.0152 | 0.398 | 0.147 | 0.553 |
Table 2 shows the process parameters involved in hot rolling the cold rolled bainitic weathering steels of examples 1-16 and comparative examples 1-4.
Table 2.
Table 3 shows the process parameters involved in cold rolling and continuous annealing of cold rolled bainitic weathering steels of examples 1-16 and comparative examples 1-4.
Table 3.
Table 4 shows the results of the mechanical properties of examples 1 to 16 and comparative examples 1 to 4 according to the present invention.
Table 4.
Tensile property test criteria in table 4: the sample was No.5, which was defined in JIS Z2241, and the sample direction was transverse; the bending test corresponds to 180 DEG bending, the diameter of the bending center is 2 times the thickness of the sample, and the direction of the sample is longitudinal.
FIG. 1 is a finished microstructure under the process of example 1, which is the desired bainitic+ferritic structure; fig. 2 is a microstructure of the finished product under the process of comparative example 2, mainly a martensite+ferrite structure.
From Table 4, the yield strength of the finished products of the examples is above 700MPa, the average value is about 790MPa, the average value of the tensile strength is about 970MPa, and the target requirement is met. In the comparative examples, the desired product properties were not finally obtained because the chemical components were not optimized or the production process could not reach the set process parameters. Specifically, comparative example 1 has a low carbon content; the soaking temperature and the quick cooling temperature of comparative example 2 are lower; the comparative example 3 has lower Mn and Cr contents and the comparative example 4 has higher rapid cooling end temperature, and because of the influence of these abnormal factors, the expected metallographic structure cannot be obtained, for example, an unexpected martensite structure can appear, or the bainite content is not high enough, and the yield strength and the tensile strength of the corresponding finished product are lower than those of the normal examples, wherein the yield strength is lower than the target 700 MPa.
While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing is a further detailed description of the invention with reference to specific embodiments, and it is not intended to limit the practice of the invention to those descriptions. Various changes in form and detail may be made therein by those skilled in the art, including a few simple inferences or alternatives, without departing from the spirit and scope of the present invention.
Claims (4)
1. A cold-rolled bainite type weathering steel is characterized by comprising the following chemical components ：C：0.13～0.16%;Mn：1.20～1.50%;Si：0.001~0.2%;P：0.008~0.025%;Alt：0.02～0.06%;Cu：0.25～0.40%;Cr：0.40～0.70%;Ni：0.10~0.30%;Ti：0.015～0.030%;Nb：0.008~0.020%; in percentage by mass, the balance being Fe and unavoidable impurities;
the microstructure of the cold-rolled bainite weathering steel consists of bainite and ferrite, wherein the volume fraction of the bainite is 40-80%;
The yield strength of the cold-rolled bainite weathering steel is more than or equal to 700MPa, the tensile strength is more than or equal to 800MPa, and the elongation is more than or equal to 5%.
2. Cold rolled bainitic weathering steel according to claim 1, characterized in that among the unavoidable impurities, the content of S is controlled: s is less than or equal to 0.01 percent.
3. The method for producing cold rolled bainitic weathering steel according to any one of claims 1 to 2, characterized by comprising the steps of: smelting, continuous casting, hot rolling, pickling, cold rolling, continuous annealing and flattening;
In the continuous annealing step, the soaking heat preservation temperature is controlled to be more than or equal to 820 ℃, the soaking heat preservation time is controlled to be 120-200 s, the slow cooling end temperature is controlled to be 700-730 ℃, the rapid cooling end temperature is controlled to be 340-360 ℃, and the rapid cooling speed is controlled to be 55-70 ℃/s.
4. A method of preparation according to claim 3, wherein the method of preparation is controlled to meet at least one of the following process parameters:
In the hot rolling step, the heating temperature is controlled to 1150-1220 ℃, the finishing temperature is controlled to 850-910 ℃, and the coiling temperature is controlled to 480-540 ℃;
In the cold rolling step, the rolling mill reduction is controlled to be 55-70%.
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