CN115852245A - Cold-rolled bainite weathering steel and preparation method thereof - Google Patents
Cold-rolled bainite weathering steel and preparation method thereof Download PDFInfo
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Abstract
The invention discloses cold-rolled bainite weathering steel which is characterized by comprising the following chemical components in percentage by mass: c:0.13 to 0.16 percent; mn:1.20 to 1.50 percent; si:0.001 to 0.2 percent; p:0.008 to 0.025 percent; and (3) Alt:0.02 to 0.06 percent; cu:0.25 to 0.40 percent; cr:0.40 to 0.70 percent; ni:0.10 to 0.30 percent; ti:0.015 to 0.030 percent; nb:0.008 to 0.020 percent; fe is more than or equal to 90 percent; 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 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 to ensure that the expected strength is obtained under a certain heat treatment process and the finished product has good weather resistance, and the cold-rolled bainite type weather resistant steel has good mechanical properties by combining and controlling the steel to contain a multiphase microstructure taking 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 weathering steel and a preparation method thereof.
Background
With the requirements of global warming and energy conservation and emission reduction, all countries in the world take actions consistently. In 9 months in 2020, the government of China makes a commitment to the great meeting of the United nations, strives for carbon peak reaching 2030 years ago, and strives to achieve carbon neutralization 2060 years ago. Therefore, the high strength and the weight reduction have important significance in the transportation industry, and the high strength and the weight reduction of the sheet steel strip also become the development trend of the steel industry. The cold-rolled ultrahigh-strength weathering steel is mainly applied to production and manufacturing of side plates and top plates of containers, and mainly needs to meet the requirements of two aspects: weather resistance and yield strength.
According to statistics, about 1/6 of the steel in the world is lost due to corrosion every year. The weathering steel is produced under the background, and is characterized in that a small amount of alloy elements such as Cu, P, cr, ni and the like are added into the steel. The function of the oxide layer enables the steel material to form a compact amorphous spinel 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 permeating into the steel matrix, thereby improving the atmospheric corrosion resistance of the steel material.
The main purpose of the steel with ultrahigh yield strength is to reduce the thickness of the steel by improving the strength of the steel strip, so as to improve the transportation efficiency and reduce the energy consumption and carbon emission. In the first few years of the twenty-first century, container panels typically had a thickness of about 1.6mm and a matrix yield strength of about 350 MPa. With the development of the production technology of cold-rolled ultrahigh-strength steel, the thickness of the material used for the panel is reduced to about 1.2mm, and the yield strength is correspondingly improved to 700MPa or above.
With the development of the production technology of the ultra-high strength steel weathering steel, related patents are also applied domestically. For example, chinese invention patent CN101376950A discloses an ultra-high strength cold-rolled weather-resistant steel plate and a manufacturing method thereof, the method adopts chemical components (wt%): c:0.09 to 0.16, si:0.20 to 0.60, mn: 1.00-2.00, P: not more than 0.030, not more than 0.015, not more than 0.008 of N, al:0.02 to 0.06, cu:0.20 to 0.40, cr:0.40 to 0.60, mo:0.05 to 0.25, nb + Ti: 0.04-0.08 percent, and the balance of Fe and inevitable impurities. According to the method, the annealing soaking temperature is 680-790 ℃, the preferred embodiment is 700-740 ℃, and the method belongs to a low-temperature annealing conventional production process. The main disadvantages of this method are that phase transformation strengthening is not used to increase the strength of the steel, and that more precious alloys such as Mo, nb, ti, etc. need to be added, which results in increased costs. Meanwhile, during continuous annealing low-temperature production, the internal stress of the strip steel is released unevenly, and the problem of plate shape possibly exists.
The Chinese patent invention CN103266274A discloses an ultra-high strength cold-rolled weather-resistant steel plate and a manufacturing method thereof, and the ultra-high strength cold-rolled weather-resistant steel plate comprises the following chemical elements in percentage by mass: 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 0.035wt%; p is less than or equal to 0.03 percent; and satisfies that 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 the martensite, the high annealing soaking temperature, namely 850-880 ℃, is required, and the cooling speed is more than 100 ℃/s. The annealing condition corresponding to the patent is harsh, and the requirement on the rapid cooling capacity of the annealing unit is high. 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, because the tensile strength is too high, the cracking problem of the strip steel is easy to occur in certain application occasions.
Chinese invention patent CN107841689A discloses a weather-resistant steel sheet and a manufacturing method thereof, which comprises the following components by mass percent: 0.04 to 0.10%, si:0.18 to 0.35%, mn: 1.00-1.60%, P:0.008 to 0.015%, cu:0.25 to 0.45%, cr:0.40 to 0.60%, ni:0.30 to 0.50%, alt:0.02 to 0.05%, nb:0.01 to 0.05 percent, and the balance of iron and inevitable impurities. The manufacturing method related to the patent comprises smelting, refining, continuous casting, heating and rolling, wherein the initial rolling temperature in the finish rolling stage is 850-970 ℃, the finish rolling temperature is 780-860 ℃, and the time of the finish rolling is 10-30 seconds, which is also a key process point of the patent. The corresponding product is a hot rolled product, and does not relate to the production and manufacture of cold rolled ultrahigh-strength weathering steel.
Chinese patent CN107829024A discloses an ultra-high strength weather-proof steel plate above 700MPa level and its hot continuous rolling production method, the chemical components are carbon: 0.06 to 0.08%, silicon: 0.15 to 0.25%, manganese: 1.25 to 1.35%, phosphorus: less than or equal to 0.018%, sulfur: less than or equal to 0.005 percent, total aluminum: 0.02 to 0.05%, niobium: 0.05 to 0.07%, titanium: 0.09 to 0.13 percent, chromium: 0.37 to 0.45%, copper: 0.20 to 0.28%, nickel: 0.10 to 0.15%, nitrogen: less than or equal to 0.0050 percent and the balance of iron. The discharge temperature of the manufacturing process provided by the patent is controlled to be 1250-1280 ℃, and the coiling temperature is 570-610 ℃. The thickness of a finished product corresponding to the patent is 1.5-6.0 mm, the corresponding product form is a hot rolled product, and the production and the manufacture of cold rolled ultrahigh-strength weathering steel are not involved.
Disclosure of Invention
In one aspect, the invention provides cold-rolled bainite weathering steel which is characterized by comprising the following chemical components in percentage by mass: c:0.13 to 0.16 percent; mn:1.20 to 1.50 percent; si:0.001 to 0.2 percent; p:0.008 to 0.025 percent; and (3) Alt:0.02 to 0.06 percent; cu:0.25 to 0.40 percent; cr:0.40 to 0.70 percent; ni:0.10 to 0.30 percent; ti:0.015 to 0.030 percent; nb:0.008 to 0.020 percent; fe is more than or equal to 90 percent; 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 technical scheme of the application, the expected strength can be obtained under a certain heat treatment process by controlling the contents of chemical components in the cold-rolled bainite weathering steel, such as reasonably controlling the contents of C and Mn elements; and the finished product can obtain good weather resistance by controlling the contents of Cu and Cr elements. The cold-rolled bainite weathering steel has a multiphase microstructure taking bainite and ferrite as matrixes in combination control, so that the cold-rolled bainite 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, and the elongation is more than or equal to 5 percent.
The design considerations of the chemical elements and their interactions with each other and the limitations of the chemical composition of the claimed alloys are briefly described below.
C: carbon is the most important matrix strengthening element in steel production, the production cost is the lowest, the steel strength can be effectively improved, but excessive carbon has adverse effect on welding performance. The carbon content needs to be controlled within a reasonable range, and in the application, the mass percent of C is controlled to be 0.13-0.16%.
Mn: manganese is a solid-solution strengthening element in steel, and also increases hardenability of steel, contributing to improvement of strength of steel sheet, but also deteriorates weldability of steel when Mn content is too high. Compared with carbon, the manganese element can improve the strength and keep 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 improve the plasticity; however, when the Si is excessively added, the surface problems of the working procedures such as hot rolling red iron sheet and the like can be caused, and in the application, the mass percent of the Si is controlled to be 0.001-0.2%;
p: on one hand, the phosphorus element can form a corrosion-resistant barrier layer with Cu to improve the atmospheric corrosion resistance of the steel plate, and on the other hand, the phosphorus element can also reduce the welding performance and the cold bending performance of the strip steel. Comprehensively considered, in the cold-rolled bainite weathering steel, the mass percent of phosphorus is controlled to be 0.008-0.025%.
Al: the main purpose of adding aluminum element in steel is to deoxidize. Because molten steel has certain free oxygen after the converter is finished, the free oxygen is removed by adding aluminum so as to reduce the endogenous inclusions in the steel. Meanwhile, a certain amount of excess aluminum is kept, and AlN particles can be formed with N, so that crystal grains are refined, and the yield strength of a finished product is improved. In the present application, the total content of Al (Alt) is controlled to be 0.02 to 0.06%.
Cu: the copper element is a key control element of the weathering steel, and can promote the surface of the steel plate to form a stable and compact corrosion product, thereby achieving the purpose of atmospheric corrosion resistance. For this purpose, the copper content is generally not less than 0.2%. On the other hand, the melting point of copper is relatively low, and during the heating process of the slab, the copper-rich phase on the surface layer of the slab can cause surface cracking when reaching a certain degree in a molten state, thereby causing the defect of copper brittleness, so 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 one hand, the chromium element is a solid solution strengthening element and can improve the strength of the matrix; on the other hand, the addition of chromium and copper simultaneously can form a dense oxide film on the surface of the steel sheet to improve weather resistance. However, too high a chromium addition reduces the weldability of the finished product. 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 brittleness on the other hand; in addition, the nickel element can also 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 strong affinity with nitrogen, oxygen and carbon, and can generate corresponding compounds with the titanium. The yield strength and the forming performance of the finished product can be improved after precipitation strengthening and fine grain strengthening. In the present application, the content of titanium is controlled to 0.015 to 0.030%.
Nb: niobium has similar action with titanium, can form a niobium carbide compound with carbon, and plays roles of precipitation strengthening and fine grain strengthening, thereby improving the yield strength of the strip steel. In addition, the niobium alloy has a high unit price, and excessive addition causes production cost. In the present application, the content of niobium is controlled to 0.008 to 0.020%.
Further, the balance of chemical components in the cold-rolled bainite weathering steel is Fe and inevitable impurities.
Further, among the above inevitable 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 under the condition that the condition allows, in order to obtain cold-rolled steel with better performance, the content of the impurity element in the steel is reduced as much as possible.
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, acid washing, cold rolling, continuous annealing and leveling; the cold-rolled bainite weathering steel comprises the following chemical components in percentage by mass: c:0.13 to 0.16 percent; si:0.001 to 0.2 percent; mn:1.20 to 1.50 percent; p:0.008 to 0.025 percent; and (3) Alt:0.02 to 0.06 percent; cu:0.25 to 0.40 percent; cr:0.40 to 0.70 percent; ni:0.10 to 0.30 percent; nb:0.008 to 0.020 percent; ti:0.015 to 0.030 percent; fe is more than or equal to 90 percent;
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, the steel with the chemical components can be subjected to two rolling (hot rolling and cold rolling) and continuous annealing steps to obtain the cold-rolled bainite weathering steel, and the cold-rolled bainite weathering steel contains 40-80% of bainite in volume fraction 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 percent, and the requirements of steel reinforcement and weight reduction can be met.
Further, in the continuous annealing step, the soaking temperature is controlled to be more than or equal to 820 ℃, the soaking time is 120-200 s, the slow cooling finishing temperature is controlled to be 700-730 ℃, the fast cooling finishing temperature is controlled to be 340-360 ℃, and the fast cooling rate is controlled to be 55-70 ℃/s.
In the application, the main purpose of controlling the annealing soaking heat preservation temperature to be more than 820 ℃ and preserving the heat for 120-200 s is to fully recrystallize and austenitize the rolled hard structure; slowly cooling to the slow cooling ending temperature of 700-730 ℃, and then cooling to the bainite transformation zone temperature of 340-360 ℃ at a fast cooling rate of 55-70 ℃/s, namely the fast cooling ending temperature. The rapid cooling rate of 55-70 ℃/s is adopted to cool the steel plate to 340-360 ℃ so as to obtain a structure with a target bainite volume fraction, thereby improving the yield strength of a finished product. Compared with a 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 performance of the cold-rolled bainite weathering steel can be obtained under the condition of limited rapid cooling capacity.
Further, in the hot rolling step, the heating temperature is controlled to be 1150 to 1220 ℃, the finishing temperature is controlled to be 850 to 910 ℃, and the coiling temperature is controlled to be 480 to 540 ℃.
For a hot rolling process, the lower heating temperature of the plate blank is 1150-1220 ℃, so that the defect of copper brittleness of the plate blank is reduced as much as possible on the premise of ensuring the full dissolution of C and N compounds; when the hot coil is coiled, the coiling temperature is 480-540 ℃, and the coiling is mainly considered at a lower temperature, so that the hot coil is prevented from being flatly coiled.
In addition, in the cold rolling step, the rolling reduction can be controlled to be 55 to 70%. When the reduction rate is low, hot rolling crystal grains are not completely rolled, long and broken, accumulated deformation energy is insufficient, the size of recrystallized crystal grains is relatively large during annealing, and the yield strength of a finished product is reduced; and the increased deformation can cause larger roller loss and bring about the problems of hard-rolled coil shape and the like. But increasing the amount of deformation is beneficial to lowering the annealing soaking temperature and increasing the strip yield strength. Comprehensively considering, the rolling reduction of the rolling mill is controlled to be 55-70%.
The invention has the beneficial effects that:
1. in the chemical components, the carbon and manganese contents are moderate, so that the finished product can obtain certain strength; 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 crystal grains.
2. The long-flow manufacturing method provided by the invention comprises the steps of hot rolling and cold rolling, 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 the cold-rolled steel sheet manufactured by the bainite transformation process can be used to manufacture a panel for a container in a general continuous annealing line. 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 bainite type weathering steel of example 1;
fig. 2 is a microstructure photograph of the cold rolled bainite type weathering steel of comparative example 2.
Detailed Description
The following description is given by way of example of the present invention and other advantages and features of the present invention will become apparent to those skilled in the art from the following detailed description. While the invention will be described in conjunction with the preferred embodiments, it is not intended that features of the invention be limited to these embodiments. On the contrary, the invention is described in connection with the embodiments for the purpose of covering alternatives or modifications that may be extended based on the claims of the present invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The invention may be practiced without these particulars. Moreover, some of the specific details have been omitted from the description in order not to obscure or obscure the focus of the present invention. It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other without conflict.
Examples 1 to 16 and comparative examples 1 to 4
The cold-rolled bainite weathering steel of examples 1 to 16 and comparative examples 1 to 4 of the present invention was prepared by the following steps:
step 1, smelting. In this step, blast furnace molten iron is blown through a steelmaking converter unit and then refined by a vacuum cycle degassing (RH) method.
Specifically, liquid iron is produced in a large reaction vessel using iron ore, coke and other solvents in a blast furnace, and is transported to a steel plant via a torpedo car, and is subjected to desulfurization, desilication and the like during transportation. The chemical element components of the molten iron are controlled according to the conventional control requirements. In the converter process, the top and bottom composite oxygen blowing is utilized to blow the molten iron, and non-metallic inclusions and various impurities in the molten iron are removed. During refining, secondary refining is carried out on the steel ladle molten steel by using vacuum circulating degassing equipment, the main purposes are degassing and deoxidation, and alloy is added, so that the chemical element components of the molten steel are adjusted to be within the 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, continuously casting. Injecting the molten steel subjected to secondary refining into a tundish, and controlling the superheat degree of the molten steel according to 10-20 ℃; the steel billet is rapidly cooled and solidified into a solid state in continuous casting equipment and cut into a steel billet with a certain size by flame, the continuous casting speed is controlled according to 1.0-1.5 m/min, and the thickness of the steel billet is 230-250 mm.
And 3, hot rolling. In the step, the steel billet is reheated and rolled into a hot-rolled coil with a certain thickness range according to certain process requirements, and the main process of hot rolling comprises the following slab heating temperature: the temperature of 1150-1220 ℃, the heat preservation time of the plate blank is more than 150min, the plate blank enters a 7-stand finishing mill after 5-pass rough rolling, and the finishing temperature of the plate blank out of the finishing mill is 850-920 ℃; and controlling the coiling temperature of the strip steel to be 480-540 ℃ after laminar cooling. The thickness of the hot-rolled strip steel is only the middle thickness and ranges from 2.3 mm to 6.0mm.
And 4, acid washing. The conventional acid washing process is adopted. The main purpose of the step is to remove the iron scale and the dirty impurities on the surface of the hot rolled coil and achieve certain surface cleanliness, and the thickness of the strip steel is not changed in the process.
And 5, cold rolling. The acid-washing coil is used as a raw material, and the main purpose is to further roll and thin the strip steel and ensure certain plate shape, surface roughness and thickness precision. The key technology of the process is that the deformation, namely the rolling reduction, is generally controlled to be about 55 to 70 percent, and the product of the process is generally called hard rolling.
And 6, continuously annealing. The method is characterized in that a hard-rolled coil is used as a raw material to carry out heat treatment, and the main purpose is to recrystallize a hard-rolled structure through the heat treatment and obtain a desired metallographic structure with a certain proportion, so that the plasticity of the steel is improved and a certain strength is achieved. In the step, the annealing soaking heat preservation temperature is controlled to be more than or equal to 820 ℃, and the soaking heat preservation time is as follows: 120-200 s; slow cooling end temperature: 700 to 730 ℃; fast cooling end temperature: 340-360 ℃, fast cooling rate: 55-70 ℃/s.
And 7, leveling.
Chemical compositions of cold-rolled bainite weathering steel in the above examples and comparative examples and process parameters of the preparation process are specifically referred to the following tables.
Table 1 lists the mass percentages of the respective chemical elements of the cold-rolled bainite weathering steel of examples 1 to 16 and comparative examples 1 to 4.
Table 1 (balance Fe and unavoidable impurities other than S)
| Serial number | C | Si | Mn | P | S | Alt | Nb | Ti | Cu | Ni | Cr |
| Comparative example1 | 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 |
| Practice ofExample 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 the hot rolling process of the cold-rolled bainite weathering steels of examples 1-16 and comparative examples 1-4.
Table 2.
Table 3 shows the process parameters involved in the cold rolling and continuous annealing processes of the cold rolled bainite weathering steels of examples 1 to 16 and comparative examples 1 to 4.
Table 3.
Table 4 shows the results of the measurement of mechanical properties in examples 1 to 16 of the present invention and comparative examples 1 to 4.
Table 4.
Tensile properties test criteria in table 4: the sample is a No.5 sample prescribed in JIS Z2241, and the sample direction is the transverse direction; the bending test corresponds to 180-degree bending, the diameter of a bending core is 2 times of the thickness of a sample, and the direction of the sample is longitudinal.
FIG. 1 is a microstructure of the finished product of the process of example 1, which is the expected bainite + ferrite structure; fig. 2 is the finished microstructure of the comparative example 2 process, mainly a martensite + ferrite structure.
From the table 4, the yield strengths of the finished products of the examples are all above 700MPa, the average value is about 790MPa, and the average value of the tensile strength is about 970MPa, so that the target requirements are met. In the comparative example, the expected product performance is not finally obtained because the chemical components are not optimized or the production process cannot reach the set process parameters. Specifically, comparative example 1 has a low carbon content; comparative example 2 the soaking temperature and the rapid cooling temperature are lower; the Mn and Cr contents in comparative example 3 are lower and the rapid cooling end temperature in comparative example 4 is higher, because of the influence of these abnormal factors, the expected metallographic structure cannot be obtained, for example, an undesirable martensite structure may appear, or the bainite content is not high enough, corresponding to a yield strength and tensile strength of the finished product lower than those of the normal example, wherein the yield strength is lower than the target 700MPa requirement.
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 more detailed description of the invention, taken in conjunction with the specific embodiments thereof, and that no limitation of the invention is intended thereby. Various changes in form and detail, including simple deductions or substitutions, may be made by those skilled in the art without departing from the spirit and scope of the invention.
Claims (6)
1. The cold-rolled bainite weathering steel is characterized by comprising the following chemical components in percentage by mass: c:0.13 to 0.16 percent; mn:1.20 to 1.50 percent; si:0.001 to 0.2 percent; p:0.008 to 0.025 percent; and (3) Alt:0.02 to 0.06 percent; cu:0.25 to 0.40 percent; cr:0.40 to 0.70 percent; ni:0.10 to 0.30 percent; ti:0.015 to 0.030 percent; nb:0.008 to 0.020 percent; fe is more than or equal to 90 percent;
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%.
2. The cold rolled bainite weathering steel according to claim 1, characterized in that the balance of the chemical composition is Fe and unavoidable impurities.
3. The cold rolled bainite weathering steel according to claim 2, characterized in that, among the inevitable impurities, the content of S is controlled: s is less than or equal to 0.01 percent.
4. A preparation method of cold-rolled bainite weathering steel is characterized by comprising the following steps: smelting, continuous casting, hot rolling, acid washing, cold rolling, continuous annealing and leveling;
the cold-rolled bainite weathering steel comprises the following chemical components in percentage by mass: c:0.13 to 0.16 percent; si:0.001 to 0.2 percent; mn:1.20 to 1.50 percent; p:0.008 to 0.025 percent; and (3) Alt:0.02 to 0.06 percent; cu:0.25 to 0.40 percent; cr:0.40 to 0.70 percent; ni:0.10 to 0.30 percent; nb:0.008 to 0.020 percent; ti:0.015 to 0.030 percent; fe is more than or equal to 90 percent;
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%.
5. The preparation method according to claim 4, wherein in the continuous annealing step, the soaking temperature is controlled to be not less than 820 ℃, the soaking time is 120-200 s, the slow cooling finishing temperature is controlled to be 700-730 ℃, the fast cooling finishing temperature is controlled to be 340-360 ℃, and the fast cooling rate is controlled to be 55-70 ℃/s.
6. The method according to claim 4, wherein the method is controlled to meet at least one of the following process parameters:
in the hot rolling step, the heating temperature is controlled to be 1150-1220 ℃, the finishing temperature is controlled to be 850-910 ℃, and the coiling temperature is controlled to be 480-540 ℃;
in the cold rolling step, the rolling mill reduction is controlled to be 55-70%.
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