CN110629125A - Cold-rolled steel plate with excellent aging resistance for continuous brazing type double-layer coil-welded pipe - Google Patents
Cold-rolled steel plate with excellent aging resistance for continuous brazing type double-layer coil-welded pipe Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/003—Cementite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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Abstract
The invention discloses a cold-rolled steel plate with excellent aging resistance for a continuous brazing type double-layer coil welded pipe, which solves the technical problem of poor aging resistance when the existing cold-rolled steel plate produced by a continuous annealing mode is used for the continuous brazing type double-layer coil welded pipe. The invention provides a cold-rolled steel plate with excellent aging resistance for a continuous brazing type double-layer coil-welded pipe, which comprises the following chemical components in percentage by weight: c: 0.03-0.07%, Si is less than or equal to 0.05%, Mn: 0.10-0.25%, P is less than or equal to 0.025%, S is less than or equal to 0.020%, Alt: 0.03-0.06%, N is less than or equal to 0.003%, and the balance is Fe and inevitable impurities. The hardness value of the cold-rolled steel plate with the thickness of 0.3-0.5mm is 49-55HR30 Tm. The cold-rolled steel plate is mainly used for manufacturing a double-layer roll-welded pipe for an automobile oil pipe.
Description
Technical Field
The invention relates to a cold-rolled steel plate for a double-layer roll-welded pipe and a production method thereof, in particular to a cold-rolled steel plate with excellent aging resistance for a continuous brazing type double-layer roll-welded pipe and a production method thereof, belonging to the technical field of iron-based alloy.
Background
The double-layer coil welded pipe, also called Bundy pipe, is generally formed by winding a precision steel belt plated with copper on two sides around a central core rod at 720 degrees, then performing high-temperature welding of two pipe walls by using a copper-plated film as brazing filler metal, and finally performing cooling, passivation and other processes to form the double-layer steel pipe with excellent fatigue resistance and good leakage resistance, and is widely applied to the field of various automobile oil pipes.
At present, the manufacturing process of the double-layer roll welded pipe is divided into two processes, one process is a continuous brazing process which is to roll the pipe and then directly heat the pipe to 1120 ℃ through resistance heating in 1-2s to complete instantaneous brazing of the double-layer pipe wall, and then immediately cool the pipe in a water-cooled sleeve at a cooling rate of 30-40 ℃/s; the other is a discontinuous brazing process which comprises the steps of firstly cutting to length after manufacturing the tube, then feeding a plurality of welded tubes into a radiant heating furnace together, gradually heating to 1120 ℃ after about 50 seconds, then continuously preserving heat for about 10-15 seconds to complete brazing, and finally cooling along with the furnace at a cooling rate of 15-25 ℃/s. The former process is adopted by most double-layer coil welded pipe manufacturers because of small occupied area, low investment and flexible production.
Since the beginning of the commercial production of the double-layer coil welded pipe, the cover annealing material is used for a long time, and the lower strength of the cover annealing material is mainly considered, so that the coil pipe forming is facilitated. However, the annealing of the annealing material adopts the whole coil to be placed into a bell-type furnace for heat preservation, so that the performance difference caused by uneven heating of the coil core and the coil tail inevitably exists, and meanwhile, certain interlayer adhesion is generated in the whole coil annealing, and the surface quality of the strip steel is influenced. Because most of the double-layer roll-welded pipes are precision welded pipes with the diameter less than 10mm, the double-layer roll-welded pipes are mainly used for automobile safety parts, and the double-layer roll-welded pipes have higher requirements on the mechanical property and the stability of the surface quality of strip steel, a part of manufacturers try to use continuous annealing materials with more advantages in the mechanical property and the surface quality.
It is known that at present, some discontinuous brazing manufacturers at home and abroad successfully use continuous annealing materials, but on a continuous brazing production line, a welded pipe made of the continuous annealing materials has an aging phenomenon that the elongation rate is reduced from the initial 30% to about 15% after being placed for a period of time, the subsequent processing of the pipe is seriously influenced, the elongation rate of the welded pipe made of the covering and annealing materials on the same production line is only reduced from 32% to about 25%, and the ageing resistance of the continuous annealing pipe is obviously different from that of the covering and annealing pipe. The aging properties of the steel material are mainly caused by precipitation of free C, N atoms supersaturated and solid in the steel from the crystal grains with time, and the larger the supersaturation amount is, the stronger the aging properties are.
The aging resistant schemes adopted by the cold-rolled steel sheet mainly comprise the following two schemes: the first scheme is that an ultra-low carbon design with the carbon content less than 0.01% is adopted, the carbon content of interstitial solid solution in ferrite is fundamentally reduced, for example, an aging-resistant steel plate with excellent processability and a manufacturing method thereof are disclosed in Chinese patent CN101775540A, a low yield strength aging-resistant continuous annealing cold-rolled steel plate and a production method thereof are disclosed in Chinese patent CN101956133A, and a strain aging hardening type steel plate with excellent aging resistance after coating and baking and a manufacturing method thereof are disclosed in Japanese patent CN 103221567A; in the first scheme, because the carbon content is extremely low, refining treatment is generally adopted for steel making, the cost is high, and after the ultra-low carbon cold-rolled steel plate is subjected to high-temperature brazing, the strength of a finished pipe is relatively low, so that the use requirement of the double-layer roll-welded pipe for the automobile cannot be met. The second scheme is that the carbon content is between 0.01 and 0.15 percent + micro-alloy design of Ti, Cr, Nb, B and the like, C, N compounds are formed by micro-alloy elements to reduce the solid solution amount of C, N atoms in ferrite, thereby reducing the timeliness; the second proposal adds various micro-alloys, so the recrystallization temperature can rise obviously, and the corresponding annealing temperature is generally required to be above 800 ℃ in order to meet the strength requirement of the double-layer coil-welded pipe cold-rolled steel plate, but for the steel with the thickness of 0.3-0.5mm, the continuous annealing production is extremely difficult at the high temperature.
The range of the carbon content of the cold-rolled strip steel for the double-layer coil welded pipe disclosed by the Chinese patent CN102925794 and the manufacturing method thereof is 0.015-0.054%, the continuous annealing temperature is 715-755 ℃, under the components and the process, the obtained continuous annealing strip steel structure is uncertain, which has little influence on the discontinuous brazing process, but for the continuous brazing process, the timeliness difference of the finished pipe is very large, and the cold-rolled strip steel is not suitable for the production of the continuous brazing type double-layer coil welded pipe.
Chinese patent CN104419866A discloses a continuous brazing type double-layer welded pipe and a manufacturing method thereof, wherein high temperature annealing at 740 ℃ or higher is adopted, so the structure of the obtained strip steel is ferrite + pearlite, and the pearlite is prior to the ferrite to generate austenite transformation during heating, which causes the carbon content in the austenite to be rapidly increased, thus being not favorable for the timeliness of the welded pipe and being not suitable for the continuous brazing process of the double-layer coiled welded pipe.
Disclosure of Invention
The invention aims to provide a cold-rolled steel plate with excellent aging resistance for a continuous brazing type double-layer coil-welded pipe and a production method thereof, and solves the technical problem of poor aging resistance of the welded pipe when the existing cold-rolled steel plate produced by a continuous annealing mode is used for the continuous brazing type double-layer coil-welded pipe.
The technical scheme of the invention is based on the research of the applicant on two production lines of continuous brazing and non-continuous brazing, and the research shows that in the non-continuous brazing process, because the heating speed is low, the continuous returned material and the cover returned material Ac1The temperature is about 800 ℃ and Ac3The temperature is about 950 ℃, therefore, under the soldering process of keeping the temperature at 1120 ℃ for more than 10s, the steel tube structure is completely austenitized, iron ferrite is converted into austenite, carbide can generate certain redissolution and component homogenization, the growth of eutectoid ferrite grains and the desolvation and precipitation of solid-solution carbon atoms are completed in the following furnace cooling process of relatively slow 15-25 ℃/s, and the final structure, mechanical property and ageing resistance of the welded tube are basically determined by the components and the cooling speed of the strip steel, therefore, under the discontinuous soldering process, continuous casting materials, hood casting materials with similar components and different original structure forms of the continuous casting materials and the hood casting materials have no obvious influence on the structure and the ageing property of the final welded tube. In the continuous brazing process, due to the adoption of rapid heating, the A of the same materialc1The temperature rises sharply to about 960 ℃ (due to resistance instant high temperature brazing, A)c3Temperature not measurable), a of continuous returned material upon coolingr3The temperature is 860 ℃, and the cover annealing material is 790 ℃, so that the austenitizing degree of the steel pipe in the process is obviously different from the complete austenitizing in the discontinuous brazing process, and the austenitizing degrees of the continuous annealing material and the cover annealing material are also different. Then 30-40Under the relatively fast sleeve water cooling process, partially redissolved carbide can not be effectively precipitated to cause further supersaturation of carbon atoms in welded pipe tissues, and because the continuous annealing material contains more supersaturated solid solution carbon and the cover annealing material contains lower supersaturated solid solution carbon, compared with the cover annealing material, the continuous annealing material shows the increase of strength after pipe manufacturing on one hand and poor aging resistance on the other hand. Under the continuous brazing process, the structure and the supersaturated solid solution carbon content of the strip steel, namely the timeliness, are partially inherited to the welded pipe due to insufficient austenitization of the strip steel.
It can be known from the aging analysis of the continuous brazing process that in order to improve the aging of the continuously annealed welded pipe, on one hand, the content of supersaturated solid-solution carbon of the continuously annealed strip steel per se needs to be reduced as much as possible, that is, the aging of the strip steel per se needs to be improved, and on the other hand, the further supersaturation caused by the re-dissolution of carbon in the heat treatment process needs to be reduced as much as possible, and both can be improved through the production process and the structural characteristics of the continuously annealed material.
The technical idea of the invention is to solve the problems, firstly, on a continuous brazing production line, due to rapid heating and rapid cooling, the austenitizing of the strip steel is insufficient at high temperature, and partial timeliness of the strip steel can be inherited to a welded pipe, so that the supersaturation solid solution C, N content of the strip steel can be controlled to reduce the timeliness of the welded pipe through the adjustment of the components and the process of the strip steel; secondly, by controlling the structure form of the strip steel, particularly the size and the distribution of cementite particles, under the condition of meeting the requirement of the basic mechanical property of the coiled pipe forming, the content of supersaturated solid solution C, N in the finished pipe is reduced by the least re-dissolution of carbide in the quick heating process of the pipe, and the timeliness of the welded pipe is reduced.
The technical scheme adopted by the invention is that the cold-rolled steel plate with excellent aging resistance for the continuous brazing type double-layer coil-welded pipe comprises the following chemical components in percentage by weight: c: 0.03-0.07%, Si is less than or equal to 0.05%, Mn: 0.10-0.25%, P is less than or equal to 0.025%, S is less than or equal to 0.020%, Alt: 0.03-0.06%, N is less than or equal to 0.003%, and the balance is Fe and inevitable impurities.
The metallographic structure of the cold-rolled steel plate is equiaxed ferrite grains and cementite which is uniformly distributed, and the grain size grade of the structure is I9.0-10.0 grade; the grain size of the cementite is 0.5-2.0 μm; the distribution density is 10000-2Yield strength R of cold rolled steel sheet having a thickness of 0.3 to 0.5mmp0.2230-300MPa, tensile strength Rm350-400MPa, elongation after fracture A50mm35-45% and hardness value of 49-55HR30 Tm.
The cold-rolled steel plate is mainly used for producing the automobile oil pipe by a continuous brazing type double-layer coil-welded pipe production line.
The reason why the chemical composition of the cold-rolled steel sheet for the continuous brazing type double-layer coil welded pipe excellent in aging resistance according to the present invention is limited to the above range is as follows:
carbon: research shows that after recrystallization annealing, most of precipitated cementite of a cold-rolled sheet with the carbon content lower than 0.03% is distributed in a free state, and the particle size is smaller than 0.5um, so that in the actual brazing process of a user, the small-particle cementite is easy to dissolve back to further increase supersaturated solid-solution carbon in the pipe, and the timeliness of the pipe is extremely unfavorable. When the carbon content is more than 0.03%, A is adoptedc1The obtained cold plate structure is ferrite plus pearlite at the annealing temperature of (730 ℃), but the pearlite can generate austenite transformation in preference to the ferrite when being heated, so that the carbon content in the austenite is increased, and the carbon atom supersaturation is caused when the ferrite is transformed subsequently, thereby influencing the aging of the welded pipe. Instead, 700 ℃ to A is adoptedc1The annealing temperature is (730 ℃), the obtained cold plate structure is ferrite and cementite which is uniformly distributed, and the relatively large cementite particles can effectively reduce the carbon redissolution and reduce the timeliness of the welded pipe. At the same time, the carbon content must not be too high, otherwise the cold plate strength is too high to facilitate coil forming. Therefore, the present application limits the carbon content to between 0.03 and 0.07% by repeated experiments.
Silicon: si in the low-carbon steel is an inevitable impurity element, the plasticity and the forming performance of the cold-rolled steel sheet are seriously damaged by the Si content, and the surface quality is also influenced to a certain extent. However, if the Si content is too low, the cost of the steel refining process is increased. The invention limits the Si content to be less than or equal to 0.05 percent.
Manganese: the main role of manganese in this application is to form suitable MnS particles in order to eliminate the detrimental effects due to the inevitable S in the steel. In addition, an Mn/S ratio exceeding 40 also increases the driving force for MnS formation in the matrix, and further decreases the volume fraction of precipitates in the grain boundary, thereby reducing the embrittlement thereof. However, Mn is also a strengthening element, and the content of Mn is not too high, otherwise, the strength of the steel plate is too high to be beneficial to coil pipe forming. Therefore, the content of Mn in the range of 0.10% to 0.25% is limited by the present invention.
Phosphorus, sulfur: phosphorus and sulfur are harmful elements in steel, and the two elements are expected to be controlled at a lower level in cold-rolled low-carbon steel, but the invention limits S to be less than or equal to 0.020 percent and P to be less than or equal to 0.025 percent in consideration of actual process control capacity.
Nitrogen: nitrogen elements that are dissolved in the steel are important factors that affect the aging properties of the steel sheet. In the application, because the strip steel adopts continuous annealing, C, N atoms can not be precipitated in the form of carbon and nitride as cover annealing, and the timeliness of the strip steel is influenced, therefore, the nitrogen content in the strip steel needs to be strictly controlled to reduce the timeliness influence, but the invention limits the N to be less than or equal to the practical process control capability
0.003％。
Aluminum: aluminum can form aluminum nitride with free nitrogen in steel to fix a part of nitrogen atoms, and the number of solid-solution nitrogen atoms is reduced, thereby being beneficial to improving the anti-aging property of the steel plate. Meanwhile, the ALN particles also provide nucleation particles for the subsequent precipitation of carbides, so that the precipitation of carbon atoms is promoted, the solid solution amount is reduced, and the timeliness of the strip steel is improved. However, when the amount of Al is too high, the cost of the alloy is increased, and Al, which is an excessive deoxidation product, is formed2O3And impurities are mixed, so that the fatigue resistance of the pipe is not facilitated. The invention limits the Alt content to be 0.03-0.06%.
A method for producing a cold rolled steel sheet excellent in aging resistance for a continuous brazing type double-layer coil welded pipe, comprising:
continuously casting molten steel to obtain a continuous casting plate blank, wherein the molten steel comprises the following chemical components in percentage by weight: c: 0.03-0.07%, Si is less than or equal to 0.05%, Mn: 0.10-0.25%, P is less than or equal to 0.025%, S is less than or equal to 0.020%, Alt: 0.03-0.06%, N is less than or equal to 0.003%, and the balance is Fe and inevitable impurities;
heating the continuous casting plate blank to 1200-1230 ℃ by a heating furnace and then carrying out hot rolling, wherein the hot rolling is a two-stage rolling process, the rough rolling is 5-pass continuous rolling, the finish rolling is 7-pass continuous rolling, the finish rolling temperature is 860-900 ℃, after the finish rolling, the thickness of the steel plate is controlled to be 2.5-3.0mm, the post-stage cooling is adopted in the laminar cooling stage, and the coiling temperature is 680-720 ℃ to obtain a hot rolled steel coil;
the hot rolled steel coil is uncoiled again and then is annealed and leveled by an acid cleaning, a cold rolling and a vertical continuous annealing furnace, and a finished cold rolled steel plate with the thickness of 0.3-0.5mm is obtained by coiling, wherein the cold rolling reduction rate is 85-90%, the annealing temperature of the strip steel in a hard rolling state after the cold rolling in a soaking section of the vertical continuous annealing furnace is 700-; the flat elongation is 0.8-1.5%.
The production process adopted by the invention has the following reasons:
1. setting of heating temperature of continuous casting slab
The heating temperature of the continuous casting slab is generally ensured in order to ensure that the hot coil can still be ensured at A during multi-pass rollingc3Deformation above austenite temperature and dynamic recovery recrystallization, and avoids the plate shape problem caused by mixed crystal of ferrite and austenite during rolling. For the present application, the higher heating temperature is set to obtain a hot rolled structure with larger ferrite grains after coiling, so as to compensate the influence of the strength rise of the cold plate on the pipe forming of users after the carbon content is increased. Therefore, the present application sets the tapping temperature at 1200-.
2. Setting of finish Rolling finishing temperature
The finishing temperature of finish rolling is set to be above the Ar3 line when rolling is finished, and is set to be 860-910 ℃ according to component design.
3. Setting of coiling temperature in Hot Rolling
The hot rolling coiling temperature mainly influences the precipitation of two-phase particles such as nitrides and carbides, and the coiling temperature set in the method is higher, so that the ALN can be more sufficiently precipitated during the temperature period and the subsequent slow cooling process, the content of solid solution nitrogen in the steel is reduced, the timeliness of a cold plate is reduced, but more iron scales are generated on the surface of strip steel due to the overhigh coiling temperature, and the surface quality is influenced, so the method sets the coiling temperature to be 680-720 ℃.
4. Setting of Cold Rolling reduction
The cold rolling reduction rate mainly determines the deformation of the cold-rolled sheet, on one hand, the thickness precision and the sheet shape of the final cold-rolled sheet are determined, on the other hand, the recovery power of annealing recrystallization is influenced, the higher cold rolling reduction rate is favorable for generating larger deformation energy so as to reduce the recrystallization temperature and be favorable for subsequent annealing, but the overhigh reduction rate influences the production stability and safety of the cold-rolling unit. Therefore, the cold rolling reduction is set to 85 to 90% in the present application.
5. Setting of annealing temperature and annealing time
In the application, the annealing temperature and the annealing time are set to complete the recovery recrystallization of the cold-rolled sheet, eliminate the work hardening, the internal defects of the crystal, the anisotropy in mechanical property and the like generated in the cold-rolling process, meet the mechanical property requirement of the steel for the double-layer welding pipe, and mainly control the precipitation quantity, the form and the distribution of carbide. From the process characteristics of the continuous brazing, it is known that, during high-temperature brazing, the carbides in the steel plate inevitably re-dissolve to a certain degree, and the re-dissolving amount directly affects the total supersaturated solid-solution carbon content in the welded pipe, namely the timeliness of the pipe, so that the re-dissolving amount of the carbides needs to be reduced as much as possible. Multiple experiments prove that the carbon atom redissolution phenomenon in the process can be effectively reduced when the carbide particles are larger than 0.5 mu m, but the carbide particles larger than 2.0 mu m can also cause the deterioration of the mechanical property of the strip steel and is not beneficial to the reel pipe forming of users. Further, the distribution density of carbide also affects the degree of austenitization during high-temperature heating, and the larger the carbide density, the more austenite-form core particles, that is, the more carbon that can be redissolved. In combination with the above points, the annealing temperature of the strip steel in the soaking section of the vertical continuous annealing furnace is set to be 700-
60-120s, obtaining the steel plate with the basic structure of equiaxed ferrite and uniformly distributed cementite, wherein the grain size grade is I9-10, the particle size of the cementite is 0.5-2.0 mu m, and the distribution density is 10000-25000 cementite/mm2The steel plate can meet the mechanical property required by users, and can reduce the re-dissolution of carbon atoms as much as possible, thereby reducing the timeliness of the welded pipe.
6. Setting of the Flat elongation
The leveling rate is set mainly for eliminating the yield platform of the cold plate and ensuring the formability of the material, and the leveling rate can be controlled to be 0.8-1.5% in the application.
The metallographic structure of the cold-rolled steel plate produced by the method is equiaxed ferrite grains and cementite which is uniformly distributed, and the grain size grade of the structure is I9-10 grade; the grain size of the cementite is 0.5-2.0 μm; the distribution density is 10000-2Yield strength R of cold rolled steel sheet having a thickness of 0.3 to 0.5mmp0.2230-300MPa, tensile strength Rm350-400MPa, elongation after fracture A50mm35-45% and hardness value of 49-55HR30 Tm.
Compared with the prior art, the invention has the following positive effects: the continuous annealing cold-rolled steel plate has the advantages of being stable in mechanical property, good in surface quality and high in comprehensive yield of users, and through the optimal design of steel plate components and tissues, the timeliness of the manufactured welded pipe is remarkably improved, and the problem that the conventional production line user faces the common continuous annealing steel plate can be well solved.
Drawings
FIG. 1 is a metallographic structure diagram of a cold-rolled steel sheet according to example 1 of the present invention.
FIG. 2 is a metallographic structure diagram of a radial cross section of a double-layer welded pipe made of a cold-rolled steel sheet according to example 1 of the present invention by a continuous brazing process.
Detailed Description
The invention is further illustrated below with reference to examples 1 to 3, as shown in tables 1 to 5.
Table 1 shows the chemical composition (in weight%) of the steels of the examples of the invention, the balance being Fe and unavoidable impurities.
Table 1 chemical composition of the steels of the examples of the invention, in units: and (4) weight percentage.
The method comprises the steps of smelting in a converter and refining in an RH furnace to obtain molten steel with chemical components meeting requirements, continuously casting the molten steel under the protection of Ar blowing in the whole process to obtain a continuous casting plate blank, wherein the thickness of the continuous casting plate blank is 210-230 mm, the width of the continuous casting plate blank is 800-1100 mm, and the length of the continuous casting plate blank is 5000-10000 mm.
Sending the fixed-length plate blank produced in the steel-making process to a heating furnace for reheating, taking out of the furnace for dephosphorization, and sending the plate blank to a continuous hot continuous rolling mill for rolling; controlling rolling through a rough rolling mill and a finish rolling continuous mill unit, coiling after laminar cooling, and producing a qualified hot rolled steel coil by adopting post-stage cooling through laminar cooling; the thickness of the hot rolled steel plate is 2.5-3.5mm, and the control parameters of the hot rolling process are shown in Table 2.
TABLE 2 Hot Rolling Process control parameters of the inventive examples
And (2) rewinding the hot rolled steel coil, carrying out acid washing, carrying out primary cold rolling on a reversible rolling mill or a 5-stand cold continuous rolling mill, wherein the reduction rate of the cold rolling is 85-90%, and annealing, flattening and coiling the cold rolled hard strip steel in a vertical continuous annealing furnace to obtain a finished cold rolled steel plate with the thickness of 0.3-0.5 mm. The annealing process comprises the following steps: the temperature of the strip steel in a soaking section of the vertical continuous annealing furnace is 700-730 ℃, and the annealing time in the soaking section is 60-120 s; the leveling elongation is 0.8-1.5%; the control parameters of the cold rolling, annealing and flattening processes are shown in Table 3.
TABLE 3 control parameters of the cold rolling and annealing processes of the present invention
Referring to fig. 1, the metallographic structure of the cold-rolled steel sheet obtained by the method is equiaxed ferrite grains + uniformly distributed cementite, and the grain size grade of the structure is i 9.0-10.0; the grain size of the cementite is 0.5-2.0 μm; the distribution density is 10000-2Yield strength R of cold rolled steel sheetp0.2230-300MPa, tensile strength Rm350-400MPa, elongation after fracture A50mm35-45% and hardness value of 49-55HR30 Tm.
The cold-rolled steel sheet obtained by the invention is subjected to a GB/T228.1-2010 metal material tensile test part 1: tensile test was conducted according to the Room temperature test method, microstructure observation was conducted according to the method for evaluating the microstructure of GB/T13299 Steel, hardness was measured according to the method for testing Rockwell hardness of GB/T230.1 Metal materials, and the mechanical properties of cold-rolled steel sheets are shown in Table 4.
TABLE 4 mechanical Properties of Cold-rolled Steel sheets according to examples of the invention
The method for preparing the double-layer welded pipe by using the cold-rolled steel plate comprises the following steps of:
1) uncoiling the cold-rolled coil with the thickness of 0.3-0.5mm, and carrying out double-sided copper plating on the cold-rolled steel plate, wherein the thickness of the copper plating is 2.8-3.6 mu m;
2) longitudinally slitting to form a copper-plated narrow band with the required width of the coil;
3) pressing grooves on two sides of the strip steel: pressing slopes on two sides of the narrow band to ensure that the inner and outer seams are attached to the pipe wall after pipe coiling;
4) continuously coiling the double-sided copper-plated cold-rolled steel plate at 720 degrees by a forming machine to prepare a pipe body with the outer diameter of 4.75-8 mm;
5) the brazing furnace heats and brazes the manufactured tube body, the heating speed is 250-280 ℃/s, the temperature of a welding section is 1120-1150 ℃, the heat preservation time is 0.5-1.0s, and the cooling speed is 30-40 ℃/s.
The surface of the finished welded pipe has no obvious mechanical defect and no cold joint, the yield strength of the welded pipe is more than or equal to 200MPa, the tensile strength is more than or equal to 300MPa, and the elongation A after 2 weeks50mm≥20％。
The outside diameters of the double-layer coil-welded tube and the brazing process used are shown in table 5.
The cold-rolled steel plate obtained by the method is subjected to the conventional continuous double-layer welded pipe production line to manufacture the double-layer welded pipe, referring to fig. 2, the metallographic structure of the radial section of the welded pipe is ferrite and pearlite, the grain size grade is I6.0-7.5, the mechanical property of a sample pipe is detected according to part 1 of a metal material tensile test, namely a room temperature test method GB/T228.1-2010, and the performance parameters of the double-layer welded pipe are shown in table 5.
TABLE 5 Properties of welded pipes made of cold-rolled steel sheets according to examples of the present invention
In addition to the above embodiments, the present invention may have other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.
Claims (4)
1. A cold-rolled steel plate with excellent aging resistance for a continuous brazing type double-layer coil-welded pipe comprises the following chemical components in percentage by weight: c: 0.03-0.07%, Si is less than or equal to 0.05%, Mn: 0.10-0.25%, P is less than or equal to 0.025%, S is less than or equal to 0.020%, Alt: 0.03-0.06%, N is less than or equal to 0.003%, and the balance is Fe and inevitable impurities; the metallographic structure of the cold-rolled steel plate is equiaxed ferrite grains and cementite which is uniformly distributed, and the grain size grade of the structure is I9.0-10.0 grade; the grain size of the cementite is 0.5-2.0 μm; the distribution density is 10000-2。
2. The cold rolled steel sheet for a continuous brazing type double layer coil welded pipe excellent in aging resistance as claimed in claim 1, wherein the yield strength R of the cold rolled steel sheet having a thickness of 0.3 to 0.5mmp0.2230-300MPa, tensile strength Rm350-400MPa, and stretch after breakageLength of growth A50mm35-45% and hardness value of 49-55HR30 Tm.
3. A method for producing a cold-rolled steel sheet excellent in aging resistance for a continuous brazing type double-layer coil welded pipe, characterized by comprising the steps of:
continuously casting molten steel to obtain a continuous casting plate blank, wherein the molten steel comprises the following chemical components in percentage by weight: c: 0.03-0.07%, Si is less than or equal to 0.05%, Mn: 0.10-0.25%, P is less than or equal to 0.025%, S is less than or equal to 0.020%, Alt: 0.03-0.06%, N is less than or equal to 0.003%, and the balance is Fe and inevitable impurities;
heating the continuous casting plate blank to 1200-1230 ℃ by a heating furnace, and then carrying out hot rolling, wherein the hot rolling is a two-stage rolling process, the rough rolling is 5-pass continuous rolling, the finish rolling is 7-pass continuous rolling, the finish temperature of the finish rolling is 860-910 ℃, after the finish rolling, the laminar cooling stage adopts the post-stage cooling, and the coiling temperature is 680-720 ℃ to obtain a hot rolled steel coil;
the hot rolled steel coil is uncoiled again and then is annealed and leveled by an acid cleaning, a cold rolling and a vertical continuous annealing furnace, and a finished cold rolled steel plate with the thickness of 0.3-0.5mm is obtained by coiling, wherein the cold rolling reduction rate is 85-90%, the annealing temperature of the steel strip in a hard rolling state after the cold rolling in a soaking section of the vertical continuous annealing furnace is 700-730 ℃, the annealing time of the steel strip in the soaking section is 60-120s, and the leveling elongation rate is 0.8-1.5%.
4. The method of producing a cold rolled steel sheet for a continuously brazed double-layer coil welded pipe excellent in aging resistance as claimed in claim 3, wherein the thickness of the hot rolled steel sheet is controlled to 2.5 to 3.0mm after the finish hot rolling.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114472896A (en) * | 2022-01-20 | 2022-05-13 | 南京惠诚工具制造有限公司 | Method for strengthening hardness of brazing tool blank |
| WO2024082755A1 (en) * | 2022-10-17 | 2024-04-25 | 江苏省沙钢钢铁研究院有限公司 | Tin plate and manufacturing method therefor |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102925794A (en) * | 2011-08-11 | 2013-02-13 | 上海梅山钢铁股份有限公司 | Cold-rolled steel strip for double-layer welded tube |
| CN107881409A (en) * | 2016-09-29 | 2018-04-06 | 上海梅山钢铁股份有限公司 | A kind of side's tank cold rolling tin plate and its manufacture method |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102925794A (en) * | 2011-08-11 | 2013-02-13 | 上海梅山钢铁股份有限公司 | Cold-rolled steel strip for double-layer welded tube |
| CN107881409A (en) * | 2016-09-29 | 2018-04-06 | 上海梅山钢铁股份有限公司 | A kind of side's tank cold rolling tin plate and its manufacture method |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114472896A (en) * | 2022-01-20 | 2022-05-13 | 南京惠诚工具制造有限公司 | Method for strengthening hardness of brazing tool blank |
| CN114472896B (en) * | 2022-01-20 | 2023-12-12 | 南京惠诚工具制造有限公司 | Method for reinforcing hardness of brazing tool blank |
| WO2024082755A1 (en) * | 2022-10-17 | 2024-04-25 | 江苏省沙钢钢铁研究院有限公司 | Tin plate and manufacturing method therefor |
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