CN105369134A - Hot rolled steel plate for 400MPa-level acid-pickling-free automobile structure and production method of hot rolled steel plate - Google Patents
Hot rolled steel plate for 400MPa-level acid-pickling-free automobile structure and production method of hot rolled steel plate Download PDFInfo
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- CN105369134A CN105369134A CN201510778750.6A CN201510778750A CN105369134A CN 105369134 A CN105369134 A CN 105369134A CN 201510778750 A CN201510778750 A CN 201510778750A CN 105369134 A CN105369134 A CN 105369134A
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 116
- 239000010959 steel Substances 0.000 title claims abstract description 116
- 238000004519 manufacturing process Methods 0.000 title abstract description 14
- 238000000034 method Methods 0.000 claims abstract description 49
- 239000000126 substance Substances 0.000 claims abstract description 12
- 238000002360 preparation method Methods 0.000 claims abstract description 8
- 238000005096 rolling process Methods 0.000 claims description 60
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 58
- 238000005098 hot rolling Methods 0.000 claims description 23
- 238000001816 cooling Methods 0.000 claims description 22
- 229910052742 iron Inorganic materials 0.000 claims description 20
- 238000003723 Smelting Methods 0.000 claims description 19
- 238000009749 continuous casting Methods 0.000 claims description 14
- 230000000694 effects Effects 0.000 claims description 9
- 238000010438 heat treatment Methods 0.000 claims description 9
- 238000007670 refining Methods 0.000 claims description 9
- 238000010079 rubber tapping Methods 0.000 claims description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 8
- 229910052760 oxygen Inorganic materials 0.000 claims description 8
- 239000001301 oxygen Substances 0.000 claims description 8
- 229910000859 α-Fe Inorganic materials 0.000 claims description 7
- 229910001562 pearlite Inorganic materials 0.000 claims description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 238000003303 reheating Methods 0.000 claims description 5
- 239000013078 crystal Substances 0.000 claims description 3
- 238000005452 bending Methods 0.000 abstract description 7
- 238000005272 metallurgy Methods 0.000 abstract description 2
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 18
- 239000011572 manganese Substances 0.000 description 13
- 239000002253 acid Substances 0.000 description 11
- 229910052786 argon Inorganic materials 0.000 description 9
- 238000005554 pickling Methods 0.000 description 9
- SZVJSHCCFOBDDC-UHFFFAOYSA-N ferrosoferric oxide Chemical group O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 description 8
- 229910000746 Structural steel Inorganic materials 0.000 description 7
- 238000005266 casting Methods 0.000 description 7
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 6
- 238000005275 alloying Methods 0.000 description 6
- 229910052782 aluminium Inorganic materials 0.000 description 6
- 238000007664 blowing Methods 0.000 description 6
- 238000012360 testing method Methods 0.000 description 6
- 229910052748 manganese Inorganic materials 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 4
- 239000000956 alloy Substances 0.000 description 4
- 239000003575 carbonaceous material Substances 0.000 description 4
- 238000011161 development Methods 0.000 description 4
- 238000005485 electric heating Methods 0.000 description 4
- 229910000640 Fe alloy Inorganic materials 0.000 description 3
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 229910001566 austenite Inorganic materials 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 239000007769 metal material Substances 0.000 description 3
- 238000005728 strengthening Methods 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- 238000003466 welding Methods 0.000 description 3
- 229910000914 Mn alloy Inorganic materials 0.000 description 2
- 229910018643 Mn—Si Inorganic materials 0.000 description 2
- 229910008455 Si—Ca Inorganic materials 0.000 description 2
- CYUOWZRAOZFACA-UHFFFAOYSA-N aluminum iron Chemical compound [Al].[Fe] CYUOWZRAOZFACA-UHFFFAOYSA-N 0.000 description 2
- 239000010426 asphalt Substances 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 230000003749 cleanliness Effects 0.000 description 2
- 239000000571 coke Substances 0.000 description 2
- PYLLWONICXJARP-UHFFFAOYSA-N manganese silicon Chemical compound [Si].[Mn] PYLLWONICXJARP-UHFFFAOYSA-N 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000003973 paint Substances 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 229910014458 Ca-Si Inorganic materials 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 229910000592 Ferroniobium Inorganic materials 0.000 description 1
- 241001062472 Stokellia anisodon Species 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- -1 aluminum-manganese-iron Chemical compound 0.000 description 1
- RHZUVFJBSILHOK-UHFFFAOYSA-N anthracen-1-ylmethanolate Chemical compound C1=CC=C2C=C3C(C[O-])=CC=CC3=CC2=C1 RHZUVFJBSILHOK-UHFFFAOYSA-N 0.000 description 1
- 239000003830 anthracite Substances 0.000 description 1
- 238000001636 atomic emission spectroscopy Methods 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 210000001787 dendrite Anatomy 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 230000001050 lubricating effect Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 235000021110 pickles Nutrition 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 239000002893 slag Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 230000008646 thermal stress Effects 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- 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
-
- 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
- C21D2211/009—Pearlite
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
The invention belongs to the technical field of metallurgy and particularly relates to a production and preparation method of a hot rolled steel plate for a 400MPa-level acid-pickling-free automobile structure. Chemical components of the hot rolled steel plate for the 400MPa-level acid-pickling-free automobile structure include, by weight, 0.05-0.10% of C, 0.05-0.15% of Si, 0.7-1.00% of Mn, 0.002-0.006% of N, 0-0.025% of P, 0-0.015% of S, 0.02-0.06% of Al and the balance Fe. According to a finished steel strip obtained through the method, the yield strength is larger than or equal to 255 MPa, the tensile strength is larger than or equal to 400 MPa, the ductility is larger than or equal to 34%, and the cold bending property is good.
Description
Technical Field
The invention belongs to the technical field of metallurgy, and particularly relates to a production method and a preparation method of a 400 MPa-grade pickling-free hot-rolled automobile structural steel plate.
Background
With the increasing development of national economy, the automobile industry has become the strut industry in China, the consumption of hot rolled steel plates for automobiles is increased year by year, and automobile manufacturers have made requirements for developing steel products which can be free from acid pickling or are easy to acid pickling according to the requirements of energy conservation, emission reduction, environmental protection, safety and the like of modern automobiles. The scale generated on the surface of the hot rolled steel product is Fe3O4+ Fe instead of Fe3O4+ FeO type, even with the need to produce multilayer Fe3O4An oxide. Due to Fe3O4The alloy has low hardness (HV 350-500), good plasticity and good adhesion, so that peeling and cracking caused by bending in the subsequent deep processing process can be avoided, and the iron oxide scale can play a role in lubricating between a tool and a workpiece. In this way, hot rolling can be simplified or even completely eliminatedThe pickling process is also helpful for improving the adhesive force of the paint coating.
At present, rust inhibitors sprayed on the surface of hot-rolled strip steel are developed by people in China based on atmosphere control in the process of forming iron scales, and Fe can be promoted by using the method3O4But requires an additional cooling equipment and thus a large investment, and at the same time, this method cannot produce Fe3O4+ Fe scale structure which is easily deformable. The technology adopted in japan, korea, australia, etc. is to control the type and thickness of iron scales in hot rolling production, and only careful control of the hot rolling process, particularly the cooling process after rolling, is required without adding new equipment. A lot of work has been done in this respect in japan, korea and australia. NKK, nippon steel, kawasaki steel and the like in japan are leading positions in developing hot-rolled black-skin steel technology. The development of hot-rolled black skin steel in the steel industry of China is still in the exploration stage at present, and hot-rolled plate users such as automobile manufacturers have strong requirements for the development. Therefore, the development of hot-rolled black steel which is easy to pickle or is free from pickling becomes an important technical research and development work.
For materials of a miniature passenger car, a 400 MPa-grade hot-rolled structural steel plate belongs to main application materials in a lower car body structure, and steel materials are required to have good strength and toughness, forming performance, sufficient structural rigidity and welding performance so as to meet the requirements of stamping forming and welding processes of automobile parts and resist local deformation in a loading process, so that impact energy is absorbed to the maximum extent, and the safety of a car body is ensured. The general production mode mainly considers the obdurability matching of steel, utilizes the fine grain strengthening and the solid solution strengthening to the maximum extent to improve the performance of the steel plate, adopts the acid cleaning process to remove a surface oxide layer at the later stage, and utilizes a phosphating film formed by the phosphating process to improve the bonding capacity of the steel plate and finish paint. In recent years, in order to meet the demand for weight reduction of vehicles, some automobile manufacturers have demanded a hot-rolled steel sheet for an automobile structure of 400MPa class to be used at low cost and free from pickling surface quality, and the main points are shown in table 1.
Table 1400MPa level hot-rolled structural steel mechanical property and technological property requirements
The hot rolled steel plate for the 400 MPa-level automobile structure is designed at home and abroad by adopting a low C-Mn microalloying scheme, the Mn content is generally 1.0%, the C content is generally about 0.10%, and the hot rolling process adopts controlled rolling and controlled cooling.
Disclosure of Invention
Aiming at the defects, the invention provides a 400 MPa-grade acid-washing-free hot-rolled automobile structural steel plate with excellent comprehensive performance, which has good room-temperature mechanical property and process property, and Fe in iron scale on the surface of a finished product3O4The proportion of the steel is more than 80 percent, the steel can meet the pickling-free production requirement of automobile component enterprises, and the cost performance of the steel is high.
The technical scheme of the invention is as follows:
the invention aims to solve the first technical problem of providing a hot rolled steel plate for a 400 MPa-grade pickling-free automobile structure, which comprises the following chemical components in percentage by weight: c: 0.05 to 0.10, Si: 0.05-0.15, Mn: 0.7-1.00, N: 0.002 to 0.006, P: 0 to 0.025, S: 0-0.015, Al: 0.02-0.06 wt%, and the balance Fe.
Furthermore, the microstructure structure of the hot-rolled steel plate for the 400 MPa-grade pickling-free automobile structure comprises ferrite and pearlite, wherein the volume percentage of the ferrite is 88-90% and the volume percentage of the pearlite is 10-12% based on the total volume of the crystal structure. The volume percent ferrite and pearlite can be measured by methods known to those skilled in the art, such as GB/T6394 metallographic methods. The hot rolled steel plate for the 400 MPa-level automobile structure provided by the invention has good room-temperature mechanical property and process property, and completely meets the requirements of technical indexes.
Furthermore, the yield strength of the hot-rolled steel plate is more than or equal to 255MPa, the tensile strength is more than or equal to 400MPa, and the elongation is more than or equal to 34%.
Further, Fe in iron scale on the surface of the hot rolled steel plate3O4The content is more than or equal to 80 percent.
Further, the thickness of the iron scale on the surface of the hot rolled steel plate is 7-9 mu m.
The second technical problem to be solved by the invention is to provide a preparation method of the hot rolled steel plate for the 400 MPa-grade pickling-free automobile structure, which comprises the steps of converter smelting, LF refining, continuous casting billet reheating, hot rolling, cooling and coiling; wherein,
the reheating temperature of the continuous casting billet is 1210-1230 ℃, and the heating time is 1.2-1.8 hours;
in the hot rolling procedure, the rough rolling starting temperature is 1173-1200 ℃, and the descaling water pressure is more than or equal to 21 MPa; the initial rolling temperature of finish rolling is less than or equal to 1020 ℃, the initial rolling speed is more than or equal to 1.5m/s, the finish rolling temperature is 860-890 ℃, and the finish rolling speed is more than or equal to 7.8 m/s;
the coiling temperature is 560-590 ℃;
the chemical components of the steel billet are as follows: c: 0.05 to 0.10, Si: 0.05-0.15, Mn: 0.7-1.00, N: 0.002 to 0.006, P: 0 to 0.025, S: 0-0.015, Al: 0.02-0.06 wt%, and the balance Fe.
Further, in the hot rolling procedure, the pressure of rough rolling descaling water is more than or equal to 21 MPa; the initial rolling speed of the finish rolling is more than or equal to 1.5m/s, and the final rolling speed of the finish rolling is more than or equal to 7.8 m/s.
Further, in the above method, the cooling step employs a sparse cooling method.
Further, in the converter smelting process, the tapping temperature is 1660-1680 ℃, and the oxygen activity at the pre-deoxidation end point is less than 80ppm during tapping.
The invention has the beneficial effects that:
1. the method adopts the process measures of controlling the chemical component range, the hot rolling heating temperature, the finish rolling temperature, the coiling temperature and the like in the production process, and the obtained steel strip finished product has the yield strength of more than or equal to 255MPa, the tensile strength of more than or equal to 400MPa, the elongation of more than or equal to 34 percent and excellent cold bending performance.
2. The low equivalent weight scheme is adopted during the design of chemical components, and the welding performance of the steel plate is excellent.
3. The external refining process adopts Si-Ca wires for sulfide modification treatment, sulfide generally exists in a strip shape or a short rod shape in steel types and is not beneficial to the stamping performance of steel, so the external refining process adopts sulfide modification treatment, Ca: s is more than or equal to 2.0, the cleanliness of the molten steel is improved, the shape of the residual non-metallic inclusions in the steel is changed into a hammer-like shape or a spherical shape from a strip shape or a short rod shape which is distributed along the rolling direction before treatment, and the cold forming performance of the steel plate is improved.
4. Fe in iron scale on surface of finished product3O4The proportion of the acid pickling agent is over 80 percent, and the acid pickling agent can effectively meet the requirement of users on acid pickling prevention.
5. Compared with the hot rolled steel plate with the same grade produced by low C-Mn-Si alloying, the invention has the advantages of simple production process, lower production cost, capability of effectively replacing an acid pickling process, higher cost performance and good popularization and application prospect.
Detailed Description
The invention relates to a production method of a hot rolled steel plate for a 400 MPa-grade pickling-free automobile structure, which comprises the following process flows of:
converter smelting → LF refining → electric heating → continuous casting → hot rolling → cooling → coiling → finishing → packaging and warehousing; in the invention, the billet can be prepared from blast furnace molten iron by the procedures of converter smelting, LF refining, electric heating and continuous casting by adopting a method known by a person skilled in the art.
The converter smelting is to smelt blast furnace molten iron and smelting furnace burden in a converter to obtain molten steel, and then the molten steel is deoxidized and alloyed; in the alloying step, a carbonaceous material, an aluminum-manganese-iron alloy and aluminum pellets are added into the deoxidized molten steel to obtain molten steel (based on the total weight of the molten steel, calculated by a simple substance) C: 0.05 to 0.10, Si: 0.05-0.15, Mn: 0.7-1.00, N: 0.002 to 0.006, P: 0 to 0.025, S: 0-0.015, Al: 0.02-0.06 wt%, and the balance Fe. In order to ensure that the content of S in the charged raw materials is less than or equal to 0.015 percent of the total weight of charged molten iron, low-sulfur molten iron or semi-steel smelting can be adopted. In order to prevent burning loss of metal elements, particularly manganese elements, the temperature in the smelting process and the oxygen activity during tapping are strictly controlled, the smelting condition is that the tapping temperature is 1660-1680 ℃, and the oxygen activity condition of a pre-deoxidation end point during tapping is [ a ]0]<80 ppm. The carbonaceous material added in the smelting process is a carbonaceous material known in the art, and is preferably one or more of asphalt coke, anthracite and carbon powder. The smelting time is the conventional smelting time, and is preferably 35-45 minutes.
The purpose of molten steel deoxidation is to reduce the oxygen activity of molten steel so as to improve the alloy yield, the deoxidizer is ferro-aluminum, and the addition amount of the deoxidizer is preferably 400-550 Kg/furnace.
The alloying step is fed in batches, with external refining using methods known to those skilled in the art. And the alloying step after deoxidation comprises the steps of adding aluminum iron, a carbonaceous material, a silicon-manganese alloy and ferrocolumbium into the molten steel after deoxidation to obtain molten steel (based on the total weight of the molten steel, calculated by a simple substance) C: 0.05 to 0.10, Si: 0.05-0.15, Mn: 0.7-1.00, N: 0.002 to 0.006, P: 0 to 0.025, S: 0-0.015, Al: 0.02-0.06 wt%, and the balance Fe.
In order to ensure the uniformity of the chemical components of the steel, the molten steel tank is subjected to bottom blowing argon treatment after alloying. The bottom blowing argon treatment conditions are that the temperature is 1600-1650 ℃, the pressure is 200-400 Pa, and the time is 4-8 minutes.
The LF refining step is used for finely adjusting the oxygen activity, the purity and the temperature of the molten steel, the oxygen activity of the molten steel is controlled to be 20-40 ppm by utilizing secondary Al wire feeding final deoxidation, argon with the pressure of 200-400 Pa is introduced into the bottom of the molten steel for 4-6 minutes, and the argon flow is in a condition that the molten steel is not turned over greatly, so that the molten steel is prevented from being oxidized secondarily and the temperature is prevented from being reduced too fast, impurities in the steel are enabled to float sufficiently, and the cleanliness of steel is further improved. After electrically heating and feeding Al wire, feeding Ca-Si wire (containing Ca more than or equal to 24% and having specification of phi 10mm) with the addition of 1000-1200 m/furnace.
The electric heating step is an operation for bringing the steel slab to a temperature suitable for casting, and is a basic process for continuous casting molten steel production. The billet may be heated using various heating apparatuses and heating methods known to those skilled in the art.
The continuous casting step may be performed by a method known to those skilled in the art, and the method of the present invention comprises casting the refined molten steel into a previously roasted tundish, and casting the molten steel into a slab by a full-flow protected continuous casting machine. After casting, cooling may be carried out according to a conventional method, such as natural cooling at room temperature.
The hot rolling step is to roll the cast slab after heating. The rolling is carried out to achieve the required thickness of the continuous casting slab of the 400 MPa-grade automobile structural steel. The hot rolled plate steel strip is subjected to 6 rough rolling passes and 5-6 finish rolling passes, and the thickness of a hot rolled blank is reduced by 3-9 mm by one pass of rolling of each frame.
The initial rolling temperature of hot rolling refers to the temperature of a billet entering a rolling mill, and the micro-alloy elements can be fully dissolved by heating at the temperature, so that the effect of poor performance caused by dendritic crystal segregation and uneven distribution of the micro-alloy elements in the steel of a continuous casting slab is eliminated. The finish rolling temperature of hot rolling refers to the temperature of the steel strip exiting the finishing mill group, and in order to make the thickness and the mechanical property of the finished product uniform, a hot rolling intermediate billet hot rolling box process technology is adopted to keep the material head, the middle and the tail of the hot rolling intermediate billet at specific finish rolling temperature before finish rolling. The hot rolling heating temperature is 1210-1230 ℃, the time is 1.2-1.8 hours, the initial rolling temperature of the hot rolling step is 1130-1200 ℃, the descaling water pressure is more than or equal to 21MPa, the finish rolling initial temperature is less than or equal to 1020 ℃, the initial rolling speed is more than or equal to 1.5m/s, the finish rolling temperature is 860-890 ℃, and the finish rolling outlet rolling speed is more than or equal to 7.8 m/s; the finishing temperature is 860-890 ℃; the temperature control in the hot rolling process can ensure that the steel is in a complete austenite structure before a finish rolling outlet; and the too coarse austenite structure is avoided, the grain size of ferrite of a hot-rolled finished product is favorably controlled to be 5.6-7.9 microns, and the fine-grain strengthening effect is improved.
The cooling step adopts a sparse cooling mode, and aims to reduce the thermal stress of the surface oxide layer and avoid the phenomenon that the surface oxide layer forms micro cracks due to the over-high cooling speed, so that the bonding force between the oxide layer and the base is reduced. The sheet steel strip includes a rolled sheet steel strip which is cooled to adjust the structure state inside the steel, and then is wound into a coil. In order to meet the structural and performance requirements of hot rolled sheet, the strip exiting the rolling mill must be cooled to coiling temperature at a high cooling rate in a short period of time. For example, the cooling speed is 10-30 ℃/s, and the temperature is cooled to 560-590 ℃.
The detection method of the chemical components in the invention is a carbon steel and middle and low alloy steel spark source atomic emission spectrometry, and the national standard is GB/T4336.
The invention adopts a low C-Mn-Si alloying scheme and a controlled rolling and controlled cooling mode for production, targeted external refining measures are adopted after smelting, the influence of inclusions on cold bending forming performance is reduced, and a controlled rolling and controlled cooling method is adopted for hot rolling to obtain a certain amount of ferrite and pearlite structures. The inspection result shows that the hot rolled steel plate for the 400 MPa-level automobile structure produced by the method has good room-temperature mechanical property and process property, and Fe in the iron scale on the surface of the finished product3O4The proportion of the steel exceeds 80 percent, can meet the pickling-free production requirement of automobile component enterprises, has high cost performance of steel, and has good popularization and application prospect.
The invention is further illustrated by the following examples. The examples are intended to illustrate the invention only and are not intended to limit the invention in any way.
Example 1
a. Smelting molten steel: the smelting equipment is a 220-ton combined blowing converter, blast furnace molten iron is used as a raw material, the temperature of the blast furnace molten iron is 1365 ℃, steelmaking auxiliary materials are added to be smelted to 1680 ℃, steel is discharged to a molten steel tank, 1000Kg of aluminum-iron alloy (Anyang Jiaxin refractory Co., Ltd.) is added for pre-deoxidation when steel is discharged to 1/3, and then asphalt coke (Panzhihua Yangchun metallurgical auxiliary materials Co., Ltd.) and silicon-manganese alloy (Deshang Fe alloy Co., Ltd.) are added into the deoxidized molten steel, so that the content of each component in the molten steel is (based on the total weight of the molten steel, wt%) C: 0.07, Si: 0.10, Mn: 0.90, P: 0.014, S: 0.006, Al:0.05, N: 0.0040 and the balance Fe. And then, carrying out bottom blowing argon treatment on the molten steel tank on a small platform outside the furnace, wherein the argon pressure is 200-400 Pa, and the time is 4 minutes.
The oxygen content in the deoxidized molten steel is controlled to be 10 ppm-50 ppm by controlling the addition amount of the deoxidizer, so that the oxidation of manganese is prevented as far as possible, and the manganese in the prepared hot-rolled structural steel exists in a simple substance rather than an oxide form, so that the function of the simple substance manganese is fully exerted.
b. LF electric heating: and (3) performing final deoxidation by feeding an Al wire for the second time, introducing argon with certain pressure (200-400 Pa) into the bottom of the molten steel ladle for 6 minutes, blowing the argon, adding a Si-Ca wire with the thickness of 1000m into the steel ladle through a wire feeder after blowing the argon, and performing LF treatment at the termination temperature of 1590 ℃.
c. Continuous casting: the molten steel tank is transported to a casting position, an aluminum stopper (Anyang auxiliary Co., Ltd.) is adopted as a sliding water gap at the bottom of the molten steel tank, the molten steel automatically flows into a tundish, and the molten steel is drained to a crystallizer through the aluminum stopper for continuous casting; and carrying out protective casting by adopting the covering slag in the whole process, and cooling the casting product to form a slab.
d. Hot rolling: the reheating temperature of the continuous casting slab is 1226 ℃ (eliminating dendrite segregation and controlling the size of original austenite grains), and the time is 1.6 hours; the rough rolling temperature is 1140 ℃, the descaling water pressure is 22MPa, the finish rolling start temperature is 1010 ℃, and the start rolling speed is 1.8 m/s; the finish rolling temperature is 872 ℃, and the finish rolling outlet rolling speed is 8.5 m/s; the cooling step adopts a sparse cooling mode; the coiling temperature was 570 ℃. The rolling passes of the finish rolling are 7, and the thickness of the intermediate blank is respectively 38-21 mm, 21-13 mm, 13-9 mm, 9-6.7 mm, 6.7-5.6 mm and 5.6-5 mm in each pass of rolling.
e. And (3) finishing: and the steel strip is packaged and put in storage after being coiled by a flattening unit.
The prepared plate coil is subjected to mechanical property test, and the yield strength Rel, the tensile strength Rm and the elongation A at room temperature are respectively detected200mmThe tensile property is carried out according to the GB/T228 metal material room temperature tensile test method. The yield strength (Rel) of the finished product is 311MPa, the tensile strength (Rm) is 425MPa, and the elongation (A)50mm) 38 percent, the cold bending process test performance is qualified, the thickness of the iron scale on the surface of the finished hot rolled steel plate is 8.5 mu m, and the Fe in the iron scale on the surface3O4The proportion of the acid washing-free hot-rolled steel plate reaches 85 percent, and the technical condition requirement of the 400MPa acid washing-free hot-rolled steel plate for the automobile structure is met.
Example 2
The preparation method is basically the same as that of the embodiment 1, except that the molten steel obtained by smelting in the converter comprises the following components: 0.07, Si: 0.11, Mn: 0.87, P: 0.015, S: 0.007, Al: 0.04, N: 0.0036 and the balance of Fe; the tapping temperature of a plate blank of a hot rolled steel plate produced by the molten steel is 1220 ℃, the finish rolling start rolling speed is 1.88m/s, and the finish rolling exit rolling speed is 8.7 m/s; the finishing temperature is 878 ℃, the coiling temperature is 565 ℃, and the thickness of the hot-rolled finished product is 4.5 mm.
The prepared plate coil is subjected to mechanical property test, and the tensile strength Rm and the elongation A at room temperature are respectively detected200mmThe tensile property is carried out according to the GB/T228 metal material room temperature tensile test method. The yield strength (Rel) of the finished product is 310MPa, the tensile strength (Rm) is 420MPa, and the elongation (A)50mm) 39 percent, qualified cold bending process test performance, 7.9 mu m of finished product iron oxide skin thickness and surfaceFe in iron scale3O4The proportion of the acid washing-free hot-rolled steel plate reaches 86 percent, and the technical condition requirement of the 400MPa acid washing-free hot-rolled steel plate with the automobile structure is met.
Comparative example 1
The preparation method is basically the same as that of the embodiment 1, except that the molten steel obtained by smelting in the converter comprises the following components: 0.09%, Si: 0.19%, Mn: 0.90%, P: 0.016%, S: 0.007 percent of Al, 0.056 percent of Al and the balance of Fe, and the tapping temperature of a plate blank is 1200 ℃, the finish rolling start rolling speed is 1.30m/s, and the finish rolling outlet rolling speed is 6.0 m/s; the finishing temperature is 890 ℃, the coiling temperature is 620 ℃, and the thickness of the hot-rolled finished product is 5.0 mm.
The prepared plate coil is subjected to mechanical property test, and the tensile strength Rm and the elongation A at room temperature are respectively detected50mmThe tensile property is carried out according to the GB/T228 metal material room temperature tensile test method. The yield strength (Rel) of the finished product is 330MPa, the tensile strength (Rm) is 430MPa, and the elongation (A)50mm) 34 percent, qualified cold bending process test performance, 12 mu m of finished product surface iron scale and Fe in the surface iron scale3O4The proportion of (A) is 60%, and the thickness and the scale structure of the scale on the surface of the obtained steel plate do not meet the technical condition requirements of the pickling-free hot-rolled automobile structural steel plate with the pressure of 400 MPa.
Claims (9)
- The 1.400 MPa-grade acid-washing-free hot rolled steel plate for the automobile structure is characterized by comprising the following chemical components in percentage by weight: c: 0.05 to 0.10, Si: 0.05-0.15, Mn: 0.7-1.00, N: 0.002 to 0.006, P: 0 to 0.025, S: 0-0.015, Al: 0.02-0.06 wt%, and the balance Fe.
- 2. The hot-rolled steel sheet for the 400MPa grade pickling-free automobile structure according to claim 1, wherein the microstructure of the hot-rolled steel sheet comprises ferrite and pearlite, and the volume percentage of the ferrite is 88-90% and the volume percentage of the pearlite is 10-12% based on the total volume of the crystal structure.
- 3. The hot-rolled steel plate for the 400 MPa-grade pickling-free automobile structure according to claim 1 or 2, wherein the yield strength of the hot-rolled steel plate is not less than 255MPa, the tensile strength of the hot-rolled steel plate is not less than 400MPa, and the elongation of the hot-rolled steel plate is not less than 34%.
- 4. The hot-rolled steel plate for the 400 MPa-grade pickling-free automobile structure according to any one of claims 1 to 3, wherein Fe in iron scale on the surface of the hot-rolled steel plate3O4The content is more than or equal to 80 percent.
- 5. The hot-rolled steel plate for the 400 MPa-grade pickling-free automobile structure according to any one of claims 1 to 4, wherein the thickness of an iron scale on the surface of the hot-rolled steel plate is 7 to 9 μm.
- 6. The preparation method of the 400 MPa-grade acid-washing-free hot rolled steel plate for the automobile structure comprises the steps of converter smelting, LF refining, continuous casting billet reheating, hot rolling, cooling and coiling; it is characterized in that the preparation method is characterized in that,the reheating temperature of the continuous casting billet is 1210-1230 ℃, and the heating time is 1.2-1.8 hours;in the hot rolling procedure, the rough rolling start rolling temperature is 1173-1200 ℃, the finish rolling start rolling temperature is less than or equal to 1020 ℃, and the finish rolling temperature is 860-890 ℃;the coiling temperature is 560-590 ℃.
- 7. The method for preparing the hot rolled steel plate for the 400 MPa-grade pickling-free automobile structure according to claim 6, wherein in a converter smelting process, the tapping temperature is 1660-1680 ℃, and the oxygen activity at the pre-deoxidation end point during tapping is less than 80 ppm.
- 8. The preparation method of the hot rolled steel plate for the 400 MPa-grade pickling-free automobile structure according to claim 6 or 7, characterized in that in the hot rolling process, the descaling water pressure is more than or equal to 21MPa, the rolling starting speed of finish rolling is more than or equal to 1.5m/s, and the rolling finishing speed of finish rolling is more than or equal to 7.8 m/s.
- 9. The method for preparing the hot rolled steel plate for the 400 MPa-grade pickling-free automobile structure according to any one of claims 6 to 8, wherein a sparse cooling mode is adopted in a cooling process.
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| CN106636924A (en) * | 2016-12-30 | 2017-05-10 | 武钢集团昆明钢铁股份有限公司 | 235 MPa level shock-proof hot-rolled steel plate and steel strip for building structure and preparation method thereof |
| CN107904503A (en) * | 2017-11-24 | 2018-04-13 | 攀钢集团攀枝花钢铁研究院有限公司 | Pickling vehicle structure steel plate and its production method are exempted from 510MPa grades of hot rollings |
| CN109440005A (en) * | 2018-11-14 | 2019-03-08 | 河钢股份有限公司承德分公司 | A kind of SAPH440 crystal grain refinement steel and its production method |
| CN114752725A (en) * | 2022-04-02 | 2022-07-15 | 湖南华菱涟源钢铁有限公司 | Pickled plate and production method thereof |
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