The invention belongs to the field of manufacturing hot-dip galvanized steel plates, in particular relates to a hot-dip galvanized steel plate with good adhesion of the plating layers and a production method thereof.
Hot-dip galvanized steel plates are widely applied to the manufacturing industry such as household appliance and automobile body plates due to good corrosion resistance, excellent coating and plating performance and clean appearance. Plating layers of the hot-dip galvanized steel plates are required to have strong adhesion of the plating layers and base plates to prevent dropout in case of deformation due to stamping and good welding performance, corrosion resistance and phosphatizing performance to ensure adhesion of paint film and corrosion resistance after painting. However, the hot-dip galvanized steel plates has problems of pulverization and stripping of the plating layer in stamping and machining process in practical application, damaging the plating layer and further affecting corrosion resistance and adhesion of the plating layer.
Chinese patent (publication No.: CN17011130A; and publication date: Nov. 23, 2005) and Japanese patents (Kokai patent publication No. 2002-4019 and Kokai patent publication No. 2002-4020) disclose methods for controlling surface roughness of hot-dip galvanized steel plates to prevent adhesion of metal dies in stamping and forming, and methods for improving deep drawability. However, detailed studies on such hot-dip galvanized steel plates show that adhesion with the metal die can be controlled for short friction distance from the metal die, but the adhesion is smaller while the friction distance is longer, and sometimes improvement effect can not be achieved due to different friction conditions. In addition, a method for controlling a finishing roller, rolling conditions, etc. can be deduced from the method for improving roughness in the proposals. However, in effect, zinc is easily piled and blocked on rollers, thus it is hard to form desired roughness on the surfaces of such hot-dip galvanized steel plates. In addition, Japanese patent (Koho patent publication No. 2993404) provides a process for improving adhesion of the plating film by using P-added steel containing 0.010-0.10mt % of P and 0.05-0.20 wt % of Si with Si not less than P to parent metal. However, the technique does not surely improve adhesion of the plating film for other steel plates without P. Japanese patent (Kokai patent publication No. 2001-335908) discloses the following technique: when the parent metal is low-carbon steel with 0.05-0.25wt % of C and high-strength retained austenite steel with a proper amount of Si and Al added, a proper amount of Ti, Nb, etc. are added to the steel for fixing grain boundary C to improve plating boundary strength. However, the technique relates to the retained austenite steel and is not surely effective in obtaining adequate performance for high-strength steel plates without retained austenite phase.
Adhesion of the plating layer of the galvanized steel plates is also mainly affected by composition and structure of the plating layer in addition to composition and process conditions of the base steel plates. The pulverization and the stripping are related to chemical composition and phase structure of the plating layer, and pulverization amount of the plating layer increases as iron content of the plating layer increases. The interface between the steel plate and the zinc layer is Γ phase, δ phase, ζ phase and η phase successively. The Γ phase is an intermetallic phase based on Fe5Zn21, the δ phase is an intermetallic phase based on FeZn7, the ζ phase is an intermetallic phase based on FeZn13, and the ζ phase is solid solution consisting of pure zinc and containing trace iron. The pulverization of the plating layer means that microcrack forms on an interface at two sides of the Γ phase and extends through the plating layer. When the thickness of the F phase exceeds 1.0um, the pulverization amount increases as the thickness of the Γ phase increases. Formation of thick Γ phase can be blocked if the iron content of the plating layer can be controlled to be about 11%. Therefore, main influencing factors of anti-pulverization performance are the δ phase (fine-grained structure) and the ζ phase (columnar structure). The δ phase is rigid and fragile and is unfavorable to formability. The ζ phase has comparable hardness with the base steel plates, and is favorable to releasing residual stress from the plating layer. However, the ζ phase is easily adhered to the dies due to high toughness thereof, causing surface defect or stripping of the plating layer. Therefore, the plating layer can have good formability only when the ζ phase and the δ phase therein have proper proportion. The plating structure with uneven compact δ phase failing to appear upon disappearance of the ξ phase on the surface thereof is the best.
In practice, Al is often added to liquid zinc for improving the toughness of the plating layer, and Al content of a Fe-Al intermediate transition layer between base steel and the zinc layer of the hot-dip galvanized steel plate is an important factor for measuring adhesion strength of the plating layer. However, high Al content of the Fe-Al intermediate transition layer is necessary but insufficient to achieve good adhesion of the plating layer, as the Fe-Al intermediate transition layer can have adhesive action, prevent diffusion of Fe and Zn elements and form a thin Fe-Zn alloy layer with a little δ phase and ζ phase only when zinc unsaturatedly dissolves and forms lean zinc solid solution in the Fe-Al intermediate transition layer, under which the plating layer has better adhesion. If Zn has supersaturated solubility and forms rich zinc solid solution in the Fe-Al intermediate transition layer, the absolute content of Al in the intermediate transition layer does not reduce, but weight percentage of Al significantly reduces. Meanwhile, zinc supersaturation damages homogeneity of the Fe-Al intermediate transition layer, thus causing the intermediate transition layer to lose adhesive action and preventing diffusion of the Fe and Zn elements, and forming thicker Fe-Zn alloy layer with much δ phase and ζ phase, simultaneously damaging the adhesion of the zinc layer. In the prior art, the adhesion between the plating layer and the base steel is improved by a technique of forming a film on surface by changing the composition of the steel plates or controlling the surface roughness of the hot-dip galvanized steel plate, but the effect is not better. At present, there is no report on any method available for improving the adhesion between the plating layer and the base steel by controlling the composition and the structure of the plating layer.
The first technical problem to be solved by the invention is to provide a hot-dip galvanized steel plate with high adhesion between a plating layer and base steel.
The technical proposal for solving the technical problem is as follows: atomic concentration ratio Al/Zn of Al and Zn in a Fe-Al intermediate transition layer between base steel and a plating layer of the hot-dip galvanized steel plate is 0.9-1.2.
The invention further provides a hot-dip galvanized steel plate with high adhesion between a plating layer and base steel and better plating structure. Atomic concentration ratio Al/Zn of Al and Zn in a Fe-Al intermediate transition layer between base steel and a plating layer of the hot-dip galvanized steel plate is 0.9-1.2, and intensity of grain orientation Zn(002) peak of the plating layer is 25000-35000 cts.
The second technical problem to be solved by the invention is to provide a production method of a hot-dip galvanized steel plate. Atomic concentration ratio Al/Zn of Al and Zn in a Fe-Al intermediate transition layer between base steel and a plating layer of the steel plate produced by the method is 0.9-1.2.
The technical proposal for solving the technical problem is as follows: a steel plate is pickled, annealed and hot-dip galvanized. During the hot-dip galvanization operation, temperature of the steel plate is 455-465° while being sent to plating bath, temperature of the plating bath in a zinc pot is 450-460°, weight percentage of Fe in the plating bath is less than 0.03%, weight percentage of Al in the plating bath is 0.16-0.25%, speed of a unit is 100-120 m/min, high-span temperature of a cooling section is 210-245°, and cooling rate of the steel plate is 0-90%.
Preferred proposal 1: a production method of a hot-dip galvanized steel plate comprises pickling and annealing a steel plate for hot-dip galvanization operation. During the hot-dip galvanization operation, temperature of the steel plate is 455-465° while being sent to plating bath, temperature of the plating bath in a zinc pot is 450-460°, weight percentage of Fe in the plating bath is less than 0.03%, weight percentage of Al in the plating bath is 0.16-0.18%, speed of a unit is 100-110 m/min, high-span temperature of a cooling section is 210-220°, and cooling rate of the steel plate is 0%.
Preferred proposal 2: a production method of a hot-dip galvanized steel plate comprises pickling and annealing a steel plate for hot-dip galvanization operation. During the hot-dip galvanization operation, temperature of the steel plate is 475-485° while being sent to plating bath, temperature of the plating bath in a zinc pot is 450-460°, weight percentage of Fe in the plating bath is less than 0.03%, speed of a unit is 100-110 m/min, cooling rate of the steel plate is 0%, high-span temperature of a cooling section is 235-245°, and weight percentage of Al in the plating bath is not less than 0.16% but not more than 0.18%.
Preferred proposal 3: a production method of a hot-dip galvanized steel plate comprises pickling and annealing a steel plate for hot-dip galvanization operation. During the hot-dip galvanization operation, temperature of the steel plate is 475-485° while being sent to plating bath, temperature of the plating bath in a zinc pot is 450-460°, weight percentage of Fe in the plating bath is less than 0.03%, weight percentage of Al in the plating bath is more than 0.18% but not more than 0.21%, speed of a unit is 100-110 m/min, cooling rate of the steel plate is 0%, and high-span temperature of a cooling section is 235-245°.
Preferred proposal 4: a production method of a hot-dip galvanized steel plate comprises pickling and annealing a steel plate for hot-dip galvanization operation. During the hot-dip galvanization operation, temperature of the steel plate is 455-465° while being sent to plating bath, temperature of the plating bath in a zinc pot is 450-460°, weight percentage of Fe in the plating bath is less than 0.03%, weight percentage of Al in the plating bath is 0.16-0.18%, speed of a unit is 110-120 m/min, and the steel plate is forcibly cooled by air cooling at the cooling rate of 70-90% after being taken out of the zinc pot (for natural cooling at the cooling rate of 0% when all cold air nozzles are closed, opening ratio of the cold air nozzles is 70-90%).
Preferred proposal 5: a production method of a hot-dip galvanized steel plate comprises pickling and annealing a steel plate for hot-dip galvanization operation. During the hot-dip galvanization operation, temperature of the steel plate is 455-465° while being sent to plating bath, temperature of the plating bath in a zinc pot is 450-460°, weight percentage of Al in the plating bath is 0.21-0.25%, weight percentage of Fe in the plating bath is less than 0.03%, speed of a unit is 100-110 m/min, cooling rate of the steel plate is 0%, and high-span temperature of a cooling section is 235-245°.
Further, the steel plate to be galvanized contains 0.03-0.07% of C, 0.01-0.03% of Mn, 0.19-0.30% of Si, 0.006-0.019% of P, 0.009-0.020% of S, 0.02-0.07% of Al and Fe based on weight percentage.
Thickness of the steel plate to be galvanized is 0.8 mm, weight of a zinc layer is 180-195 g/m2 after galvanization, and surface of the zinc layer is subject to SiO2 passivation treatment.
The invention has the following advantages:
(1) hot-dip galvanization process conditions of the invention cause the Fe-Al intermediate transition layer between the base steel and the plating layer to prevent mutual diffusion of Fe and Zn and reduce formation of the Fe-Zn alloy layer, and the plating layer does not have Γ phase, but has relatively thin δ phase and a little ξ phase, and the plating layer mostly consists of the η phase, which improve adhesion of the plating layer of the hot-dip galvanized steel plate, and reduces dropout, stripping, etc. of zinc powder thereof;
(2) the hot-dip galvanization process conditions of the invention help optimize grain orientation of the plating layer of the hot-dip galvanized steel plate, and obviously improve scratch resistance, wear resistance and adhesion of the plating layer; and
(3) the hot-dip galvanization production process of the invention is simple and has low cost.
The invention will be further described in conjunction with the following embodiments. The examples are only for illustration rather than limiting the invention in any way.
Atomic concentration ratio Al/Zn of Al and Zn in a Fe-Al intermediate transition layer between base steel and a plating layer of the hot-dip galvanized steel plate of the invention is 0.9-1.2. Further, intensity of grain orientation Zn(002) peak of the plating layer is 25000-35000 cts.
A specific production method of the hot-dip galvanized steel plate is as follows:
A steel plate is pickled and annealed for hot-dip galvanization operation. During the hot-dip galvanization operation, temperature of the steel plate is 455-485° while being sent to plating bath, temperature of the plating bath in a zinc pot is 450-460°, weight percentage of Fe in the plating bath is less than 0.03%, weight percentage of Al in the plating bath is 0.16-0.25%, speed of a unit is 100-120 m/min, high-span temperature of a cooling section is 210-245°, and cooling rate of the steel plate is 0-90%. The section at which the galvanized steel plate is drawn from the zinc pot and moved vertically and upwardly to a first deflecting roller of a cooling tower is called a precooling section (generally 15-30 m). To freeze the plating layer in front of the first deflecting roller, a row of cold air nozzles are arranged against an air knife thereabove for forced cooling by blowing cold air. A horizontal cooling section that strip steel enters the cooling tower by the first deflecting roller is called a high-span section which is provided with 4 sets of air boxes for adjusting temperature. High-span temperature is the temperature of the conveyed steel plate when entering the high-span section.
Preferred proposal 1: a production method of a hot-dip galvanized steel plate comprises pickling and annealing a steel plate for hot-dip galvanization operation. During the hot-dip galvanization operation, temperature of the steel plate is 455-465° while being sent to plating bath, temperature of the plating bath in a zinc pot is 450-460°, weight percentage of Fe in the plating bath is less than 0.03%, weight percentage of Al in the plating bath is 0.16-0.18%, speed of a unit is 100-110 m/min, high-span temperature of a cooling section is 210-220°, and cooling rate of the steel plate is 0%. In the production method of the hot-dip galvanized steel plate, Al/Zn ratio of a Fe-Al intermediate transition layer is controlled by the high-span temperature of the cooling section in the hot-dip galvanization process to reduce formation of a Fe-Zn alloy layer and improve adhesion of a plating layer. 0% cooling rate of the steel plate means that all cold air nozzles are closed at the precooling section and natural cooling is performed only by heat radiation and convection. Atomic concentration ratio Al/Zn of Al and Zn in the Fe-Al intermediate transition layer between base steel and a plating layer produced by the method is 0.9-1.2.
Preferred proposal 2: a production method of a hot-dip galvanized steel plate comprises pickling and annealing a steel plate for hot-dip galvanization operation. During the hot-dip galvanization operation, temperature of the steel plate is 475-485° while being sent to plating bath, temperature of the plating bath in a zinc pot is 450-460°, weight percentage of Fe in the plating bath is less than 0.03%, speed of a unit is 100-110 m/min, cooling rate of the steel plate is 0%, high-span temperature of a cooling section is 235-245°, and weight percentage of Al in the plating bath is not less than 0.16% but not more than 0.18%. Atomic concentration ratio Al/Zn of Al and Zn in a Fe-Al intermediate transition layer between base steel and a plating layer produced by the method is 0.9-1.2, and intensity of grain orientation Zn(002) peak of the plating layer is 25000-35000 cts.
Preferred proposal 3: a production method of a hot-dip galvanized steel plate comprises pickling and annealing a steel plate for hot-dip galvanization operation. During the hot-dip galvanization operation, temperature of the steel plate is 475-485° while being sent to plating bath, temperature of the plating bath in a zinc pot is 450-460°, weight percentage of Fe in the plating bath is less than 0.03%, weight percentage of Al in the plating bath is more than 0.18% but not more than 0.21%, speed of a unit is 100-110 m/min, cooling rate of the steel plate is 0%, and high-span temperature of a cooling section is 235-245°. Atomic concentration ratio Al/Zn of Al and Zn in a Fe-Al intermediate transition layer between base steel and a plating layer produced by the method is 0.9-1.2, and Intensity of grain orientation Zn(002) peak of the plating layer is 25000-35000 cts.
In the first two production methods of the hot-dip galvanized steel plate, the Al/Zn ratio of the Fe-Al intermediate transition layer is controlled by temperature of the steel plate while being sent to plating bath in the hot-dip galvanization process so as to reduce formation of the Fe-Zn alloy layer, adjust optimum grain orientation of the plating layer and improve adhesion thereof.
Preferred proposal 4: a production method of a hot-dip galvanized steel plate comprises pickling and annealing a steel plate for hot-dip galvanization operation. During the hot-dip galvanization operation, temperature of the steel plate is 455-465° while being sent to plating bath, temperature of the plating bath in a zinc pot is 450-460°, weight percentage of Fe in the plating bath is less than 0.03%, weight percentage of Al in the plating bath is 0.16-0.18%, speed of a unit is 110-120 m/min, and the steel plate is forcibly cooled by air cooling at the cooling rate of 70-90% after being taken out of the zinc pot (for natural cooling at the cooling rate of 0% when all cold air nozzles are closed, opening ratio of the cold air nozzles is 70-90%). Atomic concentration ratio Al/Zn of Al and Zn in the Fe-Al intermediate transition layer between base steel and a plating layer produced by the method is 0.9-1.2, and intensity of grain orientation Zn(002) peak of the plating layer is 25000-35000 cts. In the production method of the hot-dip galvanized steel plate, the Al/Zn ratio of the Fe-Al intermediate transition layer is controlled by the cooling rate of the steel plate after being drawn from the zinc pot in the hot-dip galvanization process so as to reduce formation of a Fe-Zn alloy layer, adjust optimum grain orientation of the plating layer and improve adhesion thereof.
Preferred proposal 5: a production method of a hot-dip galvanized steel plate comprises pickling and annealing a steel plate for hot-dip galvanization operation. During the hot-dip galvanization operation, temperature of the steel plate is 455-465° while being sent to plating bath, temperature of the plating bath in a zinc pot is 450-460°, weight percentage of Al in the plating bath is 0.21-0.25%, weight percentage of Fe in the plating bath is less than 0.03%, speed of a unit is 100-110 m/min, cooling rate of the steel plate is 0%, and high-span temperature of a cooling section is 235-245°. Atomic concentration ratio Al/Zn of Al and Zn in a Fe-Al intermediate transition layer between base steel and a plating layer produced by the method is 0.9-1.2, and intensity of grain orientation Zn(002) peak of the plating layer is 25000-35000 cts. In the production method of the hot-dip galvanized steel plate, the Al/Zn ratio of the Fe-Al intermediate transition layer is controlled by Al content of the plating bath in the hot-dip galvanization process so as to reduce formation of a Fe-Zn alloy layer, adjust optimum grain orientation of the plating layer and improve adhesion thereof.
The steel plate to be galvanized contains 0.03-0.07% of C, 0.01-0.03% of Mn, 0.19-0.30% of Si, 0.006-0.019% of P, 0.009-0.020% of S, 0.02-0.07% of Al and Fe based on weight percentage.
Thickness of the steel plate to be galvanized is 0.8 mm, weight of a zinc layer is 180-195 g/m2 after galvanization, and surface of the zinc layer is subject to SiO2 passivation treatment.
A DX51D cold-rolled steel plate which was 0.8 mm thick and contained 0.03-0.07% of C, 0.01-0.03% of Mn, 0.19-0.30% of Si, 0.006-0.019% of P, 0.009-0.020% of S, 0.02-0.07% of Al, Fe and inevitable impurities was pickled and annealed for hot-dip galvanization operation under various hot-dip galvanization process conditions listed in Table 1. Initial temperature of plating bath in a zinc pot was 450°, Fe content was less than 0.03% and Al content was 0.160-0.180% in the plating bath, speed of a unit was 100 m/min, high-span temperature of a cooling section was 240°, cooling rate was 0%, and temperature of the steel plate was adjusted to 475-485° while being sent to the plating bath for the hot-dip galvanization operation to obtain samples of examples 1 to 5; and temperature of the steel plate was respectively adjusted to 455-465° and 440-450° while being sent to the plating bath for hot-dip galvanization operation to obtain samples of comparative examples 6 to 10 and 11 to 15. Weight of a zinc layer was controlled to be 180-195 g/m2, and surface of the zinc layer was subject to SiO2 passivation treatment.
(1) Fe-Al intermediate transition layers, cross-section morphologies and structures of plating layers
As thickness of Fe-Al intermediate transition layer ranged from dozens to hundreds of nanometers, the intermediate transition layers can hardly be shown by a conventional metallurgical sample preparation method. In the metallurgical sample preparation of the invention, oblique mounting was adopted and mounting material was bakelite powder. Three hot-dip galvanized steel plate samples were glued together by 502 super glue, arranged in parallel on an oblique block forming an inclination angle of 30° with a horizontal plane and then mounted on a hot mounting press. Visible range of the whole section of the ground and polished steel plate was increased approximately once, and the Fe-Al intermediate transition layers between interfaces of various plating layers and base steel were obviously shown. Atomic and mass percentage of various major elements in the Fe-Al intermediate transition layers of the plating layers were determined by virtue of spectrum surface scanning by an electronic probe (model: EPMA1600) and spot composition analysis. All samples used by EPMA were unetched metallurgical samples subject to the oblique mounting. EPMA surface scanning results showed that all experimental examples and comparative examples had dark black bands, i.e. the Fe-Al intermediate transition layers as shown in
In typical metallurgical samples of the plating layers, EPMA line scanning chromatogram measured by EPMA showed that Al element had the highest content in the intermediate transition layer, and Zn element content gradually increased and Fe element content gradually decreased from the base steel to the plating surface.
Metallurgical samples were ground and polished, etched in 2% nital etching solution and then metallographically photographed by a 100x high-performance optical metallographic microscope (model: OLYMPUS BX51).
Mass percentages of elements of all phases in the plating structure were determined by EPM spectrum spot composition analysis. The δ phase, ζ phase and η phase can be judged to exist in the plating layers based on mass percentages of the Fe and Zn elements of all phases in the plating layers and metallographs of the plating structures.
For hot-dip galvanized steel plates with good adhesion, when the Fe-Al intermediate transition layer with higher Al content was formed between base steel and the plating layers and only when Zn unsaturatedly dissolved and generated lean zinc solid solution in the Fe-Al intermediate transition layer, the layer can have adhesive action and the effect of preventing Fe-Zn diffusion, and formed thin Fe-Zn alloy layer with reduced δ phase and ζ phase, and δ phase and ξ phase reduced, under which the plating layer had good adhesion.
Surfaces of the plating layers were not treated, and small-angle diffraction (glancing angle: 5°) was respectively performed on the plating layers by an x-ray diffractometer (XRD) to determine diffraction peak intensity of the plating layers.
Anti-drop performance of the plating layers was tested by “U”-shape bend tests. The bend test was performed according to National Standard GB/T 232-1999 (Metallic Materials—Bend Test) and sample preparation referred to GB/T 2975-1998 (Steel and Steel Products-Location and Preparation of Test Pieces for Mechanical Testing).
Scratch resistance tests of the plating layers were performed on a CETR UMT-2 multi-functional friction and wear tester from U.S., a scratch test device was adopted therein, and pressure head for the scratch tests contained shovel-shaped diamond with curvature radius of the head being 800 μm. A loading mode of linear increase was adopted and load was increased from 0.5 N to 2 N in the scratch tests. After tests, an Ambios XP2 profilometer was used to measure scratch profiles and morphologies of the various plating layers after the tests.
Wear resistance tests of the plating layers was performed on a reciprocating sliding friction test platform of a CETR UMT-2 multi-functional friction and wear tester from U.S.. Upper samples (ground samples) were stainless steel balls with diameter of 10 mm, and lower samples were the hot-dip galvanized steel plate. Reciprocating sliding friction and wear test parameters were as follows: normal load Fn=2 N, reciprocating displacement amplitude D=2 mm, relative movement speed V=2 mm/s, running time t=1000 s and cycle index N=500. After the test, an Ambios XP2 profilometer was adopted for measuring profiles and morphologies of wear marks of the various plating layers after the tests.
Table 3 lists overall evaluation on adhesion of the plating layers of various samples of experimental examples and comparative examples according to the following standards: ∘ good (the number of good ∘ is more than 2 and the number of slightly poor is only 1); slightly poor (the number of good ∘ is 1 and the number of slightly poor is 2): and × poor (the number of poor × is more than 2 or the number of slightly poor is 2 and the number of poor × is 1).
From evaluation results in Table 3, compared with previous steel plates (comparative examples 6 to 15), the hot-dip galvanized steel plate (experimental examples 1 to 5) obtained by increasing temperature of the steel plates at zinc pots to 475-485° and keeping other processes unchanged in the hot-dip galvanization process was characterized in that Al/Zn ratios of the Fe-Al intermediate transition layers of the plating layers were more than 0.9, δ phase and ξ phase of the plating layers reduced and η phase of the pure zinc layers increased; grains of the plating layers of experimental examples (samples 1 to 5) presented preferred orientation of Zn(002), and diffraction intensities of the Zn(002) peaks were significantly improved to be more than 34000 cts, thus significantly improving the anti-drop performance, scratch resistance and wear resistance of the plating layers, and obviously improving adhesion between the plating layers and the base steel.
In the experimental examples and comparative examples, it can be judged that the plating layers had good adhesion when the Al/Zn ratios were more than 0.9, the plating layers mainly had η phase, and adhesion of the plating layers was better when diffraction intensities of Zn(002) peaks thereof were more than 34000 cts by measuring atomic concentration ratios of Al and Zn in the Fe-Al intermediate transition layers, various phase structures of the plating layers and preferred grain orientation of the plating layers, and referring to adhesion evaluation of various plating layers.
A DX1 cold-rolled steel plate which was 0.8 mm thick and contained 0.03-0.07% of C, 0.01-0.03% of Mn, 0.19-0.30% of Si, 0.006-0.019% of P, 0.009-0.020% of S, 0.02-0.07% of Al, Fe and inevitable impurities was pickled and annealed for hot-dip galvanization operation under hot-dip galvanization process conditions listed in Table 4. Initial temperature of the plating bath in a zinc pot was 450°, Fe content was less than 0.03% in the plating bath, speed of a unit is 100 m/min, high-span temperature of a cooling section was 240°, and cooling rate was 0%. Temperature of the steel plate was adjusted to 475° while being sent to the plating bath, and Al content of the plating bath was adjusted to more than 0.18% but not more than 0.21% for hot-dip galvanization operation to obtain experimental examples 16 to 20. Temperature of the steel plate was adjusted to 460° while being sent to plating bath, and Al content of the plating bath was adjusted to 0.16-0.17% for hot-dip galvanization operation to obtain comparative examples 21 to 25. Weight of a zinc layer was controlled to be about 180-195 g/m2, and surface of the zinc layer was subject to SiO2 passivation treatment.
The following measuring methods and evaluation standards were the same as those of example 1.
Spectrum surface scanning chromatograms of sections of the plating layers of experimental examples 16 to 20 by an electronic probe (model: EPMA1600) had the same results as experimental example 1 (refer to
Table 6 lists average friction coefficients of various samples of experimental examples 16 to 20 and comparative examples 21 to 25 after 100 friction cycles.
From evaluation results in Table 6, compared with previous steel plates (comparative examples 21 to 25), the hot-dip galvanized steel plate (experimental examples 16 to 20) obtained by increasing temperature of strip steel while being sent to the plating bath to 475° and controlling Al content of the plating bath to be more than 0.18% but not more than 0.21%, but keeping other processes unchanged in the hot-dip galvanization process was characterized in that Al/Zn ratios of the Fe-Al intermediate transition layers of plating layers were 0.963-1.134 and more than those of experimental examples 1-6. δ phase and ξ phase of the plating layers obviously reduced, and η phase of the pure zinc layers increased and Zn(002) grains with preferred orientation were formed, thus significantly improving anti-drop performance, scratch resistance and wear resistance of the plating layers, and obviously improving adhesion between the plating layers and the base steel.
A DX51D cold-rolled steel plate which was 0.8 mm thick and contained 0.03-0.07% of C, 0.01-0.03% of Mn, 0.19-0.30% of Si, 0.006-0.019% of P, 0.009-0.020% of S, 0.02-0.07% of Al, Fe and impurities was pickled and annealed for hot-dip galvanization operation under hot-dip galvanization process conditions listed in Table 7. Temperature of plating bath in a zinc pot was 450°, Fe content was less than 0.03% and Al content was 0.16-0.18% in the plating bath, temperature of the steel plate was 460° while being sent to the plating bath, and speed of a unit was 100 m/min. The steel plate was drawn from the zinc pot and then forcibly cooled by air cooling to obtain experimental examples 21 to 30 at the cooling rate of 70-90%, comparative examples 26 to 30 at the cooling rate of 30-50% and comparative examples 31 to 35 at the cooling rate of 0% (natural air cooling). Weight of a zinc layer was controlled to be about 180 g/m2 and surface of the zinc layer was subject to SiO2 passivation treatment. Grain orientation of the plating layers and adhesion of the plating layers such as anti-drop performance, scratch resistance and wear resistance were evaluated by the following method.
The following measuring methods and evaluation standards were the same as those of example 1.
Table 8 lists average friction coefficients of various samples of experimental examples and comparative examples after 100 friction cycles.
From evaluation results in Table 8, compared with previous steel plates (comparative examples), the hot-dip galvanized steel plate (experimental examples) obtained by increasing cooling rate of the steel plate to 70-90%, but keeping other processes unchanged in the hot-dip galvanization process is characterized in that grains of the plating layers presented preferred orientation of Zn(002), thus significantly improving anti-drop performance, scratch resistance and wear resistance of the plating layers, and obviously improving adhesion between the plating layers and the base steel.
A DX1 cold-rolled steel plate which was 0.8 mm thick and contained 0.03-0.07% of C, 0.01-0.03% of Mn, 0.19-0.30% of Si, 0.006-0.019% of P, 0.009-0.020% of S, 0.02-0.07% of Al, Fe and inevitable impurities was pickled and annealed for hot-dip galvanization operation under hot-dip galvanization process conditions listed in Table 9. Initial temperature of plating bath in a zinc pot was 450°, Fe content was less than 0.03% in the plating bath, temperature of the steel plate was 460° while being sent to the plating bath, speed of a unit was 100 m/min, high-span temperature of a cooling section was 240°, and cooling rate was 0%. Al content of the plating bath wais adjusted to 0.21-0.25% for hot-dip galvanization operation to obtain experimental examples 31 to 35; and Al content of the plating bath was adjusted to 0.16-0.18% for hot-dip galvanization operation to obtain comparative examples 36 to 40. Weight of a zinc layer was controlled to be about 180-195 g/m2 and surface of the zinc layer was subject to SiO2 passivation treatment.
The following measuring methods and evaluation standards were the same as those of example 1.
Typical spectrum surface scanning chromatograms of sections of the plating layers of experimental example 31 by an electronic probe (model: EPMA1600) had the same results as experimental example 1 (refer to
Table 11 lists average friction coefficients of various samples of examples and comparative examples after 100 friction cycles.
From evaluation results in Table 11, compared with previous steel plates (comparative examples), the hot-dip galvanized steel plate (experimental examples) obtained by controlling Al content of the plating bath to be 0.21-0.25%, but keeping other processes unchanged in the hot-dip galvanization process was characterized in that Al/Zn ratios of the Fe-Al intermediate transition layers of the plating layers were 0.940-1.125, δ phase and ξ phase of the plating layers obviously reduced, and η phase of the pure zinc layers increased and Zn(002) grains with preferred orientation were formed, thus significantly improving anti-drop performance, scratch resistance and wear resistance of the plating layers, and obviously improving adhesion between the plating layers and the base steel.
A DX1 cold-rolled steel plate which was 0.8 mm thick and contained 0.03-0.07% of C, 0.01-0.03% of Mn, 0.19-0.30% of Si, 0.006-0.019% of P, 0.009-0.020% of S, 0.02-0.07% of Al, Fe and impurities was pickled and annealed for hot-dip galvanization operation under hot-dip galvanization process conditions listed in Table 12. Temperature of plating bath in a zinc pot was 450°, Fe content was less than 0.03% and Al content was 0.16-0.18% in the plating bath, temperature of the steel plate was 460° while being sent to plating bath, speed of a unit is 100 m/min, cooling rate was 0%, and high-span temperature of a cooling section was adjusted to 210-220° to obtain experimental examples 36 to 42; and the high-span temperature of the cooling section was adjusted to 240-260° to obtain comparative examples 41 to 47. Weight of a zinc layer was controlled to be about 180-195 g/m2 and surface of the zinc layer was subject to SiO2 passivation treatment.
Typical spectrum surface scanning chromatograms of sections of the plating layers of experimental example 36 by an electronic probe (model: EPMA1600) had the same results as experimental example 1 (refer to
Table 13 lists average friction coefficient of various samples of experimental examples and comparative examples after 100 friction cycles.
From evaluation results in Table 13, compared with previous steel plates (comparative examples), the hot-dip galvanized steel plate (experimental examples) obtained by adjusting high-span temperature of the cooling section to 210-220°, but keeping other processes unchanged in the hot-dip galvanization process was characterized in that Al/Zn ratios of the Fe-Al intermediate transition layers of the plating layers were 0.757-0.884, δ phase and ξ phase of the plating layers obviously reduced, and η phase of the pure zinc layers increased, thus significantly improving anti-drop performance, scratch resistance and wear resistance of the plating layers, and obviously improving adhesion between the plating layers and the base steel.
Number | Date | Country | Kind |
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200810303233.3 | Jul 2008 | CN | national |
200810303257.9 | Jul 2008 | CN | national |
200810303258.3 | Jul 2008 | CN | national |
200810303272.3 | Jul 2008 | CN | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/CN2009/073004 | 7/30/2009 | WO | 00 | 7/5/2011 |