CN114032457A - Continuous hot-dip galvanized high-strength steel plate and manufacturing method thereof - Google Patents
Continuous hot-dip galvanized high-strength steel plate and manufacturing method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- 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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- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C18/00—Alloys based on zinc
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- C22C18/00—Alloys based on zinc
- C22C18/04—Alloys based on zinc with aluminium as the next major constituent
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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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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; Strips
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Abstract
The invention relates to the field of steel preparation, in particular to a continuous hot-dip galvanized high-strength steel plate and a manufacturing method thereof, wherein the steel plate comprises the following chemical components in percentage by mass: c: 0.1-0.3%, Mn: 0.5-3%, Si: 0.2-1%, Cr: 0.1-0.6%, the balance being Fe and inevitable impurity elements; the steel plate comprises a surface layer and an intermediate layer, wherein the mass fraction ratio of the chemical components of the surface layer to the chemical components of the steel plate comprises: c is less than or equal to 0.5, Mn is less than or equal to 0.3, Si is less than or equal to 0.3, and Cr is less than or equal to 0.8; the chemical components of the surface layer of the designed steel plate are obviously different from the chemical components of the steel plate, so that the austenitizing temperature of the surface layer is obviously increased, the surface layer can keep a ferrite state in the welding process, austenite transformation is not carried out, the brittleness of liquid metal is improved, and cracks are avoided.
Description
Technical Field
The invention relates to the field of steel preparation, in particular to a continuous hot-dip galvanized high-strength steel plate and a manufacturing method thereof.
Background
Continuous hot dip galvanized high strength steel is an important raw material for producing automobile bodies. Compared with the traditional steel plate, the thickness of the steel plate can be obviously reduced on the premise that the safety performance can be guaranteed by using high-strength steel, so that the light weight is realized. Steel sheets have poor corrosion resistance in the atmosphere and need to be specially treated, and hot dip galvanizing is a common method for improving the corrosion resistance of steel sheets. By using hot-dip galvanized high-strength steel, on one hand, light weight can be realized, and on the other hand, the corrosion life can be prolonged.
The traditional continuous hot-dip galvanized high-strength steel has certain application problems, and the hot-dip galvanized high-strength steel is easy to generate surface cracks of a steel plate in the welding process of a vehicle body. In the welding process, the temperature near the welding point often exceeds the melting point temperature of the zinc coating, so that the zinc coating is locally melted, and meanwhile, the welded local high temperature can also enable the microstructure of the high-strength steel to be completely changed into austenite, so that the strength is obviously reduced. The melted zinc easily diffuses along the grain boundary of austenite on the surface of the steel sheet, causing brittleness of the grain boundary of austenite. When the steel sheet is cooled down, austenite is transformed into ferrite or martensite again, and grain boundaries are subjected to large stress concentration, resulting in cracks at the grain boundary positions. Therefore, hot-dip galvanized high-strength steel is likely to have cracks on the surface of the steel sheet after welding. Such cracking is commonly referred to as liquid metal induced cracking, and the tendency of high strength steels to crack during high temperature welding is referred to as liquid metal brittleness.
Disclosure of Invention
The application provides a continuous hot-dip galvanized high-strength steel plate and a manufacturing method thereof, which aim to solve the technical problem that cracks are easy to appear on the surface of the steel plate when the hot-dip galvanized high-strength steel is welded in the prior art.
In a first aspect, the present application provides a continuous hot-dip galvanized high strength steel sheet having a chemical composition comprising, in mass percent: c: 0.1-0.3%, Mn: 0.5-3%, Si: 0.2-1%, Cr: 0.1-0.6%, the balance being Fe and inevitable impurity elements;
the steel plate comprises a surface layer and an intermediate layer, wherein the mass fraction ratio of the chemical components of the surface layer to the chemical components of the steel plate comprises: c is less than or equal to 0.5, Mn is less than or equal to 0.3, Si is less than or equal to 0.3, and Cr is less than or equal to 0.8.
Optionally, the thickness of the surface layer is less than or equal to 1 micron; the mass fraction ratio of the chemical components of the surface layer to the chemical components of the steel plate is as follows: c is more than or equal to 0.3 and less than or equal to 0.5.
Optionally, the surface layer of the steel plate further comprises a zinc alloy coating, and the thickness of the zinc alloy coating ranges from 3 microns to 20 microns.
Optionally, the chemical composition of the zinc alloy coating comprises, by mass: al: 0.2-2%, Mg: 0 to 1.5 percent, and the balance of Zn and inevitable impurity elements.
In a second aspect, the present application provides a method of manufacturing a continuous hot-dip galvanized high-strength steel sheet, the method including:
obtaining chemical components of the steel plate, and processing to obtain the steel plate;
carrying out heat treatment on the steel plate to obtain a heat-treated steel plate;
obtaining chemical components of the zinc alloy coating to obtain alloy plating solution;
carrying out first heating on the alloy plating solution to obtain a preheated plating solution;
immersing the heat-treated steel plate into the preheating plating solution to obtain a steel plate with a plating layer;
and carrying out primary cooling on the steel plate with the coating to obtain a hot-dip galvanized high-strength steel plate.
Optionally, the temperature of the pre-heating plating solution is 440-.
Optionally, the difference between the temperature of the steel plate after heat treatment and the temperature of the preheated plating solution is less than or equal to 10 ℃.
Optionally, the heat treatment sequentially comprises: second heating, heat preservation and second cooling; the end temperature of the second heating is 700-900 ℃.
Optionally, in the second heating, when the temperature of the steel plate is less than 600 ℃ and more than 800 ℃, the dew point temperature is less than or equal to-40 ℃; when the temperature of the steel plate is 600-800 ℃, the dew point temperature is 20-50 ℃.
Optionally, the heat preservation time is 60 to 120 seconds, and the heat preservation atmosphere includes: the dew point temperature is less than or equal to-40 ℃, and the mass fraction of hydrogen is more than or equal to 1%.
Compared with the prior art, the technical scheme provided by the embodiment of the application has the following advantages:
according to the hot-dip galvanized high-strength steel plate provided by the embodiment of the application, the chemical components of the surface layer of the steel plate are obviously different from those of the steel plate, the mass fraction ratio of the chemical components of the surface layer to those of the steel plate is controlled, and the austenitizing temperature of the surface layer is obviously increased by reducing the contents of carbon, manganese, silicon and chromium elements in the surface layer of the steel plate, so that the surface layer can keep a ferrite state in the welding process without austenite transformation, the brittleness of liquid metal is improved, and cracks are avoided; the method ensures that the austenite is not easily formed on the surface of the steel at the local high temperature of welding, the liquid zinc cannot permeate into austenite crystal boundaries to cause cracks of the high-strength steel, and if the austenite is not formed, the cracks caused by the liquid metal can be obviously reduced.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive exercise.
Fig. 1 is a schematic flowchart illustrating a method for manufacturing a steel sheet of a continuous hot-dip galvanized high-strength steel according to an embodiment of the present disclosure;
FIG. 2 is a schematic cross-sectional view of a product according to an embodiment of the present disclosure;
fig. 3 is a schematic cross-sectional structure of a product provided in comparative example 1 of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Fig. 1 is a schematic flow chart of an xx method according to an embodiment of the present application.
In an embodiment of the present application, there is provided a continuous hot-dip galvanized high-strength steel sheet, comprising, in mass fraction: c: 0.1-0.3%, Mn: 0.5-3%, Si: 0.2-1%, Cr: 0.1-0.6%, the balance being Fe and inevitable impurity elements;
the steel plate comprises a surface layer and an intermediate layer, wherein the mass fraction ratio of the chemical components of the surface layer to the chemical components of the steel plate comprises: c is less than or equal to 0.5, Mn is less than or equal to 0.3, Si is less than or equal to 0.3, and Cr is less than or equal to 0.8.
In the embodiment of the application: carbon is a basic strengthening element in steel, has a strong gap strengthening effect, and is therefore an indispensable or deficient alloy element. However, the addition of too much carbon element can cause the toughness of the high-strength steel to be obviously reduced, the high-strength steel cannot be used for forming automobile bodies, and simultaneously, the austenite temperature of the high-strength steel is too low, and liquid metal cracks and surface corrosion are easy to occur. Therefore, the content of carbon element is required to be 0.1-0.3%.
Manganese is also a solid solution strengthening element and is an element for stabilizing austenite, the austenite temperature can be obviously reduced, and the high-strength steel can obtain more austenite in the heat treatment process, so that martensite is formed after cooling, and the strength of the high-strength steel is improved. Of course, too high a manganese content results in too stable austenite, resulting in insufficient strength of the high-strength steel, and too low an austenite temperature of the high-strength steel, which is very susceptible to liquid metal cracking and surface corrosion. In addition, too much manganese easily forms oxides on the surface, deteriorating hot-dip galvanizability, causing a decrease in the coating adhesion. Therefore, the content range of manganese element is required to be 0.5-3%.
Silicon is a solid solution strengthening element, and is solid-dissolved in ferrite, and the strengthening effect is slightly better than that of manganese. Meanwhile, the silicon element can promote austenite to be refined and improve the elongation of the high-strength steel, so that the content of the silicon element is more than or equal to 0.2 percent. However, too much silicon element easily causes iron sheet which is difficult to remove on the surface in the hot rolling process, more oxide is formed on the surface in the heat treatment process, and the adhesiveness of the hot-dip galvanizing coating is reduced, so that the content of the silicon element is not more than 1%.
The chromium element has the function of stabilizing martensite at high temperature, so that the strength of the high-strength steel is not obviously reduced in the hot dip plating process, and the content is more than or equal to 0.1 percent. However, since excessive chromium combines with carbon to form precipitates, deteriorating toughness and lowering strength, the chromium content C is 0.5 or less.
In the embodiment of the present application, selecting the mass fraction ratio of the chemical components of the surface layer to the chemical components of the steel plate includes: c is less than or equal to 0.5, Mn is less than or equal to 0.3, Si is less than or equal to 0.3, and Cr is less than or equal to 0.8, so that the chemical composition of the steel surface layer is different from that of the steel plate, the situation that the austenite is not easily formed on the steel surface can be avoided, and cracks caused by liquid metal can be remarkably reduced. The cracks in the high strength steel are caused by the penetration of liquid zinc into the austenite grain boundaries. Chromium does not greatly affect the austenite temperature, and both carbon and manganese can be significantly reduced to the austenite temperature. Silicon refines austenite, causing grain boundaries to increase. Therefore, the reduction of carbon, manganese and silicon elements on the surface layer is beneficial to reducing the brittleness of the liquid metal. However, if the carbon content of the surface layer is too small, the surface layer has coarse grains, so that it is difficult to form sufficient nuclei for nucleation of the coating layer on the surface of the steel sheet during hot dip coating, thereby impairing the adhesion of the coating layer to the steel sheet.
As an alternative embodiment, the thickness of the surface layer is less than or equal to 1 micron; the mass fraction ratio of the chemical components of the surface layer to the chemical components of the steel plate is as follows: c is more than or equal to 0.3 and less than or equal to 0.5.
In the embodiment of the application, the mass fraction ratio of the chemical components of the surface layer to the chemical components of the steel plate is controlled, and the austenitizing temperature of the surface layer is remarkably increased by reducing the contents of carbon, manganese, silicon and chromium elements in the surface layer of the steel plate, so that the surface layer can keep a ferrite state in the welding process and austenite transformation is not performed. Wherein the surface layer only needs to meet the requirement that the surface layer for welding can reach the mass fraction ratio. All the upper and lower surface layers may satisfy the mass fraction ratio.
As an alternative embodiment, the surface layer of the steel sheet further includes a zinc alloy plating layer, and the thickness of the zinc alloy plating layer may be in a range of 3 to 20 μm.
In the embodiment of the application, the surface coating of the continuous hot-dip galvanized high-strength steel has the function of improving the corrosion resistance of the steel plate. The surface zinc coating has a sacrificial anode protection effect, and an anode reaction is easy to occur in the corrosion process, so that the anode reaction of the steel plate is prevented. The coating thickness cannot be too thin. However, if the coating layer is too thick, a large amount of liquid zinc is likely to appear in the welding, so that the liquid zinc is likely to be present in the embodiment of the present application, and in the continuous hot dip galvanizing coating layer, Al element can improve the adhesion between the coating layer and the steel plate and improve the corrosion resistance of the coating layer. However, too much Al element causes brittleness of the plating layer, and is not suitable for press forming of automobile parts. In addition, the addition of Al element can also reduce the melting point of the coating, so that the coating is easier to melt in welding, and the brittleness of liquid metal is improved. Therefore, the Al element content is in the range of 0.2 to 2%. In addition, the corrosion resistance of the coating can be further improved by adding the Mg element, meanwhile, the Mg and the Zn can form a high-melting-point compound, the melting of the coating during welding can be hindered to a certain extent, and in addition, a thick oxide film can be formed on the surface of the coating by adding the Mg element, so that even if the coating is melted during welding, the viscosity of the molten coating is also very high, the molten coating is not easy to permeate into a steel plate grain boundary, and the brittleness of liquid metal is reduced. However, the addition of Mg also reduces the melting point of the plating layer, so that the plating layer is easier to melt in welding, and the brittleness of liquid metal is improved. Therefore, the Mg element content is in the range of 0 to 1.5%.
In the embodiment of the present application, there is provided a method for manufacturing a continuous hot-dip galvanized high-strength steel sheet, as shown in fig. 1, the method including the steps of:
s1, obtaining chemical components of the steel plate, and processing to obtain the steel plate;
s2, carrying out heat treatment on the steel plate to obtain a heat-treated steel plate;
s3, obtaining chemical components of the zinc alloy coating to obtain an alloy plating solution;
s4, carrying out first heating on the alloy plating solution to obtain a preheated plating solution;
s5, immersing the heat-treated steel plate into the preheating plating solution to obtain a steel plate with a plating layer;
s6, carrying out first cooling on the steel plate with the coating to obtain a hot-dip galvanized high-strength steel plate.
As an alternative embodiment, the temperature of the pre-heated plating solution may be 440-480 ℃.
In the embodiment of the application, the steps are as follows: obtaining chemical components of the steel plate, and processing to obtain the steel plate; carrying out heat treatment on the steel plate to obtain a heat-treated steel plate; and the steps of: obtaining chemical components of the zinc alloy coating to obtain alloy plating solution;
and carrying out first heating on the alloy plating solution to obtain a preheated plating solution. The sequence of the two is not limited, and any implementation mode can be adopted to achieve the purpose of the invention.
In the present embodiment, preheating the plating solution is necessary because the plating solution solidifies if the temperature is too low: too low a temperature of the plating solution causes the plating solution to solidify too fast during cooling, resulting in a part of aluminum forming a fine supersaturated aluminum-rich phase in the plating layer, thereby impairing the reaction between aluminum and the steel sheet, resulting in a decrease in the adhesion between the plating layer and the steel sheet. Therefore, the lowest temperature of the plating solution temperature cannot be less than 440 DEG C
In the embodiment of the application, the temperature of the plating solution cannot be too high: in the high-temperature plating solution of the steel plate, Fe element in the steel plate can rapidly react with alloy elements in the plating solution to form coarse compound particles, so that the toughness of the plating layer is deteriorated, the adhesion of the plating layer is reduced, and the temperature of the plating solution is required to be less than or equal to 480 ℃.
As an alternative embodiment, the difference between the temperature of the steel plate after the heat treatment and the temperature of the preheated plating solution is less than or equal to 10 ℃.
In the examples of the present application, the temperature of the high-strength steel after the heat treatment cannot be too high or too low. If the temperature is too high and is much higher than the temperature of the plating solution, the high-strength steel reacts violently with Al element in the plating solution during hot dipping to form a coarse and irregular interface compound layer. Such an irregular compound layer causes unstable adhesion between the plating layer and the steel sheet, and partially causes dezincification during forming. If the temperature is too low and is far lower than the temperature of the plating solution, the reaction between the high-strength steel and Al element in the plating solution is insufficient during hot dip plating, a continuous and compact compound interface layer cannot be formed to cover the surface of the steel plate, and the adhesion between the plating layer and the steel plate is too poor, so that dezincification during stamping is easily caused. Therefore, the difference between the temperature of the steel plate after heat treatment and the temperature of the plating solution is required to be less than or equal to 10 ℃.
As an alternative embodiment, the heat treatment comprises in sequence: second heating, heat preservation and second cooling; the temperature of the second heating is 700-900 ℃.
As an alternative embodiment, in the second heating, the dew point temperature is ≦ -40 ℃ when the temperature of the steel sheet is <600 ℃ and > 800 ℃; when the temperature of the steel plate is 600-800 ℃, the dew point temperature is 20-50 ℃.
In the embodiment of the application, the high-strength steel is heated, and the carbon in the surface layer of the high-strength steel can be volatilized by controlling the heating temperature and the atmosphere dew point temperature in different heating stages, and meanwhile, a layer of iron oxide is formed on the surface of the steel plate, so that elements such as Si, Mn and Cr in the high-strength steel are prevented from being precipitated on the surface of the steel plate. Generally, the formation temperature of iron oxides needs to exceed 600 ℃ and the required dew point temperature exceeds 0 ℃. When the heating temperature exceeds 600 ℃, the oxygen content in the atmosphere can be increased by increasing the dew point temperature of the atmosphere, so that obvious iron oxide is formed on the surface, and part of carbon in the surface layer is formed into carbon monoxide to volatilize, namely the surface layer is decarburized. It is noted that if the dew point temperature is too high, iron oxides are rapidly formed, which in turn may hinder decarburization of the surface layer, which is detrimental to the brittleness of the liquid metal. However, if the dew point temperature is less than 20 ℃ but exceeds 0 ℃, it may result in difficulty in forming a continuous iron oxide layer, thereby decarburizing too much in the steel sheet to deteriorate the tensile strength of the high-strength steel, and may cause coarsening of grains in the surface layer, so that it may be difficult to form a sufficient core for nucleation of the plating layer on the surface of the steel sheet at the time of hot dip plating, thereby impairing the adhesion of the plating layer to the steel sheet. If the dew point temperature is too low and is lower than 0 ℃, an iron oxide layer and surface decarburization cannot be formed, so that more alloy elements are enriched on the surface, and the brittleness of the liquid metal is deteriorated. Therefore, dew point temperatures in the range of 20-50 ℃ are required. Meanwhile, if the final heating temperature exceeds 900 ℃, the iron oxide on the surface can be thickened obviously and is difficult to be reduced subsequently, and the crystal grains on the surface layer can be increased obviously, so that the coating adhesiveness is reduced obviously.
In the embodiment of the application, when the temperature exceeds 800 ℃, the atmosphere dew point temperature needs to be quickly reduced, otherwise, the iron oxide on the surface can be quickly thickened, and cannot be reduced by reducing the dew point temperature in the subsequent heat treatment process, so that the coating adhesion is reduced, and the dew point temperature is required to be less than or equal to 40 ℃.
In the embodiment of the present application, when the heating temperature is less than 600 ℃, the increase of the atmosphere dew point temperature does not form oxides of surface iron, but causes severe decarburization of the surface, resulting in insufficient carbon in the surface layer, deteriorating the tensile strength of high-strength steel, and causing coarse grains in the surface layer, making it difficult to form a sufficient core of a plated layer on the surface of a steel sheet during hot dip plating, thereby weakening the adhesion of the plated layer to the steel sheet.
As an alternative embodiment, the holding time may be 60 to 120 seconds, and the atmosphere of the holding includes: the dew point temperature is less than or equal to-40 ℃, and the mass fraction of hydrogen is more than or equal to 1%.
In the heat preservation process, the lower dew point temperature and more than or equal to 1 percent of hydrogen are used, so that the iron oxide on the surface can be reduced into iron. In order to sufficiently reduce iron oxides, a certain time and a certain hydrogen content are required. The invention requires the time of the heat preservation section to be not less than 60 seconds, and the hydrogen content is not less than 1 percent. Otherwise, some iron oxide remains on the surface, which causes the adhesion of the zinc coating to be reduced. If the holding period is too long, the alloy elements in the steel plate will diffuse into the reduced iron, so that the content of the alloy elements in the surface layer of the steel plate is increased, and the effect of weakening the brittleness of the liquid metal cannot be achieved. The holding period does not exceed 120 seconds. The lower dew point temperature of the incubation ensures that iron oxides can be reduced to iron. If the dew point temperature is too high, iron oxides are not sufficiently reduced to iron, and also more alloying elements are concentrated on the surface of the steel sheet, resulting in a failure to impair the brittleness of the liquid metal.
In this embodiment, no oxidizing medium, such as water, carbon dioxide, oxygen, etc., is used in the second cooling process. It is necessary to avoid oxidation of the high-strength steel sheet, thereby deteriorating hot-dip galvanization of the high-strength steel and causing a decrease in the adhesiveness of the hot-dip plated layer, so that oxidizing media including water, carbon dioxide, oxygen, etc. cannot be used.
Hereinafter, the superiority of the present invention will be compared by different examples and comparative examples.
The characteristics of the plating layers are shown in table 1, and the preparation processes are shown in table 2. The Ni element depth is measured by glow discharge spectroscopy, and the position where the Ni element content is reduced to 37% of the maximum value in the glow spectrum is used as the Ni element distribution depth. [ C }/C, [ Mn ]/Mn, [ Si ]// Si, and [ Cr ]/Cr represent mass fraction ratios of chemical components of the surface layer to chemical components of the steel sheet.
Table 1 coating characteristics table.
Table 2 a table of process parameters was prepared.
The hot dip galvanized high strength steel prepared according to the process parameters in the above examples and comparative examples was evaluated for plating adhesion and liquid metal brittleness. And bending the hot-dip galvanized high-strength steel by 180 degrees, wherein the bending radius is the same as the thickness of the steel plate, and then observing whether the coating at the bent outer edge is peeled off. If peeling occurred, it was X, and peeling did not occur, it was O. The hot dip galvanized high strength steel is heated to 1000 ℃ at a speed of 20K/s, is kept warm for 20 seconds, is subjected to tensile deformation of 20% during the heat preservation, has a deformation rate of 0.1/s, and is then rapidly cooled to room temperature. And observing and measuring cracks appearing on the surface layer of the high-strength steel plate, measuring the density of the cracks and measuring the maximum depth of the cracks.
Table 3 results of the plating at the bent outer edge.
In the third table, the bending test was performed on the examples, and the plating layer on the outer edge did not peel off, while the plating layer on the outer edge of the comparative example did peel off, and the crack density was small in the examples, the crack density in the comparative example is high, the total crack depth of the example is far less than that of the comparative example, the micro cracks in the example do not influence the quality of the steel, negligible, schematic cross-sectional structures of examples and comparative examples are shown in fig. 2 and 3, illustrating that the mass fraction ratio of the chemical composition of the surface layer of the examples to that of the steel sheet is controlled, so that the austenitizing temperature of the surface layer is significantly increased in the examples, therefore, the surface layer can keep a ferrite state in the welding process, austenite transformation is not carried out, the brittleness of liquid metal in the embodiment is improved, cracks are avoided, and the technical problem that deep cracks are easy to appear on the surface of a steel plate of hot-dip galvanized high-strength steel during welding is solved.
It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The foregoing are merely exemplary embodiments of the present invention, which enable those skilled in the art to understand or practice the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A continuous hot dip galvanized high strength steel sheet characterized by comprising, in mass fraction: c: 0.1-0.3%, Mn: 0.5-3%, Si: 0.2-1%, Cr: 0.1-0.6%, the balance being Fe and inevitable impurity elements;
the steel plate comprises a surface layer and an intermediate layer, wherein the mass fraction ratio of the chemical components of the surface layer to the chemical components of the steel plate comprises: c is less than or equal to 0.5, Mn is less than or equal to 0.3, Si is less than or equal to 0.3, and Cr is less than or equal to 0.8.
2. The steel plate of claim 1, wherein the thickness of the surface layer is less than or equal to 1 micron; the mass fraction ratio of the chemical components of the surface layer to the chemical components of the steel plate is as follows: c is more than or equal to 0.3 and less than or equal to 0.5.
3. The steel sheet according to claim 1, wherein the surface layer of the steel sheet further comprises a zinc alloy plating layer having a thickness in a range of 3 to 20 μm.
4. The steel sheet according to claim 1, wherein the chemical composition of the zinc alloy plating layer comprises, in mass fraction: al: 0.2-2%, Mg: 0 to 1.5 percent, and the balance of Zn and inevitable impurity elements.
5. A method of manufacturing a continuous hot-dip galvanized high-strength steel sheet according to any one of claims 1 to 4, the method comprising:
obtaining chemical components of the steel plate, and processing to obtain the steel plate;
carrying out heat treatment on the steel plate to obtain a heat-treated steel plate;
obtaining chemical components of the zinc alloy coating to obtain alloy plating solution;
carrying out first heating on the alloy plating solution to obtain a preheated plating solution;
immersing the heat-treated steel plate into the preheating plating solution to obtain a steel plate with a plating layer;
and carrying out primary cooling on the steel plate with the coating to obtain a hot-dip galvanized high-strength steel plate.
6. The method for manufacturing a continuous hot-dip galvanized high-strength steel sheet according to claim 4, wherein the temperature of the preheated bath is 440-480 ℃.
7. The method of manufacturing a continuous hot-dip galvanized high-strength steel sheet according to claim 4, wherein the difference between the temperature of the steel sheet after the heat treatment and the temperature of the preheated bath is 10 ℃ or less.
8. The method of manufacturing a continuous hot-dip galvanized high-strength steel sheet according to claim 4, wherein the heat treatment sequentially includes: second heating, heat preservation and second cooling; the end temperature of the second heating is 700-900 ℃.
9. The method of manufacturing a continuous hot-dip galvanized high-strength steel sheet according to claim 8, wherein, in the second heating, when the temperature of the steel sheet is <600 ℃ and > 800 ℃, the dew-point temperature is ≦ 40 ℃; when the temperature of the steel plate is 600-800 ℃, the dew point temperature is 20-50 ℃.
10. The method of claim 8, wherein the maintaining time is 60-120 seconds, and the maintaining atmosphere comprises: the dew point temperature is less than or equal to-40 ℃, and the mass fraction of hydrogen is more than or equal to 1%.
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