CN111850262A - Production method of ultra-low carbon baking hardening continuous hot-dip galvanized steel sheet - Google Patents
Production method of ultra-low carbon baking hardening continuous hot-dip galvanized steel sheet Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
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- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/54—Furnaces for treating strips or wire
- C21D9/56—Continuous furnaces for strip or wire
- C21D9/561—Continuous furnaces for strip or wire with a controlled atmosphere or vacuum
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- 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/54—Furnaces for treating strips or wire
- C21D9/56—Continuous furnaces for strip or wire
- C21D9/573—Continuous furnaces for strip or wire with cooling
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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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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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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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
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/10—Oxidising
- C23C8/12—Oxidising using elemental oxygen or ozone
- C23C8/14—Oxidising of ferrous surfaces
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- C—CHEMISTRY; METALLURGY
- 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
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/10—Oxidising
- C23C8/16—Oxidising using oxygen-containing compounds, e.g. water, carbon dioxide
- C23C8/18—Oxidising of ferrous surfaces
Abstract
A method for producing ultra-low carbon baking-hardened continuous hot-dip galvanized steel sheet is characterized in that a carbon oxidation control device is additionally arranged in a vertical continuous heating furnace on a continuous hot-dip galvanizing production line, air or oxygen is mixed into nitrogen, the surface of the steel sheet in the annealing process is sprayed through the carbon oxidation control device, the surface of the steel sheet is subjected to controlled decarburization and controlled oxidation, and the oxidized surface of the steel sheet is reduced into carbon-poor sponge iron by hydrogen in basic protective atmosphere in subsequent soaking and cooling sections. The invention changes the local atmosphere state by blowing air or oxygen to the surface of the steel plate in the annealing process through the decarburization oxidation device. So that the original reducing atmosphere is changed into a slight oxidizing atmosphere in a certain furnace section area, and under the action of temperature, carbon on the surface of the steel plate is subjected to oxidation reaction to generate C2The O gas is separated from the steel plate, so that the free carbon content of the surface of the steel plate is adjusted, a carbon-poor layer with a certain thickness is obtained, and the aim of improving the aging resistance of the steel plate is fulfilled.
Description
Technical Field
The invention relates to the field of metallurgy-metal material processing, in particular to a production method of an ultra-low carbon baking hardening continuous hot galvanized steel plate. The product is applied to an automobile outer cover.
Background
The ultra-low carbon bake-hardening steel is a high-quality automobile steel plate which has lower yield strength before stamping forming, and the yield strength can be improved to a certain extent after stamping forming and baking finish temperature aging treatment, and is mainly used for automobile outer plates. The product is characterized in that: the organic combination of the strength, the deep drawing performance and the anti-sinking performance of the part is realized. Meanwhile, the product has the disadvantage that if the aging index (AI value > 30MPa) or the bake hardening value (BH2) is more than 50MPa, the storage time is less than three months, and orange peel stamping or cracking is easily caused when stamping is performed again. The essential reason for this defect is that the product contains a large amount of free carbon and nitrogen, and C, N atoms dissolved in the ferrite precipitate from the ferrite lattice under the action of both time and temperature, which causes a certain degree of change in mechanical properties such as tensile strength and yield strength. We want the lower this change at room temperature the better; the larger the change after stamping, the better, namely, the better the processing performance and the using performance by utilizing the characteristics of lower yield strength during stamping and higher yield strength during baking finish.
Bake hardenability, BH, (i.e., Bake Hardening adhesiveness) means that the steel sheet has a low yield strength in a supply state after annealing, hot galvanizing and flattening, and is suitable for stamping; the yield strength of the stamping part is improved within a certain range under the influence of temperature in the subsequent painting and baking process, and the improved value is called a baking hardening value, namely a BH value for short. The bake-hardening value is obtained on the premise that the steel contains a certain amount of free carbon.
Since the steel grade also undergoes mechanical property changes under natural temperature conditions, which are factors that are not favorable for maintaining its workability, the changes are controlled to the minimum extent possible. To assess this property, it is called aging resistance. For the aging resistance, the aging resistance at room temperature of the bake-hardened steel sheet is generally measured by the length of aging resistance or the aging index AI value.
The BH value is measured under the conditions that the prestretching strain amount is 2 percent and the aging condition is 170 ℃ for 20 minutes; the pre-stretching strain of AI value is 8%, the aging condition is 100 ℃, l hour.
The BH value and the AI value are similar in evaluation method and value, generally the BH value is high, and the AI value is inevitably high. And AI values are always less than BH values.
C, N atoms are mostly separated along dislocation in the natural aging process, if crystal lattices contain excessive free carbon or nitrogen, the aging process has short time which is not enough to meet the requirement of the turnover process, and the processing performance is influenced because the mechanical performance is deteriorated in the stamping process; in addition to affecting the mechanical properties, the surface quality of the stamping is sometimes affected by the formation of "kosher gas clusters".
Because of the characteristics of the aged steel, the advantages of the aged steel are utilized as much as possible, and the defects of the aged steel are avoided. The aging-resistant hot-dip galvanized bake-hardened steel or the manufacturing method for improving the aging resistance is developed, the storage period is strived for to be as long as possible, and the method has important economic benefits and social benefits.
The development of the bake-hardened steel plate in China goes through three stages. It can also be said that it is produced by three methods. In the first stage, the aluminum killed steel added with phosphorus is adopted for production; in the second stage, low-carbon aluminum killed steel is adopted for production; the third stage is to produce a bake-hardened steel sheet from a microalloyed steel with an ultra-low carbon content with a suitable control of the amount of free carbon, the steel sheet having properties that are better than the first two in resistance to natural aging. Research and development of zinc-coated bake-hardened steel sheets are hot issues in recent years, and a great deal of research work has been conducted on the aspects of the zinc coating process and the properties of the base metal and the coating metal. A systematic comparison of the components and processes of the low-carbon and ultra-low-carbon bake-hardening steel sheets for producing the hot-dip galvanized bake-hardening steel sheets by pincfler et al is carried out, and the hot-dip galvanized bake-hardening steel sheets produced by the ultra-low-carbon bake-hardening steel sheets are considered to have mechanical properties superior to those of the first two stages. At present, bake hardening hot-dip galvanized steel sheets for automobiles are produced at home and abroad by controlling aging by adding a certain amount of microalloy elements of strong carbon and nitride, such as niobium, titanium or vanadium, to ultra-low carbon steel, forming carbon and nitrogen compounds from the elements, and neutralizing excess free carbon and nitrogen. In addition to the above conditions, some manufacturers adjusted the pyrolysis amount of NbC by the annealing temperature to obtain an appropriate amount of free carbon.
For slow aging ultra low carbon microalloyed bake hardened steel sheet, the number of solid solution atoms is controlled by the ratio of the microalloying element Ti or (and) Nb to atoms such as C, N and S. However, in steel making, there is a certain amount of fluctuation in the composition of each alloy. Since the elements fluctuate, the proportional relationship between them is not well controlled, and thus the aging resistance is not well controlled. In production practice, this often occurs. In the prior art, the carbon content in the steel is difficult to accurately control in a small range. The contents of niobium and titanium can not be determined accurately. In this state, the resulting product has either an excessively high bake hardening value or a poor aging resistance; if not, the baking hardening value is ultralow and does not reach the standard. Even in a well-matched state, the aging resistance is maintained at about three months. In summer, the probability of problems is greater due to the heat of the day.
In order to solve the problem, a great deal of research is carried out, but most of the research focuses on how to detect the alloy elements more accurately; how to accurately realize the proportional relation of alloy components; how to control the presence of excess (or deficiency) elements during the manufacturing process; at present, the technical conditions limit the effects of the efforts and the market requirements are not met.
Disclosure of Invention
The invention aims to provide a method for producing an ultra-low carbon bake-hardening continuous hot-dip galvanized steel sheet, which can produce an aging-resistant ultra-low carbon hot-dip galvanized bake-hardening steel sheet with good processing performance and service performance, and the aging resistance of the steel sheet exceeds six months.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for producing ultra-low carbon baking-hardened continuous hot-dip galvanized steel sheet is characterized in that a carbon oxidation control device is additionally arranged in a vertical continuous heating furnace on a continuous hot-dip galvanizing production line, air or oxygen is mixed into nitrogen, the surface of the steel sheet in the annealing process is sprayed through the carbon oxidation control device, the surface of the steel sheet is subjected to controlled decarburization and controlled oxidation, and the oxidized surface of the steel sheet is reduced into carbon-poor sponge iron by hydrogen in basic protective atmosphere in subsequent soaking and cooling sections.
The air flow is controlled to be 0-15m3The dew point of the local area sprayed in the furnace is controlled at 0- (-45) DEG C, and the preheating temperature of the steel plate when air is sprayed is 200-900 ℃.
The oxygen flow is controlled to be 0-3m3The dew point of the local area sprayed in the furnace is controlled at 0- (-45) DEG C, and the preheating temperature of the steel plate when oxygen is sprayed is 200-900 ℃.
The basic protective atmosphere in the vertical continuous heating furnace is protective gas consisting of nitrogen, hydrogen accounting for 4-6% of the total gas volume content and a small amount of impurities.
The aging resistance of the ultra-low carbon baking-hardened continuous hot-dip galvanized steel sheet exceeds six months.
The carbon control oxidation device comprises two groups of spray pipes and an input main pipeline which are arranged oppositely, the two groups of spray pipes are communicated with the input main pipeline, a steel plate passes through the two groups of spray pipes, and a gap is formed in one side, opposite to the steel plate channel, of the two groups of spray pipes.
The spray pipe is of an inner-layer and outer-layer casing pipe structure, gaps or through holes are uniformly distributed in the inner pipe, a supporting and positioning plate is arranged between the inner pipe and the outer pipe, the supporting and positioning plate is provided with the through holes, and the inner pipe is communicated with the input main pipeline.
Compared with the prior art, the invention has the beneficial effects that:
1) the invention sprays mixed gas of nitrogen and air (or oxygen) on the surface of the steel plate in the annealing process through the carbon-control oxidation device, thereby changing the local atmosphere state. So that the original reducing atmosphere is changed into a slight oxidizing atmosphere in a certain furnace section area, and under the action of temperature, carbon on the surface of the steel plate is subjected to oxidation reaction to generate C2The O gas is separated from the steel plate, so that the free carbon content of the surface of the steel plate is adjusted, a carbon-poor layer with a certain thickness is obtained, and the aim of improving the aging resistance of the steel plate is fulfilled.
2) Under the action of the gas circulation rule in the furnace, the furnace areas of the heating section and the subsequent soaking section, the heat preservation section, the cooling section and the like still adopt the nitrogen-hydrogen-based reducing atmosphere, so that the iron oxide on the surface of the steel strip is reduced into carbon-poor sponge iron after the steel strip enters the area, and the hot galvanizing is facilitated.
Drawings
FIG. 1 is a schematic representation of a carbon control oxidation apparatus of the present invention.
FIG. 2 is a production flow diagram of the present invention.
In the figure: 1-supporting positioning plate, 2-inner pipe, 3-outer pipe, 4-input main pipe, 5-inlet, 6-valve, 7-flowmeter and 8-corrugated pipe.
Detailed Description
The present invention will be described in detail below, but the scope of the present invention is not limited to the following embodiments.
A method for producing ultra-low carbon baking-hardened continuous hot-dip galvanized steel sheet is characterized in that a carbon oxidation control device is additionally arranged in a vertical continuous heating furnace on a continuous hot-dip galvanizing production line, air or oxygen is mixed into nitrogen, the surface of the steel sheet in the annealing process is sprayed through the carbon oxidation control device, the surface of the steel sheet is subjected to controlled decarburization and controlled oxidation, and the oxidized surface of the steel sheet is reduced into carbon-poor sponge iron by hydrogen in basic protective atmosphere in subsequent soaking and cooling sections. The method is used for adjusting the free carbon content of the steel plate and obtaining a carbon-poor layer with a certain thickness, thereby achieving the purpose of improving the aging resistance.
The air flow is controlled to be 0-15m3The dew point of the local area sprayed in the furnace is controlled at 0- (-45) DEG C, and the preheating temperature of the steel plate when air is sprayed is 200-900 ℃.
The oxygen flow is controlled to be 0-3m3The dew point of the local area sprayed in the furnace is controlled at 0- (-45) DEG C, and the preheating temperature of the steel plate when oxygen is sprayed is 200-900 ℃.
The basic protective atmosphere in the vertical continuous heating furnace is protective gas consisting of nitrogen, hydrogen accounting for 4-6% of the total gas volume content and a small amount of impurities.
The aging resistance of the ultra-low carbon bake-hardening continuous hot-dip galvanized steel sheet is more than six months, and the mechanical property is still within the standard requirement range.
As shown in fig. 1, the carbon oxidation control device comprises two groups of nozzles and an input main pipeline 4 which are arranged oppositely, the two groups of nozzles are communicated with the input main pipeline 4, a steel plate passes through the two groups of nozzles, and a gap is arranged at one side of the two groups of nozzles, which is opposite to the steel plate channel.
The nitrogen-air (or oxygen) mixture is blown to the surface of the steel strip preheated to 200 to 900 c through the slits of the nozzles parallel to both sides of the steel strip. Oxygen in the mixed gas can react with hydrogen in the furnace, carbon element in the steel plate and iron element on the surface of the steel plate The element undergoes an oxidation reaction. CO produced by reaction of carbon with an oxidizing atmosphere2The gas escapes from the steel plate, thereby reducing the amount of free carbon. At the same time, the oxidizing atmosphere also causes an oxidation reaction with iron of the steel sheet to produce iron oxide series. Respectively generate Fe according to different concentrations of oxidizing atmosphere2O3；Fe3O4(ii) a FeO; the iron oxide is reduced by hydrogen in the protective gas in the subsequent process in the heating furnace to become sponge iron. Sponge iron is a carbon-poor layer. The carbon-poor layer thickness varies with the degree of oxidation. Due to the presence of the carbon-poor layer, a space is reserved for carbon diffusion in the underburized portion deep in the steel sheet.
The spray tube is two-layer sleeve structure inside and outside, and the equipartition has gap or through-hole on inner tube 2, is equipped with between inner tube 2 and outer tube 3 and supports locating plate 1 be equipped with the through-hole on supporting locating plate 1, inner tube 2 and input main pipeline 4 intercommunication. The mixed gas enters the inner pipe 2 from the input main pipeline 4, uniformly fills an interlayer between the inner pipe 2 and the outer pipe 3 through uniformly distributed gaps or through holes on the inner pipe 2, and is sprayed to the surface of the steel plate through the gaps on the outer pipe 3. The corrugated pipe 8 is arranged at the joint of the inner pipe 2 and the input main pipeline 4 and is used for absorbing the influence of expansion and contraction on size change.
The manufacturing method of the invention aims at the slow aging and ultra-low carbon bake hardening hot galvanized steel sheet required by various standards. The main components of the steel grade related to the invention are shown in the table 1.
Table 1: the invention is applicable to steel grade components (the balance being iron and unavoidable impurities).
| C | Si | Mn | P | S | ALs | Nb | Ti | N | |
| MIN | 0.0014 | 0 | 0.10 | 0.005 | 0.000 | 0.030 | 0.001 | 0.002 | 0.00 |
| MAX | 0.0045 | 0.10 | 0.50 | 0.035 | 0.010 | 0.080 | 0.010 | 0.010 | 0.003 |
The production method of the invention is that the steel strip enters a hot galvanizing production line after the conventional steel making, hot rolling and cold rolling, and the steel strip is made into a finished product through the processes of cleaning, heating, cooling, hot galvanizing, cooling, finishing (straightening), curling and rolling, etc. In a continuous annealing furnace, the strip temperature typically varies between room temperature and 900 ℃. Referring to fig. 2, the present invention is to additionally provide a carbon oxidation control device between the preheating zone and the heating zone of the continuous heating furnace, to spray nitrogen-air (or oxygen) mixture gas to the surface of the steel sheet, and to decarburize and oxidize iron on the surface of the steel sheet using the mixture gas of nitrogen and an oxidizing medium. The oxidized surface of the steel plate is reduced into carbon-poor sponge iron by hydrogen in subsequent heating, soaking and cooling sections. The sponge iron state is a well-established surface state suitable for hot galvanizing.
The invention changes the local atmosphere state by the carbon-control oxidation device. So that the original reducing atmosphere is changed into a slightly oxidizing atmosphere in a certain furnace section area. The reaction amount of free carbon in the steel plate, namely the depth of the decarburized layer is different due to different degrees of oxidizing atmosphere; the amount of decarburization and the thickness of the carbon-poor layer determine the aging resistance of the hot-dip galvanized steel sheet.
Under the action of the gas circulation rule in the furnace, the furnace areas of the heating section and the subsequent soaking section, the heat preservation section, the cooling section and the like still adopt the nitrogen-hydrogen-based reducing atmosphere, so that the iron oxide on the surface of the steel strip is reduced into carbon-poor sponge iron after the steel strip enters the area, and the hot galvanizing is facilitated.
The control of the degree of the oxidizing atmosphere in the annealing furnace is realized by two parameters of the flow rate of the input nitrogen-air (or oxygen) mixed gas and the local dew point in the furnace. If the free carbon in the steel sheet is high, the flow rate and dew point are higher. Otherwise, the pressure is lower until no air or oxygen is fed.
Example 1:
the example provides a method for producing an aging-resistant ultra-low carbon bake-hardening hot-dip galvanized steel sheet. The steel coil comprises the following chemical components in percentage by mass: 0.0025 percent of C; 0.20 percent of Mn; si 0.012%; p is 0.011 percent; 0.004 percent of S; als 0.041%; 0.007 percent of Ti; nb 0.0025 percent; 0.0029% of N, and the balance of Fe and inevitable impurities. Hot rolling and cold rolling to a continuous hot galvanizing production line.
And filling nitrogen-hydrogen protective gas in a continuous annealing furnace on a hot galvanizing production line. The annealing process of the cold-rolled steel strip is completed in a preheating section, a heating section, a soaking section and a cooling section of a continuous annealing furnace. A carbon-controlled oxidation device is additionally arranged between the preheating section and the heating section, and nitrogen-air mixed gas with the nitrogen flow of 200m is sprayed on the surface of the steel strip preheated to 200-900 DEG C 3Air flow 1.0 m/hr3Hour/hour, so that the local dew point is controlled at-30 ℃. The steel sheet, which has been heated to a certain degree at this time, is decarburized and oxidized under the action of a large pressure and a large partial pressure of oxygen. The oxidized surface of the steel plate is reduced into sponge iron by high-temperature nitrogen-hydrogen mixed gas in a subsequent heating section, a soaking section and a cooling section, and the sponge iron enters a zinc pot to finish the hot galvanizing process.
The properties of the hot dip galvanized steel sheet treated by the above-mentioned method are shown in Table 2.
Table 2: example 1 Steel sheet Properties
Example 2:
the example provides a method for producing an aging-resistant ultra-low carbon bake-hardening hot-dip galvanized steel sheet. The steel grade comprises the following chemical components in percentage by mass: 0.0029 percent of C; 0.44 percent of Mn; 0.08 percent of Si; p is 0.030%; 0.004 percent of S; als0.043%; 0.007 percent of Ti; 0.003 percent of Nb; 0.002% of N, and the balance of Fe and inevitable impurities. Hot rolling and cold rolling to a continuous hot galvanizing production line.
And filling nitrogen-hydrogen protective gas in a continuous annealing furnace on a hot galvanizing production line. The annealing process of the cold-rolled steel strip is completed in a preheating section, a heating section, a soaking section and a cooling section of a continuous annealing furnace. A carbon-controlled oxidation device between the preheating section and the heating section, and nitrogen-oxygen mixed gas is sprayed on the surface of the steel strip preheated to 200-900 ℃, and the nitrogen flow is controlled at 200m 3The oxygen flow rate is controlled at 0.6 m/hour3Hour/hour, so that the local dew point is controlled at-22 ℃. At this time, the steel sheet is decarburized and oxidized. The oxidized surface of the steel plate is returned in the following heating section-soaking section-cooling sectionAnd (4) feeding the original sponge iron into a zinc pot to finish the hot galvanizing process.
The properties of the hot dip galvanized steel sheet treated by the above-mentioned method are shown in Table 3.
Table 3: example 2 Steel sheet Properties
Comparative example:
this example provides a method for producing a control plate of an ultra-low carbon bake-hardened hot-dip galvanized steel sheet. The steel grade comprises the following chemical components in percentage by mass: c0.0026; 0.42 percent of Mn; 0.08 percent of Si; p0.027%; s0.004; als 0.044%; 0.006 percent of Ti; 0.002% of Nb; 0.002% of N, and the balance of Fe and inevitable impurities. Hot rolling and cold rolling to a continuous hot galvanizing production line.
And filling nitrogen-hydrogen protective gas in a continuous annealing furnace on a hot galvanizing production line. The annealing process of the cold-rolled steel strip is completed in a preheating section, a heating section, a soaking section and a cooling section of a continuous annealing furnace. A carbon control oxidation device is not arranged between the preheating section and the heating section, and the dew point is controlled at-45 ℃. At the moment, the steel plate is subjected to minimum decarburization and oxidation, and then enters a zinc pot to finish the hot galvanizing process. As can be seen from table 4, the steel sheets had poor aging resistance. All indexes in the initial state meet the standard requirements. The same steel coil can not reach the standards when stored for less than three months under natural conditions.
Table 4: comparative example Steel sheet Properties
Unqualified steel coils can crack or have texture that influences the appearance when the punching press.
Claims (7)
1. A production method of an ultra-low carbon baking hardening continuous hot-dip galvanized steel sheet is characterized in that a carbon oxidation control device is additionally arranged in a vertical continuous heating furnace on a continuous hot-dip galvanizing production line, air or oxygen is mixed into nitrogen, the surface of the steel sheet in the annealing process is sprayed through the carbon oxidation control device, the surface of the steel sheet is subjected to controlled decarburization and controlled oxidation, and the oxidized surface of the steel sheet is reduced into carbon-poor sponge iron by hydrogen in basic protective atmosphere in subsequent soaking and cooling sections.
2. The method for producing an ultra-low carbon bake-hardening continuous hot-dip galvanized steel sheet according to claim 1, wherein the air flow rate is controlled to be 0 to 15m3The dew point of the local area sprayed in the furnace is controlled at 0- (-45) DEG C, and the preheating temperature of the steel plate when air is sprayed is 200-900 ℃.
3. The method for producing an ultra-low carbon bake-hardening continuous hot-dip galvanized steel sheet according to claim 1, wherein the oxygen flow rate is controlled to be 0 to 3m3The dew point of the local area sprayed in the furnace is controlled at 0- (-45) DEG C, and the preheating temperature of the steel plate when oxygen is sprayed is 200-900 ℃.
4. The method for producing an ultra-low carbon bake-hardening continuous hot-dip galvanized steel sheet according to claim 1, wherein the basic protective atmosphere in the vertical continuous heating furnace is a protective gas consisting of nitrogen gas, hydrogen gas in an amount of 4-6% by volume of the total gas, and a small amount of impurities.
5. The method for producing an ultra-low carbon bake-hardening continuous hot-dip galvanized steel sheet according to claim 1, wherein the ultra-low carbon bake-hardening continuous hot-dip galvanized steel sheet has an aging resistance of more than six months.
6. The method for producing ultra-low carbon bake-hardening continuous hot-dip galvanized steel sheet according to claim 1, wherein the carbon oxidation control device comprises two groups of opposing nozzles and an input main pipe, the two groups of nozzles are communicated with the input main pipe, the steel sheet passes between the two groups of nozzles, and a gap is formed on the side of the two groups of nozzles opposite to the steel sheet passage.
7. The method for manufacturing ultra-low carbon bake-hardening continuous hot-dip galvanized steel sheet according to claim 1, wherein the spraying pipe has a double-pipe structure with an inner pipe and an outer pipe, the inner pipe is uniformly provided with gaps or through holes, a supporting and positioning plate is arranged between the inner pipe and the outer pipe, the supporting and positioning plate is provided with through holes, and the inner pipe is communicated with the input main pipeline.
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| CN111636031A (en) * | 2020-06-03 | 2020-09-08 | 北京首钢股份有限公司 | Ultra-low carbon bake-hardening steel and production method thereof |
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