CN115058675A - A method for improving the coating quality of hot dip galvanized high-strength steel - Google Patents

Abstract

The invention relates to a method for improving the quality of a hot-dip high-strength steel coating, which comprises the following steps: firstly, preparing a billet according to target components, and rolling the billet into a strip steel; then, on a continuous hot galvanizing production line, the strip steel is firstly heated to a preheating temperature of 600-700 ℃, the heat preservation time is 10-30 s, and the heating atmosphere is O ₂ And N ₂ The dew point of the mixed gas is 0-10 ℃; heating the steel strip to the annealing temperature at the speed of 10K/s, wherein the heat preservation time is 180-300 s, and the annealing atmosphere is N ₂ And H ₂ The dew point of the mixed gas is-30 to-10 ℃; and finally, cooling the strip steel to the temperature of a zinc pot, and immersing the strip steel into a plating solution for hot dipping. The invention adopts a method of controlling different atmospheres and dew point temperatures in the temperature rise stage and the heat preservation stage of the annealing process to generate different oxygen partial pressures so as to generate MnO & Fe on the surface of an annealed steel plate _metall And the layer is easy to react with Al so as to ensure good wettability of the surface of the steel plate and obtain excellent coating quality.

Description

A method for improving the quality of hot dip galvanized high-strength steel coating

technical field

The invention belongs to the field of metal smelting, and relates to a method for improving the quality of a hot-dip plated high-strength steel coating, in particular to a hot-dip plated advanced high-strength medium-manganese steel coated steel sheet and a production method thereof.

Background technique

In recent years, realizing the lightweight and high safety of automobiles is the development trend of the global automobile industry, and high-strength steel (AHSS) is increasingly used in the field of automobile steel. The concept of AHSS is to add Mn and other less noble elements such as Si to steel to achieve the required mechanical properties by expressing a multiphase structure and selectively induced plasticity, the TRIP or TWIP effect. As one of the third-generation advanced high-strength steels (AHSS), medium manganese steel has received extensive attention from researchers due to its high strength and good plasticity. However, the corrosion resistance of bare medium manganese steel is poor. Direct use on the car body will affect the life, beauty and driving safety of the car. Typically, the steel substrate is hot-dip galvanized, and the corrosion chemical potential of zinc in the coating is lower than that of iron, which can provide effective sacrificial anode protection.

However, the steel strip immersed in the zinc solution needs to have good wettability with the zinc solution to form a uniform coating with strong adhesion to the substrate. The surface tension leads to poor wettability, which is prone to leakage plating. In order to adjust the volume fraction of austenite and ensure excellent mechanical properties, considerable alloying elements such as Mn or Si are often added to medium manganese steel. In the annealing process of the continuous hot-dip galvanizing production line, even if the reducing H ₂ +N ₂ gas is introduced into the furnace, there is still a small amount of water vapor and oxygen mixed in it. Although it is not enough to oxidize Fe element, it has a great affinity with oxygen. The alloying elements such as Mn and Si will diffuse and segregate on the surface of the steel sheet and react with oxygen in the annealing atmosphere to form oxides. Subsequently, when the steel strip enters the zinc pot, these oxides have a physical barrier effect on the diffusion of zinc and iron, which makes the wettability of the zinc solution on the surface of the steel plate worse, resulting in leakage plating.

Reaction wettability during hot dip plating refers to the dissolution reaction between the steel surface and aluminum in the hot dip galvanizing solution. A certain amount of Al is added to the zinc pot to form a Fe ₂ Al ₅ interface layer, which inhibits the formation of brittle iron-zinc intermetallic compounds. . In order to eliminate the adverse effect of alloying element preferential oxidation (selective oxidation) of matrix element Fe on the surface wettability of high-strength steel, the currently disclosed solutions mainly include pre-plating metal before annealing, pickling before immersion in plating solution, and controlling annealing atmosphere.

For example, the patent number is: CN 100577843C, the name is: steel strip coating method and the invention patent of the steel strip provided with the coating layer discloses a method for preparing a high-Mn steel metal coating by pre-coating an aluminum layer before annealing, the said The Mn mass percentage of the steel is 6-30%, and the fully covered metal is obtained by applying an aluminum layer (preferably PVD method) to the steel strip before the final annealing, and applying the plating layer to the aluminum layer after the final annealing. coating. The coating prepared by this method has excellent corrosion resistance and excellent weldability, but the efficiency of this pre-plating method is very low, and it is difficult to meet the requirements of continuous industrial production. Not only that, the hardware investment of pre-plating equipment will also be very high.

For example, the patent number is CN 108929992A, the name is: a kind of hot-dip plated medium manganese steel and its manufacturing method The invention patent discloses a method for preparing hot-dip plated medium manganese steel by pickling before plating, the medium manganese steel The mass percentages of Mn and Si are 5 to 12% and 0.1 to 2.0%, respectively. After primary annealing and pickling, hot dip galvanizing is performed after secondary annealing, which has excellent surface quality and good coating adhesion. Medium manganese steel. The key to this method is to perform primary annealing and pickling on the continuous annealing production line, and then perform secondary annealing and hot dip plating on the continuous hot-dip galvanizing production line. Adding to the complexity of the pickling section equipment, coiling, transporting and re-uncoiling the strip on multiple production lines still greatly increases the cost of production.

For example, the patent number is: CN106854747B, the name is: a method for preparing zinc-containing Al ₂ O ₃ and SiO ₂ thin films on the surface of Fe-based materials in a low dew point environment The invention patent discloses a method to obtain Fe-based materials by controlling the atmosphere in the furnace The preparation method of the Zn-containing oxide film on the surface of the alloy is characterized in that by heating the mixed powder of Zn and ZnO in a furnace, a constant low oxygen pressure is generated in the confined space, so that the oxide containing metal Zn is generated on the surface of the Fe-based material material film. The metal oxide film obtained by this method can improve the corrosion resistance of Fe-based materials, but the production conditions are very harsh and cannot meet the requirements of industrial production.

To sum up, the above-mentioned methods all have the problems of high input cost and difficult production process. Therefore, if an economical method for producing hot-dip plated medium-manganese steel with excellent surface quality and coating adhesion can be provided, it will be of great significance to promote the industrial application of medium-manganese steel and reduce the weight of automobiles.

SUMMARY OF THE INVENTION

In view of the shortcomings and deficiencies of the above-mentioned prior art, the present invention provides a method for improving the coating quality of hot-dip galvanized high-strength steel, and adopts a method of controlling the different atmospheres and dew point temperatures of the heating stage and the holding stage of the annealing process to generate different oxygen partial pressures, A MnO·Fe _metall layer is formed on the surface of the annealed steel sheet, which is easy to react with Al to ensure good wettability of the steel sheet surface and obtain excellent coating quality. The method does not require additional production equipment and technology, and has low operation difficulty and low cost.

The specific plans are as follows:

A method for improving the quality of hot dip galvanized high-strength steel coating, comprising the following steps:

S1, prepare steel billets according to the target composition, and roll the steel billets into strip steel;

S2. On the continuous hot-dip galvanizing production line, first heat the strip to a preheating temperature, the preheating temperature is 600-700°C, the holding time is 10-30s, and the heating atmosphere is a mixed gas of O ₂ and N ₂ , the dew point is 0～10℃; then the steel strip is heated to the annealing temperature at a speed of 10K/s, the holding time is 180～300s, the annealing atmosphere is a mixed gas of H ₂ and N ₂ , and the dew point is -30～-10 °C;

S3. After cooling the strip to the temperature of the zinc pot, it is immersed in a plating solution for hot dip plating.

Further, the chemical composition of the strip steel in step S1 is 0.1-0.3% C, 0.5-3% Si, 5-12% Mn, 0-3% Al, < 0.02% P, < 0.02% P, < 0.02%S, <0.005%N, the balance is Fe and inevitable impurities.

Preferably, the rolling method of the strip steel in step S1 is cold rolling. Preferably, in step S2, the heating atmosphere is a mixed gas of O ₂ and N ₂ , the volume content of O ₂ is 0.5-1%, and the dew point is 5-10° C.; the annealing atmosphere is a mixed gas of H ₂ and N ₂ , H ₂ The volume content is 5~20%, and the dew point is -30~-10℃.

Further, the composition of the plating solution in step S3 is calculated as: 0.5≤Al≤3% by mass percentage, and the balance is Zn and other unavoidable impurities.

The beneficial effects of the present invention are:

①The present invention adopts the method of controlling the different atmospheres and dew point temperatures in the heating stage and the heat preservation stage of the annealing process to generate different oxygen partial pressures, so that a MnO·Fe _metall layer is formed on the surface of the annealed steel sheet, which is easy to react with Al to ensure good wetting of the steel sheet surface. to obtain excellent coating quality.

②Compared with the prior art, the method of the present invention has low energy consumption, low pollution and low cost.

③ The method of the present invention does not require additional production equipment and processes, has low operational difficulty and high yield, and is of great significance to promoting the industrial application of medium manganese steel and reducing the weight of automobiles.

Description of drawings

Fig. 1 is the surface morphology of high-strength steel after hot-dip plating by the method described in Comparative Example 1.

FIG. 2 shows the surface morphology of the high-strength steel after hot-dip plating by the method described in Example 1. FIG.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Unless otherwise specified, all terms used in the specification have the meanings commonly understood by those skilled in the art. Well-known functions or constructions are not described in detail for brevity and/or clarity.

The test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial sources unless otherwise specified.

First, the components prepared by cold rolling process are (by mass percentage): C: 0.1-0.3%, Si: 0.5-3%, Mn: 5-12%, Al: 0-3%, P<0.02%, S< 0.02%, N < 0.005%, the balance is Fe and unavoidable impurities.

Then, on a continuous hot dip coating production line, the strip steel is first heated to a preheating temperature of 600-700° C., the holding time is 10-30 s, the heating atmosphere is a mixed gas of O ₂ and N ₂ , and the volume fraction of O ₂ is 0.5～1%, the dew point is 0～10℃; then the steel strip is heated to the annealing temperature, the holding time is 180～300s, the annealing atmosphere is a mixed gas of H ₂ and N ₂ , and the volume fraction of H ₂ is 5～20%, The dew point is -30～-10℃.

Next, after cooling the strip steel to the temperature of the zinc pot, it is immersed in a plating solution of 0.5≤Al≤3% (by mass percentage), and the remainder is Zn and other inevitable impurities for hot dip plating That's it.

It should be noted that the above method only limits the core parameters in the preparation process, and the method also includes the conventional steps in casting, cold rolling and hot dip plating, and the process steps are performed in the manner disclosed in the prior art, To meet the process requirements can be.

The following will be further elaborated in conjunction with the following examples and comparative examples.

Example 1

(1) The components prepared by cold rolling process are (by mass percentage): C: 0.1-0.3%, Si: 0.5-3%, Mn: 5-12%, Al: 0-3%, P<0.02%, S <0.02%, N<0.005%, the balance is Fe and unavoidable impurities in strip steel.

(2) On the continuous hot-dip coating production line, the strip steel is preheated to 600°C, the holding time is 20s, the heating atmosphere is a mixed gas of 0.8% _O2 and _N2 , and the dew point is 10°C; Heating at a rate of 10K/s to the annealing temperature, the holding time is 220s, the annealing atmosphere is a mixed gas of 5% _H2 and _N2 , and the dew point is -10 °C.

(3) After cooling the strip steel to the temperature of the zinc pot, immerse it in a plating solution of 2% Al by mass percentage, and the remainder is Zn and other unavoidable impurities to carry out hot dip plating.

Examples 2 to 3

The methods of Examples 2 to 3 are basically the same as those of Example 1, except that the volume fraction of O ₂ in the heating atmosphere is 0.5% and 1%, respectively.

Examples 4 to 5

The methods of Examples 4 to 5 are basically the same as those of Example 3, except that the preheating temperatures are 650°C and 700°C, respectively.

Examples 6 to 7

The methods of Examples 6 to 7 are basically the same as those of Example 3, except that the dew point temperatures during the heating process are 0°C and 5°C, respectively; and the holding times are 10s and 30s, respectively.

Examples 8 to 9

The methods of Examples 8 to 9 are basically the same as those of Example 3, except that the volume fraction of _H2 in the annealing atmosphere is 10% and 20%, respectively, the dew point temperature is -20°C and -30°C, and the holding time is 180s, respectively. and 300s.

Comparative Example 1

(1) The components prepared by cold rolling process are (by mass percentage): C: 0.1-0.3%, Si: 0.5-3%, Mn: 5-12%, Al: 0-3%, P<0.02%, S <0.02%, N<0.005%, the balance is Fe and unavoidable impurities in strip steel.

(2) The steel strip is heated to the annealing temperature at a rate of 10K/s, the holding time is 220s, the annealing atmosphere is a mixed gas of 5% _H2 and _N2 , and the dew point is -10°C.

(3) After cooling the strip steel to the temperature of the zinc pot, immerse it in a plating solution of 2% Al by mass percentage, and the remainder is Zn and other unavoidable impurities to carry out hot dip plating.

test result

The surface morphology of the high-strength steel prepared by the method of Example and Comparative Example 1 after hot dip plating was observed and compared, and the results are shown in Table (1). wettability for excellent coating quality.

Table 1 embodiment and comparative example 1 method to prepare the high-strength steel surface platability comparison table

○ represents the degree of platability, and the more ○, the better the platability.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be The technical solutions described in the foregoing embodiments are modified, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (5)

1. a method for improving the quality of hot dip galvanized high-strength steel coating, is characterized in that, described method comprises the steps: S1, prepare steel billets according to the target composition, and roll the steel billets into strip steel; S2. On the continuous hot-dip galvanizing production line, first heat the strip to a preheating temperature, the preheating temperature is 600-700°C, the holding time is 10-30s, and the heating atmosphere is a mixed gas of O ₂ and N ₂ , the dew point is 0～10℃; then the steel strip is heated to the annealing temperature at a speed of 10K/s, the holding time is 180～300s, the annealing atmosphere is a mixed gas of H ₂ and N ₂ , and the dew point is -30～-10 °C; S3. After cooling the strip to the temperature of the zinc pot, it is immersed in a plating solution for hot dip plating. 2. The method according to claim 1, wherein the chemical composition of the strip steel in step S1 is 0.1-0.3% C, 0.5-3% Si, 5-12% Mn by mass percentage, 0～3%Al, <0.02%P, <0.02%S, <0.005%N, the balance is Fe and inevitable impurities. 3 . The method according to claim 1 , wherein the rolling method of the strip in step S1 is cold rolling. 4 . 4 . The method according to claim 1 , wherein in step S2, the preheating atmosphere is a mixed gas of O ₂ and N ₂ , the volume content of O ₂ is 0.5-1%, and the dew point is 0-10° C.; the said The annealing atmosphere is a mixed gas of H ₂ and N ₂ , the volume content of H ₂ is 5-20%, and the dew point is -30--10°C. 5 . The method according to claim 1 , wherein the composition of the plating solution in step S3 is calculated as: 0.5≤Al≤3% by mass percentage, and the remainder is Zn and other unavoidable impurities. 6 .

Images