TW201536954A - Hot-dip galvanizing method for silicon-manganese high strength steel - Google Patents

Abstract

The present invention relates to a hot-dip galvanizing method for silicon-manganese high strength steel, the method comprising the steps of: (a) providing a steel material containing silicon and manganese; (b) at the dew point temperature, subjecting the steel material to an annealing step so as to form a ternary silicon-manganese oxide on the steel material surface; (c) after the annealing step, immersing the steel material in an aluminum-containing zinc bath for galvanizing, thus making the ternary silicon-manganese oxide on the steel material surface reduced to form an Fe-Al layer, wherein the coverage rate of the Fe-Al layer is greater than 70%; and (d) taking out the galvanized steel, and removing the excess liquid zinc on the steel material. In this way, it is possible to improve the galvanizing susceptibility of steel and reduce defects generation of uncoated dots.

Description

Method for hot dip galvanizing of bismuth manganese high strength steel

The invention relates to a method for galvanizing steel materials, in particular to a method for hot dip galvanizing of yttrium manganese high strength steel.

In order to cope with the crisis of future oil supply shortage and global warming, reducing the weight of the car body to reduce fuel consumption has become the goal of all car manufacturers. However, in order to simultaneously consider safety, processability and corrosion resistance, the use of advanced high-strength steel (such as duplex steel or phase change induced plastic steel) is an inevitable trend in automobile production.

The basic composition of the conventional phase-induced plasticity steel is iron-0.2% carbon-2% manganese-1.5% bismuth. The high hardening energy provided by carbon and manganese retains a certain proportion of Worthite iron after annealing in the two-phase zone. The ductile iron metamorphosis is further used to further improve the hardening energy of the Worthite iron, so that it is still a metastable phase at room temperature, and can be transformed into a granulated iron during the plastic deformation, and the strain of the phase transformation is transformed into a plastic deformation. The strain required to improve the plasticity of the material. This property is called phase change induced plasticity. The purpose of adding antimony is to prevent the carbide from precipitating when the toughened iron is metamorphosed, resulting in deterioration of ductility and reduction of the stacking energy and providing solid solution strengthening.

However, the conventional phase change induces plastic steel to be alloyed with oxygen, which has a better affinity with oxygen, so that it can be oxidized on the surface of the steel even under the protection of a reducing atmosphere. The surface oxide formed may hinder the formation of the iron-aluminum barrier layer during hot dip galvanizing, so that the zinc liquid lacks sufficient wettability, resulting in poor galvanization or formation of unplated defects.

Therefore, it is necessary to provide an innovative and progressive 矽 manganese high-strength steel hot dip galvanizing The method to solve the above problem.

The invention provides a method for hot dip galvanizing of bismuth manganese high strength steel, comprising the steps of: (a) providing a bismuth manganese-containing steel material; (b) performing an annealing treatment step on the steel material at a dew point temperature, so that The surface of the steel forms a ternary manganese oxide; (c) the annealed steel is immersed in an aluminum-containing zinc bath for galvanizing, and the ternary manganese oxide on the surface of the steel is reduced by aluminum to form an iron An aluminum layer having a coverage of greater than 70%; and (d) removing the galvanized steel and removing excess zinc from the steel.

The invention is annealed at a dew point temperature, which contributes to the formation of ternary lanthanum manganese oxide on the surface of the steel, and hot dip galvanizing in the aluminum bath containing aluminum promotes high coverage of ternary lanthanum manganese oxide reduction. The iron-aluminum layer, which increases the wettability between the steel and the zinc liquid, thereby improving the galvanization of the steel and reducing the occurrence of unplated defects.

The embodiments of the present invention can be more clearly understood, and the objects, features, and advantages of the present invention will become more apparent. The details are as follows.

S11~S14‧‧‧Steps

1 is a flow chart showing a method for hot dip galvanizing of bismuth manganese high strength steel according to the present invention; FIG. 2 is a graph showing a process temperature rise and fall curve of hot dip galvanizing of bismuth manganese high strength steel according to the present invention; The photomicrograph of the appearance of the galvanized layer after galvanizing the steel of 1.33; FIG. 4 shows the photomicrograph of the galvanized layer after galvanization of the steel with a weight percentage of manganese of 1.0 inventive; and FIG. 5 shows the second example of the invention. A photomicrograph of the appearance of a galvanized layer after galvanizing a steel with a weight percentage of 0.5.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart showing the method of hot dip galvanizing of bismuth manganese high strength steel of the present invention. Referring to step S11 of Figure 1, a manganese-containing steel is provided. In the present embodiment, the steel has a cerium manganese weight percentage (wt%) of not more than 1.0. Alternatively, in another embodiment, the steel may have a cerium manganese weight percentage (wt%) of from 1.0 to 1.5. Further, the steel material may be selected from one of the following: a phase change induced plastic steel and a duplex steel.

Fig. 2 is a graph showing the process of raising and lowering the temperature of the hot dip galvanizing of the yttrium manganese high strength steel of the present invention. Referring to step S12 and FIG. 2 of FIG. 1, the steel is subjected to an annealing treatment step at a dew point temperature to form a ternary lanthanum manganese oxide on the surface of the steel. When the weight percentage of lanthanum manganese of the steel is not more than 1.0, the preferred dew point temperature is -30 ° C to 0 ° C. When the weight percentage of lanthanum manganese of the steel is from 1.0 to 1.5, the preferred dew point temperature is not lower than 0 °C.

The annealing treatment step comprises first heating the steel to 800 ° C at a heating rate of 5 ° C per second and annealing at a constant temperature for 60 seconds, and then cooling the steel to 460 ° C at a cooling rate of 15 ° C per second for 60 seconds. In addition, in this step, the chemical composition of the ternary manganese oxide is xMnO. SiO ₂ and x is from 0.5 to 2.

Referring to step S13 and FIG. 2 of FIG. 1 , the annealed steel is immersed in an aluminum-containing zinc bath for galvanizing, and the ternary lanthanum manganese oxide on the surface of the steel is reduced by aluminum to form an iron-aluminum layer. And the coverage of the iron-aluminum layer is greater than 70%. In this step, the temperature of the zinc bath was 460 °C.

When the weight percent of cerium manganese of the steel is not more than 1.0 and the dew point temperature is -30 ° C to 0 ° C, the preferred aluminum content of the zinc bath is 0.14 to 0.20 weight percent, and preferably the galvanizing time is 1 to 10 seconds. When the weight percentage of lanthanum manganese of the steel material is 1.0 to 1.5 and the dew point temperature is not lower than 0 ° C, the preferred aluminum content of the zinc bath is not less than 0.20% by weight, and preferably the galvanizing time is not less than 3 seconds.

Referring to step S14 of Figure 1, the galvanized steel is removed and the excess on the steel is removed. Zinc solution. In this step, the excess zinc liquid on the steel is blown off with high pressure nitrogen to control the thickness of the galvanized layer to about 10 microns.

The invention is illustrated by the following examples, which are not intended to be limited to the scope of the invention.

[Comparative Example 1]

Referring to Fig. 3, it is a micrograph showing the appearance of a galvanized layer after galvanization of a steel having a weight percentage of manganese of 1.33 in Comparative Example 1. Fig. 3(a) shows the result of annealing the steel at a dew point of 0 ° C and immersing a zinc bath with an aluminum content of 0.16 wt% for 1 second. It can be observed that the galvanizing layer of the immersion plating for 1 second has poor galvanizing properties (not More plating points). Fig. 3(b) shows the result of annealing the steel at a dew point of 0 ° C and immersing a zinc bath with an aluminum content of 0.16 wt% for 10 seconds. It can be observed that even if the immersion time is extended to 10 seconds, the galvanization cannot be effectively improved. Sex. Therefore, for a steel having a weight percentage of cerium manganese of 1.33, annealed at a dew point of 0 ° C, the aluminum content of the zinc bath must be not less than 0.20 weight percent in order to obtain good galvanizing properties.

[Inventive Example 1]

Referring to Fig. 4, there is shown a micrograph of the appearance of a galvanized layer after galvanization of a steel material having a manganese weight percentage of 1.0 in Inventive Example 1. Figure 4 shows that the weight percentage of lanthanum manganese in the steel is reduced to 1.0, and the zinc bath is annealed at a dew point of -30 ° C and immersed in a zinc bath with an aluminum content of 0.14 weight percent for 10 seconds. It can be observed that when the weight percentage of lanthanum manganese is reduced to 1.0 and When the dew point drops to -30 ° C, a longer galvanizing time is required to obtain good galvanizing properties.

[Inventive Example 2]

Referring to Fig. 5, there is shown a photomicrograph of the appearance of a galvanized layer after galvanization of a steel material having a cerium weight percentage of 0.5 in Inventive Example 2. Figure 5 shows that the weight percentage of lanthanum manganese in the steel is reduced to 0.5, and the zinc bath is annealed at a dew point of -30 ° C and immersed in a zinc bath having an aluminum content of 0.14 wt% for 1 second. It can be observed that when the weight percentage of lanthanum manganese is reduced to 0.5 , just immerse for 1 second, you can get Good galvanizing.

The above examples clearly show that the reduction in the weight percentage of manganese in the steel, the increase in the dew point, the increase in the aluminum content of the zinc bath and the extension of the galvanizing time all improve the galvanizing properties of the steel.

Table 1 summarizes the galvanic analysis results of three different bismuth manganese weight percentages of steels at different dew point temperatures and zinc bath aluminum contents in Comparative Example 1, Inventive Example 1, and Inventive Example 2. The results in Table 1 show that the galvanized layer having a good surface quality can be obtained by appropriately controlling the weight percentage of cerium manganese, the dew point temperature, and the aluminum content of the zinc bath. In addition, from the results of Table 1, it can be found that the coverage of the iron-aluminum layer is the key to determining the galvanization. When the coverage of the iron-aluminum layer is greater than 70%, the zinc liquid can be completely wetted to the steel material, and a galvanized layer which is completely wetted and has no unplated spots can be obtained.

The formation of the iron-aluminum layer depends on the type of oxide formed on the surface of the steel during annealing. In the low bismuth manganese weight percentage and high dew point atmosphere, it is easy to form crystalline ternary lanthanum manganese oxide xMnO. SiO ₂ , and this oxide is easily reduced by aluminum in the zinc bath, thereby providing a large number of nucleation sites of the iron-aluminum phase, so that a continuous iron-aluminum layer is easily formed. Conversely, as the weight percentage of cerium manganese increases and the dew point temperature decreases, the surface SiO ₂ oxide content increases, and even a continuous film is formed to hinder the nucleation growth of the iron-aluminum phase. Therefore, the weight percentage of manganese in steel should be controlled as much as 1 below, and the dew point temperature should be as high as -30 ° C. The aluminum content of the zinc bath should be at least 0.14 weight percent (wt%) to obtain coverage greater than 70% iron and aluminum layer, which in turn obtains good galvanizing properties.

The invention is annealed at a dew point temperature, which contributes to the formation of ternary lanthanum manganese oxide on the surface of the steel, and hot dip galvanizing in the aluminum bath containing aluminum promotes high coverage of ternary lanthanum manganese oxide reduction. The iron-aluminum layer, which increases the wettability between the steel and the zinc liquid, thereby improving the galvanization of the steel and reducing the occurrence of unplated defects.

The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the scope of the present invention. The scope of the invention should be as set forth in the appended claims.

S11~S14‧‧‧Steps

Claims (13)

A method for hot dip galvanizing of bismuth manganese high strength steel, comprising the steps of: (a) providing a bismuth manganese-containing steel; and (b) subjecting the steel to an annealing treatment step at a dew point temperature to make the steel surface Forming ternary lanthanum manganese oxide; (c) immersing the annealed steel in an aluminum-containing zinc bath for galvanizing, and reducing the ternary lanthanum manganese oxide on the surface of the steel by aluminum to form an iron-aluminum layer, And the coverage of the iron-aluminum layer is greater than 70%; and (d) the galvanized steel is taken out, and the excess zinc liquid on the steel is removed. The method of claim 1, wherein the steel of step (a) has a cerium manganese weight percentage of not more than 1.0. The method of claim 2, wherein the dew point temperature of step (b) is -30 ° C to 0 ° C. The method of claim 2, wherein the zinc bath of step (c) has an aluminum content of from 0.14 to 0.20 weight percent. The method of claim 2, wherein the galvanizing time of the step (c) is from 1 to 10 seconds. The method of claim 1, wherein the steel of step (a) has a cerium manganese weight percentage of 1.0 to 1.5. The method of claim 6, wherein the dew point temperature of the step (b) is not lower than 0 °C. The method of claim 6, wherein the zinc bath of the step (c) has an aluminum content of not less than 0.20% by weight. The method of claim 6, wherein the galvanizing time of the step (c) is not less than 3 seconds. The method of claim 1, wherein the annealing step of the step (b) comprises first heating the steel to 80 ° C at a heating rate of 5 ° C per second and annealing at a constant temperature for 60 seconds, and then at a cooling rate of 15 ° C per second. The steel was cooled to 460 ° C and held for 60 seconds. The method of claim 1, wherein the chemical composition of the ternary manganese oxide of step (b) is xMnO. SiO ₂ and x is from 0.5 to 2. The method of claim 1, wherein the step (d) is to blow off the excess zinc liquid on the steel by high pressure nitrogen. The method of claim 1, wherein the step (d) comprises controlling the thickness of the galvanized layer to about 10 microns.