TWI580799B - High strength and high elongation hot dip galvanized steel manufacturing method - Google Patents

Description

Method for manufacturing high strength and high elongation hot dip galvanized steel

The present invention relates to a method for producing a steel material, and more particularly to a method for producing a high strength and high elongation hot dip galvanized steel material.

In order to meet the demand for energy saving and carbon reduction, the automotive industry is committed to reducing the weight of the car body to reduce fuel consumption and achieve energy saving and carbon reduction.

It is known that the effective way to reduce the weight of the car body is to thin the thickness of the steel plate for the car body. However, when the thickness of the steel plate is thinned, the safety of the car body cannot be sacrificed. Therefore, the strength and ductility of the car body steel plate are necessary. Further improvement.

In recent years, the iron and steel industry has developed manganese-cerium high-strength dual-phase steel and phase-change-induced plastic steel that meet the above requirements, and is used as a steel body plate. However, the high-strength dual-phase steel and phase-induced plasticity steel of manganese-germanium have poor hot-dip galvanizing properties, which makes it still limited in vehicle body applications.

Therefore, it is necessary to provide an innovative and progressive method for manufacturing high strength and high elongation hot dip galvanized steel to solve the above problems.

The invention provides a method for manufacturing a high strength and high elongation hot dip galvanized steel, comprising the steps of: providing a steel material comprising 0.05-0.65 wt% carbon, 5.0-8.0 wt% manganese, 0.5-3.5 wt% niobium, 0.01-0.1wt% aluminum and the rest of the iron and unavoidable impurities; hot rolling the steel so that the microstructure of the steel contains more than 10% of the Worthite iron and the rest of the ferrite; pickling and cold rolling The steel; the steel is continuously annealed; and the steel is cooled to 450-550 ° C, and the cooled steel is immersed in an aluminum-containing zinc bath for hot dip Zinc-plated, which is a high-strength, high-elasticity hot-dip galvanized steel.

The invention can produce high-strength and high-elasticity hot-dip galvanized steel with tensile strength greater than 1400 MPa and uniform elongation and total elongation greater than 25% by controlling steel composition, annealing conditions and hot dip galvanizing conditions. The properties of steel meet the requirements of the properties of steel sheets and steels with high strength and high elongation.

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~S15‧‧‧Steps

1 is a flow chart showing a method for producing a high-strength and high-elasticity hot-dip galvanized steel according to the present invention; FIG. 2 is a graph showing tensile strength-elongation curves of the steel of the invention and the steel of the comparative example; and FIG. 3 is a view showing the steel of the invention and a comparative example. An electron micrograph of the surface oxide morphology of the steel after annealing at different dew point temperatures; and Figure 4 shows a photograph of the surface of the coating after the hot dip galvanizing of the steel at 0 °C dew point annealing.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart showing the manufacturing method of the high strength and high elongation hot dip galvanized steel of the present invention. Referring to step S11 of FIG. 1, a steel material is provided, which comprises 0.05-0.65 wt% carbon, 5.0-8.0 wt% manganese, 0.5-3.5 wt% bismuth, 0.01-0.1 wt% aluminum, and the balance of iron and unavoidable impurities. . In this step, the steel is produced by continuous casting. And preferably, the sum of the manganese content and the cerium content is more than 5% by weight and less than 10% by weight to ensure that the steel can obtain more than 10% of the residual Worthite iron after the final heat treatment, and the strain is induced by the strain. Provide the mechanical properties required for steel.

Further, the steel may also include titanium, vanadium, niobium, phosphorus, and copper, and the aforementioned respective element contents are less than 0.1% by weight, and the total content is less than 0.3% by weight.

Referring to step S12, hot rolling the steel material so that the microstructure of the steel material comprises 10% On the Worthfield iron and the rest of the fat iron. Preferably, the hot rolling heating temperature is 1100 to 1300 ° C, the hot rolling finishing temperature is 800 to 950 ° C, and the hot rolling coil temperature is 500 to 650 ° C.

Referring to step S13, the steel is pickled and cold rolled. Preferably, the cold rolling reduction is 20 to 70%.

Referring to step S14, the steel is continuously annealed. Preferably, the annealing temperature is 550 to 850 ° C and the annealing time is 20 to 300 seconds. As the steel is heated during the annealing process before hot dip galvanizing, the alloys such as bismuth, aluminum and manganese added to the steel are segregated to the surface oxidation, thereby producing an oxide film and causing the steel to be in hot dip galvanizing. The wettability of the surface deteriorates so that the zinc layer cannot adhere or generate a large amount of unplated spots. Therefore, in order to overcome the above problems, in the present embodiment, the dew point temperature of the annealing atmosphere should be higher than -20 ° C, so that manganese oxide (MnO) and porosity (SiMn) O _{x having} a particle diameter of more than 50 nm can be formed on the surface of the steel material. Or (SiAlMn)O _x amorphous oxide.

Referring to step S15, the steel is cooled to 450-550 ° C, and the cooled steel is immersed in an aluminum-containing zinc bath for hot dip galvanizing to obtain a high strength and high elongation hot dip galvanized steel. Preferably, the cooling rate is 3-50 ° C / sec, and the aluminum content of the zinc bath is 1.5-10.0 wt%, which can reduce manganese oxide (MnO) by increasing the aluminum content in the zinc bath to 1.5 wt% or more. Removal and reduction of a small amount of porous (SiMn)O _x or (SiAlMn)O _x amorphous oxide by aluminothermic reduction reaction, so that the iron-aluminum intermetallic compound can be formed in the iron-zinc interface, thereby greatly increasing the zinc liquid The wettability of the steel surface, and the hot-dip galvanized coating with excellent surface uniformity and adhesion. Further, in the present embodiment, the preferred galvanizing time is 2 to 10 seconds.

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

Inventive examples used steels of 6 wt% manganese-3 wt% 矽-0.15 wt% carbon, and comparative examples used steels of 2 wt% manganese-2 wt% 矽-0.15 wt% carbon. Inventive Example Steel and Comparative Steel After a similar hot-cold rolling process, and then annealed at 780 ° C and 700 ° C, respectively, tensile test Test.

Referring to Fig. 2, there is shown a tensile strength-elongation curve of the steel of the inventive example and the comparative steel. The results of Fig. 2 show that the tensile strength of the comparative steel material was only 1192 MPa, the uniform elongation was 13%, the total elongation was 17%, and the strong plastic product was 20 GPa%. In the invention, the tensile strength of the steel exceeds 1400 MPa, the uniform elongation and the total elongation exceed 25%, and the strong plastic product exceeds 35 GPa%, which is far superior to the comparative steel.

Referring to Fig. 3, there is shown an electron micrograph of the surface oxide morphology of the inventive steel and the comparative steel after annealing at different dew point temperatures. Fig. 3 shows that the steel of the comparative example has a coarser grain size formed on the surface of the steel after dew point annealing at -30 ° C, and a large area of continuous amorphous oxide is formed. However, after the steel of the invention was annealed at 0 ° C, the surface oxide particle size was fine and only partially covered.

Referring to Figure 4, it is a photograph showing the surface of the coating after the hot dip galvanizing of the steel at a dew point of 0 °C. Fig. 4 shows that the comparative steel was immersed in a zinc bath having an aluminum content of 0.7 wt% for hot dip galvanizing, and a large number of unplated spots appeared on the surface of the steel plating. In the invention, the steel material was immersed in a zinc bath having an aluminum content of 2.5 wt% and 5 wt% for hot dip galvanizing, and the surface of the steel plating layer was flat and had no unplated spots. Further, the results of the 90 degree bending test of the steel of the invention showed that the plating layer did not peel off.

The above experimental results prove that the present invention can produce high strength and high elongation hot dip with tensile strength greater than 1400 MPa and uniform elongation and total elongation greater than 25% by controlling the steel composition, annealing conditions and hot dip galvanizing conditions. Galvanized steel, the properties of which meet the properties of high-strength and high-elongation steel for steel.

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.

511~S15‧‧‧Steps

Claims (13)

A method for manufacturing a high strength and high elongation hot dip galvanized steel, comprising the steps of: (a) providing a steel material comprising 0.05-0.65 wt% carbon, 5.0-8.0 wt% manganese, 0.5-3.5 wt% niobium, 0.01-0.1wt% aluminum and the rest of the iron and unavoidable impurities; (b) hot rolling the steel material so that the microstructure of the steel material contains more than 10% of the Worthite iron and the rest of the ferrite iron; Pickling and cold rolling the steel; (d) continuously annealing the steel, the dew point temperature of the annealing atmosphere is higher than -20 ° C; and (e) cooling the steel to 450-550 ° C, and cooling the steel Immersed in an aluminum-containing zinc bath for hot dip galvanizing to obtain a high strength and high elongation hot dip galvanized steel. The method for producing a high strength and high elongation hot dip galvanized steel material according to claim 1, wherein the steel material of the step (a) is obtained by continuous casting. The method for manufacturing a high-strength and high-elasticity hot-dip galvanized steel according to claim 1, wherein the steel of the step (a) further comprises titanium, vanadium, niobium, phosphorus and copper, and the content of each of the foregoing elements is less than 0.1% by weight. And the total content is less than 0.3% by weight. A method for producing a high-strength, high-elasticity hot-dip galvanized steel material according to claim 1, wherein the hot rolling heating temperature in the step (b) is 1100 to 1300 ° C, and the hot rolling rolling temperature is 800 to 950 ° C, hot rolling coil The temperature is 500 to 650 °C. The method for producing a high strength and high elongation hot dip galvanized steel material according to claim 1, wherein the cold rolling reduction rate of the step (c) is 20 to 70%. The method for producing a high strength and high elongation hot dip galvanized steel material according to claim 1, wherein the annealing temperature of the step (d) is 550 to 850 °C. The method for producing a high strength and high elongation hot dip galvanized steel material according to claim 1, wherein the annealing time of the step (d) is 20 to 300 seconds. A method of producing a high strength, high elongation hot dip galvanized steel material according to claim 1, wherein the cooling rate of the step (e) is 3 to 50 ° C / sec. A method for producing a high strength, high elongation hot dip galvanized steel material according to claim 1, wherein the zinc bath of the step (e) has an aluminum content of from 1.5 to 10.0% by weight. A method for producing a high strength, high elongation hot dip galvanized steel material according to claim 1, wherein the galvanizing time of the step (e) is 2 to 10 seconds. The method for producing a high-strength, high-elasticity hot-dip galvanized steel material according to claim 1, wherein the high-strength high-elasticity hot-dip galvanized steel obtained by the step (e) has a tensile strength of more than 1400 MPa. The method for producing a high-strength, high-elasticity hot-dip galvanized steel material according to claim 1, wherein the high-strength high-elasticity hot-dip galvanized steel obtained by the step (e) has a uniform elongation of more than 25%. The method for producing a high strength and high elongation hot dip galvanized steel material according to claim 1, wherein the high elongation high elongation hot dip galvanized steel obtained by the step (e) has a total elongation of more than 25%.