TWI711706B - Automobile steel material with high yield strength and method of manufacturing the same - Google Patents

Abstract

The present invention relates to an automobile steel material with high yield strength and method of manufacturing the same. The microstructure of the automobile steel material includes a specific proportion of bainite and martensite, thereby enhancing yield strength and tensile strength, and remaining good bendability of the automobile steel material.

Description

Automobile steel material with high yield strength and manufacturing method thereof

The present invention relates to a steel material for automobiles and a manufacturing method thereof, and in particular to a steel material for automobiles with high yield strength (YS) and a manufacturing method thereof.

Dual-phase steel has both high work hardening rate and high processing formability. The high work hardening rate can prevent local deformation in the stamping process, and the high processing formability is conducive to forming and improving the absorption capacity of collision energy, so it is suitable for application Steel for automobiles.

Although dual-phase steel can solve the contradiction between high tensile strength and formability. However, recently, dual-phase steels with high tensile strength have gradually generated a demand for high yield strength, which is applied to easily formed automobile parts, such as bumpers and thresholds. Since the dual-phase steel is composed of two phases of martensite and ferrite, and there are many free differences in the ferrite, it is easy to plastically deform early when subjected to force, so the dual-phase steel The yield strength is too low, and it is difficult to meet the deformation resistance requirements of simple formed automobile parts.

In view of this, there is an urgent need to develop an automotive steel with high yield strength and a manufacturing method thereof to improve the aforementioned shortcomings of dual-phase steel.

In view of this, one aspect of the present invention is to provide a steel for automobiles with high yield strength, and another aspect of the present invention is to provide a method for manufacturing automotive steel with high yield strength to improve the above Disadvantages.

According to one aspect of the present invention, a steel material for automobiles with high yield strength is provided. The aforementioned automobile steel materials include 0.50 wt% to 0.58 wt% silicon, 0.15 wt% to 0.25 wt% molybdenum, 0.035 wt% to 0.037 wt% niobium, 0.023 wt% to 0.028 wt% boron, and the balance of iron And inevitable impurities. The yield strength of the aforementioned automobile steel material is at least 700 MPa, and the metallographic structure of the aforementioned automobile steel material includes bainite with a volume fraction of at least 30% and Asada loose iron with a volume fraction of at least 5%.

According to an embodiment of the present invention, the metallographic structure includes toughened iron with a volume fraction of 30% to 51%, Asada iron with a volume fraction of 5% to 15%, and a volume fraction of 35% to 65%. Fat iron.

According to another embodiment of the present invention, the aforementioned automobile steel material optionally contains 0.09 wt% to 0.15 wt% carbon, 1.0 wt% to 2.5 wt% manganese, 0.02 wt% to 0.04 wt% aluminum, and no more than 0.02 wt% Percentage of phosphorus, and no more than 0.015% by weight of sulfur.

According to another embodiment of the present invention, the tensile strength of the steel for automobiles is at least 980 MPa, the elongation of the steel for automobiles is not more than 12.1%, and the 90 degree bending radius of the steel for automobiles is less than or equal to that of the automobile. Use 2.5 times the thickness of steel.

According to another aspect of the present invention, a method for manufacturing automobile steel with high yield strength is provided. In the foregoing manufacturing method, first, a steel blank is provided. The aforementioned steel billet contains 0.50 wt% to 0.58 wt% silicon, 0.15 wt% to 0.25 wt% molybdenum, 0.035 wt% to 0.037 wt% niobium, 0.023 wt% to 0.028 wt% boron, and the balance of iron and Inevitable impurities.

Next, a heating step is performed on the steel blank. After the aforementioned heating step, the aforementioned steel blank is subjected to a hot rolling step, wherein the finishing temperature of the hot rolling step is 880°C to 950°C, and the coil temperature of the hot rolling step is 500°C to 700°C to obtain hot rolled steel .

After the hot rolling step, the hot rolled steel is subjected to a cold rolling step, wherein the cold rolling rate of the cold rolling step is at least 50% to obtain the cold rolled steel.

Then, the aforementioned cold-rolled steel material is subjected to an annealing step and a cooling step to obtain automobile steel material, wherein the yield strength of the automobile steel material is at least 700 MPa, and the metallographic structure of the aforementioned automobile steel material includes a volume fraction of at least 30% Toughened iron and Asada bulk iron with a volume fraction of at least 5%.

According to another embodiment of the present invention, the heating temperature of the aforementioned heating step is 1150° C. to 1300° C., and the aforementioned heating step is held for 2 hours to 4 hours.

According to another embodiment of the present invention, after the hot rolling step, the step of pickling the hot rolled steel is optionally included.

According to another embodiment of the present invention, the annealing temperature in the annealing step is 780° C. to 840° C., and the annealing step is held for 60 seconds to 120 seconds.

According to another embodiment of the present invention, the cooling step includes a first cooling treatment and a second cooling treatment, and the cooling rate of the first cooling treatment is 5°C/sec to 20°C/sec, so as to reduce the annealed cold rolled steel Cool to 560°C to 580°C and hold the temperature for 30 seconds to 60 seconds. The cooling rate of the second cooling treatment is from 20°C/sec to 100°C/sec to cool the cold-rolled steel material after the first cooling treatment to the chamber. temperature.

According to another embodiment of the present invention, the tensile strength of the steel for automobiles is at least 980 MPa, the elongation of the steel for automobiles is not more than 12.1%, and the 90 degree bending radius of the steel for automobiles is less than or equal to that of the automobile. Use 2.5 times the thickness of steel.

In summary, the metallographic structure of the automotive steel and the manufacturing method of the present invention contains a specific ratio of toughened iron and Matian loose iron, which can improve the yield strength and tensile strength of the automotive steel and maintain good bending properties. .

The manufacture and use of the embodiments of the present invention are discussed in detail below. However, it is understandable that the embodiments provide many applicable inventive concepts, which can be implemented in various specific contents. The specific embodiments discussed are for illustration only, and are not intended to limit the scope of the invention.

One aspect of the present invention is to provide a steel material for automobiles with high yield strength. Automobile steel contains silicon, molybdenum, niobium, boron and the rest of iron and unavoidable impurities. The metallographic structure of the resulting automobile steel contains a specific ratio of toughened iron and Matian loose iron, which can increase the yield of automobile steel Strength and tensile strength, and retain good flexibility.

The unavoidable impurities referred to herein in the present invention refer to impurities that cannot be separated during the steelmaking process.

The high yield strength referred to herein in the present invention means that the yield strength of steel for automobiles is at least 700 MPa. The high tensile strength referred to herein in the present invention means that the tensile strength of steel for automobiles is at least 980 MPa. The bendability referred to herein in the present invention means that when the bendability is evaluated with a bending radius of 90 degrees, the aforementioned automotive steel materials have good bendability, which is beneficial for subsequent processing and forming. In addition, the elongation of the automotive steel material of the present invention should be controlled within an appropriate range, for example, not more than 12.1%.

The types and contents of the aforementioned elements will affect the metallographic structure, yield strength, tensile strength and bendability of automotive steel materials after being processed by a specific process. In some embodiments, the metallurgical structure of the automobile steel material includes a specific ratio of toughened iron and Asada loose iron. In the above embodiments, the specific ratio is defined in terms of volume fraction. The metallographic structure of automotive steel materials may include, for example, toughened iron with a volume fraction of at least 30% and Asada with a volume fraction of at least 5%. For dual-phase steels such as bulk iron, however, in other embodiments, the above specific ratio can also be defined in other ways, such as area fraction. In other embodiments, the metallographic structure of the steel material for automobiles may include three-phase steels such as toughened iron, hemp iron, and ferrous iron in a specific proportion. The metallurgical structure of the steel materials for automobile may include, for example, a volume fraction of 30. % To 51% toughened iron, Asada loose iron with a volume fraction of 5% to 15%, and fat grain iron with a volume fraction of 35% to 65%, and the yield strength of the aforementioned automotive steel is at least 700 MPa.

It is said that the steel for automobiles contains 0.50 wt% to 0.58 wt% of silicon, of which silicon is a solid solution strengthening and ferrous iron stabilizing element. When the content of silicon is less than 0.50% by weight, the metallurgical structure of the steel for automobiles contains ferrous iron with a volume fraction of less than 35%. When the content of silicon is greater than 0.58% by weight, the metallurgical structure of the steel for automobiles contains ferrous iron with a volume fraction greater than 65%.

In the above embodiment, the automotive steel contains 0.15 wt% to 0.25 wt% of molybdenum, where molybdenum can inhibit the formation of ferrous iron phase and increase the volume fraction of toughened iron and Asada loose iron. When the content of molybdenum is less than 0.15 weight percent, the metallurgical structure of the automotive steel contains ferrous iron with a volume fraction greater than 65%. When the content of molybdenum is greater than 0.25 weight percent, the metallurgical structure of the automotive steel contains ferrous iron with a volume fraction of less than 35%.

In the above embodiment, the automotive steel contains 0.035 wt% to 0.037 wt% of niobium, wherein niobium forms a compound with carbon or nitrogen, which can refine crystal grains, increase the bendability of the steel, and increase the yield strength of the steel. When the content of niobium is less than 0.035 weight percent, the yield strength of the steel for automobiles is less than 700 MPa. When the content of niobium is greater than 0.037 weight percent, the bendability of the automotive steel is not conducive to subsequent processing and forming.

In the above embodiment, the steel material for automobiles contains 0.023 to 0.028 weight percent of boron. Boron can effectively inhibit the production of fertilizer particles and increase the volume fraction of loose iron in Asada. When the content of boron is less than 0.023% by weight, the metallurgical structure of the steel for automobiles contains Asada loose iron with a volume fraction of less than 5%. When the content of boron is greater than 0.028% by weight, the metallurgical structure of the automotive steel includes Asada loose iron with a volume fraction greater than 15%. Therefore, it is necessary to control the content of silicon, molybdenum, niobium, and boron in the automotive steel to be within the above-mentioned range, so that the resulting automotive steel has a predetermined ratio of metallographic structure, yield strength and flexibility.

Furthermore, in addition to silicon, molybdenum, niobium and boron, the content of other elements will also affect the metallographic structure, yield strength, tensile strength and bendability of automotive steel. In some embodiments, based on the total weight of the automobile steel material being 100% by weight, the automobile steel material optionally includes 0.09% to 0.15% by weight of carbon, 1.0% to 2.5% by weight of manganese, and 0.02% to 0.04% by weight. Percentage of aluminum, no more than 0.02 weight percent of phosphorus, and no more than 0.015 weight percent of sulfur.

Preferably, based on the total weight of the automobile steel material being 100% by weight, the automobile steel material optionally contains 0.09% to 0.11% by weight of carbon, 2.00% to 2.13% by weight of manganese, and 0.031% to 0.033% by weight. Aluminum, 0.010 wt% to 0.013 wt% phosphorus, and at least 0.02 wt% to 0.04 wt% sulfur.

It is said that the steel for automobiles contains 0.09 wt% to 0.15 wt% carbon, of which carbon is a steel strengthening element. When the carbon content is 0.09 wt% to 0.15 wt%, the metallographic structure of the automotive steel includes toughened iron with a volume fraction of at least 30% and Matian bulk iron with a volume fraction of at least 5%.

In the above embodiment, the steel material for automobiles contains 1.0 wt% to 2.5 wt% of manganese, where manganese can increase the volume fraction of toughened iron and Matian loose iron. When the content of manganese is 1.0 wt% to 2.5 wt%, the metallographic structure of the steel for automobiles includes toughened iron with a volume fraction of at least 30% and Asada scattered iron with a volume fraction of at least 5%.

In the above embodiment, the steel material for automobiles contains 0.02 wt% to 0.04 wt% aluminum, and aluminum is mainly used for deoxidation during steelmaking.

In the above embodiment, the steel material for automobiles contains no more than 0.02 weight percent of phosphorus, where phosphorus is an impurity in the steel material.

In the above embodiment, the steel for automobiles contains no more than 0.015 weight percent of sulfur, where sulfur is an impurity in the steel.

In some embodiments, the metallurgical structure of the automotive steel includes toughened iron with a volume fraction of 30% to 51%, a matian iron with a volume fraction of 5% to 15%, and a volume fraction of 35% to 65. % Of ferrite iron, the yield strength of automotive steel is at least 700 MPa. In some embodiments, the tensile strength of the automotive steel is at least 980 MPa. In some embodiments, the elongation of the automotive steel material is not more than 12.1%. In some embodiments, the 90-degree bending radius of the automotive steel is less than or equal to 2.5 times the thickness of the aforementioned automotive steel.

Another aspect of the present invention is to provide a method for manufacturing automobile steel with high yield strength. The aforementioned manufacturing method includes a step of providing a steel billet, a heating step, a step of hot rolling the heated steel billet, a step of cold rolling the hot-rolled steel after hot rolling, and the step of annealing and cooling the cold-rolled steel after cold rolling. step.

In the foregoing manufacturing method, first, a steel blank is provided. In some embodiments, the aforementioned steel billet includes 0.50 wt% to 0.58 wt% silicon, 0.15 wt% to 0.25 wt% molybdenum, 0.035 wt% to 0.037 wt% niobium, 0.023 wt% to 0.028 wt% boron, And the balance of iron and unavoidable impurities. The effects of the element types and contents of the aforementioned steel blanks on the metallographic structure, yield strength, tensile strength and bendability of automotive steel materials are as described above, and will not be repeated here. In addition, the temperature and time of the aforementioned heating step, hot rolling step, cold rolling step, annealing step, and cooling step also affect the metallographic structure, yield strength and tensile strength of the automotive steel.

The aforementioned heating step is to produce austenitic iron from the steel billet, so as to facilitate the subsequent use of a rolling roller to perform a hot rolling step on the heated steel billet. In some embodiments, the steel billet is heated to a temperature range of 1150°C to 1300°C, and the temperature is maintained for 2 hours to 4 hours. When the heating temperature is in the range of 1150°C to 1300°C, all the elements in the steel billet can be completely dissolved, which facilitates the steel billet to be easily rolled during subsequent hot rolling.

After the aforementioned heating step, a hot rolling step is performed. In the hot rolling step, at the finishing temperature of 880°C to 950°C, the metallographic phase of the steel is austenitic iron, and at the subsequent coiling temperature of 500°C to 700°C, the metallographic phase of the steel changes Tough iron.

In some embodiments, after the aforementioned hot rolling step, a pickling step is first performed to remove the hot-rolled scale on the surface of the hot-rolled steel, and the cold rolling step is continued.

In some embodiments, the cold rolling rate is at least 50%. When the cold rolling rate is less than 50%, the metallographic structure of the automotive steel will be uneven, which will affect the tensile properties and bendability.

After the aforementioned cold rolling step, an annealing step is performed. In the annealing step, the temperature is controlled at 780°C to 840°C, and the temperature is maintained for 60 seconds to 120 seconds. At this time, the cold-rolled steel changed from a toughened iron phase to two phases of fat iron and austenitic iron. In some embodiments, the metallurgical structure of the steel includes fat grain iron with a volume fraction of 35% to 65% and the remaining austenitic iron.

In some embodiments, after the aforementioned annealing step, a cooling step is performed, wherein the cooling step includes a first cooling treatment and a second cooling treatment. In the first cooling treatment, the annealed steel material is cooled to a range of 560°C to 580°C at a cooling rate of 5°C/sec to 20°C/sec, and the temperature is maintained for 30 seconds to 60 seconds to make the steel The iron phase is transformed into a toughened iron phase. In some embodiments, the metallurgical structure of the steel includes fat grain iron with a volume fraction of 35% to 65%, toughened iron with a volume fraction of 30% to 51%, and the remaining austenitic iron.

In the second cooling treatment, the steel after the first cooling treatment is cooled to room temperature at a cooling rate of 20°C/sec to 100°C/sec, so that the remaining austenitic iron phase of the steel is transformed into a volume fraction It is 5% to 15% of Asada scattered iron phase. Therefore, by controlling the temperature and time of each step in the manufacturing method of automotive steel materials, the resulting automotive steel materials will always have a predetermined ratio of metallographic structure and yield strength.

In some embodiments, the steel blank contains 0.50 wt% to 0.58 wt% silicon, 0.15 wt% to 0.25 wt% molybdenum, 0.035 wt% to 0.037 wt% niobium, and 0.023 wt% to 0.028 wt% boron.

In some embodiments, the metallurgical structure of the automotive steel includes toughened iron with a volume fraction of at least 30% and Matian loose iron with a volume fraction of at least 5%, and the yield strength of the automotive steel is at least 700 MPa. In some embodiments, the tensile strength of the automotive steel is at least 980 MPa. In some embodiments, the elongation of the automotive steel material is not more than 12.1%. In some embodiments, the 90-degree bending radius of the automotive steel is less than or equal to 2.5 times the thickness of the automotive steel.

When steel billets with the aforementioned silicon, molybdenum, niobium and boron contents are used and the aforementioned manufacturing method is used to manufacture automotive steel, the metallographic structure of the automotive steel includes toughened iron with a volume fraction of at least 30% and a volume fraction At least 5% of Matian loose iron, the yield strength of automotive steel is at least 700 MPa, the tensile strength of automotive steel is at least 980 MPa, the elongation of automotive steel is no more than 12.1%, and the automotive steel is 90 degrees The bending radius is less than or equal to 2.5 times the thickness of automotive steel.

In short, the automotive steel of the present invention controls the content of silicon, molybdenum, niobium, and boron and the specific ratio of toughened iron and Matian scattered iron, so that the automotive steel produced has better yield strength and resistance. Tensile strength and good bendability are retained, and it can indeed impart high deformation resistance and bending workability to automotive steel materials.

The following examples are used to illustrate the application of the present invention, but they are not intended to limit the present invention. Anyone who is familiar with the art can make various changes and modifications without departing from the spirit and scope of the present invention. Example 1

In Example 1, the steel billet contains 0.5800 weight percent silicon, 0.2000 weight percent molybdenum, 0.0360 weight percent niobium, 0.0028 weight percent boron, 0.0900 weight percent carbon, 2.1300 weight percent manganese, and 0.0310 weight percent aluminum , 0.0100 weight percent of phosphorus, 0.0040 weight percent of sulfur, and the balance of iron and unavoidable impurities. Heat the aforementioned steel billet to a temperature range of 1150°C to 1300°C and hold the temperature for 2 hours to 4 hours. Then, a hot rolling step is performed, wherein the finishing temperature is 880°C to 950°C, and the coil temperature is in the range of 500°C to 700°C to obtain a hot rolled steel.

Then, a cold rolling step is performed in which the aforementioned hot rolled steel material is cold rolled using a cold rolling rate of at least 50%. Then, after heating to the range of 780°C to 840°C, the temperature is held for 60 seconds to 120 seconds, and annealing is performed. Then, a cooling step is performed, in which the aforementioned steel material is cooled to the range of 560°C to 580°C using a cooling rate of 5°C/sec to 20°C/sec, and then the temperature is maintained for 30 seconds to 60 seconds; and then 20°C/sec to 100°C is used The cooling rate per second was used to cool the steel material to room temperature. The evaluation results are shown in Table 1. Example 2 to Example 3 and Comparative Example 1 to Comparative Example 3

Example 2 to Example 3 and Comparative Example 1 to Comparative Example 3 were carried out in the same manner as in Example 1. The difference is that the element content of the steel blanks of Examples 2 to 3 and Comparative Examples 1 to 3 is not completely the same as that of Example 1. The specific conditions and evaluation results of Example 2 to Example 3 and Comparative Example 1 to Comparative Example 3 are shown in Table 1. Evaluation method 1. Measurement of metallographic structure

The volume fraction of the metallographic structure referred to here in the present invention is to use a scanning electron microscope or an optical microscope to capture images of the automotive steel materials of each embodiment and comparative example, and to measure the fat iron, toughened iron and An example of the area percentage occupied by Asada bulk iron, and the average of 5 obtained area percentage examples as the volume fraction, the unit of which is %. The measurement results of the metallographic structure of the automotive steel materials of the foregoing examples and comparative examples As shown in Table 1, and FIG. 1A shows a scanning electron microscope image of the automobile steel material of Example 1, and FIG. 1B shows an optical microscope image of the automobile steel material of Comparative Example 1.

Please refer to Table 1. The symbol "F" in the metallographic structure column represents fat iron, the symbol "B" represents toughened iron, and the symbol "M" represents Matian loose iron. For example, "F+B+M" indicates that the metallurgical structure has fat grain iron, toughened iron, and Asada loose iron, and "F+M" indicates that the metallurgical structure has fat grain iron and Asada loose iron. In addition, the symbol "O" in the determination field means that the steel for automobiles contains the metallographic structure of toughened iron with a volume fraction of at least 30% and Asada bulk iron with a volume fraction of at least 5%; the symbol "X" means automobile The steel material used contains the metallographic structure of toughened iron with a volume fraction of less than 30% and/or Asada bulk iron with a volume fraction of less than 5%. 2. Yield strength test

The yield strength referred to here in the present invention is tested according to the standard method CNS 2112, G2014 to measure the yield strength of Examples 1 to 3 and Comparative Examples 1 to 3, the unit is MPa, and the measurement results of the yield strength As shown in Table 1. 3. Test of tensile strength

The tensile strength referred to in the present invention is tested in accordance with the standard method CNS 2112, G2014 to measure the tensile strength of Examples 1 to 3 and Comparative Examples 1 to 3, in MPa, and the tensile strength The measurement results are shown in Table 1. 4. Test of elongation

The elongation referred to here in the present invention is tested according to the standard method CNS 2112, G2014, and the gauge length is 50 mm to measure the elongation of Examples 1 to 3 and Comparative Examples 1 to 3, and the unit is% , And the measurement results of elongation are shown in Table 1. 5. Flexibility test

The bendability referred to herein in the present invention is based on the V block method defined by the standard method JIS Z 2248 to evaluate the 90 degree bending radius. In short, this method cuts a long strip of steel (with a thickness of 1.5 mm) along the rolling direction and the direction perpendicular to the thickness direction (width direction), and uses this steel as a test piece. The aforementioned steel material was bent in a 90-degree V shape, and the radius without cracking was used as the minimum bending radius to evaluate the bendability. The relevant measurement results are shown in Table 1. Please refer to Table 1. The symbol "N" in the flexibility column indicates that the bending test has not been performed.

Table 1

Please refer to Table 1. Compared with the automotive steel materials of Comparative Examples 1 to 3, the automotive steel materials of Examples 1 to 3 have higher yield strength and higher tensile strength, and have fertilizer grain iron , The metallographic structure of toughened iron and Matian scattered iron, wherein the metallographic structure of the automotive steel materials of Examples 1 to 3 includes toughened iron with a volume fraction of at least 30% and a volume fraction of at least 5% Matian scattered iron.

Please refer to FIGS. 1A and 1B, where FIG. 1A is a scanning electron microscope image of the automotive steel material of Example 1 of the present invention, and FIG. 1B is an optical microscope image of the automotive steel material of Comparative Example 1 of the present invention. In FIGS. 1A and 1B, the symbol "α" indicates fat iron, the symbol "B" indicates toughened iron, and the symbol "M" indicates Asada loose iron. As shown in Fig. 1A and Fig. 1B, the automobile steel material of Example 1 has the metallographic structure of fat grain iron, toughened iron, and Matian loose iron, while the automobile steel material of Comparative Example 1 only has fat grain iron and Matian loose iron. The metallographic organization.

In summary, the application of the automotive steel with high yield strength and the manufacturing method of the present invention is obtained by controlling the content of silicon, molybdenum, niobium and boron and the specific ratio of toughened iron to matian scattered iron The automotive steel has high yield strength and tensile strength, and retains good bending properties, so as to give automotive steels high deformation resistance and bending workability.

It is understandable that although the present invention takes the specific composition, specific metallographic structure, specific manufacturing method and specific evaluation method as examples to illustrate the automotive steel with high yield strength and the manufacturing method thereof, the technical field of the present invention Anyone with ordinary knowledge in the above knows that the present invention is not limited to this. Without departing from the spirit and scope of the present invention, the present invention can also be carried out by using other compositions, other metallographic structures, other manufacturing methods, or other evaluation methods.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention. Retouching, therefore, the scope of protection of the present invention shall be subject to the scope of the attached patent application.

no

In order to have a more complete understanding of the embodiments of the present invention and its advantages, please refer to the following description and the corresponding drawings. It must be emphasized that the various features are not drawn to scale and are for illustration purposes only. The contents of the relevant diagrams are described as follows: [Figure 1A] is a scanning electron microscope image of a steel material for automobiles in an embodiment of the present invention. [Figure 1B] is an optical microscope image of a steel material for automobiles in a comparative example of the present invention.

Claims (10)

A steel for automobiles with high yield strength, including: 0.50 wt% to 0.58 wt% of silicon; 0.15 wt% to 0.25 wt% of molybdenum; 0.035 wt% to 0.037 wt% of niobium; 0.023 weight percent to 0.028 weight percent of boron; and The remaining amount of iron and unavoidable impurities, and The yield strength of the automotive steel is at least 700 MPa, and a metallurgical structure of the automotive steel includes toughened iron with a volume fraction of at least 30% and Matian loose iron with a volume fraction of at least 5%. The automotive steel according to claim 1, wherein the metallographic structure includes the toughened iron with a volume fraction of 30% to 51%, the Asada bulk iron with a volume fraction of 5% to 15%, and a volume fraction It is 35% to 65% of ferrite iron. The steel for automobiles mentioned in claim 1, further including: 0.09 weight percent to 0.15 weight percent of carbon; 1.0 weight percent to 2.5 weight percent of manganese; 0.02 weight percent to 0.04 weight percent of aluminum; Not more than 0.02 weight percent phosphorus; and Not more than 0.015 weight percent of sulfur. The automotive steel according to claim 1, wherein the tensile strength of the automotive steel is at least 980 MPa, the elongation of the automotive steel is not more than 12.1%, and the 90-degree bending radius of the automotive steel is less than or Equal to 2.5 times the thickness of the automobile steel. A manufacturing method of automotive steel with high yield strength, including: A steel billet is provided, wherein the steel billet contains 0.50 wt% to 0.58 wt% silicon, 0.15 wt% to 0.25 wt% molybdenum, 0.035 wt% to 0.037 wt% niobium, 0.023 wt% to 0.028 wt% boron, and The remaining amount of iron and unavoidable impurities; Performing a heating step on the steel blank; A hot rolling step is performed on the steel billet, wherein a finishing temperature of one of the hot rolling steps is 880°C to 950°C, and a coil temperature of one of the hot rolling steps is 500°C to 700°C to obtain a hot rolled steel ； Performing a cold rolling step on the hot-rolled steel, wherein one of the cold-rolling steps has a cold rolling rate of at least 50% to obtain a cold-rolled steel; and An annealing step and a cooling step are performed on the cold-rolled steel to obtain the automotive steel, wherein the yield strength of the automotive steel is at least 700 MPa, and the metallographic structure of the automotive steel includes a volume fraction of at least 30% toughened iron and Asada bulk iron with a volume fraction of at least 5%. The method for manufacturing steel materials for automobiles according to claim 5, wherein one of the heating steps has a heating temperature of 1150° C. to 1300° C., and the heating step is held for 2 hours to 4 hours. According to claim 5, the method for manufacturing steel materials for automobiles further includes a pickling step for the hot-rolled steel materials after the hot rolling step. The method for manufacturing automobile steel materials according to claim 5, wherein one of the annealing steps has an annealing temperature of 780° C. to 840° C., and the annealing step is held for 60 seconds to 120 seconds. The manufacturing method of automotive steel according to claim 5, wherein the cooling step includes a first cooling treatment and a second cooling treatment, and a cooling rate of the first cooling treatment is 5°C/sec to 20°C/sec , To cool the annealed cold-rolled steel to 560°C to 580°C and hold the temperature for 30 seconds to 60 seconds, one of the second cooling treatments has a cooling rate of 20°C/sec to 100°C/sec, so as to After a cooling treatment, the cold-rolled steel material is cooled to room temperature. The method for manufacturing automobile steel materials as described in claim 5, wherein the tensile strength of the automobile steel materials is at least 980 MPa, the elongation rate of the automobile steel materials is not more than 12.1%, and the automobile steel materials are bent at 90 degrees The radius is less than or equal to 2.5 times the thickness of the automobile steel.

Images