TW201444983A - High-strength steel material and method for manufacturing the same - Google Patents

Abstract

A high-strength steel material and a method for manufacturing the same are described. The high-strength steel material includes carbon with a weight percent from 0.05% to 0.22%, manganese with a weight percent from 0.05% to 1.50%, phosphorous with a weight percent from 0.07% to 0.12%, sulfur with a weight percent under 0.02%, silicon with a weight percent under 0.04%, aluminum with a weight percent from 0.025% to 0.100%, nitrogen with a weight percent from 0.002% to 0.009%, titanium with a weight percent under 0.004% and iron with the remnant content.

Description

High-strength steel and its manufacturing method

This invention relates to a steel material, and more particularly to a high strength steel (HSS) and method of making same.

The traditional high-strength steel has a Tensile Strength (TS) of 300 MPa to 700 MPa. The deep drawability and elongation (Elongation; EL) of high-strength steels often decrease with increasing strength. For example, when the tensile strength of high-strength steel is increased from 370 MPa to 590 MPa, the elongation of steel is greatly reduced from 34% to 20%. Moreover, it is worth noting that when the tensile strength of high-strength steel is greater than 400 MPa, the elongation of the steel is less than 30%. This means that when the strength of the high-strength steel is increased, the formability is lowered, which causes a problem that the steel material is cracked during the forming process.

Take the J2340 specification of the Society of Automotive Engineers (SAE) as an example, taking steel with a tensile strength greater than 490 MPa, such as 420X steel. This steel material is formed by precipitation strengthening using niobium, titanium, vanadium, carbon and nitrogen, thereby achieving steel reinforcement to obtain the required strength. The mechanical properties of the SAE J2340 420X steel are greater than 490 MPa, the yield strength (YS) is greater than 420 MPa, and the elongation is greater than 18%. It can be seen that although this steel The strength of the material is large, but the elongation is low, which is not conducive to the forming process.

Therefore, one aspect of the present invention is to provide a high-strength steel material and a method for manufacturing the same, which can improve the strength of the steel and the ductility of the steel by adjusting the composition of the steel preform and/or the process control at each stage. And formability.

Another aspect of the present invention provides a high-strength steel material and a method of manufacturing the same, which utilizes a box-type annealing (BA) technique to anneal a finished steel material, thereby producing a steel sheet having a large thickness.

According to the above object of the present invention, a high strength steel material is proposed. The high-strength steel material comprises carbon in an amount of 0.05 wt% to 0.22 wt%, manganese in an amount of 0.05 wt% to 1.50 wt%, phosphorus in a content of 0.07 wt% to 0.12 wt%, sulfur in an amount of less than 0.02 wt%, and a content of less than 0.04 wt. % 矽, content 0.025 wt% to 0.100 wt% aluminum, 0.002 wt% to 0.009 wt% nitrogen, less than 0.004 wt% titanium, and iron having the remaining content.

According to an embodiment of the invention, the aluminum content is from 0.025 wt% to 0.040 wt%.

According to another embodiment of the present invention, the nitrogen content is from 0.004% by weight to 0.006% by weight.

According to the above object of the present invention, a method for producing a high-strength steel material is provided, which comprises the following steps. Provide a steel embryo. Wherein, the steel embryo comprises carbon with a content of 0.05 wt% to 0.22 wt%, manganese with a content of 0.05 wt% to 1.50 wt%, phosphorus with a content of 0.07 wt% to 0.12 wt%, sulfur having a content of less than 0.02 wt%, and a content of less than 0.04. Wt% of 矽, content of 0.025wt% to 0.100wt% Aluminium, a content of 0.002% by weight to 0.009% by weight of nitrogen, a content of less than 0.004% by weight of titanium, and iron having a residual content. A hot rolling process is carried out on the steel blank. A cold rolling process is performed on the steel blank after the hot rolling process to obtain a finished steel. A box annealing process is performed on the finished steel.

According to an embodiment of the present invention, the performing the hot rolling process comprises controlling a finishing temperature to be greater than or equal to 850 °C.

According to another embodiment of the present invention, the cold rolling process described above comprises controlling a cold rolling reduction rate of from 35% to 70%.

According to still another embodiment of the present invention, the performing the box annealing process comprises: controlling a process temperature between 650 ° C and 730 ° C, and controlling a process time from 8 hours to 15 hours.

According to still another embodiment of the present invention, the method for manufacturing the high-strength steel material further comprises: adjusting the tensile strength according to one of the high-strength steel materials and using a prediction formula to adjust the composition of the steel embryo, and one of the cold rolling reductions. Rate and / or one of the process temperatures of the box annealing process. Among them, the prediction formula is: preset tensile strength = strength of steel embryo + 0.0032 × (ppm value of manganese content) + 0.0678 × (ppm value of phosphorus content) + 0.5 × (cold rolling reduction rate - 49% ) +0.33 × (710 ° C - process temperature) + 0.066 × (ppm value of carbon content).

According to still another embodiment of the present invention, the aluminum content is from 0.025 wt% to 0.040 wt%.

According to still another embodiment of the present invention, the nitrogen content is 0.004 wr% to 0.006 wt%.

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The above and other objects, features, advantages and embodiments of the present invention will become more apparent and understood. 1 is a flow chart showing the manufacture of a high-strength steel according to an embodiment of the present invention.

2 is a graph showing the tensile strength and elongation of a high-strength steel according to an embodiment of the present invention, a microalloyed steel of the American Iron and Steel Institute (AISI), and a generally continuously annealed steel.

In view of the fact that conventional high-strength steels cannot be effectively combined in strength, elongation and deep drawability, the present invention proposes an increase in steel strength by adjusting the composition of the steel and/or the process of each stage. Both ductility and formability.

In an embodiment of the present invention, the mechanical properties of the high strength steel may include a tensile strength of 300 MPa to 600 MPa, a relief strength of 200 MPa to 400 MPa, and an elongation of 30% to 40%. This high-strength steel can be used for parts that require high strength and large deformation, such as front and rear bumpers, fenders, hoods, doors, etc. In addition to providing sufficient strength of the finished product to enhance safety, it can provide good formability during manufacturing, which is beneficial to reduce production costs and improve process yield.

In one embodiment, the composition of the high-strength steel may include, for example, a content of 0.05% by weight to 0.22% by weight of carbon, a content of 0.05% by weight to 1.50% by weight of manganese, and a content of 0.07% by weight to 0.12% by weight of phosphorus. Less than 0.02% by weight of sulfur, less than 0.04% by weight of cerium, 0.025% by weight to 0.100% by weight of aluminum, 0.002% by weight to 0.009% by weight of nitrogen, and less than 0.004% by weight of titanium And iron with the remaining content. In a preferred embodiment, the aluminum content may be, for example, from 0.025 wt% to 0.040 wt%. Further, the content of nitrogen may be, for example, 0.004% by weight to 0.006% by weight.

In one embodiment, when a high-strength steel material is produced, techniques such as texture control, solid solution strengthening, grain refinement strengthening, and spheroidized ferritic carbon iron dispersion strengthening can be used to enhance the strength of the steel. Take into account the elongation and deep drawability of steel. Please refer to FIG. 1 , which is a flow chart showing the manufacture of a high-strength steel according to an embodiment of the present invention. When making this high strength steel, the steel blank can be provided first as in step 102 of method 100. In an embodiment, the composition of the steel preform may comprise a content of 0.05% by weight to 0.22% by weight of carbon, a content of 0.05% by weight to 1.50% by weight of manganese, a content of 0.07% by weight to 0.12% by weight of phosphorus, and a content of less than 0.02. The wt% sulfur, the content of less than 0.04 wt% of antimony, the content of 0.025 wt% to 0.100 wt% of aluminum, the content of 0.002 wt% to 0.009 wt% of nitrogen, the content of less than 0.004 wt% of titanium and the balance of iron. In a preferred embodiment, the aluminum content may be, for example, from 0.025 wt% to 0.040 wt%. Further, the content of nitrogen may be, for example, 0.004% by weight to 0.006% by weight. The step 102 of providing the steel blank can use the steel blank as a raw material for the steel making process.

Next, as described in step 104, the steel blank is subjected to a hot rolling pass. In one embodiment, the rolling temperature can be controlled, for example, to greater than or equal to 850 ° C when the steel blank is subjected to a hot rolling pass. Next, after the hot rolling process of the steel blank is performed as described in step 106, the hot rolled steel blank is subjected to a cold rolling process to obtain a rolled steel. In an embodiment, the cold rolling reduction of the cold rolling pass may be controlled to, for example, 35% to 70% when the cold rolling of the steel blank is performed.

After the rolled steel material is formed, the finished steel can be subjected to a box annealing process as described in step 108 to obtain a desired high strength steel material. In other embodiments, the steel may be further tempered and finished during the encapsulation annealing process depending on the product requirements. In an exemplary embodiment, the process temperature may be controlled to, for example, 650 ° C to 730 ° C when the finished steel is subjected to a box annealing process, and the process time may be controlled, for example, from 8 hours to 15 hours. Since this embodiment adopts a box-type annealing process, a thick steel material having a thickness of 2.0 mm to 3.2 mm can be produced.

By applying the steel preform composition and process proposal of this embodiment, the assembly of the steel embryo after the hot rolling, cold rolling and sealing annealing processes can be controlled, and the elongation, deep drawing and high strength can be obtained. Steel.

In one embodiment, an experimental analysis is performed on the hot rolling finish temperature, the cold rolling reduction rate, and the process temperature of the box annealing in the process parameters of the high strength steel. In addition, in this embodiment, the metallurgical prediction formula is derived for the chemical composition of the steel preform, the process parameters of the steel, and the tensile strength of the obtained steel, such as the following formula (1): preset tensile strength = steel embryo Strength +0.0032×(ppm value of manganese content of steel embryo)+0.0678×(ppm value of phosphorus content of steel embryo)+0.5×(cold rolling reduction rate-49%)+0.33×(710°C-hot rolling range temperature ) +0.066 × (ppm value of carbon content of steel embryo) (Equation 1)

Therefore, according to the preset tensile strength of the high-strength steel, the above prediction formula can be used to adjust the composition of the steel blank, the cold rolling reduction rate of the cold rolling process, and/or the process temperature of the sealed annealing process. In addition, metallographic and transmission electron microscopy can be used for hot rolling, cold rolling and box annealing. Detailed analysis of the microstructure and aggregate structure of the process stage to understand the metallurgical mechanism of high strength and high deep drawability.

The technical contents and effects of the present embodiment will be more specifically described below using a plurality of embodiments. Table 1 below lists the mechanical properties of the steels obtained under the above-mentioned metallurgical prediction formulas and experimentally obtained under the steel embryo components and process conditions of these examples. In these examples, the remaining trace elements such as barium, sulfur, aluminum, nitrogen and titanium in the steel embryo are as described in the above examples.

It can be seen from the above Table 1 that the elongation of high-strength steel with tensile strength greater than 400 Mpa is greater than 30%. Therefore, in the present embodiment, it is proposed that a steel material having high strength and an elongation ratio can be obtained by adjusting the chemical composition and the process parameters. Such high-strength steel has good formability and is advantageous for subsequent forming processing.

Please refer to FIG. 2, which is a graph showing the relationship between tensile strength and elongation of a high-strength steel according to an embodiment of the present invention, a microalloyed steel of the American Iron and Steel Association, and a steel which is generally continuously annealed. As can be seen from Fig. 2, as the tensile strength increases, the elongation of the micro-alloyed steel of the American Iron and Steel Association and the steel which is generally continuously annealed rapidly decreases rapidly. on the other hand, As the tensile strength increases, the decrease in the elongation of the steel after the sealed annealing process and the steel after the sealed annealing process in the embodiment of the present invention is significantly more moderate.

As can be seen from the above embodiments, one of the advantages of the present invention is that by adjusting the composition of the steel preform and/or the process control at each stage, the ductility and formability of the steel can be achieved while increasing the strength of the steel.

As can be seen from the above embodiments, another advantage of the present invention is that since the present invention utilizes a box-type annealing technique to anneal a finished steel material, a steel sheet having a large thickness can be produced.

While the present invention has been described above by way of example, it is not intended to be construed as a limitation of the scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

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Claims (10)

A high-strength steel material comprising: carbon in an amount of 0.05 wt% to 0.22 wt%; manganese in a content of 0.05 wt% to 1.50 wt%; phosphorus in a content of 0.07 wt% to 0.12 wt%; sulfur in an amount of less than 0.02 wt%; 0.04 wt% of bismuth; content of 0.025 wt% to 0.100 wt% of aluminum; content of 0.002 wt% to 0.009 wt% of nitrogen; content of less than 0.004 wt% of titanium; and iron having a residual content. The high strength steel material according to claim 1, wherein the aluminum content is from 0.025 wt% to 0.040 wt%. The high strength steel material according to claim 1, wherein the nitrogen content is from 0.004 wt% to 0.006 wt%. A method for manufacturing a high-strength steel material, comprising: providing a steel embryo, wherein the steel embryo comprises carbon in an amount of 0.05 wt% to 0.22 wt%, manganese in a content of 0.05 wt% to 1.50 wt%, and a content of 0.07 wt% to 0.12 wt%. Phosphorus, content of less than 0.02% by weight of sulfur, content of less than 0.04% by weight of cerium, content of 0.025% by weight to 0.100% by weight of aluminum, content of 0.002% by weight to 0.009% by weight of nitrogen, content of less than 0.004% by weight of titanium, and Iron having a residual content; performing a hot rolling process on the steel preform; The steel preform after the hot rolling process is subjected to a cold rolling process to obtain a finished steel; and a box annealing process is performed on the finished steel. The method for producing a high-strength steel material according to claim 4, wherein the hot rolling pass comprises controlling a finishing temperature to be greater than or equal to 850 °C. The method for producing a high-strength steel material according to claim 4, wherein the cold rolling process comprises controlling a cold rolling reduction rate to 35% to 70%. The method of manufacturing a high-strength steel according to claim 4, wherein the box annealing process comprises: controlling a process temperature at 650 ° C to 720 ° C; and controlling a process time from 8 hours to 15 hours. The method for manufacturing a high-strength steel material according to claim 4, further comprising: adjusting a tensile strength according to one of the high-strength steel materials and adjusting a composition of the steel preform by using a prediction formula, and cold rolling of the cold rolling process The reduction rate and/or one of the process temperatures of the box annealing process, wherein the prediction formula is: the predetermined tensile strength = the strength of the steel embryo + 0.0032 × (the ppm value of the manganese content) + 0.0678 × ( The ppm value of the phosphorus content) + 0.5 × (the cold rolling reduction rate - 49%) + 0.33 × (710 ° C - the process temperature) + 0.066 × (the ppm value of the carbon content). A method of manufacturing a high-strength steel material according to claim 4, wherein the method The content of aluminum is from 0.025 wt% to 0.040 wt%. The method for producing a high-strength steel material according to claim 4, wherein the nitrogen content is from 0.004% by weight to 0.006% by weight.