TWI753366B - Low yield ratio and extra-high strength steel and method for manufacturing the same - Google Patents

Abstract

A low yield ratio and extra-high strength steel and a method for manufacturing the same are described. The low yield ratio and extra-high strength steel includes carbon with a weight percentage from 0.08% to 0.15%, silicon with a weight percentage from 0.1% to 0.8%, manganese with a weight percentage from 1.0% to 1.5%, phosphorous with a weight percentage from 0.01% to 0.05%, sulfur with a weight percentage which is smaller than 0.05%, chromium with a weight percentage from 0.2% to 0.8%, niobium with a weight percentage which is smaller than 0.05%, vanadium with a weight percentage from 0.01% to 0.09%, titanium with a weight percentage from 0.1% to 0.2%, aluminum with a weight percentage from 0.01% to 0.05%, calcium with a weight percentage which is smaller than 0.05%, nitrogen with a weight percentage which is smaller than 200ppm, insignificant impurities, and balance iron.

Description

Ultra-high-strength steel with low reduction ratio and manufacturing method thereof

The present invention relates to a manufacturing method of a steel material, and more particularly, to a high-strength steel material with a low yield ratio and a manufacturing method thereof.

Duplex steel is a composite structure of steel. A dual phase steel system includes a soft iron phase and a hard iron phase interspersed within the soft iron phase. Since dual-phase steel has both soft and hard characteristics, it can not only provide sufficient safety protection, but also has excellent formability, so it can meet the needs of the new generation of automotive component steel. Generally speaking, the smaller the yield ratio is, the better the processability is. The yield ratio is defined as the ratio of yield strength to tensile strength, where yield strength is the stress required to initiate plastic deformation of a material, and tensile strength is the maximum stress a material can withstand before it ruptures.

A traditional dual phase steel is a high strength low alloy (HSLA) steel. This dual-phase steel system produces a two-phase structure of tempered loose iron and lower toughened iron in a two-stage cooling method. This production technology is to cool down the steel to 400°C to produce lower toughened iron after the steel is rolled, and then cool it again to produce Matian loose iron.

Another production technology of dual-phase steel is to add strengthening elements such as chromium (Cr), molybdenum (Mo), niobium (Nb) in its composition design, and accelerate the cooling of the finished rolled steel to 300°C to 450°C after hot rolling. . The microstructure of the dual-phase steel produced by this technology is mainly composed of ductile iron, and the rest is Matian loose iron structure, and the yield strength (YS) of this dual-phase steel can reach more than 885MPa, and the tensile strength (TS) can reach 950MPa to 1130MPa. Of course, this technology has a limited thickness of 6mm to 25mm in production.

There is also a dual-phase steel production technology that adds more than 1wt% high silicon (Si), and microalloys such as titanium (Ti) and vanadium (V) to strengthen the composition design, and adopts one-stage cooling, and the coiling temperature is 350°C to 550°C. The structure of the dual-phase steel produced by this technology is mainly ductile iron, and its tensile strength can reach 980MPa.

Therefore, an object of the present invention is to provide a kind of ultra-high-strength steel with a low reduction ratio and a manufacturing method thereof. Two-stage cooling method, and coiling of steel at extremely low coiling temperature. In this way, the shape and size of the microstructure of the steel can be further controlled, so that the steel has the advantages of low yield ratio and ultra-high strength under the same strength grade.

According to the above object of the present invention, an ultra-high-strength steel material with a low reduction ratio is proposed. The ultra-high strength steel with low reduction ratio contains 0.08wt% to 0.15wt% carbon (C), 0.1wt% to 0.8wt% silicon, 1.0wt% to 1.5wt% manganese (Mn), 0.01wt% to 0.01wt% 0.05wt% phosphorus, 0.05wt% or less sulfur (S), 0.2wt% to 0.8wt% chromium, 0.05wt% or less niobium, 0.01wt% to 0.09wt% vanadium, 0.1wt% to 0.2wt% 0.01 wt% to 0.05 wt% of aluminum (Al), 0.05 wt% or less of calcium (Ca), 200 ppm or less of nitrogen (N), insignificant impurities, and a balanced amount of iron (Fe).

According to an embodiment of the present invention, the structure of the above-mentioned ultra-high strength steel with a low reduction ratio includes ferric iron and loose iron.

According to an embodiment of the present invention, the volume percentage ratio of the above-mentioned fertilizer granulated iron and loose hemp iron is 5 to 10.

According to an embodiment of the present invention, the average particle size of the above-mentioned Matian loose iron is less than 10 μm.

According to an embodiment of the present invention, the tensile strength of the ultra-high-strength steel with low yield ratio is greater than 980 MPa, the elongation is greater than or equal to 10%, and the yield ratio is less than or equal to 0.8.

According to the above object of the present invention, another method for manufacturing ultra-high-strength steel with a low reduction ratio is proposed. In this method, a steel billet is provided. The steel billet contains 0.08wt% to 0.15wt% carbon, 0.1wt% to 0.8wt% silicon, 1.0wt% to 1.5wt% manganese, 0.01wt% to 0.05wt% phosphorus, 0.05wt% or less sulfur , 0.2wt% to 0.8wt% chromium, 0.05wt% or less niobium, 0.01wt% to 0.09wt% vanadium, 0.1wt% to 0.2wt% titanium, 0.01wt% to 0.05wt% aluminum, 0.05wt% % calcium, 200 ppm or less nitrogen, insignificant impurities, and balanced iron. A hot rolling process is performed on the steel billet to obtain finished rolled steel, wherein the finished rolling temperature of the hot rolling process is above the Ar3 temperature. Laminar cooling treatment is performed on the finished rolled steel material to cool the finished rolled steel material to a first temperature, wherein the first temperature is 600°C to 750°C. The finished rolled steel is maintained at the first temperature for a predetermined time. The finished-rolled steel material is cooled to a second temperature, wherein the second temperature is below 250°C. A coiling step is performed on the finished rolled steel to obtain a coil.

According to an embodiment of the present invention, before the hot rolling process, the above-mentioned method further includes re-heating the steel billet to raise the temperature of the steel billet to 1200°C to 1350°C.

According to an embodiment of the present invention, the above-mentioned finishing temperature is below 950°C.

According to an embodiment of the present invention, the cooling rate of the laminar cooling process is above -20°C/s.

According to an embodiment of the present invention, the above-mentioned predetermined time is 3 seconds to 15 seconds.

According to an embodiment of the present invention, the cooling rate of the above-mentioned cooling treatment is above -20°C/s.

Embodiments of the present invention provide an ultra-high-strength steel with a low yield ratio and a manufacturing method thereof. The steel billet is designed by designing the composition, and two-stage cooling treatment is adopted, and the coiling of the steel is performed at an extremely low coiling temperature. Coil, which can effectively control the microstructure and size of the steel. Therefore, the steel produced by the embodiment of the present invention has the advantages of low reduction ratio and ultra-high strength under the same strength grade.

The ultra-high-strength steel with low yield ratio according to the embodiment of the present invention mainly adds an appropriate amount of alloying elements to the low-carbon steel composition. For example, the composition design of ultra-high-strength steels with low yield ratios uses the addition of phosphorus and chromium, and the addition of microalloys such as vanadium and titanium. In some embodiments, the composition of the low yield ratio ultra-high strength steel comprises carbon, silicon, manganese, phosphorus, sulfur, chromium, niobium, vanadium, titanium, aluminum, calcium, nitrogen, insignificant impurities, and balanced amounts of iron. For example, in the ultra-high strength steel with low reduction ratio, the carbon content may be 0.08wt% to 0.15wt%, the silicon content may be 0.1wt% to 0.8wt%, and the manganese content may be 1.0wt% to 1.5wt% %, the phosphorus content can be 0.01wt% to 0.05wt%, the sulfur content can be below 0.05wt%, the chromium content can be 0.2wt% to 0.8wt%, the niobium content can be below 0.05wt%, and the vanadium content can be 0.01wt% % to 0.09wt%, titanium content may be 0.1wt% to 0.2wt%, aluminum content may be 0.01wt% to 0.05wt%, calcium content may be below 0.05wt%, and nitrogen content may be below 200ppm.

The ultra-high-strength steel with low reduction ratio can be dual-phase steel. In some examples, the ratio of the volume percentages of ferric iron to hemp iron in the structure of the steel is about 5 to about 10. The average particle size of Matian loose iron in the steel may be, for example, less than about 10 μm. The steel can have a tensile strength greater than 980MPa and an elongation greater than or equal to about 10% under the condition that the fertilizer grain iron phase and the loose iron phase have a specific volume ratio, and the average particle size of the loose iron is controlled to be less than about 10 μm. , and a drop ratio of less than or equal to about 0.8.

Please refer to FIG. 1 , which is a flow chart illustrating a method for manufacturing a low-deduction ratio ultra-high-strength steel according to an embodiment of the present invention. In some embodiments, when manufacturing ultra-high strength steel with a low yield ratio, step 100 may be performed first to provide a steel blank. In some illustrative examples, the steel billet comprises 0.08-0.15 wt% carbon, 0.1-0.8 wt% silicon, 1.0-1.5 wt% manganese, 0.01-0.05 wt% phosphorus, 0.05 wt% wt% or less sulfur, 0.2 wt% to 0.8 wt% chromium, 0.05 wt% or less niobium, 0.01 wt% to 0.09 wt% vanadium, 0.1 wt% to 0.2 wt% titanium, 0.01 wt% to 0.05 wt% 0.05 wt% or less of calcium, 200 ppm or less of nitrogen, insignificant impurities, and a balanced amount of iron.

Next, the steel billets can be processed using, for example, steelmaking or electric furnace methods. If step 110 is performed, the steel blank is reheated, thereby increasing the temperature of the steel blank. In some examples, the reheat treatment can increase the temperature of the steel billet to about 1200°C to about 1350°C. After the reheat treatment, step 120 may be performed to perform a hot rolling process on the heated steel billet to obtain finished rolled steel. In some instances, the hot rolling process for the steel billet may be controlled to be above the Ar3 temperature. The Ar3 temperature refers to the initial temperature at which the iron from the hot-rolled steel billet is transformed into ferrite iron during the cooling process. Therefore, controlling the finishing temperature of the hot rolling process of the steel billet to be above the Ar3 temperature means that the hot rolling of the steel billet is completed in the iron phase of the Vostian. In some exemplary examples, the finishing temperature of the hot rolling process can be further controlled below about 950°C.

After the hot rolling process of the steel billet is completed, step 130 may be performed to first perform laminar cooling treatment on the finished rolled steel material, and then use, for example, water spray to accelerate the cooling of the finished rolled steel material to the first temperature. The laminar cooling process cools the finished rolled steel to the ferrite transformation zone. In some illustrative examples, the cooling rate of the laminar cooling process may be greater than about -20°C/s. In addition, the first temperature of the finished rolling steel may be, for example, about 600°C to about 750°C.

After the laminar cooling treatment of the rolled steel material is completed, step 140 may be performed to maintain the finished rolled steel material at the first temperature for a predetermined time. Through such a temperature-holding treatment, an appropriate amount of ferritic iron and carbon-rich Wesfield iron can be produced in the finished rolled steel. In some exemplary examples, the predetermined temperature holding time may be about 3 seconds to about 15 seconds. In some instances, the temperature-holding treatment of the finished rolled steel may be air-cooled and temperature-holding.

Next, step 150 may be performed to perform a cooling treatment on the finished rolled steel after the temperature holding treatment, so as to further accelerate the temperature of the finished rolled steel to cool to a second temperature. In some demonstrative examples, a water spray may be used to cool the finished rolled steel to the second temperature. Through this cooling treatment, the Wostian iron in the steel can be metamorphosed to completely produce loose iron, so that the steel has a dual-phase structure composed of fertilized iron and loose iron. In some illustrative examples, the cooling rate of this cooling process may be above about -20°C/s.

In this embodiment, an appropriate amount of elements such as phosphorus, chromium, vanadium, and titanium are added to the components of low-carbon steel, and the rolling temperature of the hot rolling process, the temperature after laminar cooling treatment and cooling treatment, and the temperature of the steel plate are controlled in coordination with it. The temperature at the time of rolling, and the temperature-holding treatment is introduced between the laminar cooling treatment and the cooling treatment. Thereby, the microstructure and size of the steel can be controlled, so that the ratio of the volume percentage of the fertilizer granulated iron and the loose iron in the generated steel structure is about 5 to 10, and the average particle size of the loose iron in the field is about 5 to 10. less than 10μm. In this way, the steel can be made to have a tensile strength greater than 980 MPa, an elongation equal to or greater than 10%, and a yield ratio equal to or less than 0.80. Therefore, the steel produced by the embodiment of the present invention has the advantages of low reduction ratio and ultra-high strength under the same strength grade.

After the cooling treatment of the rolled steel material is completed, step 160 may be performed to coil the finished rolled steel material at the temperature after the cooling treatment to obtain a coil formed from the finished rolled steel material. In some examples, step 170 can be selectively performed according to the requirements of the process, so as to use an acid solution to perform pickling treatment on the steel coil, so that the scale formed on the surface of the steel coil can be removed, thereby substantially completing the low yield ratio The production of ultra-high-strength steel. In some instances, the coil may be reprocessed according to the application requirements after the coil is pickled.

The following uses a plurality of examples and comparative examples to describe the technical contents and effects of the present embodiment in more detail. However, it is not intended to limit the present invention, and those 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.

Please refer to Table 1 below, which lists the thickness, content of some components (wt%), hot rolling temperature control (°C), and evaluation methods, including yield strength (MPa), Tensile strength (MPa), elongation (%), and yield ratio (%). Table 1 project Element Example Comparative example 1 2 3 4 1 2 size thickness 3.5 2.6 4 3 4 4 Steel billet composition carbon 0.10 0.10 0.10 0.10 0.10 0.10 manganese 1.28 1.28 1.25 1.25 1.28 1.28 phosphorus 0.026 0.026 0.024 0.024 0.026 0.026 sulfur 0.002 0.002 0.001 0.001 0.002 0.002 silicon 0.39 0.39 0.37 0.37 0.39 0.39 aluminum 0.028 0.028 0.03 0.03 0.028 0.028 calcium 0.002 0.002 0.002 0.002 0.002 0.002 Hot rolling temperature control heating temperature 1227 1273 1214 1266 1260 1263 Finish rolling temperature 870 870 870 870 870 870 coil temperature 200 200 200 200 650 550 Evaluation method yield strength 788 784 774 794 691 762 tensile strength 1056 1077 1019 1059 803 863 Elongation 13.3 12.3 14 13.3 18.9 17.9 yield ratio 74.6 72.8 76 77.5 86.1 88.3

Examples 1 to 4 are made according to Table 1 and the steel billet components of the above-mentioned embodiment, and then steel is made, and the hot rolling process is carried out according to the heating temperature, finish rolling temperature, and coil temperature set in Table 1 to obtain hot rolled steel. . Comparative Examples 1 and 2 were prepared according to Table 1 and the ingredients of the steel billet in the above-mentioned embodiment, and then steel was made, and the hot rolling process was performed according to the heating temperature, finishing temperature, and coil temperature set in Table 1 to obtain hot-rolled steel. That is, the contents of chromium, niobium, vanadium, and titanium in the steel billet components of Examples 1 to 4 and Comparative Examples 1 and 2 are based on the steel billet components of the above-described embodiment.

It can be seen from the above table 1 that the same steel billet composition is used in Examples 1 and 2 and Comparative Examples 1 and 2, but in the case of using hot rolling processes with different temperature control conditions, Comparative Examples 1 and 2 cannot achieve the same high resistance as the Example. Tensile strength and low yield ratio.

It can be seen from the above-mentioned embodiments that one of the advantages of the present invention is that the steel composition of the ultra-high strength steel with low yield ratio and its manufacturing method of the present invention is designed to add phosphorus and chromium, and add microalloys such as vanadium and titanium, and the manufacturing process The two-stage cooling method is adopted, and the coiling of the steel is carried out at a very low coiling temperature. In this way, the shape and size of the microstructure of the steel can be further controlled, so that the steel has the advantages of low yield ratio and ultra-high strength under the same strength grade.

Although the present invention has been disclosed as above with examples, it is not intended to limit the present invention. Anyone with ordinary knowledge in this technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be determined by the scope of the appended patent application.

100: Steps 110: Steps 120: Steps 130: Steps 140: Steps 150: Steps 160: Steps 170: Steps

In order to make the above and other objects, features, advantages and embodiments of the present invention more clearly understood, the accompanying drawings are described as follows: [FIG. 1] is a flow chart illustrating a method for manufacturing a low-deduction ratio ultra-high-strength steel according to an embodiment of the present invention.

Domestic storage information (please note in the order of storage institution, date and number) none Foreign deposit information (please note in the order of deposit country, institution, date and number) none

100: Steps

110: Steps

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Claims (9)

An ultra-high strength steel with a low reduction ratio, comprising: 0.08wt% to 0.15wt% carbon; 0.1wt% to 0.8wt% silicon; 1.0wt% to 1.5wt% manganese; 0.01wt% to 0.05wt% Phosphorus; 0.05wt% or less sulfur; 0.2wt% to 0.8wt% chromium; 0.05wt% or less niobium; 0.01wt% to 0.09wt% vanadium; 0.1wt% to 0.2wt% titanium; 0.01wt% to 0.05 wt % aluminum; 0.05 wt % or less calcium; 200 ppm or less nitrogen; insignificant impurities; and a balanced amount of iron, wherein the structure of the low-reduction ratio ultra-high-strength steel comprises ferric iron and hemp iron, And the volume percentage ratio of the fertilizer granulated iron and the hemp field iron is 5 to 10. The ultra-high-strength steel with low yield ratio according to claim 1, wherein the average particle size of the Matian loose iron is less than 10 μm. Ultra-high-strength steel with low yield ratio as described in claim 1, The tensile strength of the ultra-high strength steel with low yield ratio is greater than 980MPa, the elongation is greater than or equal to 10%, and the yield ratio is less than or equal to 0.8. A method for manufacturing ultra-high strength steel with low reduction ratio, comprising: providing a steel blank, wherein the steel blank comprises: 0.08wt% to 0.15wt% carbon; 0.1wt% to 0.8wt% silicon; 1.0wt% to 1.0wt% 1.5wt% manganese; 0.01wt% to 0.05wt% phosphorus; 0.05wt% or less sulfur; 0.2wt% to 0.8wt% chromium; 0.05wt% or less niobium; 0.01wt% to 0.09wt% vanadium; 0.1 wt% to 0.2 wt% titanium; 0.01 wt% to 0.05 wt% aluminum; 0.05 wt% or less calcium; 200 ppm or less nitrogen; insignificant impurities; a rolling process to obtain a finished rolled steel, wherein a finished rolling temperature of the hot rolling process is above an Ar3 temperature; the finished rolled steel is subjected to laminar flow cooling treatment to cool the finished rolled steel to a first temperature, wherein the first temperature is 600°C to 750°C; maintaining the finished-rolled steel material at the first temperature for a preset time; performing a cooling treatment on the finished-rolled steel material to cool the finished-rolled steel material to a second temperature, wherein the second temperature is below 250°C; and performing a coiling step on the finished rolled steel to obtain a steel coil. The method as claimed in claim 4, wherein before the hot rolling process, the method further comprises performing a reheat treatment on the steel billet to heat the steel billet to 1200°C to 1350°C. The method of claim 4, wherein the finishing temperature is 950°C or lower. The method of claim 4, wherein the cooling rate of the laminar cooling process is -20°C/s or more. The method of claim 4, wherein the cooling rate of the cooling treatment is -20°C/s or more. The method of claim 4, wherein the preset time is 3 seconds to 15 seconds.

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