CN116254479A - Hot-rolled thin ultra-high strength steel for automobile structure and production method thereof - Google Patents

Abstract

The invention discloses a hot-rolled thin-gauge ultra-high-strength automobile structural steel and a production method thereof, wherein C: 0.07%-0.11%, Si: ≤0.20%, Mn: 1.30-1.70%, and P≤0.015 %, S≤0.004%, Nb: 0.030%‑0.060%, Ti: 0.10%‑0.15%, Mo: 0.10‑0.20%, Als: 0.015%‑0.050%, N≤0.0035%, the balance is Fe and other impurities . Smelting: control the content of O and N in the steel to avoid over-oxidation of molten steel, and use a sliding plate to block slag and tap the steel to control the amount of slag after tapping; adopt LF+RH double refining process, the LF treatment cycle is ≥20min, and the soft blowing time is not Less than 15min; continuous casting: the whole process of argon protection pouring, the superheat is controlled at 15-35°C, and the liquid level fluctuation of the crystallizer is controlled to be ≤±3mm; heating: heating time is ≥230min, the temperature of the soaking section is ≥40min, and the furnace temperature after heating Control at ≥1240°C; rough rolling final pass: control within the range of 1070-1110°C; finish rolling: use 7 units for rolling, optimize rolling force distribution; finish rolling and final rolling: control within the range of 870-910°C ;Cooling and coiling: ordinary laminar flow sparse cooling mode is adopted for cooling, the coiling temperature is controlled within the range of 590-620°C, and stacking and slow cooling is carried out after rolling for ≥72h.

Description

A kind of hot-rolled thin-gauge ultra-high-strength automobile structural steel and its production method

technical field

The invention belongs to the technical field of metallurgy, and in particular relates to a hot-rolled thin-gauge ultra-high-strength automobile structural steel and a production method thereof.

Background technique

As a big automobile country in my country, with the rapid development of the transportation industry, the lightweight of automobiles can reduce the weight of the car body and reduce energy consumption on the premise of ensuring safety performance. As an important part of the lightweight material selection of vehicles, high-strength steel can significantly improve the collision safety performance of vehicles. The main way to reduce the weight of automobiles is to reduce the thickness of the steel while increasing the strength of the steel, thereby reducing the weight of the vehicle. How to stably produce ultra-high-strength automotive structural steel with a high yield is a technical problem to be solved in this field. At the same time, the rolling stability of hot-rolled thin-gauge ultra-high-strength steel strips in wide-width rolling mills is poor, and problems such as tailing and steel jamming are prone to occur, and the yield rate is low due to plate shape problems.

Patent No. CN114774788A discloses "a 900MPa grade high surface quality pickled automotive steel and its manufacturing method and application", the composition mass percentage of the steel is: C: 0.070-0.10%, Si: 0.22-0.32%, Mn: 1.60-2.20%, P≤0.015%, S≤0.008%, Nb: 0.020-0.080%, Ti: 0.10-0.15%, Al: 0.030-0.060%, Mo: 0.10-0.20%, Cr: 0.20-0.50%, And Mo/3+Cr≥0.6%, Ca≤0.008%, the balance is Fe and inevitable inclusions. In the invention, the acid-washed automobile steel with tensile strength ≥ 900 MPa and high surface can be obtained through the process. In this invention, Nb+Ti+Mo+Cr alloy elements are added, and the cost of the alloy is relatively high. At the same time, the content of Mn element is relatively high, which further increases the cost.

Patent No. CN112410668A discloses "a 780MPa grade automobile structural steel and production method", the composition mass percentage of steel is: C: 0.090-0.13%, Si: 0.02-0.15%, Mn: 1.65-1.90%, Al: 0.010-0.040%, Nb: 0.055-0.070%, Ti: 0.050-0.070%, Cr: 0.30-0.40%, Cu: 0.30-0.65%, Sb: 0.15-0.30%, Ni: 0.020-0.045%, Bi: 0.010 -0.045%, P: ≤0.015%, S: ≤0.006%, and the rest are Fe and unavoidable impurities. This patent states that steel for automotive structures with a tensile strength of ≥780 MPa can be obtained with excellent mechanical properties and anti-corrosion properties. In the examples, the tensile strength reaches ≥900 MPa. Although the addition of Sb and Bi elements in this patent can enhance the anti-corrosion effect, these two elements are rarely used in industrial production and are harmful elements, which are not suitable for large-scale industrial production.

Therefore, there is a need for a hot-rolled thin-gauge ultra-high-strength automotive structural steel with low alloy cost, simple process and stable production and a production method thereof.

Contents of the invention

The object of the present invention is to provide a hot-rolled thin-gauge ultra-high-strength automotive structural steel and a production method thereof.

The technical solution adopted by the present invention to solve the technical problem is: a kind of hot-rolled thin-gauge ultra-high-strength automobile structural steel, calculated by weight percentage as C: 0.07%-0.11%, Si: ≤0.20%, Mn: 1.30-1.70 %, P≤0.015%, S≤0.004%, Nb: 0.030%-0.060%, Ti: 0.10%-0.15%, Mo: 0.10-0.20%, Als: 0.015%-0.050%, N≤0.0035%, balance For Fe and other impurities.

Specifically, the yield strength of the steel is ≥ 820 MPa, the tensile strength is ≥ 900 MPa, and the elongation is ≥ 18%, and its metallographic structure includes ferrite + a small amount of pearlite.

A method for producing hot-rolled thin-gauge ultra-high-strength automotive structural steel, comprising the following steps:

1) Smelting: Control the content of O and N in the steel to avoid over-oxidation of molten steel, and use a slide plate to stop the slag and tap the steel to control the amount of slag after tapping; adopt LF+RH double refining process, LF treatment cycle ≥ 20min, soft blowing The time is not less than 15 minutes;

2) Continuous casting: the whole process is protected by argon gas, the superheat is controlled at 15-35°C, and the liquid level fluctuation of the crystallizer is controlled to be ≤±3mm;

3) Heating: Heating time ≥ 230min, soaking section temperature ≥ 40min, after heating, the furnace temperature is controlled at ≥ 1240°C;

4) Final pass of rough rolling: controlled within the range of 1070-1110°C;

5) Finish rolling: rolling with 7 units;

6) Finish rolling and finishing rolling: controlled within the range of 870-910°C;

7) Cooling and coiling: Cooling adopts the ordinary laminar flow sparse cooling mode, the coiling temperature is controlled within the range of 590-620°C, and stacking and slow cooling is carried out after rolling for ≥72h.

Specifically, the method also includes rough rolling descaling, the pressure of rough rolling descaling is ≥ 25 MPa, and all passes are used for descaling.

Specifically, the rolling of the 7 units includes F1 rolling force controlled at 21000-25000KN, F2 rolling force controlled at 22000-26000KN, F3 rolling force controlled at 20000-24000KN, F4 rolling force controlled at 17000-21000KN , F5 rolling force is controlled at 11000-15000KN, F6 rolling force is controlled at 9000-13000KN, F7 rolling force is controlled at 8000-12000KN.

The present invention has the following beneficial effects:

1) Optimizing alloy design, using Nb+Ti+Mo composite alloy to improve material strength, low alloy cost, and no harmful elements;

2) Adopting reasonable heating time, furnace temperature, exit temperature of rough rolling, finishing temperature of finishing rolling and coiling temperature control performance, to obtain good tensile properties;

3) The rolling force distribution of the 7 sets of finishing rolling and the ordinary laminar flow sparse cooling mode are adopted to realize the stable rolling of thin-gauge ultra-high-strength steel hot-rolled coils in the wide-width rolling set.

Detailed ways

The present invention will now be described in further detail.

A stable production method for hot-rolled thin-gauge ultra-high-strength automotive structural steel. Through composition design, clean smelting, continuous casting, rolling and other processes, the content of N element is controlled below 35ppm; the rolling force of 7 sets of finishing rolling is optimized Allocation, using ordinary laminar flow sparse cooling mode, solves the problems of poor rolling stability and plate shape problems of thin-gauge ultra-high-strength steel strips in wide-width rolling mills, which lead to jamming and low yields. Steel strips with yield strength ≥ 820MPa, tensile strength ≥ 900MPa, and elongation after fracture ≥ 18% are produced, which have the characteristics of stable quality, simple process, and easy industrial production of wide-width rolling and thin-gauge ultra-high-strength steel.

A method for producing hot-rolled thin-gauge ultra-high-strength automotive structural steel, comprising the following steps:

1) Smelting: C: 0.07%-0.11%, Si: ≤0.20%, Mn: 1.30-1.70%, P≤0.015%, S≤0.004%, Nb: 0.030%-0.060%, Ti: 0.10%-0.15%, Mo: 0.10-0.20%, Als: 0.015%-0.050%, N≤0.0035%, the balance is Fe and other impurities; the content of O and N in the steel must be strictly controlled to avoid overoxidation of molten steel, Sliding plate is used to stop the slag and tap the steel, and the amount of slag under tapping is strictly controlled; LF+RH double refining process is adopted, the LF treatment cycle is ≥ 20 minutes, and the soft blowing time is not less than 15 minutes;

2) Continuous casting: The whole process of continuous casting process is protected by argon gas, the superheat is controlled at 15-35°C, the liquid level fluctuation of the crystallizer is controlled to be ≤±3mm, and the purity of molten steel is improved to improve the quality of the billet;

3) Heating: The heating time is ≥230min. In order to ensure that the slab is fully heated in the heating furnace, the soaking period of the slab should not be less than 40min, and the temperature of the slab out of the steel strip should be controlled at ≥1240°C; The Ti content is relatively large, so high-temperature firing is used to ensure that the coarse TiC in the billet is fully dissolved during the continuous casting process, so as to ensure that a sufficient number of fine TiC particles are precipitated during the rolling process;

4) Final pass of rough rolling: the final pass process of rough rolling of the steel strip is controlled at 1070-1110°C; the rough rolling process is rolled above the recrystallization temperature, and uniform and fine austenite is obtained through repeated deformation and recrystallization of austenite. Tensitic grains;

5) Rolling force of finishing rolling unit 7: F1 rolling force is controlled at 21000-25000KN, F2 rolling force is controlled at 22000-26000KN, F3 rolling force is controlled at 20000-24000KN, F4 rolling force is controlled at 17000-21000KN, The rolling force of F5 is controlled at 11000-15000KN, the rolling force of F6 is controlled at 9000-13000KN, and the rolling force of F7 is controlled at 8000-12000KN. Steel passability and rolling stability of high-strength steel;

6) Finish rolling and finishing rolling process: the finishing rolling and finishing rolling process of the steel strip is controlled at 870-910°C; through rolling in the non-recrystallized zone, flat austenite is obtained and transformed into uniform and fine ferrite in the subsequent cooling process , this final rolling temperature setting can ensure the stability of rolling and give full play to the precipitation strengthening effect of alloying elements;

7) Cooling and coiling process: ordinary laminar flow sparse cooling mode is adopted for cooling. The sparse cooling mode can reduce the internal stress of the steel strip on the basis of conventional plate shape control and optimize the plate shape of the steel strip; the coiling temperature is controlled at 590-620 In the range of ℃, higher coiling temperature will reduce the strength of ferrite, and lower coiling temperature will affect the precipitation strengthening effect of alloying elements, thereby reducing the strength of the steel strip; The slow cooling of the stack can further release the internal stress of the steel strip, and at the same time, the slow cooling of the stack can improve the temperature uniformity of the steel coil and reduce the performance fluctuation of the coil;

8) Rough rolling descaling pressure ≥ 25MPa, take the whole pass descaling.

The thickness of the steel coil is ≤4mm, the metallographic structure of the steel coil contains ferrite + a small amount of pearlite, the yield strength of the steel coil is ≥820MPa, the tensile strength is ≥900MPa, and the elongation is ≥18%.

Example 1:

A hot-rolled thin-gauge ultra-high-strength automotive structural steel, the chemical composition and weight percentage of which are C: 0.085%, Si: 0.2%, Mn: 1.50%, P: 0.014%, S: 0.0010%, Nb: 0.058%, Ti: 0.126%, Mo: 0.15%, Als: 0.034%, N: 0.0023%, the balance is Fe and other impurities, the thickness of the steel coil is 3.0mm, and the metallographic structure includes ferrite + pearlite.

A production method of hot-rolled thin-gauge automotive structural steel, comprising the steps of smelting, continuous casting, heating, rough rolling, finish rolling, cooling, and coiling:

1) Smelting process: LF+RH double refining process is adopted, the LF treatment cycle is 22 minutes, and the RH soft blowing time is 16 minutes;

2) Continuous casting process: the whole process is protected by argon gas, the superheat is controlled at 20°C, and the liquid level fluctuation of the crystallizer is controlled to be ≤ ± 3mm, which can improve the purity of molten steel and improve the quality of casting slabs;

3) Heating process: the temperature of the slab out of the furnace is controlled at 1240°C, and the heating time is 240 minutes. In order to ensure that the slab is fully heated in the heating furnace, the time of the slab in the soaking section is 43 minutes;

4) Rough rolling process: the descaling pressure is 25MPa, the whole pass descaling is adopted, and the outlet temperature of the final pass is 1105°C;

5) Rolling force of 7 units of finishing rolling: F1: 23800KN, F2: 24533KN, F3: 22081KN, F4: 19636KN, F5: 13503KN, F6: 11573KN, F7: 10777KN;

6) In the finish rolling process, the final rolling temperature is 895°C;

7) In the cooling process, the laminar sparse cooling mode is adopted, and the ultra-fast cooling rate is 20°C/s;

8) In the coiling process, the coiling temperature is 600° C., the yield strength ReL is 850 MPa, the tensile strength Rm is 933 MPa, and the elongation is 20%.

Example 1:

A hot-rolled thin-gauge ultra-high-strength automotive structural steel, the chemical composition and weight percentage of which are C: 0.080%, Si: 0.2%, Mn: 1.480%, P: 0.014%, S: 0.0010%, Nb: 0.054%, Ti: 0.123%, Mo: 0.12%, Als: 0.034%, N: 0.0026%, the balance is Fe and other impurities, the thickness of the steel coil is 2.0mm, and the metallographic structure includes ferrite + pearlite.

A production method of hot-rolled thin-gauge automotive structural steel, comprising the steps of smelting, continuous casting, heating, rough rolling, finish rolling, cooling, and coiling:

1) Smelting process: LF+RH double refining process is adopted, the LF treatment cycle is 20 minutes, and the RH soft blowing time is 15 minutes;

2) Continuous casting process: the whole process is protected by argon gas, the superheat is controlled at 20°C, and the liquid level fluctuation of the crystallizer is controlled to be ≤ ± 3mm, which can improve the purity of molten steel and improve the quality of casting slabs;

3) Heating process: the temperature of the slab out of the furnace is controlled at 1256°C, and the heating time is 253 minutes. In order to ensure that the slab is fully heated in the heating furnace, the time of the slab in the soaking section is 46 minutes;

4) Rough rolling process: the descaling pressure is 25MPa, the whole pass descaling is adopted, and the outlet temperature of the final pass is 1050°C;

5) Rolling force of finishing rolling unit 7: F1: 22783KN, F2: 24325KN, F3: 22176KN, F4: 19789KN, F5: 13646KN, F6: 11643KN, F7: 11215KN:

6) Finish rolling process: the final rolling temperature is 903°C;

7) Cooling process: laminar sparse cooling mode is adopted, and the ultra-fast cooling rate is 20°C/s;

8) Coiling process: the coiling temperature is 614° C., the yield strength ReL is 865 MPa, the tensile strength Rm is 947 MPa, and the elongation is 19.5%.

The present invention is not limited to the above-mentioned embodiments, and anyone should know that any structural changes made under the inspiration of the present invention, and any technical solutions that are the same as or similar to the present invention, all fall within the protection scope of the present invention.

The technologies, shapes and construction parts not described in detail in the present invention are all known technologies.

Claims (4)

1. A hot-rolled thin-gauge ultra-high-strength automotive structural steel, characterized in that, by weight percentage, it is C: 0.07%-0.11%, Si: ≤0.20%, Mn: 1.30-1.70%, P≤0.015%, S≤0.004%, Nb: 0.030%-0.060%, Ti: 0.10%-0.15%, Mo: 0.10-0.20%, Als: 0.015%-0.050%, N≤0.0035%, and the balance is Fe and other impurities. 2. A kind of hot-rolled thin-gauge ultra-high-strength automotive structural steel according to claim 1, characterized in that, the yield strength of the steel is ≥820MPa, the tensile strength is ≥900MPa, the elongation is ≥18%, and its metallographic The structure contains ferrite + a small amount of pearlite. 3. A method for producing hot-rolled thin-gauge ultra-high-strength automotive structural steel based on claim 1, characterized in that it comprises the following steps: 1) Heating: Heating time ≥ 230min, soaking section temperature ≥ 40min, after heating, the furnace temperature is controlled at ≥ 1240°C; 2) The final pass of rough rolling: controlled within the range of 1070-1110°C; 3) Finish rolling: 7 sets of rolling are used, 7 sets of rolling include F1 rolling force controlled at 21000-25000KN, F2 rolling force controlled at 22000-26000KN, F3 rolling force controlled at 20000-24000KN, F4 rolling force The rolling force of F5 is controlled at 17000-21000KN, the rolling force of F5 is controlled at 11000-15000KN, the rolling force of F6 is controlled at 9000-13000KN, and the rolling force of F7 is controlled at 8000-12000KN; 4) Finish rolling and finishing rolling: controlled within the range of 870-910°C; 5) Cooling and coiling: Cooling adopts ordinary laminar flow sparse cooling mode, the coiling temperature is controlled within the range of 590-620°C, and stacking and slow cooling is carried out after rolling for ≥72h. 4. A method for producing hot-rolled thin-gauge ultra-high-strength automotive structural steel according to claim 3, characterized in that the method also includes rough rolling and descaling, the pressure of rough rolling and descaling is ≥ 25MPa, and all passes are taken descaling.