A kind of nb microalloyed high-strength and high-hole expansion steel and its production method

Abstract

A kind of Nb microalloyed high-strength and high-hole reaming steel and its production method, its chemical composition weight percent is: C 0.01-0.05%, Si 0.2-0.6%, Mn: 0.8-1.5%, P≤0.02%, S≤0.005 %, N≤0.008%, Als<0.001%, Ca≤0.0050%, Nb 0.01‑0.08%, Mn / S>250, total oxygen [O] T : 0.007~0.020%, remaining Fe and unavoidable impurities. The present invention selectively adds microalloying elements such as Nb to the steel; during the smelting process, by controlling the basicity of slag, the type and melting point of inclusions in the steel, the content of free oxygen in molten steel, and the content of acid-soluble aluminum Als; Strip continuous casting casts the cast strip, and the cast strip directly enters a lower airtight chamber with a non-oxidizing atmosphere, and enters the on-line rolling mill for hot rolling under airtight conditions; the strip is cooled by gas atomization cooling after rolling, and finally The produced steel coils can be used directly as hot-rolled sheets or after pickling-tempering.

Description

technical field [0001] The invention relates to the manufacturing technology of high hole-enlarging steel, in particular to a Nb microalloyed high-strength and high-hole-enlarging steel and a production method thereof. Background technique [0002] Most of the traditional thin strips are produced by continuous rolling of slabs with a thickness of 70-200mm. The traditional hot rolling process is: continuous casting + slab reheating and heat preservation + rough rolling + finishing rolling + cooling + Coiling, that is, firstly obtain a slab with a thickness of about 200mm through continuous casting, reheat and keep the slab, and then perform rough rolling and finishing rolling to obtain a steel strip with a thickness generally greater than 2mm. Laminar cooling and coiling complete the entire hot rolling production process. If it is necessary to produce a steel strip with a thickness of less than 1.5mm (inclusive), it is relatively difficult, and it is usually completed by sub...

AI Technical Summary

Problems solved by technology

[0008] With the increasing requirements of automobile design on the chassis structure, the forming of parts is more complex, and the requirements for flanging and hole reaming performance of steel plates are further improved. The strength and rigidity of parts can be improved through the shape design of flanging and local reaming of automobile parts, which can To achieve the purpose of reducing the thickness and weight of automobile steel plates, traditional carbon-manganese solid-solution strengthened steel and low-alloy precipitation-strengthened steel structural steel plates are difficult to meet the forming requirements of automobile chassis and cantilever parts, such as traditional 440MPa steel plate carbon-manganese solid-solution strengthened steel and low-alloy The hole expansion rate of precipitation strengthened steel is only between 50% and 70%, thus the high hole expansion steel was born

In the 1990s, the United States and Japan successively developed hot-rolled steel sheets with high hole expansion performance of 440-780MPa, and the hole expansion rate was 70%-131%. They are mainly used in formability, especially those that require good flanging performance. For automobile chassis, wheels and other parts, the hole expansion performance of the steel plate is related to the composition, strength and structure uniformity of the steel plate. Because it contains more precious alloy elements Cr, Nb, Ti, V and Mo, etc. Ferrite / bainite dual phase structure can be obtained under the same conditions, but its cost is higher

At the same time, the contact of high-temperature strip steel with cooling water will cause many problems: first, water spots (rust spots) will be formed on the surface of the strip steel, which will affect the surface quality; second, the cooling water used for laminar flow cooling or spray cooling It is easy to cause uneven local cooling on the surface of the strip, resulting in uneven microstructure inside the strip, resulting in uneven properties of the strip and affecting product quality; third, uneven local cooling on the surface of the strip will cause deterioration of the shape of the strip , affecting the shape quality

[0017] Chinese patents CN105154769 and CN106119702 respectively disclose a kind of 780MPa and 980MPa grade hot-rolled high-strength high-reaming steel and its manufacturing method, both of which are in the category of high-strength steel. Multi-microalloying elements are used to strengthen the steel type, and the alloy cost is relatively high; at the same time, its production method adopts traditional continuous casting + traditional hot rolling process to produce

[0018] International patent WO200928515 uses C, Si, Mn to add a small amount of Nb, Ti alloy elements, and can produce reaming steel with a tensile strength above 490MPa. Hot rolling must adopt a two-stage laminar flow cooling method, which can be more accurately simulated in the laboratory. However, in hot rolling production, the strip speed changes greatly during hot rolling, and the temperature of the steel plate in the air cooling section cannot be measured. A two-stage cooling model is used to control laminar cooling, and the steel plate The actual temperature fluctuates greatly, which will easily lead to large fluctuations in the performance of the steel coil head, middle and tail

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