Production method of hot-rolled SPFH590 high-strength plate strip for wheel with small performance difference of same plate

Abstract

The invention provides a production method of a hot-rolled SPFH590 high-strength plate strip for wheels. The hot-rolled SPFH590 high-strength plate strip is small in performance difference of the same plate. The hot-rolled SPFH590 high-strength plate strip comprises the following chemical components in percentage by weight: 0.05-0.12 wt% of C, less than or equal to 0.12 wt% of Si, 1.30-1.70 wt% of Mn, less than or equal to 0.020 wt% of P, less than or equal to 0.010 wt% of S, 0.020-0.080 wt% of Nb, 0.010-0.050 wt% of Ti, 0.020-0.045 wt% of Alt and less than or equal to 0.0080 wt% of N, the process route comprises the steps of molten iron desulphurization, converter smelting, LF refining, slab continuous casting, slab heating, descaling, rough rolling, heat preservation, finish rolling, laminar cooling, coiling, packaging and warehousing. The tapping temperature is 1210 to 1260 DEG C; the rough rolling temperature is 1040 to 1120 DEG C; the finish rolling temperature is 840-900 DEG C; and the laminar cooling temperature is 560-620 DEG C. According to the SPFH590 wheel steel produced through the method, the yield strength ReH ranges from 529 MPa to 585 MPa, the tensile strength Rm ranges from 610 MPa to 652 MPa, and the comprehensive performance is excellent.

Description

Technical Field

[0001] The present invention relates to the field of steel production and manufacturing, and particularly to a production method of hot-rolled SPFH590 high-strength steel strip for wheels, especially a production method of hot-rolled SPFH590 high-strength steel strip for wheels with small difference in properties of the same plate. Background Art

[0002] SPFH590 high-strength wheel steel is a grade in Japanese standard JIS G 3134:2018 "Hot-rolled high-strength steel plates, sheets and strips with improved workability for automotive structures", and the yield strength R eH ≥420 MPa is required, the tensile strength R m is ≥590 MPa, the elongation A for a thickness of 1.6 to <2.0 mm 50 ≥19%, the elongation A for a thickness of 2.0 to <2.5 mm 50 ≥20%, the elongation A for a thickness of 2.5 to <3.25 mm 50 ≥21%, the elongation A for a thickness of 3.25 to 6.0 mm 50 ≥22%, and the 180° cold bending property is qualified. This steel plate is mainly used for manufacturing automobile wheels. With the changes in the wheel processing and manufacturing and the service environment, while requiring high strength, high plasticity and toughness, the wheel steel needs to have excellent welding and fatigue properties, and the requirement for the stability of the tissue properties is getting higher and higher.

[0003] However, at present, there are problems such as large fluctuations in the properties of the same coil and easy occurrence of fatigue fracture in SPFH590 high-strength wheel steel. How to reduce the difference in properties of the same plate strip, improve the stability of the tissue properties, and have both high strength, high plasticity and toughness and fatigue comprehensive properties has always been a major difficulty.

[0004] In summary, the following problems exist in the prior art: how to reduce the difference in properties of the same plate strip of SPFH590 high-strength wheel steel, improve the stability of the tissue properties, and have both high strength, high plasticity and toughness and fatigue comprehensive properties. Summary of the Invention

[0005] The present invention provides a production method of hot-rolled SPFH590 high-strength steel strip for wheels, especially a production method of hot-rolled SPFH590 high-strength steel strip for wheels with small difference in properties of the same plate, which can effectively reduce the difference in properties of the same plate strip of SPFH590 high-strength wheel steel, improve the fatigue performance, and make it have both high strength, high plasticity and toughness and fatigue comprehensive properties, so that the SPFH590 high-strength wheel steel has both high strength and high plasticity and toughness comprehensive properties. The purpose of the present invention is to provide a production and manufacturing method of SPFH590 wheel steel with high strength, high plasticity and toughness, high fatigue performance and low difference in properties of the same plate through specific composition design, matching specific rolling parameters and laminar cooling process.

[0006] To this end, the present invention provides a method for producing hot-rolled SPFH590 high-strength steel strip for wheels, comprising:

[0007] The chemical composition of the steel strip by weight percentage is: C: 0.05 - 0.12 wt%, Si: ≤0.12 wt%, Mn: 1.30 - 1.70 wt%, P ≤0.020 wt%, S ≤0.010 wt%, Nb: 0.020 - 0.080 wt%, Ti: 0.010 - 0.050 wt%, Alt: 0.020 - 0.045 wt%, N ≤0.0080 wt%.

[0008] The process route is: hot metal desulfurization, converter smelting, LF refining, slab continuous casting, slab heating, descaling, rough rolling, heat preservation, finish rolling, laminar flow cooling, coiling, packaging, and warehousing;

[0009] The tapping temperature is 1210 - 1260 °C; the rough rolling temperature is 1040 - 1120 °C; the finish rolling temperature is 840 - 900 °C; the finish rolling speed is 8 - 12 m / s; the forward 2 / 4 cooling mode is used for laminar flow cooling, and the laminar flow cooling temperature is 560 - 620 °C.

[0010] Further, for a slab with a total length of 8 m, a thickness of 230 mm, and a width of 800 - 1600 mm, producing a steel strip with a thickness of 1.6 mm (the length of the finished coil is, for example, 1032 m), the tapping temperature: the head and middle sections are 1233 °C, the middle and tail sections are 1252 °C, the rough rolling temperature is 1100 °C, the finish rolling temperature is 885 °C, the finish rolling speed: the head and middle sections are 9.8 m / s, the middle and tail sections are 11.7 m / s, the laminar flow cooling mode is forward 2 / 4 cooling, and the coiling temperature is 612 °C. Herein, the head and middle sections refer to the first 1 / 2 section, and the middle and tail sections refer to the latter 1 / 2 section.

[0011] Further, for a slab with a total length of 8 m, a thickness of 230 mm, and a width of 800 - 1600 mm, producing a steel strip with a thickness of 2.0 mm (the length of the finished product is, for example, 912 m), the tapping temperature: the head and middle sections are 1230 °C, the middle and tail sections are 1250 °C, the rough rolling temperature is 1096 °C, the finish rolling temperature is 892 °C, the finish rolling speed: the head and middle sections are 9.5 m / s, the middle and tail sections are 12.0 m / s, the laminar flow cooling mode is forward 2 / 4 cooling, and the coiling temperature is 610 °C.

[0012] Further, for a slab with a total length of 9.1 m, a thickness of 230 mm, and a width of 800 - 1600 mm, producing a steel strip with a thickness of 3.0 mm (the length of the finished product is, for example, 682 m), the tapping temperature: the head and middle sections are 1230 °C, the middle and tail sections are 1248 °C, the rough rolling temperature is 1090 °C, the finish rolling temperature is 889 °C, the finish rolling speed in the head and middle sections: 9.0 m / s, the middle and tail sections are 11.3 m / s, the laminar flow cooling mode is forward 2 / 4 cooling, and the coiling temperature is 586 °C.

[0013] Furthermore, for a slab with a full length of 11 m, a thickness of 230 mm, and a width of 800 - 1600 mm, the production specification thickness is 6.0 mm (the finished product length is, for example, 413 m), the tapping temperature: 1215 °C for the head and middle sections, 1234 °C for the middle and tail sections, the rough rolling temperature is 1063 °C, the finish rolling temperature is 856 °C, the finish rolling speed: 8.3 m / s for the head and middle sections, 10.5 m / s for the middle and tail sections, the laminar cooling mode is forward 2 / 4 cooling, and the coiling temperature is 571 °C.

[0014] The present invention also provides a hot-rolled SPFH590 high-strength steel strip for wheels with small difference in properties across the same plate. The chemical composition of the steel strip by weight percentage is as follows: C: 0.05 - 0.12 wt%, Si: ≤0.12 wt%, Mn: 1.30 - 1.70 wt%, P ≤0.020 wt%, S ≤0.010 wt%, Nb: 0.020 - 0.080 wt%, Ti: 0.010 - 0.050 wt%, Alt: 0.020 - 0.045 wt%, N ≤0.0080 wt%.

[0015] Furthermore, the thickness of the hot-rolled SPFH590 high-strength steel strip for wheels is 1.6 - 6.0 mm.

[0016] Furthermore, the width of the hot-rolled SPFH590 high-strength steel strip for wheels is 800 - 1630 mm.

[0017] The SPFH590 wheel steel produced by the present invention has a yield strength R eH of 529 - 585 MPa and a tensile strength R m of 610 - 652 MPa. The strength difference at different positions of the head, middle, and tail of the same plate is ≤10 MPa, the elongation A 50 is 22.0 - 25.5%, and the 180° cold bending property is qualified; the banded structure is ≤0.5 grade, the grain size reaches above 12.5 grades, the grains are fine and the tissue uniformity is good; the steel quality is pure, various inclusions are below grade 0.5, and TiN particles ≤5 μm; the steel plate can withstand a maximum stress of more than 490 MPa under the conditions of a stress ratio R = 0.1 and 10 million fatigue cycles, and the comprehensive performance is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a metallographic structure photograph of the product in Example 5 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the present invention will now be described.

[0020] The object of the present invention is to provide a manufacturing method for SPFH590 steel wheels with high strength, high plastic toughness, high fatigue performance and low difference in properties across the same plate by means of specific component design, matching specific rolling parameters and laminar cooling process. To achieve the above object, the technical solution adopted by the present invention is as follows:

[0021] The chemical composition by weight percentage is: C: 0.05 - 0.12 wt%, Si: ≤0.12 wt%, Mn: 1.30 - 1.70 wt%, P ≤0.020 wt%, S ≤0.010 wt%, Nb: 0.020 - 0.080 wt%, Ti: 0.010 - 0.050 wt%, Alt: 0.020 - 0.045 wt%, N ≤0.0080 wt%;

[0022] The process route is: hot metal desulfurization → converter smelting → LF refining → slab continuous casting → slab heating → descaling → rough rolling → heat preservation → finish rolling → laminar cooling → coiling → packaging → warehousing. Among them, the process characteristics of each stage are as follows:

[0023] Converter steel smelting: Hot metal desulfurization is carried out to ensure that the P content of the hot metal entering the furnace is ≤0.135% and the S content is ≤0.010%. Class I scrap is used to reduce the external input of harmful impurity elements. The whole process uses bottom blowing argon gas. The converter end-point control C is 0.03% - 0.06 wt%, and P ≤0.015 wt%.

[0024] LF steel refining treatment: The molten steel is desulfurized, the temperature is balanced, alloying treatment is carried out and inclusions are removed in the LF furnace; soft blowing argon is carried out for 10 - 15 min before the end of refining, and the calming time is 22 - 35 min.

[0025] Slab continuous casting: The tundish pouring temperature is 1537 - 1548 °C. The slab box board protective slag is used. The casting speed of the slab is 0.90 - 1.40 m / min. The electromagnetic stirring process is used to reduce the center segregation of the slab and improve the internal quality of the slab.

[0026] Slab heating process: The slab thickness is 230 mm, the width is 800 - 1600 mm, and the length is 7000 - 11000 mm. The content of the microalloying element Nb in the slab is high. To ensure that the second phase of Nb in the steel is fully dissolved so as to precipitate sufficiently in the subsequent controlled rolling and controlled cooling process and better play the strengthening role, the heating temperature, especially the soaking section temperature, should be controlled above 1210 - 1260 °C and the heating time should be ≥150 min; at the same time, the tapping temperature of the middle and tail sections of the casting billet is controlled to be 15 - 20 °C higher than that of the head and middle sections, so as to effectively reduce the temperature difference between the head, middle and tail of the slab during rolling.

[0027] Rolling process: The rough rolling temperature is 1030 - 1120°C, and the finish rolling temperature is 840 - 900°C. By setting a heat preservation cover between rough and finish rolling, combined with a speed-up rolling mode where the finish rolling speed in the head and middle sections of the strip is 8 - 10 m / s and the finish rolling speed in the middle and tail sections is increased to 10 - 12 m / s, the temperature difference between the head, middle, and tail at the entrance and exit of finish rolling of the strip is ≤20°C; High-pressure water descaling is used to reduce defects such as the pressing-in of surface scale and pitting, ensuring the surface quality of the steel plate.

[0028] Cooling process: In order to refine grains, improve the strength, plasticity, and toughness of the strip, and reduce the difference in properties within the same plate, the laminar cooling uses the forward 2 / 4 cooling mode to improve the cooling uniformity of the strip, and the laminar cooling temperature is 560 - 620°C.

[0029] Storage: The rolled steel coils are stacked and slowly cooled in the high-temperature coil storage, avoiding stacking at the tuyere.

[0030] In the present invention, by controlling the tapping temperature of the middle and tail sections of the continuous casting billet to be 15 - 20°C higher than that of the head and middle sections, the temperature difference between the head, middle, and tail of the strip during rolling can be effectively reduced. By controlling the finish rolling speed in the head and middle sections of the strip to be 8 - 10 m / s and the finish rolling speed in the middle and tail sections to be increased to 10 - 12 m / s in the speed-up rolling mode, the temperature difference between the head, middle, and tail at the entrance and exit of finish rolling of the strip is ≤20°C; For finished steel strips of different thicknesses, corresponding tapping temperatures of the middle and tail sections and the head and middle sections, finish rolling speeds of the head and middle sections and the middle and tail sections are formulated. The laminar cooling uses the forward 2 / 4 cooling mode to improve the cooling uniformity of the strip. The final yield strength R eH is 529 - 585 MPa, the tensile strength R m is 610 - 652 MPa, the strength difference at different positions of the head, middle, and tail within the same plate is ≤10 MPa, the elongation A 50 is 22.0 - 25.5%, the 180° cold bending property is qualified; the banded structure is ≤0.5 grade, the grain size reaches above 12.5 grades, the grains are fine and the tissue uniformity is good; the steel quality is pure, various inclusions are below 0.5 grade, and TiN particles are ≤5 μm; The steel plate can withstand a maximum stress of more than 490 MPa under the conditions of a stress ratio R = 0.1 and 10 million fatigue cycles, and the comprehensive performance is excellent.

[0031] The following is the hot-rolled SPFH590 high-strength strip for wheels and its production method according to the present invention, adopting the following component ratios and specific processes. Among them, Table 1 shows the compositions of the steels in each example (by weight percentage). Table 2 shows the process parameters of the steels in each example, Table 3 shows the comprehensive properties corresponding to the high-strength steel plates described in each example of Table 1 and Table 2, and Table 4 shows the metallographic structure and fatigue properties of each example, Figure 1 is the metallographic structure of the product of Example 5.

[0032] The chemical composition by weight percentage is as follows: C: 0.05 - 0.12 wt%, Si: ≤0.12 wt%, Mn: 1.30 - 1.70 wt%, P ≤0.020 wt%, S ≤0.010 wt%, Nb: 0.020 - 0.080 wt%, Ti: 0.010 - 0.050 wt%, Alt: 0.020 - 0.045 wt%, N ≤0.0080 wt%.

[0033] Table 1: Chemical composition of the product (wt%)

[0034] Example C Si Mn P S Nb Ti Alt N Example 1 0.07 0.03 1.62 0.013 0.003 0.038 0.034 0.032 0.0046 Example 2 0.09 0.05 1.57 0.015 0.004 0.048 0.035 0.028 0.0052 Example 3 0.06 0.03 1.60 0.014 0.004 0.043 0.028 0.030 0.0050 Example 4 0.09 0.06 1.58 0.014 0.005 0.062 0.030 0.028 0.0056 Example 5 0.10 0.04 1.65 0.015 0.005 0.065 0.031 0.027 0.0050

[0035] The slab tapping temperature is 1210 - 1260 °C. Control the tapping temperature of the middle and tail sections of the continuous casting billet to be 15 - 20 °C higher than that of the head and middle sections, reducing the temperature difference between the head, middle, and tail of the strip head during rolling; the rough rolling temperature is 1040 - 1120 °C, the finish rolling temperature is 840 - 900 °C. A heat preservation cover is set between rough rolling and finish rolling. The rolling speed of the strip head in the middle section of finish rolling is 8 - 10 m / s, and the rolling speed of the middle and tail sections of finish rolling is increased to 10 - 12 m / s for the speed-up rolling mode, effectively reducing the strip temperature difference while improving production efficiency, making the temperature difference between the head, middle, and tail at the entrance and exit of finish rolling of the strip ≤20 °C; the laminar cooling uses the forward 2 / 4 cooling mode (4 groups of laminar cooling water tanks are opened 2 groups from front to back, and 10 groups in the densification section are opened 4 groups, and side spraying is used to wash away the surface water in time to ensure uniform cooling of the whole strip; and the strip is cooled immediately after leaving the finish rolling mill to avoid the precipitation of proeutectoid ferrite and refine the grains, ensuring the uniformity of the structure), and the laminar cooling temperature is 560 - 620 °C.

[0036] Table 2: Specific process parameters of each example

[0037]

[0038] Yield strength R eH is 529 - 585 MPa, tensile strength R m is 610 - 652 MPa, and the strength difference at different positions of the same strip head, middle, and tail is ≤10 MPa. For example, the yield strength R eH The strength difference at different positions of the same strip head, middle, and tail is generally controlled at 5 - 10 MPa, most are controlled at 5 - 8 MPa, and half of the products can be controlled at 5 - 6 MPa; the tensile strength R m The strength difference at different positions of the same strip head, middle, and tail is generally controlled at 2 - 10 MPa, many examples are controlled at 2 - 9 MPa, and in some examples, the product can be controlled at 2 - 6 MPa; elongation A 50 is 22.0 - 25.5%, the 180° cold bending performance is qualified, and the comprehensive performance is excellent. The mechanical properties of the products in each example are shown in Table 3.

[0039] Table 3: Mechanical properties of the products in each example

[0040]

[0041] The metallographic structure of the hot-rolled SPFH590 high-strength steel wheel for each example is ferrite, a small amount of pearlite, and granular carbide. The banded structure is ≤ grade 0.5, and can even reach grade 0. The grain size reaches above grade 12.5 and even up to grade 13.0. The grains are fine and the tissue uniformity is good. The steel quality is pure, and various inclusions are below grade 0.5, and the TiN particles are ≤ 5 μm. The TiN particles in Example 5 are 3 μm. The steel plate can withstand a maximum stress of more than 490 MPa under the conditions of a stress ratio R = 0.1 and 10 million fatigue cycles. For example, it can reach 490 MPa. The metallographic structure and fatigue performance of each example are shown in Table 4.

[0042] Table 4: Metallographic structure and fatigue performance of each example

[0043] Example Specification / mm Banded structure / grade Grain size / grade Maximum fatigue stress / MPa Example 1 1.6 0 13.0 495 Example 2 2.0 0.5 13.0 490 Example 3 3.0 0.5 13.0 490 Example 4 4.0 0 12.5 495 Example 5 6.0 0.5 12.5 495

[0044] The above is only a schematic specific implementation manner of the present invention and is not intended to limit the scope of the present invention. The various components of the present invention can be combined with each other under the condition of no conflict. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principle of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A production method of hot-rolled SPFH590 high-strength steel strip for wheels with small difference in performance of the same plate, characterized in that, The production method of hot-rolled SPFH590 high-strength steel strip for wheels includes: The chemical composition of the steel strip by weight percentage is: C: 0.05 - 0.12 wt%, Si: ≤0.12 wt%, Mn: 1.30 - 1.70 wt%, P ≤0.020 wt%, S ≤0.010 wt%, Nb: 0.020 - 0.080 wt%, Ti: 0.010 - 0.050 wt%, Alt: 0.020 - 0.045 wt%, N ≤0.0080 wt%; The process route is: hot metal desulfurization, converter smelting, LF refining, slab continuous casting, slab heating, descaling, rough rolling, heat preservation, finish rolling, laminar cooling, coiling, packaging, and warehousing; The tapping temperature is 1210 - 1260 °C; the rough rolling temperature is 1040 - 1120 °C; the finish rolling temperature is 840 - 900 °C; the finish rolling speed is 8 - 12 m / s; the forward 2 / 4 cooling mode is used for laminar cooling, and the laminar cooling temperature is 560 - 620 °C.

2. The production method of hot-rolled SPFH590 high-strength steel strip for wheels with small difference in same-plate performance as described in claim 1, characterized in that, For hot metal desulfurization, ensure that the P ≤0.135% and S ≤0.010% in the hot metal entering the furnace. Use type I scrap steel to reduce the external input of harmful impurity elements; the whole process uses bottom blowing argon gas, and the converter end-point controls C: 0.03% - 0.06 wt%, P ≤0.015 wt%.

3. The production method of hot-rolled SPFH590 high-strength steel strip for wheels with small difference in same-plate performance as claimed in claim 1, characterized in that, The molten steel is desulfurized, the temperature is balanced, alloying treatment is carried out, and inclusions are removed in the LF furnace; soft blowing argon is carried out for 10 - 15 min before the end of refining, and the calming time is 22 - 35 min.

4. The production method of hot-rolled SPFH590 high-strength steel strip for wheels with small difference in performance of the same plate as claimed in claim 1, characterized in that, The soaking section temperature is above 1210 - 1260 °C, ensuring that the heating time ≥150 min; at the same time, control the tapping temperature of the tail section of the continuous casting billet to be 15 - 20 °C higher than that of the head and middle sections.

5. The production method of hot-rolled SPFH590 high-strength steel strip for wheels with small difference in same-plate performance as claimed in claim 1, characterized in that, For the steel strip with a production specification thickness of 1.6 mm, the tapping temperature: 1233 °C for the head and middle sections, 1252 °C for the middle and tail sections, the rough rolling temperature is 1100 °C, the finish rolling temperature is 885 °C, the finish rolling speed: 9.8 m / S for the head and middle sections, 11.7 m / S for the middle and tail sections, the laminar cooling mode is forward 2 / 4 cooling, and the coiling temperature is 612 °C.

6. The production method of hot-rolled SPFH590 high-strength steel strip for wheels with small difference in same-plate performance as claimed in claim 1, characterized in that, For the production specification thickness of 2.0 mm, the tapping temperature: 1230 °C for the head and middle sections, 1250 °C for the middle and tail sections, the rough rolling temperature is 1096 °C, the finish rolling temperature is 892 °C, the finish rolling speed: 9.5 m / S for the head and middle sections, 12.0 m / S for the middle and tail sections, the laminar cooling mode is forward 2 / 4 cooling, and the coiling temperature is 610 °C.

7. The production method of hot-rolled SPFH590 high-strength steel strip for wheels with small difference in same-plate performance as claimed in claim 1, characterized in that, For the production specification thickness of 3.0 mm, the tapping temperature: 1230 °C for the head and middle sections, 1248 °C for the middle and tail sections, the rough rolling temperature is 1090 °C, the finish rolling temperature is 889 °C, the finish rolling speed for the head and middle sections: 9.0 m / S, 11.3 m / S for the middle and tail sections, the laminar cooling mode is forward 2 / 4 cooling, and the coiling temperature is 586 °C.

8. The production method of hot-rolled SPFH590 high-strength steel strip for wheels with small difference in same-plate performance as claimed in claim 1, characterized in that, For the production specification thickness of 4.0 mm, the tapping temperature: 1222 °C for the head and middle sections, 1240 °C for the middle and tail sections, the rough rolling temperature is 1075 °C, the finish rolling temperature is 862 °C, the finish rolling speed: 8.7 m / S for the head and middle sections, 11.0 m / S for the middle and tail sections, the laminar cooling mode is forward 2 / 4 cooling, and the coiling temperature is 590 °C.

9. The production method of hot-rolled SPFH590 high-strength steel strip for wheels with small difference in performance of the same plate as claimed in claim 1, characterized in that, For the production specification with a thickness of 6.0 mm, the furnace outlet temperature: 1215 °C for the head and middle sections, 1234 °C for the middle and tail sections, the rough rolling temperature is 1063 °C, the finish rolling temperature is 856 °C, the finish rolling speed: 8.3 m / S for the head and middle sections, 10.5 m / S for the middle and tail sections, the laminar cooling mode is forward 2 / 4 cooling, and the coiling temperature is 571 °C.

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