HIGH-STRENGTH THIN-GAUGE CHECKERED STEEL PLATE/STRIP AND MANUFACTURING METHOD THEREFOR

Abstract

A high-strength thin-gauge checkered steel plate/strip and a manufacturing method therefor, wherein residual elements such as Sn and Cu in steel scrap are fully utilized as alloy elements in the smelting of molten steel, and the steel has selectively added micro-alloy elements such as B; during the smelting process, the alkalinity of the slag, the types of inclusion in the steel and the melting point thereof, the content of free oxygen and the content of soluble aluminum (Als) in the molten steel are controlled; and twin-roll thin-strip continuous casting is performed to cast a cast strip (11); after exiting crystallization rollers (8a, 8b), the cast strip (11) directly enters a lower sealed chamber (10) containing a non-oxidizing atmosphere, and enters an online rolling machine (13) in a sealed manner so as to undergo hot rolling, then after rolling, the strip steel is cooled by means of air atomization. The resultant steel roll can be used directly as hot-rolled checkered plate/strip, or as a finished checkered plate/strip after being cut and finished, and is widely applicable to the fields of architecture, mechanical production, automobile, bridges, transportation, ship building, etc.

Claims

1. A high-strength thin-gauge checkered steel plate/strip, comprising the following chemical elements in weight percentages: C: ≤0.06%, Si: ≤0.5%, Mn: 0.4-1.7%, P≤0.04%, S≤0.007%, N: 0.004-0.010%, Als: <0.001%, B: 0.001-0.006%, Mn/S≥250, total oxygen [O].sub.T: 0.007-0.020%; Cu: 0.1-0.6% and/or Sn: 0.005-0.04%; and a balance of Fe and other unavoidable impurities.

2. The high-strength thin-gauge checkered steel plate/strip according to claim 1, wherein the high-strength thin-gauge checkered steel plate/strip comprises the following chemical elements in weight percentages: C: 0.02-0.06%, Si: 0.1-0.5%, Mn: 0.4-1.7%, P≤0.04%, S≤0.007%, N: 0.004-0.010%, Als: <0.001%, B: 0.001-0.006%, Mn/S≥250, any one or both of Cu: 0.1-0.6% and Sn: 0.005-0.04%, total oxygen [O].sub.T: 0.007-0.020%; and a balance of Fe and other unavoidable impurities.

3. The high-strength thin-gauge checkered steel plate/strip according to claim 1, wherein the checkered steel plate/strip has a pattern height h of at least 20% of a thickness a of a base plate/strip, i.e., h≥0.2a.

4. The high-strength thin-gauge checkered steel plate/strip according to claim 1, wherein the checkered steel plate/strip has a microstructure that is a mixed microstructure of acicular ferrite+pearlite.

5. The high-strength thin-gauge checkered steel plate/strip according to claim 1, wherein the checkered steel plate/strip has a yield strength of ≥345 MPa, a tensile strength of ≥470 MPa, and an elongation of ≥22%.

6. The high-strength thin-gauge checkered steel plate/strip according to claim 1, wherein the checkered steel plate/strip has a thickness of 0.8-2.5 mm.

7. A manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 1, comprising the following steps: 1) Smelting, wherein smelting is performed on the composition defined in claim 1; wherein a basicity a=CaO/SiO.sub.2 (mass ratio) for slagging in a steelmaking process is controlled at a<1.5; wherein a MnO/SiO.sub.2 ratio (mass ratio) in a low-melting-point MnO—SiO.sub.2—Al.sub.2O.sub.3 ternary inclusion produced from molten steel is controlled at 0.5-2; wherein a free oxygen content [O].sub.Free in the molten steel is 0.0005-0.005%; and wherein in the molten steel, Mn/S≥250; 2) Continuous casting wherein twin-roll thin strip continuous casting is used, wherein a 1.5-3 mm thick cast strip is formed from the molten steel at a smallest gap between two crystallization rolls; wherein the crystallization rolls have a diameter of 500-1500 mm; wherein water is supplied to an inside of the crystallization rolls for cooling; wherein a casting machine has a casting speed of 60-150 m/min; wherein a two-stage system for dispensing and distributing molten steel is used for molten steel delivery in the continuous casting, i.e., a tundish+a distributor; 3) Lower closed chamber protection wherein after a cast strip exits the crystallization rolls, the cast strip has a temperature of 1420-1480° C., and it enters a lower closed chamber directly, wherein a non-oxidizing gas is supplied to the lower closed chamber, wherein an oxygen concentration in the lower closed chamber is controlled at <5%; and wherein the cast strip has a temperature of 1150-1300° C. at an outlet of the lower closed chamber; 4) On-line hot rolling wherein the cast strip is delivered through pinch rolls in the lower closed chamber to a rolling mill, and rolled into a checkered plate having a thickness of 0.8-2.5 mm at a rolling temperature of 1100-1250° C. and a hot rolling reduction rate controlled at 10-50%; wherein the hot-rolled checkered steel plate/strip has a thickness of 0.8-2.5 mm; 5) Post-rolling cooling wherein the checkered steel plate/strip after the on-line hot rolling is subjected to post-rolling cooling, wherein gas atomization cooling is used for the cooling, wherein a cooling rate is 20-100° C./s; and 6) Coiling wherein the hot-rolled strip steel is coiled into a coil after the cooling, wherein a coiling temperature is controlled at 500-600° C.

8. The manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 7, wherein in step 1), an electric furnace is used for the smelting to produce the molten steel, wherein 100% steel scrap is selected as a raw material for the smelting without pre-screening; or a converter is used for the smelting to produce the molten steel, wherein steel scrap is added to the converter in an amount of ≥20% based on a raw material for the smelting without pre-screening; wherein the molten steel is then delivered to an LF furnace, VD/VOD furnace or RH furnace for refining.

9. The manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 7, wherein in step 3), the non-oxidizing gas comprises an inert gas, N.sub.2, CO.sub.2 gas produced by sublimation of dry ice, or a mixed gas of N.sub.2 and H.sub.2.

10. The manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 7, wherein in step 4), rolls used for producing the checkered steel plate/strip by rolling include an upper roll and a lower roll, wherein the upper roll is an embossed roll, and the lower roll is a flat roll; wherein the embossed roll has a surface texture including lentil-shaped features; and wherein the upper embossed roll has a roll diameter that is 0.3-3 mm larger than a roll diameter of the lower flat roll.

11. The manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 10, wherein in step 4), based on a center line of a roll body of the lower flat roll, the lower flat roll has a roll diameter at a center of the lower flat roll that is 0.15-0.22 mm smaller than roll diameters at both ends, and a parabolic roll shape with smooth transition from the center to both of the ends is formed.

12. The manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 7, wherein in step 5), the gas atomization cooling utilizes a gas-water flow ratio of 15:1-10:1, a gas pressure of 0.5-0.8 MPa, and a water pressure of 1.0-1.5 MPa, wherein the flow has a unit of m.sup.3/h.

13. The manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 7, wherein in step 5), 1-2 pairs of high-pressure lateral jet nozzles are operated at an outlet where the checkered steel plate/strip comes out after atomization cooling to purge water accumulated on a surface of the checkered steel plate/strip, wherein a nozzle pressure is 0.5-0.8 MPa, and a flow rate is 20-200 m.sup.3/h.

14. The manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 7, wherein in step 6), the coiling utilizes double-coiler coiling or Carrousel coiling.

15. The manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 7, wherein in step 6), the hot-rolled and cooled checkered steel plate/strip is coiled after a poor-quality head portion of the steel plate/strip is cut off.

16. The high-strength thin-gauge checkered steel plate/strip according to claim 6, wherein the checkered steel plate/strip has a thickness of 1.0-1.6 mm.

17. The manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 7, wherein the high-strength thin-gauge checkered steel plate/strip comprises the following chemical elements in weight percentages: C: 0.02-0.06%, Si: 0.1-0.5%, Mn: 0.4-1.7%, P≤0.04%, S≤0.007%, N: 0.004-0.010%, Als: <0.001%, B: 0.001-0.006%, Mn/S≥250, any one or both of Cu: 0.1-0.6% and Sn: 0.005-0.04%, total oxygen [O].sub.T: 0.007-0.020%; and a balance of Fe and other unavoidable impurities.

18. The manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 7, wherein the basicity a=CaO/SiO.sub.2 (mass ratio) for slagging in a steelmaking process is controlled at a<1.2, or a=0.7-1.0; and/or the MnO/SiO.sub.2 ratio (mass ratio) in a low-melting-point MnO—SiO.sub.2—Al.sub.2O.sub.3 ternary inclusion produced from molten steel is controlled at 1-1.8; and/or the crystallization rolls have a diameter of 800 mm; and/or the hot rolling reduction rate controlled at 30-50%; and/or the hot-rolled checkered steel plate/strip has a thickness of 1.0-1.6 mm.

19. The manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 7, wherein the checkered steel plate/strip has a pattern height h of at least 20% of a thickness a of a base plate/strip, i.e., h≥0.2a.

20. The manufacturing method for the high-strength thin-gauge checkered steel plate/strip according to claim 7, wherein the checkered steel plate/strip has a microstructure that is a mixed microstructure of acicular ferrite+pearlite, and/or the checkered steel plate/strip has a yield strength of ≥345 MPa, a tensile strength of ≥470 MPa, and an elongation of ≥22%.

Description

BRIEFLY DESCRIPTION OF THE DRAWINGS

[0093] FIG. 1 is a schematic view showing the process layout of a twin-roll thin strip continuous casting process.

[0094] FIG. 2 is a schematic diagram showing the relationship between Sn content and average heat flux.

[0095] FIG. 3 is a schematic diagram showing the relationship between Sn content and cast strip surface roughness.

[0096] FIG. 4 is a ternary phase diagram of MnO—SiO.sub.2—Al.sub.2O.sub.3 (shaded area: low melting point area).

[0097] FIG. 5 is a schematic diagram showing thermodynamic precipitation curves of BN and AlN.

[0098] FIG. 6 is a picture of a real checkered plate produced according to the present disclosure.

[0099] FIG. 7 is a schematic view showing the pattern thickness h of a checkered plate and the thickness a of a base plate.

DETAILED DESCRIPTION

[0100] The present disclosure will be further described with reference to the following examples, but these examples by no means limit the present disclosure. Any changes made by those skilled in the art in the implementation of the present disclosure under the inspiration of the present specification will fall within the protection scope of the claims in the present disclosure.

[0101] Referring to FIG. 1, the molten steel that conforms to the chemical composition designed according to the present disclosure passes through a ladle 1, a ladle shroud 2, a tundish 3, a submerged nozzle 4 and a distributor 5, and is then directly poured into a molten pool 7 formed with side sealing devices 6a, 6b and two counter-rotating crystallization rolls 8a, 8b capable of rapid cooling. The molten steel solidifies on the circumferential surfaces of the rotating crystallization rolls 8a, 8b to form a solidified shell which gradually grows, and then forms a 1.5-3 mm thick cast strip 11 at the minimum gap (nip point) between the two crystallization rolls. The diameter of the crystallization rolls according to the present disclosure is between 500-1500 mm, and water is supplied to the inside of the crystallization rolls for cooling. Depending on the thickness of the cast strip, the casting speed of the casting machine is in the range of 60-150 m/min.

[0102] After the cast strip 11 exits the crystallization rolls 8a and 8b, the temperature of the cast strip is 1420-1480° C., and the cast strip enters a lower closed chamber 10 directly. The lower closed chamber 10 is supplied with an inert gas to protect the strip steel, i.e. protecting the strip steel from oxidation. The anti-oxidation protective atmosphere may be N.sub.2, or Ar, or other non-oxidizing gas, such as CO.sub.2 gas obtained by sublimation of dry ice. The oxygen concentration in the lower closed chamber 10 is controlled to be <5%. The anti-oxidation protection provided by the lower closed chamber 10 to the cast strip 11 extends to the inlet of the rolling mill 13. The temperature of the cast strip at the outlet of the lower closed chamber 10 is 1150-1300° C. Then, the cast strip is delivered to the hot rolling mill 13 through a swinging guide plate 9, pinch rolls 12 and a roll table 15. After hot rolling, a hot rolled strip of 0.8-2.5 mm in thickness is formed. The rolled strip steel is cooled by gas atomization cooling with the use of a gas atomization rapid cooling device 14 to improve the temperature uniformity of the strip steel. After the head portion of the strip steel is cut off by a flying shear 16, the cut head portion falls into a flying shear pit 18 along a flying shear guide plate 17, and the hot-rolled strip with the head portion cut off enters a coiler 19 for coiling. After the steel coil is taken off the coiler, it is cooled in air to room temperature. The final steel coil produced can be used directly as a hot rolled checkered plate/strip, or as a finished checkered plate/strip after trimming-flattening. Rolls used for hot rolling include an upper roll and a lower roll, wherein the upper roll is an embossed roll, and the lower roll is a flat roll; wherein the embossed roll has a surface texture including lentil-shaped features; and wherein the upper embossed roll has a roll diameter that is 0.3-3 mm larger than a roll diameter of the lower flat roll. Based on the center line of the roll body of the lower flat roll, the lower flat roll has a roll diameter at a center of the lower flat roll that is 0.15-0.22 mm smaller than roll diameters at both ends, and a parabolic roll shape with smooth transition from the center to both of the ends is formed.

[0103] The chemical compositions of the Examples according to the present disclosure are shown in Table 1, wherein the balance is Fe and other unavoidable impurities. The process parameters of the manufacturing method according to the present disclosure are shown in Table 2, and the properties of the hot-rolled strips obtained finally are shown in Table 3.

[0104] To sum up, the final high-strength thin-gauge checkered steel plate/strip manufactured with the designed steel composition using the thin strip continuous casting process according to the present disclosure has a yield strength of ≥345 MPa, a tensile strength of ≥470 MPa, and an elongation of ≥22%, and the cold bendability is qualified. The checkered steel plate/strip produced according to the present disclosure has a pattern height h of ≥20% of the thickness a of the base plate/strip, i.e., h≥0.2a. The product can be widely used in construction, machinery manufacturing, automobiles, bridges, transportation, shipbuilding and other fields.

TABLE-US-00001 TABLE 1 Chemical compositions of the steel Examples (wt. %) C Si Mn P S N O Als Cu Sn B Ex. 1 0.02 0.23 1.35 0.008 0.004 0.0074 0.0095 0.0009 0.33 0.024 0.003 Ex. 2 0.03 0.10 0.90 0.013 0.003 0.0061 0.0110 0.0006 0.15 0.005 0.001 Ex. 3 0.03 0.34 1.28 0.015 0.004 0.0058 0.0150 0.0004 0.10 0.004 Ex. 4 0.05 0.26 1.10 0.023 0.004 0.0087 0.0130 0.0008 0.55 0.040 0.006 Ex. 5 0.04 0.44 0.65 0.009 0.002 0.0052 0.0120 0.0007 0.44 0.014 0.003 Ex. 6 0.05 0.40 0.67 0.012 0.002 0.0046 0.0070 0.0008 0.025 0.005 Ex. 7 0.06 0.18 0.85 0.015 0.003 0.0040 0.0100 0.0005 0.37 0.035 0.003 Ex. 8 0.03 0.37 1.00 0.014 0.004 0.0100 0.0088 0.0006 0.60 0.015 0.002 Ex. 9 0.04 0.36 0.84 0.018 0.003 0.0078 0.0200 0.0003 0.38 0.004 Ex. 10 0.05 0.43 0.40 0.040 0.001 0.0055 0.0125 0.0004 0.52 0.016 0.006 Ex. 11 0.04 0.50 0.65 0.030 0.002 0.0090 0.0090 0.0005 0.038 0.003 Ex. 12 0.03 0.26 1.70 0.022 0.0067 0.0085 0.0118 0.0003 0.35 0.012 0.002 Ex. 13 0.06 0.45 1.37 0.038 0.004 0.0045 0.0132 0.0006 0.032 0.005 Ex. 14 0.05 0.27 1.40 0.017 0.003 0.0064 0.0075 0.0005 0.27 0.027 0.004

TABLE-US-00002 TABLE 2 Process parameters of the Examples Oxygen Atmosphere concentration Hot-rolled Cast strip in lower in lower Hot rolling Hot rolling strip Post-rolling Coiling thickness closed closed temperature reduction thickness cooling rate/ temperature mm chamber chamber ° C. rate/% mm ° C./s ° C. Ex. 1 2.1 N.sub.2 3.5 1180 29 1.5 35 590 Ex. 2 2.5 Ar 4.2 1220 50 1.25 30 600 Ex. 3 2.2 N.sub.2 2.5 1200 45 1.2 30 560 Ex. 4 1.8 CO.sub.2 2.7 1150 31 1.25 20 550 Ex. 5 1.5 Ar 3.5 1185 33 1.0 32 580 Ex. 6 2.6 Ar 2.8 1100 42 1.5 72 570 Ex. 7 1.9 N.sub.2 1.5 1190 21 1.5 65 580 Ex. 8 1.6 CO.sub.2 0.8 1220 22 1.25 100 590 Ex. 9 1.5 N.sub.2 1.5 1250 33 1.0 22 570 Ex. 10 2.0 N.sub.2 1.9 1170 30 1.4 75 500 Ex. 11 2.6 Ar 1.8 1240 38 1.6 30 575 Ex. 12 2.2 N.sub.2 2.6 1170 43 1.25 60 585 Ex. 13 2.0 CO.sub.2 2.4 1180 50 1.0 30 590 Ex. 14 1.6 Ar 2.5 1160 31 1.1 25 580

TABLE-US-00003 TABLE 3 Properties of the steel products in the Examples Final Cast strip product Yield Tensile 180° Bend diameter thickness thickness strength strength Elongation/ d = 3a (a is Ex. mm mm MPa MPa % strip thickness) Ex. 1 2.1 1.5 355 485 23 Pass Ex. 2 2.5 1.25 348 480 26 Pass Ex. 3 2.2 1.2 370 493 24 Pass Ex. 4 1.8 1.25 354 478 27 Pass Ex. 5 1.5 1.0 363 474 25 Pass Ex. 6 2.6 1.5 348 485 24 Pass Ex. 7 1.9 1.5 358 475 22 Pass Ex. 8 1.6 1.25 352 495 23 Pass Ex. 9 1.5 1.0 361 503 27 Pass Ex. 10 2.0 1.4 358 520 25 Pass Ex. 11 2.6 1.6 356 487 24 Pass Ex. 12 2.2 1.25 359 490 27 Pass Ex. 13 2.0 1.0 356 475 23 Pass Ex. 14 1.6 1.1 360 490 26 Pass

[0105] According to the present disclosure, the thin strip continuous casting process is used to produce a thin-gauge checkered plate. Due to the thin thickness, the thin strip continuous casting process has strong manufacturing and cost advantages for a thin-gauge hot-rolled high-strength product having a thickness of less than or equal to 1.5 mm. The characteristic thickness of the thin-gauge checkered plate directly supplied in the form of a hot-rolled product is 1.0-1.6 mm. Due to the thin thickness of the product, if the traditional production line process is used to produce it, problems related with the plate shape of the product will occur, and it cannot be produced. If it's produced using the thin slab continuous casting and rolling process, the roll consumption of the rolling rolls also increases significantly. Such a production process will undoubtedly increase the production cost of the thin-gauge checkered plate. Therefore, the use of the thin strip continuous casting process to produce a thin-gauge high-strength checkered plate product can not only meet the market's requirements for high strength, thin gauge and light weight, but also reduce the production cost of the checkered plate and improve the product profitability and competitiveness.