HOT-ROLLED STEEL PLATE/STRIP FOR SULFURIC ACID DEW POINT CORROSION RESISTANCE AND MANUFACTURING METHOD THEREFOR

Abstract

A hot-rolled steel plate/strip for sulfuric acid dew point corrosion resistance and manufacturing method therefor. In said method, elements such as Sn and Cu remaining in steel scrap are fully utilized to smelt molten steel, and micro-alloy elements such as Cr, Ti, and Sb are selectively added; in a smelting process, basicity of slag, types and melting points of inclusions in steel, and a free oxygen content and an acid-soluble aluminum (Als) content in molten steel are controlled, a cast strip (11) is casted by means of twin-roll strip continuous casting, the cast strip (11) exits from crystallization rolls (8a, 8b) and directly enters a lower closed chamer (10) having a non-oxidizing atmosphere, then enters, in a closed condition, an on-line rolling mill (13) for hot rolling, after rolling, strip steel is cooled by means of gas atomization cooling, and finally the strip steel is wound up. The steel can be widely applied to the fields of products, such as tobacco baking apparatuses, air preheater heat exchange elements in industries such as petroleum, chemical industry, electric power, and metallurgy, delivery pipe, flue, and stack manufacturing structural parts, and boiler preheater and economizer equipment, of which the use environments have requirements for sulfuric acid dew point corrosion resistance performance.

Claims

1. A hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance, comprising the following chemical elements in weight percentages: C: 0.02-0.06%, Si: 0.10-0.55%, Mn: ≤1.5%, P≤0.03%, S≤0.007%, Ti: 0.03-0.15%, Cr: 0.50-1.20%, Ni: 0.10-0.30%, Sb: 0.04-0.30%, Cu: 0.20-0.60%, N: 0.004-0.010%, Als: <0.001%, one or both of Sn: 0.005-0.04% and B: 0.001-0.006%, Mn/S≥250, total oxygen [O].sub.T: 0.007-0.020%; and a balance of Fe and other unavoidable impurities.

2. The hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 1, wherein the hot-rolled steel plate/strip has a mixed microstructure of acicular ferrite and pearlite.

3. The hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 1, wherein the hot-rolled steel plate/strip has a yield strength of ≥330 MPa, a tensile strength of ≥440 MPa, an elongation of ≥22%.

4. The hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 3, wherein the hot-rolled steel plate/strip has a yield strength of 330-370 MPa, a tensile strength of 440-480 MPa, and an elongation of 22-30%.

5. The hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 1, wherein the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance has a thickness of 0.8-2.5 mm.

6. The hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 1, wherein the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance has a relative corrosion rate of ≤10% tested at 30° C., 20% concentrated sulfuric acid for 24 hours, and/or a relative corrosion rate of ≤25% tested at 70° C., 50% concentrated sulfuric acid for 24 hours.

7. The hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 1, wherein the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance comprises the following chemical elements in weight percentages: C: 0.02-0.06%, Si: 0.10-0.55%, Mn: ≤1.5%, P≤0.03%, S≤0.007%, Ti: 0.03-0.15%, Cr: 0.50-1.20%, Ni: 0.10-0.30%, Sb: 0.04-0.30%, Cu: 0.20-0.60%, N: 0.004-0.010%, Als: <0.001%, Sn: 0.005-0.04%, Mn/S>250, total oxygen [O].sub.T: 0.007-0.020%; and a balance of Fe and other unavoidable impurities.

8. The hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 1, wherein the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance comprises the following chemical elements in weight percentages: C: 0.02-0.06%, Si: 0.10-0.55%, Mn: ≤1.5%, P≤0.03%, S≤0.007%, Ti: 0.03-0.15%, Cr: 0.50-1.20%, Ni: 0.10-0.30%, Sb: 0.04-0.30%, Cu: 0.20-0.60%, 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%; and a balance of Fe and other unavoidable impurities.

9. A manufacturing method for the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 1, comprising the following steps: 1) Smelting wherein smelting is performed on the composition according to claim 1; wherein a basicity a=CaO/SiO.sub.2 for slagging in a steelmaking process is controlled at a<1.5; wherein a MnO/SiO.sub.2 ratio in molten steel for producing a low-melting-point MnO—SiO.sub.2-Al.sub.2O.sub.3 ternary inclusion 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 at the 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 from 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 rolled steel strip 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, 30-50%, wherein the steel strip after the hot rolling has a thickness of 1.2-2.0 mm; 5) Post-rolling cooling wherein the steel strip after the on-line hot rolling is post-rolling cooled, wherein the steel strip is cooled by gas atomization cooling, wherein a cooling rate of the gas atomization cooling is 20-100° C./s; and 6) Coiling wherein the hot-rolled steel strip is coiled into a steel coil after the cooling, wherein a coiling temperature is 600-700° C.

10. The manufacturing method for the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 9, wherein the method further comprises step 7): follow-up treatment, wherein the steel coil is pickled, trimmed and flattened, and then used as a pickled-flattened coil, or the steel coil is trimmed and flattened, and then used as a finished coil.

11. The manufacturing method for the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 9, wherein in step 1), electric furnace steelmaking or converter steelmaking is employed for the smelting to obtain molten steel; and then the molten steel enters an LF furnace, a VD/VOD furnace, or an RH furnace for refining.

12. The manufacturing method for the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 9, wherein in step 3), the non-oxidizing gas includes N.sub.2, Ar, or CO.sub.2 gas produced by sublimation of dry ice.

13. The manufacturing method for the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 9, 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, and the unit of the flow is m.sup.3/h.

14. The manufacturing method for the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 9, wherein in step 6), the coiling utilizes double-coiler coiling or Carrousel coiling.

15. The manufacturing method for the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 9, wherein the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance comprises Sn; in step 1), an electric furnace is used for smelting to produce molten steel, wherein 100% steel scrap is selected as the raw material for smelting without pre-screening; alternatively, a converter is used for smelting to produce molten steel, wherein steel scrap is added to the converter in an amount of 20% or more based on the raw material for smelting without pre-screening; and then, the molten steel enters an LF furnace, a VD/VOD furnace or an RH furnace for refining.

16. The hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 5, wherein the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance has a thickness of 1.2-2.0 mm.

17. The manufacturing method for the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 9, wherein: the basicity a=CaO/SiO.sub.2 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 in molten steel for producing a low-melting-point MnO—SiO.sub.2-Al.sub.2O.sub.3 ternary inclusion is controlled at 1-1.8; and/or the crystallization rolls have a diameter of 800 mm; and/or the hot rolling reduction rate is controlled at 30-50%; and/or the steel strip after the hot rolling has a thickness of 1.2-2.0 mm.

18. The manufacturing method for the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 9, wherein: the hot-rolled steel plate/strip has a mixed microstructure of acicular ferrite+pearlite; and/or the hot-rolled steel plate/strip has a yield strength of 330 MPa, a tensile strength of ≥440 MPa, an elongation of ≥22%; and/or the hot-rolled steel plate/strip has a relative corrosion rate of ≤10% tested at 30° C., 20% concentrated sulfuric acid for 24 hours, and/or a relative corrosion rate of ≤25% tested at 70° C., 50% concentrated sulfuric acid for 24 hours.

19. The manufacturing method for the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 9, wherein the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance comprises the following chemical elements in weight percentages: C: 0.02-0.06%, Si: 0.10-0.55%, Mn: ≤1.5%, P≤0.03%, S≤0.007%, Ti: 0.03-0.15%, Cr: 0.50-1.20%, Ni: 0.10-0.30%, Sb: 0.04-0.30%, Cu: 0.20-0.60%, N: 0.004-0.010%, Als: <0.001%, Sn: 0.005-0.04%, Mn/S>250, total oxygen [O].sub.T: 0.007-0.020%; and a balance of Fe and other unavoidable impurities.

20. The manufacturing method for the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance according to claim 9, wherein the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance comprises the following chemical elements in weight percentages: C: 0.02-0.06%, Si: 0.10-0.55%, Mn: ≤1.5%, P≤0.03%, S≤0.007%, Ti: 0.03-0.15%, Cr: 0.50-1.20%, Ni: 0.10-0.30%, Sb: 0.04-0.30%, Cu: 0.20-0.60%, 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%; and a balance of Fe and other unavoidable impurities.

Description

BRIEFLY DESCRIPTION OF THE DRAWINGS

[0093] FIG. 1 is a schematic view showing the process layout of the present disclosure;

[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.

DETAILED DESCRIPTION

[0098] 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.

[0099] 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 plate 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. After the cast strip 11 exits from 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. Finally, the steel coil produced may be pickled, trimmed and flattened, and then used as a pickled-flattened coil, or the steel coil produced may be trimmed and flattened, and then used as a finished coil.

[0100] The chemical compositions of examples comprising Sn according to the present disclosure are shown in Table 1, and 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 mechanical properties of the hot-rolled strips obtained finally are shown in Table 3.

[0101] The sulfuric acid corrosion resistance test was carried out on the steel products from the examples according to the standard JB/T 7901-1999: Laboratory Uniform Corrosion Full Immersion Test Method for Metal Materials. The sulfuric acid corrosion resistance test was carried out, and the relative corrosion rate of the material was measured. The test results are shown in Table 4. Test condition 1: test temperature of 30° C. and sulfuric acid concentration of 20%, the full immersion test time of 24 hours; Test condition 2: test temperature of 70° C. and sulfuric acid concentration of 50%, the full immersion test time of 24 hours. The grade of the comparative sample is Q235B.

[0102] To sum up, the hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance manufactured by thin strip continuous casting technology according to the designed range of the steel composition provided by the present disclosure has a yield strength of ≥330 MPa, a tensile strength of ≥440 MPa, an elongation of ≥22% and a qualified cold bendability. The comparison of the corrosion resistance results also shows that: the relative corrosion rate of the inventive steel is ≤10% (test temperature 30° C., sulfuric acid concentration 20 wt %, full immersion test time 24 hours); and the relative corrosion rate is ≤25% (test temperature 70° C., sulfuric acid concentration 50 wt %, full immersion test time 24 hours). The steel of the present disclosure can be widely used in tobacco baking equipment, heat exchange elements of air preheaters in petroleum, chemical industry, electric power, metallurgy and other industries, conveying pipes and flues, stack manufacturing structural parts, boiler preheaters and economizer equipment and other product fields that require sulfuric acid dew point corrosion resistance in their use environment.

TABLE-US-00001 TABLE 1 Chemical compositions of the steel Examples (wt. %) Ex. No. C Si Mn P S N O Als Cr Ni Sb Ti Cu Sn 1 0.026 0.29 1.36 0.018 0.005 0.0074 0.0093 0.0009 0.72 0.18 0.08 0.05 0.38 0.025 2 0.045 0.10 0.91 0.023 0.003 0.0061 0.0110 0.0006 0.50 0.23 0.19 0.08 0.25 0.005 3 0.054 0.38 1.27 0.015 0.004 0.0058 0.0150 0.0004 1.03 0.30 0.25 0.13 0.20 0.034 4 0.020 0.25 1.10 0.013 0.004 0.0087 0.0130 0.0008 1.13 0.16 0.04 0.03 0.38 0.040 5 0.023 0.44 0.65 0.009 0.002 0.0052 0.0120 0.0007 1.20 0.27 0.28 0.09 0.44 0.016 6 0.032 0.43 0.67 0.022 0.002 0.0046 0.0070 0.0008 0.92 0.10 0.13 0.08 0.53 0.037 7 0.041 0.18 0.85 0.015 0.003 0.0040 0.0100 0.0005 0.70 0.26 0.30 0.15 0.27 0.033 8 0.048 0.52 1.00 0.014 0.004 0.0100 0.0085 0.0006 0.82 0.17 0.26 0.04 0.60 0.014 9 0.036 0.33 0.85 0.018 0.003 0.0078 0.0200 0.0003 1.06 0.14 0.24 0.14 0.45 0.028 10 0.060 0.44 0.40 0.030 0.001 0.0055 0.0125 0.0004 1.15 0.29 0.15 0.06 0.52 0.015 11 0.057 0.55 0.66 0.010 0.002 0.0090 0.0090 0.0005 0.95 0.13 0.22 0.14 0.48 0.007 12 0.035 0.29 1.50 0.012 0.006 0.0085 0.0118 0.0003 0.87 0.24 0.09 0.12 0.35 0.013 13 0.048 0.47 1.27 0.008 0.004 0.0045 0.0132 0.0006 0.64 0.19 0.15 0.06 0.45 0.036 14 0.024 0.25 1.42 0.017 0.003 0.0064 0.0075 0.0005 0.78 0.28 0.26 0.07 0.27 0.008

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, Ex. No. mm chamber chamber % ° C. rate, % mm ° C./s ° C. 1 1.90 N.sub.2 3.5 1180 29 1.35 35 690 2 2.20 Ar 4.2 1220 25 1.65 30 600 3 2.00 N.sub.2 2.5 1200 35 1.30 30 660 4 2.10 CO.sub.2 2.7 1150 29 1.50 20 650 5 2.40 Ar 3.5 1185 50 1.20 32 680 6 2.40 Ar 2.8 1100 23 1.85 72 670 7 2.30 N.sub.2 1.5 1190 22 1.80 65 680 8 2.00 CO.sub.2 0.8 1220 38 1.25 100 690 9 2.70 N.sub.2 1.5 1250 26 2.00 22 670 10 2.00 N.sub.2 1.9 1170 30 1.40 75 700 11 2.10 Ar 1.8 1240 29 1.50 30 675 12 2.10 N.sub.2 2.6 1170 24 1.60 60 685 13 2.20 CO.sub.2 2.4 1180 23 1.70 30 690 14 2.20 Ar 2.5 1160 25 1.65 25 680

TABLE-US-00003 TABLE 3 Mechanical properties of the steel products in the Examples Cast strip Final product Yield Tensile 180° bend thickness thickness strength strength Elongation diameter Ex. No. mm mm MPa MPa % d = 3a 1 1.90 1.35 338 455 23 Pass 2 2.20 1.65 342 463 23 Pass 3 2.00 1.30 351 455 25 Pass 4 2.10 1.50 348 462 22 Pass 5 2.40 1.20 362 465 26 Pass 6 2.40 1.85 346 458 25 Pass 7 2.30 1.80 349 466 26 Pass 8 2.00 1.25 347 458 28 Pass 9 2.70 2.00 356 475 27 Pass 10 2.00 1.40 365 457 25 Pass 11 2.10 1.50 359 464 23 Pass 12 2.10 1.60 348 454 24 Pass 13 2.20 1.70 358 468 23 Pass 14 2.20 1.65 355 474 25 Pass

TABLE-US-00004 TABLE 4 Test results of the sulfuric acid corrosion resistance of the steel products in the Examples Relative corrosion rate, % test temperature: 30° C., test temperature: 70° C., sulfuric acid concentration: sulfuric acid concentration: Test 20%, full immersion test time: 50%, full immersion test time: conditions 24 hours 24 hours Q235B 100 100 Ex. 1 9.64 24.65 Ex. 2 9.72 23.48 Ex. 3 8.88 22.54 Ex. 4 8.74 23.73 Ex. 5 8.85 23.68 Ex. 6 8.87 22.75 Ex. 7 9.66 23.73 Ex. 8 9.58 22.72 Ex. 9 9.55 24.58 Ex. 10 9.39 23.73 Ex. 11 8.63 23.76 Ex. 12 9.32 23.58 Ex. 13 9.42 22.28 Ex. 14 9.68 24.76

[0103] The chemical compositions of Examples comprising B according to the present disclosure are shown in Table 5, and the balance is Fe and other unavoidable impurities. The process parameters of the manufacturing method according to the present disclosure are shown in Table 6, and the mechanical properties of the hot-rolled strips obtained finally are shown in Table 7.

[0104] The sulfuric acid corrosion resistance test was carried out on the steel products from the examples according to the standard JB/T 7901-1999: Laboratory Uniform Corrosion Full Immersion Test Method for Metal Materials. The sulfuric acid corrosion resistance test was carried out, and the relative corrosion rate of the material was measured. The test results are shown in Table 8. Test condition 1: test temperature of 30° C. and sulfuric acid concentration of 20%, the full immersion test time of 24 hours; test condition 2: test temperature of 70° C. and sulfuric acid concentration of 50%, the full immersion test time of 24 hours. The grade of the comparative sample is Q235B.

[0105] To sum up, the B-containing hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance manufactured by thin strip continuous casting technology according to the designed range of the steel composition provided by the present disclosure has a yield strength of ≥330 MPa, a tensile strength of ≥440 MPa, an elongation of ≥22% and a qualified cold bendability. The comparison of the corrosion resistance results also shows that: the relative corrosion rate of the inventive steel is ≤10% (test temperature 30° C., sulfuric acid concentration 20 wt %, full immersion test time 24 hours); and the relative corrosion rate is ≤25% (test temperature 70° C., sulfuric acid concentration 50 wt %, full immersion test time 24 hours). The steel of the present disclosure can be widely used in tobacco baking equipment, heat exchange elements of air preheaters in petroleum, chemical industry, electric power, metallurgy and other industries, conveying pipes and flues, stack manufacturing structural parts, boiler preheaters and economizer equipment and other product fields that require sulfuric acid dew point corrosion resistance in their use environment.

TABLE-US-00005 TABLE 5 Chemical compositions of the steel Examples (wt. %) Ex. No. C Si Mn P S N O Als Cr Ni Sb Ti Cu B 15 0.027 0.27 1.36 0.018 0.005 0.0074 0.0093 0.0009 0.73 0.17 0.07 0.05 0.37 0.004 16 0.045 0.10 0.91 0.023 0.003 0.0061 0.0110 0.0006 0.50 0.25 0.18 0.08 0.24 0.001 17 0.054 0.36 1.27 0.015 0.004 0.0058 0.0150 0.0004 1.01 0.30 0.29 0.13 0.20 0.003 18 0.020 0.25 1.16 0.013 0.004 0.0087 0.0130 0.0008 1.12 0.16 0.04 0.03 0.32 0.005 19 0.023 0.44 0.65 0.009 0.002 0.0052 0.0120 0.0007 1.20 0.28 0.27 0.09 0.45 0.006 20 0.032 0.43 0.64 0.022 0.002 0.0046 0.0070 0.0008 0.93 0.10 0.18 0.08 0.53 0.004 21 0.041 0.19 0.83 0.015 0.003 0.0040 0.0100 0.0005 0.74 0.25 0.30 0.15 0.27 0.003 22 0.049 0.52 1.02 0.014 0.004 0.0100 0.0085 0.0006 0.84 0.17 0.25 0.04 0.60 0.002 23 0.038 0.31 0.81 0.018 0.003 0.0078 0.0200 0.0003 1.07 0.14 0.24 0.14 0.46 0.003 24 0.060 0.49 0.40 0.030 0.001 0.0055 0.0125 0.0004 1.18 0.26 0.13 0.06 0.53 0.004 25 0.057 0.55 0.66 0.010 0.002 0.0090 0.0090 0.0005 0.97 0.15 0.22 0.14 0.49 0.005 26 0.036 0.28 1.50 0.012 0.006 0.0085 0.0118 0.0003 0.88 0.27 0.09 0.12 0.37 0.002 27 0.045 0.47 1.38 0.008 0.004 0.0045 0.0132 0.0006 0.66 0.18 0.11 0.06 0.45 0.004 28 0.024 0.26 1.40 0.017 0.003 0.0064 0.0075 0.0005 0.78 0.29 0.26 0.07 0.28 0.003

TABLE-US-00006 TABLE 6 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 temperature Ex. No. mm chamber chamber % ° C. rate, % mm rate, ° C./s ° C. 15 1.90 N.sub.2 3.5 1180 29 1.35 35 690 16 2.20 Ar 4.2 1220 27 1.60 30 600 17 2.00 N.sub.2 2.5 1200 33 1.35 30 660 18 2.10 N.sub.2 2.7 1150 26 1.55 20 650 19 2.40 Ar 3.5 1185 50 1.20 32 680 20 2.40 Ar 2.8 1100 23 1.85 72 670 21 2.30 N.sub.2 1.5 1190 22 1.80 65 680 22 2.00 N.sub.2 0.8 1220 33 1.35 100 690 23 2.70 N.sub.2 1.5 1250 26 2.00 22 670 24 2.00 N.sub.2 1.9 1170 28 1.45 75 700 25 2.10 Ar 1.8 1240 26 1.55 30 675 26 2.10 N.sub.2 2.6 1170 24 1.60 60 685 27 2.20 N.sub.2 2.4 1180 25 1.65 30 690 28 2.20 Ar 2.5 1160 23 1.70 25 680

TABLE-US-00007 TABLE 7 Mechanical properties of the steel products in the Examples Cast strip Final product Yield Tensile 180° bend thickness thickness strength strength Elongation diameter Ex. No. mm mm MPa MPa % d = 3a 15 1.90 1.35 338 460 25 Pass 16 2.20 1.60 346 465 24 Pass 17 2.00 1.35 344 458 24 Pass 18 2.10 1.55 338 462 22 Pass 19 2.40 1.20 350 463 28 Pass 20 2.40 1.85 347 448 26 Pass 21 2.30 1.80 344 465 28 Pass 22 2.00 1.35 335 455 29 Pass 23 2.70 2.00 350 473 27 Pass 24 2.00 1.45 364 458 25 Pass 25 2.10 1.55 357 464 24 Pass 26 2.10 1.60 343 450 25 Pass 27 2.20 1.65 356 466 23 Pass 28 2.20 1.70 348 465 28 Pass

TABLE-US-00008 TABLE 8 Test results of the sulfuric acid corrosion resistance of the steel products in the Examples Relative corrosion rate, % test temperature: 30° C., test temperature: 70° C., sulfuric acid concentration: sulfuric acid concentration: Test 20%, full immersion test time: 50%, full immersion test time: conditions 24 hours 24 hours Q235B 100 100 Ex. 15 9.46 24.38 Ex. 16 9.34 23.59 Ex. 17 8.37 21.57 Ex. 18 9.79 23.64 Ex. 19 8.86 23.79 Ex. 20 8.75 20.58 Ex. 21 9.58 23.76 Ex. 22 9.49 22.83 Ex. 23 9.58 24.55 Ex. 24 9.39 23.66 Ex. 25 8.68 23.84 Ex. 26 9.43 23.55 Ex. 27 9.69 23.25 Ex. 28 9.86 24.67

[0106] The chemical compositions of Examples according to the present disclosure are shown in Table 9, and the balance is Fe and other unavoidable impurities. The process parameters of the manufacturing method according to the present disclosure are shown in Table 10, and the mechanical properties of the hot-rolled strips obtained finally are shown in Table 11.

[0107] The sulfuric acid corrosion resistance test was carried out on the steel products from the examples according to the standard JB/T 7901-1999: Laboratory Uniform Corrosion Full Immersion Test Method for Metal Materials. The sulfuric acid corrosion resistance test was carried out, and the relative corrosion rate of the material was measured. The test results are shown in Table 12. Test condition 1: test temperature of 30° C. and sulfuric acid concentration of 20%, the full immersion test time of 24 hours; test condition 2: test temperature of 70° C. and sulfuric acid concentration of 50%, the full immersion test time of 24 hours. The grade of the comparative sample is Q235B.

[0108] The data in Table 11 show that the thin-gauge hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance manufactured by thin strip continuous casting technology according to the designed range of the steel composition provided by the present disclosure has a yield strength of ≥330 MPa, a tensile strength of ≥440 MPa, an elongation of ≥22% and a qualified cold bendability.

[0109] The comparison of the corrosion resistance results in Table 12 also shows that: the relative corrosion rate of the inventive steel is ≤10% (test temperature 30° C., sulfuric acid concentration 20 wt %, full immersion test time 24 hours); and the relative corrosion rate is ≤25% (test temperature 70° C., sulfuric acid concentration 50 wt %, full immersion test time 24 hours). The steel of the present disclosure can be widely used in tobacco baking equipment, heat exchange elements of air preheaters in petroleum, chemical industry, electric power, metallurgy and other industries, conveying pipes and flues, stack manufacturing structural parts, boiler preheaters and economizer equipment and other product fields that require sulfuric acid dew point corrosion resistance in their use environment.

TABLE-US-00009 TABLE 9 Chemical compositions of the steel Examples (wt. %) Ex. No. C Si Mn P S N O Als Cr Ni Sb Ti Cu Sn B 29 0.025 0.25 1.35 0.018 0.005 0.0074 0.0096 0.0009 0.72 0.18 0.08 0.05 0.38 0.026 0.003 30 0.046 0.10 0.90 0.023 0.003 0.0061 0.0110 0.0006 0.50 0.23 0.19 0.08 0.25 0.005 0.001 31 0.058 0.38 1.28 0.015 0.004 0.0058 0.0150 0.0004 1.03 0.30 0.25 0.13 0.20 0.033 0.004 32 0.020 0.26 1.10 0.013 0.004 0.0087 0.0130 0.0008 1.13 0.16 0.04 0.03 0.38 0.040 0.006 33 0.022 0.47 0.65 0.009 0.002 0.0052 0.0120 0.0007 1.20 0.27 0.28 0.09 0.44 0.014 0.003 34 0.037 0.43 0.67 0.022 0.002 0.0046 0.0070 0.0008 0.92 0.10 0.13 0.08 0.53 0.038 0.005 35 0.045 0.19 0.85 0.015 0.003 0.0040 0.0100 0.0005 0.70 0.26 0.30 0.15 0.27 0.035 0.003 36 0.048 0.51 1.00 0.014 0.004 0.0100 0.0085 0.0006 0.82 0.17 0.26 0.04 0.60 0.015 0.002 37 0.036 0.35 0.84 0.018 0.003 0.0078 0.0200 0.0003 1.06 0.14 0.24 0.14 0.45 0.027 0.004 38 0.060 0.45 0.40 0.030 0.001 0.0055 0.0125 0.0004 1.15 0.29 0.15 0.06 0.52 0.016 0.006 39 0.057 0.55 0.65 0.010 0.002 0.0090 0.0090 0.0005 0.95 0.13 0.22 0.14 0.48 0.008 0.003 40 0.033 0.27 1.50 0.012 0.006 0.0085 0.0118 0.0003 0.87 0.24 0.09 0.12 0.35 0.012 0.002 41 0.049 0.48 1.37 0.008 0.004 0.0045 0.0132 0.0006 0.64 0.19 0.15 0.06 0.45 0.038 0.005 42 0.025 0.23 1.40 0.017 0.003 0.0064 0.0075 0.0005 0.78 0.28 0.26 0.07 0.27 0.007 0.004

TABLE-US-00010 TABLE 10 Process parameters of the Examples Oxygen Atmosphere concentration Hot rolling Hot-rolled Cast strip in lower in lower Hot rolling reduction strip Post-rolling Coiling thickness closed closed temperature rate, thickness, cooling rate, temperature Ex. No. mm chamber chamber % ° C. % mm ° C./s ° C. 29 1.90 N.sub.2 3.5 1180 29 1.35 35 690 30 2.20 Ar 4.2 1220 25 1.65 30 600 31 2.00 N.sub.2 2.5 1200 35 1.30 30 660 32 2.10 CO.sub.2 2.7 1150 29 1.50 20 650 33 2.40 Ar 3.5 1185 50 1.20 32 680 34 2.40 Ar 2.8 1100 23 1.85 72 670 35 2.30 N.sub.2 1.5 1190 22 1.80 65 680 36 2.00 CO.sub.2 0.8 1220 38 1.25 100 690 37 2.70 N.sub.2 1.5 1250 26 2.00 22 670 38 2.00 N.sub.2 1.9 1170 30 1.40 75 700 39 2.10 Ar 1.8 1240 29 1.50 30 675 40 2.10 N.sub.2 2.6 1170 24 1.60 60 685 41 2.20 CO.sub.2 2.4 1180 23 1.70 30 690 42 2.20 Ar 2.5 1160 25 1.65 25 680

TABLE-US-00011 TABLE 11 Mechanical properties of the steel products in the Examples Cast strip Final product Yield Tensile 180° bend thickness thickness strength strength Elongation diameter d = 3a Ex. No. mm mm MPa MPa % (a = strip thickness) 29 1.90 1.35 335 450 24 Pass 30 2.20 1.65 341 460 23 Pass 31 2.00 1.30 350 445 24 Pass 32 2.10 1.50 338 452 22 Pass 33 2.40 1.20 360 463 27 Pass 34 2.40 1.85 347 448 26 Pass 35 2.30 1.80 344 465 28 Pass 36 2.00 1.25 335 455 28 Pass 37 2.70 2.00 350 473 27 Pass 38 2.00 1.40 364 458 25 Pass 39 2.10 1.50 357 464 23 Pass 40 2.10 1.60 346 450 25 Pass 41 2.20 1.70 356 466 23 Pass 42 2.20 1.65 358 477 26 Pass

TABLE-US-00012 TABLE 12 Test results of the sulfuric acid corrosion resistance of the steel products in the Examples Relative corrosion rate, % test temperature: 30° C., test temperature: 70° C., sulfuric acid concentration: sulfuric acid concentration: Test 20%, full immersion test time: 50%, full immersion test time: conditions 24 hours 24 hours Q235B 100 100 Ex. 29 9.60 24.45 Ex. 30 9.62 23.68 Ex. 31 8.38 21.54 Ex. 32 8.79 23.43 Ex. 33 8.83 23.38 Ex. 34 8.89 20.65 Ex. 35 9.56 23.83 Ex. 36 9.56 22.32 Ex. 37 9.52 24.56 Ex. 38 9.19 23.43 Ex. 39 8.60 23.78 Ex. 40 9.42 23.52 Ex. 41 9.62 23.28 Ex. 42 9.87 24.36