Manufacturing method for strip casting 550 MPa-grade high strength atmospheric corrosion-resistant steel strip

Abstract

A manufacturing method for strip casting 550 MPa-grade high strength atmospheric corrosion-resistant steel strip, comprising the following steps: 1) smelting, where the chemical composition of a molten steel is that: C is between 0.03-0.08%, Si0.4%, Mn is between 0.6-1.5%, P is between 0.07-0.22%, S0.01%, N0.012%, Cu is between 0.25-0.8%, Cr is between 0.3-0.8%, and Ni is between 0.12-0.4%, additionally, also comprised is at least one micro-alloying element among Nb, V, Ti, and Mo, where Nb is between 0.01-0.08%, V is between 0.01-0.08%, Ti is between 0.01-0.08%, and Mo is between 0.1-0.4%, and where the remainder is Fe and unavoidable impurities; 2) strip casting, where a 1-5 mm-thick cast strip is casted directly; 3) cooling the strip, where the cooling rate is greater than 20 C./s; 4) online hot rolling the cast strip, where the hot rolling temperature is between 1050-1250 C., where the reduction rate is between 20-50%, and where the deformation rate is >20 s.sup.1; austenite online recrystallizing after hot rolling, where the thickness of the hot rolled strip is between 0.5-3.0 mm; and, 5) cooling and winding, where the cooling rate is between 10-80 C./s, and where the winding temperature is between 570-720 C. The microscopic structure of a steel strip acquired is primarily constituted by fine polygonal ferrite and pearlite.

Claims

1. A manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade, the method sequentially comprising the following steps: 1) smelting, wherein the molten steel has a chemical composition by weight percentage as follows: C 0.030.08%, Si0.4%, Mn 0.61.5%, P 0.070.22%, 0<S0.01%, 0<N0.012%, Cu 0.250.8%, Cr 0.30.8% and Ni 0.120.4%, and at least one microalloy element selected from Nb, V, Ti, and Mo having a content of Nb 0.010.08%, V 0.010.08%, Ti 0.010.08% and Mo 0.10.4%, and balance being Fe and inevitable impurities; 2) continuous strip casting, wherein the molten steel is introduced into a molten pool formed by a pair of relatively rotating and internally water-cooled casting rollers and side dams, and is directly cast into a cast strip having a thickness of 15 mm through rapid solidification; 3) cooling the cast strip after the continuous strip casting, wherein after being continuously cast and coming out of the casting rollers, the cast strip goes through an airtight chamber for cooling, the cooling rate is 21 C./sec. to 38 C./sec.; 4) online hot rolling the cast strip after cooling the cast strip under a hot rolling temperature of 1,0501,250 C., a reduction rate of 2050%, and a deformation rate of >20 s.sup.1, wherein the thickness of the steel strip after hot rolling is 0.53.0 mm, and online austenite recrystallization occurs upon the hot rolling of the cast strip; 5) cooling and coiling after the online hot rolling the cast strip, wherein the cooling rate of the hot-rolled strip is controlled to be 16 C./sec. to 74 C./sec., and the coiling temperature of the hot-rolled strip is controlled to be 570720 C.; and wherein the final resulting steel strip has a microstructure substantially consisting of fine polygonal ferrite and pearlite conferring a strength property and an elongation property to the steel strip.

2. The manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade according to claim 1, wherein, in step 1), the content of each of Nb, V and Ti is 0.010.05% by weight percentage, and the content of Mo is 0.10.25% by weight percentage.

3. The manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade according to claim 1, wherein, in step 4), the hot rolling temperature is in the range of 1,1001,250 C.

4. The manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade according to claim 1, wherein, in step 4), the hot rolling temperature is in the range of 1,1501,250 C.

5. The manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade according to claim 1 or claim 3, wherein, in step 4), the reduction rate of the hot rolling is 3050%.

6. The manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade according to claim 1 or claim 3, wherein, in step 4), the deformation rate of hot rolling is >30 s.sup.1.

7. The manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade according to claim 5, wherein, in step 4), the deformation rate of hot rolling is 22 s.sup.1 to 47 s.sup.1.

8. The manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade according to claim 1, wherein, in step 5), the cooling rate is in the range of 18 C./sec to 62 C./sec.

9. The manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade according to claim 1 or claim 8, wherein, in step 5), the coiling temperature is in the range of 620720 C.

10. The manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade according to claim 1, wherein, the thickness of said steel strip is less than 3 mm.

11. The manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade according to claim 1, wherein, the thickness of said steel strip is less than 2 mm.

12. The manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade according to claim 1, wherein, the thickness of said steel strip is less than 1 mm.

13. The manufacturing method of a continuous strip cast atmospheric corrosion-resistant steel strip having a high-strength of 550 MPa-grade according to claim 1 or claim 10, wherein, said steel strip has a yield strength of 550 MPa or above, a tensile strength of 650 MPa or above, and an elongation of 22% or above.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram showing the continuous strip casting process flow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(2) Referring to FIG. 1, the continuous strip casting process flow of the present invention is described below: The molten steel in the large steel ladle 1 is introduced through the long nozzle 2, tundish 3 and submersed nozzle 4 to the molten pool 7 formed by a pair of relatively rotating and internally water-cooling casting rollers (5a and 5b) and the side dams (6a and 6b), and forms the cast strip 11 15 mm in size through cooling by the water-cooling casting rollers; the steel strip then goes through the secondary cooling device 8 in the airtight chamber 10 to control its cooling rate, and is then delivered to the hot rolling mill 13 through the swinging guide plate 9 and pinch roller 12; the hot-rolled strip 0.53 mm in size formed after hot rolling then goes through the third cooling device 14, and then goes into the coiling machine 15. The steel coil is then taken down from the coiling machine for natural cooling to room temperature.

(3) In all examples of the present invention, the molten steel is produced through electric furnace smelting; see the specific chemical composition in Table 1 below. Table 2 provides the thickness and cooling rate of the cast strip produced after the continuous strip casting, the temperature, reduction rate and deformation rate of hot rolling, the thickness and cooling rate of the hot-rolled strip, the coiling temperature and other process parameters, as well as the tensile performance and bending property of the hot-rolled strip after cooling down to room temperature.

(4) It can be seen from Table 2 that, the steel strip of the present invention has a yield strength of 550 MPa or above, a tensile strength of 650 MPa or above, an elongation of 22% or above and qualified 180 bending property, as well as a superior strength and plasticity matching.

(5) TABLE-US-00001 TABLE 1 Chemical composition of the molten steel in the examples (wt. %) Example No. C Si Mn P S N Cu Cr Ni Nb V Ti Mo 1 0.053 0.26 0.85 0.17 0.004 0.0074 0.26 0.62 0.22 0.080 0.12 2 0.046 0.30 0.90 0.13 0.003 0.0061 0.41 0.50 0.34 0.024 0.048 0.010 3 0.050 0.34 0.78 0.15 0.004 0.0058 0.53 0.52 0.30 0.080 4 0.031 0.26 1.50 0.21 0.006 0.0087 0.37 0.80 0.12 0.011 0.080 5 0.044 0.34 1.25 0.09 0.005 0.0052 0.80 0.43 0.32 0.036 0.035 6 0.075 0.31 0.67 0.15 0.006 0.0046 0.50 0.35 0.40 0.012 0.40 7 0.062 0.40 1.42 0.07 0.008 0.0115 0.63 0.30 0.36 0.050 0.035 0.25 8 0.080 0.25 0.60 0.18 0.007 0.0094 0.72 0.70 0.25 0.060 0.050 0.32

(6) TABLE-US-00002 TABLE 2 Process parameters and product performance of the examples 180 Defor- Thick- bending, Thick- Cooling Temper- Reduction mation ness Cooling Flexural ness rate of ature rate of rate of of hot- rate of Coiling center of cast cast of hot hot hot rolled hot-rolled temper- Yield Tensile Elonga- diameter Example strip, strip, rolling, rolling, rolling, strip, strip, ature, strength, strength, tion, a = strip No. mm C./sec. C. % s.sup.1 mm C./sec. C. MPa MPa % thickness 1 2.8 29 1,150 42 36 1.6 18 720 566 706 24 Qualified 2 3.0 38 1,053 26 38 2.2 25 645 593 716 22 Qualified 3 2.8 23 1,210 30 39 2.0 39 630 585 680 22 Qualified 4 4.8 26 1,228 38 34 3.0 74 570 598 702 23 Qualified 5 1.0 34 1,085 46 47 0.6 20 669 596 715 23 Qualified 6 2.6 25 1,240 30 26 1.8 62 616 595 693 22 Qualified 7 4.2 21 1,100 50 22 2.1 45 620 587 685 23 Qualified 8 3.5 32 1,250 25 45 2.6 16 695 570 680 24 Qualified