High-strength high-elongation tinned primary plate and double cold reduction method therefor

Abstract

A high-strength high-elongation tinned primary plate and a double cold reduction method therefor. The tinned primary plate comprises the following components by weight from 0.065 to 0.12% of carbon, from 0.2 to 0.8% of manganese, from 0.003 to 0.015% of nitrogen, the remainder being iron and the inevitable trace impurities. The tinned primary plate is necessarily subjected to double cold reduction at a reduction of 5˜13% and a rolling tension of 50˜100 MPa. The tinned primary plate has a yield strength of Rp.sub.0.2≥520 MPa, and percentage elongations in rolling direction RD, 45° direction and perpendicular direction TD, which are all greater than or equal to 10% after bake-hardening.

Claims

1. A tinned plate, consisting of: 0.065 to 0.12 wt % of carbon, 0.2 to 0.8 wt % of manganese, 0.01 to 0.08 wt % of aluminum, 0.003 to 0.015 wt % of nitrogen, at least one of 0.001 to 0.005 wt % of boron or, 0.01 to 0.03 wt % of copper; and one or more of the following component(s): 0.01 to 0.05 wt % of chromium, 0.001 to 0.1 wt % of titanium, 0.001 to 0.2 wt % of niobium, 0.002 to 0.008 wt % of molybdenum, the remainder being iron and inevitable trace impurities, wherein the tinned plate is subjected to double cold reduction at a reduction of 5-13% and a rolling tension of 50-100 MPa; wherein the microstructure of the tinned plate consists of ferrite and granular cementite with a banded distribution; wherein, the tinned plate has a yield strength of Rp.sub.0.2≥520 MPa, and percentage elongations A % in rolling direction RD, 45 degree direction and perpendicular direction TD, which are all greater than or equal to 10% after bake-hardening.

2. A double cold reduction method for a tinned plate, wherein the tinned plate consists of: 0.065 to 0.12 wt % of carbon, 0.2 to 0.8 wt % of manganese, 0.01 to 0.08 wt % of aluminum, 0.003 to 0.015 wt % of nitrogen, at least one of 0.001 to 0.005 wt % of boron or, 0.01 to 0.03 wt % of copper; and one or more of the following component(s): 0.01 to 0.05 wt % of chromium, 0.001 to 0.1 wt % of titanium, 0.001 to 0.2 wt % of niobium, 0.002 to 0.008 wt % of molybdenum, the remainder being iron and inevitable trace impurities, wherein the tinned plate is subjected to double cold reduction at a reduction of 5-13% and a rolling tension of 50-100 MPa; wherein the microstructure of the tinned plate consists of ferrite and granular cementite with a banded distribution; wherein, the tinned plate has a yield strength of Rp.sub.0.2≥520 MPa, and percentage elongations A % in rolling direction RD, 45 degree direction and perpendicular direction TD, which are all greater than or equal to 10% after bake-hardening.

3. The double cold reduction method according to claim 2, wherein, prior to the step of double cold reduction, steps for production of the tinned plate comprise converter steelmaking, continuous casting, hot rolling, pickling, single cold reduction and continuous annealing.

4. The double cold reduction method according to claim 3, wherein, the tinned plate is subjected to hot rolling before double cold reduction, wherein slab is heated to 1120° C. or higher, finishing rolling temperature is 840° C. or higher, and coiling temperature is 650° C. or lower.

5. The double cold reduction method according to claim 3, wherein, the tinned plate is subjected to the single cold reduction, before the double cold reduction, at a reduction of 85-90%.

6. The double cold reduction method according to claim 3, wherein, the tinned plate is subjected to the continuous annealing, before double cold reduction, at an annealing temperature of 620-680° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view showing the influence of the change of reduction of double cold reduction on the yield strength Rp.sub.0.2 and the elongation A % in three directions of the steel plate after bake-hardening.

(2) FIG. 2 is a schematic view showing the influence of the rolling tension on the yield strength Rp.sub.0.2 and the elongation A % in three directions of the steel plate after bake-hardening.

DETAILED DESCRIPTION

(3) The invention will be described below by the Examples and the accompanying drawings.

(4) Table 1 lists the alloy compositions of Examples 1˜7 and Comparative Examples 1˜2 of the present invention. Table 2 lists the processes before double cold reduction of the steel plate of Examples 1˜7 and Comparative Examples 1˜2 of the present invention.

(5) Tables 3˜5 show the properties of the Examples and Comparative Examples of the present invention after bake-hardening. Table 3 shows the properties after bake-hardening the steel plates obtained by double cold reduction of Example 1 using different reduction (Examples 1-1, 1-2, 1-3, Comparative Examples 1-1, 1-2). Table 4 shows the properties after bake-hardening of the steel plates obtained by double cold reduction using different tensions of Example 2 (Example 2-1, Comparative Example 2-1). Table 5 shows the properties after bake-hardening of the steel plates obtained by double cold reduction using different reduction and tensions of Examples 3˜7 and Comparative Examples 1˜4.

(6) TABLE-US-00001 TABLE 1 Unit: mass percentage C Mn Al N B Cr Ti Nb Cu Mo Example 1 0.08 0.3 0.01 0.005 0 0 0 0 0 0.005 Example 2 0.12 0.3 0.03 0.015 0.002 0.03 0 0 0 0 Example 3 0.08 0.8 0.05 0.007 0 0 0 0.01 0.02 0 Example 4 0.10 0.6 0.06 0.005 0 0 0.005 0.005 0 0 Example 5 0.12 0.6 0.03 0.010 0.002 0.02 0 0.005 0 0 Example 6 0.07 0.4 0.03 0.012 0.002 0.005 0 0.02 0 Example 7 0.08 0.3 0.03 0.015 0.002 0.02 0.005 0 0 0 Comparative 0.05 0.3 0.03 0.005 0 0 0 0.005 0 0 Example 1 Comparative 0.15 0.1 0.04 0.003 0.002 0 0 0 0 0 Example 2 Comparative 0.10 0.6 0.06 0.005 0.005 0 0 0.005 0 0 Example 3 Comparative 0.08 0.8 0.05 0.007 0 0.02 0 0.01 0 0 Example 4

(7) TABLE-US-00002 TABLE 2 Finishing Continuous Heating rolling Coiling Single cold annealing temperature temperature temperature reduction temperature ° C. ° C. ° C. % ° C. Example 1 1180 860 600 88 670 Example 2 1180 850 600 88 670 Example 3 1180 860 640 86 670 Example 4 1130 860 600 88 630 Example 5 1150 860 640 88 670 Example 6 1180 850 600 86 630 Example 7 1130 860 640 88 670 Comparative 1180 820 650 86 700 Example 1 Comparative 1180 840 600 88 620 Example 2 Comparative 1100 840 680 80 670 Example 3 Comparative 1180 860 650 88 600 Example 4

(8) TABLE-US-00003 TABLE 3 Rolling Final Yield Double cold tension thickness strength Elongation reduction (%) (MPa) mm Direction Rp0.2 A % Example 1-1 5 80 0.247 RD 536.9 14.9 45° 531.1 19.9 TD 534.5 14.5 Example 1-2 9 0.237 RD 552.5 18.6 45° 534.1 21.4 TD 548.7 16.6 Example 1-3 13 0.226 RD 574.6 13.3 45° 558.3 19.8 TD 576.4 16.4 Comparative 3 0.252 RD 491.4 21.4 Example 1-1 45° 497.9 28.6 TD 515.1 21.6 Comparative 15 0.221 RD 620.2 4.2 Example 1-2 45° 610.5 8.3 TD 624.2 3.5 Remarks: The steel plates obtained by double cold reduction were baked at 200° C. for 30 min, and then the mechanical properties are measured. Mechanical properties were measured on tensile samples processed according to JIS5 standard. Rp0.2 is the stress at which 0.2% residual deformation occurs using as value of the yield strength, and A % is the elongation at break, and the gauge length is 50 mm.

(9) TABLE-US-00004 TABLE 4 Rolling Final Yield Double cold tension thickness strength Elongation reduction (%) (MPa) mm Direction Rp0.2 A % Example 2-1 13 100 0.226 RD 572.3 13.1 45° 555.4 18.5 TD 581.2 13.5 Comparative 120 0.226 RD 578.2 12.8 Example 2-1 45° 560.1 18.5 TD 585.4 8.9 Remarks: The steel plates obtained by double cold reduction were baked at 200° C. for 30 min, and then the mechanical properties are measured. Mechanical properties were measured on tensile samples processed according to JIS5 standard. Rp0.2 is the stress at which 0.2% residual deformation occurs using as value of the yield strength, and A % is the elongation at break, and the gauge length is 50 mm.

(10) TABLE-US-00005 TABLE 5 Rolling Final Yield Double cold tension thickness strength Elongation reduction (%) (MPa) mm Direction Rp0.2 A % Example 3 8 80 0.245 RD 563.9 14.8 45° 552.8 17.6 TD 578.3 14.5 Example 4 8 80 0.230 RD 560.4 13.5 45° 552.3 18.8 TD 570.2 15.4 Example 5 13 80 0.220 RD 592.8 12.8 45° 589.0 14.7 TD 598.4 11.9 Example 6 13 50 0.220 RD 585.4 13.1 45° 575.3 15.2 TD 588.3 12.5 Example 7 8 100 0.232 RD 568.2 14.8 45° 549.2 18.9 TD 567.4 13.6 Comparative 10 60 0.221 RD 513.5 21.8 Example 1 45° 500.4 27.3 TD 530.5 20.9 Comparative 8 120 0.240 RD 589.8 3.9 Example 2 45° 576.8 7.5 TD 594.6 5.0 Comparative 8 60 0.220 RD 523.5 22.8 Example 3 45° 510.4 23.2 TD 520.4 18.5 Comparative 8 80 0.231 RD 618.4 5.2 Example 4 45° 612.7 5.4 TD 632.2 5.8

(11) FIG. 1 shows the influence of the change of reduction of double cold reduction on the yield strength Rp.sub.0.2 and the elongation A % in three directions of the steel plate after bake-hardening. FIG. 1 is based on Examples 1-1, 1-2, 1-3, and Comparative Examples 1-1, 1-2. The solid line in the Figure is the curve of Rp.sub.0.2, and the dotted line is the curve of A %. As the reduction of double cold reduction increases, the strength increases while the elongations in three directions decrease.

(12) FIG. 2 shows the influence of the rolling tension on the yield strength Rp.sub.0.2 and the elongation A % in three directions of the steel plate after bake-hardening. FIG. 2 is based on Examples 1-3, 2-1, and Comparative Example 2-1. The solid line in the Figure is the curve of Rp.sub.0.2, and the dotted line is the curve of A %. The most obvious effect of the increase in rolling tension is that the elongation in TD direction is drastically reduced.