Method for Cold Deformation of an Austenitic Steel

Abstract

A method for partial hardening of an austenitic steel by utilizing during cold deformation the TWIP (Twinning Induced Plasticity), TWIP/TRIP or TRIP (Transformation Induced Plasticity) hardening effect. Cold deformation is carried out by cold rolling at least one surface of the steel with forming degree () of 560% in order to achieve in the steel at least two consecutive areas with different mechanical values in thickness, yield strength (R.sub.p0.2), tensile strength (Rm) and elongation, having a ratio (r) between the ultimate load ratio (F) and the thickness ratio (t) of 1.0>r>2.0, and in which the areas are mechanically connected to each other by a transition area having a thickness that is variable from the thickness of the first area in the deformation direction to the thickness of the second area in the deformation direction.

Claims

1. A method for partial hardening of an austenitic steel by utilizing during cold deformation a Twinning Induced Plasticity (TWIP), Twinning Induced Plasticity/Transformation Induced Plasticity (TWIP/TRIP) or (Transformation Induced Plasticity (TRIP) hardening effect wherein cold deformation is carried out by cold rolling at least one surface of the steel to be deformed with a forming degree () of 560% in order to achieve in the steel at least two consecutive areas with different mechanical values in thickness, yield strength (Rp0.2), tensile strength (Rm), and elongation, having a ratio (r) between an ultimate load ratio (F) and a thickness ratio (t) of 1.0>r>2.0, and in which the areas are mechanically connected to each other by a transition area having a thickness that is variable from a thickness of the first area in the deformation direction to a thickness of the second area in the deformation direction.

2. The method according to claim 1, wherein the cold rolling is carried out by flexible cold rolling.

3. The method according to claim 1, wherein the cold rolling is carried out by eccentric cold rolling.

4. The method according to claim 1, wherein the forming degree () is 1040% and the ratio (r) is 1.15>r>1.75.

5. The method according to claim 1, wherein the steel to be deformed is an austenitic TWIP steel.

6. The method according to claim 5, wherein the steel to be deformed is an austenitic stainless steel.

7. The method according to claim 1, wherein the steel to be deformed is a TRIP/TWIP steel.

8. The method according to claim 7, wherein the steel to be deformed is an austenitic duplex stainless steel.

9. The method according to claim 7, wherein the steel to be deformed is a ferritic austenitic duplex stainless steel containing more than 40 vol % austenite.

10. The method according to claim 1, wherein the steel to be deformed is a TRIP steel.

11. An automotive component comprising a cold rolled product manufactured according to claim 1 having in the at least two consecutive areas different mechanical values, deformed with the forming degree () of 560%, and having the ratio (r) between the ultimate load ratio F and the thickness ratio t of 1.0>r>2.0.

12. A commercial vehicle component comprising a semi-finished sheet, tube, or profile comprising a cold rolled product manufactured according to claim 1 having in the at least two consecutive areas different mechanical values, deformed with the forming degree () of 560%, and having the ratio (r) between the ultimate load ratio F and the thickness ratio t of 1.0>r>2.0.

13. A tube manufactured from a strip or slit strip comprising a cold rolled product manufactured according to claim 1 having in the at least two consecutive areas different mechanical values, deformed with the forming degree () of 560%, and having the ratio (r) between the ultimate load ratio F and the thickness ratio t of 1.0>r>2.0.

14. (canceled)

15. A component with non-magnetic properties for battery electric vehicles a cold rolled product manufactured according to claim 1 having in the at least two consecutive areas different mechanical values, deformed with the forming degree () of 560% and having the ratio (r) between the ultimate load ratio F and the thickness ratio t of 1.0>r>2.0.

16. A component for transportation applications comprising a cold rolled product manufactured according to claim 1 having in the at least two consecutive areas different mechanical values, deformed with the forming degree () of 560%, and having the ratio (r) between the ultimate load ratio F and the thickness ratio t of 1.0>r>2.0, wherein the component is rollformed or hydroformed.

17. The method according to claim 7, wherein the steel to be deformed is a ferritic austenitic duplex stainless steel containing more than 50 vol % austenite.

18. The automotive component of claim 11, wherein the automotive component is an airbag bush or an automotive car body component.

19. The automotive component of claim 18, wherein the automotive car body component is a chassis-part, a subframe, a pillar, a cross member channel, a rocker rail, or a crash-relevant door-side impact beam.

20. A railway vehicle component with a continuous length 2000 mm comprising a cold rolled product manufactured according to claim 1 having in the at least two consecutive areas different mechanical values, deformed with the forming degree (1) of 560%, and having the ratio (r) between the ultimate load ratio F and the thickness ratio t of 1.0>r>2.0.

21. The railway vehicle component of claim 20, wherein the component comprises a side wall, a floor, or a roof.

Description

[0044] The present invention is described in more details referring to the following drawings where

[0045] FIG. 1 shows a preferred embodiment of the present invention shown in schematic manner and seen as an axonometric projection,

[0046] FIG. 2 shows another preferred embodiment of the present invention shown in schematic manner and seen as an axonometric projection.

[0047] In FIG. 1 a piece of TWIP material 1 is flexible cold rolled both on the upper surface 2 and on the lower surface 3 with the rolling direction 4. The material piece 1 has a first area 5 where the material is thick and the material is more ductile and at the same time hardened. The material piece further has a transition area 6 where the material thickness is variable so that the thickness is lowering from the first area 5 to the second area 7 where the material has higher strength, but lower ductile.

[0048] In FIG. 2 a piece of TWIP material 11 is flexible cold rolled only on the upper surface 12 with the rolling direction 13. As in the embodiment of FIG. 1, the material piece 11 has a first area 14 where the material is thick and the material is more ductile and at the same time hardened. The material piece 11 further has a transition area 15 where the material thickness is variable so that the thickness is lowering from the first area 14 to the second area 16 where the material has higher strength, but lower ductile.

[0049] The method according to the present invention was tested with the TWIP (Twinning Induced Plasticity) austenitic steels which chemical compositions in weight % are in the following table 1.

TABLE-US-00001 TABLE 1 Alloy Cr Mn Ni C N A (melt1) 16 18 2 0.3 0.4 B (melt2) 14 15 2 0.3 0.6 C (melt3) 12 20 2 0.08 D (melt4) 6 14 0.5 0.08 0.2 E (melt5) 18 6 2.5 0.06

[0050] The alloys A-C and E are austenitic stainless steels, while the alloy D is an austenitic steel.

[0051] The measurements of yield strength R.sub.p0.2, tensile strength R, and elongation A.sub.80 for each alloy A-E were done before and after the flexible cold rolling where the alloys were rolled on both the upper surface and the lower surface. The results of the measurements as well as the initial thickness and the resulting thickness are described in the following table 2.

TABLE-US-00002 TABLE 2 Initial Initial Resulting Resulting Initial yield tensile Initial Resulting yield tensile Resulting thickness strength strength elongation thickness strength strength elongation Alloy mm MPa MPa A80 mm MPa MPa A80 A (melt1) 2.0 520 965 51 1.6 1040 1280 13 B (melt2) 1.0 770 1120 33 0.9 1025 1250 14 C (melt3) 2.0 490 947 45 1.4 1180 1392 7 D (melt4) 1.6 380 770 41 1.3 725 914 14 E (melt5) 1.5 368 802 50 1.2 622 1090 15

[0052] The results in the table 2 show that the yield strength R.sub.p0.2 and the tensile strength R.sub.m increase essentially during the flexible rolling, while the elongation A.sub.80 decreases essentially during the flexible rolling.

[0053] The method according to the present invention was also tested with the TRIP (Transformation Induced Plasticity) or TRIP/TWIP austenitic or ferritic austenitic duplex standardized steels which chemical compositions in weight % are in the following table 3.

TABLE-US-00003 TABLE 3 Grade Cr Mn Ni C Mo N 1.4301 18 1.2 8.0 0.04 1.4318 17 1.0 7.5 0.02 0.14 1.4362 22 1.3 3.8 0.02 0.10 1.4401 17 1.2 10.5 0.02 2.2 1.4462 22 1.4 5.8 0.02 3.0 0.17

[0054] In the table 3 the grades 1.4362 and 1.4462 are ferritic austenitic duplex stainless steels, and the others 1.4301, 1.4318 and 1.4401 are austenitic stainless steels.

[0055] Before and after the flexible rolling, the mechanical values, yield strength R.sub.p0.2, tensile strength R.sub.m and elongation, for the grades of the table 3 are tested, and the results with the initial thickness before the flexible rolling and the resulting thickness after the flexible rolling are described in the following table 4.

TABLE-US-00004 TABLE 4 Initial Initial Resulting Resulting Initial yield tensile Initial Resulting yield tensile Resulting thickness strength strength elongation thickness strength strength elongation Grade mm MPa MPa A80 mm MPa MPa A80 1.4301 2.0 275 680 56 1.4 900 1080 12 1.4318 2.0 390 735 47 1.4 905 1090 20 1.4362 2.0 550 715 31 1.4 1055 1175 5 1.4401 2.0 310 590 53 1.4 802 935 13 1.4462 2.0 655 825 32 1.2 1190 1380 5

[0056] The results in the table 4 show that beside the austenitic stainless TWIP steels also the duplex stainless TRIP or TWIP/TRIP steels with an austenite content more than 40 vol %, preferably more than 50 vol %, have high suitability for hardened areas in a flexible rolling process.

[0057] For the TWIP, TWIP/TRIP and TRIP steels in accordance with the invention it was tested the effect of the forming degree . The table 5 shows the results for low nickel austenitic stainless steel B of the table 1.

TABLE-US-00005 TABLE 5 Rm t F F % [MPa] [mm] [Nmm] % r r.sub. 0 935 2 1870 5 1020 1.9 1938 104 1.09 21.8 10 1080 1.8 1944 104 1.16 11.6 20 1340 1.6 2144 115 1.43 7.2 25 1410 1.5 2115 113 1.51 6.0 40 1650 1.2 1980 106 1.76 4.4 50* 1800 1 1800 96 1.93 3.9 60* 1890 0.8 1512 81 2.02 3.4 *Outside the invention

[0058] The table 6 shows the results for austenitic stainless steel 1.4318

TABLE-US-00006 TABLE 6 Rm t F F % [MPa] [mm] [Nmm] % r r.sub. 0 715 2 1430 10 800 1.8 1440 101 1.12 11.2 20 925 1.6 1480 103 1.29 6.5 25 990 1.5 1485 104 1.38 5.5 40 1280 1.2 1536 107 1.79 4.5 50 1440 1 1440 101 2.01 4.0 60* 1565 0.8 1252 88 2.19 3.6 *Outside invention

[0059] The table 7 shows the results for duplex austenitic ferritic stainless steel 1.4362.

TABLE-US-00007 TABLE 7 Rm t F F % [MPa] [mm] [Nmm] % r r.sub. 0 715 2 1430 5 805 1.9 1530 107 1.13 22.5 10 900 1.8 1620 113 1.26 12.6 20 1080 1.6 1728 121 1.51 7.6 25 1125 1.5 1688 118 1.57 6.3 40 1310 1.2 1572 110 1.83 4.6 50* 1366 1 1366 96 1.91 3.8 *Outside the invention

[0060] The table 8 shows the results for duplex austenitic ferritic stainless steel 1.4462.

TABLE-US-00008 TABLE 8 Rm t F F % [MPa] [mm] [Nmm] % r r.sub. 0 825 2 1650 5 910 1.9 1729 105 1.10 22.1 10 1020 1.8 1836 111 1.24 12.4 20 1165 1.6 1864 113 1.41 7.1 25 1250 1.5 1875 114 1.52 6.1 40 1405 1.2 1686 102 1.70 4.3 50* 1470 1 1470 89 1.78 3.6 60* 1495 0.8 1196 72 1.81 3.0 *Outside invention

[0061] The table 9 shows the results for austenitic stainless steel 1.4301.

TABLE-US-00009 TABLE 9 Rm t F F % [MPa] [mm] [Nmm] % r r.sub. 0 665 2 1330 5 698 1.9 1326 100 1.05 21 10 760 1.8 1368 103 1.14 11.4 20 925 1.6 1480 111 1.39 6.95 25 1005 1.5 1508 113 1.51 6.05 40 1155 1.2 1386 104 1.74 4.34 50* 1290 1 1290 97 1.94 3.88 60* 1465 0.8 1172 88 2.20 3.67 *Outside the invention