METHOD FOR PARTIAL COLD DEFORMATION OF STEEL WITH HOMOGENEOUS THICKNESS

Abstract

The invention relates to a method for partial hardening of a steel sheet by cold deformation, where the partial hardening of a steel is done by a cold deformation with a multi-step rolling and annealing process and in order to have a steel sheet with a homogeneous thickness steel sheet is used with at least two areas having different values in mechanical and/or physical properties in longitudinal direction of the material.

Claims

1. Method for partial hardening of a steel by cold deformation characterized in that a multi-step rolling and annealing process in order to have a steel sheet with a homogeneous thickness is used with at least two areas having different values in mechanical and/or physical properties in longitudinal direction of the material.

2. Method according to the claim 1, characterized in that the rolling is carried out by flexible cold rolling.

3. Method according to the claim 1, characterized in that the rolling is carried out by eccentric cold rolling.

4. Method according to claim 1, characterized in that the forming degree (Φ) is in the range of 10≤Φ≤60%, more preferably up to 40% and the ratio (r) is in the range of 1.2>r>1.75.

5. Method according to claim 1, characterized in that the material to be deformed is preferably a stainless steel, more preferably an austenitic stainless steel.

6. Method according to claim 1, characterized in that the material to be deformed is an austenitic TWIP hardening steel, more preferably a stable-austenitic TWIP steel.

7. Method according to claim 1, characterized in that the material to be deformed is a duplex stainless steel.

8. Use of a cold rolled product manufactured according to the claim 1 characterized in that having different mechanical values in at least two consecutive areas deformed with forming degree (Φ) in the range of 5≤Φ≤60% and having the ratio (r) between ultimate load ratio ΔF as an automotive component like an airbag bush, a chassis-part, subframe, pillar, cross member, channel, dashboard support, beam or rocker rail.

9. Use of a cold rolled product manufactured according to the claim 1 characterized in that having different mechanical values in at least two consecutive areas deformed with forming degree (Φ) in the range of 5≤Φ≤60% and having the ratio (r) between ultimate load ratio ΔF as one closed cross-ring for vehicles where the formally pillars and cross-members of roof and floor are integrated.

10. Use of a cold rolled product manufactured according to the claim 1 characterized in that having different mechanical values in at least two consecutive areas deformed with forming degree (Φ) in the range of 5≤Φ≤60% and having the ratio (r) between ultimate load ratio ΔF as member for battery compartment protection whereby the higher strength areas are used as non-deformable zones and conversely the higher ductility areas of the material are used for constructive provided deformation zones which protrudes sideward of the battery compartment.

11. Use of a cold rolled product manufactured according to the claim 1 characterized in that having different mechanical values in at least two consecutive areas deformed with a forming degree (Φ) in the range of 5≤Φ≤60% and having the ratio (r) between ultimate load ratio ΔF as an automotive component with a semi-finished sheet, tube or profile, a railway vehicle component with a continuous length ≥2000 mm like a side wall, floor or roof.

12. Use of a cold rolled product manufactured according to the claim 1 characterized in that having in at least two consecutive areas different mechanical values deformed with forming degree (Φ) at the range of 5≤Φ≤60% and having the ratio (r) between ultimate load ratio ΔF and the thickness ratio Δt at the range of 1.0>r>2.0 as a component with non-magnetic properties for battery electric vehicles.

13. Use of a cold rolled product manufactured according to the claim 1 characterized in that having in at least two consecutive areas different mechanical values deformed with forming degree (Φ) at the range of 5≤Φ≤60% and having the ratio (r) between ultimate load ratio ΔF and the thickness ratio Δt at the range of 1.0>r>2.0 as a hydroformed component.

14. Use of a cold rolled product manufactured according to the claim 1 characterized in that having in at least two consecutive areas different mechanical values deformed with forming degree (Φ) at the range of 5≤Φ≤60% and having the ratio (r) between ultimate load ratio ΔF and the thickness ratio Δt at the range of 1.0>r>2.0 as a semi-finished longitudinally-welded tube.

Description

[0052] The present invention is described in more detail referring to the following drawings where

[0053] FIG. 1 shows the first process step where partially/locally cold deformed areas have the desired final thickness and shows an increase of strength with a concurrent decrease of elongation at that part of the deformed product,

[0054] FIG. 2 shows the material after the final process step executed in reverse order to the first step so that now the formerly thicker areas are cold deformed to the thickness level of the already thin deformed areas,

[0055] FIG. 3 shows one preferable application example of the material produced with the method of the present invention,

[0056] FIG. 4 shows another preferable application example of the material produced with the method of the present invention,

[0057] FIG. 5 shows another preferred usage of the material produced with the method of the present invention.

[0058] In FIG. 1 is presented state of the art, where area 2 with the higher thickness (t.sub.i=initial thickness) is used for higher load areas by having in all material areas constant mechanical-technological values. Area 1 represents the thinned-out area with the final thickness t.sub.f after cold-rolling. FIG. 1 also represents step 1 of the present invention.

[0059] In FIG. 2 is presented the invention where area 2 with the cold-hardening and therefore a higher strength level is used for higher load areas by having a constant thickness t.sub.f (final thickness after processing) in all material areas.

[0060] FIG. 3 represents an automotive b-pillar. In the upper area, which is the neck and head area of the passenger, a higher initial strength level is needed to create a preferably non-deformable component area and therefore to protect the passenger. For the lower area of the b-pillar a significantly more ductile material is needed to allow the complex forming of the part during component manufacturing. At the same time, a preferably high remaining ductility after forming is necessary to absorb the energy during a crash and protect the passenger in this way.

[0061] FIG. 4 represents an automotive dashboard support beam. The material produced with the method of the present invention was further processed to a longitudinal-welded tube having at least two areas with different values in mechanical and/or physical properties in longitudinal direction of the tube. Then a hydroforming process follows to form out the final component geometry. Areas without or with just a low forming degree can be designed with a higher initial strength with the method of the present invention. On the other side complex formed areas are dimensioned with more ductility with the method of the present invention. Using a fully-austenitic TWIP steel, the complex formed areas will harden during component manufacturing and the lower or non-formed areas have an initially high strength because of the method of the present invention.

[0062] FIG. 5 represents a cutting pattern of a coil or strip produced with the method of the present invention. Thereby a cross ring integrating the formally single parts of two b-pillars, a roof cross member and a floor cross member. In doing so, various cross rings can be parallel arranged across the width to have an optimal material capacity with low volume of waste. FIG. 5 and therefore the cross rings can be arranged repetitive in rolling direction meaning in coil or strip length having recurring the same rolling and cutting order. In FIG. 5 the higher strength but lower ductility material areas are identified with “HS/LD” usually needed and exemplary signed in FIG. 5 for the b-pillar trees and the roof cross member. In these areas, an impact-resistance having non-deformable zones are necessary. On the other side lower strength but higher ductility material areas are marked with “LS/HD” usually needed and exemplary signed in FIG. 5 for the b-pillar feets, the b-pillar links to the roof and the underbody cross member. The feets of the b-pillars have the task to absorb the crash energy whereas the b-pillar links to the roof needs a high ductility to connect the areas with the roof longitudinal structures. Furthermore, the underbody cross member will be complex formed to increase component stiffness and therefore a high ductility is needed there. The transition zones between the high and lower strength material areas are characterized in FIG. 5 with “T”.

[0063] The method according to the present invention was tested with the stainless steels 1.4301 (TRIP-hardened austenitic, CrNi alloyed), 1.4462 (ferritic-austenitic Duplex structure, CrNiMo alloyed) and 1.4678 (TWIP-hardened fully-austenitic, CrMn alloyed). The results are shown in table 2.

TABLE-US-00002 TABLE 2 Tensile Tensile Forming Initial Resulting strength strength Ratio degree Relation thickness thickness [MPa] [MPa] r φ r.sub.φ Grade [mm] [mm] Area 1 Area 2 [—] [%] [—] 1.4301 2.0 1.6 665 925 1.39 20 7.0 1.4462 2.0 1.2 825 1405 1.70 40 4.3 1.4678 2.0 1.5 935 1040 1.51 25 6.0