Method for manufacturing a component of austenitic TWIP or TRIP/TWIP steel

Abstract

The present invention relates to a method for manufacturing a component of austenitic TWIP or TRIP/TWIP steel. A flat product (1) is deformed by achieving at least one indentation (16) on at least one surface of the flat product (1) in order to have in the deformed product (5) areas of a high strength steel embedded in a matrix of a ductile material. The invention also relates to the use of the component where areas of a high strength steel embedded in a matrix of a ductile material are required in the same component.

Claims

1. A high strength sheet comprising austenitic twinning induced plasticity (TWIP) or transformation induced plasticity/twinning induced plasticity (TRIP/TWIP) steel with deformed indentations having areas of high strength in a matrix of ductile material, wherein a hardness of the sheet in an area of the indentations is reversible by annealing the sheet at a temperature of 900-1250° C.

2. The high strength sheet of claim 1, wherein the annealing temperature is 900-1050° C.

3. The high strength sheet of claim 1, wherein the sheet comprises 10-25 weight % manganese and has interstitial disengaged nitrogen and carbon atoms, wherein a total carbon and nitrogen content is 0.4-0.8 weight %.

4. The high strength sheet of claim 3, wherein the sheet further comprises 10-20.5 weight % chromium and 3.5-9.5 weight % nickel.

5. The high strength sheet of claim 1, wherein the sheet has a stacking fault energy of 20-30 mJ/m.sup.2.

6. The high strength sheet according to claim 1, wherein a thickness of the sheet in an area outside of the indentations is 0.15-4.0 millimeter.

7. The high strength sheet according to claim 6, wherein a depth of the indentations is up to 30% of a thickness of the sheet in an area outside of the indentations.

8. The high strength sheet according to claim 7, wherein the TWIP or TRIP/TWIP effect is directly proportional to the indentation depth.

9. The high strength sheet according to claim 6, wherein the indentations have a shape of a honeycomb, a wave, a triangle, a rectangle, a circle, a cross, a line, a ripple, a cobweb, or any combination of these geometries.

10. A method for manufacturing the high strength sheet of claim 1, wherein an austenitic twinning induced plasticity (TWIP) or transformation induced plasticity/twinning induced plasticity (TRIP/TWIP) steel sheet is deformed by achieving at least one indentation on at least one surface of the steel sheet in order to have, in the deformed product, areas of a high strength embedded in a matrix of a ductile material.

11. The method according to claim 10, wherein deformation of the steel sheet is achieved by cold rolling using at least one roll that is a profiled roll in order to create at least one indentation in a direction transverse to the rolling direction with a desired geometry on the surface of the steel sheet.

12. The method according to claim 10, wherein deformation of the steel sheet is achieved by cold rolling using at least one roll that is a profiled roll in order to create two or more indentations in a direction parallel to the rolling direction with a desired geometry on the surface of the steel sheet.

13. The method according to claim 10, wherein deformation of the steel sheet is achieved by cold rolling using at least one roll that is a profiled roll in order to create two or more indentations both in a direction transverse to the rolling direction and in a direction parallel to the rolling direction with a desired geometry on the surface of the steel sheet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The deformed product manufactured in accordance with the present invention is described in more detail referring to the following drawings, where

(2) FIG. 1 illustrates one preferred embodiment of the invention schematically as a distortion view seen from the side after deformation,

(3) FIG. 2 illustrates a partial and enlarged point for the embodiment of the FIG. 1,

(4) FIG. 3 illustrates the effect of depth of indentations, and

(5) FIG. 4 illustrates the comparison of properties between the deformed product of the invention and the deformed standard material.

DESCRIPTION OF THE INVENTION

(6) The material of the FIGS. 1-4 is an austenitic stainless steel having the TWIP effect and containing as the main components with iron in weight % 0.3 carbon, 16% manganese, 14% chromium, less than 0.5% nickel and 0.3% nitrogen.

(7) According to FIG. 1 a flat strip 1 is running through a cold rolling mill, which is illustrated by the working rolls 2 and 3. The rolls 2 and 3 are profiled to create indentations both in the direction transverse to the rolling direction and in the direction parallel to the rolling direction which indentations form a honeycomb structure 4 on the surfaces of the deformed strip 5.

(8) In FIG. 2 it is shown one part of the deformed strip 5 of FIG. 1. The initial thickness of the flat strip is shown as the reference number 13 and the depth of an indentation, with the value of 30%, as the reference number 14. The deformed strip 5 with the deformed thickness 12 has on the surfaces non-deformed areas 15 with high ductility and high elongation. The indentations 16 created by the working rolls 2 and 3 (FIG. 1) of the cold rolling mill form high deformed areas with high strength and high hardness on the surfaces of the deformed strip with the thickness 12.

(9) FIG. 3 shows test results in a coordination where the horizontal axis represents measuring points in a test sample which was deformed in accordance with the present invention. The test sample was deformed in five areas 21, 22, 23, 24 and 25 having different indentation depths of 180, 80, 75, 90 and 155 micrometer respectively. The vertical axis of the coordination represents local Vickers hardness (HV1). The test results of FIG. 3 show that the Vickers hardness (HV1) is directly proportional to the indentation depth in the test sample.

(10) FIG. 4 shows test results when the elongation (A.sub.80) and the yield strength R.sub.p0.2 were measured from the test samples where the test samples (invention_1 . . . 5 were deformed in order to create indentations on the surface of the material in accordance with the present invention. The other test samples (old_1 . . . 5 were not deformed because of the comparison. FIG. 4 shows that the non-deformed test samples have greater elongation values than the deformed test samples, but the non-deformed test samples have an essential decrease in the yield strength when compared with the deformed test sample. The deformation for creating indentations on the surface of the material achieves to have both high strength and high elongation simultaneously.