Method for producing hot-formed and press-hardened automobile column
A method for producing an automobile column is disclosed. The automobile column has a region of a first type and a region of a second type which have mutually different strengths. A transition region having a width of less than 50 mm is formed between the two regions. The automobile column has in the region of the first type a bainitic structure and in the region of the second type a martensitic structure.
1. A method for producing a hot-formed and press-hardened automobile column having at least two regions of different hardness, said method comprising the steps of:
providing a hardenable metal plate or semi-finished product and heating the hardenable metal plate or semi-finished product to at least an austenizing temperature,
intermediately cooling a first region of the metal plate or semi-finished product with a cooldown speed selected to be greater than a lower critical cooldown speed of a material of the metal plate or semi-finished product, and
hot-forming and press-hardening the metal plate or semi-finished product in a press-hardening tool to form the automobile column
wherein the first region has a stretchability A50 between 10% and 30%,
wherein a yield strength or a tensile strength decreases or increases in a transition region between the first region and the second region with a gradient of more than 200 N/mm 2 per 10 mm, and
wherein the first region contains a mixed structure of martensite, bainite and at least one of ferrite and perlite and wherein a bainite content of the first region is more than 50%.
2. The method of claim 1 , wherein a second region is held above the austenizing temperature until the second region is transported into the press-hardening tool.
3. The method of claim 1 , wherein the cooldown speed during intermediate cooling of the first region is selected such that a bainitic structure is obtained.
4. The method of claim 3 , wherein the first region is cooled to a cooling temperature between 600 and 400° C.
5. The method of claim 4 , wherein the first region is cooled to a cooling temperature of about 500° C.
6. The method of claim 3 , wherein the first region is held at the cooling temperature for a predetermined time.
7. The method of claim 3 , wherein the first region is held at the cooling temperature isothermally.
8. The method of claim 1 , wherein the mixed structure of the first region is obtained by quenching the first region in the press-hardening tool from a bainitic structure transformation stage.
9. The method of claim 1 , further comprising the step of holding the first region isothermally so as to form a substantially pure bainitic structure by press-hardening.
10. The method of claim 1 , wherein the cooldown speed of the intermediate cooling is selected to be greater than an upper critical cooling-down speed.
11. The method of claim 1 , wherein the intermediate cooling of the region of first region is performed in the press-hardening tool.
12. The method of claim 11 , wherein the intermediate cooling of first region is performed by using cooling plates arranged in the press-hardening tool.
13. The method of claim 1 , wherein the metal plate is pre-formed into a semi-finished product while cold before being heated to at least the austenizing temperature.
14. The method of claim 1 , wherein the first region has a tensile strength between 500 and 1000 N/mm 2 .
15. The method of claim 2 , wherein a transition region between the first region and the second region smaller than 80 mm.
16. The method of claim 2 , wherein at least portions of the first region are enclosed by the region of the second type.
17. The method of claim 2 , wherein the first region is completely enclosed by the region of the second type.
18. The method of claim 1 , wherein the first region is spot-shaped with a diameter of less than 40 mm.
19. The method of claim 1 , further comprising constructing the first region as a flange, a connecting flange or an outside edge of the automobile column, or a combination thereof.
20. The method of claim 1 , wherein the first region is formed in regions of the automobile column which are subject to strong deformations in a crash or which are configured to dissipate crash energy through deformations.
21. The method of claim 2 , wherein the first region has an increased wall thickness in relation to the second region.
22. The method of claim 1 , further comprising forming a passage or an edge, or both, in the first region after the hot-forming.
23. The method of claim 1 , wherein a yield strength or a tensile strength decreases or increases in a transition region between the first region and the second region with a gradient of more than 400 N/mm 2 per 10 mm.
24. The method of claim 2 , wherein the second region has a strength of more than 1000 N/mm 2 .
25. The method of claim 2 , wherein the second region has a strength of more than 1200 N/mm 2 .
26. The method of claim 2 , wherein the second region has a strength of more than 1400 N/mm 2 .
27. The method of claim 1 , wherein first region has a yield strength between 200 and 800 N/mm 2 .
28. The method of claim 1 , further comprising manufacturing the automobile column from a Tailor Welded Blank or a Tailor Rolled Blank.