HOHERFESTER MEHRPHASENSTAHL MIT AUSGEZEICHNETEN UMFORMEIGENSCHAFTEN HIGH STRENGTH MULTI-PHASE STEEL HAVING EXCELLENT FORMING PROPERTIES

• US 20140034196A1
• Filed: 11/30/2011
• Published: 02/06/2014
• Est. Priority Date: 01/26/2011
• Status: Abandoned Application

• Current Assignee: Salzgitter Flachstahl GmbH (Salzgitter AG)
• Original Assignee: Jorg Heinecke, Phillip Wullner
• Inventors: Wedemeier, Andreas, Schulz, Thomas, Pohl, Michael, Wllner, Phillip, Heinecke, Jrg, Schlegel, Christian
• Application Number:
  US13/981,870
• Publication Number:
  US 20140034196A1
• Time in Patent Office: Days
• US Class Current: 148/661
• CPC Class Codes: C21D 1/185 from an intercritical temperature
• CPC Class Codes: C21D 2211/002 Bainite
• CPC Class Codes: C21D 2211/005 Ferrite
• CPC Class Codes: C21D 8/0226 Hot rolling
• CPC Class Codes: C21D 8/0236 Cold rolling
• CPC Class Codes: C21D 8/0247 characterised by the heat treatment
• CPC Class Codes: C22C 1/02 by melting C22C1/1036 takes precedence
• CPC Class Codes: C22C 38/00 Ferrous alloys, e.g. steel alloys cast-iron alloys C22C37/00
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/22 with molybdenum or tungsten
• CPC Class Codes: C22C 38/26 with niobium or tantalum
• CPC Class Codes: C22C 38/28 with titanium or zirconium
• CPC Class Codes: C22C 38/32 with boron
• CPC Class Codes: C22C 38/38 with more than 1.5% by weight of manganese

Abstract

The invention relates to a high strength multi-phase steel for a cold- or hot-rolled steel strip having excellent forming properties, in particular for light vehicle construction, comprising the elements (contents in mass %): C 0.060 to=0.115; Al 0.020 to=0.060; Si 0.100 to=0.500; Mn 1.300 to=2.500; P=0.025; S=0.0100; Cr 0.280 to=0.480; Mo<0.150; Ti=0.005 to=0.050; Nb=0.005 to=0.050; B=0.0005 to=0.0060; N=0.0100; the remainder being iron including the usual elements present in steel and which are not mentioned above.

Claims

1-18. -18. (canceled)

19. A high strength multiphase steel for a cold or hot-rolled steel strip with excellent forming properties, in particular for lightweight vehicle construction comprising in weight %:

20. The steel of claim 19, wherein the Mo content is ≦

0.100%.

21. The steel of claim 19, wherein the Mo content is ≦

0.050%.

22. The steel of claim 19, wherein the Nb content is ≦

0.045%.

23. The steel of claim 19, wherein the Nb content is ≦

0.040%.

24. The steel of claim 19, wherein the Ti content is ≦

0.045%.

25. The steel of claim 19, wherein the Ti content is ≦

0.040%.

26. The steel of claim 19, wherein the B content is ≦

0.005%.

27. The steel of claim 19, wherein the B content is ≦

0.0040%.

28. The steel of claim 19, wherein the N content is ≦

0.0090%.

29. The steel of claim 19, wherein the N content is ≦

0.0070%.

30. The steel of claim 19, with a total content of Ti, Nb and B of ≦

0.106%.

31. The steel of claim 19, with a total content of Ti, Nb, B and Mo of ≦

0.256%.

32. A method for producing a cold or hot rolled steel strip from the high strength multiphase steel of claim 19, comprising:

heating the cold-rolled strip in a continuous annealing furnace to an annealing temperature in the range from 700 to 950°

C.;

cooling the annealed steel strip to an intermediate temperature of from 200 to 250°

C. at a cooling speed between 15 and 100°

C./s; and

cooling the steel strip from the intermediate temperature to room temperature with a cooling speed of 2 to 30°

C./s or with a cooling speed between 15 and 100°

C./s, wherein for the cooling speed of 2 and 30 C/s the steel strip is cooled on air, wherein a multiphase microstructure is established in the steel strip by the annealing and cooling steps.

33. The method of claim 32, further comprising after the heating step and prior to the cooling steps, hot dip coating the steel strip by inserting the steel strip into a melting bath.

34. The method of claim 32, further comprising after cooling to the intermediate temperature,

holding the steel strip at the intermediate temperature for 1 to 20 seconds;

reheating the steel strip to a temperature of 420 to 470°

C.;

hot dip coating the steel strip by inserting the steel strip into a melting bath; and

cooling the steel strip to the intermediate temperature of 200 to 250°

C. with a cooling speed between 15 and 100 °

C./s, wherein the cooling to room temperature is performed with the cooling speed of from 2 and 30°

C./s.

35. The method of claim 32, further comprising dressing the steel strip.

36. The method of claim 32, further comprising straightening the steel strip by stretching and bending.