High strength hot dip galvanised steel strip

Abstract

A high strength hot dip galvanised steel strip consisting, in mass percent, of the following elements: 0.10-0.21% C, 1.45-2.20% Mn, max. 1.50% Si, 0.1-1.50% Al, 0.001-0.04% P, 0.0005-0.005% B, 0.005-0.30% V, max. 0.015% N, max. 0.05% S, and, optionally, one or more elements: max. 0.004% Ca, max. 0.10% Nb, max. 0.50% Cr, max. 0.20% Mo, max. 0.20%, Ni, max. 0.20% Cu, and max. 0.20% Ti the balance of the composition consisting of Fe and inevitable impurities. The steel has good surface finish and increased mechanical strength, in particular high overall strength, ductility and plasticity. It also relates to a process for the manufacture of a high strength hot dip galvanised steel strip and to the products thereof.

Claims

1. A high strength hot dip galvanised steel strip consisting, in mass percent, of the following elements: 0.10-0.21% C 1.50-2.10% Mn 0.2-1.50% Si 0.1-1.50% Al 0.001-0.04% P 0.001-0.005% B 0.05-0.30% V max. 0.015% N max. 0.05% S and, optionally, one or more elements selected from: max. 0.004% Ca max. 0.10% Nb max. 0.50% Cr max. 0.20% Mo max. 0.20%, Ni max. 0.20% Cu max. 0.20% Ti wherein the amount of Al+Si is 0.70-1.60 mass %, the balance of the composition consisting of Fe and inevitable impurities, wherein the strip has undergone a cold rolling reduction of 40% or more starting from a hot rolled thickness of 2.0-4.0 mm, and wherein vanadium precipitates are present in the hot rolled strip after annealing of the strip; and wherein the strip has an ultimate tensile strength Rm above 650 MPA and 0.2% roof strength Rp of 300-700 MPa after temper rolling which occurred after the annealing.

2. The steel strip according to claim 1, wherein the amount of Al+Si is 0.70-1.50 mass %.

3. The steel strip according to claim 1, wherein the amount of V is 0.06-0.20 mass %.

4. The steel strip according to claim 3, wherein the amount of B is 0.0019-0.005 mass.

5. The steel strip according to claim 4, wherein the amount of C is 0.10-0.20 mass %, wherein the amount of Si is 0.2-1.0 mass %.

6. The steel strip according to claim 5, wherein the amount of Al is 0.1-1.0 mass %.

7. The steel strip according to claim 1, wherein the steel strip has a microstructure consisting of 20-50 volume % ferrite, 15-25 volume % retained austenite and martensite and 5-15 volume % retained austenite, the remainder being tempered martensite, bainite, cementite, and precipitates/inclusions, the sum adds up to 100%.

8. The steel strip according to claim 1, wherein the hot dip galvanised steel strip has an ultimate tensile strength Rm of 700-1150 MPa after temper rolling.

9. The steel strip according to claim 1, wherein the steel strip is a TRIP assisted dual phase or a complex phase steel strip.

10. The steel strip according to claim 1, wherein the amount of Al+Si is 0.80-1.40 mass %.

11. The steel strip according to claim 1, the amount of C is 0.11-0.19 mass %.

12. The steel strip according to claim 1, wherein the amount of Si is 0.2-0.8 mass %.

13. The steel strip according to claim 1, wherein the amount of B amount is 0.001-0.004 mass %.

14. The steel strip according to claim 1, wherein the amount of V is 0.05-0.20 mass Vo.

15. The steel strip according to claim 1, wherein the amount of Al is 0.2-0.9 mass %.

16. A steel strip produced according to claim 1, wherein the steel strip is a TRIP assisted dual phase or a complex phase steel strip.

17. The steel strip according to claim 1, wherein the amount of Al+Si is 0.80-1.20 mass %.

18. The steel strip according to claim 1, the amount of C is 0.12-0.18 mass %, wherein the amount of Si is 0.30-0.70 mass %, wherein the amount of Al is 0.2-0.8 mass %.

19. The method for producing a high strength hot dip galvanised steel strip according to claim 1, comprising the steps of: a) the cast steel is hot-rolled to a thickness of 2.0-4.0 mm and coiled at a coiling temperature C.sub.T, wherein the coiled hot-rolled steel strip has a microstructure consisting of 40-80 volume % ferrite, 20-50 volume % pearlite and/or bainite, and less than 10 volume % cementite/precipitates/inclusions, wherein the sum adds up to 100%, b) the strip is pickled, c) the strip is then cold-rolled with a reduction of 40% or more, d) the strip is intercritically annealed, e) the strip is post-annealed in the overage section, optionally undergoes quenching and partitioning or quenching and tempering, f) the strip is hot-dip galvanised, g) the strip is temper rolled.

20. The method according to claim 19, wherein the cast steel undergoes said hot rolling to the thickness of 2.0-4.0 mm and is coiled at the coiling temperature C.sub.T between Bs+50 C. and Ms temperature, resulting in an intermediate hot-rolled steel strip having the microstructure consisting of 40-80 volume % ferrite, 20-50 volume % pearlite and/or bainite, and less than 10 volume % cementite/precipitates/inclusions, wherein the sum adds up to 100%.

21. The method according to claim 19, wherein the steel strip is TRIP assisted Dual Phase steel strip, wherein the cold rolled material is intercritically annealed, wherein either a heating rate of at most 40 C./s is used, and/or an intermediate soak of 1-100 seconds is used before achieving Ac1 temperature, resulting in a strip having more than 90% recrystallized ferrite of the ferrite fraction present in the TRIP assisted Dual Phase steel and resulting in a n.sub.4-6 value of 0.18 or higher, wherein n.sub.4-6 is the specific hardenability value between 4 and 6% elongation.

22. The method according to claim 19, wherein the steel strip is high strength cold rolled TRIP assisted dual phase steel strip, comprising the steps of: a) the cast steel undergoes said hot-rolling to the thickness of 2.0-4.0 mm and coiled at the coiling temperature C.sub.T, wherein the coiled hot-rolled steel strip has the microstructure consisting of 40-80 volume % ferrite, 20-50 volume % pearlite and/or bainite, and less than 10 volume % cementite/precipitates/inclusions, the sum adds up to 100%, b) the strip undergoes said pickling, c) the strip then undergoes said cold-rolling with a reduction of 40% or more, d) the strip undergoes the annealing heat treatment between transformation temperatures A.sub.c1 and A.sub.c3, followed by one or more cooling phases at a cooling rate V.sub.cs when the temperature is below A.sub.c3, followed by a overage phase at an overage temperature T.sub.oa for a overage time t.sub.oa, being chosen in such a way that the microstructure of said steel consists of ferrite, bainite, residual austenite and, optionally martensite and/or cementite, e) optionally the annealed strip undergoes the quenching and partitioning or quenching and tempering in the overage section, f) the strip undergoes said hot-dip galvanizing, g) the strip undergoes said temper rolling with an elongation of less than 0.7%, preferably less than 0.5%.

23. The method according to claim 19, wherein the steel strip is a high strength cold rolled complex phase steel strip, comprising the steps of: a) the cast steel undergoes said hot-rolling to the thickness of 2.0-4.0 mm and coiled at the coiling temperature C.sub.T, wherein the coiled hot-rolled steel strip has the microstructure consisting of 40-80 volume % ferrite, 20-50 volume % pearlite and/or bainite, and less than 10 volume % cementite/precipitates/inclusions, the sum adds up to 100%, b) the strip undergoes said pickling, c) the strip undergoes said cold-rolling with a reduction above 40% reduction, d) the strip undergoes the annealing heat treatment above A.sub.c1+50 C., followed by one or more cooling phases at a cooling rate V.sub.cs when the temperature is below A.sub.c3, followed by a cooling phase at an overage temperature T.sub.oa for a overage time t.sub.oa, being chosen in such a way that the microstructure of said steel consists of ferrite, bainite, residual austenite and, optionally martensite and/or cementite, e) optionally the annealed strip undergoes quenching and partitioning or quenching and tempering in the overage section, f) the strip undergoes said hot-dip galvanizing, g) the strip undergoes said temper rolling with a reduction of 0.4-2.0%.

24. The method according to claim 20, wherein the steel strip is TRIP assisted Dual Phase steel strip, wherein the cold rolled material is intercritically annealed, wherein either a heating rate of at most 40 C./s is used, and/or an intermediate soak of 1-100 seconds is used before achieving Ac1 temperature, resulting in a strip having more than 90% recrystallized ferrite of the ferrite fraction present in the TRIP assisted Dual Phase steel and resulting in a n.sub.4-6 value of 0.18 or higher, wherein n.sub.4-6 is the specific hardenability value between 4 and 6% elongation.

25. A high strength hot dip galvanised steel strip consisting, in mass percent, of the following elements: 0.10-0.21% C 1.45-2.20% Mn max 1.50% Si 0.1-1.50% Al 0.001-0.04% P 0.0005-0.005% B 0.005-0.30% V max. 0.015% N max. 0.05% S and, optionally, one or more elements selected from: max. 0.004% Ca max. 0.10% Nb max. 0.50% Cr max. 0.20% Mo max. 0.20%, Ni max. 0.20% Cu max. 0.20% Ti, wherein the amount of Al+Si is 0.70-1.60 mass %, the balance of the composition consisting of Fe and inevitable impurities, wherein the hot dip galvanised steel strip has an ultimate tensile strength Rm of at least 650 MPa and/or a 0.2% proof strength Rp of 300-700 MPa after temper rolling and wherein the difference between the middle and the edges of the steel strip is less than 60 MPa for Rp and/or Rm.

26. The steel strip according to claim 25, wherein the difference between the middle and the edges of the hot dip galvanised steel strip is less than 40 MPa for Rp and/or Rm.

27. The steel strip according to claim 25, wherein the difference between the middle and the edges of the hot dip galvanised steel strip is less than 30 MPa for Rp and/or Rm.

28. The steel strip according to claim 25, wherein the hot dip galvanised steel strip has ultimate tensile strength Rm of 650-1160 MPa and/or 0.2% proof strength Rp of 300-700 MPa after temper rolling and wherein the difference between the middle and the edges of the steel strip is less than 60 MPa for Rp and/or Rm.

29. The steel strip according to claim 25, wherein the hot dip galvanised steel strip has ultimate tensile strength Rm of 700-1150 MPa and/or 0.2% proof strength Rp of 300-700 MPa after temper rolling and wherein the difference between the middle and the edges of the steel strip is less than 60 MPa for Rp and/or Rm.

30. The steel strip according to claim 29, wherein the difference between the middle and the edges of the steel strip is less than 40 MPa for Rp and/or Rm.

31. The steel strip according to claim 29, wherein the difference between the middle and the edges of the steel strip is less than 30 MPa for Rp and/or Rm.

32. The steel strip according to claim 25, wherein the hot dip galvanised steel strip has ultimate tensile strength Rm of 730-1130 MPa and/or 0.2% proof strength Rp of 300-700 MPa after temper rolling and wherein the difference between the middle and the edges of the steel strip is less than 60 MPa for Rp and/or Rm.

33. The steel strip according to claim 31, wherein the difference between the middle and the edges of the steel strip is less than 40 MPa for Rp and/or Rm.

34. The steel strip according to claim 31, wherein the difference between the middle and the edges of the steel strip is less than 30 MPa for Rp and/or Rm.

35. A high strength hot dip galvanised steel strip consisting, in mass percent, of the following elements: 0.145-0.18% C 1.50-2.10% Mn 0.390-0.8% Si 0.406-0.619% Al 0.001-0.04% P 0.0019-0.004% B 0.05-0.20% V max. 0.015% N max. 0.05% S and, optionally, one or more elements selected from: max. 0.04% Ca max. 0.10% Nb max. 0.50% Cr max. 0.20% Mo max. 0.20%, Ni max. 0.20% Cu max. 0.20% Ti wherein the amount of Al+Si is 0.80-1.20 mass %, the balance of the composition consisting of Fe and inevitable impurities, wherein the strip has undergone a cold rolling reduction of 40% or more starting from a hot rolled thickness of 2.0-4.0 mm, and wherein vanadium precipitates are present in the hot rolled strip after annealing of the strip; and wherein the hot dip galvanised steel strip has an ultimate tensile strength Rm of 731 to 1104 MPa and A80 total elongation of 13.4 to 23.5% after annealing of the strip.

36. The steel strip according to claim 35, wherein the amount of V is 0.06-0.172 mass %, wherein vanadium precipitation did not occur as the strip had undergone the cold rolling reduction of 40% or more starting from the hot rolled thickness of 2.0-4.0 mm, and wherein the annealing which the strip had undergone was with an annealing soak temperature between 770 and 880 C. after the hot rolling and cold rolling of the steel strip.

Description

(1) FIG. 1: Yield and tensile strength tensile values of composition L1 at head, middle and tail along the length of the coil. The horizontal axis represents the width: left edge, middle and right edge of the coil section.

(2) FIG. 2top: hardenability coefficient (n-value) versus tensile strength (Rm) for a series of continuously annealed alloy without vanadium (T0) and with vanadium (T1). The material was not temper rolled after annealing.

(3) FIG. 3bottom: Tensile strength (Rm) versus Ductility (total elongation (A80) times tensile strength (Rm)) for a series of continuously annealed alloy without vanadium (T0) and with vanadium (T1). The material was not temper rolled after annealing.

(4) FIG. 4: Microstructure images of the TRIP assisted Dual Phase and Complex Phase cold-rolled end product at a quarter gauge.

EXAMPLE 1

(5) Steel composition L2 was cast and hot-rolled to a finishing temperature of approximately 930 C., above the A.sub.c3 temperature of approximately 920 C. and was cooled with a cooling rate of approximately 100 C./s to a coiling temperature of approximately 510 C. The material was subsequently cooled to room temperature with a cooling rate of 1 C./min. The end gauge was 3.7 mm. The material was cold-rolled to 1.2 mm, then continuously annealed at a top temperature of approximately 840 C., cooled to approximately 400 C. and held at this temperature for 60 seconds, then heated to approximately 470 C. for galvanization and finally cooled to room temperature. The measured tensile properties are described in Table 3.

EXAMPLE 2

(6) Several coils of the T1 steel composition having 1.3 mm gauge were manufactured under the same conditions as in example 1. In addition, a temper mill elongation 0.4% was applied. The homogeneity test was performed on the zinc coated strip end product of said coils. The tensile properties Rp and Rm were measured at the coil midwidth and edge positions at the beginning, middle and end of the coil. The experimental results represented in FIG. 1 showing yield and tensile strength values in head, middle and tail at mid-width and edge of the coil and these vary at maximum 30 MPa.

EXAMPLE 3

(7) From steel composition T1 Complex Phase steel strip was produced by hot rolling as in example 1, cold rolled to 1.3 mm and annealed at approximately 840 C. for at least 40 seconds according to the description. After hot dip galvanising, the strip was temper rolled with a reduction of approximately 0.9%. The resulting steel strip is a complex phase steel with an increased Rp compared to the examples of Table 3.

EXAMPLE 4

(8) Steel composition T0 without vanadium and T1 containing vanadium were manufactured. 1.3 mm gauge cold rolled steel composition T0 and T1 were continuously annealed. The annealing soak temperature ranged between 770 and 880 C. Subsequently the samples were overaged between 390 and 470 C., zinc coated at 460 C. for a few seconds and cooled to room temperature. Tensile tests were made of each annealing conditions.

(9) During the development of the high strength hot dip galvanizing steel strips according to the invention, a number of strip coils have been produced as indicated in Table 1. T0-T4 are line trial compositions and temper rolled, and L1-L4 are lab cast alloy compositions without being temper rolled according to the invention.

(10) TABLE-US-00001 TABLE 1 Steel compositions in milli-wt % and B, N, Ca and S in wt-ppm. C Mn Si Al V P Cr Ti Mo Cu Ni Nb B N Ca S Cast mwt % wt-ppm T0 149 2057 392 602 4 10 28 6 8 20 19 ND 24 30 14 <10 T1 150 2031 406 589 60 9 25 6 7 20 18 1 25 28 16 <10Top of Form T2 147 2028 402 584 62 10 22 6 6 21 12 1 21 29 14 <10 T3 155 2040 406 600 64 10 22 5 5 20 12 ND 19 28 14 <10 T4 149 2062 408 602 60 9 16 11 5 18 18 6 21 40 15 <10 T5 145 2000 455 519 61 13 23 7 4 15 15 ND 20 21 6 10 L1 148 1702 422 609 62 12 1 2 3 ND ND ND 23 27 ND 23 L2 147 2020 425 619 62 12 1 2 3 ND ND ND 22 28 ND 22 L3 150 1513 610 405 119 11 1 1 3 ND ND ND 22 29 ND 30 L4 165 2031 616 409 120 11 2 2 3 ND ND ND 22 32 ND 30 L5 184 2073 622 450 61 13 1 1 4 ND ND ND 22 39 ND 1 L6 184 2050 614 438 120 12 1 1 3 ND ND ND 20 34 ND 9 L7 173 2071 612 441 115 14 1 1 3 ND ND 1 24 43 ND 2 L8 198 2064 615 429 115 15 1 1 3 ND ND 1 24 38 ND 3 L9 180 2054 605 427 172 12 1 1 4 ND ND 1 23 42 ND 9 L10 183 2051 1008 440 172 13 1 1 3 ND ND 1 24 40 ND 11 L11 185 2043 607 406 118 12 1 1 102 ND ND 1 21 30 ND 5 L12 185 2039 608 414 118 13 1 110 3 ND ND 1 23.5 33 ND 2 L13 185 2040 400 410 130 10 310 ND ND 8 ND ND 20 50 ND 12 L14 180 2050 390 410 100 10 ND ND ND 8 ND ND 20 60 ND 10 ND: Not Detected

(11) Table 2 indicates the Al+Si sum, the calculated Bainite start (Bs) and martensite start (Ms) temperatures, and the calculated phase transition temperatures A.sub.c1 and A.sub.c3 of the cast compositions.

(12) TABLE-US-00002 TABLE 2 Al + Si Bs Ms Ac1 Ac3 Cast milli-wt % T/ C. T/ C. T/ C. T/ C. T0 994 601 416 723 912 T1 995 603 416 725 912 T2 986 605 418 725 913 T3 1006 602 413 724 911 T4 1074 600 411 726 914 L1 1031 634 427 731 924 L2 1044 607 418 725 917 L3 1015 646 430 739 924 L4 1025 597 406 730 906 L5 1072 587 396 728 901 L6 1052 590 396 729 901 L7 1053 591 401 729 904 L8 1044 585 389 728 895 L9 1032 591 398 729 901 L10 1448 581 392 739 921 L11 1013 583 397 729 905 L12 1022 590 396 729 910 L13 810 575 396 729 884 L14 800 596 401 723 888

(13) Table 3 shows the yield strength (Rp.sub.0.2), tensile strength (Rm), uniform elongation (Ag), total elongation (A80) and the work hardening coefficient (n) or n-value at mid coil. Hole expansion was determined for T0 and T1.

(14) TABLE-US-00003 TABLE 3 Hole Cast Rp.sub.0.2 (MPa) Rm (MPa) Ag (%) A80/JIS (%) n-value expansion (%) T0 435 760 16.4 24.2 (A80) 0.16 22-26 Comparative example T1 485 801 14.6 21.8 (A80) 0.15 22-26 Invention T2 482 805 14.6 21.3 (A80) 0.14 Invention T3 490 809 14.5 22.0 (A80) 0.14 Invention T4 489 798 14.4 23.5 (A80) 0.15 32 Invention L1 358 731 16.7 20.2 (A80) 0.20 Invention L2 408 862 14.0 18.2 (A80) 0.15 Invention L3 385 738 18.3 22.1 (A80) 0.21 Invention L4 506 1010 10.6 13.6 (A80) 0.12 Invention L5 404 895 15.1 20.3 (JIS) 0.17 Invention L6 444 981 12.4 17.4 (JIS) 0.15 Invention L9 480 1012 12.3 16.5 (JIS) 0.14 Invention L10 542 1104 10.4 14.8 (JIS) <0.10 Invention L11 531 1091 10.4 13.4 (JIS) 0.11 Invention L12 414 970 14.2 18.8 (JIS) 0.16 Invention L13 515 1071 10.7 14.1 (A80) 0.11 Invention L14 420 950 12.3 13.6 (A80) 0.15 Invention

(15) In Table 3 all steel strips show a high strength Rm of above 730 MPa. The comparison of T0 with T1 to T3 clearly shows a substantial difference in Rm, wherein a higher strength steel strip of around 800 MPa is obtained, if vanadium is present. It is therefore obvious that the vanadium addition increases strength. This is also supported by the fact that although the hole expansion in T0 and T1 is similar, the tensile strength Rm of T1 is by 40 MPa higher compared to T0.

(16) Table 3 further shows that due to the higher vanadium amount in L4, a high tensile strength above 1000 MPa can be obtained. Although in L1 and L3 the strength Rm is similar, L3 having higher vanadium content, shows better n-value and elongation (A80). It is further clear from table 3 that the variation of the amounts of the other alloys with vanadium results in high strength steel strips with improved elongation and n-values.

(17) T1 alloy was hot rolled, cold rolled and continuous annealed using a complex phase annealing cycle according to the invention and subsequently temper rolled with 0.9%. The results are shown in table 4. Table 4 clearly shows that a high strength steel having complex phase steel properties can be obtained. High Rp and Rm between 780-920 MPa are typical values for complex phase high strength steel.

(18) TABLE-US-00004 TABLE 4 Tensile properties at mid coil for material T1. Yield strength was measured after 0.9% temper mill elongation. Tensile properties for L5-L14 (not temper rolled). Cast Rp (MPa) Rm (MPa) Ag (%) A80/JIS (%) n-value T1 620 872 11.5 17.6 (A80) 0.11 T1 600 910 10.8 18.3 (A80) 0.10 L5 493 1004 13.0 17.6 (JIS) 0.14 L6 556 1091 10.8 15.1 (JIS) 0.12 L7 553 1108 10.3 14.2 (JIS) <0.10 L9 577 1129 9.8 13.1 (JIS) <0.10 L11 613 1150 9.0 12.7 (JIS) <0.10 L12 447 994 13.7 18.6 (JIS) 0.15 L13 589 1146 8.8 11.7 (A80) <0.10 L14 507 1040 11.3 15.9 (A80) 0.12

(19) FIG. 2 shows a plot with tensile strength values versus n-value from the tensile test and FIG. 3 shows the calculated ductility versus tensile strength. For TRIP assisted Dual Phase materials it is of importance to maximise the hardening coefficient n and ductility (A80*RM) whereas at the same time maximise the tensile strength Rm so that stretch forming and deep drawing properties are optimum while high strength is obtained.

(20) In FIGS. 2 and 3 the white diamond symbols and dotted line represent the data of the example T0 without vanadium. The solid line and black and grey square symbols show the example T1 with vanadium.

(21) FIGS. 2 and 3 clearly show that the steel composition with vanadium retains its strength in the 800 MPa range while allowing a significant improvement in hardening coefficient (FIG. 2) and ductility (FIG. 3) at the 800 MPa strength level. This leads to improved formability, in particular improved stretch forming and deep drawing.

(22) FIG. 4 are microstructure images at a quarter thickness of a complex phase steel strip and a TRIP assisted dual phase steel strip based on composition T1 and manufactured according to the method described above.

(23) The optical microscope images are obtained after Picral and SMB etching. In the Picral graphs the dark areas represent bainite, martensite or tempered martensite. In the Nital graph the off-white areas indicate ferrite. In the SMB etching the dark grey areas represent martensite formation and the light areas ferrite.

(24) In the TRIP assisted Dual Phase microstructure on the left-hand side in FIG. 4 there are off-white areas where the sizes can exceed 10 m. These areas denote the presence of ferrite and the large size of the ferrite give the material its characteristic low yield stress. The retained austenite contents were measured with X-ray diffraction and amount to around 10%. This gives the dual phase material its TRIP assisted character.

(25) The differences between TRIP assisted Dual Phase strip on the left-hand side and Complex Phase strip on the right-hand side are clearly visible. The white coloured areas of the Complex Phase strip are finer and there are more brown coloured areas in the SMB etching which refers to the formation of (tempered) martensite.

(26) The complex phase microstructure is featured with finer light off-white areas, showing that ferrite grains are finer. There are more dark grey areas in the SMB etching and these are typical for the presence of lower carbon (tempered) martensite and/or bainite. The combination of these phenomena lead to a higher Rp and obvious the retained austenite contents are lower. This is typical for a complex phase type of steel.

(27) TABLE-US-00005 TABLE 5 Tensile test parameters of a tensile test performed in the directions 0, 45 and 90 to the rolling direction. angle with rolling direction R.sub.P R.sub.M A.sub.g A80 n n.sub.4.sub..sub.6 r 90 519 817 13 18 0.14 0.18 0.9 0 506 817 14 21 0.15 0.19 0.7 45 514 811 14 20 0.15 0.18 0.9

(28) Minimum anisotropy of the TRIP assisted Dual Phase steel strip T1 was measured by performing tensile tests in the directions 0, 45 and 90 compared to the rolling direction. Table 5 shows that there is a minimum difference in Rp and Rm and Ag, n-value and Lankford coefficient or r-value in these 3 directions. A minimum difference in tensile values over the three directions indicates that the material is uniformly deformable independently of the rolling direction. A minimum anisotropy is of advantage for homogeneous stretching or deep drawing deformation. N4_6 values are 0.18 or exceed these values and it was seen that this is related to a low heating rate or soak before austenite formation, allowing more than 90% of (precipitate containing) ferrite to recrystallize before austenite starts to form. This soak can be a hold temperature time at a temperature below the Ac1 temperature for 1-100 seconds. Optionally, the soak consists of a heating or a cooling traject or any combination of the soak options. Irrespective of the heating with soak, it is done in such a way that the heated strip is hold for 1-100 s in a temperature regime below Ac1 temperature, for example between 350 C. and A.sub.c1 temperature.