HIGH-STRENGTH AIR-HARDENING MULTIPHASE STEEL HAVING EXCELLENT PROCESSING PROPERTIES, AND METHOD FOR MANUFACTURING A STRIP OF SAID STEEL
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Abstract
A high-strength air-hardenable multiphase steel having minimal tensile strengths in a non air hardened state of 750 MPa and excellent processing properties, said steel comprising the following elements in % by weight: C≥0.075 to ≤0.115; Si≥0.200 to ≤0.300; Mn≥1.700 to ≤2.300; Cr≥0.280 to ≤0.4800; Al≥0.020 to ≤0.060; N≥0.0020 to ≤0.0120; S≤0.0050; Nb≥0.005 to ≤0.050; Ti≥0.005 to ≤0.050; B≥0.0005 to ≤0.0060; Ca≥0.0005 to ≤0.0060; Cu≤0.050; Ni≤0.050; remainder iron, including usual steel accompanying smelting related impurities, wherein for a widest possible process window during continuous annealing of hot rolled or cold rolled strips made from the steel a sum content of M+Si+Cr in the steel is a function of a thickness of the steel strips according to the following relationship: for strip thicknesses of up to 1.00 mm the sum content of M+Si+Cr is ≥2.350 and ≤2.500%, for strip thicknesses of over 1.00 to 2.00 mm the sum of Mn+Si+Cr is ≥2.500 and ≤2.950%, and for strip thicknesses of over 2.00 mm the sum of Mn+Si+Cr is ≥2.950 and ≤3.250%.
4 Citations
66 Claims
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1-33. -33. (canceled)
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34. A high-strength air-hardenable multiphase steel having minimal tensile strengths in a non air hardened state of 750 MPa and excellent processing properties, said steel comprising the following elements in % by weight:
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C≥
0.075 to ≤
0.115Si≥
0.200 to ≤
0.300Mn≥
1,700 to ≤
2.300Cr≥
0.280 to ≤
0.4800Al≥
0.020 to ≤
0.060N≥
0.0020 to ≤
0.0120S≤
0.0050Nb≥
0.005 to ≤
0.050Ti≥
0.005 to ≤
0.050B≥
0.0005 to ≤
0.0060Ca≥
0.0005 to ≤
0.0060Cu≤
0.050Ni≤
0.050remainder iron, including usual steel accompanying smelting related impurities, wherein for a widest possible process window during continuous annealing of hot rolled or cold rolled strips made from said steel a sum content of M+Si+Cr in said steel is a function of a thickness of the steel strips according to the following relationship; for strip thicknesses of up to 1.00 mm the sum content of M+Si+Cr is ≥
2.350 and ≤
2.500%,for strip thicknesses of over 1.00 to 2.00 mm the sum of Mn+Si+Cr is ≥
2.500 and ≤
2.950%, andfor strip thicknesses of over 2.00 mm the sum of Mn+Si+Cr is ≥
2.950 and ≤
3.250%. - View Dependent Claims (35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53)
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54. The method of claim 54, further comprising after the heating step and during the cooling to the first intermediate temperature step hot dip coating the steel strip in a hot dip bath, wherein the cooling to the first intermediate temperature is interrupted prior to entry into the hot dip bath, and after the cooling to the first intermediate temperature the steel strip is treated as set forth under a), wherein the second intermediate temperature is 200 to 250°
- C. and the cooling from the second intermediate temperature to room temperature is conducted with a cooling rate of about 2 and 30°
C./s. - View Dependent Claims (55, 56, 57, 58, 59, 60, 61)
- C. and the cooling from the second intermediate temperature to room temperature is conducted with a cooling rate of about 2 and 30°
- 62. The steel strip of claim 62, having a minimum hole-expansion value according to ISO 16630 of 30% in a non-air-hardened state.
Specification