Zinc or zinc-alloy coated strip or steel with improved zinc adhesion

A zinc or zinc-alloy coated cold rolled steel strip or sheet,

• a) having a composition comprising of in wt. %:
• C
• 0.08-0.28
• Mn
• 1.4-4.5
• Cr
• 0.01-0.5
• Si
• 0.01-2.5
• Al
• 0.01-2.0
• Si + Al
• ≥0.1
• Si + Al + Cr
• ≥0.4
• Nb
• ≤0.1
• Ti
• ≤0.1
• Mo
• ≤0.5
• Ca
• ≤0.05
• V
• ≤0.1
• Cu
• 0.06%
• Ni
• 0.08%
• B
• 0.0006%
• P[[]]
• 0.02%
• S
• 0.005%
• As
• 0.010%
• Zr
• 0.006%
• Sn
• 0.015%
• O
• 0.0003
• N
• 0.015%
• balance Fe apart from impurities;
• b) fulfilling the following conditions:
• TS tensile strength (Rm)
• 950-1550 MPa
• YS yield strength (Rp0.2)
• 350-1400 MPa
• YR yield ratio (Rp0.2/Rm)
• ≥0.35
• bendability (Ri/t)
• ≤4
• HER hole expansion ratio (λ)
• 15;
• c) having a multiphase microstructure comprising in vol %
• tempered martensite +
• bainite
• ≥40
• fresh martensite
• ≤30
• retained austenite
• 5-20
• polygonal ferrite
• ≤35;
• d) having a hydrogen concentration of less than 0.2 ppm of the steel;
• e) having a zinc or zinc-alloy coating;
• f) wherein the amount of retained austenite was measured by means of the saturation magnetization method described in detail in Proc. Int. Conf. on TRIP-aided high strength ferrous alloys (2002), Ghent, Belgium, p. 61-64;
• g) wherein the bendability is determined in accordance with JIS Z2248;
• h) wherein the yield strength and tensile strength are determined according to the European norm EN 10002 Part 1;
• i) wherein the HER (1) is determined according to ISO/WD 16630:2009 (E).