Method for improving the formability of steel blanks

A method to improve a formability of a steel blank, the method comprising the steps of:

• providing a steel blank having a zinc based metallic coating on at least a portion of an upper face or a lower face, a microstructure containing, in area percentage, 5% to 50% martensite and 50% to 95% ferrite, and an ultimate tensile strength of at least 500 MPa,
• performing a heat-treatment operation on the steel blank having the zinc based metallic coating by directing a thermal energy Q provided by at least one heat source on a part of a peripheral thickness of the steel blank to form a peripheral heated portion and a heat-treated volume, the peripheral heated portion being part of the heat-treated volume, the temperature of the heat-treated volume being greater than 400° C. and less than or equal to 730° C., wherein an entire volume of the steel blank stays solid during the heat-treatment operation, and wherein a thickness of the metallic coating after heat treatment in the heat-treated volume decreases by less than 30% as compared to a thickness of the metallic coating outside the heat-treated volume, and
• wherein hole expansion ratio measured in the heat-treated volume is at least 50% higher than hole expansion ratio measured in the steel blank outside of the heat-treated volume.