Patent ID: 11905599
Assignee: PSITEC OY
Field: Materials, metallurgy (Chemistry)
Classification: CPC C  B | IPC C

Claim 0:
1. A method for manufacturing hot dip galvanized rolled steel product, said method comprising:
providing a rolled steel product;
heating the rolled steel product in an oxidizing atmosphere and creating a layer of iron oxide on the surface of the rolled steel product, wherein the iron oxide is FeO;
annealing and holding the rolled steel product in a dry, reducing atmosphere and maintaining a layer of iron oxide, created in the heating step, on the surface of the rolled steel product during the annealing and holding;
cooling the rolled steel product in a first cooling step to a first temperature in a first temperature range of 560-600° C. and holding the rolled steel product at the first temperature for 3-10 seconds;
quenching said rolled steel product, covered with the layer of iron oxide, in a second cooling step by immersing it into a zinc bath containing aluminium having a temperature between 440-450° C. for 1-5 seconds;
cooling the rolled steel product in a third cooling step to room temperature,
wherein the first, second, and third cooling steps are performed consecutively in this order,
wherein the cooled rolled steel product has lower bainite and auto-tempered martensite microstructures, and
wherein the third cooling step further comprises:
(a) cooling the rolled steel product to a second temperature in a second temperature range of 320-400° C. and holding the rolled steel product at the second temperature for at least 10 seconds,
(b) cooling the rolled steel product further to a third temperature in a third temperature range of 280-320° C., and
(c) cooling the rolled steel product further to a fourth temperature in fourth temperature range of 220-280° C. and holding the rolled steel product at the fourth temperature for at least 100 seconds, before cooling said rolled steel product to room temperature, such that the cooling in (a), (b), and (c) is performed consecutively in this order.