Development of Cold-Rolled Batch Annealed Steels for Continuous Galvalume Line to Produce Zincalume Coated Steel With Good Cold Formability Properties and Aging Resistance

摘要

Continuous galvalume line which is equipped with annealing furnace, usually use a full hard cold rolled coil (FH-CRC) as raw material to produce 'zincalume' coated steel. Due to the limitation of time and furnace temperature capability, the properties of the 'zincalume' coated steel are usually still hard, less ductile and more susceptible to strain aging. Therefore, the 'zincalume' coated steel is not suitable forparts which require a good formability properties. In order to obtain a good formability properties, several trials of low carbon cold-rolled batch annealed steel as a feed to the galvalume coating line has been done. In these trials, three types of low carbon steel were selected and used. The flow process were started from hot strip mill, pickling, cold rolling, batch annealing, temper rolling and galvalume coating line. A number of samples for tensile testing and microstructure evaluation were taken before and after the galvalume coating line. The results shows that after reheating or hot-dip coating, mechanical properties (tensile and yield strength) of the steels were increased, while formability properties (elongation and r- value) were decreased. This is a normal phenomenon after hot-dipping. This phenomenon usually called 'aging' in carbon steel. By using IF steel (steel C) with additional 0.1 percent Ti, the aging problem can be avoided and good cold formability properties can be achieved.