Strain Aging of a Cold-Rolled Ti-Added Ultra Low Carbon Steel with Bake Hardenability

摘要

An ultra-low carbon bake-hardening steel bearing 0.0013 weight percent titanium was temper-rolled in the mill to investigate exactly and effectively the strain aging behavior. Correlation between the natural aging at room temperature and the accelerated aging at elevated temperatures of 70 deg C and 100 deg C was also studied. Accelerated aging at 100 deg C for 60 minutes, which has been extensively used as a criterion for occurrence of ambient strain aging, showed a very different aging behavior from the steel aged at 20 deg C for 2 months. It was found that the ambient strain aging behavior could be better evaluated by the upper yield point or the difference between upper and lower yield points rather than the 0.2 percent yield point elongation measured in the tensile test after aging at 100 deg C for 60 minutes. Increasing the temper rolling extension from 0.8 to 1.5 percent retarded'the occurrence of the ambient strain aging of bake hardening steel.