Inspection Test on DIN 10049 Changing Sampling Length Selection Rule of ISO 4288

In view of the objective condition that all car enterprise standards require the automotive steel sheet surface roughness Ra<2 μm, surface roughness contrast test was done to many specimens with different surface morphology characteristics by using different sampling length (mainly 0.8 mm and 2.5 mm) and sampling interval numbers, in order to test whether it is reasonable that DIN EN 10049-2006 changed sampling length from 0.8 mm of ISO 4288:1996 to 2.5 mm for automotive steel sheet surface roughness measurement. The results show that the changing trend of surface roughness by using 0.8 mm and 2.5 mm sampling length was different for different sheets, and it was decided by the surface morphology characteristics of the sheet specimens, which was not consistent with the traditional view that the measured Ra value increased with the increase of sampling length. So from the view of promoting world trade, obeying ISO 4288:1996 and selecting 0.8 mm sampling length for automotive steel sheet Ra measurement are favorable for data tracing.