The pickling process is not suitable, such as the concentration of pickling, the temperature is low, the pickling speed is too fast, the pickling time is insufficient, or the ferrous iron concentration is too high, and the acid solution is not added in time;

Stretching descaler has insufficient stretching coefficient, so that the iron sheet is not fully broken and Strip steel shape is poor, such as sickle bend, wave shape, etc., so that the mechanical descaling effect is poor, easy to cause partial under-washing.

Structural Grades	C	Mn	P	S	Cu	Ni	Cr	Mo	V	Cb	Ti
30,33,36,40	0.25	0.9	0.035	0.04	0.2	0.2	0.15	0.06	0.008	0.008	0.025
36T2,45-80	0.25	1.35	0.035	0.04	0.2	0.2	0.15	0.06	0.008	0.008	0.025
45T2	.02- 0.08	.30- 1.0	.03- .07	0.025	0.2	0.2	0.15	0.06	0.008	0.008	0.025