The defects are spotted, strip-like or scaly black spots, the distribution area is not the same, and the depth of the pressing is different. Such iron sheets are difficult to wash out in the pickling process, and pits are formed when the iron sheets fall off.

The heating temperature of the slab is too high, and the time is too long; the furnace has a strong oxidizing atmosphere, and the furnace is pressed while the iron oxide scale is rolled;

The high pressure water pressure is insufficient, and the scale is not cleaned before rolling;

The high pressure heating temperature cold rolled coil water nozzle is blocked, and the local scale is not removed;

sets of scales open the number of groups is not enough, descaling is not clean.

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