PURPOSE: To increase a line speed in a method for pickling a stainless steel strip, by using a sulfuric acid and a mixture of hydrofluoric acid and nitric acid by using a hydrochloric acid in place of the sulfuric acid under specific conditions.
CONSTITUTION: A stainless band steel is dipped in a hydrochloric acid (aq. soln.) under the conditions satisfying the equations I , II [T: liquid temp. (°C), C: concn. (%) of hydrochloric acid] whereby the band steel is roughly descaled as the 1st stage. Such band steel is dipped in a mixture of hydrofluoric acid and nitric acid (an aq. mixed soln. of nitric acid and HF) and is thus descaled thoroughly as the 2nd stage. The speed of pickling is then increased and the amt. of the NOx generated in the stage of pickling with the mixture of hydrofluoric acid and nitric acid is decreased. A sizable part of the scale is removed in the 1st stage and the dissolution amt. of steel in the mixture of hydrofluoric acid and nitric acid is decreased as compared to the case of sulfuric acid. Particularly when T and C are high, the band steel is descaled roughly in the 1st stage but if the dipping in the mixture of hydrofluoric acid and nitric acid is omitted, satisfactory corrosion resistance is not obtained.
ISHIKAWA MASAAKI
TAKEDA MOTOHIKO
OKA YUTAKA
| JPS571590A | 1982-01-06 |