Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Patent
1989-10-12
1991-10-29
McFarlane, Anthony
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
134 9, 134 14, 134 15, 148 12B, 148 12E, 156664, C23G 102, C23G 108
Patent
active
050613219
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
This invention relates to a pickling method for electrical steel bands.
BACKGROUND OF THE INVENTION
An electrical steel sheet is produced through processes of hot rolling a slab, annealing, if required, the hot rolled steel band for improving magnetic properties, pickling, cold rolling and finish annealing. It is known that this kind of steel is inferior in de-scaling properties during pickling, depending upon Si content as an essential element. There have been proposals for improving the de-scaling properties, e.g., in Japanese Patent Laid-Open Nos. 76,422/79, 33,436/81 or 138,014/85.
However with respect to the pickling of the hot rolled band, a big problem is involved about interglanular corrosions, irrespective of the de-scaling. If the electrical steel band is coiled at high temperatures after the hot rolling, the steel surface is effected with interglanular oxidation. If the pickling is continued unnecessarily after completion of the de-scaling, the corrosion grows as pitting in preference around the grain boundaries by the interglanular oxidation, and this fine cracks during a subsequent cold rolling, and deteriorates surface properties after the cold rolling. The fine cracks make various problems which not only degrade product values because of outer appearances of the products, but also deteriorate the magnetic properties, especially iron losses, by generating fine grains in the surface layers during finish annealing, and further cause of nonuniformity of insulation coatings.
Each of the above conventional proposals deals with the de-scaling only as the problem, and none of them specifies the pickling conditions by taking the intergranular corrosion into consideration.
DISCLOSURE OF THE INVENTION
In view of these foregoing problems, this invention optimizes the pickling conditions not only in the de-scaling properties but the intergranular corrosion in order to provide desired de-scaling properties and realize a pickling method enabling one to exactly check the interglanular corrosion.
For accomplishing the object, the invention is characterized by pickling, with hydrochloric acid, a hot rolled steel band containing Si: 0.2 to 4.0 wt % coiled at temperature of CT or annealed after coiling, satisfying following conditions: in a case of Si.ltoreq.1.0 wt %
CT: coiling temperature (.degree. C.) of the hot rolled band
(%Si): Si content (wt %); for period of pickling time satisfying a following condition
(%Si): Si content (wt %) of the hot rolled band
t: pickling time (sec)
T: temperature (K) of pickling liquid
B: -0.48(HCl).sup.2 +15.1(HCl)+5.03 wherein (HCl): HCl concentration (wt %) of pickling liquid
Q: 5300 cal/mol
R: 1.986 cal/mol.K
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the presence and absence of the interglanular corrosions in the hot rolled steel bands in relation between Si contents and coiling temperatures CT;
FIG. 2 shows the influences of Si content and the pickling time on the de-scaling properties and the interglanular corrosions;
FIG. 3 shows the influences of the pickling temperature and the pickling time on the de-scaling properties and the interglanular corrosions; and
FIG. 4 shows the influences of HCl concentration of the pickling liquid and the pickling time on the de-scaling properties and the intergranular corrosion.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be explained in detail together with limiting reasons.
In the invention, the picklings are carried out on hot rolled silicon steel bands (including as-coiled ones and annealed ones after coiling) under specified conditions for avoiding the interglanular corrosions.
Through the inventors' experiments it was seen that the interglanular corrosion occurred in the hot rolled band having Si content and the coiling temperature in specified scopes. Therefore, in the invention, an object is limited to particular hot rolled steel bands which are determined with Si content and the coiling temperature.
FIG. 1 shows, in relation between Si content and coiling te
REFERENCES:
patent: 3932237 (1976-01-01), Irie et al.
patent: 3950572 (1976-04-01), Ayusawa et al.
patent: 4002489 (1977-01-01), Hedqvist et al.
patent: 4144379 (1979-03-01), Patil et al.
patent: 4885041 (1989-12-01), den Hartog et al.
Hosoya Yoshihiro
Jitsukawa Masaharu
Nishimoto Akihiko
Tomita Kunikazu
Urabe Toshiaki
McFarlane Anthony
NKK Corporation
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