Coating processes – With pretreatment of the base – Heating or drying pretreatment
Patent
1995-02-13
1997-10-14
Utech, Benjamin
Coating processes
With pretreatment of the base
Heating or drying pretreatment
4273768, 427431, 427432, B05D 302
Patent
active
056770057
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method for hot dip galvanizing high tensile steel strips with minimal bare spots which starts with high tensile steel strips for use in automobile bodies and manufactures hot dip galvanized and galvannealed steel strips.
BACKGROUND ART
Heretofore, various surface treated steel strips having improved corrosion resistance have been used as automotive steel strips. Among them, widespread are galvanized steel strips which are manufactured in a continuous hot dip galvanizing line wherein recrystallization annealing and galvanizing are carried out in a common line, because of a high degree of corrosion resistance and low cost manufacture as well as galvannealed steel strips which are manufactured by subjecting the galvanized steel strips to heat treatment, because of weldability and press workability in addition to corrosion resistance.
Meanwhile, a global environment problem is recently highlighted and it is urgently required to reduce the weight of automobiles for fuel consumption improvement. With this target, high strength/high tensile steel strips whose strength is increased were developed. Zinc hot dip galvanizing and galvannealing are now required for providing corrosion resistance.
High tensile steel strips are increased in strength by adding Si, Mn, Cr or the like to steel. In manufacturing zinc hot dip galvanized steel strips through a continuous galvanizing line (abbreviated as CGL, hereinafter), the components added for strength enhancement tend to concentrate at the steel strip surface during annealing reduction. These elements as oxides form an oxide film at the surface.
As a consequence, a significant loss of wettability occurs between steel strip and molten zinc, resulting in bare spots, uncoated defects or uncovered defects.
Prior art methods devised for preventing generation of bare spots include a method of electroplating steel strip prior to its entry into CGL (see JP-A 194156/1990) and a method of providing a surface layer of steel having a low content of Si, Mn or the like by a cladding technique for improving plating wettability (see JP-A 199363/1991). Also proposed is a method of further adding Ti to steel for improving wettability to molten zinc (see JP-A 148073/1992).
Although hot dip galvanizing of a high strength steel strip containing Si, Mn or the like becomes possible by carrying out electroplating of a Ni or Fe system on the steel strip prior to its entry into CGL, there are accompanying drawbacks including addition of an electroplating plant, complication by an increased number of steps, and low productivity. The platability improvement by cladding also complicates the process and invites a lowering of productivity.
Further, from the standpoint of increasing the speed of movement of phosphorus-added steel during manufacture of a hot dip galvannealed steel strip, JP-A 243751/1991 discloses a method of pickling annealed phosphorus-added steel to remove a P-concentrated layer for promoting alloying. However, bare spots on steel strips having Si, Mn or Cr added thereto, to which the present invention addresses, cannot be eliminated merely by removing P from the steel strip surface after annealing, as will be described later.
More particularly, what is disclosed in JP-A 243751/1991 is merely to remove a P-concentrated layer by pickling to improve the alloying rate of P-added steel thereby increasing the manufacturing speed of steel during production of a hot dip galvannealed steel strip. However, no consideration is given to bare spots associated with steel strips having Si, Mn or Cr added thereto, which this invention addresses. Accordingly, even if alloying after galvanizing might be successfully promoted by removal of a P-concentrated layer pursuant to this prior art technique, generation of bare spots in a galvanized coating itself cannot be successfully prevented. This prior art technique does not attempt to improve the galvanized coating itself; thus hot dip galvannealed steel strip of quality cannot be manufactured since pl
REFERENCES:
patent: 4143184 (1979-03-01), Paulus et al.
patent: 4415415 (1983-11-01), Zaremski
patent: 5175026 (1992-12-01), Bertol et al.
Fujibayashi Nobue
Isobe Makoto
Kyono Kazuaki
Morito Nobuyuki
Totsuka Nobuo
Kawasaki Steel Corporation
Miller Austin R.
Utech Benjamin
LandOfFree
Method for hot dip galvanizing high tensile steel strip with min does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for hot dip galvanizing high tensile steel strip with min, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for hot dip galvanizing high tensile steel strip with min will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1553386