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Galvanized DDS grade steel with welt marks




June 26, 2011

Hi,

I am working in a steel mill in southern North America. I am new to the industry fresh from school. Having gone to a grad school I am being assigned to projects which needs some R&D. One of my first task was to look into welts issue on Deep Drawing steels.

"Welts"- small approx. 1 cm long and couple of mm wide faults and are aligned perpendicular to the rolling direction. I have pictures but not sure where to upload. I did some EDS analysis and found no significant variation in chemistry in the fault and no fault region except the fact that Oxygen is marginally higher and that Al is also slightly higher (close to <1 wt.%). I do not trust any readings from EDS with less that 2 wt.% since I believe it is not accurate.

A cross sectional microstructure reveals the coating to be thicker in these regions- approximately 4-5 times of the no fault regions.

Can anybody suggest possible causes. I can surely provide more information.

Thanks in advance,
Dash

Abhilash Dash
engineer - Starkville, Mississippi, USA


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Ed. note: Please e-mail the pics to mooney@finishing.com, Abhilash.


June 28, 2011

Sir:

Are you an operator of a continuous sheet galvanizing line? If so what is your usual aluminum concentration in your zinc? Do you use hot 5% hydrogen + nitrogen just prior to going into the zinc?

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA



57378


August 1, 2011

Please provide us:
1. Zinc Bath Chemistry
2. Steel Chemistry
Hopefully I can do something for you.

Umesh Dalela
- Mumbai, Maharashtra, India




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