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Liquid Metal Embrittlement Issues with Rolled Steel Shapes

2006

I am involved in a project where galvanized WT sections were delivered to a construction site with extensive cracking propagating from the cut web. The WT members were A36 steel, were Charpy V notch tested for steel brittleness and were fabricated and galvanized in accordance with AWS1.1 and ASTM A123 according to Standard Specifications. It is hypothesized that the cracking was due to Liquid Metal Embrittlement (LME) and that the specifications followed "are defective."

Is there a history of LME problems with galvanizing of rolled shapes and, if these problems exist, are these sufficient to warrant revisiting the specifications noted above.

Tom Schneider
- Fairfax, Virginia

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First of two simultaneous responses -- 2006

Tom:
Check the tin (Sn) content in the zinc.
Regards,

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

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Second of two simultaneous responses --

The cracking was due to high residual stresses adjacent to the cut web edges. ASTM A123 requires compliance with ASTM A143 Standard Practice for Safeguarding Against Embrittlement of Hot-Dip Galvanized Structural Steel Products and Procedure for Detecting Embrittlement,' and ASTM A385, 'Standard Practice for Providing High-Quality Zinc Coatings (Hot-Dip).'

Paragraph 6 of A143 describes cold work and treatments thereof (reaming or grinding of highly stressed holes & edges, thermal stress relief).

LME is normally not a problem with HDG. It can occur with baths contaminated tin, or with high strength steels such as 4140. Tons of hot-rolled steel is HDG in large tanks throughout the world.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2006

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LME is better known as LMAC (Liquid metal assisted cracking).
There seems to be no known examples of the liquid zinc being the CAUSE, but some isolated examples of liquid zinc opening up cracks that have been caused by either defective steel, or by stresses in fabrication.

Its a rare phenomenon, as mentioned above sometimes seen where Sn is in the liquid metal.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

2006

Liquid Metal Embrittlement is known as Liquid Metal Assisted Cracking in the UK. I note that one person has stated that it is due to either steel or fabrication defects, this is not true it is caused by the galvanizing process. It is also not that rare as I have a number of known projects that have suffered extensive cracking. Information is available on SCOSS and BCSA web sites.

Chris Murgatroyd
- London, UK
2007