316L Chain Eroding/Stretching

[Murdul]

We use 316L stainless chain to drop Zinc Ingots into a galvanizing bath. The bath temperature is 880F. Bath chemistry is 99.5%Zn 0.30%Al 0.005%Fe 0.015%Sb. The chain is submerged beneathe the bath while the ingots melt. The chain is only removed from the bath when more ingots are needed. On average the chain is out of the bath for a matter of minutes every 2-3 hours.

The problem is the chain which holds the ingots used to last 6 months without showing signs of deteriation, we changed it out to err on the side of caution. Now we have to change the chain every 3 months and many chain links are elongated and/or eroded at the time of change. We are trying to find the reason for the change. Why is the chain eroding so quickly when in the past it would last 6 months or longer and show pracitcally no wear. The problem has been ongoing for ~9months. With one chain completly failing after 3 months in service.

We have not changed chain supplier, the stamping is the same, we have not changed bath temperature, ingot supplier nor bath chemistry.

 

[MikeHalloran]

Have the chain's chemistry analyzed; it smells like you're not getting what you paid for anymore.



Mike Halloran
Pembroke Pines, FL, USA

 

[blacksmith37]

This may not be your problem, but "pure" zinc dissolves carbon steel very quickly; "Prime Western" zinc flowing in Sch 80 pipe goes through the wall in 10 minutes(at 700F). However zinc die casting alloys are not nearly so aggressive, presumably the small amount of alloy reduces the zincs' activity.

 

[EdStainless]

I am assuming that you monitor bath chem closely and would know if that had changed. That leaves the chain.
If the links are weaker than they were before they may have switched to low carbon alloy from a higher carbon grade.
or....it may not even be 316.

you need to do some analysis and talk with your supplier.

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Plymouth Tube

 

[Murdul]

Thanks for the replies.

Mike and Ed we did try a second chain from a different supplier and had the same results. Forgot to note this above. However they are both from the same vendor. The stampings are different from chain to chain. In the end we will likely make sure we are getting 316L but we are stumped at this point.

Blacksmith, We do monitor bath chemistry closely. We have seen nothing abnormal.

We recently checked for a potential difference from the chain to the pot and found nothing there as well.

 

[EdStainless]

My guess is that the old ones are not "L", but have a higher carbon.

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Plymouth Tube

 

[metengr]

You might want to review the article below regarding the use of austenitic stainless steels in any liquid zinc bath.

http://www.mae.wvu.edu/barbero/pdf/2007-Xu-MMT.pdf

You have some time of process change that must be identified or use an alternative chain material.

 

[arunmrao]

Probably as Ed said it could be high in carbon 0.12% -0.15%,or the original chain could be 309 grade which is quite popular for such applications.



_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr

 

[Metaljon]

The 316 chain will be quite reactive with the molten zinc. The critical area of highest erosion will be an the interface of the molten zinc to air. Temperature of the bath and amount of residual aluminium is critical in rate of erosion. The aluminium content makes the bath more reactive and will shorten the life of the chain. 253MA is the best stainless steel for this application but you would need to make up special chain. I would have thought that 316 would be better than 316L due to the slightly higher yield strength and less prone to stretching.

 

[JamesCKelly]

My guess is your supplier was sold 304 bar, which THEIR supplier claimed to be 316. That 2% molybdenum in 316 is what gives 316 better molten zinc resistance than 304.

Carbon content is unlikely to be the issue. All, or 99% of all, 316 is really 316L (S31603) with enough process modifications that it meets the strength requirements of 316 (S31600). It is then dual certified to meet both specifications.

I am pleased to hear that 253 MA performs well in molten zinc, presume it is the 1.7% silicon that provides resistance. Would love to know the source of this information.

AL-6XN with 6% molybdenum has much better resistance to molten zinc than does 316L. Base metal cost of AL-6XN is roughly 2-1/2 times that of 316L, the cost of the finished chain may or may not be in that ratio.