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Greetings to all in 2023,

Our process involves casting a tin alloy (whitemetal) onto low-carbon steel - typically A36 plate, 1020 tubing, A105 forgings, and similar. We have had two incidents with large forgings from two different forging houses (foreign and domestic) where the tin would not bond to a significant fraction of the surface area. Grit blasting and aggressive caustic cleaning did not improve the situation. In one case, the chromium content was on the high end of the specification. In the current case, a 1033 steel, the elements are within specification (specification used for over a decade). The forging was annealed at 1550F and furnace cooled. We are analyzing a black "ooze" coming from the metal when exposed to our zinc chloride flux.

We are starting a more thorough investigation of the current "challenging" forging. I intend to obtain material samples from a region with a tin bond to and from a problem area to consider the potential for material segregation. I am curious if the increasing use of recycled steel has added new trace elements, which could be concern, to typical steels.

Another line of thought is that the heat treatment may have been incomplete. I would re-anneal a large section of material to explore this option.

I would be interested in other suggestions that the community might have?

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Lyle Branagan
Engineering Manager
Pioneer Motor Bearing Company
Kings Mountain NC USA
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Have you cut, ground, and polished the samples from both an adhering region and a non adhering region?  Visually you might be able to see a difference if there are "impurities", or grain structure size difference from prior heat treating (maybe even voids if the black "ooze" is trapped in voids)?  Not an expert on this but you might be able to see something at 200x, 400x, or 800x.  Just a thought.  If you send samples off to be chemically analyzed it might not be a bad idea to have a sample microhardness tested and a micrograph of the sample.

Just my thoughts, like I said no expert but it sounds like something is different and you might be onto something with the recycled material.

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David Lammers
Manufacturing Engineer
Total Component Solutions
Sioux Center IA
(712) 451-6646
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Original Message:
Sent: 01-02-2023 19:17
From: Lyle Branagan
Subject: Tin bonding to low carbon steel forging

Greetings to all in 2023,

Our process involves casting a tin alloy (whitemetal) onto low-carbon steel - typically A36 plate, 1020 tubing, A105 forgings, and similar. We have had two incidents with large forgings from two different forging houses (foreign and domestic) where the tin would not bond to a significant fraction of the surface area. Grit blasting and aggressive caustic cleaning did not improve the situation. In one case, the chromium content was on the high end of the specification. In the current case, a 1033 steel, the elements are within specification (specification used for over a decade). The forging was annealed at 1550F and furnace cooled. We are analyzing a black "ooze" coming from the metal when exposed to our zinc chloride flux.

We are starting a more thorough investigation of the current "challenging" forging. I intend to obtain material samples from a region with a tin bond to and from a problem area to consider the potential for material segregation. I am curious if the increasing use of recycled steel has added new trace elements, which could be concern, to typical steels.

Another line of thought is that the heat treatment may have been incomplete. I would re-anneal a large section of material to explore this option.

I would be interested in other suggestions that the community might have?

------------------------------
Lyle Branagan
Engineering Manager
Pioneer Motor Bearing Company
Kings Mountain NC USA
------------------------------