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Furnace Brazed

Need help understanding microstructure versus formability?

My company, in the last several years, has changed a tube manufacturing process from a furnace braze process with forced air cooling to a continuous braze process using induction heat with a 300' long water jacket cooling pipe. The grain structure of the original product had an even appearance throughout the cross section. The grains were all large. We no issues forming this low carbon steel into flares. The new induction heated with pipe cool process delivers a grain structure that has small grains on 1/2 of the cross section and large grains on the other 1/2. I'm not an expert, but obviously this relates to the tube cooling at different rates acrossed the tube wall. My question is, how does this "Dual" grain structure affect the formability? Our endform process has been significantly destabilized by this new process. We see lot to lot variation that is crazy. The steel does not "Flow" consistently from flare to flare or lot to lot. HELP.

I found this article http://www.ias.ac.in/matersci/bmsaug2001/361.pdf by searching on http://scholar.google.com and it appears to address some of your problems, albeit in a slightly different manufacturing context.

Also, http://scholar.google.com/scholar?hl=en&lr=&q=cache:6pK3jsq7CbAJ:db1.wdc-jp.com/isij/pdf/200106/is410520.pdf+low+carbon+steel+grain+size+effect+on+formability may be relevant.

I'm not an expert, but I'd guess that your process variability for the endform process is due to the variations in strength at the boundary of the different grain structures.

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