Trouble With Bronze Elongation % Values below minimium. 3

[Tklfserve]

One of Vendors, makes Bronze Impellers from 20 to 300 kgs is having issues acheving the full elongation values for a nominial (88/10/2) Bronze Compostion. That requires a 13% minimium elongation value to comply with AS1565/Grade C92610A.
From what I can discern the chemical compostion complies with the specification. We had some earlier troble with excessive Phosporous levels and have dropped it down to 0.010 % which is about as low as we are prepared to go with out taking risks with gassy metal - this did help, but not enough. What do I look at next???
[Currently, I'm looking at filtering the testbars, But are we missing the Obvious?]
I'm attaching some 'vetted-out' test reports so you get the idea.

 

[TVP]

I would investigate the microstructure, specifically, grain size and porosity. Elongation (fracture strain) of any type of casting, not just bronzes, is significantly affected by both of these.

 

[Tklfserve]

Thanks TVP. - good advice, I'll see if we can get a micro done and see what that turns up - Has anybody got any more further thoughts?

 

[unclesyd]

If my memory cells are in alignment after many years, 50+, we used to add an deoxidation step to this alloy along with several others.
I'm trying to recall what the deoxidizer was, Lithium keeps popping up as one of the deox materials. It was encapsulated in a Cu tube and my job was to charge the tube to the bottom of the electric rocking furnace after they withdrew the electrodes.

Anecdotal:
About ten minutes after I had added the deox. one of the seals on the horizontal electrode blew out and high pressure hydraulic fluid went straight into the furnace. The resultant explosion took out two additional furnaces and one of the 10 or so workers burned, one died from the burns.

 

[Tklfserve]

Thanks, Unclesyd this is helpful as well, and I had been given some thought to the same idea about the possibility of using a partial substitution of lithium as a deoxidizer but hadn't heard of any one doing with this type of alloy.

I'm familiar with using this, along with Calcium boride as a deoxidation in high conductivity copper.

Has anyone used this, or other meaningful deoxidizers or grain refiners.
[see TVP Comments]other than 'phosphorus or lithium' for 88/10/2 alloy? Or suggest best deoxidizer practice?

P.S. A very good reminder about safety hazards with dealing with molten metal, for all of us in the foundry industry can take it a bit too lightly
I recall a giant explosion with a 3 ton electric arc furnace when a 'wet' back charge was put in. It burnt the roof timbers, partially disabled the crane and heard about 1/2 mile away - lucky nobody got hurt!
I think they say, the ratio is about 200 near misses to 1 fatality…
…So safety is a really big issue!

 

[metengr]

Great post, unclesyd. I appreciate your experience.

 

[unclesyd]

Here is paper on the production of some of the copper alloys that includes a table of the relative effectiveness of several deoxidizers.
My recall doesn't have the high conductivity it use to but I believe we used Lithium as it was very fast allowing for a quick grab sample of the heat.

http://www.tdr.cesca.es/TESIS_UPC/AVAILABLE/TDX-0104105-092144//03Vggf03de11.pdf

 

[Tklfserve]

Question: What about the pouring-temperature of the teat bar?
The casting is thin sectioned and poured at 1200°C or 2190°F along with the test-bar at the same time.
Is 1150°C or 2100°F for the testbar more appropriate
I recall reading A obsolete Foundry article. that the grain structure changes in form and size with decreasing pouring temperature for 85-5-5-5 at least.

Does anybody stipulate a 'pouring temperature range' for testbars with this material 88/10/2 ??