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OT material inclusions

I was running some medical parts one time some years back, they were 2" 2011 aluminum. Once the part was finished and parted off you could set it on a bench and bubbles would come from the center for several seconds. 20,000 lbs went to the recycler as the .002ish hole in the stock would let bacteria live in it so it couldn't be used. About six months later the mill let us know the material was not pre heated enough durring processing and an inclusion aprk .002 down the center of 20,000 lbs of 12 foot bars had an oxidized inclusion, its hard to wrap your head around a thing like that.
 
We had a problem with some water cooling jackets on new bearing boxes not holding pressure when they were pressure tested after welding. Checked all the welds and no leaks anywhere. Checked in the middle of the solid steel slab and found a bunch of leaks. Asked the supplier and found out it was Chinese origin steel.
 
Have noticed problems with imported steel even back in the late 80's. We sent a medium size stripper plate (22 x 12 x 3/4) of O-1 to the HT we'd been using. It came back with a huge laminar fracture that extended half way across the plate. It had to have left the mill with all that stress.

The WEDM guy (same company and era) kept breaking the wire on a die insert he was trying to cut. After 3 breaks he dug out this match-head sized chunk of a white(ish) material. He couldn't figure out what it was that a WEDM couldn't burn through and supposed it was a mineral inclusion of some sort.

Articles from some of the trade mags of that era advised which mills were reducing/eliminating processes in order to compete with imported steel back then. The steel in that video set a new standard for quality.
 
I was in a "melt Shop" on a factory tour last year.

They have a 50 ton arc furnace, and then it get's poured into a 100 ton "refiner".
So 100 tons, smaller electrodes (to keep arcing) induction stirring, wire fed alloy addition (real time computer analysis) and all under full vacuum, and argon shielding,

IIRC the time in the "mixer" was about 1/2 hour, so everything is made clean.

So you can buy good, clean, in tolerance steels.
 
AD Design said:
The WEDM guy (same company and era) kept breaking the wire on a die insert he was trying to cut. After 3 breaks he dug out this match-head sized chunk of a white(ish) material. He couldn't figure out what it was that a WEDM couldn't burn through and supposed it was a mineral inclusion of some sort.
Click to expand...

This is why you shouldn't put cigarette butts in beer cans, you may get them back some day
 
About 20 years ago I was running some 1" 1018 purchased from Ryerson (no clue which country it was from) and hit a bunch of small inclusions. The last one stopped the spindle and cracked my cut off blade holder. The cutoff holder was shop built from A-6 tool steel hardened and ground. Made me sick and have not run any 1018 since. I have been asked to a couple of times and give the customer a choice 12L17 or take it else where.

My guess was the inclusions were crunched up carbide inserts.
 
inclusions can be not melted items like carbide inserts but usually are slag or metal oxides. molten metal has a layer of slag on top even when they skim most of it off some can get into the pour
.
typically there are deoxiders in cast iron and steel. a common one is silica forms silicon dioxide or sand. carbon and iron carbides can slowly try to take oxygen from iron oxide. cast iron can be soft gray iron and hard white iron spots if silica ratio is not uniform in the metal due to slag partially deoxidized
.
the slag and partially deoxidized inclusions can be very hard at times. rolled metal they get squashed thinner and longer. when small and thin enough they go unnoticed most times. as they get mildly bigger machinist might just say material acts abrasive and tools dull sooner. when slag inclusions grain of rice size or bigger is when you get to the sudden tool failure size where drill bits and milling cutters and inserts can fail in less than 1 second
 
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