Hi John & charged-up Galoots !
When I warned about the dire consequences of HE:
> Galoots whose saws become brittle after electrolysis
> can prevent that by baking the saws around 300 F for
> several hours immediately after the electrolysis to
> drive off the hydrogen that causes the embrittlement
> (actually, delayed cracking due to residual stress).
John Ruth put 2&2 together regarding electrolysis:
> > This has set me to wondering if there are other tool items
> > besides saws which need to be thus protected from Hydrogen
> > embrittlement after electrolysis.
You betcha there are.
In industrial circles (pressure vessels, actually) one gets
especially nervous when the steel used under stress with hydrogen
present has a Brinell hardness number over 300. I don't have my
conversion table from Brinell to Rockwell C in front of me, but
experience says that a tool with a Rockwell C hardness over forty
is at risk of embrittlement if it's not promptly baked after the
kind of big time exposure to hydrogen that electrolysis causes.
Electroplating is another nasty way of getting HE.
The time of baking should be comparable to the time of electrolysis.
Just soaking in the sodium carbonate solution isn't harmful, BTW
(it removes the grease and loosens non-crosslinked paint nicely).
Below Rockwell C40 the main risk of hydrogen damage is from
blistering by hydrogen gas that is generated inside internal
seams; that means that wrought iron or poor-quality steel
should also be baked. Also not electrolzyed for long times.
What sorts of tools are at risk ?
Toughened or carburized wrenches (not the easily dented ones).
Chisels; knives; screwdrivers; scraper blades; plane blades
(mebbe even cap irons); wood-boring bits; twist drills; machinists
layout tools, such as spring-joint calipers, trammel points; any
sort of steel spring; plated tools, whose plating is likely to be
lifted if the original plating was at all imperfect; hammers; etc.
Oh, yeah: saw blades.
What sorts of tools are "safe ?"
Plane bodies; any cast iron (but watch out for flame-hardened
stuff like lathe beds and white iron like cheap scissors); screws
(except socket-head cap screws); soft steel; sheet metal frames
of tailed appliances; not such a long list, actually.
Hydrogen embrittlement can produce spectacular failures.
A mill roll I was called in to investigate disintegrated inside
a packing crate made of two-by-six timbers; the pieces of the roll
(made of 52100 steel) went right through those two-by-sixes. The
management & staff were rightly alarmed by that event. The roll
was about a foot in diameter by four feet long; I could pick up
any of the remaining pieces with one hand. Most square footage
of fracture surface I have ever seen in one place; and I've
looked at broken ships.
The mill roll was exceptional because it had been quenched and
tempered to produce a hard outer surface, which left the exterior
under compression and the interior in tension. When a hydrogen
flake (internal crack, left over from much earlier processing at
the steel mill) let go, it was like springing a snare; the exterior
compression launched the roll fragments in all directions. It had
recently been treated electrolytically, but the exposure time was
not long enough for any hydrogen to diffuse to the center of the
roll. I blamed the occurrence on the low temperature in the
shipping room where the crated roll was awaiting pickup on a cold
winter's night (when all the mice had the shit scared out of them).
The offending hydrogen had gotten into the steel during the melting
operation, from moisture in the air.
Theoretically, the limiting velocity of such fragments is the
speed of sound in the material - about 1000 feet per second for
steel, which can make cookie-cutter holes (aka Fearless Fosdicks)
in windows, walls, and heads.
Hope none of you tries to electrolyze a 1000 pound mill roll.
At least the tools we process are under water at the time; or in
SWMBO's oven immediately afterwards, so the occasional fragment
hits something other than us first.
Best regards,
George Langford
amenex@a...
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