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View Full Version : 4140 inclusion or machining error



Sophiedoc
08-03-2012, 07:36 PM
About year ago i picked up a round of 4140 which I turned and milled for several projects.A few days ago i was drilling some holes in the end of a piece I had turned down when the drill suddenly began screeching and would cut no further.More force shattered the quarter inch bit.I could not cut through with a carbide mill.Was this possibly work hardening or an inclusion. I could grind the area successfully but my curiosity ruined the project.This piece of steel came from a local machine shop whom I trust.I had considered annealing but didn't proceed with that approach.Ideas?

Boucher
08-03-2012, 07:56 PM
I recently had a similar experience. My material was purchased from a local steel supplier about 10-12 years ago. I have used several pieces and part of this piece before encountering the problem. It appears to be a very hard zone. I broke out the Big Rosebud heated it and dropped it in a bucket of lime. Machined very nice after that. I wish that I had tried a file on it first. I didnít get any certs on this material when I purchased it. The steel supplier is a good company that I had nothing but good experience with. I also recently encountered a ball bearing type inclusion in a piece of 3Ē diameter 1018.

Dr Stan
08-03-2012, 08:06 PM
This type of thing happens every now & then. One of my memorable events caused by an inclusion happened as a fellow machinist was making a cam on a Bridgeport tracer mill when he encountered a piece of file in the casting. Needless to say neither the end mill nor the casting were salvageable.

kf2qd
08-03-2012, 09:44 PM
Have even seen stuff like that when plasma cutting - A long cut down the side of a piece of 5/8 or 3/4 that was about the size of a vienna sausage cut in half and stuck on the cut surface. And HARD!!!

J Tiers
08-03-2012, 10:26 PM
How do these hard inclusions survive the melting process in their general original shape and hardness? You'd think that the material would be annealed by the usual gradual cooling inherent in most processing. Especially if buried inside a larger piece, where anything happening at the surface would not be a strong effect.

HSS, well, possibly, and maybe air hardening steel..... but FILES? they are usually just high carbon, IIRC, so they should anneal decently inside anything else.

Dr Stan
08-03-2012, 10:30 PM
HSS, well, possibly, and maybe air hardening steel..... but FILES? they are usually just high carbon, IIRC, so they should anneal decently inside anything else.

Yes one would think so, but weird things do happen.

Rich Carlstedt
08-03-2012, 11:09 PM
We made many of our dies ( for plastic film) out of 4140 and 4340
Yes, You run into inclusions fairly often in general run steel products.
For our more expensive parts we always ordered AQ forgings ( Aircraft Quality !)
The steel was checked with ultrasonic probes and if they found an inclusion of a size in a given volume,(say 1/64" in a cubic inch )
the forging was rejected.
The reasons for these inclusions are many.

Rich

gwilson
08-04-2012, 12:02 AM
Semi melted ball bearings and other tool ruining trash have been found in Chinese steel as posted on the PM forum. Much less likely on USA steel,buy still possible. Sometimes tool steels will get just a tad too hot when cutting or drilling it. I've had 01 suddenly surface harden when filing it too vigorously. Hardens VERY shallow,but enough to ruin file teeth.

cuslog
08-04-2012, 12:29 AM
I've had a couple of incidents when drilling multiple holes in 4140.
It was drilling nice for several holes but then on the last 1/2" of the last hole it started to feel like the drill was getting a bit dull. "Oh well its the last hole, just push a bit harder, get through it, sharpen later"
NOPE --- drill bit turned RED instantly, had a spare sharp drill handy, tried it, instant screeching. That 4140 was workhardened, hard like a diamond

bborr01
08-04-2012, 11:56 AM
I have read that some foundries will toss un-melted scrap into a casting to help cool it faster. It is referred to as a "chill". There have been some pictures of various semi-melted inclusions on the net.

Brian

Grind Hard
08-04-2012, 12:10 PM
Also quality-control and production-floor discipline are non-existent in many of the "lower tier" foreign steel mills.

Friend of mine who works for a large well-known metal-supplier based in Rochester has detailed the following situations:

1) He has witnessed situations where workers at a mill in India basically threw floor-sweeps including undifferentiated scrap-metal into a pot moments before a pour.

2) Same variation, but tossed into an ingot after a pour.

3) Workers just walking past and tossing "whatever" into various melts because no one stops them.

He says the immediate floor-management doesn't care because they are basically zero-skill grunt-labor themselves being forced to make quotas. The next higher tier doesn't care either as they are looking to meet corporate targets. Corporate doesn't care because someone is always willing to buy the lowest-cost product.


He has on file several dozen castings with files, gears, BBs and other unidentifiable items in them, sheet-stock with highly visible inclusions that "must have" damaged the rolling mill based on the repeating pattern after the inclusion... and numerous examples of material not matching the written specs. Not "slightly off" but totally wildly different. Again he has these on file with actual samples. We're talking cold-rolled "regular" sheet-metal steel sent in place of certified SS, SS of a "lesser" grade being passed as a higher grade... and so on.

Apparently it is "much worse" with the Asian and Indian steel-mills than it is with the Russian and European steels that they buy... while "stuff happens" with those products it's much much less frequent and the post-incident service is much better.


Boils down to "know your supplier and find someone you can trust at a price you can afford." Price-you-can-afford is the key here, cheap is as cheap does, and when you go that route quality will suffer... even at the Home Shop level.

Sophiedoc
08-04-2012, 07:19 PM
After reading this I don't feel so bad since other have had the same experience.Project was ruined and it sound like I should have tried annealing-thanks all.

Grind Hard
08-04-2012, 09:09 PM
My brother was telling me the other day when I took him some blades... he uses a resin supplier named RTP for certain grades and types of material.

They are a custom compounder and he tells me they used them for years on years at one company he worked for... and they never had issues.

Fast forward 20 years now... He bought two batches of OSHA-Yellow specialty resin both of which were sent back promptly because the resin was severely contaminated.

We're talking 4,000 pound batches.

Turns out RTP does maintain "non-Asian manufacturing capability" but is now mainly an importer and reseller of resin from Mainland China... Where you can get it compounded with forbidden ingredients under the lowest possible safety conditions for pennies a pound. Whip up a new spec-sheet when it comes off the boat and jack it up to current market prices and... profit.


Really eye-opening to know this stuff goes on, apparently all hours of the day in all industries. Makes me shake my head and wonder what kind of disaster it'll take to change this sort of mindset.

J Tiers
08-04-2012, 11:12 PM
Turns out RTP does maintain "non-Asian manufacturing capability" but is now mainly an importer and reseller of resin from Mainland China... Where you can get it compounded with forbidden ingredients under the lowest possible safety conditions for pennies a pound. Whip up a new spec-sheet when it comes off the boat and jack it up to current market prices and... profit.


Really eye-opening to know this stuff goes on, apparently all hours of the day in all industries. Makes me shake my head and wonder what kind of disaster it'll take to change this sort of mindset.

I think you have discovered the "job creation" mindset......... anything is OK if it creates a few "jobs" here pushing pallets around.......at $5.75 per hour (yes I know that wage is illegal.....but people are paid that wage every day in the US, even if the NOMINAL wage is at the legal minimum. It's called "working off the clock", and many employers require it... Don't like it? Then quit and go figure out how to pay the rent with no income.)

It may not be the importer's fault..... the chinese have been known to bite rather large corporations the same way, often after several production runs that were correct. I've had stuff like that happen also............. known, previously rejected parts show up in the units...... apparently with the hope that nobody is watching anymore.