loaded question of the day!

[blaser.306]

I am working on a project in the shop and need some insight. The part in question will have a final diameter of .874" x 5.900" long with a .435" blind hole running thru the majority of it's length! I will either have to try and source some 4140 htsr or 4140 (4142) pre hard. My question to those with experience is how much distortion can I expect when heat treating , and how much should I leave for clean up afterwards ? Ideally I will be looking 37rC when finished . Thanks in advance, as mentioned I am just looking for " guidelines " and will proceed with caution along this path. This is something I would really prefer to do once as heat treating one piece is $125.00 minimum charge plus shipping. Any input would be appreciated.

 

[T Bredehoft]

This piece is smaller than the third joint of my little finger. buy a foot of 7/8" 4140 annealed (with luck it' will be be about 35 rC,) make as many as it takes to get a perfect one. Or specify heat treat to your specifications when you buy it, it will cut with high speed if you aren't in a hurry.

 

[rgray]

I made a 1 foot long .700dia tool and left .015 for grinding and it didn't clean up. I should have straightened it before grinding I guess.
On a .590 length There will probably be very little.
Are you planning on grinding to final size? If so leave .005 oversize. Even .010 over would take little time to grind to size on a part that small.
That heat treat price is ridiculous.
Build your own oven if you need to do much heat treating.
Mine cost around $500.00 to build.
Doing it without heat treat like tom says makes perfect sense also. Spend that $125.00 on tooling if needed.

 

[blaser.306]

My understanding is that annealed will be low 20's rC and HTSR will be 28-34 So if you think that 35 rc will cut with HSS it should be no problem with carbide insert tooling then? Which begs another question, what insert would be best, My machine isn't heavy or rigid enough for negative rake angles so I have ccmt and dcmt tool holders.

 

[blaser.306]

OOPS that should have been 5.900" .590" is a little on the shortish side. My apologies.

 

[blaser.306]

I already have a Fisher Scientific Muffle oven that I bought from an older gent at a garage sale for $20.00 Canadian so the initial heat and quench realy isn't the problem, the temper cycle after @ 900 deg F . I don't have another oven that will run that kind of heat and I suspect it would take much too long for the original treating oven to cool down sufficiently to do the temper.

 

[benmychree]

4140 HT should machine with HSS without any trouble, you just need to reduce the cutting speed to a point where the tools will not dull unduly quickly. Carbide is not required.

 

[rgray]

the temper cycle after @ 900 deg F . I don't have another oven that will run that kind of heat and I suspect it would take much too long for the original treating oven to cool down sufficiently to do the temper.

I a book I have it states that 350 deg is the most popular tempering temperature.
I guess I'd temper at 350 or 400 in a toaster oven.
Could always transfer it from the toaster oven to the cooled muffle oven if needing the higher temp tempering.

 

[4GSR]

Locate a piece of ETD150. It's a 4140-4145 that has been heat treated in the high 30's. Doing this will save in having to heat treat something to the high thirties. Most steel companies that sell to the oil field stock 4140-4145 P110 material that has a 110K minimum yield and is generally in the high thirties.
Also remember, if you send something out for HT, they want a hardness range to work within. They can't hit 37 HRC right off the bat. 37-43 HRC, yes.

Tempering temperature is more like 800-850 degree F, not 350-400 degree F to get 37-43 HRC.
350-400 degree F is for a 58-62 HRC hardness.

 

[benmychree]

When I was an apprentice, I did some of the heat treating in the shop; we had a nice new Johnson semi muffle furnace and a salt bath for tempering; it used a 50/50 mixture of sodium and potassium nitrates, which have, combined. a melting point below 350deg. F, and will stay fluid down to about 275deg. F. all this takes id a suitable vessel, a gas burner and a temp control with remote sensor. It will work to over 1200 degrees F, and also function as a bluing / blackening bath at about 600- 650deg F. I earlier posted an article detailing the process, the US Armory method of bluing and blackening, with permission of American Machinist Magazine", who originally published it/ When the shop ceased operation, I bought the equipment and supplies.