Annealing 4140

[DPittman]

I've got a 8mm slice from a 4" log of 4140 that I'd like to anneal to make it easier to machine. My only "heat treating" equipment is an acetylene/oxygen torch.

I'm wondering if I can be successful in annealing said piece without having to let it soak at any certain temperature? Cooling also would not be well controlled. How much warping can I expect?

I don't plan on rehardening the piece after machining as I think it will be fine in the annealed state.

 

[Darren]

are you sure its too hard in its present state?

Heat it up red hot and cool it slowly in a bucket of dry sand. bury it

I anealled an axle by heating it red/white hot and then buryied it in sand. The next day it was soft enough to machine with carbide.

 

[kevin.decelles]

Cool it I’m your oven ….. +1 for sand too

 

[DPittman]

are you sure its too hard in its present state?

Heat it up red hot and cool it slowly in a bucket of dry sand. bury it

I anealled an axle by heating it red/white hot and then buryied it in sand. The next day it was soft enough to machine with carbide.

No I don't really know if it can be annealed further or not. I do know I can machine it with carbide and very light cuts on my little lathe but it's pretty tough slogging. I'm hopefully that I might be able to make it a bit softer and unless it warps terrible or cracks I don't think I have much to loose?

 

[140mower]

I've been known to throw the odd part in the wood stove over night and pulled out when cooled in the morning..... Don't know how smart that was, but it got things softer... Nothing seemed any worse for the wear, so to speak.

 

[Darren]

I've been known to throw the odd part in the wood stove over night and pulled out when cooled in the morning..... Don't know how smart that was, but it got things softer... Nothing seemed any worse for the wear, so to speak.

I have done that before as well, and it worked with about the same results. Not everyone has a woodstove though. And a pile of dry birch.

 

[140mower]

I have done that before as well, and it worked with about the same results. Not everyone has a woodstove though. And a pile of dry birch.

Hang on..... Aren't we all Canadians?
But you are right, I'spose.

 

[DPittman]

I've been known to throw the odd part in the wood stove over night and pulled out when cooled in the morning..... Don't know how smart that was, but it got things softer... Nothing seemed any worse for the wear, so to speak.

Ya I can imagine that would work fairly well.

 

[DPittman]

Hang on..... Aren't we all Canadians?
But you are right, I'spose.

I'm Canadian but live on the bald ass prairie so trees are few an far between.

 

[Tom Kitta]

Where did you get such slice? If it was cut off with a bandsaw its not hard at all. 4140 is about 70% or so harder then mild steel. 4330 is the real pain - that sucker is more then 2x as hard and HSS has issues with it.

Do one of the methods above and report back. Usually 4140 logs come soft, but maybe you got it out of a pin or something that was pre-hardened. Also your carbide grade may not exactly be "great".

 

[Darren]

Where did you get such slice? If it was cut off with a bandsaw its not hard at all. 4140 is about 70% or so harder then mild steel. 4330 is the real pain - that sucker is more then 2x as hard and HSS has issues with it.

Do one of the methods above and report back. Usually 4140 logs come soft, but maybe you got it out of a pin or something that was pre-hardened. Also your carbide grade may not exactly be "great".

That was my thought as well. It must have been cut from something.

 

[DPittman]

Yes I cut it from a log with my bandsaw. I have also cut 4340 logs with same bandsaw. Maybe it's already annealed as it gets, I just know that it does turn hard on my little lathe.

 

[DPittman]

Also your carbide grade may not exactly be "great".

Yes I changed carbide insert part way through turning, from cheap, unknown Chinese stuff to a decent quality stuff and noticed an impressive

 

[Dabbler]

The logs we got (including the 4330) were all annealed for machining. 4140 can be 'sticky' - and on smaller machines can require very light cuts. Try using carbide inserts that are ground and polished for aluminum. they don't last as long, but require a lot less pressure to do the same cut. and you can take a smaller chip with them as well.

 

[DPittman]

The logs we got (including the 4330) were all annealed for machining. 4140 can be 'sticky' - and on smaller machines can require very light cuts. Try using carbide inserts that are ground and polished for aluminum. they don't last as long, but require a lot less pressure to do the same cut. and you can take a smaller chip with them as well.

Good to know, thanks!

 

[Mcgyver]

where did it come from? When bought heat treated, in my experience, the chrome molys shouldn't be too bad to machine. Super tough and strong, but readily machinable. slower surface speed and challenges with a good finish, that's about it. That it seems so hard to machine, I'm wondering if it was tempered fully/properly/as much as it should/could be. If it wasn't tempered it could be quite hard, high 40's maybe (rockwell). Tempered it should be a lot less, somewhere in 20's or low 30's.

So....what you might need is tempering not annealing. Good news, its a easier. You'd have to get it up to 1600 and do a slow cool, hours, to anneal it. 1500 won't do, i.e. has to be at the critical temperature for the particular steel. But to temper, much lower temps are required. If a fire got it to 900 or 1000 (all F) that would make it a lot easier then getting it 1600. Only get it to 700? it'll still be tempered, just not down as much as if it was at a high temp. Unlike annealing which is more black and white, tempering can vary and is a function of temperature (and to a lesser degree soak time)

 

[DPittman]

where did it come from? When bought heat treated, in my experience, the chrome molys shouldn't be too bad to machine. Super tough and strong, but readily machinable. slower surface speed and challenges with a good finish, that's about it. That it seems so hard to machine, I'm wondering if it was tempered properly/as much as it should/could be. If it wasn't tempered it could be quite hard, high 40's maybe (rockwell). Tempered it should be a lot less, somewhere in high 20's low 30's.

So....what you might need is tempering not annealing. Good news, its a easier. You'd have to get it up to 1600 and do a slow cool, hours, to anneal it. 1500 won't do, i.e. has to be at the critical temperature for the particular steel. But to anneal, much lower temps are required. If a fire got it to 900 or 1000 (all F) that would make it alot easier then getting it 1600. Only get it to 700? it'll still be annealed, just not down as much as if it was at a high temp. Unlike annealing which is more black and white, tempering can vary and is a function of temperature (and to a lesser degree soak time)

Ok now I'm questioning all that I thought I knew about heat treatment of steel. Steer me back on course please.

In the most general and basic terms:
I understand annealing to be the softening of metal by bringing it to the critical temperature of the metal (eg 1600 F) and then allowing the metal to slowly cool.

I understand the hardening of metal to be bringing the metal to the critical temperature (and possibly holding it there for a period) and then quickly cooling (oil, water, air).

I understand tempering to be bringing the hardened metal back up to a specific temperature (but no where near critical temp). This allows the metal to retain its hardness but removes much of the brittleness and gives the metal a "toughness/durability".

 

[Mcgyver]

No you've got it close to perfect, I'm just an idiot. One clarrification, when you temper it doesn't retain all of its hardness. Letting it down to reduce brittleness also makes it less hard....but its still a lot harder than annealed. In the case of a chrome moly, the hardness of the tempered steel can half of the hardness before tempering so its a fairly big difference

Mixed my words up. Where I said

"But to anneal, much lower temps are required.",
should have been
"But to temper, much lower temps are required.

I corrected the post. HT Info for 4130 below