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Thread: 4140 HT same as 4140 pre hard ?
06-18-2009, 06:46 PM #1
4140 HT same as 4140 pre hard ?
I just read the 4140 pre hard thread and now I have a couple questions.
Is the pre Hard the same thing as 4140 HT ? I've always thought it was but maybe I'm wrong ?
What about HTSR ? is there another process involved with the HTSR or is stress relieving just a side benefit of the heat treat process ?
06-18-2009, 07:15 PM #2
I think it is all one and the same thing, if you are thinking in terms of standard mill products. The heat treat cycle is supposed to begin with an annealed bar, then quenched, then tempered (stress relieved) to reduce the hardness and to help the crystalline structure to have adequate time to transform into a more stable form.
Since the bar shapes are simple when quenched, there is going to be some differential in structure from the surface to the core of the bar. Machining the bar into an asymmetric shape is going to upset the existing balance of forces to some extent, and thus the warpage occurs. So the trick is to rough the shape several times and gradually machine the warped surfaces into straight surfaces. This requires clever setups to prevent inducing clamp induced distortions.
06-18-2009, 09:53 PM #3
06-19-2009, 12:18 AM #4
Walter, be careful referring people to that old post. There is some SERIOUS misinformation in the final post. (by some fellow typing in all caps).
To the OP: 4140HT (Heat treated) and 4140 QT (Quenched and tempered) and 4140 HTSR (Heat treated & stress relieved) and 4140 Pre-Hard are all basically the same thing. They are generally in the range 0f 26-32 HRc. Movement during/after machining may or may not be problematic, depending on the amount and configuration of material to be removed from the original stock, as alluded to by Hu.
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06-19-2009, 02:59 AM #5
Isnt it sumtimes refered to as 4140 pre heat treated as well.or 4140PHT,I think but not sure(am asking)that it also is called 4150??? by maybe Alro Steel??
06-19-2009, 08:03 AM #6
OK - Here is a chart with the composition of most Carbon Alloy Steels:
Here is a decent description about alloy steels:
The Wikipedia information:
And finally a list of almost all heat treatment processes:
06-19-2009, 04:01 PM #7
You might also look up ASTM-A193 as this is usually what you get when you specify pre-hardened 4140. It machines nicely.
Bear in mind that 4140 can be hardened well beyond R30-32c but then it won't be called ASTM-A193.
06-19-2009, 04:09 PM #8
06-20-2009, 11:42 AM #9
Shop I used to do a lot of repair work for calls me one afternoon about sawing some ~2.5" Inco 718 rounds. Stock was supposed to have been cut in 4 ft lengths prior to delivery. Their own horizontal saw was down awaiting some parts, which wasn't a big deal normally since it was used almost exclusively for maintenance while the bulk of their production started out as forgings from various aircraft alloys.
I'm standing in the middle of the shop talking to the turning supervisor about the specific lengths to cut for best part yield since they're going to bar pull and part off the parts. A clown who's supposedly a mechanical engineer walks up to give his input. One of those yokels wearing a pair of dress slacks that stop about 4" above his shoetops, and a belt about a foot too long, buckled leaving the extra foot dangling like something half obscene.
He chimes in to tell me I need to be real careful when I saw the stock so I don't get it too hot and "take the temper out of it". The turning supervisor rolls his eyes and adds, Yeah, don't let the saw blade get red hot or anything. I played along and told him in a real serious tone that I'd make sure and pour some water on it if I saw it changing colors.
The supposed engineer was so clueless that the fact that we were both making jokes about his "advice" flew right over his head without ever slowing down. Considering every part going out the door of that shop goes into a jet engine, I found it real comforting to know such competent technical advice was available to the production staff