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 ?
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.
You might check out this thread. I got my terminology mixed up in it and it lead to a rather lengthy discussion.
Help choosing material
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.
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??
Correct.. the last post in the referenced post should be ignored.
Originally Posted by eKretz
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:
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.
4140, 4142, 4150, and 4160 are all available as HTSR. Lovejoy-type motor couplings are typically made from 4160HTSR.
Originally Posted by Greg White