How do I through harden AISI 4340?
How do I through harden AISI 4340?
(OP)
I have a tool that is used to pre-set ferrules on tubing. It's made from A2 tool steel and hardened. The problem is that the A2 is brittle and after about 6 to 20 uses it breaks. I was looking into using a differnt material such as 4340 and have it through hardened but I'm not quite sure how to spec out the heat treatment. The tool has threads on one end so it is seeing about 15-20 ft/lbs torque when setting the ferrules. Can I get some advise from the metallurgists out there?





RE: How do I through harden AISI 4340?
RE: How do I through harden AISI 4340?
If your tool isn’t too big you can purchase preheatreated 4340.
RE: How do I through harden AISI 4340?
RE: How do I through harden AISI 4340?
In reviewing your post, I am presuming that the high hardness requirement is to resist plastic deformation during service, in lieu of wear resistance.
If this is correct, the following heat treatment specification for AISI 4340 should probably work;
1. For your application you will need to have the bar in the normalized condition for machining prior to heat treatment.
2. Heat the tool to 1525-1550 deg F and hold for 1 hour at temperature. Make sure this operation is performed in a protective atmosphere to prevent decarburization.
3. Oil quench to about 150 deg F.
4. Immediately temper at 450 deg F for 1 hour.
This temper should provide you with mechanical properties that can resist plastic deformation in your application.
If the hardness requirement must be met for wear or other reasons, you would need to switch to a tool steel like an M2 or other comparable grade. I have included a web site by Carpenter that summarizes some of the various tool steel grades and selection criteria;
http://www.crucibleservice.com/eselector/general/generaltitle.html
RE: How do I through harden AISI 4340?
If you are looking for an alternative material which is capable of 55-60 HRC and has better toughness and wear resistance than A2 you may want to consider using Crucible CPM 3V. By the way, the website provided in the post above by metengr is for Crucible, not Carpenter. The address for the data sheets on CPM 3V is
http://www.crucibleservice.com/datash/ds3Vv5b.pdf
If you have any questions regarding how to properly heat treat this grade, post them here and I will respond. Good luck.
Maui
RE: How do I through harden AISI 4340?
I think the transition from the threads to the square section is too abrupt (and probably full of sharp corners...). This coupled with the .281 hole ending at the same depth as the end of the external threads is asking for trouble. You are going from a 3/4 x 3/4 cross section to an annular section of approx .134 sq in. A-2 is really forgiving, but I'm thinking quench cracks.
Run the threaded section 1/2" beyond the bottom of the .281 hole and radius both the thread undercut and the transition to the shoulder at the 3/4 square section. I'd go at least .020" under the minor diameter for the thread undercut. Making the part out of S-7 would guarantee serviceability at some expense in life, IMO. My 2c...
RE: How do I through harden AISI 4340?
Thanks
RE: How do I through harden AISI 4340?
You really cannot have 2 major section changes and sharp corners in the same plane for quenching. That needs to be changed.