4145 Heat Treatment
4145 Heat Treatment
(OP)
The part is a 4145 tube (6" OD x 10" long x 1" wall). It will be austenitized and then needs to be heat treated to get a hardness of ~32HRc. Two options are being considered:
1) Quench to ~850F and hold for 1 hour - air cool.
2) Quench to ~700F and remove and air cool (martemper)
Both quenches would be done in a salt bath. An oil quench (with temper) is not an optionin this case. Any comments on the two processes? Any alternate suggestions? We don't currently use a salt bath so this is a new are to us.
1) Quench to ~850F and hold for 1 hour - air cool.
2) Quench to ~700F and remove and air cool (martemper)
Both quenches would be done in a salt bath. An oil quench (with temper) is not an optionin this case. Any comments on the two processes? Any alternate suggestions? We don't currently use a salt bath so this is a new are to us.





RE: 4145 Heat Treatment
RE: 4145 Heat Treatment
I appreciate the help.
RE: 4145 Heat Treatment
RE: 4145 Heat Treatment
It is unlikely that the part will survive a traditional quench to martensite. I would love to do that and then temper, but it won't work in this case due to thermal shock.
We will austenitize in a protective atmosphere. A tempering furnace is available.
RE: 4145 Heat Treatment
You do need to watch the quench rate, but you can control that.
Are you trying ot hold tight tolerances?
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: 4145 Heat Treatment
RE: 4145 Heat Treatment
How do you think the martemper will do? Some pieces will be 0.5" wall.
RE: 4145 Heat Treatment
Martempering has to be performed above the martensite start temperature for a short period to assure minimal temperature gradients before transformation of austenite to martensite. You can go with a modified martempering cycle, where you quench to below the martensite start temperature, and hold until thermal gradients are removed, and cool to room temperature. You will still need to temper to lower the hardness.
Austempering is an option for 4140 and higher carbon grades. However, you might still need to temper as a separate step to achieve the lower hardness range of 32 HRc.
Typically, for 4145, austempering will result in a minimum hardness of 35 HRc, which is slightly higher than what you are shooting for in your application.
RE: 4145 Heat Treatment
As I've stated before have a workable operation and safety plan in place and enforce both.
RE: 4145 Heat Treatment
RE: 4145 Heat Treatment
unclesyd - when you talk about compatibility I assume you mean chemically? I will have to investigate that. And I will certainly make sure the sizing can handle, with lots of room to spare, the heat input. I have not dealt with molten salts and am very concerned about operations in and out of the tank. I'm trying to get as automated (racks, cranes, carts) a system as possible.
swall - oil quenching will be fine to bring it from 700F to ~RT. That should be a limited thermal shock.
RE: 4145 Heat Treatment
RE: 4145 Heat Treatment
Unless (duh!) you are trying to re-heat treat after applying a carbide coating that brazes at over 1900 F. There is a company in Indiana that does this and I believe their process is protective atmosphere austenitize around 1650F, a low temperature salt quench (around 450 F, I think) followed by an air cool, then tempered (I'd guess around 1100 F to get 32HRC). I know the Indiana company put in a lot of research into how they could re-heat treat the parts after applying the coating.