4130 heat treatment

Date 06-25-2005 15:44

I am welding a 2x4x5” piece of 4130 to a 1” x 6” diameter base plate (two sets). I will be using 7018. I don’t anticipate a problem there. The 4130 will be used as forging dies for a power hammer (75# ram, 9”stroke, 200 bpm max). Only hot metal will be worked, although I may use some tooling between the dies on occasion. I would like to keep the faces from becoming marred. My questions are: Would flame hardening be advisable? If only .25” of the surface is hardened during flame hardening, would it be suseptable to cracking (since the substrate would be softer) while forging? Would the dies work harden enough during the forging process without treatment anyway?
Thanks.

By GRoberts (***)

Date 06-26-2005 02:03

I'm definately not an experienced forge shop guy, but from what little I know about forging dies, most of the ones I have seen get weld overlayed with hardfacing when wear is a concern. Several weld consumable suppliers specialize in this particular area and would be a great help I'm sure if you give them a call. I would try Weldmold, and Cormet.

http://www.weldmold.com/

http://www.cor-met.com/

By Ken Dougherty (**)

Date 06-26-2005 06:25

Thank you for the references. I'll check them out. In this application, the dies are exposed to pounding more than abrasion/wear. I suspect the issue would be the same with hardfacing since it is a thin shell w/respect to the rest of the die mass. I guess an analogy would be like a hard boiled egg. The shell is not well supported by the boiled egg and cracks when given a sharp blow. Would the hard "shell" of the 4130 crack from the concussion or would it be ductile enough to not crack?

By GRoberts (***)

Date 06-28-2005 02:58

Ken,
Since no one else with more tool experience has chimed in, I will take my shot at it.

Most of what I am familiar with indicates that the softer substrate is acutally beneficial because of its increased toughness. It can stop cracks from propogating beyond the hardened surface layer.
Depending on the application, a non-propogating surface crack may not be detremental to the use of a die.

By Ken Dougherty (**)

Date 06-28-2005 04:33

Thanks again for the reply. Sounds reasonable, especially given that 4130 doesn't become terribly hard anyway. The greatest hardness I have seen in any literature is Rc 52 and that was higher than all the rest at between 28 and 40 something depending upon the thickness. There is a quenching solution called "super quench" that works amazingly well on even mild steel (had to try it to believe it). In case anyone is interested, it is 5 gal of water, 5lbs of salt, 24 oz of Dawn Ultra dishsoap, and 8oz of Shaklee BasicI or 8oz of Jet Dry wetting agent (the stuff used in dishwashers to clear the spots). The formula was developed at Sandia Labs by blacksmith Rob Gunter. Apparently they were trying to not use a lye solution due to the hazards. Heat the metal to the critical temperature then quench w/constant movement. The caution is to not quench anything w/more than 30 points of carbon as it is a very severe quench. When you quench something in that solution it really squeals.

I may just experiment w/some flame hardening on my dies. I guess the worst that can happen is that I mill them again.

Thanks for the help.
Ken