help with 440C slipjoints

[jdware]

I've just started doing some slip joint folders using 440C. I'm heat treating the blades and springs in an Evenheat kiln. The blades and springs are foil wrapped and soaked at 1880F for 15 minutes, then air quenched between aluminum quench plates. Blades are tempered two hours at 325F to get a hardness of 58 - 59 RC, springs for two hours at 1100F to get a 43 to 45 RC. These were the suggested time and temps from Evenheat.

However, I'm having a problem I never had with my O-1 folders (O-1 for blades and springs) ......... the tang of the blade cuts, or grabs on the surface of the spring where it rubs, leaving gaul marks. I've tried mirror polishing the rubbing surfaces, as opposed to the 600 grit finish I normally use, but it makes no difference. Nor does the presence of oil.

My O-1 blades and springs were heated to non magnetic in a propane forge, quenched in warm oil. The springs were tempered twice with a propane torch to a bright blue - no problems with these - even when the spring pressure was too strong to allow easy opening.

Any suggestions would be much appreciated.

[Don Robinson]

Do you have a radius on the corners of the tang? Sharp corners on the blade will cut into the spring.

[jdware]

thanks Don, yes the tang is radiused with no sharp corners (like the tangs on Chris Crawford's tutorials). I've been making slipjoints for a while from O-1 and they are well finished and crafted. As I stated, I haven't had this problem at all with my O-1 blades and springs. In fact I made a spring from O-1 to test with the 440C blade and still had the same problem. I've gone back over some other posts on this forum, specifically this one:

http://www.knifenetwork.com/forum/sh...highlight=440c

This leads me to suspect that the problem might be that the blades are too hard and/or the springs too soft. I don't have a hardness tester, and have relied on published info for heat treating the 440C (although I can't find anything on temperatures for springs other than the 1100 F to get a 43-45 RC) Any further thoughts?
Jeff

[Don Robinson]

It sounds like your spring is too soft.

Tomorrow I'll look it up in my card file and see if 1100 is too high. I haven't used 440C in years.

I keep a card file with the heat treat formula and results of every knife I make.

Each batch of steel will vary in chemistry a little, so I don't rely entirely on published charts. That's also the reason I use my own hardness checker. I see the exact results each time.

[GHNorfleet]

Interested in this thread as well.

[Don Robinson]

I checked my files and I don't have a record of a slipjoint spring.

Looking at the mfr's. charts though, it seems that 1100 degrees drops right off the chart.

I'd recommend heat treating the spring again and tempering at 1030F to 1050F for two hours twice.

I always got good results on 440C with a hardening temp. of 1875F.

Good luck and let us know how it turns out.

One other thing that could be a problem is too much preload or too much rise caused by the tang corners being too far from the pivot. How far does the spring rise when you open or close the knife?

[jdware]

Don, the spring rises between 2 and 3/64". the spring's about 4" long with about 2 1/2" from the center pivot pin to the front edge of the spring. And on the smaller knives about 2/64" rise on a spring that's about 2 3/4 long with about 1 3/4" from the center pivot pin to the front edge of the spring. Neither knife seems to require excess force to open or close, tangs are nicely radiused with no sharp corners and are finely finished.

I'll try a lower temperature for tempering the springs.

Also, I've seen postings advising that the bearing surface of the spring be finished no finer than 400 grit to aid in oil retention on the surface. Any thought on that?

Thanks for your help.
Jeff

[Don Robinson]

I polish the surfaces on the spring and tang.

That's not much rise. I'm surprised it's cutting into the spring. The spring has to be soft.

[CWKnifeman]

Jeff I thought that I would chime in here as I have been making slip-joint folders out of 440-C for many years now. I normally heat treat the spring at 1050 for my springs, although I have heat treated some at 1100 ( mostly springs of very thick material for large folders).
A heat treat of 1050 to 1085 should give you a temper of around 49-47 rockwell. I normally do not heat treat my blades higher than a 57-58 rockwell for 440-C (385-400 degrees F.), this way the new owner will be able to resharpen the blade without any difficulty.
Also, if the spring lockup is to long it will cause to much tension on the spring that might also cause scarring during the closing of the blade. This might not happen during the opening of the folder, but will happen during the closing of the folder.
Hope that this is of some help.
Curtis

[jdware]

Curtis, I'm not sure exactly what you mean by the lockup being too long. Can you please explain. thanks.
Jeff

[CWKnifeman]

Jeff, what I am talking about is the lock notch of the blade tang where the spring locks up into the blade. Sometimes if this area (where the spring actually locks into the blade tang) is to long is may put undue tension on the spring especially during the closing of the blade. If the blade tension is really strong at the beginning of the closing of the blade then this might be the problem.

I am not saying that this is the problem, just pointing out one of the possible reasons for the problem. As I stated earlier the problem is probably the temper being to hig resulting in a to low of a rockwell for the spring. For 440-C normally the rockwell should be around 47 to 49 rockwell.

I hope that this helps in what I was talking about. If not then send me an e-mail and I will draw it out for you as to what I mean.
Good luck with the folder and do not let this situation deter you from using anything other than high crbon steels for your folders. Just remember that all steels have their own variables especially when spring tempers are concerned.
Curtis

[jdware]

Thanks for your suggestions....BUT.......I'm still having the same problem and it's driving me nuts. I've been making slip joints for a while now with O-1 that I've been heat treating myself......the knives are nicely made and operate smoothly, the geometry works.

So, I've been working on two 440C folders this week. The blades and springs are foil wrapped individually and go into the furnace when it's reached about 1850F, the temp rises to 1880 and they soak for 15 minutes. I pull two blades and two springs from the furnace and place them still wrapped in the foil between a pair of 1" thick aluminum quench plates with a floor fan aimed at the plates. I dropped the 440C spring tempering temperature to 1000F, and the blades are tempered at 375F.

No matter how much I reduce the spring rise (by taking material off of the tang), or reduce the spring tension (by thinning the spring) the bearing surface of the spring gauls, and then gauls the tang too! Sometimes it works smoothly for a few open and close cycles, then sticks, and sometimes it sticks on the first cycle (when closing the blade from the open position). It

Any thoughts???

[Don Robinson]

I'm gonna have to see photos of the blade and spring. I can't think of anything else without seeing it.

[jdware]

I will definitely take some pics and post. In the mean time, I also contacted a professional heat treating company for their advice. Here it is:

"I would suggest lowering the tempering temperature on the springs to around 900F. Hardness differences between components that rub together of more than 5 pts.
will cause galling. An 900F temper will get the springs to about 54RC approx. This will still work for a spring w/o breaking & should help to reduce the galling.

Recently a factory customer of ours(makes hundreds of thousands of knives a year) lowered their tempering temperature on their springs w/ great success. They increased hardness from 47RC to about 54RC & have been pleased w/ the results so far.

Hope this helps. Let me know how it works for you."

Any thoughts on this as it's a lot harder spring temper than what's generally suggested.

Jeff

[Don Robinson]

I've never used a spring that hard. If it works as they say, that's good.

However, most all experienced makers use a lower hardness with no troubles.

There's still something wrong that we haven't seen.