Is 40 Rc WAY too low for a slip joint spring?

J

JC in SC

Well-Known Member
The title pretty much sums it up. I posted a question in the heat treat forum here looking for guidance on heat treating and tempering CPM154 for a slip joint blade and spring. Perhaps I didn't use a long enough soak during HT, but after tempering at 1200F for one hour, it reads 40 Rc. This is below the 43 to 45 Rc I was expecting. Is this way too low for a slip joint spring?
 
Try it out and see if it bends or springs. I was told to harden your blade and spring at 1925 and soak for 30 min. For spring temper soak your spring at 1050 for 2hrs, twice.
 
JC,

40 is probably a bit low. It is important for the spring to be hard enough to withstand the wear that will come from the much harder blade tang. I used to shoot for around 45 Rc but after speaking with some slipjoint guys that know a helluva lot more than I do, I am now making mine a good bit harder.

I try to stay away from HT questions since it is such a touchy subject and strong opinions are common but I will say that I think your termpering temp may have been high. I do mine a longer time at a lower temp.

It is important to remember that everyone gets different results due to variables like their ovens, steel, quenching methods and countless other things that can come into play.

The great thing is that you can throw it back in the oven and try again till you get it right. Keep a good notebook of what you tried and the results.

Johnny
 
Thanks for the response Chuck. I guess I don't have to worry about it breaking since it is too soft. I'll assemble it today and see how it behaves. I think I'll adjust my heat treat and tempering profiles moving forward.
 
Hey Johnny,

Thanks for the feedback. The blade checks out at 55-56 Rc, so I think I need to repeat this little exercise. I'm going to increase my temperature to 1925°F and increase soak time to 30 minutes and decrease the tempering temperature on the spring.

Thanks,
JC
 
Johnny Roberts said:
JC,

Keep a good notebook of what you tried and the results.

Johnny
Click to expand...

Good advise, Johnny. I have a card file that's around 20 years old. that's my first reference for the next blade.

I've also downloaded and printed out all of Crucible's heat treat formulas and keep them handy.
 
You probably saw from my WIP tutorial I did about me having the same issues. Even though I used a different steel, I got a similar situation that you are in. I knew 40 was probably to low and would most likely spring like Chuck said is possible..So I re heat treated. I think I ended up with about 45 or 48..can't remember what it was now without looking. The thing is, too hard and it breaks. Too soft and it springs. The hardness is directly related to the pressure required to open and close the blade (the amount of tension you feel) but also remember this can be altered by the amount of material taken of the tip of the spring where it contacts the tang area and pivot on the blade.. Alot to think about..

Like I've said before, it would probably take years of mking these things and 100's of knives before you could pull one off without issue. There are just so many areas for problems. Good luck. I can't wait to see your completed knife.
 
I repeated HT with temp. and soak increased as noted above. Now both blade and spring are reading in the 61.x Rc range. Both are tempering now, so hopefully I'll know something by this afternoon.
 
J S Machine said:
You probably saw from my WIP tutorial I did about me having the same issues. Even though I used a different steel, I got a similar situation that you are in. I knew 40 was probably to low and would most likely spring like Chuck said is possible..So I re heat treated. I think I ended up with about 45 or 48..can't remember what it was now without looking. The thing is, too hard and it breaks. Too soft and it springs. The hardness is directly related to the pressure required to open and close the blade (the amount of tension you feel) but also remember this can be altered by the amount of material taken of the tip of the spring where it contacts the tang area and pivot on the blade.. Alot to think about..

Like I've said before, it would probably take years of mking these things and 100's of knives before you could pull one off without issue. There are just so many areas for problems. Good luck. I can't wait to see your completed knife.
Click to expand...

Yeah, I remember that. Heat treating is such a funny thing. On one hand, with all of the variables involved, it almost seems unimaginable that anyone can do anything related to heat treating consistently. Nevertheless, people do it all the time with excellent results. I hope to post a finished knife soon, pending successful heat treat and temper of course.
 
I think this last round of heat treating and tempering did the trick. I just measured 47.3 Rc on the spring. This is a little higher than recommended, but based on all the WIPs that I've seen I think it is reasonable. Hopefully it won't be a nail breaker!
 
To Adjust the tension on the spring you remove material behind the area that the tang of the blade touches. If you remove material from the tip you will lower the spring and the blade and spring spine will not be the same height.
 
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