Type of Steel for a spring in a lockback knife

[Shotgun232]

I have made quite a few fixed blade knives, and I started on a folding lock back knife about a year ago. The blade is made out of 1084FG, and I thought I would finish it up, as the semester has just ended. :grin:

I have never made a folding knife, so I am wondering what type of steel should I used to make the spring for the lock back? I have a bunch of 1084, 1095, 0-1, and D-2. and I assume making the lock back out of the same 1084fg would be okay.

Also I assume after heat treat of the spring, I should temper it for longer, to make it softer and more flexible?

Any advice would be greatly appreciated.

Thanks,
Mike

 

[Nifeman]

Hey Mike, you don't temper it longer. Temper it at a higher heat to make it softer. Look online for a steel heat color chart and you can temper with a torch. It's self explanatory...
Just reread your post. For the spring, you could use a piece of 3/32" piano wire, if you have a local hobby shop. That should already be tempered...

 

[44-henry]

All would work, but unless you have a good furnace I would stick with the 1084 or 1095, 01 and D2 are more difficult to heat treat.

 

[LRB]

Yes. 1084 or 1095. The 1084 is nearly foolproof to heat treat. For this application 1095 should work just as well. In dim light, heat to red-orange, quench in thin warmed oil, I would suggest canola, then temper in molten lead at from 700° to a tad more for 10 or 15 minutes, remove and air cool. A repeat temper would be better, but probably not entirely necessary. Tempering much below 700° invites breakage, tempering above 750° may not give it the power you may want. 01 requires a higher temper heat, and D-2 has coarse carbides that make it questionable to be used as a spring.

 

[Shotgun232]

I have an EvenHeat HT-1, so I can heat treat and temper just about any steel.....
I think I will just make the spring out of 1095.

 

[LRB]

1095 requires a very fast quench oil or you end up with a hard and soft mix in the steel matrix making the steel less strong. This condition cannot be detected by the common file test, because the file will still skate on the steel as if fully hard, as the hard spots will not allow the file to cut the soft spots. Other than the recommended commercial types, canola oil at about 130°/140°is the fastest cooling of the vege oils. For hardening, a 8/10 minute soak at 1475° is recommended, followed by the quench. For the best results, normalizing for fine grain is also recommended as a first step. Heat to 1600°, soak for a few minutes, air cool. Then heat to 1500°, air cool. Heat to 1400°, air cool. Then do your hardening process, but no hotter than 1475°. An ideal spring temper would be 700°/725°, 2 tempers of 1 hr each, quenching in water each temper. If you find the spring too strong, give it another temper at 750°. Warning. 1095 is more prone to cracking than most other steels. It probably won't, but be aware that it could. Get it into the first temper heat ASAP.

 

[Kylongrifle]

I have tried McMaster carr fast quench on 1095 and it worked very well in thin sections but I now use parks 50..Its pretty much the best thing out there for 1095 I believe. I hear Houghton's K is suppose to be very good too.

 

[LRB]

Yep. Parks #50 for the 10xx steels is about as good as it gets. The problem for most hobbiest or the occasional maker is the price of proper oils, and the minimum quanities required. For them canola oil is about as good as they can do, or will do, even though by the gallon, many might be surprised at the little difference in price there may be, and the longer useful life of formulated commercial oils.

 

[Shotgun232]

How is brownells tough-quench? It seams fairly reasonable in terms of price, and I have a free shipping coupon.

I currently used a mixture of canola and sunflower seed oil. I have pretty good results.

 

[LRB]

I've never used it, but as far as I know it is a fairly common quench with Brownell's label. If you're working 1095, I'd suggest straight canola, or look for the Parks #50. 1095 is very low in manganese making it difficult to get max hardness. Ideally, it must have a quench that will cool it from 1475° to under 1000°/900° in .6 to .8 of one second. Only brine will do that, but the Parks #50 is the next fastest, if oil quenching. There are others close to the Parks, but none surpass it. On a test chart I saw years ago, the Parks cooled 1095 in around 1.2 seconds, with canola coming in at I believe 1.6 or 8. All other vege oils were over 2 seconds. This same chart showed brine hardening to 66/67Rc,Parks 65/66, and canola 64/65Rc. I wish I had saved that test report. If buying oil for 1095, I would not trust the Tough Quench to do the job. If you are working as a hobby, the canola should be good enough, and a very good choice for the other 10xx steels. I have read from others that use canola for 01, but I think that to be a tad too fast and risky for cracking.

 

[Elnathan]

Wick,

In which case what would you recommend for O-1?

 

[LRB]

Those oils that are rated as medium fast. Parks AAA is one of the more popular, and is what I use. Tough Quench, and similar oils, but in non commercial quench oils, most of the common cooking oils should do well enough. ATF works pretty well, but the fumes stink and are probably pretty toxic in most brands. Some brands may not be as toxic as others. Some use Parks #50, but it is really overkill and may cause cracking. 01 is not terribly picky about it's quench and was designed to be relatively easy to harden. It's chrome content and other alloys make it a deep hardening and fine grained steel unless it is mistreated in the hardening process. The drawback to using 01 is the requirement of a heat regulated soak time at quench heat, which is difficult to impossible without the use of salts or a HT oven. A usable blade can be made without the heat soak, but it will be sub par compared to one that was soaked.

 

[Elnathan]

Thanks Wick. I haven't had problem with o-1 cracking, but the last knife I tried warped pretty badly, despite having been stress relieved and annealed. Irritating.

 

[LRB]

I found that quenching vertically, point down, reduces warp greatly. For me anyway. If you remove 01 from the quench while it is still a little too hot to handle bare handed, you can hand straighten most warping wearing gloves or protecting your hands with a suitable rag. You have a time window of about 5 minutes or even a little more. Conversion of austenite to martensite begins around 400° to 450°. This conversion starts off at the speed of sound, but slows and does not finish with 01 until it reaches room temp, or even a bit longer. During this conversion the steel is remarkably easy to bend and straighten while the temp is on the higher end. So easy , it is easy to over compensate in blades of 1/8" thickness or less. With experience, you can feel the rigidity coming on, telling you to when to stop. And no, I have never broken one in doing this. A2 is much the same, but I did break one A2 blade by trying to correct it after it had reached room temp, and I knew it was a risk. Lesson learned. If you still have a warp, and this works on other steels as well, go ahead and TEMPER the blade, determine the apex of the curve in the warp, polish the steel where you can see heat color, then lock it in your vise. With a hand held propane torch, heat the area of warp at the spine only, about an inch fore and aft of the apex to a deep blue or even to gray. Be very careful to not allow the heat to go to the edge. Over flex the blade beyond straight and pour water on it. It will lock straight or close to. You may have to repeat this to get it where you want.

 

[LRB]

I may be repeating what you already know, but the stress relief is done after all grinding is done to ready the blade for hardening. Grinding alone will induce stresses. The stress relief needs to be for an hour at temp. 1200° to 1250°, then air cooled. Precision ground 01 needs only a stress relief before the hardening process. It's grain structure is as good as it gets as is, unless it was forged. In that case, you have many more issues to correct before hardening.

 

[Elnathan]

I may be repeating what you already know, but the stress relief is done after all grinding is done to ready the blade for hardening. Grinding alone will induce stresses. The stress relief needs to be for an hour at temp. 1200° to 1250°, then air cooled. Precision ground 01 needs only a stress relief before the hardening process. It's grain structure is as good as it gets as is, unless it was forged. In that case, you have many more issues to correct before hardening.

No, I did not know that, although it makes perfect sense now that I think about it. I am using a charcoal forge, not an oven, so I have just been annealing it by heating it up to critical, letting it soak as best I can, and then putting it into ashes to cool overnight.

That O-1 can be straightened after a quench is also very useful info to know. I may be able to save this blade after all!

Thanks!

 

[LRB]

There is another way to straighten an already TEMPERED blade and have more control. Just takes a bit longer. C clamp the blade to a thick bar of steel, or even angle iron, with a penny spacer at the apex of the warp causing the blade to be flexed over straight, then give it another temper at 400°. Cook for at least an hour, then quench in water while still clamped in place. You may have to repeat this to get it really straight. Again, this works with most all steels. Do this in your kitchen oven using a separate oven thermometer. Range settings are never to be trusted unless proven accurate.
Just a word of advise. With your limited equipment you cannot get the real potential of performance out of 01 steel. 01 costs maybe 4 times the price of 10XX steels, which are much better suited for forging and simple heat treating, and would probably perform as well, maybe even better, as poorly HTed 01. 1084 steel is nearly fool proof in heat treat, and makes a very fine blade.
One other point. Many assume that the term "critical heat" means non-magnetic and the heat at which to quench steel for hardening. Not true. Each different steel has it's own "critical" temperature, or ideal heat range at which to quench at. Non-magnetic is 1414°, consistant, in all steels, and in reality is only phase 2 of 3 phases to reach max hardness. Minimum ideal quench heat is 1450° with most simple steels. 1475° to 1500° is usually better. Steels with more than .8% carbon are better when not heated over 1475°, but those with less carbon can handle a little higher heat nearing 1500°, but are more susceptible to warp and cracking in the quench, in that upper heat range.

 

[LRB]

I would add that with the simple 10XX steels, a magnet is handy to tell you when you have reached phase 2, and one full shade of red, or a tad more, will put you into an acceptable heat range to quench at.