When To/How To Straighten Blades?

P.Brewster

P.Brewster

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Jul 25, 2007
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On Saturday, I hardened and tempered 33 throwing knives made from Aldo's 1075.

Heat was via propane forge with no PID; quench was parks 50, temper was 600° via toaster oven with PID.

I rolled the bars flat prior to waterjet cutting. After WJ, the blanks were curled again, so I straightened them prior to grinding.

Long story short, most of them took on a curl when heated - I fixed that with tongs while hot. Some came out of the quench with a curl, so I attempted to straighten them by hand before I hit 400° (that was a guessing game as well).

In the end (after temper), I STILL had some blades with a curve... I fixed them with a lot force in a rigged-up press. That didn't seem quite right to me.

So my question is:

When is the best time to straighten? How?

Is it ok to straighten after tempering?

Would I have better luck with an oven?
 
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I had the same problem, I still not have found a solution, but it was suggested to me to normalize at a HIGH temperature, then a few others to bring the grain size back down.
 
It sounds like you should have relieved the stress in them before hardening. I like to run everything through my oven for 30 min at 1350f and let it shut off and cool slowly. Seems to do the trick for me.
 
Don't try to straighten below 400 F .In your case you could go to 600 F , your tempering temperature.
Normalizing before Q&T would be helpful.
 
I dont know but all of what ive read is with in secaonds after they are quenches straighten them and then reqwench. then bake um
 
I dont know for sure but what ive read is the second that they have been qwenched 10 seconds then straighten them then reqwench for another 20 seconds and then bake um at 400 to 500 for 15 min
 
Mine come out strait most of the time but when they don't-----
I use a aurbor press on mine justtake it esay or they will snap.
 
I agree with Bruce. Stresses are likely whats causing your issues. Either do as Bruce suggested, or if you don't have an oven, thermal cycle them in a forge 2-3X at 1200F-1350F, letting them cool between cycles. That should help considerably with warping issues.
 
I have not had a forged blade warp for over 10 years, nor have any of my students.

This is what stopped it: after forging heat the blade to a little above critical, (I test with a magnet) then quench in room temp Texaco Type A for 35 seconds, then heat it back up, quench again and then again for a total of three quenches, hold the blade in the oil for 35 seconds each quench, then two flash normalizes, followed by a full normalizing cycle, from critical to room temp, 70 degrees still air to room temp. Photomicrographs indicate an increase of uniformity in the steel with each post forging quench.

Then a 2 hour soak at 988f, cool down in my Paragon to room temp - then in the freezer, I do this three times, then grind to approximate shape and harden and temper.

This has completely stopped all blade warp for us using 52100 and 5160.
 
Thanks for the insight Ed. Thats so cool. I have quenched after forging before but never had a lab verify it. Now we know. How did you arrive at 988 soak temp?
 
I read that some makers have something like vice to clamp the blade straight during tempering. Vice and blade are going together in the oven for temperig cycle and blade is going straight from the vice.
 
You are most welcome Bruce!

5150 and 52100 air harden, at first to temper the blades we soaked at the recommended 1100 f, then I tired decreasing it and found 988 f worked and have stuck with it.

I have only used the 3 post forging quenches quenches on blades that were forged at low temp. (1,625 max. temp.) and again only on 52100 and 5160. It may work on other steels? If you try it on other steels please share the your experience with it.
 
Bruce: We started out using a soak at around 1,400 degrees, I decided to try lower temps and over time droped to 988 f. I found no significant loss of function, and the blades still performed better than those soaked at the higher temp.

Some present research indicates the recommended higher temps at some stages are not necessairy and may not lead to the most beneficial state of the steel.

The lower temp soak resulted in no negative influences. I suggest you give it a try and see if you find any differences.
 
Patrick, was this some of the 3/16ths Aldo was selling? I had posed the same question about getting the bow out of it.
 
patriqq said:
On Saturday, I hardened and tempered 33 throwing knives made from Aldo's 1075.

Heat was via propane forge with no PID; quench was parks 50, temper was 600° via toaster oven with PID.

I rolled the bars flat prior to waterjet cutting. After WJ, the blanks were curled again, so I straightened them prior to grinding.

Long story short, most of them took on a curl when heated - I fixed that with tongs while hot. Some came out of the quench with a curl, so I attempted to straighten them by hand before I hit 400° (that was a guessing game as well).

In the end (after temper), I STILL had some blades with a curve... I fixed them with a lot force in a rigged-up press. That didn't seem quite right to me.

So my question is:

When is the best time to straighten? How?

Is it ok to straighten after tempering?

Would I have better luck with an oven?
Click to expand...

There's some things I don't get. Was the steel curved when you got it or were you rolling to a set thickness? Was it hot rolled or cold rolled and is the stock hot rolled or cold rolled?

Do you know what the batch chemistry of Aldo's 1075 is (would make a little difference in normalizing temp.)?

Mike
 
All,

thanks for the tips. A lot of the advise I'll save for when I'm making real knives; there is only so much I can do on a $25 throwing knife while maintaining profitability.



Sam,

yes, it is the 3.25 x 0.188 x 48" bars of 1075. Sorry I missed your post.



Mike,

the 1075 was hot-rolled. The 48" bars were warped upon arrival. I cold-rolled them (not to thickness) to flatten, so they would sit flat in the waterjet.

I do not know the chemistry off-hand, but the analysis was posted on BF by Sam... I'll look for it tonight.

thanks
 
patriqq said:
The 1075 was hot-rolled. The 48" bars were warped upon arrival. I cold-rolled them (not to thickness) to flatten, so they would sit flat in the waterjet.

I do not know the chemistry off-hand, but the analysis was posted on BF by Sam... I'll look for it tonight.

thanks
Click to expand...

I know cold rolled (usually CRA... colled rolled and annealed) has stress in the surface from the rolling. Like a machinist would take off 0.060" So the piece wouldn't get pulled into not-flat, not-square by the residual stress.

Somewhere along the line "mete" said both CRA and HRA are actually hot rolled. There is a difference but I don't know what it is beyond the CRA surface stress. Some say HRA has a lot of decarb but I don't think that is true.

It seems to me the nature of normalizing could de-stress the steel. That is, take the set out of it after cold straightening but it might be a stress relieve cycle after straightening, maybe before and after straightening, would be needed.

The more I think about it. the steel should have equal crystals as delivered. If a person can change the set, like you did with cold rolling, a stress relieve cycle ought to leave the steel flat, with no tendency to revert.

A lot of steels call for a stress relieve after machining (grinding), too. I really don't know why the water jet process would trigger the steel's memory.

I think the sooner in the process the set is dealt with the better.

In your original post you wondered about a kiln dealing with this better. It's not like a person can't use magnets, phase-change colors, and a trained color eyeball to do things like this. It's been done well millions and millinons of times. A calibrated temperature read-out takes a huge amount of work out of the process.

I asked about the carbon content because there is a break in the normalizing temperature between 1070 and 1078 (1625 & 1600)in Heat Treater's Guide.

Mike
 
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