Need a Little 52100 Help

[Big Chris]

Long story short is I have a knife made by another maker that was sent to me by a good friend and customer that he wants "fixed". There are a lot of small issues with the knife the biggest of which I have come to discover is the knife is bent, about an 1/8" gap. The steel is 52100. I have not worked with this steel before and am not real sure of the temper temperature I should use to straighten. The knife is a large 7.5" blade combat style knife so I am guessing that a 58-59 hardness was the aim. Can someone give me a good temperature to start with for the straightening?
Much Appreciated.

 

[BluntCut MetalWorks]

I straighten 52100 blades quite often

Without knowing how this blade was ht. I think, It probably safe to straighten at around 420-440F without worry about lowering this blade rc below 58.

You already know this, so the following might be useful for some:

1. safe/better to use large pivot bolt (says 1/2" - 3/4") since warp length wise has large curvature radius. Yep, use a right bending radius that exceed Elastic Modulus and into the lower range of plastic deformation.

2. be sure bring the blade to the temperature before tighten the screw to bend the blade opposite direction for actual straightening.

 

[NickWheeler]

Chris- It isn't one of mine is it?!?!? :foot:

In a perfect world, I would say that bluntcut's advise is spot on. Unfortunately, 52100 is one of those steels that seems to have a lot of witch-craft thrown at it, so that makes it a really hard question to answer. IF the blade achieved max hardness with as close to full martensite transformation as possible, then 450F should easily be within a safe tempering range.

However, I know a lot of guys don't achieve that, and only temper their blades at like 350-375F. If the blade you have is one of those, then 450 will make it super soft.

I'm certainly NOT disagreeing with bluntcut--- but it would be safer to start with a lower temp (you can always work up).

 

[Big Chris]

Thankfully Nick, it is not one of yours. I am not skilled enough to work on one of your blades yet nor would I want to.

Bluntcut- thanks for your advice.

Next question, when I pick my straightening temperature how long should I hold it for?

 

[Willie71]

I find 52100 takes longer than simple steels. 1:30 to 2:00 is what I use. It tends to move less than the simpler steels each cycle.

 

[BluntCut MetalWorks]

... when I pick my straightening temperature how long should I hold it for?

My current process/thinking...

Depend on the blade thickness (1/8" thick is my nominal) I hold for about 5 minutes. Check & adjust until the blade is straight. Basically, use heat to shrink the elastic range and expand the plastic deformation range, so the blade plastic/bend-straight.

It's done - IF the blade had been sub-zero or cryo, which imply that the blade was free of RA, therefore no newly converted brittle martensite from RA. Note: If there are RA, conversion can taken place by a) work hardened - straightening compressed & stretched metal; b) straightening temp is higher than tempered temp.

If RA-> Martensite conversion occurred or when in doubt, then treat the straightening as a 1st temper, dip into water, back into oven for a 2nd temper - 1 or 2 hr.

 

[Michael Rader]

Also, just a tip from sorrowful experience: consider making it a regular habit to warm up the pins in your three-pin-press with a torch before putting your hot blade in it to straighten. It took me three broken blades one Winter to figure that one out.