Reply by JAAune

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Posted on Hardening metal banding for making putty knives.

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1802 posts in 2341 days

#1 posted 01-19-2013 06:53 AM

What Gunney said above is all useful information and I won’t repeat it. There are a few extra details that I will add though.

The temperature that the steel needs to be heated to is called the transformation temperature. It varies based upon the alloy and carbon content of the steel. One thing that is constant however, is that steel becomes non-magnetic when it reaches that temperature. At this point the steel will be hot enough to glow. The color varies based upon temperature.

So if you have scrap steel of unknown quality, you just have to heat it up until it reaches the non-magnetic state. Heat the steel and pull it out of the heat source and see if the magnet sticks. Remember the color of the steel so you won’t have to use the magnet while doing the actual heat treatment.

One thing that is important is to quench the steel after it’s brought up to temperature. The faster you get it from the fire into the bucket the better. Do not bring it past the transformation temperature and wait for it to drop before dunking. That results in an inferior tool.

Here’s a link that will get you up to speed on heat treatment: Heat treating tool steel

Note the tempering chart near the bottom. For a flexible putty knife somewhere around 45 Rockwell C should do the trick.

In that article, I didn’t see any mention of W-1 steel. It’s water-hardening, inexpensive and if properly hardened and tempered is excellent for woodworking applications. I recommend going with W-1 if you decide to purchase stock for cutting tools in the future. Old truck springs are decent and cheap but for putty knives, it would probably take too long for you to grind them down.

If you want something quick and easy, cheap hand saws obtained from garage sales are a good source of material. The blades should already be hardened just right for a putty knife.

-- See my work at and

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