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Heat Treat First Run

4-24-11
It's Easter Sunday and I am heat treating my first plane blade.  This one is 2 x 6 x 3/16 A2 steel. 

I spent some time online researching the proper method for treating A2.  Most sites had information similar to the method below.

Preheat: 1100/1250F (595/675C), equalize,
1350/1450F (775/790C), equalize.
High Heat: 1750/1800F (995/895C), 30/45 minutes at temperature.
Quench: Air, positive pressure vacuum to 150F (65C).
Temper: 400/1000F (205/540C), hold 2 hours at temperature, air cool. Temper twice.

I will add a 700F preheat and equalize at the beginning of the process, quench in still air in my shop, and use 375F for my temper in the kitchen oven.  To allow full equalization at the this lower temp, I will allow 2 hours per temper.  I am aiming for a Rockwell C 60 to 61.

 

The blade after shaping and sanding to 100 grit.


To prevent oxidation when the steel reaches critical temperature, the blade needs to be wrapped in stainless foil crimped around the edges to be air tight.

I added a strip of paper to each side of the blade before sealing the foil. This trick was recommended by a friend who is a professional knife maker.  The paper will burn before the blade reaches critical temperature, removing any trapped oxygen in the packet.  This helps to reduce surface oxidation on the tool steel.

I used an old pair of sheet metal seaming pliers to make sure each crimp was tight.

The packet crimped and ready for the furnace.


I cut some pieces of firebrick to hold the blade on edge in the furnace.

Safety equipment and other tools ready for action.

Rather than try to handle the lid with one hand and tongs with the other, I decided to use a couple of firebricks on the floor to set the lid aside while I removed the blade from the furnace.  This worked out nicely.


I didn't get any photos while removing the blade from the furnace or cutting the package open.  Here are the remnants of the stainless packet after removal. 

When I removed the packet form the furnace, the foil was puffed out slightly but still tightly sealed and I could see the blade glowing inside.  I held it with tongs edge toward a small fan until it stopped glowing then cut open the foil.

There was not much oxygen trapped in the packet.  The paper strips burned but only slightly.

After removing from the foil packet, I used a straight edge to check the blade for warp.  It was dead flat, so I laid it on a magnetic chuck and threw the switch to keep it flat as it cooled.

After two runs through the kitchen oven for tempering, the blade was ready for the final grind and honing.  I set it up in my Krenov plane and it worked like a charm.  I have since completed the wooden jack plane that this blade was intended for.  It works beautifully and the blade holds an edge very well.

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