Should I "Soft back draw?"

[Patrice Lemée]

Well I think that is what it is called. I see many post about heat treat and they say first step is hardening and then temper to reduce hardness. Doesn't that leaves the spine of the blade to brittle? I've read about the edge quench in WG's book. But here I see many people using the full quench, point first.



Pad

 

[silver_pilate]

I think most use the full quench because you acheive a more uniform composition in the steel, especially in higher alloy steels. A full quench will prevent the formation of pearlite or other unwanted structures at the quench line that could potentially weaken the blade. Again, this is my understanding, and maybe some of the more knowledgable people on this forum can give more details.

I full quench, temper, and then draw back the temper of the handle and spine of the knife with a torch if I feel I need a softer spine/handle. Keep the edge under water so it doesn't get too warm. It's basically a differential temper as opposed to a form of differential quenching (i.e. edge quench). In a smaller knife used for cutting chores or light work, drawing the temper back on the spine/handle isn't really even necessary. I usually do it if I am making a heavier purpose knife/camp knife with the idea that a softer handle/spine may increase the impact tolerance of the steel while still maintaining a hardened cutting edge.

--nathan

 

[Patrice Lemée]

Thanks nathan for shedding light on this for me. I like the keeping the edge in water trick. It's hard otherwise not to get it hot, well for me anyway.

Pad

 

[silver_pilate]

No problem, Pad. I've also heard people using cold potatoes to prevent overheating. Just sink the edge into a cold potato, though you're likely to get discoloration in carbon steels. If so, just sand it away. Be especially careful towards the tip as the thin steel will transfer heat faster. I usually only torch temper the spine about half way down the length of the blade and only apply heat to the spine and let the color run down the width of the blade. Control the heat by making quick, fast passes once the steel has reached temperature where light straw begins to form, and watch the colors. Shoot for just past purple, and be careful not to let the color creep too close to the cutting edge.

--nathan