View Full Version : Heat treat issues

BD Blades
05-24-2011, 09:47 AM
I am new on this forum and new to knife making. This is the third blade I have forged and thought I would throw this out for some help.

I am working on a blade of 5160 aprox 3/16" at the thickest part of the spine and aprox 5" long. I did a triple quench in mineral oil. Triple tempered in the kitchen oven getting as close to 380F as I could for 2 hours each. I used a seperate digital thermometer with a probe inside the oven to also monitor the temperature. One thing I noticed is when the oven would go though a cycle to maintain temp it would go past 392F (the limit of my digital thermometer).

The result was a blade with a slight gold color to it. This blade got sharper than any blade I have ever made or owned. I now understand scary sharp. I did a flex test by pressing the blade against the edge of the metal top to my table saw. No chipping or rolling, I chopped about halfway through a 2x2 and the blade would still shave hair, but had lost some sharpness. However, it will only get about 35 cuts on 3/4" hemp rope.

I am thinking the oven got too hot and tempered too much. Any thoughts or suggestions

05-24-2011, 09:57 AM
Part of the equation you didn't mention was the blade geometry....that will play a crucial role in how "hard or soft" a given blade should be. My methodology for 5160 is to multiple quench, and temper at 350F-375F, depending on the type of blade (hunter size blades get tempered at 350F, and larger "chopping" blade get tempered at 375F....these temps are directly related to the grind geometry I put on the blade(s).

All too often folks will think about a specific hardness level on a given steel, without taking into consideration the geometry....which is a integral part of the equation.

Long story short, my thought is that if you did a full flat grind, your likely right where you should be, if the grind is a convex, or a combo of flat with convex edge, it's likely a bit soft.

BD Blades
05-24-2011, 10:15 AM
Thanks Ed

I guess this knife would fall into the combo category. I ground it flat up to the point of heat treating it and then did a very slight convex for the final shaping. The blade would fall into the hunter type category. I am making it for utility use for a family member to take to Afganastan if it turns out right. (don't worry he also has a good factory knife as I told him my skills were limited.)