To temper or not to temper?

[fulmonty]

Hi there everybody!

I'm new to the forum, and I already have a question

I've made a bunch of lockpicks at home and a couple of tension wrenches. I had the (bad?) idea of tempering them to increase durability (I used a ligher and some water, nothing fancy).

Well, right after the temper, I wanted to test my new babies. I put the tension wrench in an old lock of mine, add tension... And then BAM! The tension wrench broke, shooting a piece of metal a few inches from my right eye.
I was shocked, also because I never expected it.
So now I have to work again for a tension wrench...

Ok, nice story, my question is: should I temper tension wrenches or leave them as they are?

Thanks and c ya soon!

[raimundo]

tempering is very tricky stuff. you have to know the metalurgy of the part. Generally speaking metal is hardened with heat and quenching, and hardened metal is 'tempered' by soaking it in a lower heat for a period of time, this 'draws' out the brittle hardness and leaves the metal with desired properties like springyness.

that said, I sometimes set a bend in metal after cold bending by holding a bic at the bend for 30 seconds, which on a thin pickshaft is enough to blue the surface. This erases the 'memory' in the metal that makes it want to unbend.
Color is important on these small pieces, straw yellow is first, then blue on the metal surface. More heat will cause the metal to glow dull red (blacksmiths work in dark rooms to see this.) then cherry red, meltdown and white hot.
If you go as far as dull red, you are probably going too far.

[raimundo]

I forgot to add, if the metal is good, I usually cold work it, and don't bother with the crapshoot of tempering. If you have to temper, expect some to be defects, or just get good metal to replace what you have.

[ratyoke]

Sounds like you just hardened it if it broke like that. If you heated red hot it then quenched it in water that would only harden it. How you harden and temper steel depends on the alloy.

[ToolyMcgee]

If you are working with stainless steel and manage to ruin the temper there is no hope of returning it with a bic, or even a torch for that matter. Not, that it can't be retempered, just not as steel with the same properties. To vague? Tempering to just right hardness can be a royal pain.