Temper Tests

I've read the tables showing what kinds of tools get tempered to what colors. And I've tempered some knives and other tools that seemed to come out okay. But I didn't feel like I really knew what temper was best for different tools. So I decided to experiment. I tried to standardize everything as much as possible, but this is a "quick and dirty" test, not a rigorous one. Still, I thought the results might be interesting.

I took some 1/4" rod from a coil spring (high carbon steel) and made some small tanged points. Roughly 1" of point and 1" of tang. I annealed them, and ground/filed/sanded just enough to get a fairly smooth, flat surface. Heated to red, quenched in oil, sanded lightly, and tempered. I tried to get a range of temper colors.

1 - quenched, not tempered at all
2 - tempered until it just barely starts to darken
3 - tempered to light yellow/straw
4 - dark yellow/straw (tip started turning purple)
5 - purple
6 - blue

I drilled holes in small pieces of scrap wood to make basic handles for all of these.

My initial idea was to stab each blade into a piece of wood and then push to one side to see if the tip broke or bent. Using a scrap piece of maple, it was hard to stab them very far in by hand, and they just pried slivers out of the wood. So I switched to using a mallet to drive the blades deeper into the wood and then pushing to one side.

With the blades driven deeper into the wood, #3 and #4 bent slightly, the rest were unaffected. I tried again, driving in a bit farther, and using a hardwood board that was harder than the maple. With this test, #1 and #2 snapped off, #4 bend a little and then snapped, and #6 bent (#5 was a bit thicker than the others). (I lost the broken tips from #2 and #4)


Results: There was a trend to being softer with higher temper temperature, but blade thickness also made a big difference. Also, all the blades were pretty sturdy and needed quite a bit of force to break or bend (even the one that was quenched and not tempered). Any of #3-#6 would have made a decent blade as long as the tip wasn't made too thin. Even a blade from #2 would have been fine for light use, as long as it wasn't used with much prying force.

I would like to do a more rigorous and precise test, and also look into the effect of different quench mediums, but for now I feel like I got a good idea of the effects of different amounts of tempering.

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