Coil Spring Tempering

deker · Mar 12, 2006

Hi,

I hardened a blade made from coil spring today and put it in the oven to temper at 425. The thermometer read between 400 and 425 for most of the hour it was in the oven. After letting it cool down, I pulled the blade out and it seemed to be a little past a dark straw to an almost golden color. I think that I should have had the rack up higher from the bottom of the oven or something.

Should I just normalize it a couple of times again and start over or will I likely be OK at a somewhat darker color than I expected to see? As for use, the shape of this knife lends itself very well to skinning, so we'll say that's what it will likely be used for.

Any thoughts?

Thanks!

-d

mete · Mar 12, 2006

Color depends on temperature, alloy surface condition , it's not exact.You might get a thermometer to check the oven controls . 400F should be fine for that application but it's not critical.

deker · Mar 12, 2006

Thanks Mete. My concern I suppose is that the oven rack was closer to the bottom and the thermometer was at the top. I was wondering if maybe the blade might have been hotter since it was closer to the heating element. It's in the freezer for tonight, then I'll temper it (with the rack higher up...) a couple more times and then get to finishing it up!

Thanks,

-d

Raymond Richard · Mar 12, 2006

deker, Most likly the oven will be hotter near the top than at the bottom since the heat will rise. How does the edge feel with a file after the one temper cycly. Most likly the coil spring is 5160 or 9260. 400 might be just alittle high but I bet its still plenty hard.

deker · Mar 13, 2006

Raymond Richard said:
deker, Most likly the oven will be hotter near the top than at the bottom since the heat will rise. How does the edge feel with a file after the one temper cycly. Most likly the coil spring is 5160 or 9260. 400 might be just alittle high but I bet its still plenty hard.

Raymond,

Looks like you're right. A (pretty new admittedly) needle file bites with very little pressure. So I suppose It's time to re-harden and try again? With it being a simple carbon steel do I need to anneal it before heat treating it again or can I just take it back up to critical and quench again?

Thanks,

-d

Bruce Bump · Mar 13, 2006

I have found that different high carbon steels have different colors when coming out of the tempering oven. I say that you should sharpen a section of the the edge and give it the brass rod test. If the edge stays bent it will need to be rehardened. No need to anneal or normalize first.
Some ovens have a wide range of temps depending on how sensitive the thermostat is. You may need to probe your oven with a thermocouple on a good pyrometer to check it. The middle rack is best. My oven burns chicken on the bottom rack and never browns on the top rack.

deker · Mar 13, 2006

Bruce Bump said:
I have found that different high carbon steels have different colors when coming out of the tempering oven. I say that you should sharpen a section of the the edge and give it the brass rod test. If the edge stays bent it will need to be rehardened. No need to anneal or normalize first.
Some ovens have a wide range of temps depending on how sensitive the thermostat is. You may need to probe your oven with a thermocouple on a good pyrometer to check it. The middle rack is best. My oven burns chicken on the bottom rack and never browns on the top rack.

Thanks Bruce,

I was kind of shying away from sharpening it until I had it properly hardened. I wory about warping during a quench of I have to re-harden. How much do I need to thin the edge out to make the brass rod test possible? I'd say that it's at ~ 1/32" right now. Also, what's the recommended brass rod diameter for the test? All I have is some 1/8" pin stock and some 1" round.

Thanks,

-d