"Non magnetic" for plain carbon steels.

[Alarion]

It seems something I believed true is not.
I thought that, for low alloy carbon steels like the 10xx series, 5160 and such (not SS and high alloy tool steels), heating to non magnetic was a fool proof way to hit austenizing temp.
But I've read on the forum hints that this may not be the case.
That the austenizing temperature doesn't match their Curie point.
Is this true and, if so, how can one compensate?
Up to now all the knives I've heat treated has been HTd this way, and seem to be pretty hard and hold a good sharp edge.
But lacking a hardness tester I wonder if I'm getting it right, or if I'm just barely there and I'm missing most of the HRc potential of the steels I use: C70 (much like 1075), K720, used Nicholson files and, right now, a Mitsubishi coil spring from the suspension of my Evo IX.

 

[mete]

The Curie point is 1414 F [not 1440 F] but the typical austenitizing temperature is 75 - 100 F above the Curie temperature !! It's a 'quesstimate' which you might deal with by experimenting .The proper way of course is to get a proper furnace which controls temperature .

 

[LRB]

Mete', I thought the Curie point was 1414° F, or is that a typo?

 

[mete]

Thanks for catching that. It's a problem when my brain is stuffed with pollen !

 

[sunshadow]

the reason the nonmagnetic "seems" to work is that most people overshoot

-page

 

[Kevin R. Cashen]

Page has it, by the time you get an entire blade to nonmagnetic in a forge the edge has most likely overshot to around 1475F or better. This makes the temp right if that is all you overshoot by!

 

[deker]

I'm right there with Page and Kevin. Now, what I did before I had the Evenheat (or what I still do when I'm teaching a class where all we have is coal forges), is to watch for decalesence/recalesence. It's a much more accurate way to get an indication of proper temps when you don't have calibrated equipment handy.

-d