How do i know if I have a good heat treat?

[verndahl]

So, my goal in learning blacksmithing was never to become a knife maker. Now here i am with some car spring (I made a Japanese leather knife out of a file for my son) and i've already made a barbecue knife and am working on another small one using up some scrap. My goal is to be able to make functional blades of any sort.
So far by blades have been "good enough". I would like to be able to heat treat and temper with the limited tools i have using using old time techniques(no fancy ovens etc.) just doesn't make sense at this point investing much money. Now i'm not necassarily looking for how too tips (cuz i think i have that down), i would just like tips on knowing if my heat treat is the best it can be.
So far i've been using a loupe to examine my edge after honing/using just like i do when i hone a razor. My heat treat consists of going just past non magnetic (might try salt next time as i hear it melts at about 1475) quenching in oil (checking with a file) then tempering to a straw color.
How would you check the efficacy of the job?

 

[Bruno]

Ok if you heat treat, non magnetic is actually not hot enough. A bit above non magnetic, you will see the blade suddenly getting brighter. That brightness is the transformation you are looking for. So that's an important indication.

After tempering, touch the steel to your sander to clean off scale and decarb, and then use a small file to see if the file skates the steel. If it does, then you have a successful heat treatment. That is what I do when I want to be sure.

That said, my quick check is running an 80 or 120 grit belt at low speed, and touching the edge to the belt. If the steel is hard, it will throw a shower of sparks, where it will not do that if the steel is still soft.

 

[verndahl]

would there be more or less sparks (compared to anealed steel) if it is hard? (cuz i do get sparks when it is anealed) I only have a one speed 32 inch grinder).

 

[Bruno]

Much more. Especially at low speed. A slow moving belt will still spark a bit but hardened steel will really throw a shower.
There is difference between how different alloys behave. A good test for you is to try a couple of pieces side by side, soft and hard.
That will quickly show the difference. Also, if the steel is hard, touching it to your belt will throw sparks without eating into the steel. If it is soft you will quickly see steel being eaten

 

[Mike Blue]

Yes. Look up "spark testing" on the net. It's a good rabbit hole for a home shop smith with a limited tool set.

 

[verndahl]

Another heat treating question, as i aim to get the blade to the right temp(evenly along the whole blade) does it hurt if the blade temp fluxuates during the process as long as it eventually all gets the same color/temp?
And what happens if the temp is higher than 1500?
Keep in mind that i'm aiming for a functional blade ( good enough)at this point in my skill level!

 

[Bruno]

No, that doesn't matter at all with plain steels. As long as you get there at an even temp, the rest is not important.
And while we could indeed argue about ideal temperature, going above 1500 is generally not an issue. It depends on what steel you work with.
Yes, it will matter to a degree, but not enough to worry about as long as it is not wildly more.