Heat treating a rasp knife went wrong

S

Steinmann

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Jan 12, 2010
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Hello everyone. I shaped the knife's pattern from an old "Sheffield Made in England" file, and then heated it to cherry red until not magnetic. Then dipped it in warmed vegetable oil (70 Celsius). It came out black but could not pass the "gliding file" test: I took a new file but it bit instead of gliding on the metal. So now I'm thinking that I can't proceed to the annealing-in-the-oven step. What am I doing wrong here? Shell I repeat the procedure another 2 times? Shell I stay in cherry red for let's say 1/2 an hour? Maybe quench in water? If water - should I pre heat it?
Any tip and help will be much appreciated.
Thank you – Michael.
 
Get some known steel. This may not be the easiest task, given that you're in Israel, but I'm sure you'll be able to find some steel locally, though it's unlikely you'll have much selection.
 
Cherry red is a very vague term with no real numbers attached. There are so many potential issues that could be at work here that troubleshooting your process becomes a chicken/egg scenario. Contrary to what someone else told you your rasp could be a wide variety of steels including case hardened mild. Your cherry red may vary between 1350 f and 1750 f Your vegetable oil may be too slow for your steel. You may be file testing a decarb layer with good steel under it

-Page
 
מִיכָאֵל‎,
As page said, there is no way to know if the problem is the metal ( most likely) or the HT.

There may be a language barrier in your question to some extent,too. -
Is this a file or a rasp? What was it used for originally?
When you say "....dipped in warm canola oil...." do you mean immersed and held there until cooled off?
How quickly did you get the blade into the oil?
The HT step when the knife is held at 205-230C in an oven for two hours is called tempering ( annealing is a softening step).

שָׁלוֹם
 
A rasp is very thick compared to a file and may not have been cooled fully.

What is the size and volume of the quench tank.

It seems that many try to cheap out on this part and use too little to properly cool the part.
Aim for a minimum of 4 litres, 20 litres of oil is common.

Having said that, that oil may not cool fast enough.
 
bladsmth said:
מִיכָאֵל‎,
As page said, there is no way to know if the problem is the metal ( most likely) or the HT.

There may be a language barrier in your question to some extent,too. -
Is this a file or a rasp? What was it used for originally? sorry, it is a metal file.
When you say "....dipped in warm canola oil...." do you mean immersed and held there until cooled off? yes.
How quickly did you get the blade into the oil? dipped it into the oil quickly, tip first.
The HT step when the knife is held at 205-230C in an oven for two hours is called tempering ( annealing is a softening step). ok - thanks.

שָׁלוֹם
Click to expand...

As it is an old file and UK made, I was thinking the steel is carbon.
Shell I water quench?

תודה
 
(Shall ,not shell - as in גם זה יעבור)

I would try a brine quench and see if that works better.

Heat to 815°C and hold for 5 minutes.
Quench in a gallon or two of brine ( one gallon water to 3/4" salt). The brine should be about 35-40°C.
Test and if hard, temper at 225°C for two hours twice.


If it does not seem hard when file tested, grind a bit off the edge and test again. Sometimes the decarb can be soft and thick enough to appear as the blade did not harden.
If it does not harden with a brine quench, the file is not hardenable.

בקשה
 
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