Heating time.

[Karst]

Hi. I came with question. I heard that you should heat knife for 10 minutes + 1 minute per 1 millimiter, so when I am heat treating a 4mm knife i should keep him in oven for around 14 minutes. But what if I am heat treating 5 knives and every one of them is 4mm thick. Am i supossed to keep them 10 + 5x4= 30minutes? Sorry for my english by the way

 

[Natlek]

No , all of them 14 minutes total time ......... Which steel is in question ?
PS . 5 knives inside oven will drop temperature down , take that into consideration .Start counting after temperature come back to set point ...

 

[Stacy E. Apelt - Bladesmith]

I have never heard of that time rule.

Normally, a blade is soaked for about 5 minutes to 10 minutes. Thickness makes no real difference in the thickness of knife blades. In industry where pieces are inches thick, it matters. Some steels need very little soak time and can be quenched after 1 minute of even heating ( 1084, 1075). Other steels have more alloying to be distributed and take up to 10 minutes (O-1, 1095, 15N20,52100)

As Natlek pointed out, it is the time at the target temperature that you count. If you open the HT oven and put the knife blades in, the temperature will drop. You watch the readout and when it returns to the target temperature start the timing count.

If doing HT in a forge, all the timing rules are pretty much useless. You get it to the right temperature by observing the color, try to hold it there for a minute or so without overheating, and quench. It is pretty much impossible to hold a knife blade for 10 minutes in a forge without serious overheating.

 

[TheEdge01]

I have never heard of that time rule.

Normally, a blade is soaked for about 5 minutes to 10 minutes. Thickness makes no real difference in the thickness of knife blades. In industry where pieces are inches thick, it matters. Some steels need very little soak time and can be quenched after 1 minute of even heating ( 1084, 1075). Other steels have more alloying to be distributed and take up to 10 minutes (O-1, 1095, 15N20,52100)

As Natlek pointed out, it is the time at the target temperature that you count. If you open the HT oven and put the knife blades in, the temperature will drop. You watch the readout and when it returns to the target temperature start the timing count.

If doing HT in a forge, all the timing rules are pretty much useless. You get it to the right temperature by observing the color, try to hold it there for a minute or so without overheating, and quench. It is pretty much impossible to hold a knife blade for 10 minutes in a forge without serious overheating.

This wasn’t addressed to me but it still answered a question I had. Thanks

 

[Scaniaman]

I have the results I want when letting the steel (AEB-L, Rwl-34, 14C28N) soak for 10-12 min after return to set point. That is after temp drop (and overshoot second to that) from opening the kiln. It usually takes up to 5 min for the kiln to go through that process after inserting the blade.

 

[Larrin]

Thickness matters even with the relatively thin cross-sections that are seen in knives. For example, see the recommended holding times vs thickness provided by Sandvik for conveyor belt furnaces where the holding time has to be tightly controlled. https://www.materials.sandvik/en-us...ning-programs/sandvik-14c28n-piece-hardening/

I prefer to recommend some minimum hold time that is a bit longer at a little bit lower temperature so that it is less sensitive to thickness differences. Metallurgists and some datasheets will recommend starting the hold time after the furnace returns to temperature but this is a useful simplification not an assumption that the piece heats through infinitely fast.