D2 Soak Time
- Thread starter Randy Wirtz
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- Dec 21, 2006
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Like Larrin just mentioned above, usually it is stated something like "Soak time is 30 minutes for the first inch of thickness, then add 1 minute per "X" amount of additional thickness". I take that to mean if the piece is 1/16" or 1" thick, the minimum soak time is 30 minutes. If the piece is thicker than 1", you add "X" amount of time per "y" amount of thickness.
D2 has a lot of carbon and a health dose of chromium, which takes either time (or temperature) to dissolve the carbides so that enough carbon is available to get the blade to harden. That time is well established by the industry, and doesn't matter if the piece is a few millimeters thick or 1/2" thick. It DOES matter if the piece is thicker than 1". Shortening the minimum recommended time window will more than likely not dissolve enough carbides, likely resulting in less than satisfactory post-quench hardness.
Nathan has done a LOT of work with D2. I would heed his advice.
D2 has a lot of carbon and a health dose of chromium, which takes either time (or temperature) to dissolve the carbides so that enough carbon is available to get the blade to harden. That time is well established by the industry, and doesn't matter if the piece is a few millimeters thick or 1/2" thick. It DOES matter if the piece is thicker than 1". Shortening the minimum recommended time window will more than likely not dissolve enough carbides, likely resulting in less than satisfactory post-quench hardness.
Nathan has done a LOT of work with D2. I would heed his advice.
Some years back, on HFB forum, Roman Landes wrote a very good post about oven time and ... here it is the full quote:
"1st - We look at the time for the part to get to the desired temperature (the ramp time)
2nd - For larger parts grater approx. 5mm in diameter, there is the need to add some more time to that. It is the time the part needs, so that the heat is evenly distributed between surface layer and core (equalizing time)
3rd - Soak time technically is netto time at the desired temperature (soak time)
So we have a need formula to summing up
Oven time = ramp time + equalizing time + soak time
While 1 and 2 are mostly dependend on the heating device, heating strategy, the geometrical shape and the heat conductivity of both the transfer medium (Air, Salt, Nitrogen, etc.) and material used in the part and thus somewhat given, 3 is dedicated to the chemical composition and the given metallurgical structure (e.g. spheroidized carbide, perlite, etc.), thus ruling the austenitization of a martensitic steel.
Many people mix things up and most of the time it is not exactly described in the literature too. So it can happen that people say soak time and actually mean oven time and this may be misleading.
Just to give you a few examples about soak times (3mm cross section medium recommended temperature)
plain 1% carbon steel may have less than 3 min until negative effects like grain growth and retain austenit will form
low alloy tool steel may have around 5-7min,
high alloy stainless (440c type) 15-20 min (RA can not be avoided!)
high alloy stainless (AEB-L type) 5-8 min (RA can not be avoided!)
high speed steel less than a minute since their average austemp usually is extremely high (1200°C+) (RA can not be avoided!)
Another important variable is the heating speed itself.
As soon AC1 is reached the ausgrain starts to grow.
So austenizing time will be different to the soak time definition as stated before.
The time between crossing AC1 and start of soak time has to be taken into account as well.
The time and temperature integrate up to a total volume of heat induced into the part creating a massive phase transformation from ferrite/perlite to austenit/carbide or even austenite only within this time period.
The shallower the ramp of the heating to desired austemp, the more happens in terms of saturation of the reaction prior to the initial soak time.
Means the more shallow ramps on has the less defined the status in the steel will be.
And the more likely are unwanted effects like grain growth and RA.
Steepness of the heating in this time will either cut soak times or the starting point of the soak time deteriorates in the ramp.
This is one major aspect why salt bath and induction heating are paramount to regular clines of even modern vacuum furnaces."
I hope this bring some light over the oven time and how to estimate it.
"1st - We look at the time for the part to get to the desired temperature (the ramp time)
2nd - For larger parts grater approx. 5mm in diameter, there is the need to add some more time to that. It is the time the part needs, so that the heat is evenly distributed between surface layer and core (equalizing time)
3rd - Soak time technically is netto time at the desired temperature (soak time)
So we have a need formula to summing up
Oven time = ramp time + equalizing time + soak time
While 1 and 2 are mostly dependend on the heating device, heating strategy, the geometrical shape and the heat conductivity of both the transfer medium (Air, Salt, Nitrogen, etc.) and material used in the part and thus somewhat given, 3 is dedicated to the chemical composition and the given metallurgical structure (e.g. spheroidized carbide, perlite, etc.), thus ruling the austenitization of a martensitic steel.
Many people mix things up and most of the time it is not exactly described in the literature too. So it can happen that people say soak time and actually mean oven time and this may be misleading.
Just to give you a few examples about soak times (3mm cross section medium recommended temperature)
plain 1% carbon steel may have less than 3 min until negative effects like grain growth and retain austenit will form
low alloy tool steel may have around 5-7min,
high alloy stainless (440c type) 15-20 min (RA can not be avoided!)
high alloy stainless (AEB-L type) 5-8 min (RA can not be avoided!)
high speed steel less than a minute since their average austemp usually is extremely high (1200°C+) (RA can not be avoided!)
Another important variable is the heating speed itself.
As soon AC1 is reached the ausgrain starts to grow.
So austenizing time will be different to the soak time definition as stated before.
The time between crossing AC1 and start of soak time has to be taken into account as well.
The time and temperature integrate up to a total volume of heat induced into the part creating a massive phase transformation from ferrite/perlite to austenit/carbide or even austenite only within this time period.
The shallower the ramp of the heating to desired austemp, the more happens in terms of saturation of the reaction prior to the initial soak time.
Means the more shallow ramps on has the less defined the status in the steel will be.
And the more likely are unwanted effects like grain growth and RA.
Steepness of the heating in this time will either cut soak times or the starting point of the soak time deteriorates in the ramp.
This is one major aspect why salt bath and induction heating are paramount to regular clines of even modern vacuum furnaces."
I hope this bring some light over the oven time and how to estimate it.