Is preheating really necessary for D2

J

jlmetcalf

Joined
Jul 5, 2005
Messages
75
I have an old Hupert furnnace that takes about an hour to ramp up to 1875 from 1400. As a result, I do not normally do a preheat; just wrap the d2 blades and stick them in at 1875, soak for 20 min and quench.

If I remember correctly from class 35 years ago, the preheat helps deal with possible stresses caused by the volumetric change that occurs when the transformation line is crossed.

However, experience is much more valuable than theory so I thought I would toss these questions out:

1. Could grain growth during the hour+ time required to reach final temp plus the 20 min soak be an issue?

2. As blades are thin and symmeterical, does a preheat really do that much good?

Thx
 
Grain growth is not a problem [that's far more of a problem with excessive temperature !]. Preheat is usually not a problem with small cross sections.
 
You might want to consider upping your soak time a bit, and allow a bit of time for the blade to reach furnace temp.
 
Thanks for the replies. I guess the question I'm really asking is:

As it takes my furnace about 90 minutes to ramp up from the preheat to austenizing (1850) should I just forget the preheat or is this time not really excessive to the point where it could cause problems (i.e. grain growth)?

Most references I could find say to heat slowly from the preheat temp to the austenizing temp. No one ever seems to define "slowly". 15 min, 1 hour, 2hours?

Thx,

Jim
 
Jim, we heat treat D-2 almost daily at work and we usually just let the furnace come up to temp (1850) with the part inside and let it soak for the required amount of time for the size of the block. That's not the outlined "correct" procedure, but over the years we have not had any problems (loss of hardness, excessive loss of carbon). Just don't wait long after it cools to draw it to the desired Rc. Joe
 
the only thing that might happen is more decarb, time alone doesnt cause grain growth(or at least a negligible amount of it) look at this thread.
 
Jim: Leave your blades in the packet on top of the furnace while it preheats, so they are warm. Put them in when it reaches temperature. Be sure to allow enough soak time. Grain growth is more from temperature than time-You can soak D2 a good while at temp-I'd recommend 30 minutes as a minimum.
 
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