S7 Tempering?

[premiertool]

Is it ok to cool S7 with a fan after removing it from the tempering oven?

 

[Metalguy]

Depends on the shape/section changes, radii, how cold is the air, etc.

I was once very surprised when a long 6" dia. drop-forged hex of 4340 cracked from one end to the other, when I let it air cool after tempering ~1100 F one cold winter night. Pretty deep crack, which scrapped the shaft.

I still don't know why that shaft cracked.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[premiertool]

It is 75 degrees in the shop, its roughly 6x9 inch, 2 inch thick. The piece of S7 has holes drilled into it.

 

[Metalguy]

I think you'll be OK with those conditions.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[EdStainless]

The problem is most common when the part has a lot of variation in section thickness.

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Plymouth Tube

 

[Maui]

Premiertool, why do you want to fan cool these parts? Is the objective to increase your production rates? I don't anticipate any significant problems if you fan cool this part after the second temper is completed, provided that the air flow is relatively uniform over the part (otherwise some amount of unwanted distortion could possibly result, depending on your part geometry and tolerances). Are you giving these two tempers?

Maui

 

[premiertool]

Just trying to speed things up. The pieces weigh about 40 lbs and it takes a couple hours to cool without using a fan We always temper twice. We are shooting for 55RC. Thanks for your opinions. Ken