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Stress due to bending?

Stress due to bending?

Stress due to bending?

(OP)
I have a product made out of 17-4 PH. We centerless grind the surface down to the O.D. of the part and heat treat is as a rod. After this, we get the hardness up to about 37±4 RC and make three bends to it. We havent had any problems until recently. The material is starting to crack and fold. We are thinking it was the material to begin with, so we take a couple of samples, and clean them and bend them. Nothing happens. No cracks, no splinters, nothing. So now I'm at the point of what do I try next.
NOTE: There were two heats of material due to availability. 1) was a Ø.130 material c'grinded to a Ø.128
2) was a Ø.140 material c'grinded to a Ø.128
Could the aditional .010 inches of material harden the material enough that it when it went to Heat treat, it was made harder than expected and made more brittle.
ALSO, when we sent the 1st batch to Heat treat and came back it had a RC of 35-37 and when we got it back the 2nd time, it came back at the hire end, round 38-40.

Question: Could the additional C'grinding have made the material harder and more brittle that when it bends it cracks? Or could it have been in Heat Treat where something happened, where it wasn't quenched rapidly enough to get full austenite? Please help, I'm curious as to what to look into next. I also want to pot and section a couple of sample to see its structure and see what happened. Would this be also a good idea?

RE: Stress due to bending?

Come back with a little more information.

What condition was the material supplied?
What is your heat treat procedure?
what is the desired hardness
What is the angle of the bends?
How much metal are you removing by grinding?

17-4 PH can and most of the time does have quite a wide and variable hardness range when heat treating, so you have to careful in using the hardness as parameter.  It does vary between heats and producers.

RE: Stress due to bending?

(OP)
What condition was the material supplied?
-Customter: 17-4 H1050, AMS5643, the customer print requires H1050, but thats after heat treat. Bar Ø.140 for one order Ø.130 for the other.

What is your heat treat procedure?
-We have none. We send it out to be processed. I wish I knew the ramping and cycle times to determine myself whether or not it reach adequate temperature and how it was cooled.

what is the desired hardness?
-RC37±4

What is the angle of the bends?
3 bends: 90° , full radius, and 30° bend.
90°: R.14, full radius: R1.10, 30°: R.25

How much metal are you removing by grinding?
-From my statement earlier: with the .130 material: .002
with the .140 :.012 .

RE: Stress due to bending?

If the material was not reannealed as the first step of heat treatment then the grinding could be the problem.  After all look at the mechanicals for hte CH condition.
Mount a sample and polish the cross section.  Take microhardnesses.  You may see very high near surface values for the problem material.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm

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