Strain-Age Embrittlement

[jzhaan55]

I have a galvanized zinc rod that is to be bent 20 degrees and I would like to test for the susceptibility for strain-age embrittlement of the final product (since the rod was bent after the hot dip galvanizing process and there will be inherent strain). Since this process will occur naturally at room temperature over a long period of time, I would like to accelerate the process with high heat. What would be a good test method to test for strain age embrittlement? I was thinking about heating the bent samples and then placing in an ice bath and performing a tensile test immediately after. If a brittle fracture is observed, then strain age-embrittlement is a factor. Is this a valid test method or is it something else?

 

[metengr]

Hardness testing should work. Perform hardness testing on the cold formed region of the pieces and a final hardness test within the same region after accelerated aging.

 

[jzhaan55]

The sample is a threaded rod and hardness testing will be an issue because of the case hardening. I could cut the rods in half at the bend site and just compare core hardness values. Do hardness values directly relate to the strain-age embrittlement process. In other words, if the strained area (the bend) is susceptible to embrittlement in the future, will it have a greater hardness value at the bent area compared to the unaccelerated samples (or will it be less)? What would be a good procedure to test this. Also, is there any literature that i could use to support this test method? thanks a lot!

-Jessica

 

[jzhaan55]

also if i have, say, a653 steel and i want to know the ductile to brittle transition temp, is there a good reference to look this up or do i need to perform the testing on my own?

 

[swall]

If it is for a real project, you must have the testing done for the particular heat of steel.

 

[mrfailure]

You should not have to worry about strain age embrittlement because you cold work the rod after galvanizing. This embrittlement usually happens if you galvanize after bending. Tests for such embrittlement are listed in ASTM A143. It sounds like a simple reverse bend test on your bend would work if there were a need for such testing.

Aaron Tanzer

http://www.lehightesting.com