.622 1018 material breaking

[Brokenwindow]

I'm currently investigating root cause for problem with material cracking. It's Ø .622-1018 material with a ksi of 85000-105000. The cracks are happening in the inside (compression) of the bend. The wire is ran through a cnc bender and is bent around a .625 roller. We are seeing about a 3-6% crack rate.

KSI/machine speed/roller pressure/etc doesn't seem to be a factor.

We have ran DOE's through our bender and are currently looking at our material suppler for assistance. All material is with astm a510 standards.

Basically I'm looking for ideas/directions to investigate.

Thanks in advance..

 

[TVP]

You need to have a proper metallurgical analysis performed. Evaluate grain size, inclusions, fractography including scanning electron microscopy.

 

[metengr]

I would agree with the advice given above.

 

[Brokenwindow]

We did have a metallurgical test performed at the beginning. It was suggested to use a spherodized annealed material. Finding something that doesn't crack is not the issue. The customer wants a root cause regardless of the fact we can use a diff material without cracking.

I need to find root cause. We have looked at chrome and nickel as being culprits, but cannot get material with these variables far enough on both sides of the spectrum to run tests.

Thanks for the replies.. I appreciate the help.

 

[mrfailure]

I'd particularly look at microstructure. Are there multiple parallel cracks on the inside radius? Do you see microstructural transformation at this surface? How does microhardness at this surface compare to the core and outside bend? Can damage observed occur from inconsistencies in the bend process such as lubrication?

 

[Brokenwindow]

We have never seen parallel cracks. all found would have 1 cracks ranging from barely visible to 80% of the wire width. This part is ran on a cnc bender with pretty tight specifications. You might see the angle vary maybe .25° in either direction. I would have to grab the lab report for the micro structure overview. I will post more when I get this.

Thanks for the replies.. they are all welcome.