Banding & Alloy Segregation

[Magnut]

My company inspects 17-4 & 15-5 PH steel. We ofter find a Banding Condition when performing magnetic particle inspection. Following metallography, we find that the Banding may be accompanied with non-metallic inclusions and/or ferrite stringers. There is minimal information regarding the characterization of the three discontinuities nor the effect they have on the mechanical properties of the material. Are there any studies that discuss:
1. The effects and characterization of Banding on PH steels?
2. The effects and characterization of ferrite stringers on PH steels?
3. The effects and characterization of non-metallic inclusions on PH steels?
Any and all info is appreciated.

 

[mcguire]

17-4, as originally developed, was recognized to have a two phase structure, martensite with about 10% ferrite. Later alloys,such as 15-5, 13-8 and custom 450, were developed to address this trait which gives poor through thickness toughness. The non-metallic inclusions should be NbC and, if that's the case, are not injurious.
It's easier to get away from the ferrite with 15-5, but the specific composition,even within specification, can cause some to exist.
You should verify that your main non-martensitic phase isn't simply retained austenite or reverted austenite from the aging heat treatment. Austenite can be eliminated by fine tuning your heat treat parameters, but you may not even need to eliminate it. It's not intrinsically bad.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[Magnut]

Thanks Mike. We are a metal finishing operation and do not perform the heat treat. Our effort is focused on inspection and finishing (cad, nickel....). I appreciate your quick response.
Regards,
Bob Potter