420 vs 420F

[mighoser]

Besides the difference in chemistry and "somewhat reduced formability and corrosion resistance", are there any other reasons for concern with regard to 420F vs 420? I've got a part which has two hardness zones which is prone to failure. I know the free machining grades 303, 303Se, 347Se, etc are banned for flight applications according to MIL-HDBK-1587. Haven't been able to find much literature comparing 420 vs 420F. If there is any risk, especially considering the complex heat treatment of my part, I would rather have increased machining time. Any reason, 420F is better? I saw a vague reference to galling resistance being improved for 420F.

Comments??

 

[MagBen]

except machinability, and maybe cost, 420F has certain nonseizing and nongalling properties in service

 

[EdStainless]

But as with any free machining grade there will be reduced fatigue resistance and increased notch sensitivity.

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P.E. Metallurgy, Plymouth Tube

 

[mighoser]

Anyone have any data on fatigue and/or notch sensitivity comparing these? Any other deleterious properties of 420F?

 

[tbuelna]

For aircraft applications, free-machining alloys like 420F are not normally acceptable. The addition of elements like sulfur or lead to make them more machinable also make them more susceptible to fractures. And fatigue is a major concern with any structural aircraft component.

 

[metengr]

I would contact Carpenter directly if you need specific data for comparison

http://cartech.ides.com/datasheet.aspx?E=70