TTT for AMS 6417 (300M) 1

[metman]

300M is a modified 4340
aka:
ASTM A579 (32)??
ASTM A646 (300ML-8)
MIL S-8844 (3)
MIL S-8844 Class 2
UNS K44220
AMS 6417

Above listings were found on metalsonline.com.

UNS number not listed on matweb.com.

Searched using 300M and then AMS 6417 and AMS6417 on asminternational.org/hbo with no results at all for this material and I am subscribed to ASM/hbo. hbo = HandBooks Online.

We have had some parts heat Treated to 270-280 ksi per AMS 2759/2 with exception of gas quench in vacuum furnace. There is probably not any problem as the microhardness test for surface contamination shows good readings. However, testing of separate coupons does not represent the mass effect of the actual part in quenching. I am more curious than concerned even though these are main landing gear parts of an airplane because we can use a portion of the part to be removed after heat treat to verify hardness.

anyone know where I can obtain TTT for 300M. Jesus is The TRUTH

 

[TVP]

metman,

I never thought I would say this, but for once, the ASM HANDBOOK series is pretty much useless. I am only saying that with respect to this specific area of Time-Temperature-Transformation (TTT) curves, though. Apparently this topic is covered in only a cursory manner, with no real examples given in either Volume 1 or Volume 4.

So, where to go for this data? The first place I would recommend would be the ASM publication Atlas of Time-Temperature Diagrams for Irons and Steels. This reference book contains 1839 diagrams on 804 pages, which has to make this the best reference available. $168.00 is the latest price that I have listed from ASM, so it is kind of pricey if you only need the one curve. You might be able to find this at a good university engineering library, or ask around to some heat treaters to see if they would let you borrow it.

My other recommendation would be the steel mill that would be producing this material for you. The only supplier that I know who produces this alloy in the U.S. is Timken Latrobe Steel. I checked their website, but did not find a TTT curve, just the usual mechanical properties, heat treat info, etc. You can try contacting them to see if they would provide a curve for you:

http://www.timken.com/timken_ols/mail/contact.asp

FYI, 300M is discussed in both Volume 1 and Volume 4, there just isn't a TTT curve included in these books. The specific articles are Ultrahigh-Strength Steels in Volume 1 (begins on page 430) and Heat Treating of Ultrahigh-Strength Steels in Volume 4 (page 207). The reason for the vacuum treatment is because 300M is quite prone to decarburization, due to the very high silicon content. It is a very deep hardening steel, and oil quenching is cited as being sufficient for producing martensite. I have a TTT curve for 4340, and it shows that it takes 20 seconds to hit the nose of the bainite curve. It seems unlikely that you would have any problems with transformation products, but I guess that landing gear parts due tend to have thick sections.

As an aside, I'm wondering why you are choosing 300M for this application? I'm sure that you are aware of 300M being sensitive to stress corrosion cracking, and that high fracture toughness alloys like Aermet 100 are now being used, due their increased resistance to SCC. My guess is that cost is the overriding concern, so I would just caution you that corrosion protection needs to be adequately addressed. Good luck.

 

[metman]

TVP,
Thanks loads. I have sent a request to Timken via the link you provided.

What did you use for key word(s)in your search on ASM that led to Vol. 1 and 4? Or did you simply go to those volumes on the Volume tree? I am very curious why my search did not lead there. To reiterate, I

Searched using 300M and then AMS 6417 and AMS6417 on asminternational.org/hbo with no results at all for this material and I am subscribed to ASM/hbo. hbo = HandBooks Online.

No I was not aware of the SCC problem with 300M. My recommendation was maraging steel but the cost is approx ten times that of 300M which is used in some landing gear app's.

We are using Cad plating. I was not consulted about this but will research its effectiveness for this app and will be interested in your comments and others on this choice.
What is your recommendation for corrosion protection if we stay with 300M. I expect this aircraft will see service near seawater although we will later have a float plane and amphibious version which surely will be exposed to that environment but of course will not have this landing gear.

Also I will look at Aermet 100. Is the cost of Aermet 100 prohibitve like Maraging Steel? I will expect to find this alloy under the same ASM/hbo sections as 300M. Please advise if not there.

Thanks again Jesus is The TRUTH

 

[TVP]

1. I did not perform a keyword search to find the articles. I am very familiar with the sections on ultrahigh-strength steels, so I already knew where to find the information. I realize that this does not help you with regards to the keyword search capabilities of the ASM site...

2. The cost of Aermet 100 is likely to be even more expensive than maraging steels, due to a number a reasons: it is a proprietary alloy of Carpenter Technology, it contains a high proportion of expensive alloying elements like cobalt and nickel, and it is produced using only the highest quality melting and production technology. For more information, I recommend you visit the Carpenter website:

http://www.cartech.com

. You must be a registered user to view all of the site, but there is no cost involved, and it is one of the best websites ever created with respect to metallurgical content. I highly recommend you acquaint yourself with high-quality companies like Carpenter, Timken Latrobe, Allegheny Ludlum, Special Metals, etc.

3. I am not really qualified to give you specific recommendations regarding corrosion protection for aircraft applications. My background is mostly automotive. What I can tell you is that cadmium plating does not provide outstanding corrosion protection-- in standardized salt spray testing (ASTM B 117) red rust starts to form in ~ 100 hours. And it is precisely the combination of 300M and cadmium plating in landing applications that has provided the background for SCC problems. You should be able to find more information on this using the ASM HANDBOOKS. Try looking around in the Corrosion volume.

I am not in the office today, so I don't have my reference materials handy, otherwise I would probably offer you some additional information regarding materials and corrosion protection. When I get back, I will peruse my collection and see what I come up with. In the meantime, you may want to post a question to the aerospace or aircraft forums here at eng-tips. Kenneth and wktaylor are both quite knowledgeable in this area, and most likely could offer you some valuable information and insights. Best of luck.

 

[metman]

TVP,

Steven Prock, Pricipal Metallurgist for high strength and CRES at Timken-Latrobe is faxing me his hard copy of TTT.

Yes I am familiar with Cartech via magnetic alloys etc. and timken via bearing app's. But was not aware of the Latrobe merger until you pointed me there. Is Special Metals the same people who make AR400 etc as part of their product line?

I will take some time to peruse the corrosion volume and also open my text by Uhlig. Thanks for corroborating my thoughts on whether to jump over to the aeospace forum. I also am already impressed with the folks on that forum but maybe I should leave that to the cognizant engineer on the landing gear.

cheers Jesus is The TRUTH

 

[TVP]

Special Metals is a leader in the production of nickel-based alloys, and was formerly known as Inco. Inco decided to concentrate only on mining, and now the down-stream stuff is handled by Special Metals. Inconel, Monel, and Incoloy are their trademarks. Their website is

http://www.specialmetals.com/

.