Extra High Strength Steel 4

[barun1]

Can anybody detail the drawbacks of using extra high strength structural steel in marine environment?

 

[Metalguy]

More susceptible to H cracking, more difficult to weld, and corrosion can be a problem if you take advantage of the strength to make the parts thinner. Protect it well and that shouldn't be a concern.

 

[boo1]

Cost is also higher.
We use 17-4 PH or A286 for our high strength applications. To reduce gaulling consider Nitronics 80.

 

[JimMetalsCeramics]

Ultra-high strength steels (e. g., Aermet) are well engineered but they represent a best efforts product. Some of them lack fracture toughness. The rest is as Metalguy has stated. Stress-corrosion cracking is an issue.

 

[CoryPad]

JimMetalsCeramics,

How can you say that AerMet alloys lack fracture toughness? They are among the toughest materials available. For example, with ultimate tensile strength of 1700 MPa, the fracture toughness is 150 MPa m^0.5. With ultimate tensile strength of 2100 MPa, the fracture toughness is 60 MPa m^0.5. There really aren't many other options for high strength, high toughness materials.


Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[JimMetalsCeramics]

Perhaps my mistake. I spoke with people at Carpenter and the Navy a year ago about an SBIR solicitation. They were looking to improve properties of a couple of high strength steels. One of them was a new Aermet. I forget the other one. They had voiced that one major problem was toughness and the other was stress corrosion cracking. I believe that the toughness was lacking in the new Aermet which was under consideration for landing gear pistons for JSF. One potential solution might be powder metallurgy fabrication.

For any given high strength steel, these are mostly new generation alloys and lack comprehensively rugged properties. You should inquire from the manfacturer those properties pertinent to your application environment. Some of these steels have excellent strength while lacking other key traits.

 

[RPstress]

Jim - Was that Aermet 310??

 

[JimMetalsCeramics]

I don't believe so.

I do know that Aermet 100 has concerns with corrosion and hydrogen embrittlement.

 

[jetmaker]

High strength steels lack durability, in that a small corrosion pit, or scratch will cause a part to fracture very rapidly and with little warning. Also, these steels suffer from stress corrosion issues, and a marine environment is not a good place for them. Finally, the use of such steels in cold water environments will only make them more brittle.

Consider something more like 15-5PH or another stainless steel rather than 4340M or Aermet.