Need Help 4140 standards

[arunmrao]

I have an enquiry to produce castings to the following specification. However, I am not familiar with NACE specification.

AISI 4140 L80 to meet NACE MR0175 – 18-22 HRC

I shall be thankful if someone can help me with it. Thanks once again

 

[unclesyd]

I don't have the NACE Spec.

Looking at it from the 4140 standpoint you will be hard pressed to get 4140 into the required hardness range. The annealed hardness is too low and unless it is a large piece even tempering at 700°C will put you at or above the upper limits. The only way to get the hardness would be to normalize and temper and I don't know whether this is permitted by NACE. We used 4140 in this condition only a few times in not very highly stressed parts.

If this is a sour gas service there are a lot more steels that can readily meet this spec.

 

[Carburize]

I think two standards are being used which are not mutually compatible. API 5AC, I believe, covers L80 pipe which is acceptable to NACE MR01 75. However the hardness will potentially be above the 18 - 22RC range which you reference which is from the main requirements of the NACE document. I don't believe that you will be able to heat treat a 4140 chemistry material, or any similar analysis for that matter, to meet the NACE hardness controls of 22Rc max. and consistently achieve the 80,000 psi yield strength of the L80 specification - in my experience the 41xx alloys can only make 75,000 psi yield and still meet 22Rc max. on a consistent basis.

 

[arunmrao]

Thanks for the help Unclesyd and Carburize. I was concerned about 18-22RC and also about the unknown. This you have both highlighted. Infact I have asked the buyer too for a clarification. If he has anything to say on this I shall keep you informed. Thanks once again.

 

[CoryPad]

It needs to be mentioned that 4140 is a WROUGHT alloy and [blue]arunmrao[/blue] is being asked to produce castings. The alloy segregation and property variations inherent in castings causes severe problems with Sulfide Stress Cracking (SSC) when parts are used in sour service.

Regards,

Cory

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

 

[Carburize]

Does the NACE document actually differentiate between product form for a given alloy chemistry?

 

[unclesyd]

We did have some pressure containing components cast to the AISI 4140 chemistry, as called out on the prints. There are some pencil notations by the 4140 call out but are unreadable, which are probably an ASTM call out.

 

[arunmrao]

I quite often produce cast parts in 4140 . I am aware of the limitation, however it is the duty of designer to select the material and specify. I have very little role to play. In case I raise an objection as in this case there are other vendors who will gladly produce (knowingly or unknowingly). This is the irony in real life situations.