Nitriding and NACE Code MR0175-3-2009 1

[Customize]

Looking at NACE MR0175 Second Edition 2009-10-15, section A.1.5.1, Requirements for overlays, surface treatments, plating, coatings, linings, ect...

It it says, "Nitriding with a maximum case depth of 0.15 mm (0.006 in) is an acceptable surface treatment."

I would think the metal would have more protection against substances such as H2S. I have seen typos in standards before, and curious if they meant minimum rather than maximum.

What would is the effect if the nitriding was deeper to 0.025 in or 0.030 in?

What could be the issues if the nitriding exceeded the 0.006 in depth for protection in product containing some H2S?

 

[TVP]

Deeper cases will make the steel more susceptible to brittle fracture.

 

[Customize]

There appears to be a lack of definition in the NACE code to whether they are talking about "Effective Case Hardening" or "Total Case Hardening". The way nitriding is called out on typical drawings implies "Total Case Hardening" which may not exceed the "Effective Case Hardening". Total case hardening is much thicker than the effective case hardening.

 

[TVP]

When using the ISO system of standards, there are three parameters that can be specified on the drawing (ISO 15787):

surface hardness
nitriding hardness depth, NHD
compound layer thickness, CLT

For specification of nitriding hardness depth, the symbol NHD is used. The limiting hardness is usually 50 HV0,5 added to the actual core hardness, with the nitriding hardness depth given as a nominal dimension in millimetres. For example, the drawing may have the following specification:

plasma nitrided
> 950 HV10
NHD = 0,3 + 0,1

This means that the surface hardness must be > 950 HV when using a 10 kgf load. The case depth must be 0,3 to 0,4 mm deep, with the value of NHD determined as the depth at which the hardness is 50 HV higher than the core hardness, using an indentation load of 0,5 kgf. The terms Effective Case Hardening and Total Case Hardening are not used. Also, note that a comma is used as the decimal separator instead of a point/period.

 

[SJones]

If you believe that there is a 'lack of definition' in ISO 15156-3, you are free to make an inquiry for interpretation

http://isotc.iso.org/livelink/livelink?func=ll&objId=3340364&objAction=browse&sort=name

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.