Part / casting Number, 2.2S Nitrated rods ?

[stretch]

Does anyone have the part / casting numbers for the 2.2S nitrated Rods ?

A picture would be even better ! Thanks in advance

Dave

[andyjboy]

Dave - relevant numbers are:

casting no - 911 103 103 0R

part no - 911.103.013.21*

photo (courtesy of Armando S):




Incidentally, the correct term for the heat-treating is nitriding - Bruce Anderson's use of the term 'nitrating' is incorrect.


* last 2 digits can be in range 21-28 depending on weight grouping

[preS]

Isn't the casting no. for both the stock and nitrided rods the same? The only tell is their color?

Richard

[andyjboy]

Yes, casting number was the same

[stretch]

Thanks Andy,

Are the rods pictured, stock 2.2S rods, or are there other casting, part numbers for the 2.2S engine ?

The search engine is not my friend on this matter.

Dave

[chris_seven]

I apologise for being picky but these rods are almost certainly manufactured from Closed Die Drop Forgings rather then castings.

Casting would have inherent issues with regard to fatigue life and notch sensitivity.

Cast Structures (even steel castings) tend to have relatively poor properties due to grain size and cooling directionality which would make them unsuitable for high performance engines. Hot work reductions of around 50% are needed to break up cast structures and produce the properties normally associated with wrought materials.

Cast rods tend to be used on low speed compressors and generator drives which don't rev beyond 3000 rpm.

I agree with Andy's comments about Nitrating being incorrect, there are many good metallurgical reasons why trying to introduce nitrates into a material would be problematic.

Unfortunately the term Nitriding is also subject to some confusion and contradicition.

Classical Nitriding is a well established process that has been used for many years. It offers significant improvements in performance with regard to surface hardness, reduction in coefficient of friction as nitrided layers are Oleophilic and most importantly fatigue life.

Traditionally nitriding was carried out in a Gaseous atmosphere of cracked Ammonia. Nitrogen was diffused into the surface of a suitable steel and reaction with certain element produced various nitrides. These nitrides created significant residual compressive stresses resulting in the improvement of mechanical properties.

Not all steels, however, are suitable for Nitriding. The classical material is EN40B which is UK specification for a Ni/Cr/Mo steel typically used for race crankshafts.

More basic carbon steels tend to be unsuitable as they predominantly form Iron Nitrides which are brittle in nature and tend to spall off a component that is subjected to bending or twisting.

Nitriding is also a relatively low temperature process which helps to reduce distortion - typical temperatures would be 950 to 1000 degF.

There is also another process known commercially as Soft Nitriding - this process is more correctly described as ferritic nitrocarburising.

Its properties, whilst beneficial, are a long way short of traditional nitriding but is does provide enhanced scuff resistance and some very small improvement in fatigue life.

It is also a relativley low temperature process, it is normally carried out using a Salt Bath and it works with virtually all steels.

Historically the process using this technology were known as Tuftriding, Tenifer and Melonite.

Many companies still offer 'Salt Bath Nitiriding' and new diffucion process have given some improvements compared to the older cyanide based treatments but IMHO they still fall along way short of traditional Gas Nitriding.

It also explains some old issues with Porsche parts.

Standard Forged Porsche Cranks are Tenifer treated. They were never 'nitrided. They are made from a basic medium carbon steel.

If you re-heat treat them after grinding send them to someone that can either Melonite treat or Tuftride them. Don't send them for gas nitriding as you may end up with the surface flaking off.

The S rods were almost certainly Tenifer treated (This process was also used for blacking Glock pistols)

Its fatigue benefit on a part such as a conrod would be minimal and with the developments in Shot Peening than tahe taken place in the last 30 years this is a much more appropriate process.


The 'Motorsport' Rocker Shafts used on the solid rockers (906, RSR, 935 etc) were also Tenifer treated as the rocker arms were prodcued wihout bushes.

Sorry to hijack the thread and bang on but I find the metallurgy is just too compelling to ignore.