Tufftride QPQ...... Nitrex/Nitreg ONC Black. 2

[Haz88]

Hi All,

This is a pretty back to basics question for you but I've been delving into the world of Nitrex/Nitreg ONC Black / Tufftride QPQ.
I have had some components (1045 steel) Tufftride & QPQ treated (in thailand). I'm a little worried my supplier has just black oxide applied to them though,

Unfortunately my only source of information is the brochures in the websites of the people claiming their process is superior and of course, yourselves.

Basically a cylindrical part i had "Tufftride & QPQ" applied to which rotates inside an aluminium ring has had either the aluminium transfer to the part or the black removed.
as I'm aware Nitrex/Nitreg ONC Black / Tufftride QPQ should have a HV of 600, much harder than 6061 - T6 AL. I lightly rubbed scotch brite on the surface and removed more black.

the Question

1) Can the black of a Nitrex/Nitreg ONC Black / Tufftride QPQ component have the black surface removed so easily,
2) if the black is to wear off does that imply the wear resistance and corrosion resistance involved with Nitrex/Nitreg ONC Black / Tufftride QPQ also gone?

thanks

 

[Tmoose]

Tufftrided corvette crankshafts of the 1960s are so hard that a brand new file skates right across the surface

 

[Haz88]

Good example thanks

 

[Kennethhp]

Hello Haz88.

I have been working at a heat treat facility for close to 2 years now (my knowledge is sparsome but i learned a thing or two )
I worked alot with the proces, gas nitriding, which is resultwise similar to a QPQ process (though thats in a salt bath)

A little theory is handy here to make you understand whats going on in a QPQ/nitrex process. (roughly)

When the steel is at its top temperature (520-570 degrees celcius) nitrogen is added at the surface of the steel in various ways. Gas nitriding use ammonia that dissociates on the surface and leaves free nitrogen which can diffuse into the steel, and QPQ use salt that basicly does the same.

The nitrogen will diffuse into the material and hopefully pair up with allowying elements, eg Aluminium and create hard aluminium nitrides. The more nitrogen diffused the more depth and hardness towards the surface you will have.
When there is added more nitrogen at the surface of the steel than can diffuse, a white layer, known as the coumpound layer, will form. This layer is high in nitrogen and CAN be as hard as (various opinions) 1300HV. This layer can vary from 0-25 microns (varies on plants, processes and steel grade)

To finish of both processes, QP - "Q"(quench) / post oxidation will oxidize the surface and create a thin (1-2microns) oxide layer (the black color you can see) that is really tough and provides excellent corrosion properties.

The black layer should never scale of easily, here where i work we gas nitride and post oxidize parts for eg. offshore windmills and jack hammers "hammer".

If you have a heat treatment facility close, send over one of your parts for a destructive analisys to see if it has any compound layer beneath the black layer. This should deffently tell wether its a QPQ process or a simple black oxide treatment.

IF it is a QPQ treatment you had, and the black layer for some reason is gone, the corrosion resistance is pretty much gone.

The wear resistance... hmmm. well 1045 doesnt contain any alloying elements thats good for QPQ/nitrding. so basicly you will only have the hardness from the compound layer. For alot of applications that is sufficient (We treat liners for large airbrakes which doesnt contain any alloying elements either, and they rely on the compound layer only)
So again if it is a QPQ treatment, then there should be wear resistance in the compound layer.

Hope it helps, if others disagree please feel free to say so
(And sorry for any spelling/gramma mistakes, english is not my native tongue)

 

[mfgenggear]

Kenneth very well explained

 

[Haz88]

Kennethhp superb!

I have been researching the process for some time which got me to the point, however what you have just written is more valuable than any website i could find as they all are just spruking themselves.

attached is an image of the part in question. as you can see one side is how it performs ( rotates inside a 6061-T6 part) and the other side is where i rubbed ever so slightly scotch brite on to see if this was actually raw material or aluminium transfer.

Your reply was fantastic and all i really need to continue my design however i thought it would be helpful to see what i was talking about.

Thanks.

 

[Haz88]

For anyone using this thread as a search for nitride/nitreg/tufftride. interally have a great mechanical/chemical analysis if their materials and exaplain if they can be nitrided well or not.

http://www.interlloy.com.au/our-products/hollow-bar/4140-high-tensile-steel-hollow-bar/

http://www.interlloy.com.au/our-products/carbon-steels/1045-medium-tensile-carbon-steel-bar/

cheers

 

[Kennethhp]

@Haz88

You are welcome.

I'm happy i can finally help out a little

I hope you will solve the issue.

 

[tbuelna]

Haz88-

Looking at the photo provided of your part, one thing I would recommend with liquid salt bath nitro-carburizing is to not case harden those small section screw threads. This will likely result in fractures at the screw thread tips.