Microstructure made from 5Cr21Mn9Ni4N

Dear all,

I seek some advice and opinion regarding this two micro-structures on how and what we can comment on the structure. Opinion and comment are really appreciated.

 

[Guest102023]

It would help to know what the material is.
The micros appear overetched.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[CoryPad]

Comparing Crack Valve and New Valve, the new one has finer grain size. The finer grain size would be due to the thermomechanical processing. Are these automotive exhaust poppet valves? Hot forged? Any surface treatments/coatings?

The Used Valve looks like it has porosity like a powdered metal part or from extensive creep damage.

 

[EdStainless]

Give us new micros, both unetched and properly etched (the new one is way over etched)
I would like to see 500x also.
Service conditions also.

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Plymouth Tube

 

[yoppu]

For more information...

The New Valve means that the valve is totally brand new and never been used.
Used Valve means that the valve is used in the same engine as "Crack Valve."
Crack Valve means that the valve found a crack from the same engine with "Used Valve."

All these valves were used for CNG mono gas engine.

 

[Maui]

What is the grade of steel from which the valves were manufactured? What is the chemical composition of the steel? What is the hardness of the parts that you took these microstructures from? How were they heat treated? These are things that we will need to know in order to provide you with an answer.

Maui

 

[Maui]

This may help you:

http://www.maneyonline.com/doi/abs/10.1179/174328407X192804

Maui

 

[Guest102023]

Help us out with the type of steel, no one here speaks euro.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[yoppu]

Dear Maui

I do not know or have any idea at all on the grade for this material, but this exhaust valve come with the engine come from France.
The chemical composition of the steel for the new valve is:
C=0.78 ; Si=0.243; Mn=8.850; Cr=18.32; Mo=0.152; Ni=2.3; Cu=0.155; v=0.07; w=0.081; P=0.0236; S=0.0124; Al=0.002; Co=0.042; Nb=0.0532;Ti=0.0129; Pb=0.038; Sn=0.0109; Mg=0.0137; As=0.0024; Ca=0.0011; Ce=0.0144; Sb=0.0161; Te=0.0066; B=0.0041; Zn=0.0373; La=0.0017; Fe=68.7

Hardness for new valve: 409 HV; USED VALVE 348 HV; CRACK 333 HV

The exhaust valve plate exposed on the high temperature approximately 700 degree C, and it is a crack when running with CNG monogas. The exhaust valve is belonged to a cylinder no 3.










? What is the hardness of the parts that you took these microstructures from? How were they heat treated? These are things that we will need to know in order to provide you with an answer.

 

[Maui]

Based on the chemistry you provided this appears to be a high carbon variation on 21-2N austenitic stainless steel. You can read a description of 21-2N at the end of this article on valve material selection guidelines, which you may find interesting:

http://fme-cat.com/docs/1108.pdf

As Cory stated above, your "Crack Valve #1" appears to possess a much coarser grain structure than your other valves do. This could be a result of the solidification characteristics found in the ingot mold that was used to cast this steel, the hot reduction practices that were used to process it, or in the thermal treatment cycles that it received during processing. I agree that the microstructures do appear to be over-etched. Better sample preparation combined with a set of higher quality images taken at 400X - 500X would be helpful here.

Have you had a reputable metallurgical laboratory perform a failure analysis on these valves? I would recommend that you have that done, since that should give you a more conclusive answer regarding the reason for failure than we can give you here simply by looking at the images provided.

Best,

Maui