Stock Inconel Material having Carbide (In Micro Examination)

[bmoorthy]

Question::

1) Should micro examination result be used for deciding the acceptance and rejection of Inconel material (From the point of view of Longevity of the end component and from the point of view of safety) when B 564 does not have any reference to Micro examination for 625 items.
2) What is the relevance of Micro examination from end application
3) Does NACE have any recommendation for expected/Required micro examination


Intended use of Material:: Valve Components (For 346 individual valves):: Pressure containing component.
Operating Zone (NACE MR 0175/ISO 15156) :: Zone 1 (113 Valves) and zone 2 (33 valves). Rest Zone 0.

Design and Operating temperature are less than 600 Deg C.

Background::

We were searching for the immediate availability of Inconel material. As the luck would have we traced it in our stores (in form of blind flanges) procured for earlier projects.

Material :: From the stores record:: Inconel 625 forging.


Following material located in stock (4 years in stores):: Properly preserved:: No objection in preservation. Manufacturers marking (Original seen). But material certificate not located (at the time of decision to test), hence following tests were conducted from a forging lot (having same heat number and Lot number)

A) Mechanical properties :: Result, Meets the ASTM B 564 values
B) Chemical Analysis :: Result meets the ASTM B 564 Values
C) Hardness:: 3 readings per sample piece:: Result:: Less than 22 HRC (In RC scale).
D) Micro Examination:: Result:: Carbide precipitation (Intergranular) about 13 a units deep seen. Prevalent.
E) PMI on all the forging:: Result:: all the results are consistent with the Chemistry reported

Another representative sample from the lot taken and heat treated to standard anneal of 1600°F (871°C) (Soak time 1 Hour) allowed to cool in furnace and the following tests were repeated.


A) Mechanical properties :: Result, Slight reduction in yield noted and 1.5% increase in elongation noted. But Meets the ASTM B 564 values
B) Chemical Analysis :: Result meets the ASTM B 564 Values (This need not have been done, but this was also done):: No change.
C) Hardness:: 3 reading:: Results:: Slight variation (average low by few points) in result, but Less than 22 HRC (In RC scale) and Less than 230 in Vickers (HV 10) Scale.
D) Micro Examination:: Result:: Carbide precipitation (Intergranular) about 10 to 11 a units seen. Prevalent.

Searching into old records, Original Material Test certificate located (But after the samples were sent for test, it was decided to any way test them !!!). Certificate shows the material is B 564 UNS N06625.

Marking Photographs sent to manufacturer and manufacturer confirms that the markings are consistent with their standard and confirms (From their record) that it is their material.

 

[EdStainless]

It would sure take more than a simple micro. I would expect Cb + Ti carbides, that is what is supposed to happen. Your 1600F stress relief anneal will cause them to grow also. This is well below solution temperature, but you don't want to solution the carbides. They need to be there fro stabilization.

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Plymouth Tube

 

[MikeMet]

Not sure what an "a" units deep is, but what you may be seeing on the surface is shallow intergranular corrosion that can be present from pickling after heat treatment, which is a common practice. I have seen times when the pickling was very heavy and surface corrosion was fairly deep.

I wouldn't worry since every other property is acceptable.