625 Macro

[jfengmet]

Hi All,

I am trying to figure out what to make of the attached picture. This is 625 that has been SA/WQ @ 2000F. You are looking at a 10in. x 10in. section of a forging. First macro (done using standard lab practices) did not show grain flow. I anticipated this because 625 is a clean, austenitic alloy. Customer did not like that and wanted to see grain flow. The attached jpeg shows an extremely aggressively over etched sample. The customer now thinks there are stringers in the material. I do not agree with this because 8 micros have been done randomly accross the sample with no indications for carbide bands or stringers. This sample also passed UT prior to being destroyed for testing. My argument is that this is an artifact of over etching. Etchant was water & HCL. This sample has since been discarded so I do not have the ability to do additional testing. Any comments would be helpful. Thanks!

 

[metengr]

The microphotograph you attached shows no magnification nor microstructural detail, it is nondescript.

 

[jfengmet]

My apologies for being unclear. This is a 10" x 10" cross section. It is a macro photo, not a micro photo. Picture was taken from a mounted camera. Photo is not magnified.

 

[metengr]

Ok. This is still a nondescript appearance, other than polishing marks highlighted by the macroetch.

 

[Metalhead97]

jfengmet,

Based on your micros, what is your expected grain size? In addition, where is the direction of metal flow?

MH

http://www.linkedin.com/pub/luke-autry/1b/510/566

 

[jfengmet]

Grain size was taken in 8 different areas. Ranges from ASTM #7 (Surface to 1/4T), to Duplex BiModal #5 to #9 (1/4T to 1/2T),to Duplex Wide Range #1 to #9 (Center). This forging was basically a thick upset disk. 22"OD x 16"Thick. It was forged in a pot die to give the OD some conical shape. The picture I attached is the center 10" x 10" section. I think bringing up the grain size is a great point, however, this seems much more random than a grain size variation.

 

[redpicker]

It sounds as if your customer is confusing micro-features with macro-features.

As far as magnification, there is a magnification factor, even if the photo was taken with a macro camera. For example, in the upper right quadrant, there are two roughly parallel dark linear features (probably what your customer is concerned about as being stringers). What would say the length of these features is?

To me, it looks like these are macro-features and are not related to carbide bands or inclusion stringers. But, making such identification from undefined photos is not likely to be very accurate. I guess if I was in your shoes, I'd want the customer to identify what is rejectable. The macro-etch was performed to reveal flow lines, which would appear to run from top to bottom, but are not very well defined. Generally, a forging is required to not have any reentrant flow lines and I'd say the etch did not reveal any reentrant flow. I am not sure the results of this test can be used to reject for micro-features. It sounds you performed the test to qualify the micro-features and the material was acceptable. What is it your customer wants?

rp

 

[jfengmet]

I would say the parrallel lines are roughly 3 inches long. My customer required a macro for grain flow. Which at the time of the order, I told them that they would not seen any in this alloy. The first macro I sent them (following standard etching times) did not show any of these anomalies, it looked like a clean, consistent structure that you would expect out of 625. The customer than came back and asked why there was no grain flow (already explained to them). Anyway, they asked to re-etch and provide new photos. After the re-etch, this is what I ended up with. Now they are asking what the dark spots are (they are trying to call them stringers which I disagree with). However, I do not know how to explain what I am seeing as it should not be related to cleanliness or carbide banding, etc.

 

[redpicker]

Why do you have to explain?

The dark spots are macroscopic features revealed by deep etching. As far as you know, there is nothing detrimental shown. As long as these are true statements, I don't see what more should be expected of you.

The trick is how to tell this to your customer without them believing that you are trying to force them to accept bad material. I think all you can do is explain what you have and ask them what they want to do. If they are wanting the material to meet additional requirements that were not part of the original purchase requirements, well, they will have to identify what those requirements are and then it becomes a commercial issue that has to ba addressed by Sales, assuming they can be met. If you let them wait on you for an answer, however, you will be one holding things up; you don't want to put yourself in that position.

rp

 

[Metalhead97]

jfengmet,

The reason why I asked about the grain size is because I wanted to see how visible the grains would be at the that scale. If this in an upset you might be able to get a better picture of the grain flow with a through-thickness macro because the metal-die friction might be limiting your metal flow near the surface. Those dark marking are not stringers, which tells me that the people your talking to are not metallurgists.


MH

http://www.linkedin.com/pub/luke-autry/1b/510/566

 

[jfengmet]

Thanks to all for your responses. I am certain that these are not stringers or material anomalies. But I still do not know what to call the dark spots. This is not your standard customer and they are requesting clarification on this Macro. My plan is to argue that these sports are artifacts of the aggressive etching process used. I will use test data and experience to rule out anything negative in the picture.

 

[redpicker]

jfengmet, Pay attention.

Unless you are prepared to prove without a doubt what is causing the dark regions, you will not win. What they are asking for is so above and beyond what the specification is asking for that they will use any uncertainty on your part as proof that you do not know what the defect is and that you are trying to force them to accept defective material. At best, they will make you scrap this material and replace it; at worst, they will use this as an excuse to cancel the order. Either way, you will not come out ahead.

Your best bet is to say the material is fine and have them explain why they have any concern. Be prepared with a copy of the material spec and have them show what section is not being complied with. It is apparent that these guys do not care about scientific reasoning, so you have to just say the material meets the specification unless they can show you it does not. I am not sure what you mean by "This is not your standard customer", but one thing is certain; you are only responsible for meeting the requirements of the specification. It sounds as if they don't know what they are asking for.

It is not your job to explain those dark spots. You are responsible for meeting the specification and keep the discussion to that and you should be OK. If you allow them to get you to say you can't say what the cause is, they will win, since that will support their contention there is something wrong that you can't, or won't, identify. Keep the discussion to the requirements in the specification, and even if they decide against using the material, they will have to pay for it. Let them cast doubt, and they won't pay. If there is something wrong, make them tell you what it is; otherwise, you can't fix it.

I am speaking from experience. I've dealt with customers like this before, and I will in the future. While I am not an advocate of "playing dumb", I have found out that keeping to the specification requirements is the only thing that will save you; if they want something that is not in the specification, make them admit that the specification does not address the issue, which makes them responsible for identifying the problem and paying for the solutiuon, not you.

rp

 

[Metalhead97]

jfengmet,

In addition to what RP said these are the times when you make friends with your quality engineer.

MH

http://www.linkedin.com/pub/luke-autry/1b/510/566