Grain Size Master Sample 1

[Josh86]

I have recently been given the task to do the grain size measurements on some steel heat treated samples. I am using equipment that can automatically detect the grain size measurement and the grain number of my samples. Can anyone direct me where to purchase a steel master sample with a known grain size? I would like to make sure this equipment is providing me with accurate results.

 

[EdStainless]

Which grain size are you measuring?
Which spec are you trying to comply with?
In steels it is common to measure the prior austenite grain size, not the finished condition (hence the requirement to heat and quench). In many specs the measurement of grain size has been replaced with chemistry controls. If you add grain refiners you cannot make coarse grain steel.
There are a number of specs which use slightly different methods.
The supplier of you equipment should be able to provide you with extensive comparisons that they did for validation of the system.
There are also a lot of tech paper published comparing methods.

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P.E. Metallurgy, Plymouth Tube

 

[AidanMc]

How is your system measuring grain size? Is it a fracture grain size and you need physical samples to compare to or are you working on a image analysis on a polished cross section?

Aidan McAllister
Metallurgical Engineer

 

[Josh86]

EdStainless,
I am still new to this and do not have the answers to all your questions, I will be looking into them. Thank you for the information and suggestions. I will be contacting the supplier.


AidanMc,

I am using physical samples that have been sectioned, mounted, polished, and Eteched. The system highlights the Grains and makes numerous lines through the image horizontal, vertical, and diagonal. then it comes up with an average grain size. If I could find a sample that has been examined and has a known grain size number I could examine it with my equipment to see if the results are similar.

 

[EdStainless]

There are linear intercept methods, circular intercept, point counts, and a few others.
They each give slightly different results.
But be warned, if these are heat treated samples then what most specs require is 'prior austenite grain size' not hat of the finished material.

I have seen people use reference photos for verification.

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P.E. Metallurgy, Plymouth Tube

 

[AidanMc]

I believe ASTM E112 has information on the image analysis algorithms that you can use to determine grain size. I'd recommend that you look into purchasing a copy of the document, it should have some advice.

Aidan McAllister
Metallurgical Engineer

 

ASTM standards are the place to start.
ASTM (or maybe ASM?) will sell you wall charts that you can use to compare with your micrographs. However, if the machine is doing it for you, no comparison is needed.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[Compositepro]

As a novice, it is very important for you to understand that particle or grain size is mathematically calculated from a distribution of shapes and sizes. It is not a physically real number. It depends on how it is measured and how the measurements are used to calculate a single representative number. For example, say you have a brick that is 3"x2"x8". What is its size? You can only report a single number. Now, say you also have a block that is 6"x8"x 16". What is the average size of your distribution? You can calculate a number average, surface area average or a volume average.