how to diffrentiate between grey and ductile cast iron? 1

[enas]

hi all
how can I diffrentiate between grey and ductile cast iron with its apperance.

 

[metengr]

If you mean just visual appearance of two castings? No, you really cannot distinguish between them. The only reliable method to evaluate the difference between grey and ductile iron castings is to compare their microstructures.

What is your situation that requires this comparison? There could be other options.

 

[arunmrao]

On visual appearance it might be difficult to distinguish. Butif you perform a ring test,grey iron will not produce a ring sound,but ductile iron will. The most comprehensive test will be a microstructure analysis.

 

[unclesyd]

There is another simple test that may work for you.
Take a small sharp chisel and get on an edge and try to peel off a small chip.
The gray iron will not make a chip of any sorts while the ductile iron will try to make a chip.

 

[metman]

unclesyd: Let's pretend that it is grey iron. When you try to peel off a small chip, what will be the reaction of the grey iron? Will the chisel break? Will the hammer fly back into your face? What...pray-tell will happen?

In deep suspense

 

[unclesyd]

As long as the iron in question hasn't been in H2 service it will not have a propensity to blow up.

The ductile iron will try to make a small curl, i.e. ductile.

The GI will be very small chips/pieces more like a dust, i.e. brittle.

Malleable will act similar to ductile iron.

Nodular iron will act the same ductile iron.

White iron will probably break the chisel.

Wrought, puddled, or charcoal iron will make a half curl.

Semi-steel will make a full curl.

I should have added that small chisel with a single bevel and the chisel inclined at 30-40 degree angle against the material in question works best.

 

[rd400guy]

arunmrao, do you have more info regarding the "ring test". We use cast iron ingot molds and notice that some of the molds (mostly confined to a Chinese supplier) are failing prematurely. It almost looks like brittle fracture. I haven't made a correlation between molds that "ring" vs. molds that "thud" and failure rate, but the observation has been made by the guys on the floor that some molds ring and some don't. At the moment, we can't justify tying up Met Lab time testing cast iron when there's stainless and high-alloy product that needs to get out the door. If you or anyone else has any insight on why some molds would ring whereas some don't and what that could signify in terms of mold life, I would appreciate it. TIA.

 

[swall]

And just what exactly is "semi-steel"?

 

[unclesyd]

Not trying to highjacking the thread.
Semi-steel is a generally a cast iron that has a high percentage of steel scrap added. The higher the percentage steel scrap the more ductile the material is.
My statement on semi-steel probably isn't true for all cases as the material we bought was quite ductile so a general statement would be that it will act similar to ductile iron.

 

[arunmrao]

rd400guy
The experience of your shop personnel is correct. This simple test can distinguish the defective ingot moulds from the good ones. I used this test 25 years ago while inspecting ingot moulds . If there are any severe internal flaws you just get a thud,discard those. By practice one can start identifying defective moulds. I do not know if there are any standards for this test .

Another interesting way of identification for ductile iron. A freshly fractured sample is smelled and tasted!! Characteristic Mg smell will indicate if treatment is complete and nodularity. This is a typical shop practice and I too have learnt it.

 

[sbi]

Quicker that all of the above, on a fresh break, breath on it the smell it, if you get a sulfer smell it will have a good chance to be ductile, my grandfather taught me that back in the 70's, and he was 3rd generation
Bill

SBI
Central Ne.,USA

 

[pooka00]

Make a small fresh cut in the metal. Ductile will smell like calcium carbide (old fassion miners lamp fuel). Grey iron will not have the smell.

 

[pooka00]

What is 302Cu and is there is spec for the material? I am checking 302SS material and found that for some reason there is 2-3% Cu.

 

[EdStainless]

When I used to use a lot of ceramic and carbide parts I bought a small instrument to measure the resonance of the parts, basically the speed of sound in the material.
I have seen this used on cast iron and also on bricks. A variation in density (for a sintered material) or damping characteristics (cast iron) will give you a different number.
If your parts (or molds) are all the same size then you can compare readings taken in different locations and directions.
We also made some white cast iron items and it could easily pick out the ones that were not fully 'white'.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[MOB1]

EdStainless is correct. If you have a large number of parts to sort it is a simple test to have a gray and ductile sample identified microscopically then have a good ultrasonic technician identify the attenuation or the speed of sound in each and then it is a simple matter to test them all at a standard location. The speed variation is significant.

 

[rorschach]

I hate to hijack a thread, and I hate to encourage it, but 302Cu is 302 SS with a couple percent of copper to slow down the strain hardening effect. Carpenter sells this alloy. how this has anything to do with cast iron, I haven't a clue. Pooka00, take a hint.

The ring test is a good easy and cheap way to check. as to why one might ring and another might not, any number of things come to mind: insufficient mixing of the molten iron during casting, gas inclusions, differences in cooling rates, incorrect alloy used. I'm sure there are probably others that don't immediately come to mind.

 

[BillPSU]

Now that we can tell between ductile and grey iron what about compacted graphite iron? And what if CG is what the foundry shipped you instead of ductile.

 

[arunmrao]

Very tricky. Perform a NDT for nodularity