Mold difference between Grey Iron and Ductile Iron

I would like to have some inputs from you, if I would like to shift from grey iron to ductile iron, do I need to change the molds as well, meaning do I need to have a new molds for ductile iron?

Please advise.

Thank you.

Regards,

Cesar M.

I would like to have some inputs from you, if I would like to shift from grey iron to ductile iron, do I need to change the molds as well, meaning do I need to have a new molds for ductile iron?

Please advise.

Thank you.

Regards,

Cesar M.

On 18 Dec 2006 01:13:49 -0800, with neither quill nor qualm, "Cesar" quickly quoth:

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The answer is "it depends".

Things you'll have to consider:

• chemistry
• temperature
• mold material
• fluidity
• solidification shrinkage
• gating/risering system
• porosity
• part geometry
• inoculation ....etc

Try starting here

============================= I'm no expert on gray v ductile/nodular iron, but I can suggest that your best bet may be to just go ahead and get some ductile pieces cast. This will also allow you to evaluate the machinability, and all the other factors.

Will the same foundry be doing the ductile that did your gray iron parts? If so, they will be the best people to ask as they are familiar with your patterns. There are a huge number of variables, possibly the greatest of which is how much allowance [oversize from net] was the original gray iron pattern/part.

Post cast heat treating may be critical for strength/machinibility.

FWIW -- Years ago I was involved in a project that did just this [change from gray to ductile/nodular]. This required no pattern problems or changes but we ran into a big jump in tool wear. Turned out that the foundry was using a high percent of automotive scrap including chrome bumpers rather than slitter scrap.

After much work we discovered that although the brinell hardness of the parts was low (enough), the chrome and copper had caused carbide precipitation in the grain boundaries. The parts were soft enough in bulk but contained highly abrasive fine particles.

Apparently this did not occur with their regular gray iron, only when the magneisium/calcium [and who knows what else now] was added to the melt to modify the gray to ductile/nodular iron.

Good luck, and let us know how things turn out.

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

We cut chrome iron all the time... full hard stuff. AS far as the difference in the mold there should be no problem since the biggest factor in the mold size is shrinkage. the shrinkage of the two metals is about the same. One thing that will change is the annealing and normalizing of the casting. If it is not done right you will have problems. Hard spots in the metal will drive you crazy replacing inserts every two minute. The right inserts are cirtical for proper cutting.

John

================= From what I understand the problem was not the chrome, but the copper (under the chrome) that caused the chrome precipitation at/in the grain boundries. Problem operation was broaching with a HSS tool.

So many ways to go wrong, so few ways to go right....