modifying ASTM A536 ductile iron standard material Grades

[Tmoose]

A 375 lb cast German component back in 2003 specified EN-GJS-700-2U material with GGG-70 in parentheses (GGG-70).
Typically GGG-70s rated UTS/YS/elongation is listed as 700 MPa / 424-440 MPa / 2%. 101,000 psi / 60-63,000 psi / 2% minimum

The common Internet equivalent for (GGG-70) is listed as ASTM A536 100-70-03.
100,000 psi / 70,000 psi / The minimum elongation is 3%.
ASTM A536 says 100-70-00 will likely require a quench and temper or normalize and temper.

I'm scared of materials with elongation <10%, so 2-3% elongation makes me think of gray cast iron and glass.

In the fine print the 2003 German Quality Requirement document said the GGG-70 etc should have minimum elongation of 5%.

Is it fair to ask our US foundry to tweak the 100-70-03 to get 5% elongation?

I'm also thinking the lower GGG-70 yield strength is closer to ASTM 80-55-06 anyhow.

thanks,

Dan T

 

[btrueblood]

Tmoose,

Yes, if you talk to a decent foundry about your requirements, they can generally tailor the heat treatment to get you what you want. I.e. you should be willing to give up a little tensile/yield strength to achieve a better elongation value. As far as materials below 10% elongation, good tool steels at full hardness (Rc 60+) get low elongation values too...which is why you shouldn't build bridges with them. We get a lot of stuff made with grade 60-40-18, generally only have occasional problems with gas porosity. The foundry we work with says this grade is generally what they get without any further heat treatment, but occasionally we get a batch of harder material that they heat treat (anneal/temper) back to softer stuff. If that casting has fairly thick walls, it might not be getting very high strength levels at the core anyway; do you cut samples from a qualification test unit to verify (or is it that important)?

 

[98RedRANG]

GGG70 is the old DIN1693 call out for pearlitic ductile iron. Its worth noting the properties are minimum properties per 'Y' blocks.
EN 1563 modified those properties a bit depending on section thickness, and depending on your part that maybe a factor. 375# is not a very big casting. Are you planning on just using block values or extracted tensile bars?

as mentioned ASTM allows tailoring of properties per agreement and a good talk with your foundrymen and I bet they can get you what you need, and let you know what the 'typical' elongation numbers they get from testing. Even with the lower %E, ductile is called ductile because it does stretch and does not have the graphite flake network that makes gray cast iron brittle. So if your remaking a casting using this grade (that has not broken due to brittleness, low impact) then I think you would be ok. With ductile I worry more about proper foundry practice then Y block values (Mg fade is real) so I like cast on test bars better then just a Y block taken at start of pour, and be sure the bars get the same heat treat as the castings.

 

[Martinos]

Do not be worried. We are working here with EN-GJS-700-2 ductile cast iron commonly, also we are doing induction hardening process in some cases and there is no problem even elongation looks terrible. Based on elongation level it may looks way too brittle, but it is not as terrific as it seems. If the graphite form and size is OK, of course.

Anyway, I know people who were working with quenched and tempered steels only (35 HRC, high toughness) and now, when they see quenched and low tempered steel (55 - 60 HRC, low toughness) they imagine this condition is like glass, but is not. I know better, I was working mainly with hard and not tough components. But, of course, always it is a matter of construction application.

In the past I was worked with ferritic-carbidic cast irons and white cast irons with not measurable elongation and with large sharp edged carbides in the microstructure. Yes, they are for me soothing brittle with way too low elongation, but still not like glass