ASTM A560- Reduced ductility

Date 03-25-2008 18:50 Edited 03-25-2008 22:47

First question I would ask before getting any longer:
Your name suggests that you live in the Far East. Were the supports bought in China? If so, that would be a sufficiently clear answer.
Giovanni S. Crisi
Sao Paulo - Brazil

By skumar_krishnan Date 03-25-2008 21:23

Dear Mr.Crisi,

Many thanks for the response. I am from India and we sourced these castings from India. We have installed these components in Canada where the ambient temperature fell below (minus)45 Degree Celcius. Could this have contributed to the failure?

By G.S.Crisi (****)

Date 03-25-2008 22:51

No, because a 50/50 alloy (50% Cr and 50% Ni) is not subjected to the ductile / fragile transition phase.
As the supports were not bought in China, we have to think of another reason, which in this moment I can't imagine.
Giovanni S. Crisi

By js55

Date 03-26-2008 13:55

Giovanni is right, there would be no ductile to brittle transition (or at least not a precipitous one) with that alloy. And even if there were, it is not a permanent transition. Once warmer temps are restored the ductility is restored as well.

By js55

Date 03-26-2008 14:03

Just to brainstorm here.
I'm just not sure you can even do anything to that material that would reduce the tensile strength by 50%. The Cr is the Cr, the NI the Ni and the Cb as well. Even extreme segragation. Even if it was brittle the tensiles would still pull, provided there was no misalignment of the clamps or dogleg in the tensile specimens where embrittlement might cause a problem. Your yield to tensile ratio might increase considerably though.
Even if you welded the things and fried the HAZ precipitating Cb carbides the size of a Volvo you wouldn't see a 50% T reduction IMO.
I think there has to have been prior fractures. Or your material isn't what its supposed to be.

By skumar_krishnan Date 03-26-2008 14:59

Gentlemen,

Many thanks for the responses. I found another interesting discussion on this subject. Please follow the link below.I will be grateful for your views.

http://www.hghouston.com/dcforum/DCForumID6/126.html

By js55

Date 03-26-2008 18:13

I see where the discussion covers the subject of elongation but not the loss of tensile strength. From 80ksi to 40ksi as yo posted, is extremely significant. Cleanliness has always been an important factor in toughness and ductility but though it may effect strength as represented in a tensile test as well, certianly not to the extent of a 50% loss IMO.
Its just difficultfo rme to imagine a scenario that would coause that loss of strength without some form of responsible discontinuity.

By GRoberts (***)

Date 03-26-2008 23:22

Casting defects could also contribute to the low ductility. Typically, the tensile samples that the foundry pulls are from seperately cast or attached test bars that may have seperate risers. They are normally very sound, and test well. If the casting has areas where shrink defects occurs due to improper risering, or a difficult casting design, and a tensile test is taken from the casting in that area, results will be significantly different. Also consider that a lot of tensile tests come from significantly smaller pieces of material than the casting, depending on how the casting was ordered. The small tests samples may have a much finer grain structure due to their solidifcation than a large or thick section casting. This is especially true in nickel alloys, or other alloys that do not have a transformation, and thus no grain refinement.

By skumar_krishnan Date 03-27-2008 18:23

Mr.Roberts/ MrJS5,

I am grateful to you both for your time and inputs.

Please will you explain me what is phase transformation and how it contributes to grain refinement? Why this phenomenon does not occur in Nickel Alloys?

Also I am hearing the term "embrittlement" very often.I am afraid I do not understand it very well. Does it refer to loss in ductiliy as a result of metallic or non metallic inclusions?

Please reply

Thanks in anticipation.

By js55

Date 03-27-2008 19:08

I think Greg is much closer to your solution than I am.
A phase is, and I am no metallurgist, in this context a lattice configuration.
BCC-Body Center Cube, FCC-Face Center Cube, HCP Hexagonal Close Packed, etc.
Many alloys will, solidify from the liquid as one 'phase' and then change its lattice configuration upon cooling. Carbon Steels for example. Carbon steels go BCC, FCC, BCC.
Many alloys will not. Ni alloys do not undergo phase transformation. They solidify FCC and stay that way.
Grain size is based upon a variety of things. Chemistry and cooling rate being predominant. If a material of a large grain size is reheated through a phase transformation temperature and then cooled faster than its original cooling rate, then you can realize grain refinement.
Embrittlement (and you can probably google a definition more sophisticated and accurate) is a term used to identify a deleterious change in the ductility of a material, and manifest in either bend or tensile testing or other mechanical testing methods.