Grain Size relation to Impact?

[bmoorthy]

Hello all

I always thought that finer the grain size, better Impact Value. This opinion was based on observations on Carbon steel materila and low alloy steel material tested at low temperatures (-30 to -40 Deg C).

Recently i came accross an article that had diametrically opposite assertion, that is the material with lower ASTM Grain Size Number (Coarser Grain) is reported to have better Impact properties than fine grain (Higher ASTM Grain Size number). But the material that were discussed were High nickel alloy.

Now the querry is, is there a relation ship between grain size and Impact properties (when tested At a given temperature). And is the relation ship inverse for High Nickel steel.

What about Austenitic stainless steel (When tested at low temperature).

 

[metengr]

Austenitic stainless steel does not exhibit true brittle fracture behavior at low service temperature, so the fine grain size correlation with impact properties is really meaningless.

For nickel-base alloys, certain types of alloys can precipitate intermetallic compounds at elevated temperature that would have an adverse effect on impact properties. Fine grain would tend to aggravate this problem.


Fine grain is desirable for applications with carbon steels or low alloy steels used in low temperature service. For elevated temperature service, creep strength is enhanced with a coarse grained structure – this applies to nickel-base, austenitic stainless steel and low alloy steels.

 

[btrueblood]

Hmm, metengr, would you say that a fine grain size in Ni alloys couldmean they've been given a great deal of cold work (strain hardening), and thus have a reduced impact strength?

 

[metengr]

btrueblood;
In the context of your question, the answer is no. Strain hardening would not impact grain size until subsequent thermal treatment. Strain hardening would affect toughness and mechanical properties.