Carbon Steel Grain Size

You'd have to ask the designer. In my experience fine grain is called out 5 or finer to astm spec.

4 is not really fine, and 5 and 6 are not considered coarse.

As a point of clarification though, are we talking about austenitic grain size or as rolled grainsize?

I'll take a look at the spec for SA516 but I don't remember such a callout ... Milo

Fine-grained steels have higher notch toughness than course-grained steels. The transition temperature is lowered as the grain size decreases. The fine-grained condition is usually due to a deoxidation practice that uses silicon, aluminium, or vanadium.

For grain size No. you can go to ASTM E112 ( GRAIN SIZE NO. 1 IS THE COURSE GRAIN , GRAIN SIZE NO. 10 IS FINE GRAIN)

Your facts are correct. They do not however help us understand why the spec requirement is 4-6, (both coarse and fine) and again we do not know if we are concerned with Austenitic grainsize or as rolled grain size.

Milo

Given the operating temperature, could this be something to do with creep resistance? Maybe trading off against notch toughness?

can anybody give me a satisfactory explanation?

at least tell me what will be the probable effect of higher grain size say 8 or more on SA516 Gr.70 at the service parameters as mentioned. this is because the plate i have procured for the new column has a grain size of 9.

regards,

Here's the deal, You haven't looked at the specs, so you can't get clarity. SA516 grade 70 cites SA 20 for grain size properties. I am using copies of ASTM same caption.

ASTM A 516 paragraph 4.1 steel making practice states "Steel shall be killed and shall conform to the fine austenitic grain size requirement of Specification A20/A 20M."

Please note it says fine austenitic grain size. That means that the grain size of 4 and 5 (coarse! ) in the range you mentioned earlier as 'acceptable' is wrong. Nonconforming. Incorrect. Out of spec. Noncompliant. Unacceptable.Disallowed. Misfeasance. Malpractice. Latent engineering defect. BAD!

A20 paragraph 8.1 "When a coarse austenitic structure is specified... The steel shall have a ...austenitic grain size number of 1-5 as determined by mcQuaid Ehn test." (Details uneeded to make point omitted for clarity.)

PLEASE GIVE THIS SOME CRITICAL THOUGHT 1-5 = COARSE; THEREFORE 4 AND 5 ARE ... COARSE! (THIS IS IMPORTANT!)

A20 paragraph 8.2 Fine Austenitic grain size:

8.2.1 "When fine austenitic grain size is specified, Aluminum shall be used as grain refining element unless the order provides otherwise..."

8.2.2 "When a fine austenitic grain size is specified ...the steel shall have a...austenitic grain size number of 5 or higher (finer) as determined by mcQuaid Ehn test..." (Details again uneeded to make point omitted)

YOUR ORIGINAL 'SPEC" RANGE INCLUDED BOTH COARSE AND FINE GRAIN SIZE NUMBERS. AS SECTION 8 OF A20 CLEARLY STATES, IT HAS TO BE EITHER COARSE OR FINE NOT BOTH COARSE AND FINE AS YOUR ORIGINAL RANGE STATED!!!

That means THE RANGE YOU WERE GIVEN AS SPEC 4-6 can't properly comply to A 516 or A20.

This was the critical point in my earlier post. I am not certain why this was not understood.

If the numbers you are giving us are indeed mcQuaid Ehn grain sizes, the 9 tells me that the material is in fact AUSTENITIC fine grain , and most likely was aluminum Grain refined, Aluminum does a great job of inoculating very fine grain sizes finer than 7...

Fine grain improves notch toughness.

As I mentioned in an earlier post, the original grain size range you cited was ambiguous and permitted both coarse and fine grain...something these specifications do NOT permit.

YOU REALLY NEED TO FIND OUT WHERE THAT AMBIGUOUS AND DEFECTIVE GRAIN SIZE RANGE CAME FROM!

Bottom line: The material with grain size of 9 conforms to SA 516 AND SA20 FINE AUSTENITIC GRAIN SIZE MATERIALS.

"I actually looked at the specs. I recommend this as a best practice."

For folks interested in some other factors that result from fine austenitic grain size, you may check out my blog on the subject here:

http://pmpaspeakingofprecision.com/2009/11/24/5-ways-fine-austenitic-grain-size-affects-your-machine-shop/

Milo

I hope this notes help you

*ASME Sec. II Part A SA-516 Steelmaking practice: the steel shall be killed and shall confirm to fine austenitic grain sise requirement of specification SA-20.

SA-20 8.2 Fine austenitic grain size

austenitic grain size number 5 or higher (finer) (not 4-6)

coarse austenitic grain size (1 to 5)

*I think the designer can adjust the minimum design metal temperature (MDMT) IF the metal produced to fine grain practice and normalized by applying the rules of ASME sec. VIII Div. 1 UCS-66 IMPACT TEST EXEMPTION CURVES

*Also you can go to SECTION I part D TABLE 1A MAXIMUM ALLOWABLE STRESS VALUES S FOR FERROUS MATERIALS and see NOTES TO TABLE 1A NOTES — GENERAL REQUIREMENTS

G14 These stress values shall be used when the grain size is not determined or is determined to be finer than ASTM No. 6.