Charpy Impact Testing 2

[Armenius]

Hello!

New to the forums and metallurgy in general. I have a question about impact testing (CAT 3). We have a material that we sent to a lab to be impact tested to meet 350WT CAT3 spec (for standard CSA G40.21-13). Prior to sending it out, I reviewed the mill test report for the chemical and mechanical properties to make an educated guess as to whether or not it would pass.

The chemical/mechanical properties met the 50WT spec as per the standard, but the impact test failed (by quite a lot). Are there any indications as to why a material would meet chemical/mechanical spec but not pass an impact test?

The material was 3/4" round bar. I have attached the mill test report with the chemical composition if you'd like to peruse it. The impact test results showed an average of about 8 ft*lb - well below the 20 required for a full specimen.

EDIT: If you're looking at the MTR attached, refer to heat # C112098

 

[racookpe1978]

The material was a round bar, but what shape was put into the Charpy anvil for impact testing?

there are significant restrictions on the dimensions of the tested piece and the break point stress riser at the notch. If they were not met, the result can't be directly compared with a "standard" result.

 

[metengr]

Most likely a combination of sulfur content and coarse grained structure from prior thermal history.

 

[Guest102023]

This grade of steel is not normalized and is essentially the same as A36.
If the MTR doesn't show Charpy test results, then the standard does not require it and by implication you should not expect it to pass.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[TVP]

I agree with metengr, sulfur is too high and grain size will be too large without normalizing. Sulfur should be ~ 0.010 maximum for achieving 20 ft lbs requirement, along with fine austenite grain size and subsequent ferritic grain size.

 

[tm0284]

Have you polished and etched a piece to look at the grain size? That should help you in determining why it didn't pass.

 

[Armenius]

Why would the Sulfur need to be .01 maximum? The standard for 350WT specifies .04 as the maximum. Just curious - new to this as I mentioned.

What in the MTR am I looking for to determine the grain size?

 

[CoryPad]

The MTR does not contain information regarding grain size. That will need to be a request you make to the steel source or an independent laboratory. While the sulfur concentration of 0.04 % maximum may be in the standard, it does not guarantee that the material will meet other properties, like impact toughness.

 

[Armenius]

I see. I was under the impression that the "WT" in the 350WT standard would refer to material properties of something that meets impact requirements.

 

[metengr]

Material ordered with WT refers to steel that meets specified tensile and impact properties. Most important...
The Purchaser, in addition to specifying the grade, specifies the required category of steel that establishes the CVN test temperature and energy level.