Charpy Values

Date 07-22-2010 17:49

It would mean the material is twice as resistant to fracture on impact wherever taken (weld charpy values are commonly measured in the weld, fusion zone, and base metal; more places in some codes) than the material your procedure was qualified with. For low temperature applications (think below freezing) this generally considered a good thing.

By eekpod

Date 07-22-2010 19:55

I have worked with material that needs to meet a "minimum" CVN requirement. It is usually 20 ft lbs at a certain degree, the least critical is 70 degrees, and more stringent temp would be 0 degrees or -20 degrees F.
So as long as your material or filler metal for that matter meets the minimum requirement, whatever it is, it is ok if it exceeds it.
So if it needs to meet 20 ft lbs at 0 degrees, but the certs/ test report says the actual value is 66 ft lbs, then you are fine. If it said 18 ft lbs, then you'd have a problem becasue it doesn't meet the minimum requirment.
There is further info on this topic in AISC 360-05 "Specification for Strucutral Steel Buildings" its a free document from AISC in Chicago.
Good Luck

By Mikeqc1 (****)

Date 07-27-2010 23:23

is the value @ the same temp?

By js55

Date 07-30-2010 12:56

As you have phrased the question it doesn't mean anything. What is important, as eekpod pointed out, is whether or not the minimum imposed requirements are met. Even when you use the exact same material, only different heats, you will have varying toughness. And generally the base metal will have better toughness than the filler metal (except for some HAZ's), unless of course you overmatch, as when nickel based alloys are used for certain low alloy dissimilars.

By HgTX

Date 07-30-2010 19:10

And most base metal and weld metal that I've encountered comes in at way above the minimum requirement. 1.5x is typical; 3x not unheard of. The only reason high CVN should ever be a concern is that it is so atypically high for that kind of material that you might suspect the test was done wrong. But high toughness is not bad for the material as long as all other properties (particularly strength) meet the appropriate requirements.

Hg

By js55

Date 08-07-2010 16:27

HgTX,
Good points. I agree. I have had many base metal CVN's so good I couldn't find a machine big enough to break em (most seem to be 180/240 ft/lbs). Fillers seldom are that good unless you are testing austenitics or at very reasonable temps in relation to the material.