Strange Impact values 2

[deco0404]

Hi there guys,

I'm not altogether familiar with mechanical testing so hoping you guys can help, it is really only a general question.

We sent some welded (Sub-arc and flux-cored GMAW) samples off for mechanical testing. There is nothing too special in the materials 350MPa C-Mn Steel with slightly overmatched fillers, no heat treatment.

When we got the mechanicals back, the impacts were all ok, but I noticed that the values in the HAZ were higher than the weld centre.

The Hardness were also higher in the HAZ than the weld ( as would be expected )With the higher hardness, I would have expected the HAZ to be slightly more brittle, and as such have lower impact strength.

Am I reading this right, and that with all things being equal, the HAZ should have lower impact energy?

Declan

 

[EdStainless]

Higher strength materials will have higher impact values, until you get too brittle.
So in your case the HAZ was stronger, giving it higher impact values, but not so strong that it became brittle.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[metengr]

No, you cannot make that kind of generalization. In many cases, grain refinement can ocurr in the base metal heat affected zone from welding or microalloying elements driving up impact energy values higher than for the weld or even the base material.

 

[PA2KS]

Along the lines of impact values can someone enlighten me on why CVN values can produce results like this, ex) 100-22-150 ft/lbs @ -21? I see it quite often (usually when CVN values are what is desired in testing) and it boggles my mind. Weld coupons are x-rayed indicating no inclusions.

 

[metengr]

Fine grained microstructure, clean metal, low oxyegn content in the weld metal, microalloy elements added to promote toughness....

 

[deco0404]

Thanks for the comments gents,

this clears things up a bit. I always understood that hardness and impact strength were related in way of;

high hardness - low impact strength
low hardness - high impact strength

obviously not.....

thanks again

Declan

 

[stanweld]

PA2KS,
The low value can be the result of improper machining of the coupon or the location at the tip of the notch relative to the specific grain structure of the weld metal or the HAZ.

Declan,
Absorbed energy values are related to both strength and ductility - not ductility alone.

 

[Guest102023]

Variability in capturing the coarse-grain HAZ at the specimen notch is the biggest factor in apparently inconsistent Cv results. Typically (a very broad generalization) the narrow CGHAZ in carbon steels has toughness inferior to that of the zones on either side of it.

 

[metman]

deco0404,

Toughness can also be characterized by the area under the stress strain curve which represents the endrgy to fracture.

So although there is a general realtionship between hardness or stength and toughness, there are many factors that contribute to the brittle/tough equation.

Hope this helps

Design for RELIABILITY, manufacturability, and maintainability