Metallurgical Notch

[ibfmining]

Hi !

I have seen several technical papers highlighting the root causes of cold bead cracking due to the formation of a martensitic structure at the HAZ. However , I have been looking for some written statement where a 40 - to - 50 HB spread (transverse micro hardness profile) between BM & HAZ associated to hardnesses values in the order of 350 HB , characterizes the so called "metallurgical notch" indicating the risk of having cold bead cracking , or H.I.C .
Does anybody know any literature which refers AND/OR mentions such a statement ?

 

[metengr]

ibfmining;
I am unaware of such a statement, especially one associated with a hardness spread or metallurgical notch effect. All you need to be aware is that susceptibility to hydrogen induced cracking is associated with the formation of certain harmful phases (like fresh martensite formed during welding), amount of residual tensile stress and the level of dissolved hydrogen.

These are no rules of thumb for the above parameters. Keep in mind that as the hardness of the weld region (BMHAZ or weld metal) increases above 35 HRC, the higher the increased risk of hydrogen induced cracking at lower residual stress levels and dissolved hydrogen.

 

[ibfmining]

Thank you metengr.

 

[Duwe6]

About 25 years ago, there was some discussion in the USA about 'hard' welds acting as stress-risers [notches] on bridges. This was dus to the dynamic nature of bridges; they are constantly bending and unbending. and any stress-concentration point is a major problem. This discussion seemed to disappear, probably based on the "continued good service" of welded bridges.

For a hard spot to cause this type of problem, there has to be regular, repeated significant flexing. Thus metengr's point -- HIC risk [and other types of enviornmentally induced cracking] *increases* with higher hardnesses. But the cause of the cracking is not a localized increase in hardness. It is just that hard areas will crack first, all other things being the same.