Macro Etch Analysis

[Macro Etch]

I'm have to write about the results from a macro etch test on a MIG weld using nitric acid but I don't know what I'm supposed to be looking for. Under the microscope I can see lines going in various directions where the weld is and then dark patches. What is this showing? I know its the grain structure but how would you describe it? Also there is a dark outline of the weld, why is it dark? And does anyone know how this errosion causes the grain structure to become more pronounced. I can't find anything to tell me.

Thank you

 

[Harry m]

I've looked a welds under microscope before but not mig, electron beam welding we use to inspect for weld position, and under fill porosity and penetration we were welding two types of materal together eg high speed and en47 etched 10%nitric l presume you have mounted and polished your sample if you can see the grain structure you may of over etched it

 

[Richard.]

The grain structure will tell you a lot about the welds toughness. If it's containing lots of very fine grains it's a tough weld that's been put down with reduced amount of heat input.
Now your lines around the outside represent two points. The inner line is the fusion zone. The slightly darker area on the outside of the fusion zone is the heat affected zone.

 

[henry Kadzielski]

Good morning gents
In macro etching you are just seeing the weld area (fusion zone, heat affected zone, and the layers of the weld beads). You can then see the level of penetration in the sample, any and the amount of porosity and any other imperfections at the point that the sample was cut. Macros are used to easily see if the weld has fused the root.
If you take a normal 'T' joint and you put a fillet weld down. When it is welded, cut polished and etched, you can see if the root (the joint between the vertical and horizontal portions) of the weld is fused and also how far it has been fused. Macros are for visual (naked eye)purposes. If more detail is required then the microscope is required. That is then another matter altogether. Hope that helps.