combining mosaic blocks

[440-c]

Guys I have a problem. I had a small billet of Crushed W's of 1084 and 15N20. I wanted to get the W's on the ends to be on the sides to make a knife blade. so I cut them on a 40 degree angle and put them together. I welded down the flat sides and the sides be fore welding them together. at this point everything seemed fine until i ground them smooth to see pattern. The pattern is there but where they were put together there is a line of lighter color across the seam. It's on the other side to so I believe it goes thru the entire new billet. What caused this line? It's not the tack weld because I just tacked it in the middle and I ground that away. I made two and the second is the same way. So every 1 1/4" there is a line down the length of the blade. Any Ideas on what happened or is it normal. Thanks

 

[FunkCoaster]

Pictures would help. Here is my suspicion:

Prior to cutting the tiles, the outside of them had some decarburization due to being exposed to atmosphere during forging.
After cutting and stacking, the decarb was now aligned inside the blade, at the juncture of your tiles.

Etching these decarb regions would produce a different color, due to it being a different structure (ie pearlite) than the heart of the tile.

If this is the case, there's nothing that can be done about it now. Earlier in the process the solution would be to grind away more on the outside the billet, and test etch to make sure you are through any decarb.

Alternatively, if there was a gap between the tiles during final welding, perhaps decarb happened at this time.

Supposing this is true, the seam might have different properties - lower hardness, different microstructure, etc. These could cause structural weakness. Not really sure on this, so take it with a grain of salt.

 

[weo]

Yes, pictures might help, but this could be nothing to worry about. Have you normalized and thermal cycled the billet yet? I've seen what I'll call (for lack of a better term) shadow weld lines on billets before, that were not visible on the final product.

Prior to cutting the tiles, the outside of them had some decarburization due to being exposed to atmosphere during forging. After cutting and stacking, the decarb was now aligned inside the blade, at the juncture of your tiles.
Etching these decarb regions would produce a different color, due to it being a different structure (ie pearlite) than the heart of the tile.
If this is the case, there's nothing that can be done about it now. Earlier in the process the solution would be to grind away more on the outside the billet, and test etch to make sure you are through any decarb.

This might be it too, but if you still have forging to do, it might not be anything to worry about due to carbon migration that happens at forging temps.