I was visiting with an old friend yesterday who knows nothing about straight razors, but has a good background in knives and such. I buy a lot of straight razors, and mentioned the fact that I have run into multiple occurences of a very odd type crack in blades. I was referring to the vertical crack in the tips of straight razors that typically extends about 1/2 to 3/4 inch into the blade. These cracks don't affect the cutting edge, since they occur about half way up the blade toward the spine.

He said something similar happens in axes, and surmised it is due to inserting a hardened core into a softer metal outer section. Something like this, he said, is done during manufacturing...
  • Split the center of an ax blade in a V shape
  • Insert into the V very hard, tempered steel
  • Heat to white heat to fuse the metals together

That creates an ax of hard metal in the middle at the cutting edge, having softer metal for most of the rest of the ax head. He said you can't visually detect that there is a difference between the two type (temper types) metals. But, that occasionally, the ax head will split where the metals were incorrectly or incompletely fused.

My friend surmised that the same thing might be done with straight razors. And, it made sense. And, it would explain the frequent, but to me odd split in the tips of some razors.

Has anyone heard of this insertion of a core of harder temper steel into straight razors?

As an add on comment, if true, it would mean that the spine would be softer than the edge. (I have honed quite a few razors, and haven't noticed. This is probably because I am very careful in how I hold the razor while honing to keep as much pressure as possible off the spine, using the spine only for establishing honing angle and not for resting during the honing pass.)