Cold welding is the process of joining metals using pristine surfaces without contaminents(oxide layers, oil, dust...) using pressure through atomic diffusion between the metal joints. Why does this process not work with carbon alloys such as stainless steel? I've only seen 1 article mention it worked with low carbon steel but it cannot be done with higher carbon steels but no explanation as to why.
I guess (from having heard a few lectures about solid state inorganics, no real experience on the subject) that complex crystalline structures that form a polycrystalline surface just don't fit together sufficiently, crystallographically, with a second surface. Even if both are polished flat down to the atomic scale.
That is especially true if they are not just metallic, but have some covalent character bonds in them too. The chance that even a tiny fraction of domains on both sides would by chance fit together is practically zero.
For the two pieces to form a continuous phase, a lot of surface atoms have to move around, and they're not going to do that if the jump to the next energetically favourable position is more than one or two atomic diameters.