Ive got an old sheffield blade, I bought it from Ebay a while back. Its almost a wedge shape. It was polished but not sharpened when I got it and I bought some scales to finish it off.

Its sharp before I start shaving but about half way through a shave it seems to start dragging a little, in fact I just managed to nick myself with it thanks to it seeming to grab.

I know nothing about straight razors although I am trying to learn. I'm happy I can get it sharp as it will cut a hanging hair no problem and it shaves just fine until like I say about half way through. Unless its something wrong with my shaving prep I wondered if the blade could be just soft? Is this possible at all?

Im not sure what heat treatment is carried out on blades where they hardened in the old days?

Thanks