I suspect the problem is two fold.....
1. The low quality of the blade itself.
2. Even though the steel is "unhardened"..... it's very likely spherodized annealed, which is an easy/cheap way to finish steel out by manufacturers.
What does that mean? Simply put, it's half way annealed. Every try to drill a hole in steel....the bit starts to cut, then after a few thousandths, cutting stops, the bit squeals and/or smokes, and you destroy the bit? That piece of steel was likely spherodized annealed. I know it sucks, but it's always a good practice, in the way of tool/bit conservation, to anneal, or at least thermal cycle "knife steel" prior to trying to cut or drill it.
I'm assuming you don't have a heat treat oven? If not, cut off the length you need for what you're doing, then pre-heat your kitchen oven at it's highest temp, then put the steel in there for at least 2 hours. When you bring it out, allow it to cool NATURALLY, then try cutting it....it's not ideal, but what you'd be doing is tempering the steel to where it's close to dead soft.....and you SHOULD be able to cut the steel.