Car key problem (result)

I posted here back in June that I had trouble getting a replacement key for my Mitsubishi (with inbuilt chip) I was pointed by 'Tim' to an Ebay supplier who did, at a very cheap price. However when I took them to to Timpson's, a locksmith and a cobbler, they all rolled their eyes and said that the keys imported from China were of such hard steel that they are likely to damage a £150 cutting tool. Whether these keys are those keys I don't know, but if nobody will try then I'm stuck with them. At £6.50 it's no great loss. In the meanwhile I repaired one of them by encasing it with Evo Stick 'Plumbers Mate Quick Repair Rutty' which is a two part resin. While not pretty, it does the job and I believe there are other resins which are not the colour of a turd, but what's done is done.

Seems surprising to me. When I replaced the "casing" for my Renault Master key (which came with a key blank) I was just able to swap over the metal key bit, so didn't need to get one cut.

I can't see any particular reason for making key blanks in particularly hard steel. Still, to check, just apply a file to a non-critical part of the key blank. If it is chrome plated, you will need a bit of pressure to get through the chrome but then I would expect it to file like mild steel or, at worst, like a "high tensile" steel bolt (which will still cut OK with a hacksaw or file with a file). If the file just "bounces off" (like a file on another file does) then evidently the blank is hardened and the guys who cut keys are quite right because their cutters are probably similar in hardness to hacksaws. (They probably won't be "glass hard" like a file, because you don't want a cutter that rotates at high speed to be brittle).