Weird metal?

[Div4gold]

I started a Avatar type display knife, got it pretty much ready for the handle. I decided I wanted to etch it so I took a couple of cut off pieces and sanded them and put mustard on one and muratic acid on the other. Couple of hours later no patina at all. I've had this piece of metal in the garage for about 20 yrs, no idea what it is. It's magnetic, hard to cut, easy to file seems fairly soft, not brittle at all. After 20 years in my high humidy climate one side had surface rust and the other side had a little but not much. I know this is a impossible question but does anyone have an idea what it might be or what may etch it?

It's been about 7 hrs now and the muratic acid piece has kind of a yellowish patina, even all over.

 

[SteelSlaver]

Will a magnet stick to it? If not it is probably something like 300 series stainless. It might also be some kind of nickle alloy. I realize this was not for a user knife but, it is another example of mystery steel problems

 

[Div4gold]

Thanks for the reply. Yeah, a magnet slams up to it hard and I welded to it using a mild steel wire feed. Made a good weld. I'm guessing a ferrous type but it doesn't take an etch like other knives I've tried to etch.