Most of the MIM parts I see are tool steel. You can MIM 4140. There's also a lot of stainless MIM where I work. MIM is a forming process, and it's very well thought out and generally well executed. I work in one of the largest metal rolling mills in the world and we use a LOT of MIM parts. Hydraulic Spools, valve internals, small gears and cams. Some of this stuff is used in brutal conditions. Untold millions of cycles. And it excels.
I haven't seen an informed opinion yet on what is wrong with MIM formed parts. Machined tool steel breaks too. It's only steel.
And I am no metallurgist. I'm no design engineer. No machinist (not much anyway)...
But I'll take MIM in any suitable application without qualms, given proper design and QA practices.
