Both of these blades are Demo Demons; the lower one has made 126 cuts through nail-embedded wood. Although the carbide tips have been dulled, they remain intact and can still cut – though at a slower rate than when sharp.
Mike Guertin recently posted an interesting blog entry on the FHB website about using Diablo Demo Demon carbide tipped recip blades while gutting a house. During that project he learned some of the same things Michael Springer learned during a 2012 test of demo blades, that the Demo Demon’s tips did not break or come off when they hit nails and that the blade outlasted bimetal when cutting abrasive material. He also noticed that the blade cut more slowly than bimetal and depleted the batteries of cordless recip saws more quickly (runtime was down 25-30%).
I’m not sure what Guertin’s Demo Demon blades looked like when he was through with them so I included a shot of one after Springer used it to make 126 cuts through nail embedded wood. It had dulled slightly and cut at half the speed it did when new—but it still cut.
Springer’s take on the carbide tipped blades he tested in 2012 (which included the nail-embedded wood cutting Demo Demon and a Lenox blade designed for wood, cement board, and fiberglass—but not nails) was as follows:
“Because of the speed and longevity of the top bimetal blades, I would not recommend carbide-tooth blades for nail-embedded wood – but for cutting more than a few feet in highly abrasive materials like asphalt shingles, carbide is the way to go. For sawing abrasive material that is free of fasteners, nothing outruns the Lenox carbide. Due to the fragility of the Lenox's teeth, however, I would recommend the slower but far tougher Diablo Demo Demon carbide for cutting abrasive material that might contain hidden nails.”
Guertin refers to Springer’s test and concurs with his conclusions about cutting nail embedded wood, “My experience corresponded with Michael's evaluation. Basically the right blade for the task at hand. Given the premium cost for the carbide tipped Demo Demons (about $1/blade inch), I'd use them for those abrasive material cutting tasks and stick with bimetal blades for cutting through clean, nail-embedded wood at a little less than half the cost per blade and higher cutting speed.”