While others elected not to post the technique used to weld up their blades, I'll simply say I hardface my blades. I have predominately sandy soil, and it does not take long to wear or erode out a set of blades. I had been building up the old blades, with a filler rod, then putting down 2 or so passes with a hard facing rod, and then grinding them back to shape and sharpness . They have worked out extremely well. Especially on my high lift blades on my JD L & G tractor, which would split or fork on the ends after just one season. I merely weld in the lift area with hard face, now I get a couple of seasons. From previous posts I compain a lot about prices some dealers charge, and JD is among the top gougers in my area. $47.00 for 2, 19 3/8" for a 38" mower deck blades is rediculous. But I can change my blades on my bush hog (Hardee 52" Tiger Cub) for $13.00 each, and these blades are approximately 1/2" x 4" x 18" in size, as compared to the JD mower blades which are about 1 1/2" x 19 3/8" x about 3/16".
I was shown a neat idea by a friend. Use the old blade, and cut off the worn out sharpened ends, and buy those small hay cutting blades and attach them on the old blade with grade 8 bolts. These blades do not create a windrow, and just merely cut and lay the grass down in place. They don't have a lot of lift, but its sufficient in most cases, and the price is right, and they are reversible so you get two cutting edges out of each section.
I had also experimented taking a worn out blade, and making a pivoting end like on a bush hog out of them. I obtained a pretty good supply of new odd ball blades all of the same size, which I cut the ends off and drilled to allow installation of a bushing and grade 8 bolt for a pivot, and attached these to the original blades whose ends were removed so it was basically a flat piece of spring steel stock. While they worked it was more of a pian in the butt to drill holes in these blades, than it was to build up a new or used blade with a hard face rod.