Buy new blades! It's not worth the risk. The heat could damage the blades, and then they come apart.Just not worth it to me.
Hmm we have had a local welding shop build up the tips of our bushhog blades since 1969 and never had a problem . They add about 4"s where we have a longer wear period . The look like a one sided axle . It's cheaper for us to just have two sets of blades and have them retipped than buy new all the time . And we get long life out of the retipped blades on staying sharp . Not sure on the steel that's used but it stays sharper than new blades . Sent from my iPhone 5 using TractorByNet