Cobalt Bi-Hard Hacksaw Blades. Century Cobalt Bi-Hard Blades Offer An Unique Design That Stays Cooler, And Remains Sharper While Cutting Harder Materials Like Steel Or Other Hard Metals. One Piece Construction, Cannot Edge Strip And Avoids Any Of The Weld Line Problems Associated With Bi-Metals Blades. Century’s Staged Heat Treated Process Creates The Strongest Teeth (Rockwell Hardness C65) While The Backbone Is Heat Treated To A Lower Degree (C42-C50) Enabling Its Flexibility.