A significant number of crease nail pullers are returned to suppliers each year because of damage that can be avoided – not as a result of defective material or workmanship. It is possible for heat treatment or defective metal to be a problem but be sure you used your tool correctly before returning it. Be sure that you cut or rasp the clinches off before trying to pull the nails. Start the tool opened as wide as possible to allow the points to penetrate any dirt or debris in the crease and get under the nail head. The nail puller has to get under the head of the nail to work properly. If you only have contact with the tips of the tool and then squeeze and try to pull the nail without first lifting it you are asking for trouble. (Photo 6 shows damaged tip of nail puller, likely a result of trying to pull the nail before getting the puller tips completely under the nail head. Notice the other puller has no damage and has been used much longer, but more correctly.)
Once you are under the head, a steady squeezing pressure should pop the nail loose. You can often hear the nail break loose from the crease. You will see that the nail head is fit snugly into the cavity of the pullers if you have used the tool correctly. When the head is in this cavity, the pressure of the rolling motion you use to pull the nail will not cause damage to the tool.
From time to time you may want to touch up the nail puller tips so they can penetrate the debris in the crease and get under the nail head. You should also be sure the tool is not too thick to fit into the crease. If it appears to be too thick you can use a belt sander to dress them to a thickness that works. Be careful not to grind too aggressively or for too long. You don’t want heat to build up and destroy the heat treat. If you can’t hold the tool because of the heat or it develops a blue color– it’s too hot. Quench it occasionally as you go through this grinding process.