Lawn mower blades normally last a long time and if yours are wearing out quickly, there are probably some external factors that you might not think about.
My first question is, are you cutting your grass when it has dew on it or is wet from rain? Water is very tough on lawn mower blades. Water is a solid and when the blade hits it, it quickly dulls the blade and begins to wear it out. Wait until the grass dries before you mow each time and this will place a lot less wear on those lawn mower blades.
Do you have tough grasses in your area? If you live in the south, this could be your problem. Thick lush grass will quickly wear out those lawn mower blades as well. Try cutting it more frequently or change to a different blade that is designed to handle these types of grasses. Better quality steel is the answer here.
Is there a lot of sand in your lawn? Sand is the big killer of lawn mower blades. You can upgrade to a better grade steel, but the sand is going to continue to wear out those blades.
For help selecting a lawn mower blade in your area, visit our Locations page for a small engine repair shop near you.