Good quality hammers should be forged from steel bar (often EN9) and then heat treated. The striking face should be hardened, but behind it the material should be left softer in order to act as a form of cushion. If the whole head was hardened equally the chances of the hammer shattering in use would be greatly multiplied. The forging and the heat treatment are both very important
It should be remembered that incorrectly hardened striking tools can be very dangerous and the user should be careful never to buy inferior hammers and ensure that the hammers are of known pedigree
The hardened striking faces of hammers should never be used to hit another hardened surface. This can result in the face chipping and possible danger to the operator.
Strike squarely, avoiding glancing blows. Never strike with the side of a hammer.
Always wear safety goggles when using a hammer
Do not use a hammer with a damaged shaft or loose head
Remember that left for a long time in very dry conditions, wood can dry out. Always check to ensure that that has not happened to your hammer handle
Always use the correct hammer for the job