The Hammer Head
Once we have our drop forged hammer head it's time to ensure that the metal can withstand a good hammering.
Up to three different heat treatment processes can be used on a hammer head - these have to be applied very precisely to make sure the head is in the best shape for its intended job.
Firstly, to get rid of the internal stress we mentioned earlier, the hammer head is given a 'normalising' heat treatment. This involves heating the head to a specific, red hot, temperature and holding it at that temperature for a while. It is then allowed to cool slowly in the air - imagine it as relaxing under a hot sun. We now have a hammer head that won't crack or chip when used.
Now that the whole head has been treated against general damage it's time to treat each part individually for its specific job:
The face of the hammer needs to be harder than what it's designed to hit, (masonry nails can be very hard), but the area about 3mm below the face needs to softer in order to absorb the impact of each blow.
To achieve this complex effect the face of the hammer is induction hardened. Only the face and its immediate surrounding area are heated by an electrical current to a precise temperature and then quenched (quickly cooled) in water.
Up to three different heat treatment processes can be used on a hammer head
On a claw hammer the claw is also induction hardened but instead of water the claw is quenched in oil. This gives it a lower hardness but makes it much tougher and more able to cope with the bending stresses caused when pulling nails out.